AlllOD IfiSTl?

NATL INST OF STANDARDS & TECH R.I.C.

A1 11 0098591 7 l| Mechanical Failures/Detection, diaanosis QC100 .U57 V494;1977 C.I NBS-PUB-C 1977

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NBS SPECIAL PUBLICATION 494

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Nafjonal Bureau of Stan'dar^ OCT 1 ? 1977

Detection, Diagnosis and Prognosis

Proceedings of the 26th Meeting of the

Mechanical Failures Prevention Group,

held at the IIT Research Institute,

Chicago, IlHnois, May 17-19, 1977

Edited by

T. Robert Shives and William A. Willard

Metallurgy Division

Institute for Materials Research

National Bureau of Standards

Washington, D C. 20234

The 26th meeting of the MFPG and these proceedings were sponsored by the Institute for Materials Research of the National Bureau of Standards, Washington, DC 20234; the Office of Naval Research,

Department of the Navy, Arlington, VA 22217; the Naval Air Development Center, Department of the Navy, Warminster, PA 18974; the Frankford Arsenal, Philadelphia, PA 19137; the Federal Aviation Administration, Department of Transportation, Washington, DC 20591; the National Aeronautics and

Space Administration, Goddard Space Flight Center, Greenbelt, MD 20771; and the Energy Research and Development Administration, Washington, DC 20545.

U.S. DEPARTMENT OF COMMERCE, Juanita M. Kreps, Secretary

Dr. Sidney Harman, Under Secretary

Jordan J. Baruch, Assistant Secretary for Science and Technology

0 , NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Acting Director

Issued September 1977
Library of Congress Cataloging in Publication Data

Mechanical Failures Prevention Group.

MFPG—detection, diagnosis, and prognosis.

(NBS special publication ; 494) "Sponsored by the Institute for Materials Research of the National Bureau of Standards. . . [et al.]" Supt. of Docs no. €13.10:494

1. Fracture mechanics—Congresses. I. Shives, T. R. II. Willard, William A. III. United States. National Bureau of Standards. Institute for Materials Research. IV. Title. V. Series: United States. National Bureau of Standards. Special publication ; 494. QC100.U57 no. 494 [TA409] 602Ms [620.ri26] 77-14098

National Bureau of Standards Special Publication 494

Nat. Bur. Stand. (U.S.), Spec. Pubi. 494, 296 pages (Sept. 1977) CODEN: XNBSAV

For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402

Stock No. 003-003-01844-9

{^ U.S. GOVERNMENT PRINTING OFFICE : 1977 O—240-848
FOREWORD

The 26th meeting of the Mechanical Failures Prevention Group was held

May 17-19, 1977, at the IIT Research Institute in Chicago, Illinois.

The program was organized by the MFPG committee on Detection, Diagnosis,

and Prognosis under the chairmanship of Henry R. Hegner of CARD, Inc.

The committee, the session chairmen, and especially the speakers are to

be commended for the excellent program.

Most of the papers in these Proceedings are presented as submitted by

the authors on camera ready copy with some minor editorial changes.

Special appreciation is extended to, Mr. H. G. Tobin Assistant Director,

Electronics Division, IIT Research Institute for inviting the MFPG to

use the very fine facilities of the Research Institute for this con- ference, Mr. Edward P. Fahy, Materials Manager at IITRI and members of

his staff for the meeting arrangements, and to Robert M. Whittier of

Endevco for meeting publicity.

Appreciation is also extended to the following members of the MBS

Metallurgy Division: T. Robert Shives and William A. Willard for their

editing, organization, and preparation of the Proceedings, Paul M.

Fleming for handling financial matters, Todd Eudy for photographic work,

Larry W. Ketron for drafting work, and to Marian L. Slusser for typing.

HARRY C. BURNETT

Executive Secretary, MFPG

Metallurgy Division

National Bureau of Standards

III
i 1I
TABLE OF CONTENTS

Page

FOREWORD III

SESSION I : OIL ANALYSIS REVISITED

1. Statistical Analysis of Wear Metal Concentration 3

Measurements in Oil; Calculation of Significant

Wear Metal Production Rates. Karl Scheller* and

Kent J. Eisentraut

2. Effective Fluid Analysis of Oil-Wetted Systems 24

Through Proper Planning and Interpretation.

R. K. Tessmann* and G. E. Maroney

3. Oil Analysis/Wear Particle Analysis. Peter B. Senholzi 27

4. Application of Ferrographic Lube Oil Analysis to 33

U.S.N. Ship Systems. Gerald F. Rester

5. Effectiveness of the Real Time Ferrograph and Other 49

Oil Monitors as Related to Oil Filtration.

Raymond Valori

6. Ferrographic Separation of Organic Compounds. 73

E. Roderic Bowen* and Vernon C. Westcott

SESSION II: SIGNATURE ANALYSIS TECHNIQUES

1. Mechanical Signature Analysis as a First Step in 77

Quantifying the Characteristics of Operating

Machinery. John S. Mitchell

2. Spectrum Analysis and Machinery Monitoring. 79

George F. Lang

3. Comparison of Vibration Signature Analysis Techniques. 82

John L. Frarey

V
4. The Role of Signal Processing in Machinery Vibration 93

Analysis. James H. Hamilton

5. Diagnostic Techniques for Steam Turbines. R. L. 97

Bannister,* R. L. Osborne and S. J. Jennings

6. Experimental Determination of Radial Magnetic Forces 117

as a Function of Rotor Offset in a Large Induction

Motor. Robert L. Leon

SESSION III: NEW DETECTION, DIAGNOSIS AND PROGNOSIS TECHNIQUES

AND EQUIPMENT

1. A New Chip Detector -- Reliable, Versatile, and 123

Inexpensive. Thomas Tauber

2. Another Look at Time Waveform Analysis. J. B. Catlin 133

3. The Advent of Sophisticated Fluid Power Systems and 138

Its Impact on Preventative Maintenance in the

Military. Michael W. Wigton

4. Tire Degradation Monitoring. Wieslaw Lichodziejeswki 146

5. Use of Microprocessors in Analysis of Acoustic 152

Emission Weld Monitoring Data. R. N. Clark* and

T. A. Mathieson

6. Pictorial History of the Development of Proximity 167

Probes for Use in High Temperature Liquid Metals

Environment. Leo Hoogenboom

SESSION IV: RAILROAD SYSTEM DIAGNOSTICS

1. Department of Transportation System for Train 191

Accident Reduction (DOT- STAR) . James K. O'Steen

2. Conparison of Vibration Analysis Techniques for 205

Railroad Roller Bearing Diagnostics. Warren D.

Waldron

VI
SESSION V: LAND VEHICLE DIAGNOSTICS

1. Maintenance Management Through Diagnosis. 225

Richard G. Salter

2. Vehicle Monitoring System. S. C. Hadden, R. E. Hanson 238

and M. W. Stewich*

3. Systemized Diesel Engine Diagnostics. Henry J. 249

Mercik, Jr.

LIST OF REGISTRANTS FOR THE 26th MFPG MEETING 259

MFPG PUBLICATIONS 268

APPENDIX

Remote Diagnostic Techniques Used in Viking Lander 273

Operations. Parker S. Stafford (Banquet Speaker)

The following registrants gave presentations at the syn^osium, but did

not submit a manuscript for publication:

John Dunmore, "Updating Signature Analysis Techniques," Session II.

Jerry Allen, "Bearing Vibration Crest Detection," Session III.

Raymond Ehrenbeck, "Overview of Department of Transportation Sponsored

Diagnostic System Development," Session IV.

David R. Sutliff* and Nicholas J. Darien, "Development of Data Collection System for Railroad Testing," Session IV.

J. E. Johnson* and Lloyd H. Emery, "Nondestructive Testing of On-Vehicle

Tires Using Random Mechanical Excitation," Session V

* Indicates speaker when a paper had more than one author.

VII
ABSTRACT

These proceedings consist of a group of twenty four submitted

papers from the 26th meeting of the Mechanical Failures Prevention

Group which was held at the IIT Research Institute in Chicago, Illinois

on Nby 17-19, 1977. The central theme of the proceedings is detection,

diagnosis and prognosis as related to mechanical failure. Papers are presented that discuss oil analysis, signature analysis techniques, new

detection, diagnosis and prognosis techniques and equipment, railroad

system diagnostics, and land vehicle diagnostics.

Key words : Failure detection, failure diagnosis; failure prevention;

ferrography ; land vehicle diagnostics; oil analysis; railroad system

diagnostics; signature analysis; wear

UNITS AND SYMBOLS

Customary United States units and symbols appear in many of the

papers in these proceedings. The participants in the 26th meeting of

the Mechanical Failures Prevention Group have used the established units

and symbols commonly employed in their professional fields. However,

as an aid to the reader in increasing familiarity with and usage of the

metric system of units (SI) , the following references are given:

NBS Special Publication, SP330, 1974 Edition, "The International System

of Units."

ISO International Standard 1000 (1973 Edition) , "SI Units and Recommendations for Use of Their Multiples."

E380-76 ASTM/IEEE Standard Metric Practice (Institute of Electrical and

Electronics Engineers, Inc. Standard 268-1976).

Disclaimer:

Certain trade names and company products are identified in order to

adequately specify the experimental procedure. In no case does such

identification imply recommendation or endorsement by the National

Bureau of Standards, nor does it imply that the products are necessarily the best available for the purpose.

VIII
SESSION I

OIL

ANALYSIS

REVISITED

CHAIRMAN: J . M . PEREZ

CATERPILLAR TRACTOR COMPANY

STATISTICAL ANALYSIS OF WEAR METAL CONCENTRATION MEASUEEMENTS IN OIL;

CALCULATION OF SIGNIFICANT WEAR METAL PRODUCTION RATES

Karl Scheller

Southeastern Center

For

Electrical Engineering Education, Inc.

202-D Samford Hall

Auburn University

Auburn, Alabama 36 830

and

Kent J. Eisentraut

Air Force Materials Laboratory

Air Force Systems Command

Wright-Patterson AFB , Ohio U5I+33

The service life of aircraft engines and various other types of

lubricated equipment in the Air Force is currently being monitored in

the USAF Spectrometric Oil Analysis Program (SOAP) in which

concentrations of "wear metal in lubricating oil in the parts per

million range are determined spectrometrically . These measurements

generally ignore the effects of oil consumption and subsequent make-up

and pay only qualitative heed to the rate of increase of wear metal

concentrations. SOAP laboratories are provided with Wearmetal Tables to

aid them in evaluating the significance of the wear metal concentrations.

The Tables, particularized for each item of monitored equipment,

recommend maintenance actions depending upon the wear metal

concentrations of significant elements. It is not intended that the

laboratory analyst use the Tables on an absolute go-no go basis.

Recommendations are to be tempered in the light of the past SOAP and

maintenance history of the equipment and its operating conditions

,

augmented by a healthy measure of the analysts SOAP experience and

judgment in ascertaining the trend of the data. When this becomes

difficult, it is suggested that a simple plot of wear metal

concentration values against equipment operating time be prepared as an

aid. For equipment such as the TF^l-1 engine, which powers the A-7D

aircraft, the lubricant capacity is small (ca. 3 gal) and the oil

consumption rates are not infrequently as large as one quart per hour,

with post-flight oil additions ranging up to 25^ of the total oil

volume. Under these circumstances the effect of oil consumption on measured wear metal concentrations is appreciable and must be

considered in a proper evaluation of the data. This report discusses

5
methods that have "been proposed to simultaneously accoTint for the

effect of oil consumption and engine operating time in a quantitative

manner. Attention has been focused on the TF^+l-l engine because of its

particular sensitivity to oil consumption effects. The techniques

described and developed here are, of course, generally applicable to

other engines and lubricated equipment.

The SOAP Wearmetal Table for the TFUI-1 engine, shown in Figure 1,

is typical of those for engines. Three different sets of guideline

concentration values are given for the three types of instruments

available at SOAP laboratories, Baird-Atomic A/E35U-1 and A/E35U-3

emission spectrometers and the Perkin-Elmer 303/305 atomic absorption

spectrometer. Recommended action codes are listed to the left of the

Tables and explained below them. For this engine, especial caution is

urged in using the Table alone as a basis for evaluating the

significance of wear metal data. Trend analysis in the form of a plot

of analytical results against operating time is strongly recommended.

Accordingly, typical SOAP records for iron in the oil from three TF^l

engines are graphed in Figure 2. All are highly erratic in character

and any trends deduced from them are subject to doubt. In a broad

qualitative sense, one might assert that iron is increasing rapidly for

Engine A, less rapidly for Engine B, and is substantially constant for

Engine C. However, one must have misgivings about the repeated

increases and decreases in metal content, particularly marked in

Engine A. The immediate explanation that suggests itself for this

behavior is the low precision of the measurements. Upon examination of

this possibility, however, one learns that the instruments are required

to have a repeatability (standard deviation) of Ippm in this range of

iron concentration and that they are checked frequently for conformance

to this specification. Proceeding upon the premise that the data are within the required precision limits , the effect of oil consumption

becomes the next likely candidate as the primary cause of the anomalous

concentration variation.

Figure 3 illustrates the effect of oil consumption on the

measured wear metal concentrations of an engine similar in

characteristics to the TFU1-1. Assuming the oil is absolutely clean

initially and is sampled (and topped) at equal time intervals, the

concentration will build up smoothly to an asymptotic limit of Tppm for

the given conditions . In contrast , if the engine were not consuming oil

,

the wear metal concentration would increase in linear fashion imtil the

engine failed or the oil was changed. Thus after 100 hours of operating

time, for example, the measured concentration woTild be Tppm while the

concentration indicative of the actual engine wear would be 35ppni, well

above the guideline for removal. Of course, in a real case the sampling

intervals are not equal and the measurements are only reproducible to

±lppm; thus the concentration values would tend to fluctuate about

their asymptotic limit much in the manner of that shown for Engine C in

Figure 2, in which a limiting concentration appears to have been

attained.

k
Since measured wear metal concentrations and their simple variance with

time have serioios deficiencies for use as engine serviceability

criteria, particularly in the case of oil-consuming engines, the use of

wear metal production rates (WMPR) has "been proposed for this purpose.

These may he calculated hy the various approximate and one differential

(and presumahly more exact) relationship given in Figure U, the latter

described by Lotan (Ref. l). All are derived from a simple material

balance. The three approximate equations differ in their assimptions

regarding the wear metal concentration in lost oil while Lotan 's relationship assumes a constant rate of oil loss at a variable

concentration and a constant wear metal production rate. The various

formulas are applied to SOAP data for a TF^+l-l engine in Figure 5«

Results are calculated following the customary noted practice. As might

have been expected, the approximation using the average value of the

concentration yields the same result as the differential relationship

while the assumption that the oil loss occ\irs at the final or the

initial concentration gives a WMPR that is high or low respectively. In

the interests of the simplest arithmetic. Approximation 2 was used for

all further wear metal production rate calculations.

In certain situations , it may be of interest to calculate the

wear metal production rate where the oil system is topped off several

times between analyses. A method for accomplishing this is outlined in

Figure 6. The relationship shown here is similar to the one found in

Reference 1, though its derivation is different and much less elaborate

than the latter. Though Air Force practice, sampling after each flight,

virtually eliminates the use of this equation for its intended purpose,

it has some utility in calculating average rates from a total elapsed

time, a total oil volume added, a given number of fillings, and the

initial and final analyses.

Concentration-time data and derived wear metal production rates

are depicted in Figure 7 for a fairly typical SOAP iron record on a

TFi+l engine. The average oil consumption over the time period covered

in the plot was approximately 0.25 quarts/hr (moderate and

representative of the engines for which oil consumption data was

available). The wear metal production rate graph proves to be both

disappointing and disturbing. At best it mirrors the trend of the

concentration curve in greatly magnified fashion, with some minor

deviations due to the effect of oil addition (notably in the range from

23-29 hours where the concentration is constant). Its worst aspects are the nimierous negative values of the WMPR and its highly erratic nature,

varying widely from point-to-point. The physical interpretation of the

negative WMPR values is that the engine is cleaning itself, an obvious

impossibility. Hence they must be ascribed to the slight (and expected)

variability in the concentration measurements. Since the concentration

appears to be sensibly constant , one is led to determine the average

concentration and the standard deviation of the measurements. The

results indicate that the concentration is probably constant over the

entire operating time and that the precision of the measurements is

comfortably within the specified limit of Ippm. Reasoning that since the
concentration is constant, the WMPR might well be also, the same procedure is applied to these values with dismaying results. The

precision of the calculated WMPR's is twice the mean value. The

relative difference in the precision of the concentration measurements

as compared with the wear metal production rates calculated from them

is strikingly demonstrated in Figure 8, where the 95% confidence limits

on "both values are plotted to the same scale. These results are not

unique to this engine hut representative of others analyzed. The

variability of the WMPR's is approximately an order of magnitude

greater than the variability of the concentration measurements, if one assumes that we are obtaining a very imprecise estimate of a constant

value

As already indicated, the expression developed for calciilation of

the wear metal production rates for the case of n fillings between two

analyses (Figure 6) may be utilized to derive an average WMPR. For this

engine (SN 167O) , it is found to be 2.h3 for the recorded operating

time and conditions. An estimate of this sort is somewhat reassuring in

that it masks negative values and point-to-point variation in the

averaging process. However, its precision (theoretically of the same order as the concentration measurements) cannot be deduced from a single set of data and its accuracy is indeterminate, since the

calculated WMPR (r) is so highly dependent upon the final analysis

(Cg^). For a sufficiently large set of data points, the mcertainty of

the estimate can be reduced by forming subsets of adequate size and

number and obtaining the distribution of the rates calculated for each

subset. In general, such a procedure is not very feasible, since an engine may well reach a critical condition before enough measurements

are accumulated for a reliable analysis of the data.

An alternative procedure for extracting wear metal production

rates from concentration measurements as a function of operating time

is to perform a linear regression analysis upon the data on the

assumption that the WMPR is reasonably constant. This method will yield

a trivial and incorrect result (r=0) when the concentration is

ostensibly constant (as in Fig\ire 7) • In most instances, however, the

concentration measurements exhibit an increasing trend with time. A

representative example of such behavior is shown in Figure 9. The

rather wide fluctuations in concentration displayed by these data are undoubtedly due in part to the effects of oil consumption, which were

not reported for this engine. Linear regression analysis produces a rather satisfactory correlation of the data as measured by the

correlation coefficient of 0.9^1 as compared with unity for an exact

fit. The wear metal production rate is deduced from the slope of the

straight correlation line with the indicated standard deviation. By

contrast, the graph of the WMPR follows its usual erratic course,

magnifying the fluctuations in the concentration. It exhibits no discernible trend, is nowhere alarmingly large and even tends to

decrease as the concentration climbs to a value high enough to signal

maintenance action. Furthermore the average of the graphed WMPR values

(2.45) is only "JOfo of that found from the linear correlation and its

6
standard deviation is thirty times as large.

It is interesting to compare the relative trends in concentration

and WMPR for an engine removed for teardown upon the basis of a SOAP

laboratory recommendation. Such data are shown in Figure 10 for an engine used in Reference 2 to illustrate the utility of the WMPR

concept. The concentration trends upward (with considerable

fluctuation) rising from 6 to 12ppm in the interval between 5 and 38

hours of operation. In the next hour of operation it rises abruptly to

l6ppm. The WMPR graph exhibits a magnified fluctuation but no discernible trend over the same time interval. In the last hour of

operation, the WMPR jumps from 6 to 50 mg/hr. It is contended that this

is a much clearer indication of engine deterioration than the jimp in

concentration, even though the prior WMPR history gave no indication

whatsoever of abnormal wear. Before discussing this further, it is well

to note that the entire range of WMPR values prior to the last hour of

operation falls well within the 9'?% confidence belt (ca. -10 to 15

mg/hr) , a fact that raises considerable doubt regarding their

interpretation.

In order to assess the significance of a large increase in WMPR,

it is necessaiy to obtain an estimate of the possible errors in the

calcxilation. This problem is addressed in Figure 11, which outlines the

procedure to be followed in estimating errors and tabulates their

maximum possible values as a function of concentration. For the engine

under consideration (SN 1175? Figure 10, operating interval of one

hour, concentration of 15ppm) , the maximum error at the 93% confidence

limit can be as large as 39 mg/hr. Thus there is at least a 3%

probability of calculating a WMPR of approximately kk mg/hr on a random error basis and the significance of the value of 50 mg/hr

actually obtained is open to question. Consideration of the large

inherent error possible in calculated WMPR's and their inevitable

erratic nature leads to the conclusion that they are not suitable

indexes of engine wear and should not be used as a criteria for

maintenance action.

One must next confront the problem of evaluating the significance

of a large increase in concentration. A method for accomplishing this

p-urpose is illustrated in Figure 12 for the data on Engine SN 1175 used

in Fig-ure 10. Assuming a constant WMPR, linear regression analysis

yields the best least squares fit line to the concentration

measurements. The correlation coefficient, Ri:0.92, indicates that the

assumption is reasonable. Superposition of the 95^ confidence limit belt

on the linear regres.sion line demonstrates that the final concentration

measurement of l6ppm lies well outside these limits. Calculation of the

probable deviation of a measurement from the least squares fit line

indicates that there is less than a 1% chance of obtaining such a value

as a result of random error. It is now justifiable to conclude that the

engine has indeed begun to wear abnormally and to call for appropriate

maintenance action.

Though the technique just described provides a satisfactory

assessment of the concentration measurements and statistically valid

7
vear metal production rates , it does not account for the effect of oil

consumption. Certainly the wear metal production rate of I.89 found for

Engine SN 1175 (Figure 12) must he too low. To compensate for the oil

consumption and dilution effects a corrected concentration may he

calculated from the expression given in Figure 13. The corrected

concentration is, of course, that fictitious value that would he

measured if all the wear metal stayed in the system and only the oil

were consumed.

The concentration measiirements for Engine SN 1175 » compensated

for oil consumption in accordaace with this procedixre are depicted in

Figure ih together with their fitted linear regression line and

superimposed 95^ confidence belt. Comparison with Figure 12 indicates

that the fit of the data has been noticeably improved (correlation

coefficient increases from 0.92 to O.96) and the wear metal production

rate is approximately doubled and of higher relative precision. The most

important conclusion to be drawn from this exercise is that oil addition

data is necessary for a valid and meaningfial assessment of engine wear

from concentration measurements on oil-consuming engines.

To drive home further the importance of oil addition data,

corrected and measured concentrations are presented in Figure 15 for

Engine SN 167O (previously discussed in Figures 7 and 8). The oil

consumption effect is magnified in this instance by the condition that

the contaminant level appears to have reached its limiting

concentration. Correlation coefficients and derived WMPR's are given

for the two sets of data, though the linear regression lines themselves

are omitted for the sake of reduced clutter. As has been already stated,

the virtually constant concentration results in a trivial and incorrect

WMPR of approximately zero and a corresponding low correlation

coefficient. Compensation for oil consmption dramatically increases

the correlation coefficient and produces a plausible wear metal

production rate.

In summary it may be stated that:

1. Linear regression analysis of wear metal concentration

measurements offer a great improvement over current qualitative

trending methods in evaluating engine service life.

2. Oil addition data is indispensable for the interpretation of

concentration measurements from oil-consuming engines.

3. Proposed point-to-point calculation of wear metal production

rates will not serve as a suitable index of engine wear due to their

inherent low precision.

k. The techniques proposed here seem to account satisfactorily

for the effect of oil consiimption and engine operating time on wear

metal concentration measurements.

References

(1) . Lotan, D. , SNECMA Document MFTM No. IO56U, "An Investigation

into the Rate of Contamination of the Oil Circuit of a Turbojet Engine"

(2) . Cuellar, J.P. , Jr. and Staph, H.E., Southwest Research

Institute Report No. RS-63O, July 1975- "Task Report, Task 3 - Wear

Metal Production Rate Compensation".

8
A/E.35U 1

Fe Ag Al Cr Mg

A 0- 13 0-1 0-2 0-1 0-7 0-2

K 14-19 2-3 3-4 2-3 7-9 3-4

T 2 0+ 4+ 5+ 4+ 10 + 5+

Fe Ag Al

A/E35U 3

Cr Cu Mg

A 0-21 0-3 0-3 0-4 0- 10 0-4

K 2 2-29 4 4 N/A 11-14 5-6

T 30f 5 + 5+ 5 + 154- 7+

Atomic Absorption

Fe Ag Al Cr Cu Mg

A 0- 10 0-2 0-2 0-2 0-5 0-2

K 11-14 N/A N/A N/A 6-7 3

T 15 + 3+ 3+ 3+ 8 + 4 +

Codes

A - Continue routine sampling.

K - Submit redtagged sample as soon as possible. Suspect possible discrepancy due to increasing

wearmetal trends, recommend maintenance

inspection. If aircraft has flown since last sample, ground unit until results of this sample are known.

T — Ground unit, examine for suspected discrepancy. Advise laboratory of findings.

Figure 1
10
EFFECT OF OIL CONSUMPTION (AND ADDITION)

ON MEASURED WEAR METAL CONCENTRATIONS

0 25 50 75 100 125

ENGINE OPERATING TIME. HR8.

Figure 3

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25
EFFECTIVE FLUID ANALYSIS OF OIL-WETTED SYSTEMS THROUGH

PROPER PLANNING AND INTERPRETATION

R. K. Tessmann and G. E. Maroney

Program Manager Program Manager

Fluid Power Research Center

Oklahoma State University

Stillwater, Oklahoma

A major dilemma which has long faced engineers concerned with the prevention of

mechanical failures is the early detection of such events. In the case of systems composed of oil-wetted components, the assessment of wearing processes is hampered by the

necessity to contain the fluid. That is, the critical mating surfaces cannot be viewed

directly to appraise deterioration. In general, there are three methods used for deducing

the internal state of such components. The first approach and probably the most widely used is associated with external performance degradation (changes in leakage, heat

level, vibration, noise levels, etc.). The second procedure involves the dismantling of

the system to "pull an inspection." The third technique and the subject of discussion

here is fluid analysis.

The use of fluid analysis for the detection and prevention of failures in oil-wetted sy- stems has undoubtedly been spurred by the cost factor associated with maintenance and

down time. As oil-wetted systems have grown in complexity, the cost of their mainten- ance and down time as well as their initial cost has increased. However, to be effective,

any diagnostic program which relies upon fluid analysis must be properly planned and

interpreted. The planning phase involves such aspects as sampling location, sample

extraction, and sample container cleanliness. These aspects must be carefully considered

to be certain that a representative sample is acquired. Once the analysis has been accomplished, it is necessary to interpret the results in terms of wearing processes occurring in the system components.

Basically, most fluid analysis techniques used today actually evaluate some portion of

the contaminants entrained in the system fluid. The contamination level in an oil-wetted

system is a dynamic parameter. For example, it can increase or decrease, depending

upon the amount of ingression from the external environment and the rate of generation from internal surfaces. Also, the contamination level, in general, will be lower

downstream of the system filter than it is upstream. Thus, it is important to consider

these factors when obtaining a fluid sample.

The sampling procedure which is followed is another critical factor in the sample acquisition process. Since most contaminants of interest in an oil-wetted system will settle when the fluid is permitted to remain stationary, the sampling procedure most often

2h
recommended is called dynamic line sampling. This technique requires that the fluid

be extracted from a turbulent region of the connecting lines while the system fluid is circulating. Reservoir sampling is also used effectively when care is taken to see that

adequate mixing occurs within the reservoir. In addition, the location within the reser- voir is important with such a technique.

Sample container cleanliness is very critical. All of the contamination in the container

prior to placing the fluid in it will be added to that already entrained. Standard procedures are available for fluid sampling and evaluating container cleanliness. If proper

consideration is given to sampling location, sampling technique, and container cleanliness, a sample of fluid will be acquired which is representative of the system fluid.

If oil-wetted systems are defined to include both hydraulic and lubrication systems,

there are five fluid analysis techniques in widespread use: (1) particle counting, (2)

gravimetric analysis, (3) pad comparison, (4) Ferrography, and (5) spectrographic

analysis. These five methods can be divided into two categories. The first three techniques are concerned with the total particulate contamination present in the sample,

while the latter two are normally used for wear debris evaluation. Thus, the interpretation which can be made from the data obtained from each of these methods is dependent upon the category into which it falls. That is, it is very difficult to assess the

concentration and particle size distribution of the wear debris present in the sample

from any of the first three methods listed.

Particle counting provides information relative both to particle size distribution and

contaminant concentration. Obviously, a high concentration of very large particles will result in early failure of any oil-wetted component. Gravimetric analysis can only

produce data relative to the total concentration of contaminant, while pad comparison

relies upon the similarity between a membrane produced from the fluid sample and a standard membrane. Each of these three analysis techniques provides data upon which

a diagnostic appraisal can be made; however, particle counting data are much more

complete.

The two analysis methods which are primarily concerned with the type and concentration of wear debris provide acutely different information. Spectrographic analysis produces data relative to the concentrations of various elements, while Ferrography provides

morphological results in regard to the wear debris. Both of these techniques have been

and are being used effectively. The point to be made here is that the two methods

offer different types of information, and the interpretation must take this into account.

The main objective of any diagnostic effort is to determine what, if any, corrective

action should be taken. Replacing the system filter with one which is more efficient or reducing the rate of ingestion of external contaminants will reduce the contamination

level of the system and, in general, extend the service life of the components. In addition, the severity of the operating conditions will directly influence the wear rate of

oil-wetted components. Thus, if it is found through the process of fluid analysis that

25
the system is being subjected to conditions wliich result in excessive wear, tliere are two obvious courses of action: (1) modify the duty cycle or (2) change to better

components (filters, seals, pumps, etc.).

Modification of the operational duty cycle is usually not a satisfactory corrective action.

Such a change means that the machine will not perform effectively at the intended power level. For example, in order to reduce the operating severity on a bearing, the speed

or load or both must be reduced. In the case of a hydraulic system, the pressure can

be reduced, which means that the system cannot transmit as much horsepower. Thus,

corrective action normally takes the form of component replacement. However, merely

changing a worn component with a new one will not remedy the cause of the potential

failure. If the component life was not adequate, then something must be done about

the conditions which caused the premature failure. In many cases, providing better

contaminant protection is the answer. This can be accomplished by more effective

filtration or by improving the seals and breathers to exclude contamination from the

external environment. However, no matter what corrective action is deemed necessary, some consideration must be given to the cause of the failure if longer component life

is desired.

26
OIL ANALYSIS /WEAR PARTICLE ANALYSIS

Peter B. Senholzl

Naval Air Engineering Center

Lakehurst, New Jersey 08733

INTRODUCTION

Oil analysis has been applied for many decades as a preventive

maintenance concept utilized to predict impending mechanical failure

through examination of used oil samples. Initially, physical properties

of oil were considered indicators of equipment wear. However,

meaningful results were not obtained until examination emphasis shifted

to the analysis of oil carried wear particles. The term oil analysis

has thus become synonymous with oil particle analysis or wear particle

analysis.

The oil analysis concept is based on the premise that all

mechanical systems experience the process of wear during operation.

This wear process results in the production of wear debris or wear

particles which are indicative of the respective wear surface condition.

In the case of lubricated components these wear particles are picked up

and circulated by the lubricant. Thus an examination or oil analysis

of a lubricant sample can non-destructively reflect component surface

wear condition.

Several oil analysis techniques are currently being utilized for

government and industrial applications. These techniques, however,

lack a firm technical basis. They are based on assumed monitored

parameters and are applied, with varying degrees of success, by trial

and error.

PROGRAM DESCRIPTION

In 1973, the Naval Air Engineering Center, under the sponsorship

of the Naval Air Systems Command, initiated an ambitious research

program with the goal of placing oil analysis on a firm technical basis.

This goal was to be accomplished through an intensive correlation

effort relating wear particle characteristics to component surface wear

condition. Such wear particle correlations serve to hi-light critical

characteristics/parameters which are directly relatable to component

surface wear condition.

27
The Naval Air Engineering Center Program consists of two phases;

a laboratory phase and a system application phase.

(1) Laboratory Phase

The laboratory phase of the program involves

the bench testing of prime oil lubricated

components. The objective of this phase is to

monitor both the component surface wear

condition and the respective generated wear

particle characteristics throughout the life of the

component. Correlations can then be drawn

between surface wear progression and particle

characteristic/parameter trends. Trend

analysis will serve to identify critical

particle characteristics which reflect

the wear state of oil lubricated components.

(2) System Application Phase

The second phase of the program involves the

application of laboratory findings to "field"

operating systems. The objective of this

phase is to verify laboratory component test

results and conclusions.

Laboratory bench testing has been completed under the program and

the system application effort is presently near completion.

PROGRAM RESULTS AND CONCLUSIONS

Oil analysis has traditionally been thought of as a one step,

straight forward testing procedure. However, in actuality, oil

analysis is a critical combination of techniques, test procedures,

and analysis criteria. The total progression can be divided into

five major elements; sample, detection, diagnosis, prognosis, and

prescription.

(1) Sample

The sample element of the oil analysis process involves

obtaining a timely, representative lubricant sample

from a mechanical system.

28
(2) Detection

The detection element provides a first cut or preliminary

determination as to the health of a machine. (i.e. is

the machine wearing normally or abnormally?) If no abnormalities are detected, no future analysis is

required. If an abnormality is detected or suspect,

the lubricant sample is transitioned to the next oil

analysis element.

(3) Diagnosis

The diagnosis element serves to further clarify

the machinery wear abnormality. It provides a determination as to what machine component/

components are wearing and proceeds to define

what wear mode/modes are present. Based on these determinations the analysis is transitioned

to the next element.

(4) Prognosis

The prognosis element of the analysis process

serves to define the course of the machinery

wear abnormality. It provides a prediction

of the residual life/time till failure based

on the wearing component and the wear mode

progression.

(5) Prescription

The last element of the analysis process serves

to define a course of corrective action. It

provides maintenance recommendations based on residual life, wearing component, and wear mode.

The sample element of the process is based primarily on technique.

The elements of detection and diagnosis are based on monitored wear

particle characteristics and/or parameters, and lastly, the elements

of prognosis and prescription rely heavily on analysis criteria.

Primary objectives of the Naval Air Engineering Center research

program is to define critical parameters that would effectively

implement the detection and diagnosis oil analysis process elements.

For this reason, discussion in this paper will be limited to these

two elements.

29
Detection

As Indicated above, the purpose of the detection

element is to provide a determination as to the

health of a machine. Based on the program testing, severe wear can be effectively detected by

monitoring both wear particle quantity and size

distribution. Particle quantity as well as the

ratio of large (7-15 jm) to small (2-5 ^iim) particles

increase substantially during an abnormal wear

situation.

Diagnosis

Once the abnormality has been detected, it is the

purpose of the diagnosis element to provide a determination as to what component /components are wearing as well as what wear mode/modes are present.

Again, based on the program testing, further

clarification of a severe wear condition can be

accomplished by performing an elemental analysis

and a morphology classification of the wear debris.

It is obvious that elemental wear debris analysis

can be directly related to wear component material.

Wear particle morphology (i.e. shape, size, color,

etc.) also can be related to a wear component and

further serves to reflect the relevent wear mode.

These morphology relationships have been thoroughly

documented under the oil analysis research effort.

SUMMARY

Present oil analysis techniques are based on assumed monitoring

parameters and applied by trial and error. The Naval Air Engineering

Center has Instituted a program witl; the goal of placing oil analysis

on a firm technical basis. Oil lubricated components have been bench

tested in order to formulate correlations between wear particle

characteristics/parameters and surface wear progression. Critical

parameters defined by bench testing and verified by field testing are:

- quantity

- size

- elemental composition

- morphology

I 50
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51
Based on the implementation of the above critical parameters,

the overall oil analysis decision process can be summarized in

figure (1).

The completion of this research effort will serve as a firm

technical basis for the application of wear particle analysis to

mechanical system diagnostics as well as mechanical system design.

This application reflects great potential for substantial cost,

material and manpower savings. Civilian and military sectors of

society stand to benefit from wear particle analysis research.

REFERENCES

1. Dalai, H. , et al, "Progression of Surface Damage and Oil Wear

Debris Accumulation in Rolling Contact Fatigue", U.S. Naval

Air Engineering Center, Final Report on Contract Number

N00156-74-C-1634, SKF Report AL75T007 (1975)

2. Leonard, L. , et al, "Analysis of Sliding Wear in a Test Diesel

Engine", U.S. Naval Air Engineering Center, Final Report on Contract Number N00156-73-C-0764, Franklin Institute Research

Laboratories Report (1975)

3. Wescott, V. C, et al, "Oil Analysis Program", U. S. Naval Air

Engineering Center, Final Report on Contract Number

N00156-74-C-1682, Foxboro-Trans Sonics Report (1975)

4. Bowen, C. R. , and Seifert, W. , "Ferrography - A New Tool for

Analyzing Wear Conditions", Fluid Power Testing Symposium (1976)

5. Scott, D. ; Seifert, W. W. ; and Wescott, V. C, "The Particles of

Wear", Scientific American, Vol. 230, No. 5, pp 88-97 (May 1974)

6. Dalai, H. and Senholzi, P. B., "Characteristics of Wear Particles

Generated During Failure Progression of Roller Bearings", ASLE

Paper presented at ASLE Annual Meeting (1976)

7. Senholzi, P. B., "Tri Service R&D Oil Analysis Program - Background,

Description and Results", Fluid Power Research Conference

(October 1975)

8. Senholzi, P. B., "Tri Service Oil Analysis R&D Program",

Mechanical Failures Prevention Group (1975)

9. Senholzi, P. B., "Technical Approach to the Exploratory Development

Oil Analysis Program", Naval Air Engineering Center (1973)

10. Senholzi, P. B., Bowen, C. R. , "Oil Analysis Research"* National

Conference on Fluid Power (October 1976)

52
APPLICATION OF FERROGRAPHIC LUBE OIL

ANALYSIS TO U.S.N. SHIP SYSTEMS

Gerald F. Rester

Naval Ship Engineering Center

Washington, D. C. 20362

Naval Ship Engineering Center (NAVSEC) has used Ferrographic Lube Oil

Analysis on a production basis for two years and is firmly convinced of

its effectiveness in predicting mechanical failure. The mission of

Naval Ship Engineering Center is to perform engineering and material

management functions for ship, system, equipment and material requirements in support of Naval Sea Systems Command. NAVSEC provides support

of program requirements for ship design, system and equipment design,

procurement, installation, material management and maintenance engineering. NAVSEC considers Ferrographic Oil Analysis a modem tool of maintenance engineering.

This paper will describe briefly the scope of NAVSEC 's Ferrographic

program, how it is used, and results of the program to date. It will

also discuss briefly how criteria are set for making Ferrograms and the

trade-offs resulting in the decision to place analysis capability on- site at the maintenance base.

NAVSEC 's maintenance engineering program has established Ferrographic

analysis at three intermediate maintenance activities, servicing three

squadrons of ships, approximately ten ships per squadron. Each oil

lubricated equipment in the program is sampled on an average of once

every three months, normally following the quarterly refit. Sixteen

equipments periodically sanpled include four main feed pump motors,

auxiliary diesel engine sump, main propulsion lube oil system, two ship

service turbine generators, two refrigeration compressors, and the ship's

air compressors. Air conditioning compressor lube oil samples and ship's

hydraulic oil samples have recently been added to the program. An occa- sional grease sample is analyzed when it can be obtained when a bearing

is being changed. Analysis and follow-up at one Intermediate Maintenance Activity (IMA) site, of approximately 160 samples per quarter,

require about one third of the trained analyst's work time. It has been

found to be well worth the time and expense.

Early sponsorship of further development of Ferrography at Trans -Sonics

by the Office of Naval Research led to a program by Naval Air Propulsion

Center and Naval Air Engineering Center. It involved collecting a number of samples of oil from different types of equipment and having

them analyzed at Trans -Sonics. NAVSEC was asked to participate, and

provided periodic samples from main feed pump motors from a number of

ships. Results were so encouraging that in 1975, when this program was

55
drawing to a conclusion, NAVSEC procured a set of equipment for one IMA. site and had personnel trained in analysis. For reasons that will be

discussed later, it was decided to locate the analysis capability on- site where sampling could be controlled and feedback and follow-up with

ship's operating and maintenance personnel would be facilitated. This

on-site analysis capability is backed up by engineering support at

NAVSEC.

Following a year's evaluation at one IMA. site, NAVSEC procured two

additional sets of Ferrographic equipment and expanded the program to

include approximately thirty ships at three sites. This application is

truly a production use of Ferrography and is the largest production

application known to NAVSEC within the Department of Defense.

Sampling of oil from the various equipments is done by trained technicians in accordance with uniform standard established procedures. It

is normally done during post refit sea trials - from equipment whose

operation is secured for the sampling process. Uniformity in sampling

is necessary to obtain consistent Direct Reading (DR) results for

trending. When the ship returns from sea trials and prior to operational deployment, all samples are run through the DR Ferrogram Reader.

This instrument, shown on the left side of the Duplex Ferrograph (Fig.

1) , can be operated with little training. DR readings require about

five minutes per oil sample. They represent a measure of the optical

density of the particles deposited in the precipitator tube as oil is

flowed through the highly divergent magnetic field. In general, the

"Small" reading represents particles of normal wear and the Large DR

represents particles of abnormal wear. A reading of 100 represents

approximately 50% transmission of light through the particles to the

calibrated photo cell. In normal wear, the "S" reading may exceed the

"L" reading, but as the wear becomes severe and approaches failure, the

ratio of DRl to DRg becomes large. Fig. 2 shows a plot of the DR

readings from quarterly samples. This data is trendable, and NAVSEC

has found that when DRl exceeds a pre-established cut-off or threshold

value, a Ferrogram slide should be made for further analysis. Setting

of the cut-off values will be discussed later.

The right hand side of the Duplex Ferrograph is the Ferrograph Analyzer - used for making slides for detailed wear particle analysis. When the

oil is gravity flowed down the slide (Fig. 3) , over the highly divergent magnetic field, the particles of wear and some particles of

contamination are deposited. After the Ferrogram is washed and fixed,

it becomes a permanent record of the wear condition of the particular

equipment on that date.

Analysis of the Ferrogram takes special training, and NAVSEC 's on-site

analysts have received it at the Trans-Sonics plant, as well as on-site.

Using the Ferroscope (Fig. 4), a special microscope with a unique dual

5if
illumination system, the technician classifies the number and types of

particles, and gives his judgement of the wear condition. This information, and comments, are filled in on the form shown in Fig. 5. Spectrometric results are inserted for later comparison when the data

is received from the remote laboratory. The Ferroscope's illumination

system (Fig. 6) selectively provides red reflective and/or green transmitted light. Thus color combinations reveal whether a particle is

opaque metal or translucent salts, oxides or other contaminants. Other

features include calibrated vernier focus adjustment to estimate

particle thickness, and a filar eyepiece scale to estimate length and

width

.

It is well known that the material, size and shape of particles of wear

give an excellent indication of the wear condition. Ferrography is the

only method available to NAVSEC to determine size and shape of these

particles. Site analysts in the NAVSEC Ferrographic program can and do

make maintenance recommendations to the engineering officers of ships

in the program. In a fifteen month period at the first IMA. site using

Ferrography, thirty such recommendations included 7 to change the oil,

15 to flush the sump and and change oil, 3 to change oil and place in

standby, 4 to replace bearing (s) and 1 miscellaneous.

It is inqDortant to note that NAVSEC has found Ferrography to be such a sensitive indicator of wear that the analyst sometimes observes

gradual bearing degradation over a period including several samples.

He must exercise discretion not to recommend premature change of

bearings. This maintenance action usually awaits evidence of bearing

noise, as detected by NAVSEC 's complementary vibration analysis program.

Quarterly, each IMA site makes a report to NAVSEC, summarizing all

samples taken, DRs and their plots, Ferrogram analysis reports, and

recommendations made to ships. Site analysts often consult with NAVSEC

engineers by telephone or message, and sometimes samples are sent to

Trans-Sonics to confirm, or expand on, a finding. An engineer at NAVSEC

evaluates results shown in the quarterly reports, and is developing

techniques to apply statistical analysis to the data as the size of the

data base increases.

In a fifteen month period, IMA site "A" made DR readings on 495 samples

from the squadron it was servicing (Fig. 7). 121 (24.4%) of these

samples were also made into Ferrogram slides, almost all 121 having

exceeded the established cut-off values. Of the 121 Ferrograms, 51

were judged to show normal wear, 51 were in the "caution" area, and 19

were considered to be in a "very high" wear status. Thus 57.8% of the

Ferrograms made (14% of all samples taken) showed wear above normal.

It is interesting to note that all 19 "very high" wear samples were

from drive motors for main feed pumps, four of which are on every ship.

All four bearing change recommendations mentioned above were for these

pun^ motors.

35
Except for special tests desired, Ferrogram slides are made only when

large DR values exceed a predetermined cut-off value for each equipment.

These values will vary between equipments because of differences in

machine design and the operating environment. They are adjusted from

time to time as the data base becomes larger and experience is gained.

Equipment modification or operational changes can also cause a change

in cut-off values. Cut-off values are set by NAVSEC by engineering

judgement, based on:

• Average of previous readings

• Distribution of previous readings

• Percentage of samples that exceed the cut-off

• Consideration of the specific equipment and its

maintenance and failure history

Statistical analysis was performed on the entire population of DRl

values for one type of main feed pump motor. It showed (Fig. 8) that

the data is not normally distributed but is skewed to the right. Therefore the normal statistical formulae for prediction do not apply for

this data. However, plots of distribution and relative cumulative

frequency (R.C.F.) are useful to the engineer in setting the cut-off

values. The R.C.F. plot for this motor (Fig. 9) shows that 70.6% of

the readings fall below the cut-off value of 50 and therefore 29.4% of

the samples would be made into Ferrograms for further analysis. From

a sample of three ships during a fifteen month period, 25 Ferrograms

were made from 73 oil samples from this particular pump motor. 24 of

these Ferrograms were judged to show wear greater than normal. This

indicates that the DRl cut-off value was correctly chosen, as the time

and cost for making Ferrograms was not expended needlessly on normal

wear samples.

Following is a brief summary of trade offs involved in a management

decision to place the analysis capability on-site at the IMA maintenance bases. The decision was necessary when the ONR/NAVAIR program

was greatly reduced, and NAVSEC had made the decision to continue with

Ferrography. It was felt that ultimately NAVSEC would desire support

at three sites. However, establishing three labs, without first evaluating on-site operation of one, seemed a high risk option. Therefore

the approach to on-site analysis was viewed from the standpoint of one site first and the other two later if results warranted. The other two

approaches considered were: (1) to continue analysis at Trans-Sonics,

and (2) to set up a Ferrography lab at an existing Naval laboratory

where a technician would be trained for the job. Fig. 10, tabulating

a trade-off of advantages, shows the on-site approach to be clearly

superior. Sampling and analysis can be done by one technician, who is

familiar with the equipment sampled, as well as its operation. He can

discuss its maintenance history with the ship's crew, and be thoroughly

familiar with any past problems. He can also follow up to see the

36
effects of implementing his recommendations. When disadvantages are compared (Fig. 11) , those of the on-site option are far less significant. A close look at costs considered a contract with the factory as compared to the costs of capital equipment, training, consumables, and

cost for the analyst's time. On-site analysis turned out to be far less

costly.

The recommendation was therefore made, approved, and implemented, to

provide an on-site analysis capability at one site for evaluation, and

follow-up with two additional sites when results were sufficiently

encouraging. All three locations are now in a full production testing

operation, and NAVSEC is completely pleased with the results.

In summary, this paper has discussed the scope of the NAVSEC Ferrographic program, how we use it, a summary of results, how large DR cutoff values are selected, and trade-offs leading to a decision as to

where to put the analysis capability.

Finally, to those considering a production Ferrographic Lube Oil

Analysis capability, NAVSEC recommends that every consideration be

given to placing the analysis function as close to the maintenance

activity as feasible. Technicians thoroughly familiar with the equipment sampled, and trained in Ferrography, make excellent analysts.

37
Figure 1

58
Figure 2

59
ko
FERROSCOPE
FERROGRAPHIC ANALYSIS REPORT

SAMPLE NO. : 842 DATE : 1 SEPT 1976 SHIPj

EQUIPMENT : #1 SSTG DATE OF SAMPLE : 26 AUG 1976

D. R. RESULTS : 55/4 FERROGRAM NO. : 1924 DILUTION FACTOR : N/A

VOLUME OF OIL PASSED ALONG FERROGRAM : N/A HOURS ON OIL : N/A

1 1 rCO ur rHniiuLLO NONE FFW rcvi MRDFRATF HEAVY

NORMAI RIIRRINR WFAR VYAA

FATIGUE CHUNKS XX

CUniNG WEAR XX

SEVERE WEAR XX

LAMINAR WEAR XX

SPHERICAL XX

OXIDE XX

DARK METALLO-OXIDE XX

NON-FERROUS, METALLIC XX

NON-METALLIC, CRYSTALLINE XX

CORROSIVE WEAR XX

NON-METALLIC, AMORPHOUS XX

CONSIDERED JUDGEMENT OF WEAR SITUATION :

XX NORMAL CAUTION VERY HIGH

SPECTROGRAPHIC RESULTS •-

FE PB CU CR AL Nl AG SN SI MG

PPM

COMMENTS : FERROGRAM HAS FEW ABNORMAL WEAR PARTICLES - MOSTLY OXIDES.

Figure 5

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FERROSCOPE BICHROMATIC

ILLUMINATION

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EFFECTIVENESS OF THE REAL TIME FERROGRAPH AND

OTHER OIL MONITORS AS RELATED TO OIL FILTRATION

Raymond Valor

i

Naval Air Propulsion Test Center, Trenton, NJ 08628

Abstract ; A development model of an oil monitor known as the Real

Time (R.T.) Ferrograph was evaluated on a bench tester to determine

its effectiveness in detecting scoring and contact fatigue type

failures, especially as influenced by various levels of oil filtration.

Comparisons of the outputs were made with spectrometric oil analysis

(SOA) , a light scattering and attenuation device, an X-ray fluorescence

device, a particle counter, and the analytical Ferrograph. Results

of the testing showed the R.T. Ferrograph to be effective in detecting

failures at or above the 40 micron filtration level. In addition

it correlates well with the other oil monitors. Below the 40 micron

filtration level the R.T. Ferrograph was found to be ineffective. An

ancillary evaluation of a capacitive discharge chip detector placed

in the oil loop was perfomed. The results showed that this was a promising method of reducing false failure indications by burning off

non-failure related magnetic fuzz while at the same time maintaining

its effectiveness in indicating a real failure.

Introduction; Ferrography is a technique for magnetically depositing

metallic wear particles, by size, onto a glass slide or tube for

examination. The application of Ferrographic oil analysis involves

two steps, namely; 1) indicating a measure of the amount of both large

(above 5 micrometers) and small microscopic wear particles in a sample of oil and 2) microscopically examining the wear particles'

morphology. The first step indicates the wear severity or abnormality

of oil wetted components while step 2 is used to identify the type of wear and possibly, the wearing component (bearing, gear, etc.). Step

2, being a time consuming and therefore relatively expensive process, i

usually performed only when step 1 indicates an abnormal wear

situation. Over the past several years Ferrographic analysis has been

used successfully to aid in the prediction of failures of oil wetted

components. In order to indicate failure on a more timely basis in

critical equipment such as aircraft gas turbine engines, the Naval Air

Propulsion Test Center has been active in developing, under contract

to Foxboro Trans-Sonics , Inc., an airborne unit known as the Real Time

(R.T.) Ferrograph which is capable of performing the step 1 function.

Details of the development program are described in Reference 1- This

paper will concern itself with the evaluation of a development model of

the R.T. Ferrograph. This unit is suitable as an in-line device only

on stationary equipment. Because oil filtration levels vary widely

from one model engine to another as shown in Figure 1, the effect of

this parameter on the effectiveness of the R.T. Ferrograph was consider

important in the evaluation for purposes of defining its applicability

or for determining that further development of the R.T. Ferrograph is

^9
required. For comparison purposes other oil monitoring devices were

used at various times during the evaluation testing. They included:

a. an in-line X-ray fluorescence device developed by United

Technologies, Inc.

b. a light scattering device developed by General Electric and

known as the G.E.O.M,

c. an emission spectrograph,

d. a Royco particle counter.

In addition, a new type of chip detector designed to eliminate false

failure indications by sparking or burning off undesirable metallic

"fuzz" was placed in the oil circulating loop for a large portion of

the test program.

Description; A bench tester, known as the Geared Roller Test Machine

(GRTM) , was used in the evaluation program. This machine is used

primarily for disc scoring tests, A cross section of the test section

is shown in Figure 2, The test specimens are two 3 inch diameter

discs which are loaded against each other and are operated, each at a different peripheral velocity so that both sliding and rolling take

place at the same time. The slide-to-roll ratio can be varied and

controlled by varying the speed ratio of the phasing gears. In addition,

elliptical phasing gears were available so that the slide-to-roll ratio

over the circumference of the test discs will vary to simulate the

action on a gear tooth surface. For the purposes of this evaluation

the machine was modified so that, in addition to disc scoring tests,

bearing rolling contact fatigue tests could also be run.

The lubrication system is shown schematically in Figure 3, The oil

recirculating system was capable of being operated in filter by-pass

so that different size filters could be inserted without shutting off

the system. As shown in Figure 3, the R.T. Ferrograph has its own recirculating oil system in which it cyclically measures the large and

small particle density. One complete cycle consists of a flushing

phase and a precipitation phase. The internal operation of the R.T.

Ferrograph is shown schematically in Figure 4. During the flushing

phase the oil is pumped through the glass precipitator tube to back

flush particles deposited from the previous precipitation phase. Once

the flushing phase is complete the pump automatically shuts off and a variable density magnetic field is automatically turned on. At the same time the oil in reservoir above the precipitator tube flows by

gravity through the precipitator tube to the main oil reservoir. Particl

deposit by size along the glass tube. The measurement of the quantity

of particles deposited at each location (large and small) is accomplished

by measuring the attentuation of a beam of light passed through the

glass tube by a fiber optic cable to a photo resistor which produces a

50
voltage output that represents the percentage area covered. The

percentage area covered at the large particle location is symbolized

by Al and the area covered at the small particle location by Ag.

A third fiber optic cable is placed outside the magnetic field and

is used to adjust the lamp voltage so as to maintain a constant

electrical resistance through the photo resistors, i.e., this

compensates for oil discoloration. For simplicity in the monitoring

of machinery it is desirable to combine the two values (Al and Ag)

into one number (index) which will indicate that either failure or a high wear situation is in progress. Two such severity indices have

been suggested:

1, Al (AL-Ag) - This value reflects both a size distribution

(A^-Ag) and the influence of large particle generation which is

thought to indicate the onset of abnormal wear.

2. (A^+Ag) (A^-Ag) = A-^^-A^^ - This value indicates the influence

of the total particle count (Aj^+Ag) and the particle size distribution

(AL-Ag)

o

Test Results and Discussion

Disc Scoring Tests at Varying Slide-to-Roll Ratios - No Filtration

The purpose of this series of tests was to determine the R.T. Ferrograph's

ability to distinguish among various severity levels of wear. Tests

were run at five (5) different slide-to-roll ratios (0, 0.1, 0.2, 0.27,

0.33), The severity of the condition increases with increasing slideto-roll ratio. The tests were run at a 4741N load. No filter was used

in any of the tests. The tests were run for four hours or until scoring

failure of the discs occurred. Figure 5 clearly demonstrates that there

is a direct relationship between R.T. Ferrograph response and the wear

severity level. In the three cases where no failures occurred, the

Ferrograph readings increased slightly and then leveled off indicating

a normal wear situation. The initial increase in level was probably

a reflection of break-in wear in which the surface asperities were

initially worn off. The two cases where failure occurred showed

continuously increasing values of Ferrograph reading with time. The rate

of increase was higher for the failure which experienced the more

severe operating condition. In addition the Ferrograph correlated with

the level of iron in the oil as measured by emission spectroscopy.

Another disc scoring test using elliptical phasing gears was run in

which the slide-to-roll ratio varied over the circumference of the

test discs from 0 to 0.33. Data from this test was obtained for the R.T.

Ferrograph, goA, G.E.O.M, and the X-ray fluorescence units. The

results are plotted in Figure 6. All units increased in their reading

as the test approached failure. The increase in readings was sharp

for all the methods except for the G.E.O.M,

51
Effect of Filtration - Disc Scoring Tests

A series of disc scoring tests were run at five different filtration

levels; namely; filters having nominal ratings of 10, 25, 40, 75 and

^^(no filter) micrometers. The purpose of these tests was to

determine the effectiveness of various oil monitors with filtration

level. A scoring test was run at each filtration level. After the

completion of each test, the oil was recirculated through the system

using a filter of the next finer level from that on which the test was run. Readings on the oil monitors were taken after 5 minutes of

recirculation, after which the next finer filter was inserted into

the system and again readings were taken after 5 minutes. This

process finished with the use of the 10 micron filter. The results of

the testing are shown in Figure 7. Scoring was made to occur several

times during the course of each test. At the 10 and 25 micrometer

level the R.T. Ferrograph showed no indication of failure or abnormal

wear throughout the entire test. At the 40 micrometer filtration

level there is some indication of wear at the time the first scoring

occurred after which a leveling off in readings is indicated. Definite

abnormal wear indications are evident for the 75 micrometer and no filtration levels at the time the first scoring occurred after which

a leveling off of the reading occurred. The effect of reducing the

reading by filtration is evident during the recirculating test. In

the case where no filter was used, the recirculating tests show a severe drop in reading for filter levels below 40 micrometers,

indicating that most of the particles are below the 40 micrometer level.

Spectrometric oil analysis for iron and G.E.O.M. data as obtained

during the scoring tests showed trends similar to the R.T. Ferrograph.

However, during the recirculating oil test the effect of filtration was

not nearly as dramatic in reducing the readings. The particle size

distribution at the end of each test was measured using a Royco particle

counter. The results are plotted in Figure 8. Examination of the case where no filtration is used will give an indication of the amount of

particles generated within each size range. The majority of wear

particles generated are in the 2-10 micron range. The second largest

group of particles are in the 10-25 micron range. These two groups

taken together constitute over 99 percent of all particles generated.

Therefore the overwhelming majority of particles generated from a scoring type of wear process are below 25 microns in size. Use of the

10 or 25 micron filter did not substantially reduce the number of

particles in the 2-10 micron range, but did for the 10-25 micron range.

This fact , taken together with the previous data showing that the oil

monitors could not detect failures using 10 and 25 micron filters,

indicates that the monitors are (1) not capable of detecting particles

in the 2-10 micron range, (2) are most sensitive at detecting particles

in the 10-25 micron range.

52
Effect of Filtration - Bearing Fatigue Spalling Tests

A test series similar to that for disc scoring was run for rolling

contact fatigue. An NJ212 roller bearing was run to initial spalling

at each filtration level at a load of 18085N. After initial spalling

the load was reduced and the bearing run to final failure. Initial

and final failure are compared in Figure 9. The response of the various

monitors with time at the various filtration levels are shown in

Figure 10. Also shown are the recirculation tests. All test bearings

failed by spalling as intended except the bearing which ran without

filtration. This bearing failed because of excessive cage wear. In

Figure 9 the arrow indicates when initial spall failure took place.

The R.T. Ferrograph results show no indication of failure at the 40

micron level or below. At the 75 micron and the no filter levels, the

increasing trend in reading level indicates a failure in progress.

The effect of filtration on the Ferrograph readings is also obvious

during the recirculation tests. The spectrometric results gave some Indication of failure at the 40 micron level in addition to those

detectable at the 25 and 10 micron levels. The G.E.O.M. scatter

indication showed an increasing trend in reading at all filtration levels

except for the 10 micrometer level. The recirculation tests show a reduction in readings with decreasing filter rating for both the SOA and

G.E.O.M. However the effect is not as dramatic as with the R.T. Ferrograph. The UTRC X-ray oil monitor was run only in the case in which no filter was used. Comparison of the X-ray unit with the other monitors

is shown in Figure 11. It can be seen that the X-ray unit showed the same trend in readings as did the other monitors. The PPM level of iron

indicated by the X-ray unit was much lower than that indicated by emission

spectroscopy. The particle size distribution at the end of each test was measured using the Royco particle counter. Again as in the disc scoring

tests 99 percent of the particles generated are below 25 microns in size

as shown in Figure 12.

Summary of Effectiveness of Oil Monitors at Various Filtration Levels

The data presented thus far was reviewed for each monitor and a subjective judgement was made to determine the effectiveness of each

monitor at the various levels of filtration. These results are given

in Table I for both the disc scoring and bearing fatigue tests. If

a monitor was not evaluated at a particular filtration level an N/A

(not applicable) is indicated in the Table. A question mark in the

Table indicates that the data showed a possible, but not a clearly

definable, trend toward indicating a failure.

The tests run at the coarser levels of filtration have all of the oil

monitors clearly indicating a failure. As the levels of filtration

become finer, the ability of all the oil monitors to detect a failure

lessens as seen in Table I. This series of data shows that the oil

monitors limit to decisively detect failure is a level of approximately

25 micrometers. Any filtration range above 25 micrometers, shows high

correlation among the monitors when there are large concentrations of

wear particles.

55
Correlation of R.T. Ferrograph with Analytical Ferrograph

The Analytical Ferrograph Is a laboratory device which Is used to

precipitate wear particles from an oil sample to a glass slide for

microscopic examination. The particles are precipitated according

to size along the length of the slide in a manner similar to that

of the R.T. Ferrograph. The resulting slide Is called a Ferrogram.

An Important parameter of wear Indication Is the amount of build up of

particles where the oil first contacts the Ferrogram substrate.

This Is called the height of the entry deposit. This would correspond

to the Al value on the R.T. Ferrograph. Ferrograms were made from

oil samples taken from both disc scoring and bearing fatigue tests

conducted at the 7 5 micron filtration level. In addition Ferrograms

were made for the recirculating tests. Comparison between the

percent large area covered (A-[^) and the height of entry deposit

on the Ferrogram Is seen In Figures 13 and 14 for both tests. The

two values are seen to give excellent correlation.

Capacltlve Discharge Chip Detector

There Is presently considerable Interest by helicopter manufacturers,

engine companies and the military In replacing presently used magnetic

chip detectors with capacltlve discharge (burn-off type) chip detectors

In order to reduce the number of false Indications caused by the

accumulation of small magnetic particles and debris. The burn-off

type chip detector operates by discharging an electrical spark after a bulld-up of magnetic particles causes bridging of the gap. If the

particles are small enough to be burned off, no failure Indication

registers. The charge will be built up again on capacitors located

Internally In the chip detector. However, particles or chunks which

are too large to burn off will continue to bridge the gap after

discharge has taken place and will register a failure Indication. For

a given gap size, the size of particles which can be burned off depends

on the magnitude of the electrical discharge which can be varied by

the capacitance.

This type of chip detector was placed In the recirculating oil loop

through all the disc scoring and most of the bearing spalllng filtration

tests. The output of the detector was monitored on a Vlscorder to

record any discharges which took place. The first discharge of the

detector occurred during the bearing tests. The unit discharged 22

times In 25 minutes after which it indicated a failure. The unit had

been in the system 44.3 hours before a failure indication occurred.

Over that period of time 4 disc scoring tests and three bearing tests

had been run to failure. During the test in which the discharges

occurred the R.T. Ferrograph oil monitor showed a rapid Increase in

reading level as shown in Figure 15. The wear particles were removed

from the chip detector, filtered and the size distribution estimated

as shown in Table II. The distribution of particle size shows that
the particles are relatively small. This indicates that small

particles are capable of bridging the gap and indicating a failure

without being "burned off". It is speculated that the increase

in particle generation as the failure progressed (indicated by

Figure 15) was so rapid that the small particles accumulated on the

chip detector and bridged the gap before the capacitor could

fully recharge to "burn off" the particles.

The fact that the chip detector indicated a real failure before the

failure reached a point where large chunks of metal were being

generated shows that its effectiveness is not substantially impaired

by its burn off characteristics. On the other hand the fact that

there were 22 discharges indicates that the chip detector is capable

of burning off small particles.

To obtain optimum effectiveness from this type of chip detector

the design (i.e. gap size, capacitor strength, magnet strength)

should be tailored to the wear generating characteristics of

machinery being monitored.

Conclusions

1. The R.T, Ferrograph, as presently configured, is effective in

detecting bearing and disc scoring type failures, if the nominal oil

filtration level is above 40 micrometers. At filtration levels below

40 micrometers the R.T. Ferrograph is ineffective. At the 40

level its effectiveness is questionable,

2. Under conditions when the R.T. Ferrograph is an effective (i.e.

above 40 micrometers) failure detector, it correlates well with other

detection methods i.e. analytical ferrograph, SOA, X-ray, and light

scattering,

3. The preponderence (99 percent) of wear particle generation

resulting from disc scoring and bearing fatigue spalling failure is

in the size range from 2 to 25 micrometers.

4. Comparison of all the oil detection methods has shown the bench

type light scattering method to be effective over the largest filtration

range.

5. Capacitive discharge chip detectors offer a promising method of

reducing false failure indication while at the same time maintaining

an effective level of actual failure indication.

References

1. Obendorfer R.E., Lazarick R.T., "Development of a Real Time Airborne

Ferrograph"^ Proceedings of the 25th Defense Conference on Non Destructive

Testing, Sept. 1, 1976 , Bos ton Mass.

55
FIGURE 1

: nomiMal micron rating for various

56
57
58
FIGURE 4

INLET VENT LINE

FROM PUMP TO TANK TOP

MANIFOLD

RESTRICTOR

RESERVOIR

PHOTO

RESISTOR

BANK

PRECIPITATOR

TUBE

MANIFOLD OIL SAMPLE

RETURN

FLUSHING

OIL RETURN

INTERNAL OIL FLOW & OPTICAL SYSTEM OF TYPE

7081 FERROGRAPH

59
SCORING FAILURE

TIME-HOURS

SCORING FAILURE

TIME-HOURS TIME-HOURS

FIGURE 5 COMPARISONS OF THE R.T. FERROGRAPH READINGS AND SOA FOR VARIOUS SLIDE-TO-ROLL RATIOS ON THE GRTM

60
o

S [3aniiN9vi/y hoj mm^ 33sl ogm moiinow iio

61
FIGURE 7 OIL MONITOR READINGS VS PERCENT

RUNNING TIME FOR THE DISC SCORING TEST SERIES

LEGEND 0 NO flUER

75 ju M FILTER A 40 ^ M FILTER NOTE: ARROWS INDICATE POINTS AT

<J> 25;^ M FILTER WHICH SCORING OCCURRED < 10 M M FILTER

TOTAL RUNNING TIME - PERCENT NOMINAL FILTER RATING pi M

TOTAL RUNNING TIME - PERCENT NOMINAL FILTER RATING -/(M

62
65

FIGURE 10 OIL MONITOR READINGS VS PERCENT

RUNNING TIME FOR THE BEARING TEST SERIES

NOTE: INITIAL FATIGUE SPALL OCCURRED WHERE LEGEND O NO FILTER

ARROW POINTS TO PLOTTING SYMBOL Q 75 M M FILTER A 40>> M FILTER

TOTAL wmm ^ml - kbcent nqmmal filter rating u m

TOTAL RUNNING TIME - PERCENT NOMINAL FILTER RATING-/JM

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72
FERROGRAPHIC SEPARATION OF ORGANIC COMPOUNDS

E, R. Bowen and V. C. Westcott

Foxboro/Trans - Sonics , Inc

Burlington, MA 01803

The separation of particles from a fluid medium by a magnetic force is

analagous to separation by a gravimetric force. Any motion of a particle

relative to its surrounding fluid medium due to a magnetic field as a function of the relative magnetic susceptibilities of both the particle

and fluid, in much the same way as gravimetrically induced motion is a function of the relative densities. Consequently, for magnetic separation to be achievable, there most exist a difference in the magnetic

susceptibility of the particle relative to the fluid medium.

If a sufficiently high combination of field strength (B) and field gradient (B) exists, this difference in magnetic susceptibility need not be

great. That is, it is neither fundamental nor necessary that the particles be ferromagnetic. Indeed, current Ferrograph Analyzers readily

separate paramagnetic particles and non-magnetic particles which have

induced magnetic moments due to attachment during the wear process of

relatively small amounts of ferromagnetic material.

The following text briefly describes how chemical adsorption has been

used to induce paramagnetism in certain organic materials.

The majority of organic compounds are polar in nature. That is, while

the molecule is macroscopically electrically balanced, local imbalances

exist within the molecule. For instance, the polymer viton has the

following molecular structure:

While the overall structure is electrically balanced, the carbon-halogen

side chains are polar. Consequently, although one cannot expect any

ionic bonding, such structures might be expected to behave electrostatically.

- CH2 - CF2 - C - CH2 -

F

n

C - F6

73
Even theoretically non-polar polymers such as polyethlyene appear to

exhibit polar characteristics, apparently due to macroscopic straining

during extrusion and radiation induced cross -linking.

It has been found that when metal cations o£ magnetic elements such

as iron or nickel are introduced into a mixture of organic particles and

a liquid, sufficient metal cations are adsorbed onto the surface of the

particles to raise the magnetic moment of the particles above that of

the fluid medium. Thus, a magnetic separation is achievable. The

cations are introduced as salts that are soluble in the fluid medium.

In the case of aqueous solutions, this is relatively easy, while their

use with oleophilic mistures may require the use of transitionary fluids

such as an alcohol.

While the modes of attachment of these cations to the particles is understood, the precise magnetic moment of the attached cation and the parameters which influence that value as compared to the free cations in the

fluid are unclear. Consequently, work is being undertaken to qualify

the technique and establish its field of applicability.

The technique is currently being applied in two areas of research.

Firstly, analysis of human synovial fluid for particles of bone and

cartilage. Here there exists an excellent opportunity to significantly

improve the diagnostic tools available for the examination of arthritis

and other joint disorders.

Secondly, in the separation and examination of organic particles in

machine hydraulic fluids. The particles are generated by the wear of

seals and gaskets within the system. Currently, there are no indirect means of positively assessing the wear of these seals.

7^
SESSION I I

SIGNATURE

ANALYSIS

TECHNIQUES

CHAIRMAN: R . F . MISIAIEX

NAVAL SHIP ENGINEERING CENTER

MECHANICAL SIGNATURE ANALYSIS AS A FIRST STEP

IN QUANTIFYING THE CHARACTERISTICS OF OPERATING MACHINERY

John S. Mitchell

Endevco-Machinery Health Monitoring Division

33052 Calle Aviodor

San Juan Capistrano, CA 92675

Although techniques are available to experimentally determine the characteristics

of operating machinery they are generally precluded in all but extreme cases by

considerations of time and cost. As a result, the most common method to analyze

machinery depends on spectrum or signature analysis to quantify characteristics.

From this point on machinery analysis is a learning process where components and

characteristics are related to their generating mechanism or event. The knowledge

thus gained then becomes the key to deciphering the performance of other machines

and the process repeats.

The events and characteristics focused on during a typical analysis may be common

to a machine type, common to a component such as an anti friction bearing,

symptomatic of a problem such as bearing instability or coupling misalignment or perhaps even generated by a combination of the foregoing.

Assessing characteristics by machine type is relatively simple to execute and has

been used for years on machinery such as jet engines where a large number of

identical units can be sampled. Selecting the signature obtained from one unit as a norm to which others are compared is one technique, however, a more accurate

method is to construct a statistical median signature from a large sample group.

Although the median signature may not represent a specific unit it, plus some

tolerances, provides a convenient baseline to gain a rapid and accurate assessment

of the condition of similar machinery.

When the machines are not identical but only similar the problem becomes much

more difficult. Gears, for example, may behave quite differently due to differences

in design and construction. In a situation such as this it is necessary to seek out

common factors, learn how they behave as a group, then attempt to extrapolate that

knowledge to other units. A recent series of unconnected gear failures is a good

illustration of the latter, for in each case the symptoms of failure were the same

although the gears operated at different speeds. Although the commonalities may

not be recognized until long after the actual occurrence the lessons learned will

hopefully enable early recognition of future problems and thereby play a decisive

role in preventing outright failure.

77
Identifying the characteristics of specific mechanical components such as blading

and anti friction bearings is generally not difficult. The difficulty, however, arises

when one attempts to assess condition from a vibration signature. In many cases the

differences between a good component and a bad component are very subtle in nature and difficult to detect. Quite often the subtleties can be greatly enhanced

by pre conditioning such as envelope detecting a high frequency signal prior to

reducing it to its spectral representation.

The symptoms of common problems such as instability, unbalance or misalignment

are generally very similar between machine types even though the machines themselves may be quite different. The general approach and fundamental rules of

diagnostic analysis have been known for years and are only being refined by signature analysis.

Despite the fact that the instrumentation for signature analysis is highly refined and

well understood interpretative skills are still in their infancy. Signature analysis

provides the vehicle; what is needed now is study, comparison, extrapolation and

of course learning through failures as well as successes to build a sound technology.

78
SPECTRUM ANALYSIS AND MACHINERY MONITORING

George F. Lang

Nicolet Scientific Corporation

245 Livingston Street

Northvale, New Jersey 07647

Process industries have long recognized the value of applying trend

analysis to the maintenance of expensive equipment. In its simplest

form trend analysis embodies measuring certain specific variables from

an operating machine at regular intervals throughout the life of that

machine. Problems are frequently predicted before catastrophic failures

occur by noticing unusual changes in the level of a monitored variable.

Initial trend analysis using vibration data was conducted by recording

overall levels of vibration at specific locations on a machine. The

most frequent choice trend variable for such simple studies is velocity

measured around the bearing locations of the machine. A considerable

body of historical information lends credence to the argument that

machines in a similar state of health exhibit similar velocity levels

regardless of their operating speeds. Although a somewhat simplistic

assumption, this observation had lead to the widespread use of velocity

trending as a "frequency independent" indicator of a machine's vibratory state.

More modern approaches to the problem involve recording spectra from

measured variables rather than a simple overall level. In these more modern implementations, the most popular measurement variable is the

relative displacement between rotating shafts and their fixed supports.

Most frequently these measurements are made from proximity detectors

permanently installed near the bearing caps of the monitored machine.

Typically, two proximity probes (perpendicular to one another) are installed at each bearing location. In some installations, an additional probe is used to view the position of a thrust washer giving an indication of axial excursion of the shaft. Axial motion is also

monitored in many programs by measuring axial direction velocity in the

neighborhood of the bearing cap.

The signals from these fixed transducers are monitored by recording

spectra in each position on a regular interval. Comparison of these

spectra can indicate changes in the balance (due to rotor wear or loading) as an increase in the rotative speed component of the spectra.

The long term operating speed stability of the machine may also be

trended by the frequency location of the rotative speed component. An

increase in harmonics of rotative speed is often indicative of misalignment or looseness between elements of the machine occurring due to

79
changes in the foundation or thermal shifts. Additionally, subrotative components (as well as harmonics of rotative speed) are indicative of the state of health and clearance of fluid film bearings.

Such measurements generally fall in the "low" frequency category and are indicative of the condition of the machine at the time the measurements are taken. Prediction of machine failure is normally not done

from such measurements, rather they are used to justify corrective

action on a scheduled basis.

"Higher" frequency observations, normally made by measuring accelerations from the fixed system of the machine, are often indicative of

gear and bearing wear. Such trending is based on changes at frequencies

associated with the contact rate of gear teeth or rolling elements of

bearings. In general, these measurements are used to "head off"

problems before they display themselves in the lower frequency measurements as "today's problem".

Trending spectra of both types often permit the early detection of

difficulties in the peripherals associated with large machines.

Potential control system failures often give early warning in terms of

the speed stability exhibited during the spectrum measurement. Observation of permanently installed transducers during typical operating

cycle often disclose difficulties associated with peripheral plumbing,

lubrication pumps, filters, etc.

Spectrum analysis can be particularly useful during the normal startups and shut-downs of a major machine. During initial commissioning of

such a machine basic parameters such as the frequency of shaft critical

speeds and local structure resonances can be identified. The start-up

and shut-down operations often allow forcing functions to be applied to

the machine that are not normally seen during the operating cycle.

These forcing functions can disclose mechanisms of the machine that

should be well understood as an aid to interpretation of possible

difficulties indicated by trending spectra. Machine run-ups are particularly useful for determining the state of balance of the machine

as well as shaft clearances from seals and fluid film bearings.

The following figure is a "stacked plot" of 45 spectra recorded in

rapid sequence during the start-up cycle of a small machine. These

spectra were recorded from a horizontally oriented proximity probe near

one of the bearings of the machine. The rather dominant "mountain

range" running from the lower lefthand corner to the upper righthand

corner is the path line of the rotative speed of the machine. This

path line generally discloses the critical speeds of the machine

although it is often necessary to record two perpendicular transducers

to be certain all criticals have been examined. This is especially true

in machines that lack S3mimetry of bearing stiffness.

80
2nd crHical ipe«J (6190 RPM)

•xcitad by unbal«nc«

FREQUENCY (1000'S RPM)

Below the rotative speed path line, a small "mountain range" can be

seen. This is the path line of the second harmonic of rotative speed.

A lack of significant amplitude in this path line indicates that no major misalignments or foundation looseness are present. In general,

either of these conditions will cause the motion of the shaft to be

non-sinusoidal, with a strong increase in the harmonics of rotative

speed

.

Of particular importance in the above figure is the very small

"mountain range" occurring in the 3000-4000 RPM range above the

rotative speed path line. This is an indication of sub-rotative speed

excitation. Such excitations are normally indicative of an instability

in the system. This is typical of a machine with a seal rub or bearing

clearance problem. In this example, the instability was deliberately

introduced by causing a metallic "rub" between the shaft and the

housing of the machine. Although sufficient clearance existed to

preclude any rubbing in the operating speed of the machine, during the

run-up a particular set of circumstances formed that caused the subrotative excitation. These conditions are typical of those required for

sub-rotative response. They are:

1. The machine must have some initial unbalance. In a practical sense

all operating machinery have some residual unbalance.

2. A close clearance must exist between the fixed and rotating elements

of the system.

3. The machine must be operating at a rotative speed that is approximately twice one of its critical speeds.

In the above figure, sub-rotative response occurred when the machine

was running approximately twice its 3450 RPM first critical speed. Subrotative responses of this form are a very strong indication that the

machine in question should be closely monitored on a frequent basis.

Possible locations of interference should be identified. Appropriate

components should be on hand prior to next scheduled stoppage of the

equipment. Further, during the shut down of the equipment every effort

should be made to pass through the "twice critical" speed regime as rapidly as possible to minimize the damage potential.

81
COMPARISON OF VIBRATION SIGNATURE ANALYSIS TECHNIQUES

John L, Frarey

Shaker Research Corporation

Northway 10 Executive Park

Ballston Lake, New York 12019

Many different approaches are used in the analysis of vibration data.

Too often a machinery monitoring system will be developed that is based

on a single approach. This reduces the value of the system because to

extract the maximum diagnostic information usually requires a combination of analysis techniques selected on the basis of expected machine

failure modes. This paper describes several techniques and briefly

describes a machinery monitoring system to be installed in a nuclear

power plant that combines all the techniques discussed.

Figure 1 displays spectra from the same machine for a displacement

sensor, a velocity sensor and an accelerometer. It is obvious that if

it is desired to monitor once per rev motions of a shaft in a slow

machine that displacement probes offer significant advantages. On the

other hand, if high frequency gear mesh signals are of interest then an accelerometer based system is favored. Velocity is a useful compromise

between the two and many alarm systems are based on a velocity amplitude

limit.

Many investigators are using accelerometers to provide data on very much

higher frequencies than shown in Figure 1. Figure 2 shows the accelerometer output for a rub condition in a hydrogen compressor. The

information that is useful here is the source of excitation for this

high frequency resonance. An analysis technique to handle this high

frequency vibration is shown in Figure 3. Amplitude pulsations are shown in the amplitude versus time displays and the resultant spectra

before and after demodulation are also shown. The impact rate for the

excitation is available from the frequency content of the low frequency

demodulated spectrum.

Figure 4 compares two spectra, one from the low frequency vibration

region and the other a spectrum of a demodulated high frequency

resonance. In addition to higher signal levels, the demodulated spectrum

allows the analysis of signals occurring at electrical noise frequencies.

The other extreme in vibration frequency response is information con- tained in the D.C, levels produced by displacement probes. Figure 5

shows the shaft locus in a bearing and shows that at low powers, the

shaft rides against the top half of the bearing. In this particular

case, the bearing is not designed for this type of operation and damage

to the machine results in continued operation at this condition.

82
Another technique that is used to extract a signal from noise is time

series averaging. Figure 6 shows the improvement in signal to noise

ratio by synchronously averaging a signal buried in noise.

Synchronous signal sampling has other valuable side benefits. Runout

errors in displacement probes may be removed by synchronously sampling

the probe output at an N/ rev rate at low speeds and subtracting this

signal (again synchronously) at all higher speeds. Figure 7 shows the

runout memorized and subtracted to remove the error. Figure 8 shows

the benefits obtained by runout correction for an amplitude versus speed plot of the once per rev vibration component in a machine start

up. Figure 8 c^uld have been obtained by using a tracking filter if the

machine acceleration were not too great. For very fast acceleration

the data shown in Figure 8 can be calculated once for every revolution

using the relationship shown in Figure 9 if an N per rev signal is

generated by the machine.

Figure 10 is the block diagram of an automatic machinery monitoring

system that employs all the techniques discussed above. Synchronous

sampling is employed for machine start-stop data as well as runout

correction. Spectral data is available for steady-state operation and an envelope detector may be inserted ahead of the FFT for hi^

frequency analysis. The monitor provides continuous surveillance of the

machines and alarms on velocity amplitudes for accelerometers , This

portion of the system operates even if the computer malfunctions.

This system will be evaluated in a nuclear power plant in 1978.

83

9

8

7

8 12 16 20 24 28 32

KHz

Figure 2 HIGH FREQUENCY VIBRATION

85
86
in

1

1

1

54 KHZ DEMODULATED

SPECTRUM

o

c

<N

1

1 1

' 1

'

1

1 1

'

1 No' o

1

1

1

oCO

1

1

1

1

1

1

1 1

. 1

J

<w

, 1 F R E 0.

1 1 SPECTRUM

1

'

' i rJ in o -J 00

1 1

'

1 1

<

1 1

1 , 1

0 260 BOO FREQUENCY - HZ

Figure 4 LOW FREQUENCY VIBRATION

VERSUS

DEMODULATED HIGH FREQUENCY

8?
gure 5 BEARING LOCUS FOR A PUMP UNDER

VARYING LOADS AND SPEEDS

88
Signal = 0.5

Noise = 1.0

Figure 6 TIME SERIES AVERAGING

89
Figure 7a Top Uncorrected Probe Output

Runout—Bottom Memorized Runout

Figure 7b Top Uncorrected, Bottom Correct

Signal at Low Speed

90
SPEED

Figure 8 AMPLITUDE VERSUS SPEED

CORRECTED AND UNCORRECTED FOR RUNOUT

91
fir an = m / f(t)cos Wnt dt

b„ =

1 r

J,

/ f(t)SlN W„ t dt

AMPLITUDE

PHASE„= Tan\h!L)

Figure 9 CALCULATION OF SYNCHRONOUS AMPLITUDE

MACHINE 1

DRIVER

SPEED

&

PHASE

DRIVEN

TELEPHONE

INTERROGATE

MONITOR

SELECTOR

ALARM

TRANSIENT

DATA

I

I.

MINI

COMPUTER

RUNOUT

CORRECTOR

DISPLAY/ PRINTER

FFT

ENVELOPE

DETECTOR

DISK STORAGE

Figure 10 MACHINERY DIAGNOSTICS SYSTEM

92
THE ROLE OF SIGNAL PROCESSING IN MACHINERY VIBRATION ANALYSIS

James H. Hamilton

Naval Ship Engineering Center

Philadelphia Naval Base

Philadelphia, Pa. 19112

Machinery vibration analysis is an important tool in the diagnosis and prognosis of machinery problems, monitoring of vibratory

conditions, acceptance testing, and modeling of machinery systems.

With the increasing complexity of machinery systems, the more stringent noise criteria, and the continuing effort to improve operation,

machinery vibration analysis is becoming very useful to the designers,

troubleshooters , and users of such systems. The need to perform this

type of analysis was pointed out by Messrs E. Weinert and R. Badgely

in their article entitled, "Down with Vibration", when they reported

that "between 20% and 40% of all casualties, forced outages and forced

partial outages, are directly relatable to vibration". Statistics

such as these certainly emphasize the need for more and improved machinery vibration analysis.

Since machinery vibration is generated by forces within the machine, proper measurement and analysis of the vibration permit the determination of vibration sources and their severity. As a result of

this analysis, determination of the machine's health including mechanical deficiences and degradation is possible. The machinery vibration analysis technique used for accomplishing the above involves the

integration of three major areas consisting of signal acquisition,

signal processing, and data interpretation. Signal acquisition involves the sensing of the machine's vibration at specific locations

using transducers which emit signals or waveforms representative of

the vibration experienced. The signals are then conditioned using

amplification, integration, or other techniques such that they may be

processed directly or stored for later playback and processing. Signal processing, which will be discussed in more detail later, involves

the processing of the acquired signals using techniques capable of

providing required data or information in a desirable format. The

third major area, data interpretation, involves analyzing the data

provided by processing and identifying the sources of the machine's

vibration. This is accomplished by comparing the data to the calculable forcing frequencies of the machine based on design characteristics. Once the interpretation of data for sufficient locations is

complete, the vibratory condition of the particular system is known.

The role of signal processing in machinery vibration analysis is

to provide the means by which we can obtain useful information or data

about a machine from its vibration signals. These signals represent95
ing the machine's vibratory motion are complex in nature and are composed of many frequencies at different amplitudes related to the

forces being generated by various components of the machine. In general, the processing will be performed such that the time varying signals are transformed into the frequency domain. Since design characteristics of the machine permit us to calculate forcing frequencies

associated with the machine at various speeds, processing in the frequency domain gives us convenient relationships to use in the interpretation of the data. Processing in the time domain can also be very

useful and, as we shall see later, has applications in machinery vibration analysis.

Processing of vibration signals will involve the basic functions

of filtering, detecting, and displaying of the data. These functions

may be accomplished using analog techniques, digital techniques, or a combination of the two. A concern of many people Involved In machinery vibration analysis work is whether to use analog or digital techniques for processing vibration signals. The main considerations in

making such a decision should be the particular processing requirements involved and anticipated future requirements. In general, digital techniques offer many advantages including decreased processing

time required, ease of performing various operations, high resolution,

good repeatability, and others. Processing systems are classified by

the type of filtering used. The two basic types are Constant Bandwidth where the bandwidth is invariant with frequency and Constant

Percentage Bandwidth where the bandwidth is variant with frequency.

The specific type required will depend on the nature of the signals

being processed and the intended application of the resulting data.

Many signal processing techniques and methods are conducive to

machinery vibration analysis. Although most signals will be stationary and periodic in nature, many of the techniques are applicable to

non-stationary signals as well. Primarily, most processing for machinery vibration analysis work is based on the Fourier Analysis concept

or the representation of a complex waveform in terms of its various

frequency components. Such processing will permit one to analyze the

vibration amplitudes (displacement, velocity, acceleration) at specific frequencies. This concept and its many variations has given us signal processing methods which are utilized extensively in today's

machinery vibration analysis work. Some of the more common methods

include:

(a) Narrowband Analysis which provides vibration amplitude vs. frequency data using narrow filtering techniques.

(b) One-Third Octave Analysis which provides vibration amplitude

vs. frequency data using filtering with bandwidths equal to

23% of specified center frequencies.

(c) Signature Ratio Analysis which provides vibration amplitude

vs. orders of rotational data. This method has the advantages of compensating for speed variations of the machine and

9h
of displaying orders directly which eliminates the need for

many calculations.

(d) Frequency Translation which provides a means of separating a selected band of frequencies from the vibration signal and

then translating that band to a lower frequency band. This

method is very advantageous in achieving increased frequency

resolution and in the analysis of modulated vibration signals.

(e) Order Tracking which provides a means of determining the re- sponse of a particular rotational order as a function of the

machine's speed. This method also permits one to determine

excitation sources for system resonances.

(f) Spectral Mapping including Time Spectral Mapping which provides representation of Amplitude vs. Frequency vs. Time and

RPM Spectral Mapping which provides representation of Amplitude vs. Frequency vs. Speed (RPM).

A method of RPM Spectral Mapping which has become very useful in

machinery vibration analysis is "Shades of Gray" processing. This is

accomplished through the use of a computerized spectrum analyzing

system with outputs displayed on a line printer/plotter. The spectra

are condensed and plotted sequentially at selected RPM Increments during the machine's; speed varying or acceleration run. The RPM at which

each spectrum was obtained is printed at the beginning of the spectrum. The vertical span for each spectrum is limited to preclude

overlapping of the spectra giving a clearer and more useful display

than normally achieved with other spectral mapping methods. The

shades of gray effect giving the necessary contrast is achieved by

automatically darkening the area under the spectra curves. Some of

the more beneficial characteristics of this type of processing include:

(a) Provides a quick look at a machine's vibratory characteristics throughout its entire operating speed range.

(b) Provides easy identification of rotational orders and system

resonances

.

(c) Provides means for determining where to concentrate processing effort for more detailed analysis. This Includes information such as which speeds spectrum analyses should be performed and which orders of rotational should be tracked.

It should be noted that this method overcomes shortcomings of some other spectral mapping methods by providing permanent printouts without using troublesome photographic methods, and by not limiting the

number of spectra which can be displayed sequentially.

Other signal processing techniques widely used as a result of

developments in Fast Four ier Transform analyzers include time domain

techniques such as signal averaging and correlation. Signal averaging is useful in signal enhancement applications since it tends to

95
eliminate or reduce non-related background noise signals. Correlation processing provides still another means of signal enhancement in

addition to aiding in the determination of similarities between signals. Other techniques using the dual channel capabilities of the

Fast Fourier Transform analyzers include cross spectrum, transfer

function, and coherence function analyses. These are very useful in

the comparison of spectra and, particularly, in the area of structural

analysis.

Now that we have considered the role that signal processing plays

and some of the applicable processing methods, it should be noted that

the types of processing required for specific applications will depend on many factors such as characteristics of the machinery system

being tested, the characteristics of the signals to be processed, and

the specific requirements of the analysts or users of the data. Although this paper emphasized the more sophisticated processing methods, the most basic of processing methods may be sufficient to satisfy your requirements. Too often, those involved in processing work

tend to "overprocess" and still fail to meet the requirements.

In summary, we have taken a brief look at machinery vibration

analysis as to what it is and why it is necessary. We have also determined that the role of signal processing is to provide the means

by which we can obtain useful information about a machine from its

vibration signals. Finally, we have considered some of the many processing techniques available and some of their specific applications.

96
DIAGNOSTIC TECHNIQUES FOR STEAM TURBINES

R. L. Bannister, R. L. Osborne, and S. J. Jennings

Steam Turbine Division

Westinghouse Electric Corporation

Lester, Pa. 19113

GENERAL DESCRIPTION AND OPERATING CONDITIONS

Diagnostic techniques discussed in this paper are for large

steam turbines. An installed turbine-generator can be over

200 ft. in length and weigh over five million pounds.

Several turbines, built to operate at specific steam pressures and temperatures, are connected in series to drive

a generator which produces the electricity our society

now takes for granted.

Units built in 1900 could generate 2 megawatts of electricity, less than a single multistory office building requires

today. Some of the turbine-generators currently being built

will be able to generate more than 1300 megawatts, or

enough electricity to supply the residental needs of over

4 million people.

The basic design of the turbine is determined by the fuel

used for steam generation. Normally used fuels fall into

two categories namely, fossil (i.e., oil, coal or natural

gas), or nuclear fission. Nuclear turbines require higher

steam flow rates than fossil units because nuclear reactors

do not make steam at temperatures and pressures as high as fossil boilers. A fossil fueled boiler may deliver 7 x 106

lb of steam per hour to a large fossil steam turbine, while

a large nuclear steam turbine. Fig. 1, will require

17 X 10^ lb of steam per hour. Depending upon the steam

supply, inlet steam pressures can vary from 1000 psi to

3500 psi and expand the steam to more than 1000 times its

original volume as it flows past the blades. When it leaves

the final row of blades, its pressure has dropped to 2 to 3

in. of mercury, absolute.

For large units, reliability is of utmost importance in the

economics of electrical energy generation. Modern turbinegenerators operate with an availability of over 90 percent;

that is, they are available to generate power 90 percent of

the time. Unscheduled down time can be expensive as shown

in Fig. 2. Using 1976 information, replacement power for

a downed 600 MW unit could cost between $200,000 to $300,000

97
per day for make-up power from another unit within a utility.

Replacement power purchased from a neighboring utility would

cost more.

TYPES OF OPERATIONAL PROBLEMS

Steam turbines generate static and dynamic signals which are

indicative of its operating performance. Measurements of

temperature, pressure, force, flow, strain, displacement,

velocity, acceleration, phase, etc, can be used to estimate

the usable work and integrity of the machine. To develop a diagnostic technique that can be used to minimize unscheduled outages, it is necessary to understand some of the

following operational problems:

• Rotor Unbalance

Rotating parts cannot be perfectly balanced during manufacturing, due to geometrical variances and the lack of perfect

homogeneity of materials. Parts may also change their dimensions under operating conditions. Identifying frequency

will be at the turbine's running speed.

• Rotor Bow

When the turbine has been shutdown, the rotor can bow if

uneven cooling occurs within its cylinder. A distance

detector can be used to measure the rotor's eccentricity

when the unit is on turning gear and operating at minimal

speed

• Rotor Whirl

Uneven leakage of steam through or past seals, at certain

load conditions, can cause an energy input to the rotor.

This causes the rotor to vibrate at its own natural frequency, which is usually less than half of the turbine's

running speed frequency.

• Rotor Impacting

Impacting exists when rotating and stationary parts come

into contact. The identifying frequency will be the subharmonic of the turbine's running speed which is the closest

subharmonic to the rotor's fundamental natural frequency.

• Bearing Instability

This phenomenon occurs when the oil film between the journal

and its bearing is not tapered as it should be for normal

98
operation. A thicker wedge of oil acts to drive the journal

within its bearing at less than half of the turbine's

running speed.

• Rotor Non -Uni f ormi ty

If the flexibility of the rotor is not equal in all directions it will have different moments of inertia. A cracked

rotor will have a double moment of inertia when the crack is

deep enough to affect the shaft's flexibility. Identifying

frequency will be twice the turbine's running speed.

• Short Circuit Torque

Electrical transients imposed on the generator will cause

the turbine rotor to vibrate at 120 Hz. If the rotor has

a torsional frequency near 120 Hz, large vibration amplitudes will occur.

• Thermal Expansion

When steam is admitted into a turbine, both the rotating and

stationary parts will expand. Because of its smaller mass,

the rotor will heat faster and expand further than the

casing. Axial clearances between the various turbine parts

are provided to allow for differential expansion in the

turbine. Contact between rotating and stationary parts may

occur if the allowable differential expansion limits are

exceeded. Displacement measurements on the rotor, casing

and a differential between the rotor and casing can be made.

• Blade Failures

When steam flow is increased and the turbine is loaded,

natural sources of excitation cause blade vibrations. There

are always some non-uniformities in the distribution of flow

around the circumference resulting from the steam inlet, the

exhaust, extraction slots and the variability of stationary

blades which cause a variable loading on the blades as they

rotate. Blade vibrations normally occur at a harmonic of

running speed or at the nozzle passing frequency. (Examples

of the type modes excited are shown in Figs. 3 and 4). An

exception to this rule is a phenomenon called blade flutter

which can occur to the last stage of low pressure blades at

reduced flow and high exhaust pressure. In this case, the

blade group's third natural frequency, a torsional mode,

is excited.

99
• Water Induction

Severe internal damage to the turbine can occur as the

result of unwanted moisture or water being emitted into the

machinery. Slugs of water can be carried over from the

boiler to the high pressure turbine or from heaters through

the extraction lines to the turbine. Static water can also

back up through the extraction lines from reheaters and feed

water heaters. Damage ranges from broken blades to rubbing,

due to differential expansion between rotor and cylinder.

When the problem first starts to occur there is no audible

characteristic frequency which identifies the problem, but

a temperature change will occur.

TURBINE SUPERVISORY INSTRUMENTATION

Turbine supervisory instrumentation is used to generate

alarms and/or trips in the event of the turbine approaching

certain defined limits which are indicative of turbine malfunction and/or failure. Measurements are compared with

predetermined limits based upon either experience or

calculations.

Turbine variables currently monitored are: rotor vibration,

rotor axial position, rotor eccentricity, casing and differential expansion, speed, governor valve position, and

turbine metal temperatures. Each measurement requires a transducer, some recording means, and a package of circuits

to make the transducer signal suitable for recording.

Vibration and eccentricity measurements include displays of

phase angle as well as detection of the peak-to-peak magnitudes of the displacement. Since a rotor will tend to bow

due to uneven cooling, rotor eccentricity is monitored

continuously while the unit is on turning gear and up to

600 RPM. Bowing of the rotor will appear as vibration over

600 RPM.

When specified, each measurement can be arranged to be

scanned by a computer. Information could be displayed on a cathode ray tube as shown in Fig. 5.

AVAILABLE MEASUREMENT AND ANALYSIS TECHNIQUES

Since the advent of the first commercially available vacuum

tube, electronic devices have been used to sense, condition,

record, store and display static and/or dynamic measurements

Rapid advancement in electronics over the past decade has

provided equipment on a commercial basis which is a definite

assist for making on-line analysis of static and dynamic

data

100
The oldest type of detector is the ear and the oldest type

of analyzer is the brain. Some mechanics can listen to an engine's airborne or s tructureborne sound (via a listening

rod) and determine the malfunctioning part, however, this

skill is more an art than a science.

Many types of sensors are available for detecting the performance of rotating machinery. These sensors may be either

contacting or non-contacting types that are sensitive to

displacement, velocity or acceleration. Examples of some of

these sensors are a linear variable differential transformer for measuring static or dynamic movement, a coil moving

in a magnetic field whose output is velocity sensitive, a crystal which produces a signal proportional to acceleration,

and a capacitive, inductive, or eddy current proximity pickup. In addition, a fiber optics or photosensor can be used

to determine displacement utilizing reflected light. Other

types of sensors, some of which are still in the development stage, utilize ultrasonics, x-rays, RF noise, infrared

radiation, and atomic radiation.

Once dynamic movement has been sensed, it must be analyzed

so that the observer or control system, can take the

appropriate action. A sound level meter or a voltmeter are

examples of instruments that will indicate the gross signal

level. If the signal happens to be of a single frequency,

the reading is quite meaningful. When required, there are

various size filters available to make a discrete frequency

analysis as shown in Fig. 6.

A popular instrument for making analyses in real time is a time-compression type spectrum analyzer. In this device,

the analog signal is first passed through a low -pass filter

after which it is sampled at a rate that is determined by

the selected frequency range of the analyzer and then

converted to a digital signal.

In addition, data reduction systems employing only digital

techniques are available for performing Fourier transforms

very quickly. Such instruments combine high speed processing ability with the flexibility of a mi ni -computer capable

of many mathematical operations, to produce a variety of

different analyses.

Probably, the greatest advance in experimental procedures

over the past decade is due to the use of computers. The

ability to reduce massive amounts of data in minimum time

has made it possible to obtain a better understanding of

the characteristics of complex machinery during various

operating phases.

101
EXAMPLES OF DIAGNOSTIC TECHNIQUES USED ON STEAM TURBINES

Blade Failures

Tuned turbine blading is designed so that resonant frequencies of the blade do not coincide with multiples of the

machine's running speed or the nozzle passing frequency.

During its design stage the resonant frequencies of the

blades are typically displayed in a Campbell Diagram, as illustrated in Fig. 7.

Final product verification can be accomplished in a customer's plant using radio-link telemetry. Miniature ratio

transmitters, operating in the commercial FM band, are

mounted in environmental, protective capsules in the balance

weight holes in the low pressure end of the turbine. Resistance strain gages are cemented to the blading at specific

locations to measure the strain amplitude and its' frequency.

To date, telemetry has been used numerous times to evaluate

the performance of low pressure turbine blades in the field.

The strain gages and wire paths will survive at temperatures

up to 500°F and centrifugal loading of 20,000 g's. The

transmitters and power supply will operate satisfactorily

at temperatures up to 300°F and centrifugal loads of

8600 g's in the presence of moisture.

The possibly does exist for using telemetry to extract infor

mation off the rotor for supervisory instrumentation. Longterm telemetry usage is currently limited by erosion from

water droplets and the power supply.

Another example of detecting a blade problem is shown in

Fig. 8. This spectrum illustrates the airborne sound levels

obtained near a low pressure turbine during normal operation

and after a fast transient condition which was a blade

failure. Using normal supervisory instrumentation, the

turbine did not shutdown automatically as a result of the

blade breakage. The increased magnitude of rotor unbalance

did not raise the vibration level at one or more of the

unit's bearings high enough to produce an alarm or trip

condition.

Use of external airborne or s tructureborne sound measurements to detect and decipher blade vibration is not as easy

task. It is certainly difficult to distinguish which row of

blades may be vibrating when the frequencies of the various

modes are similar. The important point, however, may not be

which row of blades is vibrating, but that a frequency has

appeared in the spectrum that could be critical to further

opera ti on

102
Clearances

Stationary and rotating parts sometimes come into contact

within a steam turbine. Normally, a rub is not detected

until the machine is opened up for inspection.

In several instances, Westinghouse has been successful in

pinpointing rubs associated with excessive clearance which

allow the inlet connection between the inner and outer

cylinders of a high pressure steam inlet to vibrate. From

data, similar to Fig. 9, it was possible to decide when the

bell seal used on these machines had excessive clearance.

The turbines were dismantled and the clearances restored to

normal. This action minimized the possibility of a future

mechanical problem within the inlet cylinder. When the

turbine returned to service, the characteristic vibration

disappeared.

Rotor Thermal Cycles and Cracks

A change in blade-path steam temperature will produce thermal

stresses in the rotor. Heating of the rotor surface followed

by an equal cooling constitutes a thermal cycle and imposes

on the rotor a cycle of alternating stress. Cracks will

ultimately develop after a number of cycles which depends on

the severity of the stress and the rotor's material.

The relationship between alternating stress and cyclic capacity is a known material property. Therefore, it may be

possible to predict the number of stress cycles necessary to

initiate a rotor crack.

Cracks usually propagate slowly and then have a exponential

growth, with a final rapid acceleration of growth to a burst rotor. When the crack becomes large enough, the rotor

will have a double moment of inertia which will produce a second harmonic of vibration. Of four field case histories

of cracked rotors (not Westinghouse), the second harmonic

was reported in two instances. In another case, the propagation of a thermal crack was accompanied by an increase in

transient vibration during temperature decreases over a period of three months.

During a normal turbine outage, ultrasonic and other techniques can be used to inspect rotors for cracks and thereby

eliminate the probability of a rotor burst on machines which

have been in service for a number of years.

103
Water Induction

Water induction has been a major cause of forced outages of

large steam turbines. Presence of water is first detected

by changes in the measured temperature of the affected parts,

as shown in Fig. 10. Use of metal temperature thermocouples

to determine the presence of water or cool vapor in the

turbine cylinder is an effective means of detection, but of

no use in the prevention of water or vapor injection. Thermocouples placed at strategic locations within the piping

system, however, might provide the necessary warning to

the operator.

Westinghouse is currently investigating other methods of

more rapidly identifying impending induction of water into

turbines under an Electric Power Research Institute contract.

The main objective is to sense the presence of water rapidly

enough to close valves or take other action to prevent

water from entering the turbine.

DIGITAL ELECTRO-HYDRAULIC CONTROL

The increased complexity of todays steam turbine generators

and the significantly greater investment in each power plant

demands a control and monitoring system, Fig. 11, which can

maximize the protection and efficiency of the units operation. By combining the flexibility of the digital computer

for handling complex logic decisions with the speed and high

forces of hydraulics for valve positioning, the Westinghouse

Digital Electro-Hydraulic (DEH) meets these needs.

The DEH automatically increases the turbine generator speed

or load at a rate based on calculated critical rotor

stresses, as shown in Fig. 12. All other critical turbine

generator variables are also checked. Transducer outputs

are monitored for failures. The speed channel has two out

of three redundancy checking, with automatic channel

switching in case of a contingency.

During synchronizing of the generator to the line and while

loading the unit a set of control valves modulate steam flow

to the unit under command from the digital computer. During

initial loading even heating of the turbine inlet is obtained by opening each control valve the same amount. This

is called single valve operation. Once the turbine is

heated, higher unit efficiency is obtained by sequencing

these valves to minimize pressure losses across the valves.

If a control valve fails to respond, the digital computer

will automatically sense this, switch the unit to single

valve operation and compensate for the malfunctioning valve.

lOk
During operation, if there is a contingency in the digital

computer the system automatically will switch to manual

allowing uninterrupted power generation. Also incorporated

in this portion of the system, is the overspeed protection

controller. A second, redundant overspeed trip system

also protects the unit.

During all phases of operation, the computer constantly

protects the unit, not only by scanning the actual values

of existing parameters, but also by anticipating future

values. Corrective measures are taken to avoid alarm or

trip conditions.

A modern centralized display provides communication between

the turbine-generator and the operator. Through the use of

control and display panels, a cathode ray tube, and a typewriter, the operator can digitally display information such

as temperatures, pressures and vibrations. A continuous

monitoring and alarm system assures effective and reliable

operation by supplying the operator with timely information.

EXPERIMENTAL FACILITIES

The Westinghouse Steam Turbine Division has an array of

laboratory and experimental facilities that are engaged in

developing, analyzing and verifying steam turbine design.

Some of the facilities available to help develop new diagnostic techniques include:

• Rotor Dynamics

This facility is a single mass rotor supported by two journal bearings, with precise speed control up to 7000 RPM.

Bearing geometry, oil viscosity and rotor unbalance can be

varied. The facility has been used to analyze response to

rotor unbalance and study instability phenomena such as oil whip.

Valve Test

To evaluate the acoustical, vibrational and flow characteristics of large control valves, a 7400 ft^ reverberant

chamber with permanent low-noise, high-capacity flow systems

was built. Up to 140,000 lb of steam per hour at 1100 psia,

or 200,000 lb of steam per hour at 600 psia, or 140,000 lb

of air per hour at 130 psia, is available.

105
• Large-Scale Multi-Stage Turbine

Industry's largest steam turbine test facility. Fig. 13, was

placed in operation by Westinghouse Electric Corporation

during 1975 at the Chester Plant of the Philadelphia Electric

Company. With a steam supply up to 750,000 lb per hour, low

pressure turbines, with blade lengths of up to 40 in. can be

evaluated at speeds up to 4320 RPM. Various types of diagnostic, supervisory, control and data instrumentation can

be evaluated over a wide range of power plant operating

conditions. Currently, 700 points of data and 100 points of

control and supervisory instrumentation are available.

• Controls

For dynamic simulation of control system design and plant

dynamics, advanced computer techniques are used in this

facility. Figs. 14 and 15, to analyze frequency response,

hysteresis and operating and stability characteristics.

Prototypes of new control systems, operated in conjunction

with computers simulating plant dynamics are tested for

reliability, durability and dynamics to assure troublefree operation in the field.

• Data Acquisition and Reduction

Several facilities are available for precise and responsive

data acquisition, on-line data reduction, recording and

storage for further analysis. Automatic traversing of probes

can be computer-directed in preprogrammed steps. Pressure,

temperature flow, speed, torque and frequency data can be

printed out for performance monitoring. Vibration stress

and amplitude levels, frequency and phase can also be

printed out on a routine basis from a dynamic test.

Using a Fast Fourier algorithm technique, one system processes the dynamic data using standard calculation techniques

and presents the results in terms of linear or power spectrum, auto-or-cross-correl ati on function, or coherence.

This system has also been used to generate orbital plots of

bearing data, decay curves of damping tests and analyses

of acoustical data.

FUTURE DIRECTIONS

The high capital investment and need for extreme reliability

in electrical power generation dictate expansion of the

turbine generator monitoring and diagnostic funtions. Areas

such as analysis of the vibrational characteristics of the

rotor-bearing system, continuous monitoring of the chemical

106
purity of s team , added water induction protection and

increased long term recording and trending of machine

behavior are prime candidates for future systems. Such

systems could be incorporated into the existing DEH or

structured in individual subsystems for retrofit to existing

machi nes

.

Completely automated actions will be in general reserved

for those cases where the operator does not have sufficient

time to react. Emphasis will be placed on giving the

operator increased information relative to decisions he

has to make.

107
Figure 1. 1300 MW nuclear steam turbine generator

> 500 o

cc

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200 400 600 800

RATING, MW

1000 1200

Figure 2. 1976 utility make-up power cost,

108
Ut MODE

2nd MODE

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Figure 3. Typical first three modes of a group of

last row blades.

Figure 4. Hologram of last row blades showing

deflection pattern at 4783 Hz

.

109
in

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110
Figure 6. Analysis of sound signal using different

bandwidth filters.

480

420

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180

120

60

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3

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1000 2000 3000 ' 4000 SPEED - R.P.M. 3^

Figure 7 . Typical Campbell Diagram for a group of

low pressure blades.

Ill
FREQUENCY (Hz)

Figure 8. Airborne sound spectrum before and at a

low pressure blade failure.

S- lOOr z

m2 90

80

» 70 100 200 300 400 500 FREQUENCY (Hz)

Figure 9. Airborne sound spectrum of a bell seal

clearance problem.

112
800 -

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500 - K

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0

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® 340 MW TRIP (D TURNING GEAR ON

(D TURNING GEAR TRIP 0 TURBINE DRAINS OPEN ® TURNING GEAR ON

INNER CYLINDER COVER ~-~

INNER CYLINDER BASE

0 2 4 6 8 10 12 14 16 18 20 22 24 26 HOURS FOLLOWING INITIAL TRIP

Figure 10. Abnormal high pressure - intermediate

pressure turbine cylinder cooling due

to water being induced accidentally

into cylinder by flooding from a feedwater heater. Unit could not be

placed on turning gear until there was

an acceptable temperature differential

at point 5 after a trip occurred at

point 3.

115
111+
Figure 12. Automatic turbine control-speed/load

profile

.

Figure 13. Industry's largest steam turbine test

facility.

115
Figure 14. Controls laboratory test stand

hydraulics
EXPERIMENTAL DETERMINATION OF RADIAL MAGNETIC FORCES

AS A FUNCTION OF ROTOR OFFSET IN A LARGE INDUCTION MOTOR

Robert L. Leon

Franklin Institute Research Laboratories

20th and The Parkway

Philadelphia, Pennsylvania 19103

Hundreds of motors, used to drive compressors in gaseous diffusion plants

have been uprated from 2000 HP to 3300 HP. Bearing failures have been

experienced on some of these reworked motors and the Franklin Institute

Research Laboratories (FIRL) was asked to assist in finding the cause. Since the flux density in the gap had been substantially increased, the

radial magnetic force, which acts in the direction of the minimum gap,

and is proportional to the square of the flux density, became a prime

suspect. Preliminary estimates from the motor rebuilder indicated that

a radial force of 5,400 lb would result from only a 10 mil radial offset

of the rotor within its stator. Computer analyses indicated that a radial force of less than half that estimated value could lead to bearing instability or to minimum film thickness failures depending upon its

direction.

A test was run on one uprated motor to experimentally determine the

radial magnetic force acting on the rotor, and to see how this force

varied as the gap was changed. The test served to check not only the

estimated magnetic force levels, but the resulting bearing behavior as well.

To determine the magnetic force reactions at the bearings, the horizontal and vertical displacements of each bearing housing were measured

upon the sudden removal of the magnetic force. This was brought about

by cutting the excitation to the motor at full speed.

In order to maximize these displacements, FIRL reduced the stiffness

between each bearing housing and its mounting flange by machining away

material so as to leave four supporting columns, two vertical and two

horizontal. Optimum vertical and horizontal stiffnesses were targeted

at 10^ lb/in. This value is more than 5 times the maximum film stiffness of the bearing, thus not affecting rotor-bearing performance. Yet

it is compliant enough to yield ly in. displacement for each 10 lbs of

force. With each displacement sensor able to resolve less than 2y in.,

force resolution would be 20 lbs. Since the anticipated forces were to

be in the 2,000 lb range, this resolution was felt to be more than adequate. The actual stiffness values as determined by calibration tests

on site were 1.4 x 10^ lb/in for the horizontal stiffnesses, and 0.5 x 10

lb/in for the verticals.

The displacement sensors were noncontacting eddy current probes. They

were affixed to the mounting flange and they "looked at" copper target

117
buttons bonded to the bearing housings in the plane of the mounting

flange. Copper was used due to the higher sensitivity so obtained, 500

mv/mll vs. 200 mv/mil for steel. The price paid for doing this is re- duced linear range and smaller gap setting, neither of which was a problem in this case. A Brush 6-channel strip chart recorder was used to plot the change of

the vertical and horizontal displacement components of each bearing

housing that resulted from the loss of magnetic force when the excitation to the motor was cut. In order to eliminate the high level vibration portion of these four signals, they were passed through sharp cutoff

(48 dB/octave) low pass filters set at 1 or 2 Hz. The filters also had

20 dB gain, thus raising the sensitivity to 5 volts/mil or 5 mv/y in.

The fifth channel of the strip chart recorder displayed the analog speed

output of the motor so that coincidence with motor cutoff could be noted.

Other sensors mounted on the motor included orthogonal shaft probes in

each bearing for journal position and orbits, and horizontal and vertical

accelerometers on each bearing housing. Another proximity probe was used

to sense motor rotational speed by looking at the passing of a keyway.

Still another probe was used to sense the rotational speed of an oil ring

by looking at the passing frequency of a steel Insert.

All the sensor outputs were recorded with a 14-channel FM tape recorder

allowing for relative amplitude and phase determinations during subsequent playback. Two dual-channel oscilloscopes were used for continuous

observation of both journal orbits. Also, a single channel FFT spectrum

analyzer was used to view various frequency spectra and time domain wave

forms, and these were recorded for later analysis using a digital cartridge tape recorder.

The moving of the bearing housings to vary the air gap was accomplished

with jack screws mounted to the end bells. Flats were provided on the

mounting flanges for the jack screws to act upon.

Measuring shims were used to measure rotor to stator air gaps at the

quarter points at each end. The flange mounting bolts were loosened

and using the jack screws, each bearing housing was moved till the

measuring shims indicated the rotor to be approximately centered. The

bolts were then retightened, the air gaps rechecked, and plastic tipped

locking bolts, which were used to hold the bearings tight in their seats, were snugged down. In addition, using a telescoping gage and micrometer,

the gaps between the jack-screw mounting blocks and the flats on the

mounting flanges were measured and recorded. This entire procedure was

to be repeated each time the rotor to stator air gap was changed.

The motor was now ready for its first run (rotor centered), following

calibration which was accomplished by applying a 100 lb force in the

vertical and horizontal directions at each bearing.

All the initial tests were made with the motor sitting on rubber pads on

the test floor, running with no load, for various rotor to stator air

gap conditions. Later a coupling would be put on and the motor moved to

118
a test stand where it was coupled to a load generator and run under full

load.

The sequence of testing was as follows: Rotor "centered"; 10 mils low;

20 mils low; 10 mils high; 20 mils high; 10 mils right (looking at brake

end of motor, having CCW rotation); 15 mils left; 15 mils left under

full load.

Figure 1 illustrates the resulting horizontal and vertical magnetic

force components for each of these conditions. The forces generally

follow what would be expected. That is they act in the direction of the

rotor offset (minimum gap direction) and they increase as the offset

increases. However, the magnitude of these forces is far below what had

been predicted by the motor rebuilder, approximately 20 lbs per mil-ofrotor-offset vs. 270 lbs per mil, both of these on a per bearing basis.

For the full load condition, the very high vertical couple is believed

to be the result of coupling misalignment and represents actual forces

under load due to misalignment. When the excitation is cut, the cou- pling no longer transmitting torque experiences sudden tooth to tooth

freedom and these misalignment forces disappear in rapid fashion just

like the magnetic force in question. Thus they show up as apparent

magnetic forces.

This contention is supported by the spectrum of the coupling end

vertical shaft sensor which indicates a 2X running speed displacement

component 10 dB higher than the IX running speed component while running

under load.

Measured journal orbits indicated little effect from gross (20 mil)

rotor offsets, and no discernable shift in the position of these orbits

upon the sudden removal of the excitation to the motor. This supported

the conclusion that the magnetic forces were small.

While this test was showing that the magnetic force was not the culprit,

it indicated that the bearing oil rings were. The rings were seen to

operate erratically and far too slowly at best. The worst were new

perprint rings, as had been put in the uprated motors. New, better

operating, redesigned rings are now being installed as the motors are

reworked.

This technique of filtering displacement signals to determine low

frequency or step application forces on "spring" structures in high

vibration environments can probably be used to good advantage in many

diverse applications.

119
20 MILS

120
SESSION I I I

NEW DETECTION ,

DIAGNOSIS AND

PROGNOSIS TECHNIQUES

AND EQUIPMENT

CHAIRMAN: R . A . COULOMBE

NAVAL SHIP ENGINEERING CENTER

A NEW CHIP DETECTOR - RELIABLE, VERSATILE,

AND INEXPENSIVE

Dr. Thomas Tauber

Technical Development Company, 2k E. Glenolden Avenue

Glenolden, Pa. 19036

For over a decade, electric chip detectors have been installed in

virtually all helicopter transmissions and engines and in many propulsion and drive systems of military fixed-wing aircraft. They contain a magnet which attracts the ferrous debris shed into the lube

system by failing components and retain it for later visual inspection

and failure verification. The debris particles which fall across the

gap between two electrodes act like a switch and activate a chip

warning light (see figure 1).

Electric chip detectors are surprisingly reliable indicators of incipient failure. For example, during a two-year period studied by the

Army, chip detectors on a part of the UH-l/AH-lG fleet scored 75 "hits"

(indications followed by component removal) against 9 "misses"

(component removals without chip warning) for an overall success rate

of 88^. For the transmission chip detectors, the success rate was even higher with ^0 hits and one mi ss , correspond i ng to 97-5% success.

This indication reliability is comparable to ASOAP experience overall

and outscores it considerably for the transmissions.

Unfortunately, as is widely recognized, conventional chip detectors are subject to a large number of "nuisance" indications which are not

caused by f a i 1 ure- rel ated debris. The same study shows that in addition to the 75 correct indications, there were 529 nuisance indications

305 or 58% of them were reported as being due to "wear fuzz" and 130 or 2S% due to electrical failure of the chip detection system. The

remaining cases were the result of moisture in the lube system , carbon and other metal contamination {S%) and 7% were due to unknown

causes

.

Such statistics have made chip detectors controversial over the last

few years, despite the high reliability of failure indication mentioned

earlier. In order to eliminate the nuisance indications and make chip

detectors more dependable, their causes must be understood more clearly

It goes without saying that the electrical failures which accounted for

25% of those indications are avoidable by using state-of-the-art

connectors and test circuits. Clearly, the "wear fuzz" indications are

the most important category to be eliminated.

A model for the development of the debris spectrum reflecting a typical

125
fatigue-type failure (bearing or gear spalling) is shown in figure 2.

Under normal operating conditions, a background consisting of appreciable quantities of particles usually less than 30 microns in diameter

are continuously being produced by normal wear processes. In the

diagram, the particle production rate in mg/hour is plotted on the vertical axis rather than the accumulated total. Therefore, the debris

spectrum would remain unchanged along the time axis if no failure

occurred.

As a spall develops as a result of a local fatigue crack and then propagates across the load-bearing surface, more and more debris particles

of larger and larger size are being produced. This causes both the

spectral maximum and the large-particle threshold to move to the right.

Simultaneously, the production rate of small particles also increases,

permitting indentif ication of the failure by spectrographic analysis.

The production of debris particles of approximately 500 micron and

over leads to failure indication by the chip detector.

In lube systems with very fine filtration (e.g., the newer 3 micronabsolute filters), most debris particles of the 10 micron class are removed as quickly as they are produced. With coarser filtration,

these particles slowly accumulate in the oil and, being mostly ferrous, are deposited on the chip detector. Gradually, a conductive path forms across the chip gap and the chip warning light comes on. This process

seems to be the origin of most "wear fuzz" nuisance indications. In addition to other strong evidence, this is indicated by the fact that

during the development program of the T-7OO engine, which has a 3"

micron absolute filter, no such "wear fuzz" indications were reported.

Unfortunately, many chip detector installations, especially but not

exclusively in engines and transmissions of older design, add greatly

to this problem. Figure 3 shows a typical lube system schematic of

an engine, with the chip detector installed in the main scavenge line.

For any given size of debris particle, there is a finite probability

e] that the particle will be transported to the vicinity of the chip

detector (point A). For a large number of particles, this probability

becomes the debris transport efficiency of the lube system. In the

system shown, this quantity would be zero for particles larger than

the openings in the pump inlet screen.

Once the debris is transported to the vicinity of the chip detector,

some provision must be made to either slow down the oil flow so that it can settle out or a screen must be used to capture, retain and deposit

it on the chip detector. In many installations, neither is the case

and the result is a low debris capture efficiency e2.

Finally, the indication efficiency e-^, the probability that a particle, once deposited on the chip detector, will be indicated, corresponds to

the sensitivity of the chip detector and is largely determined by its

gap size. If e].e2 is low for failure-type debris, the chip detector
sensitivity must be high to compensate for this. In practice, this means a small gap size which, in turn, leads to more nuisance indications. This is due to the fact that the transport efficiency of any

lube system is practically equal to one for particles smaller than 50

microns.

It becomes obvious that a conventional chip detector cannot successfully

cope with this problem, at least not in lube systems with coarse filtration. The reason is clearly that a chip detector responds with an indication each time the chip gap is bridged, regardless of whether the

gap consists of large quantities of small or small quantities of large

particles, or even of a fine, long sliver.

This problem can be resolved by sending a strong current pulse through

the chip gap every time there is electrical continuity. The pulse is

generated in a small capacitor network which can be located in the

chip detector (see figure 4) or elsewhere. It causes a local melting

of the kind of particles that are responsible for these indications

which interrupts the current path. Since this process occurs within a few milliseconds, local lubricant temperatures and flow conditions

have no influence on this process. On the other hand, debris particles

with more substantial cross-section conduct the current pulse unharmed

and the continuity remains.

This method can be applied in several different ways. Firstly, the

current pulse discharge can be initiated automatically every time continuity occurs. The chip light is therefore not activated, unless the

debris survives unchanged the effects of the pulse. The result is a chip detection system with a greatly reduced tendency to nuisance

indications. For example, the Hughes YAH-64 helicopter, whose transmission is equipped with such a system, experience no "wear-fuzz" type

indication through 500 hours of flight tests. The Sikorsky S-76

helicopter is also equipped with such a system. A full-flow chip

detector with screen located in its transmission is shown in figure 5.

Secondly, the current pulse can be initiated by the pilot ("manual"

system). In this case, the chip light comes on each time debris

bridges the chip gap, regardless of its cross section. The pilot initiates the pulse by pushing a panel switch and makes the usual precautionary landing only if the chip light stays on. If the chip light

goes out but comes on again after a short time, this indicates the

continuing generation of fine debris particles. This may be associated

with an early stage of a bearing spall, with a gear-scoring type of

failure or with excessive spline wear. If the current pulses are continued, this type of debris eventually saturates the chip detector and

the chip light can no longer be extinguished. This point corresponds

to the onset of the chip indication in the automatic system discussed

earlier. If desirable, it can be set at an arbitrarily low threshold

by selecting gap size and capacitance for high sensitivity.

125
With this method, prognostic information can be obtained about the

developing failure. This can be made more practical by incorporating

a counter into the chip detection system which records each successful

current pulse. This technique can be used for both automatic and

manual systems. Figure 6 shows a four-channel chip detection system

for a helicopter installation (only one of the chip detectors is shown).

The panel switch is activated when a chip indication occurs and if the

current pulse successfully removes the indication, the corresponding

counter advances.

The pulsed chip detection system is very flexible. For example, it is

equally adaptable to full-flow and to sump-type lube systems and is

easily retrof i ttable into aircraft with existing chip detector installations. It also retains one of the most important positive characteristics of most conventional chip detectors, the quick access to the

collected debris for visual failure verification without lubricant

dra i nage.

Furthermore, operational experience in several flight test programs has

shown that the pulsed chip detector offers greatly improved dependability and reliability over conventional chip detectors. Its comparatively low cost therefore qualifies it uniquely for future real-time,

airborne debris detection requirements.

126
127
128
.FAILURE OCCURS HERE

I

1 1 PUMP

INLET

SCREEN

/Si

SCAVENGE

PUMP

V

CHIP

DETECTOR

TRANSPORT EFFICIENCY ^, =

CAPTURE EFFICIENCY =

INDICATION EFFICIENCY ^. =

PARTICLES TO POINT "A" PARTICLES GENERATED

PARTICLES ON CHIP DETECTOR

PARTICLES TO POINT "A' PARTICLES INDICATED

PARTICLES ON CHIP DETECTOR

FAILURE INDICATION PROBABILITY

O ^ O ' O O = PARTICLES INDICATED ^ »2 *=^5 PARTICLES GENERATED

LOW ei^aREQUIRE HIGH SENSITIVITY I

HIGH SENSITIVITY CAUSES MORE NUISANCE INDICATIONS I

FIGURE 3

129
150
131
1
ANOTHER LOOK AT TIME WAVEFORM ANALYSIS

J. B. Catlin

IRD Mechanalysis , Inc.

6150 Huntley Road

Columbus, Ohio 43229

Determination of the mechanical condition of machineiry

through the use of vibration measurement most often involves

amplitude versus frequency analysis. This type analysis

generally provides sufficient information to permit diagnosis

of a machine's condition, but there are times when it is desirable to supplement such analyses with additional infoirmation. Although there are many analysis techniques available

to provide additional information, the use of time waveform

measurements provides a niimber of advantages, not the least

of which is the ease of acquisition.

While it is possible to obtain time waveform data with standard, or storage oscilloscopes, the real time analyzer with

its capability to easily store and display time waveform

patterns provides the real impetus for taking another look

at time waveforms as a source of diagnostic information.

Amplitude versus frequency analysis provides information as

to the distribution of the vibration energy across the frequency spectrum of interest. In addition, if such analyses

are taken at short time intervals to produce a "waterfall"

display a plot of amplitude versus frequency versus time is

developed. As a supplement to this information, the time

waveform data can provide the following:

1. a physical description of the vibration which shows whether the vibration is steady or intermittent, constant amplitude or varying, periodic or non-periodic, etc.,

2. the relation between the vibration and physical events

such as valve closure,

3. the peak overall amplitude,

4. the phase as it relates to mechanical unbalance, as well

155
as to mode shapes and harmonics,

5. the symmetry of the signal which relates to the characteristics of the forcing function and the vibrating

structure

,

6. the damping associated with the vibrating structure, and

7. the direction of initial excitation which can be used to

infer the direction of the force and the source of vibration.

When time waveform measurements are taken of different types

of machines it is immediately obvious that in many cases interpretation is aided by the use of filtering. Depending on

the specific data, high pass, low pass, or band pass filtering can greatly clarify a time waveform which would otherwise be difficult to interpret. In addition, it has also

been found that it is desirable to display the data over two

different time intervals. Displaying a relatively "long

term" time sample provides information as to general trends

of amplitude and phase; whereas a "short term" time sample,

i.e., a few cycles of the primary frequency of interest,

shows the details of the vibration which can be used to determine phase angles, direction of excitation, etc.

Although time waveformi data is particularly valuable for

analysis of non-steady state and transient vibrations , it

can also prove useful in analysis of steady state vibration.

By way of illustration, several examples are given.

Investigation of the vibration characteristics of a six cylinder 50 H.P. air conditioning motor driven compressor using

time waveform displays provided information beyond that

yielded by the standard amplitude versus frequency analyses.

In all these tests band pass filtering was used to eliminate

vibration frequencies above and below that band containing

the fundamental and second harmonic of the compressor.

The amplitude versus frequency analysis taken on the compressor for the range of 0-6000 CPM, showed that the signature was dominated by the fundamental rotational vibration

plus what appeared to be the second harmonic. The words

"appeared to be" are used because it is not possible to

13h
determine from an amplitude versus frequency plot whether

the higher frequency is in fact the second harmonic, or

merely a frequency close to that of the second harmonic.

The long term time waveform pattern for these same signals

showed that the amplitudes of both signals were quite steady

and that the phase between them was essentially constant

which confirms that the higher frequency was harmonically

related. By looking at the short term time waveform analysis

it could be seen that the harmonic was in fact the second,

since the phase angle did not change with time, and consisted

of a "jog" in what otherwise would appear to be a sine wave.

For comparison an amplitude versus frequency analysis was

made for a different point on the compressor. Again the two

dominant frequencies appeared to be the fundamental and

second harmonic, although at this position there were also

some low level random vibrations. For this position the

long term time waveform amplitude and phase trends showed an

entirely different picture from the other measurement point.

The amplitude fluctuated widely from instant to instant, and

the phase changed with time.

The short term time waveform plot also showed the random amplitudes and confirmed that the phase was changing. From this

it could be determined that the upper frequency was not a harmonic, and, therefore, most probably related to looseness

rather than misalignment or reciprocating forces.

Thus, the time waveform analyses specifically provided information as to amplitude variation, phase variation and

confirmation of the harmonic relationship between frequencies.

The investigation of time waveform analysis also included a study of a two stage, belt driven reciprocating air compressor. The compressor was driven by a 1750 RPM induction motor

through a belt reduction of 1.75/1 to give the compressor a speed of 1000 RPM.

The vibration characteristics of this machine could be divided into two frequency ranges of interest. The first was the

low frequency range which included the fundamental and second

harmonic of the compressor. These compressor frequencies are

typical of unbalance and reciprocating forced vibrations

135
found in this type machine.

These vibrations when measured at the compressor base, and

displayed as a time waveform, showed the characteristic pattern of a fundamental plus second harm.onic vibration with a 180° phase angle relationship between the fundamental and

second harmonic. Additional measurements made over the bedplate and the compressor cylinder suggested that the entire

compressor assembly was in a rocking mode of vibration at the

frequency of the second harmonic; having a nodal,, or pivot,

point approximately coincident with the centerline of the compressor crank shaft. A measurement taken at the top of the

compressor cylinder in the same direction as that taken at

the base showed that although the fundamental and second harmonic were still dominant, their phase relationship was 0°,

rather than the 180** , indicating that the cylinder top was

moving opposite to the base which is characteristic of a

rocking vibration. It should be noted that to provide positive confirmation of this rocking vibration, a once-perrevolution pulse from an electromagnetic pickup should be

superimposed on the time waveform.

The second frequency range of interest covered the high frequencies, (i.e., above 100 Hz (6000 CPM) although these were

modulated by the relatively low rotational frequencies and

their harmonics. The time waveform was measured vertically

on the top of the cylinder head, and showed the repetitive

pulses of the vibration caused by the opening and closing of

the air intake and discharge valves. The periodic vibration

pulses from this valve action could be seen in somewhat more

detail in a short term analysis, namely the sequence of:

open intake, close intake, open discharge, close discharge.

A further expanded time waveform display of one of these pulsations provided further information as to direction of the

pulse excitation and rate of decay of the vibration.

This same measurement displayed as an amplitude versus frequency analysis showed two dominant peaks: one at about

5000 Hz (300 KCPM) and the other at 11,670 Hz (700 KCPM)

which suggested excitation of two natural frequencies. This

provides an interesting comparison between amplitude versus

frequency and time waveform and indicates the value of the

time waveform in supplementing information from the standard

amplitude versus frequency analysis.

156
From the above examples involving the steady state operation

of two types of reciprocating compressors, it can be seen

that the time waveform does provide significant information

beyond that obtained from amplitude versus frequency analyses

alone.

137
THE ADVENT OF SOPHISTICATED FLUID POWER SYSTEMS

AND ITS IMPACT ON PREVENTATIVE MAINTENANCE IN THE MILITARY

Michael W. Wigton

HIAC Instruments Division

Pacific Scienfific Co

P.O. Box 3007

Montclair, California 91763

ABSTRACT

Over the years we have witnessed advances in many areas

of fluid power contamination control. These advances have

been made in many laboratories with the aid of the automatic

particle counter.

Although we are slow to see transition from laboratory

to field use, where applied, the automatic particle counter

has shown to be a valuable preventive maintenance tool.

The United States Military and many commercial firms realize

the importance of contamination monitoring, however preventive maintenance programs remain somewhat limited.

In the discussion which follows, a brief review is made

of the need for contamination monitoring and the specific

programs that have addressed those needs. Further application

of the automatic particle counter in preventive maintenance

is examined in future trends.

INTRODUCTION

Fluid power systems today are much more sophisticated

than their predecessors of ten or twenty years ago. Why are

they more sophisticated? Because we demand better performance.

Fluid power systems must react quicker, with more precision,

and definitely more reliability than earlier systems. Perhaps

the greatest impact on today's fluid power system has been

caused by computerized control. In effect the introduction

of computer interfaced fluid power has required tighter

tolerance limits in both the fluid power system and system

components

What the designer has gained in fluid power design

through improved feedback systems, precise control, computerization, and reliability; he has given up the high tolerance

of fluid power systems to withstand contamination from various

sources including particulates of wear, ingestion of sources

external to the fluid power system, as well as dirt, water,

and hydrocarbons.

138
Where screens or chip monitoring had sufficed before,

highly engineered filters are now a requirement to prevent

contamination from fouling the hydrauMcs.

Where the use of cotton bags to gather weld beads and

debris was sufficient in the past, vast filter banks and

flushing requirements are specified for initial clean up

procedures, followed by a preventive maintenance program of

monitoring hydraulic and lube oils for unacceptable levels

of contaminents

.

REVIEW

A brief review of design philosophies of various hydraulic applications will give us a good background to help understand why fluid power contamination plays an important role

today.

Surface ships, for example, are evolving from the concept

of several hydraulic systems to a more centralized system.

It used to be that a ship had separate systems for steering,

capstan, winches, elevators and so on. Filtration was either

nonexistant or minimal. Contamination related problems were

avoided by designing the fluid power system to operate on a slurry of hydraulic fluid, sand, and sea water. Perhaps this

is an exaggeration, however , even today we see many of these

old ships operating with the same dirty old sump. Break downs

still occur of course.

Recently, the U.S. Navy has initiated a program to clean

up some of these ships. The hydraulic fluid is cleaned up by

removing water and particulates, filters are installed or

improved. Not surprisingly, the performance of that system

is improving too.

There has always been some concern for subsurface craft

as far as fluid power reliability. A submarine may have two

pumps to ensure a source of fluid power, however it has only

one distribution system. Over the past decade an ambitious

program has been developed to monitor contaminant levels of

hydraulic and lube oils.

Aircraft control systems are another example of a high

risk environment where a man's life depends on a reliable

hydraulic system. Again the U.S. Navy has recognized this

and has perhaps the most aggressive and rewarding preventive

maintenance program in airborne fluid power.

It is true that a properly designed hydraulic system

would have filters in all the "right" places and thus avoid

contamination problems. In fact one might then argue that

"aircraft hydraulics do not become contaminated," but they do.

That is why in 1969 when the U.S. Navy initiated its control

program to monitor aircraft hydraulics, sixty-six reports of

hydraulic system contamination were received of which nearly

139
a third implicated damage to components. Moreover, six deaths

resulted and fourteen aircraft could not be economicallyrepaired. The total cost that year essentially due to contaminated aircraft hydraulics was $28 ,481,000 (1)

Missle systems owing to their overall function, design

and purpose, have always demanded the most of current fluid

power technology. The hydraulic fluid must be very clean,

for operation pressures are high and a sticking valve or even

altered response time could mean mission failure. Once the

missle is in the field the hydraulic system cannot be opened

up again until it comes back to the rework facilities for

periodic inspection. Owing to the size and cleanliness level

required, on-line contamination monitoring is the preferred

means, and works quite well with the HIAC Contamination

Control Monitor. Particle counts can be taken without regard

to test stand vibration, fluid temperature or viscosity

changes. All this can be done while putting the system

through dynamic check out as well.

CONTAMINATION AND PREVENTIVE MAINTENANCE

Thus far I have addressed contamination monitoring without detailing the reason behind the practice. The idea is

very simple, and perhaps taken too lightly by Engineers,

Designers, and Maintenance people: "The end result of the

presence of particulate contamination ... is to accelerate

wear (2) ." Thus if we can monitor and control the amount of

particulate contamination in a system, we have a means for

determining and controlling the useful life of the hydraulic

system.

Contamination and its control is not really new. For

we have known for some time now the effects of particles on

bearings (3) . In recent years the fluid power industry has

made significant improvements in associated areas for contaminant monitoring including instrumentation, standards, and

techniques (4,5).

We know that contamination control generally addresses

four areas:

1. Source

2 . Amount

3. Tolerance

4. Control

From a preventive maintenance point of view each area is

important. If one is to achieve contamination control of a system, one must have a knowledge of source, amount present,

and the tolerance of the system.

Recently much work has been done in addressing source

contaminants, especially "tribocontaminants ," or wear particle contamination. In fact the study has been specialized

iko
and termed Tribology. The term originated from the Greek

"tribos," meaning "rubbing" and is defined as,

"The science and technology of interacting

surfaces in relative motion and of the practices relating

thereto (6)."

A tribocontaminant is still a particle however, and as such,

the rate of generation can be monitored using a particle

counter in a regular preventive maintenance program. The end

result would be a histogram of the system under inspection.

Over a span of time the system would indicate, by means of

the particle count histogram, its transition from break-in

wear to normal operating wear, and finally, transition to

abnormal or degenerating wear; indicative of imminent failure

of the system.

It is relatively easy to access the benefits of particle

counting in preventive maintenance. Two areas of improvement

can immediately be seen:

1. Better scheduling of normal maintenance

functions.

2. Foresight as to when a system digresses

from normal to abnormal wear, at which

point proper action can be taken.

The concept of particle histograms is not totally new,

and has been used in various independent maintenance programs

and in research. I would predict that this is an area in

which we will see future growth in preventive maintenance.

The amount or level of particulate contamination a

system can endure has also been an area of great study. There

are two general ways for quantifying amount of contaminant,

i.e., a particle size distribution (7), and a gravimetric

measurement (mg/1) . While the particle size distribution

gives detailed information over a series of size ranges

(in essence a multivariable) the gravimetric is only a single

variable. Particle size distributions are hence a more sensi--

tive measure to changes in wear patterns. Nevertheless,

gravimetric analysis is used in various lubricants as a measure of contaminant level. In certain low risk or low cost

applications the measure is adequate. But where a break

down in the lubricating system can be economically disastrous,

or risk human life, a particle count distribution should be

taken as a preventive maintenance guideline.

For example, the large turbines used in power generation

by utility companies are monitored periodically to evaluate

the condition of bearings. Should the lubricant indicate

bearing degeneration of an abnormal nature, the turbine can
be scheduled for proper maintenance. The utility avoids an

emergency shutdown and such costs involved during the emergency situation.

Many studies have been done to determine what contaminant level the system can tolerate. Generally the studies

have been done on individual components used in a hydraulic

system (8) . The results look rather encouraging for future

designers as reported by Fitch (9) . It is very possible

Engineers may some day design complete systems with a product

or component normally rated for their sensitivity or lack of

it to contamination.

As stated earlier, control of particulate contaminants

is a multidimensional task incorporating source, amount

present, and tolerance of the system. I have discussed very

briefly each of these dimensions. A great amount of work

has been done in each area and research continues.

Secondly, contaminant control is more than hardware.

It is a well thought out Maintenance Plan to monitor systems,

access their various states for contaminant levels and trends

Such a program can pay off in terms of less down time, better

reliability, safety, and especially improved Maintenance

Management. Improved such that one changes from managing a maintenance program on a crisis by crisis basis, to a well

managed working schedule which forecasts when a hydraulic

system will come in for work to be done.

Finally, filtration is also very important in contamination control. Ideally we would like the filter to offer the

following characteristics:

1. Infinite restriction to the passage of

particles

2. Exhibit zero resistance to the flow of

fluid.

3. Provide unlimited capacity for retaining

particles

Obviously we can only come close to the ideal. HIAC has

aided manufacturers of filters with the development of the

Model 6+6 for determining Beta ratios. With this instrument,

manufactures are able to make particle counts and have Beta

ratios automatically printed out in accordance with adopted

multipass evaluation standards (10)

FUTURE TRENDS

Looking to the future of contamination analysis in terms

of preventive maintenance, we see great possibilities in

several areas.

Computer interfacing of hydraulic systems and contamination monitoring is an area of great potential. By mainlk2
taining historic data in the computer, trends can be analyzed

and predictions made. Not only might it be possible to predict system failure, this information would also further the

organized management of preventive maintenance by scheduling

components for inspection and system checkout.

We will no doubt see improved interfacing of hydraulic

test stands and contamination monitoring. There are many

instances where the test stand adds contaminants to essentially clean systems. Hence the incorporation of contaminant

monitoring on-line within the test stand offers advantages

over current contamination monitoring techniques.

Finally, I believe we will see the use of particle

counting extended for use in monitoring critical lubricating

oils. The method of weight measurement of contaminants is not

sensitive enough in many applications. Nor can many groups

afford a spectrometer to analyze wear metals. We are seeing

enough evidence today to seriously consider particle counts

as an excellent means of predicting bearing failure.

CONCLUSIONS

After many years of study of both particulate contamination and its effects, we are finally seeing the use of the

automatic particle counter make its transition from experimental labs to the shops for use in successful preventive

maintenance programs. While the acceptance of the automatic

particle counter has been widespread for laboratory studies,

practicle use in the field has been slow.

For those commercial industries that have made use of the

particle counter, the initial investment has paid off in many

ways: longer life of hydraulic systems, improved reliability

and forecast of potentially hazardous hydraulic systems.

A large variety of sophisticated fluid power systems

have seen the use of the automatic particle counter as a preventive maintenance tool. The applications are expanding,

and the use of the particle counter is gaining acceptance in

the field of preventive maintenance.

Through improved solid state electronics, HIAC has designed an automatic particle counter which is fairly easy to

use. The use of sample bottles for gathering samples of

hydraulic fluid necessitates an understanding of practical

techniques for obtaining reliable data. However, the recent

introduction of the HIAC Flow Control Monitor for on-line

monitoring of contaminants eliminates almost all possibilities of human errors in technique. The Monitor is pressure

and viscosity insensitive and hence ideal for in-line applications . We will indeed see further use of the particle counter

and computers. Through further research we will be able to

1^4-5
confirm trend analysis toward system or component failure.

It is very possible that the automatic particle counter/

computer interface will become one of the most important

tools in lubrication and hydraulic systems for detection,

diagnosis and prognosis of bearings in hydraulic component

failure. The payoff will be safety, reliability, and an

efficient plan of preventive maintenance action.

ikk
Dow, George C. , "New Data on Hydraulic Fluid Contamination," Mech, Summer 1975, U.S. Government Printing

Office.

Tessmann, R. K. , and Bensch, L. E., "What's Ahead in

Fluid Power Contamination Control?" Paper No. P76-25,

BFPR Annual Report No. 10, Fluid Power Research Center,

Oklahoma State University, Stillwater, Oklahoma, 1976.

ibid.

American National Standard Method for Calibration of

Liquid Automatic Particle Counters Using AC Fine Test

Dust, ANSI B93. 28-1973, NFPA Std T2. 9. 6-1972.

American National Standard Method for Extracting

Fluid Samples from the Lines of an Operating Hydraulic

Fluid Power System (for Particulate Contamination

Analysis), ANSI B93. 19-1972 ISO/DIS 4021.

Bowden, Franklin P., and Tabor, David, Friction,

Doubleday and Co., Garden City, NY 1973.

Aerospace Industries Assoc. of America, Inc., Cleanliness

Requirements of Parts Used in Hydraulic Systems, NAS 1638,

Jan. , 1964

Tessmann, R. K. , "Contaminant Wear in Hydraulic and

Lubrication Systems," Paper No P75-4, BFPR Annual Report

No 9, Fluid Power Research Center, Oklahoma State University, Stillwater, Oklahoma, 1975.

Fitch, E. C. , "Fluid Contamination Control-Its Technological Status," Paper No. P74-56, BFPR Annual Report No 8,

Fluid Power Research Center, Oklahoma State University,

Stillwater, Oklahoma, 1974.

American National Standard Multi-Pass Method for Evaluating the Filtration Performance of a Fine Hydraulic

Fluid Power Filter Element, ANSI B93. 31-1973, NFPA Std

T3. 10. 8. 8-1973.

1U5
TIRE DEGRADATION MONITORING

Wieslaw Lichodziejeswki

GARD, INC.

7449 N. Natchez Ave.

Niles, Illinois 60648

GARD, INC. has been performing nondestructive testing of tires for the

U. S. Army for over 4 years. Based upon this work, which included:

a) a detailed 500 tire ultrasonic scanning test,

b) casing water wicking tests,

c) correlation peel tests,

d) on-vehicle road test monitoring, and

e) ultrasonic inspection technique development,

it was concluded that a quick and simple nondestructive measurement

of tire casing fatigue (degradation) could be made, and that such a measurement would pay for itself in allowing a retreader to:

a) reduce in-process failures, and

b) reduce on-the-road, retread tire failures.

This saves money for both the owner and the retreader of the tires, and

provides increased safety for the user.

What do we mean by casing fatigue? It is the degree of bond between

the cords and surrounding rubber in the body of the tire. This bond

changes during the life of the tire from "tight" in a good, new tire,

to "loose" as the tire body grows during use, to "casing separation" - a failure which is characterized by cord showing on both sides of what

remains of the tire at the end of its life.

Fatigue detection is more practical as a nondestructive test of tires

than separation detection because the presence of a separation does not

necessarily mean the tire will soon fail. Large separations would be

critical to casing failure in retreaded tires. However, they are normally found during the standard retreading process, which includes

inspection in spreading, buffing, and molding. Smal

separations,

which are not now readily found, lead to many casing failures. However,

they do so only in weak casings. A strong casing, with typical small

defects, will not fail until weakened by use. As an example, many new

tires are fabricated with small separations and still provide miles of

use: thus, alone, the presence of small separations is not a practical

indicator of tire suitability for retreading. The state of casing

fatigue must also be known.

Ik6
Monitoring casing fatigue eliminates the need for emphasis on the

detection of small defects (and the elaborate scanning needed to find

them). It provides a quick, simple, and practical way to improve tire

quality and safety.

Empirically, GARD was able to establish that pulse-echo ultrasonics

could provide an indication of casing fatigue. Ultrasonics measures

the increased porosity in a casing due to cord loosening. The sensing

signal decreases, due to sound scatter, as the tire degradation in- creases.

Since pulse-echo is a single-sided inspection, on-vehicle inspections

can be performed. Figure 1 shows such readings for new tires as a function of mileage on a truck. The data is plotted as an average of

axle readings. As expected steering axle fatigue is greater than rear

axle fatigue which is greater than intermediate axle degradation.

Figure 2 shows an averaged population of new-unused, "new" retreadcandidate, newly retreaded, and retreaded retread-candidate tires

plotted against average miles as figured by the U. S. Army. As can be seen the degradation curves in Figure 1 and 2 follow each other well.

GARD, INC. has built and is marketing a pulse-echo ultrasonic Tire

Degradation Monitor (TDM) which allows the above type of measurement

to be made. (Figure 3) Its electronics are specifically designed to

provide digital readings which relate to degradation in both steel and

textile, truck and passenger, tires: readings which range roughly

from 20 to 0, 20 normally being a good tire, and 0 being a weak tire

to be rejected for retreading.

Degradation occurs uniformly around a tire, because tire use is circuferential : age, mileage, load, temperature, and pressure affect the

tire everywhere. So a tire can be sampled to get degradation information. Scanning does not have to be performed; the inspection is

quick and simple. One measurement would theoretically be enough. However, several measurements must be made so that local effects, such as bruises or splices, do not give erroneous readings.

A pulse-echo reading is sensitive to geometry. It is based upon sound

being reflected back to the probe. Thus to make an inspection practical for most tires, a mid-line tire inspection is recommended. Readings

in the shoulder area of a tire are not reliable because tires have many

different shoulder geometries, and worn tires add another significant

geometry variable.

Can this technology predict shoulder problems? (A big concern with

retreaders.) There is obviously a relationship between mid-line and

shoulder fatigue in a given tire. How consistent is it from tire to

tire? A TDM user has found he can eliminate 100% of his top ply and

50% of his shoulder casing adjustments by the mid-line degradation

inspection.
This reduction in failure rates comes about because of two factors:

a) an increased casing rejection rate due to the elimination of weak

casings which would have previously been retreaded and b) grading of

rejected casings for use. The above retreader increased his casing

rejection by 4% in reducing his casing failures as indicated. The

failures accounted for about 50% of his adjustments, which in turn

accounted for about 5% of his total retreading. He now grades his

retreaded casings for about 50% heavy and 40% light use (see Figure 4).

Figure 4. - Inspected Tires

Disposition Distribution

Reject* 4

Trailer Use 46

Any Use 50

* This rejection is before

normal visual inspection.

The retreader is saving money. The trucker has less road failures,

saves money, and has a safer road operation.

In summary, government-financed research work has uncovered a new

failure prognosis technique for tires: that of predicting casing

residual life by measuring its overall integrity, independent of

existing local anomalies. This is much like a life insurance underwriter predicting a person's remaining lifetime based upon his current

age. The insurance companies have found this to be a sound statistical

basis for doing profitable business. We feel the tire industry will now be able to do the same.

11^8

150
151
USE OF MICROPROCESSORS IN ANALYSIS OF ACOUSTIC

EMISSION WELD MONITORING DATA*

R. N. Clark and T. A. Mathieson

CARD, Incorporated

7449 North Natchez

Niles, Illinois 60648

Abstract: The use of Acoustic Emission as a nondestructive technique

for real time weld evaluation creates a need for siq)porting analysis

equipment. This equipment is needed to extract the information required

for setting parameters on acoustic emission weld monitors as well as exploring the application of Acoustic Emission to various welding

materials and processes. The equipment requirements are fast analysis

turnaround time, simplicity of operation, and maximum information

extracted from the weld. The authors are developing a system for this

analysis using wideband tape recordings from a modified video tape

recorder and a microprocessor-based computer. Analysis is made of

amplitude frequency content and pulse-realted information of the acoustic

emission bursts, and presentation of the analysis is designed for simplicity and efficiency in the operator- computer interaction. The paper

presents current results of this procedure, a description of the ana- lyzer system and associated equipment, and possibilities for future work

using microprocessors in this and in other areas.

Introduction

The study of Acoustic Emission Weld MDnitoring at CARD began in 1971 with

an effort aimed at real-time NDE of railroad tank car welding. Our goal

was to minimize radiography, particularly the shooting of multiple

radiographs of the same weld. We hoped to do this by performing "onthe-spot" inspection of welds as they were completed to allow immediate

repair and correction of welding problems. Acoustic Emission is by its

nature an "on-the-spot" phenomenon, and was determined to be a suitable

solution to this problem.

Many researchers have shown that useful information may be obtained

acoustically from stressed metal specimens.^ The welding of metals

produces a unique situation where stress is generated by the thermal

contraction of the cooling weld bead. As the weld cools, stress causes

the growth of flawed areas, particularly cracks. Since the release of

energy in a growing flaw is mechanical in nature, it is also acoustic in

* Some of the data presented in this paper was acquired as a direct of

indirect result of work done under U. S. Nuclear Regulatory Commission

Contract No. AT(49-24) -0187.

152
nature, with the frequencies of interest ultrasonic and generally lying

between 100 KHz and 1 Miz.

Many problems are involved in Acoustic Emission Weld Monitoring, however. These are generally due to extraneous and interfering noise.

This noise is due to a multitude of sources, including the noise of the

electrical arc, cooling slag, and mechanical scraping or pounding

noises. These noises tend to mask the useful information which comes

from the weld.

CARD has demonstrated that Acoustic Emission Weld Monitoring can take

place even in the presence of interference, by the use of signal processing techniques . 2 > 5 ^hg first such techniques were discovered by

trial and error, and involved many hours of manually adjusting parameters and replaying taped data. Our experience is now sufficient to

allow a more sophisticated approach to data analysis, and we felt that

future use of Acoustic Emission Weld Monitoring was sufficient cause to

develop an automatic data analysis system to fulfill our needs. It

would allow us to efficiently study new welding materials and new welding processes, to establish parameter settings for Acoustic Emission

monitoring for particular applications, and to improve settings for

systems in use, such as at our tank car manufacturing facility. To do

this economically, such a data analysis system would have to:

1. Use either live or tape recorded weld data as an input.

2. Have the capability of holding large amounts of data obtained during

one weld and to conveniently store data on all welds observed for

subsequent reprocessing.

3. Have sufficient flexibility in formatting data input and output both

to the convenience of the developer and for efficient operation of

the processor.

4. Offer simplicity of programming for efficiency in altering the way

the data is processed.

5. Be capable of gathering data in an uncontrolled environment, such

as weld lab or production floor.

We would have been forced to use a large-scale conputer as the core of

our system if microprocessors hadn't been developed. The small size,

low cost, and programmability provided by microprocessor systems

enabled us to more than meet the above requirements of Acoustic Emission

analysis. They have allowed us to develop a small, on-line, programable

monitor which will be discussed later.

The introduction of the microprocessor to the electronics industry ranks

as one of the most exciting things to happen in recent years. The

153
development of Large Scale Integration (LSI) manufacturing techniques

allows the reduction of all of the necessary functions of a computer

system to the size of a few tiny integrated circuit "chips".

In addition, mass production of the chips can and has brought the cost

down dramatically. For example, the Motorola 6800 microprocessor, which

has more confuting power than many early conputers that cost hundreds of

thousands of dollars, can be bought for $35.00. This low cost allows

the equipment designer to consider applications which he may otherwise

have rejected, or for which he would have used fixed, hardwired logic

elements

The microprocessor may be thought of as a universal logic element whose

function may be changed by means of a stored "command". A series of

these commands is called a program, or simply "software". The programmer may remove an instruction, and insert another in the program and

easily change the function of the microprocessor. Thus modifications

are easily made, and mistakes easily corrected.

In an application such as ours, turn-around time on a large-scale

machine is, at best, a matter of minutes. At worst, it can be up to a half a day. Microprocessors allow one to conveniently set up a processor that is dedicated soley to ones' project and can reliably give turnaround times in seconds. Large scale machines are still the data

storage chanpions, but with mass storage peripherals (floppy disc,

cassette) microprocessors are able to retain more data than we can presently conceive of gathering.

In the formatting of data exchange, the microprocessor has a definite

advantage. To suit many diverse users, large scale general purpose

machines are programmed to accept input according to a limited number

of formats. Each user must therefore organize his data toward the

processor's preference rather than to his individual situation. The

microprocessor allows one to easily construct his own computer and to

wire and/or program it to accept data in a format convenient to his

individual requirements

Programming a microprocessor is no more difficult than programming a large scale machine. Our processor was easily programmed in assembly

language, but systems are on the market that allow programming at higher

levels, such as BASIC, PL/1, etc.

An area in which microprocessors are better for our applications than a large-scale machine is in their greater mobility and tolerance to

environmental variance. Large-scale machines are set in air-conditioned

rooms. You go to it, it doesn't come to you. Microprocessors are portable and capable of being run anywhere a human will be comfortable.
Finally, when a large-scale machine is programmed, any further use of

that program must be done on that or a similar machine. When a microprocessor is programmed, the job of building a dedicated processor is

virtually conplete. The computer can now exist as a field-portable

electronic device by hardening the programs into PROMS.

The present configuration of the acoustic emission data processing

system is shown in Figure 1. The following discussion of its operation

refers to the block diagrams in Figures 2 and 3.

Data Gathering and Preprocessing

The function of this portion of the analyzer (Figure 2) is to:

1. Acquire acoustic emission information from the weld,

2. Break the analog information down into characteristics of interest

and

3. Put these characteristics into a digital format compatible with the

digital processor.

Information is gathered from the weld by means of (A) a piezoelectric

transducer or transducers sensitive to surface mode vibrations in the

ultrasonic range. Our experience has shown that the range of frequencies of interest is about 100 KHz to 1 Wiz. Although information is

probably present above 1 Mlz, it becomes very difficult to get useable

real world data in this region. We are continuing with our investigation in the >1 M^z region.

The analog signals are amplified after leaving the transducer (s) , and

may be tape recorded at this point (B) . We use a Sony Video tape

recorder, AV3650 which is modified to defeat the servo system on the

rotating head deck, but other equipment may be used. An audio control

track is added at this time to facilitate location of various areas of

the weld, or changes in welding conditions. This information is put in

by voice to allow addition of pertinent comments. The signal from

either "live" weld or tape recorder is then amplified and is simultaneously broken down into frequency and energy characteristics.

Frequency characteristics are determined by (c) a set of 8 band pass

filters which break the band of interest into equal percentage portions.

Each portion is rectified, filtered, and the average peak value determined. A packaged "data acquisition system" (Burr-Brown MP7208) is used

to multiplex the analog signals, digitize, and feed them to the processor system on command.

155
Energy characteristics o£ the burst are determined by a common acoustic

emission technique called "Ring Down Counting". The signal bursts of

interest are approximately exponentially damped sine waves. It can be

shown mathematically that if a threshold level is set, and if the

number of cycles of an acoustic burst exceeding that threshold are counted, then the energy contained in the burst is approximately related

to the count total by the following relationship.

Log (energy in burst) = K- (total of counts)

This method of analog to digital conversion is ideal for acoustic emission bursts, because it tends to average out fluctuations due to extraneous resonances, etc . The ring down counting equipment (d) includes

appropriate amplifiers, IKHz-llVHz bandpass filters, and gain adjustments

and consists of a modified Dunegan/Endevco (model 301) totalizer.

Additional circuitry is employed to supply the totalized ring down count

to the processor, along with information as to our currently used thresholds for energy levels for purposes of display selection, (e.g., we

may select all bursts exceeding the current low energy threshold) . The

information is fed to the processor on command.

Data Processing and Display

After the data is preprocessed, it is presented to the microprocessor

system. This system (Figure 3) does the following:

1. Accepts data in both compressed and multiplexed modes and processes

it.

2. Continuously displays 7 types of processed incoming data in real

time, if desired.

3. Allows changes of display type, scale, or grouping without disrupting the data acquisition.

4. Simultaneously stores incoming data to mass storage, if desired.

5. Recalls data from mass storage, if desired.

6. Prompts the operator in everyday English through the various data

acquisition and display options available to him.

In essence, the data processor used for acoustic emission analysis is

programmed to operate as an on-line, operator -adjustable organizer of

data derived from acoustic emission waveforms. At the heart of its

operation is the Nbtorola M6800 microprocessing unit (MPU) . This MPU,

which contains all the arithmetic and decision-making capabilities of

156
the system, is completely contained in one 40 -pin IC chip. It is this

conpactness that makes the microprocessor system so portable and so environmentally tolerant. The NPU responds to and controls the system

by means of a 16-line address bus, an 8-line data bus, and a number o£

control lines, represented in Figure 3 as one line.

The set of instructions which the MPU uses to operate the system as a data organizer is stored in several Motorola M6810 random access memory

units (RAM) . Other items stored in RAM are the English language text

by which the system and the operator communicate, the processed data,

the current display, and results of calculations directing the system

through its operations.

A key feature of this system for our application is the aforementioned

English text the system uses to prompt the operator and the operator

uses to alter the system's operation. This was implemented so that data

analysis could be done by someone who had no understanding of conputers.

An example of a system operator exchange is shown in Figure 4. This

"dialogue" is conducted using a CRT with keyboard or a TTY unit

receiving and transmitting data to a Motorola M6850 asynchronous interface adaptor (ACTA). This adaptor, and the Motorola M6820 peripheral

interface adaptor (PIA) discussed below, are the keys to the microprocessor system's ability to adapt to the data formats desired by the

operator. The physical structure of these devices is sufficiently

undefined so that an appropriate command from the operator, through

the microprocessor, can configure it to accept and/or transmit in a variety of formats. These devices are different in that the ACTA

receives and sends serial data whereas the PIA receives and sends

parallel data. The CRT-keyboard combination used in our system transmits and receives serial data in a preset format (RS232) . Thus , upon

operation initiation, our program instructs the ACIA to operate in an

RS232 format. The ACIA can then present keyboard text to or receive

CRT text from the data bus, thus creating an operator-MPU information

exchange

.

The preprocessed acoustic emission data are put on the data bus via two

modes. The multiplexed frequency band data (A) is placed directly upon

the bus upon command sent along a control line from the MPU. The ringdown count, threshold, and energy criteria data (B) are presented to the

bus in parallel form through a peripheral interface adaptor (PIA)

instructed by the , MPU to be a 16-bit data acceptor. In addition, this

PIA is instructed to initiate, upon receipt of a control signal from the

pre -processor, a high-priority temporary interruption of the MPU's

normal display and dialogue routines so that the MPU can receive,

process, and dispose of the incoming data. The way the MPU disposes of

the data in our system illustrates the versatility of the PIA.

157
I£ desired by the operator, the processed data can be displayed as it

is received, thus giving a real-time analysis of the current weld

acoustic events. This display is accomplished by presenting display

coordinate data to a PIA instructed to be a data transmitter (C) . The

output of this PIA is put through a digital -to -analogue and operational

amplifier circuit and presented, at the operator's selection, to either

an oscilloscope for online previewing of event trends, or to an x-y

plotter for the creation of hard copy of an analysis. Simultaneously,

if so desired, unprocessed data can be stored in mass storage for

further retrieval and analysis. This data is presented to a PIA

instructed to operate both as an 8-bit data acceptor and an 8-bit data

transmitter (D) . This PIA, by use of its four accessory control lines

and an additional PIA for 12 -bit control line capacity, directs the

traffic of digitized data to and from a floppy disc mass storage system.

Thus, the versatility of our acoustic emission weld data analyzer is

based on the versatility of the microprocessor and its family units.

Some Typical Results

To demonstrate the type of output the data processor gives, the results

from three weld specimens are presented in Figures 5. The type of flaw

induced in these welds was that of incomplete penetration. Dye penetrant was used to provide immediate confirmation of these flaws.

The processor generated histograms shown in Figure 5 are those of the

number of acoustic events of a given ringdown count plotted on the

vertical axis against the value of the ringdown count plotted on the

horizontal axis. In effect, the analysis corresponds to that of an energy distribution. This method of analysis creates patterns that

allow the eye to pick out subtle variations as well as continuous

emission sources such as electronic or weld arc noise.

Figure 5b shows the analysis display acquired during weld number 1, a weld in which incomplete penetration was very slight and intermittant.

Very little acoustic emission activity is present with a widely scattered energy distribution. Incomplete penetration in weld number 2 (Figure 5c) was nearly 100%. Note the dramatic increase in activity.

Weld number 3 (Figure 5a) was generated as a control having good penetration, and the analysis shows the least activity of all. Figure 6

shows variations in the frequency spectra of the above three welds.

The differences in frequency characteristics are also obvious to the

eye. We are presently at the stage where similar analyses are being

done on a mass production basis to create a large acoustic emission

data base.

Summary

To summarize, the use of microprocessors in general allows one to

construct a dedicated processor according to his specific needs, take

158
that processor anywhere he goes, and use it with a minimum of turnaround time. In addition, programming a microprocessor amounts to the

"wiring" of an electronic device dedicated to a desired process.

In our specific application, we are able to use the processor to

display distributions of ring-down count (energy) and frequency bands

during a weld or the play-back of one. Through operator interaction,

we are able to search for a promising flaw- candidate pattern and follow

it through sequences of good and bad welds. By this means, we can not

only find background noise and flaw patterns, but are able to ascertain

what adjustments of monitor parameters are necessary to exclude or enhance these patterns. This will result in a better "signal-to-noise

ratio" in the detection of weld flaws. In addition, it is our hope to

be able to tune the monitor parameters finely enough to allow not just

detection of flaws, but indications of flaw type and extent.

In addition to the analyzer system that has been described above, CARD

has constructed a new acoustic emission weld monitoring system for

particular field applications which also contains its own microprocessor

system. The development of this system followed exactly the same lines

as the development of the data processor but, whereas the processor had

been developed up to the software development stage, this system has

been carried through to the stand alone stage. Besides allowing easy

adjustment, through software, of monitoring parameters as determined by

the analyzer system; the microprocessor also allows this system to perform other functions in its idle time. The microprocessor determines,

by means of difference of arrival time, the location of an AE source

along a weld length; it controls the display of such information, and

allows the system to run on totally unattended operation. Figure 7 shows the system.

References

1. Jolly, W.D. (1968) "An In Situ Weld Defect Detector, Acoustic

Emission", BNWL-817.

2. Prine, D.W. (Dec. 1976) "Inspection of Nuclear Power Component

Welds, by In-Process Acoustic Emission Monitoring", NDT International .

3. Prine, D.W. (Nov. 1974-Mar. 1977) "Inspection of Nuclear Reactor

Welding by Acoustic Emission", (Data Report), U.S. Nuclear Regulatory Commission NUREG-0035-1, NUREG-0035-2 , NUREG-0035-3.

4. Qno, K. (Sept. 1974) "Acoustic Emission and Microscopic Deformation".

159


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162
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163
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166
PICTORIAL HISTORY OF THE DEVELOPMENT OF PROXIMITY PROBES FOR USE

IN HIGH TEMPERATURE LIQUID METALS ENVIRONMENT

Leo Hoogenboom

Mechanical Technology Incorporated

968 Albany-Shaker Road

Latham, New York 12110

Introduction

In the development and condition monitoring of machinery, it is common

practice to use any number from a large variety of sensors that provide operational and/or monitoring information. Fortunately, in many

applications the physical environment in which the sensors operate

tolerates the use of materials of moderate physical properties with

regard to temperature and contact exposure capability.

However, often in those instances where the internal environment of

machinery is hostile to many engineering materials, the need for data

is most urgent. The designers of such machinery and the designers of sensors for use in the hostile environment present inside the machinery,

face much the same problem. Their design freedom is severely limited

by:

1. Lack of choice of materials, types of construction and fabrication

methods

.

2. Need for long life, due to difficult access and replacement.

3. Lack of information on long term physical properties of composite

structures (e.g., electrical connections, metal-ceramic components).

Nevertheless, as the need arose, such sensors as proximity probes, pressure transducers, accelerometers , strain gages, microphones and others

were developed and used. Almost without exception, these were for a long time laboratory devices, due to the very limited demand for field

installations. Of those sensors that have become available commercially

very few if any are shelf items. The commercial quantities made of the

various sensors are generally very limited. Overall quality ranges from

poor to excellent. Prices are up to five times higher than those paid

for comparable devices used in less severe environments. Continuity of

availability of sensors from commercial sources has been good.

When at Mechanical Technology Incorporated (MTI) development work on sodium lubricated bearings began, it turned out that there was no com- mercial source for suitable proximity probes or pressure probes. As a result, MTI developed those sensors for its own use as well as offering

them commercially. For one of these sensors, the inductive proximity

probe, the development is traced as it can be seen in photographs of

16?
sections of actual probes. Before presenting the picture exhibit, the

principle of operation of this class of probes is described and the major

design parameters are identified. The inductive proximity probes are separated in two groups:

1. Eddy Current Proximity Probe

2. Magnetic Reluctance Proximity Probe

Eddy Current Proximity Probe

The principle of the inductive proximity sensor (eddy-current type) is

shown in Figure 1. This sensor consists of a coil powered with alternating current, resulting in an alternating EM*field around the probe.

If a conducting (nonma^gnetiO surface is brought near the coil, the

relationship between E and I changes. This change is the result of

alternating currents (eddy currents) generated in the target by the

external EM field of the probe. The eddy currents in turn generate an EM field which opposes that of the coil.

The opposing effect of the eddy current field causes the total field

inside the target to become weaker with increasing distance from the

surface. The depth at which the intensity is about 60% down from that on the surface is defined as the depth of penetration.

The effect of the target is to reduce the inductance (L) and to increase

the AC series resistance (R)

If part of the gap is filled with a conducting medium, the field of the

coil is attenuated in the same way as by the target. If the field

attenuation in the partially filled gap is small (< 10%) , the probe can

still function. This is of importance when using the probe in a corrosive environment where hermetic sealing is necessary. For that application, the probe is mounted in a hermetic envelope, typically of austenitic stainless steel. The thickness of the stainless steel in the

gap must be such that no excessive attenuation of the field occurs.

Thus, it is important to know what factors determine the depth of penetration. The depth of penetration is inversely proportional to the

square root of the electrical conductivity (p), the magnetic permeability (y) of the target material and the frequency (f) of the AC field,

as is also shown by the graph in Figure 3.

At a given operating frequency, the depth of penetration can vary two

decades between the nonmagnetic resistive materials and the magnetic

materials. Figure 3 can be used as a guide in selecting a usable com- bination of target material, probe envelope material and operating

frequency

Magnetic-Reluctance Proximity Probe

The principle of this probe is illustrated in Figure 2. The field generated by the alternating current through the coil causes magnetic flux

*EM = Electro-Magnetic

168
in the ferromagnetic core. The flux density with a core is from two to

three decades higher than without a core.

The flux passes from the core through the gap back into the core. The air gap constitutes a major part of the magnetic reluctance of the

probe. The typical increase in probe inductance when placing a ferromagnetic target in contact with the probe is 50 - 100%.

The effect of a nonmagnetic target on this probe (Figure 2) is similar

to that on the probe in Figure 1. That is, a nonmagnetic target causes

a decrease in inductance (L) and an increase in the AC series resistance

of the probe with the core. When operated with a nonmagnetic target,

the probe with core is an eddy current probe. When operated with a magnetic target, it is a magnetic-reluctance probe.

Discussion of Section Photographs

Liquid metal bearing research and development requires reliable measurement of shaft orbit. Without exception, the orbit measurement is made

with noncontacting probes. All probes are of the inductive type, of

two classes:

1. Magnetic Reluctance Probe

2. Eddy Current Probe

The reluctance probe consists of a pot core, with a coil inside it. The

eddy current probe consists of only a coil.

The construction of both types of probes is a compromise between the

need to electrically insulate the coil windings (and the entire coil)

and the need to mechanically secure the coil to the housing either

directly or first to the core and then to the housing.

The need for a practical and controllable assembly sequence of the

various parts, including making electrical connections to the mineral

insulated lead, and sealing the entire envelope hermetically, leads to

additional compromises in the entire design.

With the foregoing as an introduction, a number of actual realizations

of high temperature probe designs will be described briefly, using

photographs of metallographic sections of transducers or assembly

drawings identifying the various parts.

The metallographic specimens are made by first vacuum impregnating the

entire assembly, followed by a gradual removal of material by grinding

in a surface grinder. When the desired detail is exposed, the section

is lapped and polished and macro and micro photographs are taken. The

sections selected here are most representative of the arrangements of

probe components In the various designs.

l69
Figure 4 shows a design developed by the U.K.A.E.A, in 1967 . It has

the basic elements of the reluctance probe, coil and core. To assure

that the core is maintained in a fixed position with respect to the

housing, it has a sliding center part. This part is kept fixed forward

axially by an austenitic steel pin (matching the housing in thermal

expansion) . The core is carried through the face, of the probe to eliminate the effects of an austenitic steel cover. The lead terminations

are brought out to the side , to be accessible during assembly.

This probe was used in pairs, in push-pull, with a magnetic target ring

and with a carrier frequency of 800 Hz. Push-pull operation assures linearity and temperature compensation. This design has given satisfactory service for many hours in the English bearing research programs.

It has not been commercially available.

At about the time that the design in Figure 4 was being developed, a very different design was made commercially. Samples of it are shown

in Figures 5 and 6 and Figures 7 and 8.

Both of these designs use a core composed of a bundle of ferromagnetic

alloy wire. The wire passes through the center of the coil and is bent

around in a U-shape to provide a return path for the flux on the outside of the coil. Figure 5 shows a section on the probe center line.

Figure 6 shows a section off the center line, where the outer part of

the core is visible.

Figure 7 shows a design similar to that in Figure 5, except for the use

of a sturdy coil form. It is mounted in a holder that permits (later)

installation of a sealing diaphragm.

The designs in Figures 5 and 7 are for high temperature use, but are

not hermetic. Details of the probe from Figure 7 are shown in Figure 8.

The designs in Figures 6 and 8 were obtained commercially and were

prototypes. Their performance was inadequate.

The designs in Figures 6 and 8 were followed by the design in Figure 9.

It has also a wire core. Two identical inductors are mounted in one housing. The second inductor is used to obtain temperature compensation.

The function of the temperature compensating inductor is discussed in

connection with the following design. The design in Figure 9 was a commercial prototype. Its performance was adequate, but the manufacturer discontinued further development efforts. This led to the

development of the inductive proximity transducer at MTI in 1969 to be

S. A. Dean, B. G. Ferguson, E. Harrison and A. Stead

"A TRANSDUCER FOR MONITORING THE RADIAL CLEARANCE AT A SODIUMLUBRICATED PUMP BEARING"

United Kingdom Atomic Energy Authority

The Reactor Group - 1967 - TRG Report 1472 (R)

170
used in sodium bearing research.

A derivative of the probes shown in Figures 5-9 is shown in Figure 10.

This probe has been made commercially for about 7 years by a succession

of English companies, all under the direction of the originator of the

basic probe design. It has been used successfully in substantial

quantities by a large variety of users. The laminated core permits

operation at a carrier frequency of as high as 50 kHz without serious

degradation of the Q (Quality*) of the probe. The probe is being used

in sodium and steam environments to a temperature of 1100°F (600°C).

Overall, quality control and performance of the probes have been moderate to good over the years. No long term data has been published.

An X-Ray of this probe is shown in Figure 11. It shows the form and

the location of the lead terminations before they were disturbed by

the lead end removal.

The probe in Figure 10 operated in half-bridge configuration can be

used to make a single-ended gap measurement with a dielectric medium in

the gap. Temperature compensation is provided by the second inductor,

which has a dummy target of the same material as that of the active

(outside) target. If a conducting medium is present in the gap, and

if a nonmagnetic target (and dummy target) is used, temperature com- pensation is degraded severely. No application of the latter type

has been reported.

A probe similar to that in Figure 10 with a single (active) inductor

is shown in Figure 12. It is generally used in pairs in push-pull

to obtain temperature compensation and linearity over a wide temperature

range. The section in Figure 12 shows a cracked coil form. The

cracking was probably caused by thermal stresses. The coil was wound

wet (with application of liquid ceramic cement during winding) and

became solid after firing of the ceramic cement. Subsequent axial ex- pansion of the wire caused the coil flange to crack away. The coils

in the transducer in Figure 10 are not wet wound, and no cracking

occurred

All designs shown thus far have a coil of a length roughly equal to their

diameter placed in a magnetic core, resulting in a high inductance and

a very directional and well defined external flux pattern. The design

in Figures 13-14 is a radical departure from that concept. It only

contains a very flat coil ("pan-cake" coil) and no core.

The field of the coil reaches a distance of approximately one half coil

diameter radially and axially (front and rear). The design in Figure

13 shows a coil held in a dielectric mass. The dielectric mass is

held in a metal case at a distance from the coil where the field is

sufficiently weak. Around the coil no metal can be tolerated to within

Ratio of inductive reactance to series resistance.

171
a distance equal to the coil radius, as otherwise the coil becomes

inductively partially shorted and the probe is proportionately desensitized .

The probe design shown in Figure 14 is widely used in many applications.

It is operated with a carrier frequency of 1-3 MHz. The probe is not

hermetic. It is used at low temperatures (< 300°F). Similar probes

are also made for high temperature service, without or with a hermetic

envelope.

When operated at a very much lower carrier frequency, and when held

in a housing made of a resistive alloy, with only a thin face cover,

the probe can be made hermetic. Under these circumstances, sufficient

flux remains to permit sensing of a metal object outside the probe

housing. However, the absence of a core, and in its place the presence

of a conductive housing degrades the signal generating capability of

the probe somewhat, and hence increases the chance of drift and noise.

Also, the small section of the coil necessitates the use of very fine

wire to obtain sufficient turns (and hence inductance) to off-set the

inductance loss due to the absence of a core.

To circumvent the problems of stresses due to differential expansion,

and to locate the coil windings firmly in the transducer, the ceramic

coil form is sometimes replaced with a metallic coil form. The metal

form is coated with a ceramic coating by flame spraying to provide

the necessary insulation to ground for the coil wire.

The metal coil form causes additional losses that further reduce the

probe's signal to noise ratio.

Summary

Development of liquid metals lubricated bearings created a need for

proximity probes capable of measuring bearing orbits in sodium at high

temperature. In a nearly parallel effort, such probes were developed

by U.K.A.E.A. and by the AEC at MTI. Both probes became commercially

available. The U.K.A.E.A. probe has led to the current design as shown in Figures 10 and 12. The MTI probe design has remained the

same, except for minor changes in lead connections made in 1976 and

a different choice of coil wire alloy.

The probe sections shown illustrate the many design concepts that were

tried to satisfy the functional requirements of the measurement. When

comparing the number of components used in the various designs with

core, and the necessary assembly operations and sequence of operations,

the MTI design appears superior to any of the preceding or parallel

designs

The present state of proximity probe technology permits the fabrication

of reliable high temperature hermetic devices suitable for long term

monitoring of machinery in a sodium environment.

172
GAP

TYPICAL PROBE RESPONSE

Fig. 1 - Inductive Proximity Sensor - (eddy current type)

175
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SESSION I V

RAILROAD

SYSTEM

DIAGNOSTICS

CHAIRMAN: I . I . FRAREY

SHAKER RESEARCH CORPORATION

DEPARTMENT OF TRANSPORTATION

SYSTEM FOR TRAIN ACCIDENT REDUCTION (DOT-STAR)

James K. O'Steen

Naval Surface Weapons Center

White Oak Laboratory

Silver Spring, MD 20910

In the course of 30 billion miles traveled each year, the two

million American railroad freight cars suffer thousands of derailment

accidents, 5602 in 1970. These derailments are due to numerous causes,

but historically approximately half are due to failures of equipment or roadway. The cost of these derailments is not accurately known. But

estimates for equipment and roadway-caused accidents total approximately

60-65 million dollars for direct railroad losses, with total losses

estimated at 180-330 million dollars per year.

The largest single category of equipment-caused derailments are due

to broken or overheated journal bearings (hotboxes) , which accounted for

409 derailments and 45-75 million dollars in estimated total damages.

Other major equipment -caused derailment sources are broken truck components and car dynamics. Similarly, the majority of roadway-caused

derailments are attributable to broken rails, joints, or switches and

to improper maintenance of the roadway.

The Naval Surface Weapons Center (NSWC) became involved in this

railroad problem as a part of the Navy's Technology Transfer Program.

The Federal Railroad Administration funded NSWC to investigate possible

solutions to their problem, due to NSWC's experience in the development

of high production, low cost, and high reliability sensors. Considering the large amount of damage attributable to equipment and

roadway-caused derailments and the relatively limited number of major

causes, it is intuitive that an economically feasible solution to this

problem exists. The three most viable solutions to the prevention and/

or reduction of damage from derailment accidents for the existing fleet

are: preventative inspections and maintenance; wayside monitor systems;

and on-train monitor systems.

Each of these methods provides a cost-effective solution to part of

the derailment problem. However, the most functional and cost-effective

solution to the total problem would be a nation-wide system using all

three methods in conjunction.

The on-train monitor system is perhaps the least researched and

definitely the least deployed method of derailment prevention. On-train

systems offer substantial advantages in the detection of failure modes

that are rapid and offer little advance warning. Monitoring of potentially hazardous failure modes during every second of a vehicle's life

is the major advantage of on-train systems. However, providing an economically viable system for railway freight cars is a substantial

challenge. Objectives for such an on-train monitor system would include:

191
o low cost

o very low false alarm rate

o very low maintenance

o self-sufficient

o monitors multiple accident causes

Such an on-train monitor system is the Department of Transportation

System for Train Accident Reduction, DOT-STAR.

Preliminary studies for the DOT-STAR System evaluated the equipment

and roadway-related derailment causes that were monitorable by on-train

systems. The most economically viable equipment -related causes were

journal and roller bearing hotboxes . In both cases derailments are prevented by an on-train monitor system. Prevention of roadway-related

derailments is not economically viable with an on-train system. However,

it was determined that local derailments could probably be detected by an on-train system which could in turn prevent a general derailment (train

wreck)

In a portion of derailments, an initial local derailment of one wheel, one axle, or an entire truck will take place and the train will

proceed some distance without further disturbance. No one will be aware of the local derailment until an obstruction or further damage to the

derailed equipment leads to a general derailment, the magnitude of which

is directly related to train speed.

The number of such two-stage derailments is not readily determined

from FRA accident data. However, review of all National Transportation

Safety Board derailment accident reports between 1969 and 1976 indicate

that up to 30 per cent of all derailments are of the two-stage type.

Therefore, an effective on-train local derailment detector could substantially reduce derailment damage.

The objectives of the DOT-STAR System are three-fold. First, the

system is to detect incipient or actual derailments and provide for

action to prevent or mitigate resulting damage. Second, the system

must provide a minimum life cycle cost, require minimum maintenance, and

be compatible with railroad industry operating and maintenance procedures. Third, the system must be capable of expanding to include

additional hazards such as fire and rock-off.

The DOT-STAR System is an on-train safety system that monitors and

automatically activates the train's brake system upon the detection of

a wheel derailment or excessive axle bearing temperatures. The braking

action stops the train before either an axle bearing failure develops

into a derailment or a minor derailment develops into a major wreck.

Currently, the basic system consists of continuously-monitoring

self-powered thermal and derailment sensors connected via a wiring network to an electro-explosive valve attached to the car brake line (figure

1) . The activation of any sensor produces a pulse of electrical energy

that in turn fires the explosive valve, thereby venting the brake line

and activating the braking system.

The on-train location allows for rapid and automatic response to

derailments caused by failures of either equipment or roadway. The

system on each car is independent of the other cars on the train; this

makes the system compatible with present railroad industry operating

192
procedures

.

The system is designed with low cost, long service life, maintenance

free components to provide both minimum initial and life cycle costs.

The sensor assembly (sensors and integral power supplies) and the

electro-explosive brake venting valve are both one-shot maintenance-free

devices (figures 2,3, and 4). The wiring network is rugged, shielded,

and does not affect normal car or truck maintenance. Expansion of the

basic system is easily provided by coupling of additional sensors (fire,

rock-off, etc.) into the wiring network.

The DOT-STAR thermal sensor is designed to continuously monitor the

temperature of either journal or roller bearing assemblies. At or below

the maximum normal bearing temperatures, the sensor remains inert. If

a bearing assembly rises to a temperature above this normal maximum, the

sensor fires and transmits an electrical signal that activates the

train braking system.

Functionally, the sensor consists of three parts: a spring-loaded

"cocked" firing pin held in the ready position by a "C" configured

release pin and a thermal battery power supply (figure 5) . The heart of

the sensor, the "C" configured release ring, is made of an NSWC- developed

alloy called NITINOL. This nickel-titaniiam alloy has a memory property

such that at a given temperature NITINOL objects can be restored to their

original shape even after being "permanently" deformed out of shape.

When this closed "C" release ring is heated to its thermal transition

temperature by an overheating bearing, this release ring springs to an open "C" configuration, releasing the firing pin which in turn activates

the thermal battery power supply.

The continuing development of the DOT-STAR thermal sensor was broken

into two sequential efforts: journal and roller bearing applications.

The journal bearing work has been completed through a full field demonstration. This demonstration consisted of two phases. The first phase

was the successful demonstration of hotbox detection and train brake

application on two intentionally-caused hotboxes at a train speed of 35

mph (figures 6 and 7). The second phase, which is in progress, is

designed to demonstrate a low false alarm rate. To date 32 sensors have

each seen greater than 40,000 miles of actual service without a single

false alarm. The roller bearing application work is presently preparing

for a similar demonstration test with the expectation of similar results.

The method used to attack both problem applications is identical.

It consists of finite element computer simulations of bearing heat generation and conduction (figures 8 through 14) . These are used to predict

normal over-the-road temperatures, thermal gradients through structural

members, and temperature rise-time characteristics during hotbox conditions. These data were used in conjunction with actual measured over- the-road and hotbox temperatures to optimize the thermal sensor design

and sensor contact location.

Most of the work on derailment sensors to date has involved studying both normal over-the-road and derailment environments. Two possible

detection techniques have been determined: direct rail contact and

seismic detection. In order to eventually compare the two techniques,

substantial seismic over-the-road and derailment data have been collected.

193
From this data, we have found that under extreme winter frozen- ground

conditions, over-the-road environments such as rough track, rough

switches, etc. often exceed derailment conditions during the summer

(figures 15 and 16) . This is true for both acceleration and velocity.

Shock spectra analysis has also revealed no significant differences

between these two environments (figures 17 and 18) . Discrimination

between the two environments will require filtering and integration of

the velocity signature. NSWC is currently exploring this approach.

19^
195
SEA/soR hsseAiSLr o^joupnal h^usino

figure 3: Sensor Assembly Mounting

Locations

196
PISTON

figure 4: Electro-explosive Valve

1.0 INCH DIAMETER

SEQUENCE OF OPERATION

1. HOT BEARING DEVELOPS

2. NITINOL SENSES 250°F

3. FIRING PIN IS RELEASED

4. STAB PRIMER ACTUATES THERMAL BATTERY

5. BATTERY SUPPLIES 6.2 VOLTS TO BRAKE ACTUATOR

HOT BEARING

figure 5: D.O.T.-S.T.A.R. Thermal

Sensor

197
IddO-

-(S«.o)

figure 6: Field Test Demonstration of

D.O.T.-S.T.A.R. System.

Journal Bearing Hotbox Detected

and Train Stopped. Right Side.

figure 7: Field Test Demonstration of

D.O.T.-S.T.A.R. System.

Journal Bearing Hotbox Detected

and Train Stopped. Left Side.

198
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^0 40 (oO SO lOO /7.0 J fa

figure 10: Measured Empty Car Over-theRoad Journal Bearing

Temperatures

zo i-a so /dii /za iia

figure 11: Measured Full Car Over-theRoad Journal Bearing

Temperatures

200
\\\\\\\\\\\

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liii mm

figure 12: Typical Roller Bearing Finite

Element Net for Heat Production

and Conduction Analysis.

Break for Photographic Coverage

Several Paasea Over

ShlmB with Frequent

Stops

THERMOCOUPLE LOCATIONS

5 Adapter Underside Under Sensor Contact Point

6 Center of Adapter Underside

8 Adapter at Thermal Sensor Contact Point

80 100 120

TIME IN MINUTES

160

figure 13: Measured Full Car Roller

Bearing Operating Temperatures

at 45 MPH, 90 Ambient

Temperature

.

201
J00 ' 1 1 1 1 1

1 I —I r 0 /OO zoO 3oo ^<x> 500 ioo 700 S<x3 gao

TiVrie (S'Jr^

figure 14: Typical Predicted Roller

Bearing Hotbox Temperature

Rise Characteristics

202
philpohd depailment study 16

D n ! P EMPTY DERfllLMENT 2 CH 6 FOWKD kMEELS 2S e 19 9 242

figure 15: Typical Side Frame

Accelerations During an EmptyCar Derailment.

DErHTLMEHT STUDY DMIR U INTER TR«CK 112 CM "iOO H2 TMG HhREOURS TO MINNTAC POST 45

7 17 19 6

K

P

ItTO

10

tl Jllj ^^^^

TIME SECONDS

figure 16: Typical Side Frame

Accelerations Traversing

Rough Track.

203
COMPLEX

figure 17: Shock Spectrum Frequency

Analysis of Typical Side

Frame Accelerations Traversing

Rough Track.

COMPLEX

figure 18: Shock Spectriim Frequency

Analysis of Typical Side

Frame Accelerations During an Empty Car Derailment.

20U
COMPARISON OF VIBRATION ANALYSIS TECHNIQUES

FOR RAILROAD ROLLER BEARING DIAGNOSTICS

Warren D. Waldron

Shaker Research Corporation

Northway 10 Executive Park

Ballston Lake, New York 12019

This paper summarizes recent work at Shaker Research Corporation

Involving rallcar roller bearing defect diagnostics utilizing high

frequency vibration techniques. The general objectives of the work

are summarized In Figure 1.

Although both objectives are addressed to the same component - rallcar

roller bearings, and both employ the same basic raw data - high fte-^

quency vibration, they have vastly differing requirements. A track

side or wheel shop device requires ruggedness, simplicity (minimal

operator training) , and a sensitivity high enough to Identify defects

that are easily recognizable to the naked eye. A device used for cer- tification testing, on the other hand, must be able to discern minute

defects and can utilize more sophisticated techniques as It would be

Inherently a laboratory device. The three basic levels of sophistication used In analyzing the raw accelerometer data are summarized In

Figure 2.

Three test vehicles or rigs were employed to evaluate the high frequency

vibration approach using bearings with varying types and degrees of surface defects. The test rigs are shown in Figures 3 through 5. Four

separate types of diagnostic system tests were performed (using the

three test rigs)

.

The primary diagnostic system objectives and conclusions for each of the

tests are summarized in Figures 6 through 9. In addition to diagnostic

system evaluation, the failure progression and certification tests were

designed to study bearing failure mechanisms and times to failure of

various defect modes.

Figures 10 through 14 summarize the results of each test in terms of

bearing condition versus peak amplitude and, in the case of the cettiflcation tests (Figure 14) , the signal to noise ratio of the discrete

defect frequency contained in the demodulated signal. Specific conclusions with regard to each test were given in Figures 6 through 9. In

general it is seen that:

1. If "peak" amplitudes exceed two "g's", the bearing was unquestionably defective.

2. Below two g's, amplitude level was an unreliable Indicator of

bearing quality.

205
3. Using a spectrum analyzer to analyze the low frequency (0-200 Hz)

demodulated signal, made it possible to rate bearings in the

region below two g's.

For the wheel shop tests a modified crest factor approach was also used

as a bearing condition rating factor. In this case, approximately five

seconds of useful magnetic tape recorded raw acceleration data for each

of the 90 bearings tested was available (useful in the fact that both

load and speed were constant). For each bearing a modified crest factor

was created by manually dividing the peak by the average of the demodulated signal at the same "instant" in time. The results of this approach

is shown in Figure 15. The plot shows the percentage of the total number

of good bearings that would be rejected, the number of defective (yet not

condemnable by AAR rules) that would be rejected, and the number of con- demnable bearings that would be accepted versus detection level (modified

crest factor). For example, if the detection (rejection) level was arbitrarily set at 1.0, approximately 20% of the good bearings and 50%

of the defective bearings would have been rejected, and 20% of the con- demnable bearings would have been accepted.

Thus, it is seen that the addition of a rather simple data processing

technique (crest factor) greatly improves the discriminating power of the

high frequency variation diagnostic approach. By performing the crest

factor function electronically and improving the drive system to attain

better speed consistency, the discriminating power should be greatly

enhanced.

General conclusions with regard to the feasibility of high frequency as a railcar roller bearing diagnostic tool are summarized in Figure 16.

206
GENERAL OBJECTIVES OF WORK

EVALUATE FEASIBILITY OF DIAGNOSTIC SYSTEMS:

0 FOR DEPLOYMENT AT A WHEEL SHOP OR

AT TRACK SIDE

0 FOR USE DURING CERTIFICATION TESTS

TO INDICATE THE "INITIAL" OCCURRENCE

OF A SURFACE DEFECT.

Figure 1

207
HIGH FREQUENCY (OVER 10 KHZ) TECHNIQUES UTILIZED

0 PEAK ACCELERATION AMPLITUDE

"1

t' 1

0 PEAK/AVERAGE AMPLITUDE OF DEMODULATED HIGH FREQUENCY

SIGNAL

0 FREQUENCY DOMAIN ANALYSIS OF DEMODULATED SIGNAL IN THE

RANGE OF ROLLER PASS FREQUENCIES (0-200 HZ)

Figure 2

208
ROTATING OUTER RACE

MODERATE AXIAL LOAD

VARIABLE SPEED

UNGREASED BEARINGS

Figure 3

209
FAILURE PROGRESSION AND CERTIFICATION TESTS

0 ROTATING INNER RACE

0 HIGH SPEED (65 MPH)

0 USED TO EVALUATE BEARINGS

WITH MULTIPLE DEFECTS

Figure 4

I

210
1

WHEEL SHOP TESTS

0 ROTATING OUTER RACE

0 MODERATE SPEED (45 MPH)

0 USED TO EVALUATE A "RANDOM" SAMPLE

OF BEARINGS OF UNKNOWN QUALITY

Figure 5

211
OBJECTIVES AND CONCLUSIONS - COMPONENT TESTS

ESTABLISH FEASIBILITY

0 AMPLITUDE @ 10-40 KHZ GOOD INDICATOR OF GROSSLY

DEFECTIVE BEARINGS

0 POOR DISCRIMINATION BETWEEN NEW, GOOD, AND

"MARGINAL" BEARINGS

EXAMINE ROTATIONAL SPEED EFFECT

0 AMPLITUDE DECREASES MARKEDLY BELOW 30 MPH

DEFINE SYSTEM CONCEPT

0 H.F. (10-40 KHZ) PEAK AMPLITUDE APPROACH RECOMMENDED

Figure 6

212
OBJECTIVES AND CONCLUSIONS - FAILURE PROGRESSION TESTS

MONITOR DEFECTIVE BEARING DEGRADATION

0 DEGRADATION EVIDENT AND CONSISTENT WITH INCREASING

AMPLITUDES

FURTHER QUANTIFY AMPLITUDE/DEFECT SIZE RELATIONSHIP

0 AMPLITUDE PER SE NOT ALWAYS INDICATIVE OF DEGREE OF

DAMAGE

EVALUATE EFFECT OF GREASE

0 UNCHANNELED GREASE ATTENUATES AMPLITUDES BY 2 TO 3

0 30 TO 50 HOURS REQUIRED TO STABILIZE (VIBRATION

AND TEMPERATURE) A NEWLY GREASED BEARING

EXAMINE RADIAL LOAD EFFECT

0 LOAD HAS MINIMAL EFFECT ON VIBRATION AMPLITUDES

Figure 7

215
OBJECTIVES AND CONCLUSIONS - WHEEL SHOP TESTS

ESTABLISH FEASIBILITY OF TESTING WHILE INSTALLED ON AXLE

0 SYSTEM CLEARLY ADEQUATE FOR IDENTIFYING

"NON-REPAIRABLE" BEARINGS

IDENTIFY LIMITATIONS OF RECOMMENDED APPROACH

0 ADDED SOPHISTICATION NEEDED TO SEPARATE •

DEFECTIVE FROM GOOD BEARINGS

0 MECHANICAL APPARATUS NEEDS TO BE MORE

POWERFUL AND MASSIVE

EVALUATE ATTENUATION EFFECT OF WHEEL SET INERTIA

0 AXLE MOUNTED ACCELEROMETER ADEQUATE

Figure 8

2li+
OBJECTIVES AND CONCLUSIONS - CERTIFICATION TESTS

EVALUATE POTENTIAL APPROACHES TO IDENTIFY "FIRST" SIGNS OF DEFECT

0 CREATION OF A MINUTE DEFECT WAS REPEATABLY

IDENTIFIED USING SPECTRUM ANALYSIS (VERY

NARROW FILTERING) OF AN ENVELOPE DETECTED

HIGH FREQUENCY ACCELERATION SIGNATURE

0 HIGH PASS (OVER 10 KHZ) OR BROAD BAND

(10 to 40 KHZ) FILTERING OF THE RAW

SIGNATURE PRIOR TO ENVELOPE DETECTION

PROVIDED MORE CONSISTENT RESULTS THAN

NARROW BAND FILTERING

Figure 9

215
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ABLE

:cTs iEPAIR

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SMALL LU m

<3

2l6
217
218

I

1

220
RESULTS OF TESTS AT SOUTHERN RAILROAD WfCEL SHOP SHO*WG TYPICAL DEFECTS

Figure 15

221
SUMMARY OF CONCLUSIONS

HIGH FREQUENCY PEAK AMPLITUDE DETECTION NEAR

2 "g" LEVEL SIMPLE AND INEXPENSIVE METHOD OF

WEEDING OUT BEARINGS THAT SHOULD BE REMOVED

FROM THE POPULATION

SOME FORM OF CREST FACTOR APPROACH AFTER

DEMODULATION APPEARS PROMISING TO BETTER

DISTINQUISH GOOD FROM MARGINAL BEARINGS

IF BEARING DIAGNOSTIC SYSTEMS ARE TO BE

SUCCESSFULLY INTEGRATED INTO THE R.R. SYSTEM,

AAR REMOVAL AND CONDEMNING LIMIT RULES WILL

HAVE TO BE RE-EVALUATED WITH REGARD TO:

FREQUENCY AND PLACE OF INSPECTION — QUANTIFICATION OF DEFECT

(EYE VERSUS AMPLITUDE)

Figure 16

222
SESSION V

LAND

VEHICLE

DIAGNOSTICS

CHAIRMAN: I . A . GEORGE

PARKS COLLEGE OF ST. LOUIS UNIVERSITY

MAINTENANCE MANAGEMENT THROUGH DIAGNOSIS

Richard G. Salter

The Rand Corporation

1700 Main Street

Santa Monica, California

90406

MILITARY LAND VEHICLE MAINTENANCE*

The high cost of military vehicle maintenance has caused an increasing interest in the development of improved vehicle designs and diagnostic aids and procedures, with the objective of reducing costs. The

Defense Advanced Research Projects Agency (DARPA) , Vehicle Maintenance

Program is currently addressing the question of whether advanced technology can contribute the opportunity for reducing these costs.

Current Army vehicle maintenance procedures include a scheduled

maintenance program consisting of preoperation checks and periodic servicing. Also, corrective vehicle maintenance is performed in response to

overt failures. Experience in the realm of stationary equipment maintenance suggests the need for an added component in the Army's operational

scheme—periodic health screening.

HEALTH SCREENING

There are a number of benefits attendant to the ability to anticipate the

need for maintenance rather than just reacting to the occurrence of

failure. Failures tend to occur in a sequence or cascade of events, with

each stage increasing the probability of the catastrophic event. The

ultimate occurrence of this event can also precipitate secondary failures.

If the sequence of events, or a significant decay function within that

sequence can be detected in the early stages before failure has occurred,

a systematically planned intervention can preclude the failure occurrence.

The process, termed here health screening, can also provide the basis for

reducing the scheduled maintenance program where screening can detect

the need, and the lack of need, for servicing. A final benefit is the

capability for a more reliable determination of the probability of a given vehicle successfully completing a future mission increment, leading

in turn to a quantifiable fleet readiness prognosis.

Necessary to the implementation of a comprehensive health screening

program is an understanding of the significant generic failure models for

each vehicle type in the fleet. These models encompass the significant

wear and condition decay functions as well as the failure cascades in

Section titles in this paper are keyed to the briefing charts

attached.

225
which these functions play a role. Maintenance decision criteria can be

derived from both the absolute level of the decay phenomenon and the

rate at which decay is progressing.

A number of test equipments types can be employed to determine the

progression of the decay phenomenon. Standard shop test equipment (TMDE) can be employed but requires a skilled mechanic and a shop setting. A

significant hookup effort and the need for experience in interpretation

of results has resulted in a reticence of Army mechanics to employ this

equipment, even in the fault isolation function. The Army is currently

developing an improved unit known as STE-ICE. This equipment is portable and can be used with a diagnostic connector if the vehicle is so equipped, or with a transducer harness which improves the hookup problem

over the TMDE. STE-ICE provides the mechanic with testing logic but not

with diagnostic interpretation. The Army's ATE-ICE equipment, now in the

experimental stage, adds the capability for interpretive logic. A

limiting feature of this technique, however, is that faults must be cor- rected as they are discovered or the subsequent decisions by the device

may be in error. This limits the capability to perform a complete assessment before repair is initiated.

Dynamometers allow loading of the vehicle throughout the complete

dynamic range of the vehicle and in theory make possible a more complete

determination of vehicle condition. Another approach to dynamic evaluation would involve the miniaturization of the test equipment so that

tests may be conducted on the road, thus eliminating the high costs of

stationary energy absorption equipment. Such onboard equipments may be

either connected just for the period of the test (strap-on) or may ultimately be built into the vehicle.

A final technique for screening tests is the detection and analysis

of selected vehicle radiated signatures. The current state-of-the-art,

however, suggests that this technique is only a long-term possibility.

The radiated signal/noise characteristics from complex vehicle systems

as their condition varies is poorly understood at this time. Given that

vehicle signatures can be remotely detected, that condition/diagnostic

signals can be discriminated and that machine intelligence can yield com- prehensive assessment of vehicle condition, the technique may be con- sidered a candidate ultimate system. Difficulties, however, beyond the

problem of the capture and interpretation of signals from a complex

vehicle may include the costs and logistics of the necessary equipment,

particularly for a battlefield environment.

FAILURE MODELS

Actual vehicle failures result from a cascade or sequence of events or circumstances which ultimately lead to a catastrophic event. An ex- ample of such a sequence model may be developed around the cylinder

failure associated with overtemperature operation. Basic causes can be

of several types. Coolant loss may result from afterboil due to short

cooldown procedures or from a system leak. Inadequate frequency of preop inspection would allow this loss to progress. Or, reduced coolant

circulation could result from a clogged radiator on the coolant side, or

226
faulty pump operation due to a loose belt. Or, debris in the radiator

on the air side could cause reduced heat rejection. Each of these circumstances, or combinations of them, could cause an increasing operating

temperature trend above the thermostat control point. The shape of this

trend is important to its detectability . If this trend is undetected

due to instrumentation resolution and/or infrequent observation, it can progress to the point where a severe overtemperature condition (boil

over) results. If this condition is not observed in time, catastrophic

cylinder failure results.

FAILURE/DECAY FUNCTIONS

Ideally, a time decay function, to be useful in a screening program,

should be a graceful monotonically varying curve with a first derivative

that increases in a continuing progression. If the derivative changes

very slowly and then suddenly increases, precipitously, the short time

available to be alerted to the change will preclude intermittent sam- pling and will require continuous monitoring of the function, with an alarm to signal the "break point." In this case only built-in test

equipment can be considered competent to detect the phenomenon since

off-board periodic inspection cannot practically inspect with the necessary frequency. If significant condition phenomena exist, however,

which exhibit graceful decay functions, intermittent screen testing can

be viable,

IMPLEMENTATION PROBLEMS

The difficulty, however, is that field failure model data for Army

vehicles are woefully inadequate. The current understanding of those

models is manifest in the design and qualification test criteria cur- rently in use. It is apparent from experience with current vehicles

which survive their qualification tests but don't perform to these levels

when deployed in the field that the field deployment failure models are poorly understood. Certain vehicles, for example, require up to five

(5) engines when deployed in the field to complete the qualificationendurance time requirement. The lack of understanding of these models

means that we are ignorant of the prospects for a necessary set of

graceful decay functions, and therefore a means to determine the viability of screen testing as a means to reduce maintenance costs.

Another inadequate resource, necessary to determining this viability, is consistent and reliable maintenance costs data for the existing

fleet. Without such data it is impossible to make meaningful costeffectiveness comparisons of candidate system alternatives with current

practice. A principal difficulty, as usual, is the reliability of data

227
source documentation.

VEHICLE MONITOR SYSTEM (VMS)

A key component of the DARPA Vehicle Maintenance program is the

VMS Demonstration project. The demonstration objectives include de^- termination of the capability of current and near-term technology to

provide effective vehicle-borne instrumentation technology, and to

demonstrate the effective use of such a device in the Army field environment. In connection with this latter objective, we expect the

pilot data developed during the demonstration to provide significant

insights for the recommendation of future productive courses of action.

Participants in the demonstration in addition to the DARPA Tactical

Technology Office (TTO) are The Rand Corporation (program coordination,

test design/supporting analysis), the U.S. Arn^, TARADCOM (contract

administration, test planning and logistics) and RCA, Government and

Commercial Systems Division (hardware/ firmware development).* The cur- rent program schedule includes engineering/vehicle tests at TECOM beginning in FY 1978 and the field demonstration test beginning in FY 1979.

The results of the demonstration should allow improvements to vehicle

design and qualification criteria and a refinement in the understanding

of cost effective future Army maintenance equipments and procedures.

VMS DATA DEVELOPMENT

The VMS is conceived to provide data from the actual field operating environment on deployed vehicles. The types of data to be developed are vehicle use patterns, vehicle condition progressions, and maintenance action patterns. Use pattern and condition data are derived

from instrumented sensing of vehicle variables in a time context. Maintenance actions are derived, primarily from inputs by maintenance personnel, with attendant but unavoidable reliability questions.

In addition to developing a general understanding of the distribution of vehicle employment patterns, failure and decay correlations

will be developed. Short-term failure processes will be developed from

high resolution, real time data displays** showing causative stress ex- cursions among concurrent data variations. Long-term failure correlations will be derived primarily from cumulative stress prediction variables. Analytical techniques to be used in developing these correlations

will include LOGIT analyses (employing logistic progression failure

probability model) and exponential failure probability regressions.

Bill Stewich of RCA will describe this development in the following paper.

In general, data is compressed for storage by time stamp recording

the event of threshold crossings. Each data domain is partitioned into

bands of appropriate resolution.

228
As data is accumulated, quantitative failure models will be developed. Generic decay functions will be described such that the form of

maintenance threshold criteria can be determined and the criteria values

for specific vehicle types estimated. These functions, together with

the use and maintenance pattern data, will be used to describe the significant failure model cascades with steps in the sequence given probability allocations and individual cascades assigned frequency functions.

ANALYSIS COMPONENTS

The partition of the analysis of results is required for the isolation of independent, or mostly independent, failure mechanisms.

Physical components include the upper cylinder, engine mechanical,

cooling, fuel, starting, charging, chassis electrical, drive line and

braking subsystems. Operating components include the duty cycle (including the fraction of inoperative time, off-road operation, etc.),

the stress pattern to which the vehicle is subjected, and the actual

implementation of the scheduled maintenance actions.

UPPER CYLINDER VARIABLES

In the design of a data collection plan for use in long-term statistical failure correlation studies, it is necessary to anticipate

which variables will predict failures of the type anticipated. For

example, it has long been part of the conventional wisdom that the

engine piston-speed history is the primary predictor of the cylinder

wear phenomena—time at speeds above 2000 feet per minute increases

wear rate at increasing exponential rates, rapidly reaching a power of

four (4). I have estimated a preliminary set of independent cumulative

stress variables for purposes of initial test design. These include

the time histories spent at excess rpm, overtemperature, low temperature/

high EGT* (loading while cold) , high rpm/high EGT (heavy load condition

inertial and pressure forces both high, but balanced), high rpm/low EGT

(unbalanced inertial forces) , total cumulative hours (perhaps partitioned

by rpm threshold domains) and the duty cycle portion of time the vehicle

is dormant. Experience accumulated in early testing will help refine

this variable list.

Dependent variables will include the trend in power capacity of the

engine and imbalance among cylinders in power production (and compression) . In addition, the collection of failures as defined by the need

for maintenance are also defined as independent variables.

PRELIMINARY TEST DESIGN

As a preliminaiy starting point in the refinement of the test design and sampling plan, logit analyses are being employed to determine

the failure profile, sample size and sampling rate implied by various

stress predictors. For example, an occurrence 3 percent of the time

Exhaust Gas Temperature

229
Cin 7.5 hrs/month operation) resulting in a 3-year mean time to failure

suggest a progressive trip failure probability of 0.0014 initially (zero

hours on vehicle), 0.0028 after 4.5 hours of stress (1 1/2 years of duty),

and 0.0056 after 8.1 hours of stress (3 years). In order to be 80 percent sure that this profile, rather than a constant rate of 0.0028 prevails, a data sample of 30 vehicle-years of experience is necessary, if

the various explanatory variables are uncorrelated. If they are corre- lated (with a factor of 0.7), the experience requirement is 100 vehicleyears. If the MTBF is doubled, the sample required is reduced by 30 percent, and if quadrupled, the sample required is reduced by 50 percent.

These parameters would also imply a sampling rate resolution of approximately one data point per vehicle trip.

As the program progresses and experience and data are accumulated

(both within and outside the VMS effort) on the vehicle types to be

tested, analyses of this type will be used in refining the test design

and ultimately the interpretation of the field demonstration results.

The engineering vehicle tests will be conducted so as to benefit

the test design process as well as the proof test of the VMS design.

This will be accomplished by recovering data from the VMS on a schedule

to insure a continuous high resolution record and to accumulate the

maximum vehicle test experience on an M60 tank and an M35 2 1/2- ton

truck. Our data analysis computer code for use in evaluating these data

will emphasize the accessibility to high resolution data and the manipulation of that data into explanatory variables for long-term correlations. The results of the correlation studies of these variable com- binations will enable refinement and specification of the system firmware (PROM) including the allocation of the memory capacity among high

resolution, trip data, periodic summation/histogram data, special power

test data, and maintenance action input data. Some minor redesign of

the sensor suit is also possible.

BUILT IN DIAGNOSTICS—AN ULTIMATE CONCEPT?

It is interesting to speculate, even if not highly productive as yet, on what form an ultimate system might take in the future of Arrny

vehicle maintenance. An immediate candidate is the VSA concept but with

the recognition that such systems are probably far in the future.

There is also the added problem of using intermittent inspection in con- junction with precipitous failure behavior. Only continuous monitoring

with warning alarm plus periodic readout can satisfy the total screening

function regardless of the distribution of failure model shapes.

If we examine the prospect for eventually implementing continuous

monitoring, we find reasons for optimism. The form of system involved

is built-in diagnostics and it will derive naturally from the experience

the automotive industry is now developing as a result of imposed emission

and fuel consumption regulations. These developments will assuredly

produce inexpensive and survivable sensors and on-board microcomputers

such that the addition of the diagnostic function is a relatively small,

incremental complication.
Diagnostics will require additional computation and memory, as well

as on-board status and warning displays and a data readout feature. The

diagnostic logical analysis and limit testing can be accomplished by

means of either the on-board system or by the data recovery device

depending on cost effectiveness tradeoffs.

The benefits of such a system include two features of particular

importance in the combat environment, in addition to the general benefits of fault warning and screen testing. One of these features is the

ability to diagnose the repair requirements of a "dead" vehicle. This

capability can be readily used to determine the resources necessary to

regenerate the vehicle to service so that optimized maintenance resource

allocation can maximize total fleet readiness. The other feature is a benefit of the programmed diagnostic logic and the ease of access to

quick diagnostics at the operational level. This feature enables the

company commander to rely on his motor sergeant to optimally schedule

the maintenance of his vehicle fleet such that the fleet readiness is

maximized. In a combat situation, this close coupling of the tactical

commander with the quantitative understanding of the readiness of his

vehicle fleet could greatly enhance his unit's combat effectiveness.

251
MILITARY LAND VEHICLE MAINTENANCE

Scheduled

(\Aaintenance

Vehicle

Failure

I Periodic | -*-| Health

I Screening j

Fault

Isolation Repair

CHART 1

HEALTH SCREENING

(ANTICIPATORY MAINTENANCE) • BENEFITS: REDUCE CATASTROPHIC FAILURES REDUCE SECONDARY FAILURES REDUCE UNNECESSARY MAINTENANCE

BASIS FOR VEHICLE READINESS PROGNOSIS

• REQUIREMENT: GENERIC FAILURE MODELS

• CR ITER I A: ABSOLUTE DECAY

DECAY RATE

• TEST EQUIPMENT: STANDARD SHOP

STE-ICE (DCA )

ATE-ICE DYNAMOMETER

STRAP -ON

BUILT-IN VSA

CHART 2

252
FAILURE MODEL

Shorf Cooldown

After Boil Coolant Loss

Cooling System Leak

Clogged

Radiator Coolant Side

Loose Water Pump

Belt

Debris In Radiator

Air Side

Infrequent PREOP

Progressive Coolant

Loss

Reduced

Coolant

Circulation

Reduced

Hear

Rejection

Unobserved

Increasing Coolant

Temperature

Trend

Unobserved

Overtemperoture Operation

Boil -Over

Catastrophic Cylinder

Failure

CHART 3

FAILURE /DECAY FUNCTION

SENSED VARIABLE

FAILURE PROBABILITY

TIME / MILEAGE

CHART 4

255
IMPLEMENTATION PROBLEMS

• FAILURE MODEL DATA - DESIGN / QUALIFICATION CRITERIA - AMENABILITY TO TRENDING

• MAINTENANCE COST DATA - INCONSISTENCIES - SOURCE RELIABILITY

CHART 5

VEHICLE MONITOR SYSTEM

• OBJECTIVES VEHICLE-BORNE DIAGNOSTIC TECHNOLOGY

CONCEPT DEMONSTRATION-PILOT DATA

• PARTICIPANTS ARPA - DEMONSTRATION PROGRAM

RAND - PROGRAM COORDINATION

Test Design/Analysis TARADCOM - CONTRACT ADMINISTRATION

Test Planning/ Logistics RCA - HARDWARE DEVELOPMENT

• SCHEDULE ENGINEERING VEHICLE TESTS - BEGIN FY 1978

FIELD DEMONSTRATION TESTS - BEGIN FY 1979

• RESULTS VEHICLE DESIGN/QUALIFICATION CRITERIA

ISSUE EQUIPMENTS/ PROCEDURES

CHART 6

25^
VMS DATA DEVELOPMENT

• DATA TYPES: USE PAHERNS

CONDITION PROGRESSIONS

MAINTENANCE REQUIREMENTS

• FAILURE CORRELATIONS: SHORT TERM -- STRESS EXCURSIONS

LONG TERM - - CUMULATIVE STRESS

• TECHNIQUES: LOGIT ANALYSIS (LOGISTIC PROGRESSION

EXPONENTIAL REGRESSION

FAILURE MODEL;

DEVELOPMENT

DECAY FUNCTIONS CASCADES

CHART 7

ANALYSIS COMPONENTS

VEHICLE SUBSYSTEMS - UPPER CYLINDER - MECHANICAL/LUBRICATION - COOLING - FUEL - STARTING

CHARGING

CHASSIS ELECTRICAL

DRIVE LINE

BRAKING

• OPERATING INFLUENCES - DUTY CYCLE - STRESS - SCHEDULED MAINTENANCE

CHART 8

255
UPPER CYLINDER VARIABLES

CUMULATIVE STRESS - EXCESS RPM - OVER TEMPERATURE - LOTEMP / HIGH EOT - HI RPM / HI EOT - HI RPM / LO EGT - CUMULATIVE HOURS - DORMANT FRACTION

DECAY / FAILURE - POWER TREND - CYLINDER BALANCE - FAILURE REQUIRING MAINTENANCE

CHART 9

PRELIMINARY TEST DESIGN

EXAMPLE 3% OCCURRENCE, 7. 5 HR S / MONTH , 3 YR MTBF

FAILURE PROFILE SAMPLE SAE CUM. HRS. TRIP FAIL. PROB. • 80% SURE OF PROFILE:

0 0. 14% UNCORRELATED - 30 VEHICLE-YRS

4.5 0. 28% CORRELATED - 100 VEHICLE-YRS

8.1 0. 56% • 1.5 YR MTBF - 0.7 ( SAMPLE ) • .75 YR MTBF -0.5 (SAMPLE ) SAMPLING RATE - DATA POINT / TRIP

ENGINEERING VEHICLE TESTS • CONTINUOUS HIGH RESOLUTION DATA • MAXIMIZE VEHICLE UTILIZATION • USE TO REFINE DEMONSTRATION TEST DESIGN — Prom — Sensors — Memory Allocation

CHART 10

256
BUILT - IN DIAGNOSTICS

AN ULTIMATE CONCEPT ? • EMISSIONS AND FUEL CONSUMPTION REGULATIONS - INEXPENSIVE / SURVIVABLE SENSORS - ON - BOARD MICRO COMPUTERS

• DIAGNOSTICS - INCREMENTAL REQUIREMENT - ON - BOARD WARNING / DISPLAYS - READ -OUT DIAGNOSIS / REPAIR INSTRUCTION

• BENEFITS - MINIMUM MAINTENANCE COSTS, MAXIMUM READINESS

Anticipate Stiort and Long Term Failure Progressions - "DEAD" VEHICLE DIAGNOSIS - MOTOR SERGEANT READINESS MANAGEMENT

CHART 11

257
VEHICLE MONITORING SYSTEM

S.C. Hadden, R.E. Hanson, M.W. Stewich

RCA

Government Systems Division

Post Office Box 588

Burlington, Massachusetts 01803

RCA Government Systems Division is developing a Vehicle Monitoring

System (VMS) under contract to the Tank-Automotive Research and Develop

ment Command (TARADCOM) and the sponsorship of the Advanced Research

Projects Agency (ARPA) . The system will be a flexible research instrument to be installed in selected military vehicles for the purpose of

collecting data supporting an ARPA-TARADCOM investigation into the high

cost of operating and maintaining the land vehicle fleet. The VMS will

supply comprehensive data describing the true use, condition and maintenance exposure of its host vehicle. This data will impact future

vehicle designs and maintenance procedures.

A prototype development contract has been awarded to RCA following a Phase I design study during the summer of 1976 and design is now in pro

gress. The prototype will be installed in two high density vehicles:

the M35A2 2-1/2 ton truck and the M113A1 armored personnel carrier.

Future plans call for installing a number of these systems in a variety

of vehicles including the M151a2 1/4 ton truck (jeep) and the M48A3/

M60A1 tank.

Hardware consists of a VMS Electronics Assembly (VMSEA) and a harness

assembly, both installed in the vehicle, a Maintenance Action Input

(MAI) device, and Data Retrieval Equipment (DRE)

During the course of the investigation, the on-vehicle assemblies will

automatically collect and store vehicle generated data and maintenance

data inputted by a mechanic via his MAI whenever he services the vehicl

Following nominal one month intervals, a contact team participating in

the Investigation will rendezvous with the vehicle, connect the DRE,

extract the accumulated data and service the on-vehicle assemblies as necessary. Special vehicle tests may also be performed at this time

and their results automatically compiled with the accumulated data.

The data, encoded in digital format and requiring no human inputs other

then those of the mechanic, will then be forwarded to a processing

center for reduction and analysis.

238
Data Acquisition

The data acquisition scheme is based on collecting vehicle data which

can be processed to evaluate a specific set of Vehicle Indicators . The

indicators, which result from the first order reduction of raw VMS data

at the processing center, quantiatively describe vehicle use, condition

and maintenance exposure throughout the data collection interval. They

combine all the VMS generated data into a structured data base available

for further analysis. Table 1 lists the indicators that have been established.

The raw VMS data is acquired by monitoring key Vehicle Parameters during

normal operation or special tests and by accepting coded inputs from a mechanic. The parameters which will be monitored for four high density

vehicles are listed in Table 2.

The selection of vehicle parameters and the design characteristics of

the VMS Electronics Assembly are critically related. The assembly is

not merely a recording device. With its internal microprocessor, it

manages the acquisition of parameter data and performs data reduction to a level where the indicators' raw data requirements are met with a minimum transducer count and on-vehicle memory capacity. This is illustrated in Figure 1. For example, the on-vehicle processor can insure that

the value of some particular parameter is recorded only when it carries

some specific significance, or it can determine some critical relationship among several parameters and enter this single result into storage

rather than the values of the individual parameters themselves.

Table 1. Vehicle Indicators

Usage Indicators

Engine starts

Failed starts

Push starts

Jump starts

Cranking in gear

Oil Temperature out of range

Ambient Temperature

Electrical load

Fuel consumption

Parking brake engagement

Warm up time

Engine blipping*

Total revolutions

Clutch operation

Engine RPM

Engine overspeed

Road speed

Front wheel drive engagement

Engine load

High Load periods

Terrain exposure

Coasting mileage

Total mileage

Brake application

Cool down time

Vehicle acceleration/ deceleration

Gear ratios

Tracked vehicle turning

Mechanic's term for pulsing accelerator pedal

259
Table 1. Vehicle Indicators (Continued)

Condition Indicators

Health of - Starting system

Charging system

Fuel system

Lubrication system

Breathing system

Cooling system

Electrolyte

Drive train slippage

SI engine firing condition**

Diesel power**

Compression balance**

Fluid Levels - Engine Oil

Brake

Coolant

Maintenance Action Input Indicators

Engine Compartment Openings

Action Codes

Component identification codes

Elapsed maintenance time

Special Tests

Data collected during special tests are obtained by monitoring the same parameters providing data during normal vehicle use. These tests consist of a CI engine power test, an SI engine idle misfire test and a compression balance test, all of which are significant in describing en- gine condition. They are special in that they require unusual operator

vehicle interaction which may not occur during normal operation and,

therefore, will be performed by the contact team at the time of data retrieval. The CI power test requires that the engine be brought from

idle to governor speed at full acceleration, followed by fuel shutoff

while at governor speed; power is calculated from the acceleration and

deceleration rates. The SI engine idle misfire test is performed on a warm engine running at idle. The time intervals between 101 successive

point openings are precisely measured and misfires are detected from irregularities in these intervals. The compression balance test requires

that the engine be cranked while fuel or ignition are "off"; compression

balance is calculated from the starter current waveform.

Hardware Overview

Figure 2 illustrates the hardware configuration.

The VMSEA is the core of the system. It interfaces with the vehicle

harness assembly which terminates in transducers and switches installed

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VEHICLE PARAMETER

VEHICLE PARAMETER N

INDICATOR L

Figure 1. Data Acquisition Process

IN MAINTENANCE SHOP

MAI - USED BY MECHANIC FOR MAINTENANCE DATA ENTRY

DRE - USED BY CONTACT TEAM FOR DATA RETRIEVAL, REPROGRAMMING,

SPECIAL TESTS, AND SYSTEM CHECKOUT

WITH CONTACT TEAM

HARNESS & TRANSDUCERS - SENSE VEHICLE PARAMETERS

VMSEA - AUTOMATICALLY COLLECTS AND STORES VEHICLE DATA

INSTALLED IN VEHICLE

Figure 2. VMS Hardware Configuration

2k2
throughout the vehicle. It also interfaces with the DRE/MAI connector

which will be mounted at a location readily accessible to the mechanic

and contact team.

The MAI device will be a simple hand held unit kept at the vehicle maintenance shop. It will be equipped with three digl-switches via which the

mechanic can enter a maintenance action code, a component identification

code and the elapsed maintenance time. For example, replace/fuel injectors/thirty minutes = 001/016/030. Lights will be provided to indicate that the VMSEA is ready to accept a code and acknowledges an entry.

A small code booklet will be furnished with the device,,

The DRE equipment will be housed in a suitcase sized transport case car- ried by the contact team. It will contain a cassette type digital tape

transport to record the data retrieved from the VMSEA memory and to re- program the VMSEA program memory as required. Controls and a digital

display will also be provided to enable the contact team to verify data

transfer, determine the health of on-vehicle VMS assemblies and fault

isolate as required, and record results of the special tests.

VMSEA Design Features

The VMSEA, from both hardware and software standpoints, is the critical

system element. It is being designed for unobtrusive installation in

the vehicle, to resist tampering and record evidence of such, and to

operate in the environment of the tactical military vehicle with minimum

servicing. It will serve its function in any vehicle; only the program in

structions in the VMSEA and the harness assembly will be vehicle dedicated. Physical characteristics are presented in Table 3.

The VMSEA will contain an RCA 1802 CMOS microprocessor with 30K bytes (8

bit) of CMOS RAM memory: 12K bytes program memory, 2K bytes scratchpad

memory and 16K bytes data storage memory. Signals will enter the VMSEA

over forty-five input channels allocated among the four vehicle types as shown in Table 2. Dependent upon the nature of the signals, e.g., switch

position, analog voltage, pulse train, they will be inputted through status registers, analog multiplexer to ADCON, or handled on an interrupt

basis

.

Certain of these inputs are referred to as Action Triggers . The action

triggers, which are comprised of vehicle produced stimuli, tampering sensors, an internal clock, or connection of the DRE or MAI, cause the VMSEA

to switch between operating modes and/or to record, process and store

data.

The operating modes are active, standby, and backup. In the active mode,

the VMSEA collects, processes, stores and dumps data as directed by its

internal instruction set, action triggers, and commands received from the

DRE. In the standby mode, power is applied only to those circuits nec2U3
Table 3. VMSEA Design Characteristics

Weight

18 pounds

Size

13.5" X 9.2" X 6.8"

Power Consumption (10 to 32 volt input from vehicle)

Standby Mode - 0.3 watts

Active Mode - 15 watts

Life on Backup Battery - at least two weeks

Environment

Temperature, Operating: -40° to 145°F

Non-Operating: -70° to 185°F

Humidity: 95% condensation, occasional splashings

Altitude: to 15,000 Ft. operating, to 40,000 Ft. non-operating

Vibration: 3G (5 - 500 Hz), 50G (10 - 1500 Hz)

Design Features

Microprocessor: RCA 1802 CMOS

Memory: 30K Byte CMOS RAM

Flexibility

Pro grammab il i ty

Expandability

Applicability

Ma in ta inab ili ty

Internal self check with status display to contact team

Isolation to component level replaceable by contract team

No field calibration required

Reliability

Verification of data transfer at retrieval

MIL-STD established reliability parts

MTBF: 1030 Hours (30 months for heavy usage vehicle)

Program loading via DRE

Two spare boards with power, output channels

for transducer conditioning circuitry and memory

expansion

Applicable to all vehicle transducer sets

2hk
essary to maintain storage and recognize action triggers which switch the

VMSEA to the active mode. The backup mode is an emergency mode in which

only the clock and memory circuits are powered in the event that prime

power, normally drawn from the host vehicle's batteries, is interrupted.

The internal battery will sustain the clock and memory for at least two

weeks

.

VMSEA Data Memory

Major attention has been given to the architecture of the VMSEA data memoryo It will be implemented with solid state CMOS devices to take advantage of their reliability and low power consumption, A 16K byte (8 bit)

capacity is feasible given the density of current LSI devices and the

constraint that the VMSEA be of unobtrusive size. In order to compress

all of the significant vehicle data generated during a thirty day interval into this capacity, a scheme has been devised in which a portion of

the data, particularly that surrounding a significant event, is retained

in high resolution format while all of the data is retained in a "binned"

format

.

The high resolution format will consist of time-ordered data samples en- tered into storage at the sampling rate peculiar to each parameter. Engine speed will be sampled at a 0.1 second rate and, in the absence of a uniform acceleration, a time-tagged entry will be made for each 200 RPM

change. Should a uniform acceleration be detected, only the end points

will be recorded. Engine oil level will be sampled at a much lower rate.

The level will be measured following each shutdown and the first "low"

indication of the day will be recorded.

The sampling algorithms and high resolution format will permit a detailed

reconstruction of the vehicle operating profile when necessary. However,

the storage capacity required to retain all data in this format could become unwieldly, particularly in the case of a vehicle exposed to heavy

use. The bulk of a vehicle's operating profile can be adequately reconstructed with less temporal resolution. The microprocessor will be used

to reduce all data, originally sampled at high resolution rates, to the

compact "binned" form.

A "bin" will consist of a reserved memory segment for recording some specific result computed between selectable time limits. The contents of

each bin will be a single entry: a count of events, an accumulated time,

etc. A typical bin for storing engine speed data will contain the total

time that the speed lay between, say, 2000 and 2200 RPM during a specific

week. Another example is engine oil level; a bin will contain the number

of days that the oil was found to be low during the week. The actual bin

structure is more complicated and is designed to extract the maximum information from each parameter. Twenty-five bins will be allocated to en- gine speed data for a nominal one week interval: (a) total time between

2k^
0+ and 400 RPM, (b) total tijne in 200 RPM increments, 400 to 5000 RPM,

(c) number of 400 RPM crossings. The entire bin structure will be software adjustable.

A definite amount of storage capacity, independent of vehicle usage, can

be allocated to storing binned data. Once this allocation has been made,

the remainder of the memory can be allocated to storing high resolution

data detailing some portion of the vehicle's operating profile.

In operation, all sampled data will be both entered into high resolution

storage and processed into bin storage. When the memory capacity allocated to high resolution storage is filled, the memory contents will be

overwritten on a first in/first out basis; binned data will never be

overwritten, only updated. At any given time, the memory will contain

all the binned data accumulated since the start of the collection period

plus the most recent high resolution data.

The process will continue as described to the end of the collection interval unless some significant event occurs which will cause overwrite to

be inhibited. The VMSEA can be programmed so that any event which it can

detect can be used as an inhibit trigger; fifteen triggers can be set at

any one time. Should overwrite be inhibited by some event, e.g., a mechanic's entry that he replaced the engine, predetermined amounts of high

resolution data surrounding the change will be protected.

Figure 3 shows the memory that has been allocated for the different forms

of storage. In addition to those discussed, fixed storage areas have

been allocated for maintenance action data (forty-eight mechanic entries

plus dated detections of forty-eight compartment openings), trip data (a

set of eight data entries for one hundred automatically recognized trips),

dynamic variables of the VMSEA operating system, special test results and

confidence test results.

The 13. 3K bytes of data memory remaining after allocation of fixed storage, along with the type of vehicle and the usage which it receives, determines the percentage of total high resolution data generated in a nominal thirty day interval which can be retained. This is summarized in

Table 4. The quantitative estimates of vehicle activity were developed

by defining use elements - a minimum monthly element, a cruise element,

and a tactical off-road element - of specific duration and activity

content. The quantity of data produced by each element was calculated

and combinations of these elements were used to estimate monthly totals.

2k6
HIGH RESOLUTION DATA STORAGE

(13.3 K BYTES)

FIXED STORAGE

AREA , (2.7 K BYTES)

TOP OF STACK

FIXED LENGTH BLOCK (512 BYTES)

BOTTOM OF STACK

BIN DATA STORAGE (250 K BYTES)

TRIP DATA STORAGE

SPECIAL TEST RESULTS CONFIDENCE TEST RESULTS MAINTENANCE ACTION INPUTS OPERATING SYSTEM VARIABLES

FIRST IN/FIRST OUT MECHANISM

Figure 3. Data Memory Organization

Table 4. Estimated Amount of Monthly Data

Retained in High Resolution Format

Vehicle Type and

Monthly Use Hours

Wheeled (M151, M35)

Light 7.7

Moderate 23.4

Heavy 41.7

Tracked (M113, M48/M60)

Light 0.8

Moderate 10.7

Heavy 24.8

Data Memory Size:

Data

Generated

In Month

9.8K Bytes

26. 3K Bytes

46. IK Bytes

2.9K Bytes

15. 9K Bytes

33. 6K Bytes

Percent Retained

In High

Resolution Format

All

50%

29%

All

84%

40%

16K Bytes (8 bit)

Allocated for High Resolution Storage: 13. 3K Bytes
Confidence Tests and Fault Igolation

The VMSEA will conduct routine confidence tests to assess its own health

and that of the vehicle harness assembly. Test results will be acquired

automatically during unattended operation. The bulk of the data will be

stored and transferred to the DRE at data retrieval for forwarding to

the processing center. There it will be used to determine long term

health and calibration trends, e.g., transducer offset drifts.

A portion of the results will be processed in the VMSEA and stored in a format which can be displayed to the contact team when the DRE is connected. This will enable the contact team to make on-the-spot corrections:

replacement of internal battery, entire VMSEA, defective transducer and

repair of cables. As a typical example, the DRE might display a code

which indicates the presence of a fault in channel 32. The contact team

will then substitute a dummy harness assembly for the real one and determine if the fault persists. If it does, the VMSEA will be replaced. If

it does not, channel 32 harness wires will be checked and repaired as required. Finally, the channel 32 transducer (oil temperature RTD)

will be replaced. Replacement of certain malfunctioning transducers

may be beyond the capability of the contact team. In this case,

they will call for support.

Program Schedule

The prototype VMS system will be completed for acceptance testing during

June 1978. It will then undergo a period of testing on selected vehicles

to determine what changes should be incorporated in production units to

optimize data acquisition. When finally operational, the VMS is expected to furnish data impacting the design, operation and maintenance policies of military vehicles.

Potential Applications

The VMS is potentially applicable to all classes of vehicles - land,

marine and air. The exploitation of microprocessor technology provides

flexibility and adaptability through software changes rather than hardware re-design. In addition, it minimizes data memory requirements,

thereby allowing the use of relatively small, but relaible and rugged,

solid state memories which are well suited to application in hostile and

space limited vehicle environments.

Acknowledgement

The authors wish to acknowledge the contributions to the development of

the VMS provided by Major T. Covington, ARPA, Mr. D. Sarna, TARADCOM,

their staffs and their consultants from Rand and Battelle.

2kQ
SYSTEMIZED DIESEL ENGINE DIAGNOSTICS

Heniy J. Mercik, Jr.

Hamilton Standard Division

Iftiited Technologies Corporation

Windsor Locks, Connecticut 06096

Introduction

The advent of today's electronic systems brings engine manufacturers and

engine owners new concepts which allow non traditional methods for

inproving engine maintenance techniques. Economics of engine operation

and government environmental regulations are additional motivating

factors which are influencing the current interest in reducing maintenance costs and iirproving engine performance. A study of past maintenance practices reveals an inconsistency in procedures utilized for

diagnosing engine problems and a pattern of standard repair procedures

which are employed when a particular operational problem is reported.

The repair procedures generally result in replacement of several engine

components without seriously attempting to isolate the faulty component.

The basic problem may or may not be solved utilizing these procedures

and therefore additional maintenance may be required in a second attempt

to solve the problem. These methods are inefficient and costly, a cost

which is borne by the owner or a warranty program.

An approach for engine maintenance which shows considerable promise for

success utilizes the concept of systemizing the diagnostic procedures

for identifying problem causes and directing the mechanic to a particular repair procedure. A system for the maintenance of gasoline engine

powered vehicles is now in production. A second generation of this

system which is called Autosense^ has been developed for diagnosing

diesel engine malfunctions. The basic AutosenseR unit is utilized for

both the gasoline and diesel engine test systems and therefore minimizes

equipment costs because of the economies resulting from fabrication in

production quantities. The commercial truck market is the primary

market for which the diesel test equipment has been configured. However,

the test techniques which have been developed are suitable for application to marine, agriculture, construction, and off-highway diesel

engine maintenance.

In addition, since the system is tape controlled its uses are not

confined to testing engines. Inclusion of the proper sensors and diagnostic program on tape cassette allows expansion for testing transmissions, vehicles and other types of equipment requiring sophisticated

diagnostic procedures.

2k9
System Description

The diagnostic system is a computerized tool for fault isolation of

diesel engines and their subsystems. It consists of a conputer console

and a hand held controller. The computer console contains a data

acquisition unit, teletypewriter, computer and a tape drive system. The

transducer and solenoids for handling pneumatic and hydraulic signals

are contained in a transducer box which is mounted to the rear panel of

the console (Figure 1). The control program, test sequences, tests,

test limits and specifications are contained on a small tape cassette

which is placed into a tape reader. Reprogramming of the tape cassette

allows for specification changes or expansion for testing additional

engines and other types of equipment.

ENGINE/VEHICLE SENSORS

Figure 1. Diesel Diagnostic System Block Diagram

Sensors and sensor location was a significant consideration when con- figuring the system. The desirability to utilize engine mounted transducers is apparent, however, we selected the approach of using a transducer mounted in an enclosure at the unit. The primary reasoning which

influenced the decision was cost, durability and performance of transducers commercially available for the possible applications. If

sensors were to be specifically designed for the application, the engine

mounted sensors would be preferred.

Operation

The HTS scheme for testing is to perform all tests on the engine without

requiring a dynamometer. The non-dyno test techniques are relatively

250
new and can be run quickly in both the steady state and dynamic test

modes. A comprehensive approach to diesel engine diagnostics must

include the ability to test for particular recurring problems, engine

subsystems and individual tests independently. To inplement this

approach complaint oriented and subsystem sequences have been established which, when selected as the desired sequence for testing, automatically lead the operator through the testing cycle (Figures 2^3)

Complaint Oriented

Slow Crank

No Crank

Cranking/No Start

Hard Start - Hot

Hard Start - Cold

Low Power

Miss or Rough Running

Fast or Slow Idle

Smoke

Oil Pressure High or Low

Overheating

Figure 2. Diesel Diagnostic

Sequences

Subsystem Sequences

Fuel System

Lube System

Cooling System

Air Intake System

Turbocharger

Air Charging System

Electrical System

Individual Tests (Partial Listing)

Engine Power

Power Contribution

Relative Congression

Blow-By

Gage Accuracies

High § Low Idle

Battery Condition

Fuel Piimp Calibration

Figure 3. Procedural Test

The system is designed to diagnose engine problems with test sequences

that are executed without external loading of the engine. By analyzing

results of several tests a recommendation for a repair procedure is made

to the operator.

Low Power Diagnostic

A common complaint of diesel engine operators is low power. An example

of a diagnostic sequence for low power with its truth table and repair

codes is illustrated in Figure 4. The tests selected for the sequences

are listed on the left and the test results, pass or fail, are contained

within the matrix. As a result of the engine performance when the

diagnostic sequence is run, a pass or fail is recorded for each test.

The pass -fail results for an individual test may not reveal the problem

by itself. However, when included in a sequence containing the results

of several tests, a determination of the problem cause can be

251
established. The sum o£ the test results in a sequence will refer the

operator to a repair code which defines the problem cause and recommends

a repair procedure.

TRUTH TABLE

TEST COMP P F F P POWER P

AIR IN FUEL P F CH PT 2 P > CH PT 1 P PEAK PRESS P GOV CUT OFF P 4 i F BLOW-BY P

AIR FILTER P 4 F TURBO P F POWER COSTT P F DIAGNOSTIC CODE

DIAGNOSTIC MESSAGES MESSAGE

15 2

151

15 '

15 1

160

16 1

ENGINE NORMAL

VALVE LEAKAGE

CYLINDER OR PISTON DAMAGE

AIR IN FUEL

FUEL PUMP OUT OF CALIBRATION. RUN 928 SAME AS 155 SAME AS 155 SAME AS 155 EXCESSIVE INLET RESTRICTION SLUGGISH TURBOCHARGER

INJECTOR PROBLEM

Figure 4. Low Power Diagnostic

Horsepower

The horsepower test is a dynamic test developed for the diesel diagnostic system (Figure 5) . Data are gathered during the free accel mode

of engine operation. During a full throttle acceleration, the engine

accelerates with its own inertia as a load. Torque is determined by the

rate of acceleration times the engine inertia, T = la. Horsepower is

obtained from the torque at any speed, HP = KTN. Actually, the torque

generated during the accel is related to the specified torque, and by

applying an algorithm developed for this purpose, torque which the

engine is capable of producing can be determined.

TIME

Figure 5. Diagnostic Techniques - Power

I 252 t
Turbocharger

Tests such as the turbo tests do not require full loading but do require

a snap accel from idle to high idle and a hold at high idle for about

five seconds (Figure 6). During the snap, inlet manifold pressure data

are collected which when compared with previously established dynamic

limits provides an assessment of turbo condition. The characteristics

of turbo performance which are used in the analysis are the inlet manifold pressure depression, time of depression, pressure rise as a function of time and max value of inlet manifold pressure.

Figure 6. Turbocharger Health

Cylinder Health

A sound indicator of cylinder health is the relative compression test

(Figure 7) . By monitoring the battery current drawn during engine

cranking, an evaluation can be made as to the work required during

congress ion for each cylinder. By selecting the cylinder requiring the

most work for compression and comparing that with the work required

during the compression stroke for each of the other cylinders, an evaluation of relative compression can be established.

This test in itself will not identify the fact that a valve, ring or piston must be replaced. However, if other tests such as blow by are run in conjunction a more definite analysis can be concluded. The

system output can, therefore, differentiate between ring/cylinder

problems and valve and gasket problems.

255
DIAGNOSTIC TE:CHNIQUE

zn 4Tr err stt CRANKSHAFT ANGLE(RAOIANS)

• LOW RELATIVE CURRENT INDICATIVE OF LOW COMPRESStON

Figure 7. Relative Compression

Fuel Pump Calibration

A calibration check of the Pressure-Time (PT) type fuel pump can be

achieved by sampling fuel pressure at predetermined reference points

during a snap acceleration of the engine. These results contribute

significantly to analysis of fuel system and low power conplaints

(Figure 8)

120 RAIL FUEL PRESSURE

(PSIG)

500 1000 1500 2000 2500 ENGINE SPEED (RPM)

• FULL mROTTLE ACCELERATION

• ANEROID DEFEATED

• FOLLOWED BY DECELERATION FOR THROTTLE LEAKAGE TEST

Figure 8. Fuel Pump Calibration

Lubrication System

By locating a transducer at a point downstream of the pump and regulator

but before the oil filter, an assessment of the lube system can be

determined. During a snap accel the pressure can be tracked and the

time to reach regulation and the regulation pressure can be established

25U

4
(Figure 9). This information, when conpared with functional data from

a properly operating system , can be used to determine pumping performance, regulation, lube system flow capacity, and in some systems, the

point when piston cooling commences.

Ol 1 1 U 1 1 500 1000 1500 2000 2500 ENGINE SPEED(RPM)

• SLOPE INDICATES RELATIVE SYSTEM FLOWRATE

• BREAKPOINT OCCURS AT PRESSURE REGULATOR OPENING

• OIL TEMPERATURE ABOVE I65°F

Figure 9. Lubrication System Criteria

Lube system flow capacity can indicate a stoppage in flow passages.

This may mean a clogged filter or passage.

Relative Power Contribution

The relative power contribution test is one in which the power being

delivered by each cylinder is determined and conpared against the power

being contributed by each of the other cylinders. The cylinder found

to be delivering the most power is rated 100 percent and each of the

other cylinders is conpared to it in percent of power contribution

(Figures 10a § 10b).

DIAGNOSTIC TECHNIQUE

15 3 6 2 4

CYLINDER NUMBER

Figure 10a. Power Contribution

255
• FULL THROTTLE ACCELERATION

• TIME irfTERVAL BETWEEN ANGLES OF ROTATION

• LOW POWER CYLINDER FOUND BY SMALLER THAN NORMAL CHANGE

IN TIME INTERVAL

Figure 10b. Diagnostic Technique - Power Contribution

Cooling System

The cooling system diagnostics presents some interesting problems which

do not enter into diagnostics o£ other engine elements. This is due

to the fact that the engine cooling system is not complete in itself.

It must interface with a radiator or cooling system which is not provided by the engine manufacturer. At this time the cooling system

discussion pertains to the engine cooling system and most of the testing

will be completed with the thermostat closed.

The use of one pressure transducer and one temperature sensor can provide data to determine general system characteristics. The use of a second pressure transducer will allow for further analysis.

Using a pressure sensor and a temperature sensor just upstream of the

thermostat and running the engine at idle and high idle, thermostat

operation, pump performance and shudderstat sequence operation can be

determined, and whether the thermostat is functioning properly. Also,

by running the engine at idle and high idle with the thermostat closed, an indication of pump performance can be determined (Figure 11)

2400 RPM

50 I 1 —1

THERMOSTAT

INLET PRESSURE

(PSIG)

COOLANT TEMPERATURE(°F)

• PRESSURE DIFFERENCE BETWEEN HIGH AND LOW

SPEEDS INDICATIVE OF SYSTEM FLOW RATE

• PRESSURE DROP OCCURS WHEN THERMOSTAT OPENS

25 IDLE

140 170

Figure 11. Cooling System Criteria

256
Diagnostic System/Engine Interface

The time required for making the necessary engine connections for diagnostic testing is an important consideration which has a significant

impact on total test duration. Total test duration is that time

required to connect signal lines to the engine, conduct the test and

disconnect from the engine.

Electrical connections consist of attaching metal clips to various

locations in the electrical system. These connections are made quickly

and easily. The hydraulic and pneumatic connections are more time

consuming to make unless a quick disconnect method is utilized.

On the initial testing of the engine male quick disconnect fittings are installed at the desired locations on the engine. These fittings remain

on the engine to minimize set up time for future diagnostic testing.

The diagnostic system is equipped with mating quick set up time that can be reduced further by manifolding all hydraulic and pneumatic

signals to a conveniently located panel (Figure 12) . To implement a manifolding scheme cooperation is required by the engine and vehicle

manufacturers and the vehicle owner.

FUEL PUMP LUBE OIL IKTAKE «IR COMP FUEL FUEL PRESSURE PRESSURE MANIFOLD ACTUATOR |N RETURN

^^^J-INE___^ OR WATER

FILL VENT

LINE

Figure 12. Installation Interface

Summary

The implementation of a diagnostic product requires an awareness of what

diagnostics are and the depth of diagnostic penetration desired. The

257
following is the diagnostic definition which best describes the HTS

approach

Diagnostics are those methods used to isolate causes for performance and hardware malfunctions in engine

systems. The diagnostic objective is to isolate

faulty subsystem components involved in malperformance or failure so that repair is direct and

accurate

Therefore, diagnostics (fault finding) has the objective of isolating

internal faults. Overall performance is not the governing criteria but

is used as an indicator to determine faults.

The diagnostic system then provides for the profit conscious user a tool which will enhance his ability to increase engine productivity,

reduce maintenance costs and effect a savings in warranty costs for the

engine manufacturer.

To configure the diagnostic system and establish diagnostics the manu- facturer must comprehensively utilize mechanical, hydraulic, pneumatic,

electrical and electronic technologies together with a strong systems

engineering effort.

258
MECHANICAL FAILURES PREVENTION GROUP

26th Meeting

Detection, Diagnosis and Prognosis

List of Registrants

Jerry Allen

S.KoF. Industries

King of Prussia, PA 19406

Richard M. Anderson

Marl in Rockwell Corporation

402 Chandler Street

JamestOMi, NY 14701

Richard C. Arnold

University of Nebraska at Omaha

P. 0. Box 688

Downtown Station

Omaha, NB 68101

E, Roderic Bowen

Foxboro/ Trans -Sonics Inc.

Po Oo Box 43S

Burlington, MA 01803

Alfred P. Brackney

Monsanto Company

730 Worcester Street

Indian Orchard, MA 01151

H. C. Burnett

National Bureau of Standards

Metallurgy Division

Washington, DC 20234

Ronald Bannister

Westinghouse Electric Corporation

Lester, PA 19113

S. Bhattacharyya

I IT Research Institute

10 West 35th Street

Chicago, IL 60616

Eo Pc Blyskal

Eastern Airlines

International Airport

Miami, FL 33148

Stephen Bonifazi

Pratt § Whitney Aircraft

Box 2691

West Palm Beach, FL 33408

Jerry F. Bouska

Commonwealth Edison Company

1319 Sc First Avenue

Maywood, IL 60153

Colby E. Buzzell

General Electric Company

50 Fordham Road

Wilmington, MA 01887

Domenic Canonico

Oak Ridge National Laboratory

P. 0. Box X

Oak Ridge, IIM 37830

J. Bo Catlin

IRD Mechanalysis, Inc.

6150 Huntley Road

Columbus, OH 43229

Phillip W. Centers

AFAPL/SFL

Wright -Patterson AFB, Ohio 45433

Robert N. Clark

CARD, Inc.

7449 N. Natchez Avenue

Niles, IL 60648

259
J. Eo Clevenger

Shell Oil Company

999 E. Touhy

Des Plaines, IL 60018

George Mo Coleman

Code 18

Naval Ocean Systems Center

San Diego, CA 92152

William Ho Cooley

Endevco

4950 Harlem

Chicago, IL 60656

Raymond A. Coulombe

Naval Ship Engineering Center

Washington, DC 20362

William E. Deluhery

Caterpillar Tractor Company

Peoria, IL 61602

John Despot

Hughes Aircraft Company

18541 Santa Tomasa Circle

Fountain Valley, CA 92708

Neal DesRuisseaux

SoKoF. Industries

King o£ Prussia, PA 19406

Thomas Jo Dolan

Engineering Consultant

510 S. Highland Avenue

Champaign, IL 61820

James H, Drennan, Jr.

Bell Helicopter

Po Oo Box 482

Ft. Worth, TK 76010

Michael Drosjack

Shell Oil Conpany

Po Oo Box 3105

Houston, TK 77001

John Dunmore

Spectral Dynamics Corporation

Dymac Division

San Diego, CA

David V. Dunn

Baird Atomic

125 Middlesex Turnpike

Bedford, MA 01730

Raymond Ehrenbeck

U.S. Department of Transportation

Transportation Systems Center

Cambridge, MA

Kent J. Eisentraut

Air Force Materials Lab

Wright-Patterson AFB, OH 45433

Lloyd Ho Emery

U.S. Department of Transportation

National Highway Traffic Safety

Admin.

Washington, DC 20590

V. J. Erdeman

Eastern Airlines

International Airport

Miami, FL 33148

F. Monte Evens

Continental Oil Conpany

1000 South Pine

Ponca City, OK 74601

Paul M. Fleming

National Bureau of Standards

Metallurgy Division

Washington, DC 20234

Jack L. Frarey

Shaker Research Corporation

Northway 10 Executive Park

Ballston Lake, NY 12019

Richard Gallant

UoS. Naval Air Test Center

Patuxent River, MD 20650

260
John A. George

Parks College of St. Louis UniVo

Department of Aerospace Engro

Cahokia, IL 62206

Paul T. George

Pratt § Whitney Aircraft

Connnercial Products Division

400 Main Street, EBZG3

E. Hartford, CT 06108

Nathan Glassman

David Wo Taylor Naval Ship Research

and Development Center

Annapolis, MD 21402

Norman J. Gleicher

Ocean Environmental Systems, Ltdo

1843 Palmer Avenue

Larchment, NY 10538

W. L. Groves

Continental Oil Conpany

Box 1267

Ponca City, OK 74601

James Hamilton

Naval Ship Engineering Center

Philadelphia, PA 19112

James W, Hamach

Amoco Oil Conpany

Naperville, IL 60540

Christopher R. Harz

Rand Corporation

1700 Main Street

Santa Manica, CA 90406

Jerard Haury

U.S. Army Systems Conmand

St. Louis, MD 36166

Henry R. Hegner

CARD, Inc.

7449 No Natchez Avenue

Niles, IL 60648

Patrick Henry

Illinois Coal Gasification Group

122 South Michigan Avenue

Suite 2014

Chicago, IL 60603

Rudolph Hohenberg

Mechanical Technology Inc.

968 Albany- Shaker Road

Latham, NY 12210

Robert R. Holden

Hughes Aircraft

Los Angeles, CA

Leo Hoogenboom

Mechanical Technology, Inc.

968 Albany-Shaker Road

Latham, NY 12210

Stephen Hsu

Amoco Chemicals Corporation

1612 Wadham Place

Wheaton, IL 60187

Roger Hunthausen

U.S. Army

Eustis Directorate, AMRDL

Ft. Eustis, VA 23606

Rick Hyer

Fleet Maintenance Magazine

7300 N. Cicero Avenue

Lincolnwood, IL 60646

Alan M. Johnson

Factory Service Operations

Machinery and Systems Division

Carrier Air Conditioning Corp.

Carrier Parkway, Bldg. TR-1

Syracuse, NY 13201

James E. Johnson

Southwest Research Institute

San Antonio, TX 78284

261
John H, Johnson

Michigan Technological University

Mecho Engr.^ Engr. Mecho Depto

Houghton, MI 49931

William D. Keeley

Vibration Specialty Corpo

100 Geiger Road

Philadelphia, PA 19115

Ho K. Keswani

Gulf Research § Development Co.

P. 0. Drawer 2038

Pittsburgh, PA 15230

Raymond Bo Kight

Naval Air Rework Facility

5 Huntington Drive

Pensacola, FL 32508

Eo E. Klaus

The Pennsylvania State University

Department of Chemical Engineering

University Park, PA 16802

Alfred C. Koch

Ocean Technology

2835 N. Naomi

Burbank, CA 91504

Robert S. Kulp

Pratt § Whitney Aircraft

West Palm Beach, FL 33408

George Lang

Nicolet Scientific Corporation

North Vale, NJ 07647

Richard Lee

UoSo Government (Army)

JOAP-TSC, NARF Code 360

Pensacola, FL 32508

Rudy Lenich

Caterpillar Tractor Conpany

100 NoE. Adams Street

Peoria, XL 61629

Robert Leon

Franklin Institute Research Lab

20th Place

Philadelphia, PA 19103

L, Leonard

Franklin Institute Research Lab

20th Place

Philadelphia, PA 19103

Samuel Jo Leonardi

Mobil Research ^ Development Corp.

Paulsboro, NJ 08066

Paul Lewis

Mechanical Technology, Inc.

968 Albany-Shaker Road

Latham, NY 12110

Theodore Liber

I IT Research Institute

10 West 35th Street

Chicago, IL 60616

Wieslaw Lichodziejeswki

CARD, InCo

7449 N. Natchez Avenue

Niles, IL 60648

Basley K. Lindboom

Marl in Rockwell Corporation

Division of IRW

402 Chandler Street

Jamestown, NY 14701

Jon Lippe

SINTEF

Dept. of Machine Dynamics

N-7034

Trondheim-NTH

Norway

James R. Long

AVGO Corporation

4807 Bradford Drive

Huntsville, AL 35805

262
Bill Macaulay

Stone Piatt Electrical Canada Ltd.

165 Steelcase Road

Markham, Ontario

Canada L3R IGl

Robert E. Manning

Assoc. Research Consultant

UoSo Steel Research

Monroeville, PA 15146

Richard Manteuffel

Borg-Warner Research

1200 S. Wolf Road

Des Plaines, IL 60018

George E. Maroney

Fluid Power Research Center

Stillwater, OK 74074

Clifton S. McDonald

Fruit Growers Express Company

4928 Birch Lane

Alexandria, VA 22312

William Ro McWhirter, Jr,

David W. Taylor Naval Ship Research

and Development Center

Code 2731, Automation ^ Control Div.

Annapolis, MD 21402

Alice Mentley

Sperry Vickers

1401 Crooks Road

Troy, MI 48084

Henry J. Mercik, Jro

Hamilton Standard

Division of United Technology

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263
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26k
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265
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266
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267
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June 25-26, 1969.

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270
APPENDIX

I

j

j

i
iiiil
REMOTE DIAGNOSTIC TECHNIQUES

USED IN VIKING LANDER OPERATIONS*

Parker S. Stafford

Martin Marietta Aerospace

Jet Propulsion LaboratoryPasadena, California 91103

Abstract: The problem of monitoring performance and diagnosing malfunctions on the Viking Landers while operating on the Surface of Mars was conplicated by severe data rate and volume restrictions. This paper

describes the combination of flight hardware, flight software and ground

operations software used for planning, prediction and telemetry data

analysis functions which allowed the Viking Flight Team to successfully

operate the landers for a combined 548 Martian days to date although

many malfunctions have occurred. To illustrate the use of this system, a specific anomaly is discussed in detail.

Summary of the Problem

The design of the Viking Landers and their subsequent operations on the

Martian surface have been greatly constrained by the distances over

which the radio signals must travel and the limited view periods i\^ich are available. ^ The round trip light time from Earth to Mars to Earth

is approximately 40 minutes at distances of approximately 220 million

miles. Each lander has a view period to Earth of about 10 hours, and

although the Earth can view Mars nearly continuously through the Deep

Space Network Stations at Goldstone, California; Madrid, Spain; and

Canberra, Australia; these stations must be shared between the two

landers, the two orbiters and other projects such as Helios, Pioneer,

and Voyager. These constraints coupled with antenna size restrictions

and electrical power limitations of the spacecraft, combine to produce

very low rates and low total volume for data return when compared to

*This paper presents the results of one phase of research carried out at

the Jet Propulsion Laboratory, California Institute of Technology, under

Contract No. NAS7-100, sponsored by NASA.

^This paper will address certain aspects of operating the Viking Landers

on Mars from July 20, 1976 through May 19, 1977. The interplanetary

cruise phase (while the landers were attached to the orbiters) and the

descent to the Martian surface will not be discussed, although many of

the same points apply.

273
earth based on near-earth telemetry systems. In order to maximize

scientific data return, engineering data required to assess proper

operation or diagnose malfunctions was kept to a minimum. Therefore,

the Viking Flight Team was faced with a difficult challenge in attempting to deal with the following questions:

1. How could the lander performance be monitored so that malfunctions

could be detected quickly and with a high probability?

2. How can problems be anticipated and prevented?

3. How should problems be corrected once they are discovered to prevent

confounding the problem by acting hastily or conversely waiting too

long to respond?

The lander system designers provided capabilities within the landers

which allowed these questions to be answerable. The most inportant

capabilities derived from the redundancy requirement of the Viking

Project Specification which states,

"No single malfunction shall cause the loss of all data return

from more than one science investigation or the loss of all

engineering data."

As a result of this directive, the landers were designed to have parallel or block redundancy, or alternate functions for every critical

conponent. In addition, fuses and automatic safing modes were provided

to isolate malfunctions to a specific component and terminate operations

of that component until the VFT could reconfigure the system via com- mands from earth. As a result, the lander could be expected to survive

until the corrective action could be taken, which could be no faster

than 40 minutes and more typically several days. The remainder of the

diagnostic capability required to answer the questions is provided by

the lander telemetry subsystem, the operational planning and performance

prediction techniques used by the VFT, and the telemetry data analysis

conducted by the VFT, which are summarized in the following sections.

Figures 1 and 2 are provided for reference in these discussions. Figure

1 shows the lander functional block diamgram, including cruise and entry

subsystems. Figure 2 is a sketch of the lander after it is deployed on

the surface of Mars.

Telemetry/Communications Description

The communication links to a lander are depicted in Figure 3. Earth can communicate to the VL through the direct link (S-band) at 4 bits/second.

The lander can return data over the direct link at 250, 500, or 1000

bits per second on the "high-rate" subcarrier and at 8-1/3 bits/second

2'jk
over the low- rate engineering subcarrier. The primary downlink method

is the relay link (UHF) through which the lander can transmit data to

either of the two orbiters (when they are in view) at 16000 bits/

second. The orbiter stores the data on its tape recorder for transmission to earth typically a few hours later.

The data is gathered on the lander by the Data Acquisition and Processing Unit (DAPU) . The DAPU either provides the data directly to the

UHF or S-Band systems for real-time transmission, or stores it into the

Data Storage Memory (DSM) or on the tape recorder for later transmission.

All of these modes are controlled by sequences stored in and executed

by the Guidance Control and Sequencing Computer (not shown) which issues

commands to all other VL components to acquire, transfer and transmit

data. The types of data that are collected are shown in Figure 2. The

System Test Equipment interface was not used after launch nor the Viking

orbiter interface after VO/VL separation. Each of the science instruments supply data in frames of various lengths to the DAPU. These data

contain measurements pertinent to the instrument hardware status

(current, voltage, tenperature , mode discretes, etc.) as well as the

desired scientific information. No on-board diagnostic processing of

these data is done. The GCSC provides readouts of selected portions or

all of its memory (up to 18432 twenty-four bit words) when scheduled in

its stored sequences. This memory readout contains important information for status monitoring and diagnostic analysis such as: a count

of the number of commands received from earth, the values of all

sequencing times and subsystem commands which have been or will be

issued until modified by the next earth uplink, all instructions of the

flight program, and a table called the Rl table, which is a record of

the last 2000 commands and the times that have been issued through GCSC

register Rl to all science instruments and the DAPU. The Rl table

typically spans the last 3 to 6 days of operation.

The engineering data collected by the DAPU for landed operations (exclusive of the science and GCSC data) is formatted into two formats (termed

Format 4 and Format 5) . Format 5 consists of frames of 768 bits

containing 79 different measurements. Format 5 is designed for contin- uous data acquisition during direct links although it is occasionally

used at other times and recorded in the DSM or directly to the tape

recorder. Format 4 consists of frames of 768 bits and contains 74

measurements. It is collected one frame at a time and is scheduled by

the GCSC to provide spot sampling throughout the day between downlinks.

The engineering formats (1, 2, 2A, 2P, and 3) used prior to landing are continuous formats and were constructed similarly to Format 5 but

contained other measurements pertinent to those phases. All engineering

formats are time- tagged by the GCSC software clock, (except the cruise

Format 1 which used earth received time)

.

The normal method of data collection used during the landed mission is

to store all data except imaging and Format 5 to the DSM. The DSM holds

275
196608 bits and when it fills, the DAPU issues an interrupt to the GCSC

causing the GCSC to command the DAPU to dump the DSM contents to the

tape recorder. In this way runup and rundown of the tape recorder is

minimized. Imaging and Format 5 may be written to the DSM at 8-1/3

bits/second for special purposes. Normally, imaging and Format 5 are put out directly to the UHF or S-Band links or written directly to the

tape recorder. GCSC data is always transmitted real-time over the

links.

Table 1 illustrates the data content of a typical relay link and a typical direct link. During its primary mission a lander would have a relay link every Martian solar day (1 SOL = 24 hours 39 minutes) and a direct link every other SOL. During the extended mission (after

November 1976) the typical data return is two relay links and two direct

links per lander per week.

The Planning/Prediction Process

A fundamental prerequisite to proper performance monitoring or diagnostic analysis of an operating system is to understand thoroughly what

the nominal performance will be. Particularly in a system such as the

Viking Lander where the visibility into operating characteristics is

limited by the small data volume and intermittant data samples, the

prediction must be as complete and accurate as possible. Furthermore,

if the operating environment is unknown or unpredictable with time, the

prediction system must be constructed so that the new information from

telemetry analysis may be factored in.

The Viking Lander Mission Operations software system was designed

according to these concepts. Figure 5 shows the uplink preparation

software which is run in order to in^jlement and verify a segment (typically 6 to 10 SOLs) of the lander mission. The events leading up to

and the overall strategy employing this software system are discussed

in reference 1 and will not be repeated here. However, the simulation

and prediction functions used for performance monitoring and diagnostic

analysis will be discussed.

LSEQ (Lander Sequence of Events) generates a sequence of events at a one-second granularity from user level inputs (1)* (i.e., time and type

of pictures to take, duration of relay link, meteorology sample number

and duration) . It is a functional simulation of the VL data generation

Reference 1: Lee, B. G. and Porter, Dr. J. D. ; Design and Implementation

of Viking Mission, AIAA Paper No. 77-270, January 10, 1977.

* The numbers in this discussion refer to the numbered points in Figure

3.

276
subsystems and the on-board GCSC software. It provides a sequence o£

events listing and discrete events file (2, 4, 8) for use by other

programs, a detailed prediction** of all data to be returned (10) on each scheduled dowilink, and saves a map of the DSM and tape recorder

contents

.

The LSEQ sequence of events is also passed to the COALES (Combined

Orbiter Lander Sequencing) program to generate the operational timeline

for mission controllers and DSN personnel (9) . LCOM (Lander Command)

generates from the LSEQ files a Hamming Coded message file which will

be transmitted to the appropriate lander after the verification process

is coiiplete. LCOMSM (Lander Command Simulation) is a complete bit-forbit model of the GCSC and contains the flight program which executes

the planned mission period in the ground computer system at JPL. This

program produces a listing of all GCSC input/output to the millisecond

level which it compares to the LSEQ predicted events (3) , thus verifying

that the flight software after receipt of the command file will execute

the planned sequence. In addition, it creates a file of what the GCSC

memory readout data will contain during the direct and relay links.

Power management on the lander is a significant problem because the

Radio Isotope Thermal Generators only provide about 80 watts of power

to recharge the 4 lander batteries, although the system loads may reach

peaks of 400 watts. The LPWR1-LTEMP-LPWR2 program set allows this

problem to be analyzed prior to committing the vehicle to sequences

which may totally discharge the batteries or thermally stress components.

LPWRl (4) converts the LSEQ sequence of events into a predicted system

load (watts vs time) which LTEMP uses to predict lander tenperatures at

about 400 nodes within its thermal model. Since some components have

thermostatically controlled heaters or temperature sensitive efficiency,

LTEMP provides the predicted thermal history back to LPWR (6) for the

final energy balance prediction. From these programs, the values of all

lander tenperature measurements and the system voltage/current measurements may be predicted. Various mode discretes (tape recorder on, etc.) are also related to these predicts.

Two other programs, LDLINK and RLINK, are used to predict direct and

relay link communication performance.

From the products of these programs, it is possible to predict every

command which will be generated on board the VL if the sequence is

executed nominally, the amount and type of data vs time is known, the

RF signal strength of each is known, and a complete power and thermal

**The data type and volume is predicted but the value of each individual

measurement is not.

277
history is available. The factors which cause deviations from these

predictions are caused by planning errors, changes in the Martian

environment, or hardware degradation. It is the task of the downlink

analysis people to find these factors.

Downlink Analysis Process

The downlink data from one of the spacecraft are received at a DSN

station and transferred via high speed data lines to the Jet Propulsion

Laboratory where it is processed and displayed. Figure 6 illustrates

this system. The TUMP program operates on the data real-time and

provides decommutated data to the Ground Display video tubes. Real

time operations personnel monitor this data for quick- look status as

it is received. Important measurements are bounded by alarm limits

which will flash a warning if they stray outside of limits so that the

monitor person can notify other analysts of problems quickly. For

routine analysis, typically the next day, the data is run through DECSET

to product prints and plots of all engineering data. DECSET strips out

all science data by type and provides files to each science team for

analysis using their software. DECSET compares the GCSC memory readout

to the predicted memory readout from LC0M5M and generates a list of

non-compares which are later analyzed by Flight Software experts for

anomalous conditions. The Rl table previously described is provided

in this printout and may be compared against the LCOMSM discrete event

listing in problem diagnosis. The system data record from TLMP is also run through a program called Mark IV which provides a frame by frame

listing of all data received. This listing is useful in checking tape

recorder performance and to insure consistency between the planningLSEQ data prediction process and -what the vehicle actually returns to

earth

Although it is not shown in Figures 5 or 6, both LPWR and LTEMP are capable of reading files of downlinked power and tenperature data to use in comparison with the predicted values. In doing this, the

analysts may refine their lander models of these functions to either

upgrade accuracy or account for changing Martian environments. This is

especially important in thermal predictions since they are affected by

the optical depth of the sky, the Mars -Sun distance, time of year,

winds, and dust coating on lander surfaces.

Laboratory Support

Two inportant laboratories were used during Mission operations for

prediction, analysis, and diagnostic purposes. The first was located

at Martin Marietta in Denver and was connected to JPL by high-speed

data lines. The facility contained a complete real-time simulation

using guidance and control hardware and flight software which was used

to verify the landers descent trajectories prior to separation. For

278
cruise and landed operations the Proof Test Capsule (PTC) was used to

checkout sequences and analyze unusual hardware modes of operation.

The PTC is a complete functional lander using qualified flight hardware,

but connected to the ground checkout system. This laboratory was useful

in verification of flight software changes and diagnosis of the battery

charger failure that occurred during interplanetary cruise.

The second laboratory is located at JPL and contains a full-size mockup

of the lander with actual flight-type cameras, surface sampler and

X-ray, GCMS and Biology soil inlet systems. This lab is still in use

for design and verification of all surface sampler sequences. Since

the lander views Mars non- linearly through its cameras, it is not a straight forward process to acquire a soil sample at a specific location.

The sequence of commands (extend, elevate, azimuth, rotate, vibrate,

etc.) that the surface sampler needs can be worked out using this mockup and the Martian surface as modeled from lander pictures. Then if the

real VL surface sampler has a "no-go" either due to hardware malfunction

or unexpected environmental factors, a detailed sequence baseline has

been established for failure analysis. This laboratory was essential

during operations and allowed quick recovery from several surface

sampler problems.

Analysis of an Anomaly

On January 19, 1977, the Lander Performance Analysis Group DECSET

analysts, H. Fuquay and J. Mirphy, noticed that the VL-2 SOL 131 relay

link (which had been processed the previous night) did not contain all

the meteorology data that had been predicted. In reviewing the Mark IV

listing of all data frames received it was quickly determined that the

meteorology instrument had stopped providing data on about SOL 130,

13:42 local lander time. Management was quickly notified and an anomaly

meeting convened. At that meeting it was apparent that all the

prediction products had not yet been compared to the downlink received

so the meeting was adjourned after an action item list was generated

aimed at localizing the problem, with a status report meeting scheduled

for 9 a.m. the next day, January 20. In the meantime, the SOL 132

relay link DECSET run had been completed and found to contain no new

meteorology data. Figure 7 shows a timeline of VL-2 downlinks during

this period.

However, in reviewing the LSEQ-LC0>4SM predictions versus the data

received from the Mark IV listing and the Rl table from the GCSC, R.

Bender, the LPAG Deputy Chief, found the cause of the problem in a few

hours of analysis and discussion with subsystem experts. Figure 8 shows

the predicted versus actual timeline. The actual downline confirmed

the predictions exactly until 14:03:49 when the DSM filled and was

dumped to tape. This dump occurred about 30 minutes earlier than predicted. It was followed by a Format 4 to DSM which is always done

279
automatically by the flight software to mark the start of data in the

DSM since all the science data is not time-tagged. Then the low rate

format 5 to DSM continued and all further sequencing was normal except

no meteorology data was collected, indicating that either the instrument had failed or its data collection electronics was struck.

Using the Mark IV listing which provides a bit -by-bit accounting of

data received, R. Bender was able to construct the timeline of Figure 9.

This figure shows that when the Format 5 to DSM at 8-1/3 mode was

started, the DSM contained 189288 bits. At 190464 bits the DSM/DAPU

generates an interrupt to tell the GCSC "I am nearly full, dump me to

tape". However, from discussions with the LPAG telemetry subsystem

analyst, C. Seese, it was found that the DAPU would not generate the

interrupt until the mode in process completed (at 14:03:48 on the timelines) . In the meantime, the GCSC had received an interrupt from the

meteorology instrument at 13:57:33 saying "my buffer is full, dunp me

to the DSM". However, the GCSC says to itself, "the DAPU is busy

putting Format 5 in the DSM, I will hold the MET request until Format 5

is done". At 14:03:48 the GCSC then terminates the Format 5 to DSM

mode by issuing the command to dump MET to DSM. Milliseconds later, the

GCSC received the request from the DAPU to dunp the DSM to tape which

the GCSC issued at 14:03:49, allowing the standard 1 second for the MET

data transfer to complete. However, the MET data frame is long enough

to overflow the DSM past its upper limit, 196608 bits, at which point

the DSM automatically puts the DAPU to standby, terminating the data

shift pulses to the MET instrument before the 5156 bit frame is totally

transferred. Since the MET instrument resets its "data ready" flag

after the transfer is complete, it is hung-up waiting for a shift pulse

which never comes. The GCSC never receives another MET data ready to

command a MET dump to DSM, so MET is forgotten. The hardware design

characteristics were confirmed through discussions with MET instrument

engineers and DAPU/DSM engineers and the flight software operation

reviewed with the Lander Command and Sequencing analysts, S. Lowrie and

J. Kerekes, so R. Bender's diagnosis was complete.

The next step was to design the recovery plan. In this condition, the

MET engineers and LPAG power analysts confirmed that only 3 to 6 watts

extra power was being consumed. This level was to small to be of

concern to loss of battery capacity and it was confirmed by comparison

of LPWR predicts to downlink measurements on the SOL 132 relay link

that an additional power load of this size was present. The temperature increase was too small to be detectible by LTEMP/downlink

comparisons. There was no critical concern to lander safety, however,

the meteorology science team wanted to reinitiate data collection as soon as possible. By this time it was Thursday morning, January 20,

and too late to command the lander via the SOL 134 direct link. It was

decided to build another separate command fild for the SOL 137 uplink

already scheduled for Saturday, January 22. The solution was to simply

280
issue via real-time command, the GCSC to DAPU command to dxmp MET to

DSM. Low rate format 5 to DSM data collections which did not have a DSM to tape dump commanded immediately before them were eliminated to

prevent recurrence of the problem.

This anomaly was an interesting test of the VL data monitoring and

analysis system because it was very subtle and used most of the prediction tools. Normally, a problem such as this would have been caught by

the real-time analyst monitoring the SOL 131 relay link. Unfortunately,

due to a problem at the DSN station, a portion of the relay link data

was lost between the station and JPL and had to be recalled which

usually takes 1 to 2 days. Since the analyst did not receive all the

planned data, his analysis of data received versus predicted (total

frame counts) was incomplete, but agreed closely enough that he did not

suspect a lander problem. The SOL 131 direct link contained a DSM

dump AA^ich would have shown no MET data, but since it is the first IK

data received on the ground in a direct link, it is usually not acquired

for the first 5 minutes, and in this instance, worse than that. Therefore the problem was obscured again. It was caught by the DECSET

analyst very early in his process of evaluating the SOL 131 relay link

results. If he had missed it, it would have been caught by either the

meteorology team or the LPAG tape management analyst in later reviews.

The second interesting aspect of this problem is that it is not a hardware failure (the hardware has operated perfectly since the command fix)

but a system design deficiency which excaped detection through extensive

pre-launch testing and never occurred in mission operations for 175 SOLs

of VL-1 and 130 SOLs of VL-2 operations. It only occurs when the DSM is

used for continuous data collection (normally imaging or format 5) and

would not be a problem if the DAPU issued the GCSC interrupt immediately

rather than at the completion of the mode. Since it is inherent in the

hardware design, the Lander Command and Sequencing team has had to work

around it by taking the following actions:

1. LSEQ has been upgraded to model all data. The reason the DSM dump

occurred early was that the Format 5 to DSM during ranging in the

direct link was not modeled by the SOL 130 version of LSEQ.

2. Whenever low rate continuous data is put into the DSM, it is dumped

just prior to initiating this mode and the data volume checked to be

less than 190,000 bits.

3. If (2) cannot be done, the science instrument buffers are dumped

after completion of the continuous mode to remove any unexpected

hangups.

4. The real-time operations personnel have been instructed to check

downlink time tags of science data to insure no instrument has

281
stopped. (This cannot be done for XRFS, GCMS or Biology, since

they do not time tag their data)

Conclusions and Recommendations

This paper has attempted to illustrate how diagnostic failure analysis

is applied to the Viking Landers operating on the surface of Mars over

220 million miles from earth using a very constrained telemetry return.

At the date of this writing, Lander 1 has operated for 296 SOLs and

Lander 2 for 252 SOLs (1 SOL = Martian day of 24 hours 39 minutes) and

achieved all major science objectives planned before landing. Between

them, the landers have experienced 23 major problems all of which were

detected quickly by the Viking Flight Team and all of which were

corrected in time spans of 2 to 7 days, resulting usually in minor data

loss or delay of plans.

The system used to detect these problems and continue mission operations

is a conplex ground and flight hardware and software system summarized

herein which requires expert and dedicated people to operate. The

Viking Flight Team was made up of this type of people, most of whom had

been hand-picked from the design development and test teams who put

these systems together. Nfost projects having a similar remote diagnostic task will not have this luxury, either due to cost, or because

normally the system designers are not involved with the operation of the

system after it is delivered. Therefore, it is of interest to discuss

the strengths and weaknesses of the Viking system.

First, in order to do remote performance monitoring and diagnostic

analysis an accurate prediction system is required. This was achieved

on Viking through use of ground computer simulations which ultimately

performed very well. However, the development of this system was more

expensive than need be because of the following factors:

1. The flight software for the lander computers was developed as an independent program until launch (when it came under control of the

Flight Team) making the command software (LSEQ, LCOM/LCOMSM)

difficult to design.

2. The data system was not standardized, and was difficult to obtain

modeling information for. All science data had different formats,

different frame lengths, and several did not time tag their data.

This complicated both the prediction and downlink analysis software

and caused many uncertainties in analysis.

3. Some of the science teams had not designed their software requirements to include all the modes of operation they intended to use so the ground software could not model these modes, necessitating

changes "on the fly" during operations.

282
Second, in order to optimize data return for science, engineering data

return was kept at the minimum required for nominal performance monitoring. This could have been alleviated by making more use of dual

channel transmission and recording, one low rate channel for engineering

and high rate channel for science. The Viking orbiters made much better

use of this approach than the landers.

The Viking lander data system, on the other hand, had a near optimal

design for maximization of data return over constrained downlink

opportunities. After LSEQ modeling was shown accurate enough, tape

recorder content could be predicted to less than 15 seconds out of 40

minutes record time at 16000 bits/second. Therefore, the downlink

could be designed to contain a minimum of "margin" of filler data. This

was accomplished by buffering each instrument so that it did not have to

be serviced immediately when it had collected data, by using the DSM as temporary storage and the tape recorder as long-time storage. Data

could be saved on the tape for several downlinks and played back later;

however, the engineering data for status monitoring would be delayed

with it. This collection technique allowed many experiments to run and

collect data simultaneously with a minimum of interference and conflict

resolution.

It is a very useful technique for diagnosis to record on-board all

commands (and their times) issued by the on-board conputer. This technique was partially developed on the VL but could have been enhanced

by including all commands and doing an automatic compare of predict vs actual results.

Finally, it is desirable to automate the prediction versus actual data

comparison as much as possible to reduce operation at manpower and

increase the probability of detection of malfunctions early. The Viking

Lander process was semi -automated but required expert review of all

results. Standardization of the data system and the ground processing

software files and timing could have allowed simpler compare processes

with more automatic discrepancy detection.

285
TABLE 1

TYPICAL RELAY AND DIRECT LINK CONTENTS

A. SOL 281 Relay Link (VL-1 to VO-1)

Frames New Data

Format New Old Wrap Percent of Total

4 444 58 43 2 5 630 19 21 2

SSCA 41 0 0 .02

BIOL 21 2 1 .2

MET 660 113 22 16

XRFS 1134 118 50 2 IMAGE 1 3549 0 0 55

IMAGE 2 1200 0 0 18

GCSC 296 0 0 4

Mission Period Recorded SOL 276/13:30:00 to SOL 281/11:50:00

Efficiency = New Bits/ (Total Bits) = 96%

Total Data Returned 22611333. bits

Link Duration 25 minutes 52 seconds

B. SOL 283 Direct Link

Frames

Format New Old Wrap Comment

4 37 0 46 DSM Dump Usually Lost

MET 32 0 64 DSM Dump Usually Lost

5 (Hi) 37 0 46 DSM Dump Usually Lost

GCSC 253 0 0

5 (Lo) 15 0 0 93 Seconds Between Samples

Mission Period: Real Time SOL 283/17:20:00 to SOL 283/17:44:00

Total Data Returned 1189376. bits

2Qk
ABBREVIATIONS

bps - bits per second

COALES - Combined Lander Sequencing Program

DAPU - Data Acquisition and Processing Unit

DECSET - Downlink Decommutation Decalibration Set program

D/L - downlink to earth from VL

DSM - Data Storage Memory

DSN - Deep Space Network

FOVLIP - First -order Viking Lander Imaging Program

G(31S _ Gas Chromatograph Mass Spectrometer

GCSC - Guidance, Control, and Sequencing Conputer

HGA - High Gain Antenna

IRU - Inert ial Reference Unit

JPL - Jet Propulsion Laboratory

LCOM - Lander Command Program

LCOMSM - Lander Command Simulation Program

LDLINK - Lander Direct Link Program

LGA - Low Gain Antenna

LPWR - Lander Power program

LSEQ - Lander Sequence L of Events program IT c> LTEMP - Lander Temperature program

MET _ Meteorology Instrument

MV - millivolts

PCM - Pulse Code Nfodulation

PTC - Proof Test Capsule

Rl - Register 1 of the GCSC

RLINK - Relay Link program

RPA - Retarding Potential Analyzer

RTG - Radio Isotope Thermal Generator

SOL - Martian mean solar day (24 hours, 39 minutes, 35.25 seconds)

TLMP - Telemetry program (Lander real-time)

UAMS - Upper Atmosphere Mass Spectrometer

UHF Ultra -High Frequency

U/L Uplink to VL from earth

V volts

VFT Viking Flight Team

VL Viking Lander

VO Viking Orb iter

W watts

XRFS X-Ray Fluorescence Spectrometer

285
PYROTECHNICS

SUBSYSTEM

Initiators

POWER SUBSYSTEM ~1

vo Power VO Control

Bio- Shield Power

Asseinbly (BPA) VO

Power

RTG

RTG

Control

Power

Power

Conditioning and

Distribution Assembly (PCDA)

Load Bank

Charge Control —» VLC Power

Powaf

Batteries

(4)

STRUCTURES & MECHANISMS

SUBSYSTEM

Bktshield Aeroshell &

Base Cover

Aerodecelerator Heat Shield

Mechanisms Lander

Structure

Control

THERMAL CONTROL SUBSYSTEM

Thermal

Control

GUIDANCE CONTROL

SUBSYSTEM

I"!

Pyrotechnic

Control

Radars

Control

Guidance

Control &

Sequencing Computer

(GCSC)

I Control

Control

Valve

Drive Amplifier (VDA)

Control

Inertial Reference

Unit (IRU)

Control

Commands

Control

Control

Control

SCIENCE SUBSYSTEM 1

Surface Sampler

Landed

Science Experiment

Entry

Science Experiments

Control

Control r

PROPULSION SUBSYSTEM

RCS/Deorbit

Propulsion

Terminal Propulsion & Attitude Control

VO Hardline Commands

S-Band Communication

UHF

Communication COMMUNICATION

SUBSYSTEM

VLC Engineering Data

Data

Data

Data

I

._l

Data

Acquisition & Processing Unit (DAPU)

Tape

Recorder

Data

Storage Memory

L

TELEMETRY

SUBSYSTEM .J

Data to Earth

Earth Commands

Data Hard lined to VO

Figure 1 VIKING LANDER CAPSULE FUNCTIONAL BLOCK DIAGRAM

286

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st{BS->+*A (REV. 7-73)

U.S. DEPT. OF COMM. 1 . PUB LIGATION OR R E PORT NO . 2. Gov't Accession BIBLIOGRAPHIC DATA No. SHEET NBS SP 494

3. Recipient's Accession No.

4. TITLE AND SUBTITLE

Detection, Diagnosis and Prognosis --Proceedings o£ the

26th Meeting o£ the Mechanical Failures Prevention Group, held

at the IIT Research Institute, Chicago, 111., May 17-19, 1977

5. Publication Date September 1977

6. Performing Organization Code

7. XMXKMM EDITORS

T. Robert Shives and William A. Willard

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Work Unit No.

11. Contract/Grant No.

12. Sponsoring Organization Name and Complete Address (Street, City. State. ZIP)

Inst. for ^tIs. Res. , NBS, Washington, DC 20234; OMR, Arlington,

VA 22217; NADC, Warminster, PA 18974; Frankford Arsenal,

Philadelphia, PA 19137; FAA, Washington, DC 20591; NASA,

Greenbelt, MD 20771; ERDA, Washington, DC 20545

13. Type of Report & Period Covered

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

Library of Congress Catalog Card Number: 77-I409S

16. ABSTRACT (A 200-word or less [actual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here.) These proceedings consist of a group of twenty-four submitted papers from the

26th meeting of the Mechanical Failures Prevention Group which was held at the

IIT Research Institute in Chicago, Illinois on May 17-19, 1977. The central

theme of the proceedings is detection, diagnosis and prognosis as related to

mechanical failure. Papers are presented that discuss oil analysis, signature

analysis techniques, new detection, diagnosis and prognosis techniques and

equipment, railroad system diagnostics, and land vehicle diagnostics.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name; separated by semicolons

)

Failure detection; failure diagnosis; failure prevention; ferrography; land vehicle

diagnostics; oil analysis; railroad system diagnostics; signature analysis; wear

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