Reference

NAT'L INST. OF STAND & TECH

A1110S ^63613

Publi*

cations

R 82-2601, Parts I and II

OhhoirtL uoc. uNLV

Automatic Test Equipment

Calibration/Performance Verification

Evaluation and Research Program

(JLC/DoD Subtask 30702)

EXECUTIVE SUMMARY Part I

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Electronics and Electrical Engineering

Electrosystems Division

Washington, DC 20234

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

Electromagnetic Technology Division

Boulder, CO 80303

December 1 982

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o2-2601

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1902

Prepared for Joint Logistics Commanders Panel on Automatic Testing

DoD Joint Technical Coordination Group for Metrology

DoD Calibration Coordination Group

USAF ASD/AEGB MATE Program Office

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NATIONAL BUREAU

OF STANDARJDS

LIBRARY MAR 1G 1983

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NBSIR 82-2601, Parts I and II %

. AUTOMATIC TEST EQUIPMENT , CALIBRATION /PERFORMANCE VERIFICATION "f<

:> EVALUATION AND RESEARCH PROGRAM

(JLC/DoD SUBTASK 30702)

EXECUTIVE SUMMARY Part I

Barry A. Bell, Thomas F. Leedy, Paul S. Lederer

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Electronics and Electrical Engineering

Electrosystems Division

Washington, DC 20234

William L. Gans, Robert E. Nelson

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

Electromagnetic Technology Division

Boulder, CO 80303

December 1982

Prepared for Joint Logistics Commanders Panel on Automatic Testing

DoD Joint Technical Coordination Group for Metrology

DoD Calibration Coordination Group

USAF ASD/AEGB MATE Program Office

U.S. DEPARTMENT OF COMMERCE, Malcolm Baidrige, Secretary

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

Preface

The work described in this report was performed in response to a request by the Joint Logistics Commanders Panel on Automatic Testing

(JLC/AT). The final report issued by the Industry-Joint Service

"Automatic Test Project" (June 1980) strongly urged NBS leadership for

the metrology and calibration support of automatic test equipment

(ATE). The contents of this report are the results of an initial

attempt to respond to this mandate.

As an organization, the National Bureau of Standards (NBS) has

little experience with large, multi -function automatic test systems.

The Bureau does not manufacture, procure, or use these systems. The

strength of NBS is in metrology, and it is this strength that was applied to characterizing the performance of automated test systems.

The work reported here is experimental in nature. It does not constitute

an evaluation, certification, or endorsement of any equipment or systems.

The experiment was to determine the feasibility of applying a portable

calibration standard at the interface of third generation automatic

test equipment. There was no attempt to technically evaluate the

system measurement capability beyond what is reported.

Third generation automatic test equipment is characterized by

extensive use of computer technology to implement signal generation and

measurement within the system. The software required to program the

computer is generally "invisible" to the user of such systems. No

attempt was made to understand the system software in detail. Errors

in such software could cause apparent measurement errors. Additional

software, the NBS test applications programs, were written in ATLAS to

actually implement the measurement processes. Knowledge that the

application software was completely error free or performed exactly

what was intended is not certain.

The choice of the automatic test system for this experiment

(AN/USM-410 or EQUATE) was by mutual consent of representatives from

the U.S. Army, Air Force, and Navy. This particular system seemed a reasonable candidate since each service used at least one such system

and all could profit by the work. No attempt should be made to compare

the results from the two test stations used in this experiment. This

comparison would be unjustified from several points of view. First,

each service uses their test sytem in a different manner and for

different purposes. The particular Army system tested is used primarily

for testing field communications equipment; the Navy station primarily

tests digital logic assemblies. Secondly, somewhat different maintenance

and calibration philosophies are applied by the various services.

Thirdly, the test stations are of different age, the Navy system being

the oldest. The age of the particular machine impacts both its hardware

and software and the maintenance experience used in its support.

iii
It should be reemphasized that this work was entirely an experimental

investigation of a limited nature that was performed on only two automatic

test systems. Accordingly, any conclusions and recommendations in

this report reflect this limited sampling. Nevertheless, the results

are probably representative of many automatic test systems and demonstrate

the value of using an on-site calibration support scheme to reveal

potential measurement problemsJ

1 In order to adequately describe the systems and experiments discussed

in this report, commercial equipment and instruments are identified by

manufacturer's name or model number. In no case does such identification

imply recommendation or endorsement by the National Bureau of Standards,

nor does it imply that the material or equipment identified is necessarily

the best available for the purpose.
TABLE OF CONTENTS

Page

Preface

LIST OF FIGURES vi

LIST OF TABLES vii

1. BACKGROUND OF PROJECT 1

2. OBJECTIVES 2

3. APPROACH 2

4. CHARACTERIZATION OF SIGNAL SOURCES . . 3

4.1 DC and AC Voltage Source 3

4.2 Pulse Duration Source 5

5. FIELD TESTS OF ATE SYSTEMS 8

5.1 DC and AC Voltage Tests 8

5.2 Pulse Duration Tests 10

5.3 Time Domain Reflectometry Tests 12

6. CONCLUSIONS AND RECOMMENDATIONS 13

6.1 Feasibility of Using Dynamic Transport Standards 13

6.2 Calibration and Characterization Methods ' 13

6.3 Needs at NBS for Automated Calibration Support Systems 14

6.4 Recommendation for Future NBS ATE Efforts 15

7. REFERENCES 16

v
LIST OF FIGURES

Page

Figure 1. The limits in the changes of the output voltage

of the source over the temperature range 0° to 40°C . . * . . 17

Figure 2. The change of the dc voltage output at four selected

voltages over a period of approximately seven months 18

Figure 3. The difference, on two occasions, between the dc output

voltage of the source and the NBS Legal Volt as maintained by the Electrical Measurements and Standards

Division of NBS 19

Figure 4. The change in ac output voltage as a function of ambient

temperature 20

Figure 5. The change of the ac voltage output of the source at

four selected voltage and frequency combinations over a period of approximately seven months 21

Figure 6a. The results of the ac-dc intercomparison over the range

of 8 to 20 V ac and over the frequency range of 50 Hz

to 50 kHz 22

Figure 6b. The same intercomparison as shown in figure 6a performed

three months later 23

Figure 7. NBS pulse source 50 ns pulse direct to APMS sampler with

5 ns NBS filter (HISTOGRAM definition) . 24

Figure 8. NBS pulse source 50 ns pulse direct to APMS sampler

with 5 ns NBS filter (MIN-MAX definition) 25

Figure 9. A time domain reflectometry signature of the 50 ft DIU BNC

connector port to EQUATE 26

Figure 10. The time domain reflectometry signature of pin-pair 1 and

IS of the PIU input in the unbuffered mode 27

Figure 11. The time domain reflectometry signature of pin-pair 1 and

IS of the PIU input in the buffered mode 28

Figure 12. A Dynamic Transport Standard concept and support strategy . . 29

vi
LIST OF TABLES

Page

Table 1. Pulse generator time stability 30

Table 2. Summary of Army dc voltage observations 31

Table 3. Summary of Navy dc voltage observations 32

Table 4. Summary of Army ac voltage observations 33

Table 5. Summary of Army ac voltage observations 33

Table 6. Summary of Navy ac voltage observations 34

Table 7. Summary of Navy ac voltage observations 34

Table 8. Pulse duration measurements by EQUATE System No. 5 35

Table 9. Pulse duration measurements by EQUATE System No. 1 36

vii

AUTOMATIC TEST EQUIPMENT CALIBRATION/ PERFORMANCE

VERIFICATION EVALUATION AND RESEARCH PROGRAM

EXECUTIVE SUMMARY

Barry A. Bell, Thomas F. Leedy, William L. Gans,

Paul S. Lederer, and Robert E. Nelson

1. BACKGROUND OF PROJECT

Complex, high-speed ATE systems have unique calibration requirements

by virtue of their wide dynamic measurement range, their ability to

both supply and measure electrical signals, and their extensive use of

computer technology and software for the control of the systems.

The Department of Defense (DoD) is especially concerned that ATE

systems perform properly since such equipment is vital to assure readiness of weapons systems. Additionally, to comply with MIL-STD-45662,

Calibration Systems Requirements, DoD needs the calibration of ATE

systems to be traceable to national standards.

In recognition of the fact that automatic testing is an extremely

complex and highly dynamic technology, a Joint Logistics Corrananders

Panel on Automatic Testing was established by the services in July 1979.

The Panel identified over 80 technical tasks needed to achieve its

goals. Subtask 30702, "Calibration of ATE," has the purpose to

"determine and develop concepts (policies, standards, techniques,

practices and procedures) for on-line and off-line calibration to

verify performance of the DoD family of automatic test equipment (ATE),

with special emphasis to be placed on performance verification of

third generation and later generations of ATE."

This report describes the detailed work performed by the National

Bureau of Standards for the Joint Logistics Commanders Panel on Automatic

Testing under JLC Subtask 30702. This work was undertaken to assess

the requirements necessary for the proper calibration support of

automatic test equipment. Additionally, an experiment was performed

to determine the feasibility of applying portable calibration sources,

characterized at NBS, directly to two automatic test systems of similar

type located at different DoD facilities. Hie application of such sources to automatic test equipment does not imply that the equipment

is thereby traceable to NBS standards. Also, the measurements described

in this report represent experiments which were not performed with the

statistical rigor of an NBS calibration service.

1
2. OBJECTIVES

Key objectives of this project for FY 1980 included:

(1) The selection of representative military ATE systems following

consultation with DoD representatives; (2) site visits, selection of

electrical parameters, and the formulation of plans for their on-site

measurement and verification; and (3) the preparation of procedures and

instrument packages at NBS laboratories to carry out such measurements.

The objectives for FY 1981 were:

(1) The procurement, testing, characterizing, and calibration of

instruments for the field testing of selected ATE systems; (2) the

conducting of field measurements/verifications of ATE systems; (3) the

analysis of data and assessment of station performance quality; and (4)

the planning of a more comprehensive approach to ATE station performance

verification procedures.

3. APPROACH

Based on a number of visits to various DoD ATE installations in

the Fall of 1980 (described in detail in section 3 of the complete

report), two basic decisions were made with the concurrence of DoD.

First, the AN/USM-410 (EQUATE) ATE System was selected for on-site

testing and evaluation. The primary reasons for choosing this system

were: (1) it is a third generation ATE system using sampling techniques

for virtually all measurements and digital synthesis for most waveform

stimuli; (2) it is used by all three services; (3) it measures/generates

a wide variety and range of signals; and (4) it uses the IEEE Standard

41 6-1 978 ATLAS language. Following this decision, efforts were made to

obtain access to one or more EQUATE systems in each of the three services.

With the help of the service sponsors committee, access was obtained to

one Army and one Navy installation. An extensive ongoing workload at

the Air Force installation selected necessitated postponing a field

test of that particular EQUATE system.

The primary elements of the technical approach followed the

objectives stated above and can be summarized as follows:

The first phase was the selection (and possible modification) and

laboratory characterizati on of commercial signal sources. The selection

of those sources was dictated by the choice of ATE system to be investigated

(i.e. , its voltage, frequency or pulse measurement characteristics) as well as the availability at NBS of adequate capability for characterizing

the sources. Commercial availability, price, delivery time, and portability

aspects were also considered, as was computer control capability.

Following the selection of the EQUATE system, test parameters were

chosen based on the knowledge of its specified measurement capabilities,

combined with knowledge of the output capabilities of potential signal sources. For the dc and low frequency ac work, it was decided to use dc

2
voltages from ±100 mV to ±200 V and ac voltages from 300 mV rms to

140 V rms (at frequencies from 50 Hz to 10 MHz). For the pulse work,

pulse duration over a range from 50 to 1000 ns was selected as the

initial pulse measurement parameter.

The second phase was that of field measurements and performance

verification of selected ATE stations. For this purpose, calibrated

sources with suitable interface adapters/connectors were taken to the

ATE station. The station was programmed to measure and record a range

of source output signals as applied to randomly selected pins on the

station interface panel. In this approach, the ATE station treats the source as a typical unit under test (UUT).

The third phase was the evaluation of the field measurement data

at NBS in the light of knowledge about the performance characteristics

of the sources. Based on this, conclusions could be drawn as to the

actual measurement capability of the ATE station. Additional observations

about station operation during the field measurements were also to be

compi led.

It was recognized that these field experiments would represent

only a limited sampling of the measurement capability of selected ATE

systems. Therefore, the fourth phase of the approach was the development

of a more comprehensive proposed program for assuring better measurement

capability and traceability of military ATE systems.

4. CHARACTERIZATION OF SIGNAL SOURCES

A major part of the work for this project consisted of the testing

and calibration of stable signal sources that could provide known

stimulus values of dc and low frequency ac voltage, as well as pulsed

voltage waveforms of known duration to the ATE system under test

(AN/USM-410 EQUATE in particular). Several alternatives were possible

for this purpose:

(1) Design and construction of suitable sources at NBS.

(2) An assembly of several commercially available instruments.

(3) The use of commercial sources.

For dc and low frequency (50 Hz to 10 MHz) ac voltages, the third

alternative was taken since several meter calibrators were commercially

available which had the necessary voltage and frequency ranges. For

pulse duration, the second approach appeared to be the most feasible.

The first alternative was not possible since time restrictions did not

permit the development of NBS-designed packages.

4.1 DC and AC Voltage Source

The dc and ac source selected for the experiment was evaluated at

NBS to determine its suitability for providing known voltage amplitudes

over a range of environmental conditions. Specifically, the possible

correlations in the output of the source were measured as a function

3
of input line voltage, temperature, start-up time, and time stability

over a period of approximately seven months. From these data it is

possible to assign uncertainties to the values of the dc voltages of

less than 200 parts per million (ppm) over a range of 0.1 to 200 V dc,

and uncertainties of less than 1200 ppm to the values of ac voltages

over the range of 0.3 to 1 40 V rms ac. The assignment of uncertainty

was made by summing the errors of the output of the source for each cf

the environmental conditions listed above.

Figure 1 summarizes the results of the temperature tests for all

dc voltage outputs used from the source. The shaded area shows the

limits in the changes of these dc output levels over the temperature

range from 0° to 40°C relative to their value at 23°C. Less than

±100 ppm of change in output voltage was measured due to temperature

changes over the 40°C range observed. However, since the source was

not subjected to more than a ±5°C departure from the nominal 23°C

reference temperature during any field test, the assigned uncertainty

range for dc voltage (due to temperature) was conservatively estimated

to be no greater than 40 ppm.

Figure 2 shows the errors (departures from nominal) that were recorded for a set of four different dc voltages over a seven-month

test period. The data shown for observation number 28 are not anomalies,

but resulted from making voltage measurements when the source and

voltmeter used for these tests were not in thermal equilibrium. These

particular measurements were made less than an hour after the instruments

were exposed to ambient temperatures during one of the field visits.

Using this accumulated data, the 3a value of the 252 observations

was calculated to be 55 ppm (due to time instability), and this value

was assigned to the uncertainty of the dc voltages of the calibrator.

The dc output voltages of the source were intercompared twice to

the U.S. Legal Volt, maintained by the Electrical Measurements and

Standards Division of NBS. This standard presently has an uncertainty

of less than 1.0 ppm and intercomparisons are possible to this level.

Normally, comparisons are made in the range of 0.015 to 10 V dc. The

first comparison was made on March 19, 1981 to calibrate the source

over a range of 0.01 to 10 V. Five months later, the source was again compared to the NBS Legal Volt to determine if the former had

drifted significantly. For the second comparison, the calibration

range for the source was extended to 200 V by special arrangement with

the Electrical Measurements and Standards Division. The data obtained

during both calibrations are shown in figure 3. From these data, a 3a uncertainty of 38 ppm was assigned to the dc voltage source as compared to NBS standards over a range of 0.10 to 200 V dc.

The above uncertainties due to temperature, time, and offset from

the legal volt, therefore, sum in quadrature (square root of the sum

of the uncertainties squared) to 78 ppm. Together with effects due

to line voltage and start-up characteristics (described in detail in

the complete report), an overall worst-case uncertainty range in dc

output voltages of the source was found to be less than 200 ppm.

It should be noted that each component contributing to the uncertainty

of dc output voltage is independent of other components.

4
The ac temperature stability was measured in the same manner as the dc temperature stability. Figure 4 shows the changes in ac output

voltage referenced to the output of the source at 23°C. The maximum

change in the ac output voltage over all voltages and frequency

combinations measured was 400 ppm over the temperature range of 0 to

40°C. The assigned uncertainty range for ac voltage was estimated to

to be no greater than 80 ppm over the 23 ±5°C temperature range

encountered in the field tests.

Figure 5 shows the errors observed during the same seven-month

period indicated in figure 2 for four voltage/frequency ac outputs from

the source. As expected, the ac outputs exhibit considerably more uncertainty and time instability than for the dc outputs. It is shown

in the complete report that the predominant source of both the dc and

ac drifts were due to time instability of the voltmeter used for making

these tests. Consequently, the uncertainty assigned to the source due

to stability with time is quite conservative. Using 264 observations,

a 3a uncertainty of approximately 1720 ppm was calculated over the

seven-month interval. However, for the one- to two-week intervals

used for field testing, the time stability of the ac voltage outputs

is conservatively in the range of 800 ppm.

The ac voltage of the source was measured as a function of amplitude

and frequency by means of an NBS "Type F" set of ac-dc thermal voltage

converter standards. The details of using these standards for making

ac-dc difference measurements (in order to determine absolute ac voltage

corrections for the source) are contained in the complete report.

Figures 6a and 6b show plots of the offset corrections applied to the

ac source on the dates shown. The voltage and frequency range of the

data presented is 8 to 20 V rms and 50 Hz to 50 kHz, respectively.

From these 69 observations, the source was assigned a 3a uncertainty

range of 93 ppm as compared to NBS standards.

The above uncertainties due to temperature, time, and offset from

the legal volt, therefore, sum in quadrature to 810 ppm. Together

with effects due to line voltage and start-up characteristics, an overall worst-case uncertainty range in the ac output voltages of the source was conservatively estimated to be less than 1200 ppm. Again,

the components contributing to the uncertainties of the ac output

voltage are essentially independent of each other.

For both the ac and dc measurements, interconnection between the source and the voltmeter was made with a 2 m (6-ft) long length of

RG-58C/U cable. All measurements described above were made at the end

of the cable and interface connector combination, i.e., right at the

output connector pins. This is the same length and type of cable used

to interconnect the source and the ATE system during subsequent field

tests.

4.2 Pulse Duration Source

The system used to calibrate the pulse duration source is the NBS

Automatic Pulse Measurement System (APMS). This system consists of a minicomputer interfaced to a wideband (dc-18 GHz) sampling oscilloscope

5
through a 14-bit analog-to-digi tal (A/D) and di gi tal -to-anal og (D/A)

converter unit. Both the high-speed sampling hardware and the data

acquisition and signal analysis software developed for this system are described in detail in the complete report. Also, both the time axis

calibration and the voltage axis calibration and their associated

uncertainties (±1% of nominal/cm) are fully covered in the larger

report

Once the APMS time and voltage axis were calibrated in a manner traceable to NBS standards, the system was used to calibrate the PULSE

DURATION source. Since the pulse source was to be used to test the

ability of the EQUATE ATE station to measure the parameter PULSE

DURATION, it was necessary to calibrate the source, as nearly as possible,

at a reference plane electrically and mechanically matched to the EQUATE

UUT reference plane. Because the EQUATE station has two such planes,

the direct interface unit (DIU) and the programmable interface unit

( PIU) , it was deemed necessary to provide a set of calibrated PULSE

DURATION waveforms for each of the two different planes. The EQUATE

station is capable of measuring pulse duration (often termed "time

interval" in the manufacturer ' s literature) in the range of 20 ns to 10 us. To test this capability, the pulse source was calibrated at

nominal PULSE DURATIONS of 50 ns, 100 ns, 200 ns, 500 ns, and 1 pS.

The problem of providing a known pulse waveform in the

nanosecond/microsecond time range is primarily a problem of maintaining

a known wideband impedance match from the generator to the measurement

plane. The pulse generator output impedance is 50 ft and the EQUATE

station DIU is, in fact, a 50 D BNC coaxial connector, so the problem

of maintaining pulse wave shape fidelity at the DIU measurement plane

was simply solved by using a 2 m length of 50 ft RG-58C/U coaxial

transmission line as a wideband interconnection, for purposes of

testing the DIU, then, the pulse source was configured as the combination

of the commercial pulse generator with a 2 m section of RG-58C/U connected

to its pulse output port.

Attempting to provide a known pulse waveform to the EQUATE PIU

measurement plane was somewhat more complicated. Physically, the PIU

measurement plane is a zero-insertion-force (ZIF) 650 pin connector

configured in such a way that signal pins and signal shield pins are interspersed in a checkerboard pattern. Behind each signal and signal

shield pin pair are 1/0 buffering and terminating electronics such that

each pin pair can be switched-selected for use as a signal source port

or a signal measurement port. To provide a known pulse waveform at the

PIU plane, it was necessary to use special filters and connectors during

the calibration procedure in order to minimize distortion at the PIU

connector pins. All of these details are provided in the complete report.

The major problem that arises in the practical measurement of

PULSE DURATION is the definition and determination of the PULSE BASELINE

and PULSE TOPLINE amplitudes. Actual measured pulses seldom exhibit

perfectly flat baselines or toplines so that in performing the measurement

one usually is forced to choose, perhaps arbitrarily, a method or algorithm

6
for determining these two amplitudes. Of the four algorithms for

determining PULSE BASELINE and PULSE TOPLINE magnitudes [ 1 ]

, 2 two were chosen for use in this work. The first is the PEAK MAGNITUDE algorithm

which consists simply of choosing the smallest and largest voltage

values of the recorded waveform as the PULSE BASELINE and PULSE TOPLINE,

respectively. The second algorithm chosen, the MODE OF DENSITY

DISTRIBUTION, is a bit more complicated. The recorded pulse waveform

is superimposed upon a grid of small At rectangles in the voltage-time

plane. Then a probability density histogram is constructed by counting

the number of An - At rectangles through which the waveform passes

for each incremental magnitude. Am. The PULSE BASELINE and PULSE TOPLINE

are then defined to be the lower and upper modes (or peaks) of this

bimodal histogram, respectively.

Figures 7 and 8 are replicas of the graphical /alphanumeric printout

obtained from a pulse waveform analysis program used in the APMS. The

waveform shown in figure 7 is of the nominal 50 ns duration pulse from

the NBS source applied directly to the APMS, with the analysis based on the MIN-MAX definition for the 0 percent and 100 percent amplitude

levels. Figure 8 is the same pulse except that its parameters are based on the HISTOGRAM definition of these levels. It is apparent

from the data on base magnitude and top magnitude where the remaining

differences for pulse start time, stop time, first and second transition

duration (rise and fall times), and, finally, pulse duration occur.

The pulse duration using the HISTOGRAM algorithm was about 59 ps longer

than that obtained using the MIN-MAX method. The "+F" in the comments

line means that a Gaussian nine-pole filter was placed on the output of

the pulse source having a nominal transition duration of 5 ns. Because

the EQUATE system uses a sampling algorithm based on a MIN-MAX technique,

the NBS-cal ibrated value for the pulse durations from the pulse source

was obtained using the MIN-MAX algorithm on the APMS.

The pulse source was calibrated via the APMS in April 1981 and

again in June/July 1981. In the complete report are contained figures

similar to those of figures 7 and 8 herein which show all of the

pertinent calibration data gathered, as well as test programs, test

configurations, etc. Included also are figures showing the effects on the pulse waveforms when they are applied to the EQUATE PIU connector

via NBS adapters. Table 1 summarizes the results of the calibration

data taken for both PIU and DIU connections using the MIN-MAX 50 percent

pulse duration method. The pulse duration figures shown are the mean value of three different measurement runs made on the source by the

APMS for a given nominal pulse duration. As indicated in the last

column, the change (At) over about a three-month period shows a time stability of well less than ±1 percent. For the one- to

two-week interval used for field testing, the time stability is on the order of ±0.2 percent.

2 Numbers in brackets refer to the literature references listed at the

end of this report.

7
5. HELD TESTS OF ATE SYSTEMS

The second major part of the work on this project consisted of

transporting the calibrated sources described in section 4 to DoD field

sites where the AN/USM-410 (EQUATE) stations were located, and running

dc and low frequency ac voltage and voltage pulse duration measurements.

The two available sites that were visited are located at the U.S. Army

Depot, Tobyhanna, PA and the U.S. Naval Avionics Center, Indianapolis, IN.

EQUATE-ATLAS test programs were written for making the necessary

measurements with the assistance of system programmers and operators at

these locations familiar with developing test program sets for the

EQUATE system.

5.1 DC and AC Voltage Tests

The basic test procedure used with the dc and ac source applied to

the EQUATE system was as follows. A preprogrammed tape of test voltages

was prepared prior to the visit. After the on-site equipment had been

operated for at least eight hours, the tape was loaded into the source.

The voltage test signal from the source was applied to the PIU connector

through an adapter designed to apply the voltage to selected pairs of

measurement pins. The pairs of measurement pins were randomly chosen

to emulate a UUT that might be connected to the EQUATE system. In general, six pin-pairs were chosen for the measurements and, of these,

four pairs were remeasured to determine if measurement errors were associated with specific pairs.

Part of the experimental design of the field test included the

choice of voltage sequences that would be measured by the EQUATE systems.

It was decided that the test voltages to be measured should be a random

sequence of amplitudes and frequencies in order to emulate the testing

of a UUT whose output could assume a wide range of values. The voltage

sequence covered the range of ±0.1 through ±195 V dc and from

0.3 V ac rms through a maximum of 130 V ac (184 V ac peak). This

range was chosen to be well within the specifications of the EQUATE

system measurement capability since initial testing at upper voltage

limits gave rise to potential measurement problems. Other difficulties

concerning the field testing are detailed in the complete report.

During each field test, the measurement data were printed on a hard

copy printout on the console writer as well as written into a disk

file. In this manner the measurements were stored in machine readable

form for later data analysis. Additionally, hard copy and magnetic

tape outputs were made of the ATLAS programs that were used to acquire

the data. At NBS the magnetic tape was read, and the data on the tape were checked against the hard copy output from the EQUATE station.

The recorded measurements were then compared to the preprogrammed values

that were applied from the calibrator and the deviations were calculated.

The dc measurements consisted of 440 data points, representing 44

voltages presented to each of the six PIU pin-pairs with four pin-pairs

replicated.

8
Tables 2 and 3 give a summary of the 440 dc voltage observations

taken at each of the Army and Navy test sites, respectively. A listing

of the test program used for obtaining the data, the run sequence of

applied voltages, sample printout of the program data, etc., are all

contained in the complete report. The mean, maximum, and minimum errors

in percent are calculated on the basis of the following expressions:

Percent error = NBS source - Measurement x 1 00 . Measurement

Mean percent error is the arithmetic average of the percent errors.

Minimum percent error is the smallest percent error.

Maximum percent error is the largest percent error.

Standard deviation is a measure of the dispersion or spread of the

percent error data.

Table 2 shows that the largest measurement uncertainties occurred at

the smallest voltage levels. These uncertainties are considerably

larger than what would be expected from published specifications [2-5].

Obviously, greater errors are incurred when making null types of

measurements with such an uncertainty distribution. Also, summarizing

all of the measured data as shown does not show the channel to channel

reproducibility nor the effects of replication as detailed in the

complete report. Table 3 shows a rather different distribution of errors including an obvious malfunction indication at the +10 and +100 V levels. Asymmetry effects in the errors are also apparent, but may be

related to the malfunctions. It was subsequently learned that this

second system had a defective data converter which produced erroneous measurements only when near its full-scale input.

Tables 4 and 5 give a summary of the 463 ac rms voltage observations

taken at the Army test site. Table 4 shows the distribution of errors

for observations at the applied voltage levels from 0.30 to 70.00 V rms. Table 5 shows the distribution of these same observations as a function

of frequency from 50.00 to 50,000.00 Hz. The listing of the test

program, sample printout of the program data, the run sequence of

applied voltage/frequency combinations, etc., are contained in the

complete report. As indicated by the mean percent error distribution

in table 4, there is a distinct degradation in the mean errors for the

ac voltage measurements at 7.00, 30.00, and 70.00 V rms as compared to

the three lower levels at 0.30, 0.70, and 3.00 V rms. However, the

randomness of the observations is considerably larger at the lower

voltage levels as indicated by the larger maximum percent errors and

corresponding standard deviations. Table 5, on the other hand, shows

how relatively independent the ac voltage rms measurement uncertainties

were with respect to frequency, except at 50 kHz where considerable

dispersion occurred (only two samples per period are taken by EQUATE).

In general, these uncertainties are in the range of the errors anticipated,

although a significant number of observations (~50%) fall outside

the published specifications [2-5].

9
Tables 6 and 7 give a summary of the 463 ac rms voltage observations

taken at the Navy test site. Data were also taken at the 130.00 V rms level in this case. The distribution of these errors is rather different

than the distribution of the errors for ac voltage measurements summarized

in tables 4 and 5. As indicated by the mean percent error distribution

shown in table 6, there is a distinct degradation in the mean errors

for the four lower voltages (0.30, 0.70, 3.00, and 7.00 V rms) as compared to the three higher voltage levels (30.00, 70.00, and 130.00 V rms). Again, however, table 7 shows that the standard deviation of

the measurement errors increases somewhat at 20 kHz and substantially

at 50 kHz, being relatively independent of frequency over the remaining

range. The large maximum percent error at the 7.00 V level in table 6 was observed at 50 kHz. Except for the test points noted, most of

these observations are well within the range of the anticipated errors.

5.2 Pulse Duration Tests

Along with the dc and low frequency tests described above, the

EQUATE systems were tested for their ability to measure the parameter

PULSE DURATION over a range of 50-1000 ns. Briefly, this testing

was accomplished by programming the EQUATE station to measure the

PULSE DURATION parameter of a variety of pulses generated by the NBS

calibrated pulse source described in section 4.2.

The NBS pulse source was used to test the EQUATE station's ability

to measure PULSE DURATION through both the PIU and DIU measurement

ports. For each of these ports, pulse source pulses with a nominal

pulse amplitude of 400 mV and a pulse repetition rate of 20 kHz were

used. As mentioned earlier, nominal PULSE DURATIONS of 50, 100, 200,

500, and 1000 ns were generated by the pulse source for measurement by

the EQUATE station through the calibrated UUT output interfaces for

both the PIU and DIU connectors.

On the EQUATE system, the measurement of the parameter PULSE

DURATION is a three-step process. First the value of the 100 percent

voltage level of the pulse is measured ( VOLTAGE-P-MAX) . Then the

value of the 0 percent voltage level is measured ( V0LTAGE-P-MIN).

Finally, a time interval measurement is conducted between the computed

50 percent level positive slope portion of the pulse and the computed

50 percent level negative slope portion. This latter measurement

yields the value of the PULSE DURATION.

There are a number of important subtleties encountered when making

PULSE DURATION measurements both in terms of the pulse sampling

electronics and the measurement algorithm used in the software. The

particular problems encountered during these field tests concerning the

pulse amplitude measurements (low-speed and high-speed voltage sampler,

duty cycle, number of samples, etc.), as well as the ATLAS instructions

used to obtain the minimum/maximum voltage levels and pulse duration,

are fully described in the complete report.

10
Table 8 summarizes the pulse duration measurements made at the

Army test site showing the 50 percent pulse duration mean deviations

from the calibrated NBS value in percent. Five tables are provided in

the complete report, each one containing the measurement results for

all pulses measured on a particular PIU pin or DIU connector. These

five tables each contain the observed data (five sequential measured

values of pulse duration), the mean value of the five measurements,

and the standard deviation of these readings (for each of the six

nominal pulse durations of 50, 100, 200, 500, and 1000 ns), along with

other pertinent data. What is shown in Table 8 under each PIU pinpair or DIU connector is the difference in percent deviation from

nominal of the mean value of the pulse measurements. Consequently,

these data do not contain the maximum, minimum, and standard deviations

shown for the dc and ac voltage measurements summarized in tables 4

through 7. Nevertheless, table 8 does provide a good indication of

the variability in pulse duration error distribution, both as a function

of the nominal duration from 50 to 1000 ns and the channel to channel

reproducibility. The measurements made via the DIU ports (wider bandwidth

channels) do not appear to be significantly better than those made via

the PIU channels (note -16.1% maximum deviation). Since the NBS pulse

source has an uncertainty well below ±1 percent, these deviations

are real and significant. The small differences in NBS pulse durations

at a given nominal value are due to the differences in the calibrated

values for either a PIU or DIU connector (cf table 1).

The available documentation on the EQUATE system provided by the

manufacturer contains no information concerning measurement accuracy

specifications. The Army's system performance specifications (1976 and

1978 versions) do contain these specifications, but there is disagreement

between the two documents and in some cases the specifications are very

confusing.

For example, the accuracy specification in the 1976 document for

"rise/fall time and pulse width measurement is

±(5 ns + trigger error),"

where, on another page, trigger error is defined to be "less than

-3 ...

3.2 x 10 sensitivity

N x signal amplitude *

where N = number of cycles of input signal over which measurement took

place.

11
In the first expression, it is deduced that trigger error, being

added to 5 ns, must have units of ns also. It is not at all obvious

that the second expression for trigger error has units of ns. In addition, the interpretation of the meaning of N, for a pulse parameter

measurement, is by no means clear nor is the meaning of the units of

the term "sensitivity." In short, NBS personnel were unable to clearly

determine the accuracy specification for these parameters. Also, these

problems are not corrected or clarified in the 1978 document.

Table 9 summarizes the results of these same pulse duration

measurements made at the Navy test site. Tests with the 500 ns (sharp cutoff) pulse duration were not made at Indianapolis due to

time limitations. The nominal pulse source amplitude in this case was 2.50 V and the nominal pulse repetition frequency was 100 kHz in all cases. Also, the buffered mode of making voltage peak pulse measurements

was utilized on the PIU channels. How voltage peak maxima exhibit a monotonic increase with longer nominal pulse durations or shorter duty

cycles (which affect the resulting pulse duration measurement) is

described in the complete report. Somewhat similar to the Tobyhanna

data, the data in table 9 show erratic variation from -11.9 percent to

-0.3 percent. In general, the buffered PIU measurement data appear to

be in closer agreement with the NBS values than the unbuffered PIU

data.

5.3 Time Domain Refl ectometry Tests

The results of making PIU and DIU time domain reflectometry (TDR)

tests are shown in figures 9 through 11. Figure 9 shows the 50 ft TDR

signature looking into the single available DIU BNC connector. Ideally,

if the channel exhibited a perfect wideband 50 ft impedance match, then

the signature would appear as a smooth, uniformly flat-topped step

waveform. The small deviations from flatness observed in the second

and third time divisions are due to the TDR test pulse used and the

EQUATE system connector. The wiggles in the seventh and eighth time

divisions, however, are caused by the EQUATE DIU channel and indicate

small (a few ohms) mismatches in impedance.

Figures 10 and 11 are the TDR signatures of pin-pairs 1 and IS of

the PIU channel in the unbuffered and buffered modes, respectively. In this case the impedance deviations are much more significant than in

the DIU case. As a function of distance starting from the PIU ZIF

connector and looking into the PIU channel, the impedance first rises

to about 100 ft (positive peak at the beginning of time division four),

drops to about 25 ft, and then meanders erratically back to about 50 ft in the ninth time division. The buffered and unbuffered TDR signatures

differ noticeably only in time divisions six through nine. These large

deviations of impedance are strong indications that pulses in the

nanosecond domain measured through the PIU are appreciably distorted.

12
6. CONCLUSIONS AND RECOMMENDATIONS

This report describes the executive summary of a limited experimental

investigation of the measurement performance of two ATE stations

( AN/USM-41 0 EQUATE). From the experience of preparing transport

standards, collecting the test data, participating in various ATErelated meetings and conferences, perusal of pertinent literature,

other on-site visits, etc., conclusions and recommendations concerning

future efforts are summarized below. A more complete discussion

regarding future efforts is contained in the full report.

6.1 Feasibility of Using Dynamic Transport Standards

The concept of performing an on-site, "in-situ" test of the system

performance characteristics at the stimulus/measurement interface

connector, using wel 1 -cal i brated transport standards, has been demonstrated

to have merit. Measurement uncertainties that would otherwise be

undetermined can be quantified. An independent verification of the

accuracy specification for basic dc and ac voltage and pulse duration

measurements, common to most ATE system capability, can be established.

The accuracy of other measurement (and stimulus) parameters are also

capable of being verified in similar fashion. The in-situ system

test/calibration procedure accounts for hidden errors due to signal

path losses, noise interference from pickup and crosstalk, and drifts

or offsets in the electronics of the ATE. More subtle deleterious

effects due to special algorithms used in the computer software or transmission/decoding errors in the digital interfaces of the system

are also reflected in the data obtained from system performance

verification/calibration testing. Section 5 in this report describes

in detail the measured deviations from the nominal NBS value of the

dc/ac voltage and pulse duration data on specified channels of the two

AN/USM-41 0 systems studied. These systems utilize built-in secondary

standards for dc and ac voltage as well as for frequency (time base).

Self-check and calibration software (SYSCAL) is also provided for these

systems. Nevertheless, significant deviations, both in magnitude and

number of data points, were obtained from these two systems. Consequently,

the feasibility of the dynamic transport standard (DTS) concept for

performance checking and system calibration purposes has been verified

within the limitations mentioned.

6.2 Calibration and Characterization Methods

Several approaches and procedures are in common usage for providing

calibration support of ATE [6], As detailed in many of the papers

referenced in [6], there are numerous shortcomings to the present

piecemeal approach of removing instruments or built-in standards from the

system for calibration at a remote metrology laboratory. Because of

the need for performing maintenance and/or repair on these items,

however, it is recognized that such "off-line" procedures are often

very practical or may be the only viable calibration support available.

In some cases, the mean-time-between-fai 1 ures (MTBF) of the system is

low so that the time to run a system calibration significantly reduces

the available up-time for UUT testing. Nevertheless, where the MTBF

13
of the ATE system is high enough and transport standards can be made

available which are compatible (UUT/i nterface device adapter connectors,

loading impedances, signal levels, etc.)» procedures for calibrating

the system on-site at the UUT/i nterface device adapter terminals are preferable.

The measurement data contained in this report (from the limited

experimental investigation of two EQUATE stations) does not constitute

a comprehensive system calibration of these stations. However, these

data are an indication that such a system calibration procedure could be

used either routinely or as an occasional verification test that system

specifications are being met, in-situ. Various schemes for providing

internal calibration tests, and associated hardware adjustments or software generated offset and gain/attenuation corrections, are being

incorporated in many ATE systems. As microcomputers are utilized more

in individual instrument building blocks within a system, these internal

calibration means are distributed throughout the system. Therefore,

whether the system computer is directly involved as part of the stimulus

and measurement capability, as in the architecture of third generation

systems such as EQUATE, or whether the signal processing is more distributed, as in the architecture of "distributed intelligence" fourth

generation systems, independent verification of the calibrated system

performance at the UUT/interface adapter connector plane is an important

task in the metrology support of the system.

Figure 12 illustrates the method whereby the present calibration

services and Measurement Assurance Program (MAP), provided by NBS for

basic electrical quantities, can be augmented with the capabilities of

both ATE-specific and high accuracy DTSs, as described in [6]. A

viable method for supplementing the present ATE calibration hierarchy

would be to make use of the DTS concept. As indicated by the solid

arrowed lines, the normal path of support by means of an NBS DTS is

through a key standards or calibration laboratory. Commercial "roll-up"

standards which serve as working accuracy DTSs (dedicated, perhaps, to

a specific ATE system) are then calibrated using the NBS DTS and any

other appropriate standards. The commercial DTS, in turn, is periodically

used to provide a system calibration at the UUT/interface device adapter

of the ATE. This periodic testing of system performance serves as a verification that built-in self-tests are maintaining the quality of

the measurements of the system. The removal of certain "core" stimulus

or measurement equipment or built-in standards for testing and/or

calibration in a laboratory is still optional, of course, but may not be

necessary.

6.3 Needs at NBS for Automated Calibration Support Systems

To assure that the metrology support of ATE system performance can efficiently be traced back to national laboratory standards at NBS,

there is a considerable need at this time for developing appropriate

automatic test and calibration systems. Some of the calibration services

at NBS, in fact, are already automated. But these setups are primarily

dedicated to providing support for the relatively few and generally

fixed-value transfer standards passed between NBS and corporate level

14
standards laboratories. The DTS concept and calibration support strategy

implies a system whereby the relatively complex DTSs can be readily

maintained, i.e., wel 1 -characteri zed and calibrated. Because of the

various kinds, ranges, and levels of calibration parameters of interest,

and the need for a considerable amount of documentation, automation of

the calibration support system is essential. Desk-top or minicomputerbased systems are anticipated at NBS and at the key standards or calibration laboratory to interface with the DTSs and make the necessary

comparison measurements. A more comprehensive description of this

calibration support strategy is given in the complete project report.

6.4 Recommendation for Future NBS ATE Efforts

Having demonstrated the need for, and viability of, in-situ ATE

performance verification by means of wel 1 -characteri zed and calibrated

sources used as transport standards, we propose to continue and expand

the work. In view of the great leverage obtained by a properly performing

ATE system on military weapons readiness, an expanded NBS program is

felt to be of significant cost effectiveness to the DoD. The beneficial

results of continuing this work are the improvements in system internal

calibration and self-test programs, and maintaining better test

consistency, uniformity, and traceability of measurements made by DoD's

large inventory of ATE systems.

Immediate efforts of the present JLC 30702 Project will be directed

at extending the field studies that have been carried out by NBS staff

at both the Gaithersburg and Boulder laboratories. The details of the

proposed work are outlined under the following tasks in the complete report.

(1 ) Field Studies of Selected ATE Systems

(2) Dual -Channel Signal Source for On-Site Calibration of ATE

(3) Improved Characterization Methods for Signal Sources

(4) Improved Pulse Waveform Stimulus Source

(5) Improved Automatic Waveform Analysis and Measurement System

The above tasks will build a foundation at NBS for providing basic

metrology for supporting both present and future ATE systems used by

the DoD. We also propose a longer range effort which would develop

similar support for other critical measurement parameters in the low

frequency and pulse waveform domain, as well as coverage of RF,

microwave/millimeter wave, and optical regions of the electromagnetic

spectrum. For example, an RF signal source capable of generating

signals with amplitudes from 0.1 to 7 V rms and frequencies up to

100 MHz will be accurately characterized for stability, temperature

dependence, and other environmental effects, and its traceability

rigorously established by calibration against higher echelon laboratory

standards at NBS. This source, and other high-frequency dynamic

transport standards to be developed, will also need automatic calibration

systems at NBS for proper support as described in section 6.3.

15
7. REFERENCES

[1]

IEEE Standard on Pulse Measurement and Analysis by Objective Techniques,

[2] IEEE Std. 1 81 -1 977, July, 1 977.

Performance Requirements, Test Station, Electronic Equipment,

AN/USM-41 0( XE-3) ( V) , ET & DL 75-04513-002, Frequency Control and Signal

Processing Devices Technical Area, U.S. Army Electronics Technology

and Devices Laboratory, U.S. Army Electronics Command, 13 April 1976,

pp. 36, 37, and 42.

[3]

Performance Requirements, Test Station, Electronic Equipment,

AN/USM-41 0( XE-4) ( V) , ET & DL 76-41 0XE4-AAH, Frequency Control and

Signal Processing Devices Technical Area, U.S. Army Electronics

Technology and Devices Laboratory, U.S. Army Electronics Command,

10 September 1976, Revised 1 June, 1978, pp. 25, 26.

[4]

Hardware Development Specification, Type B, Electronic Equipment

Test Station, AN/USM-41 0( )(V), (EQUATE), Contract No.:

DAAK80-79-C-0033 SLIN 0006AR, RCA Corporation, Automated Systems,

Government Systems Division, Burlington, Mass., 15 September 1980,

Revised 10 April 1981, Tables 3. 2. 1.4. 1-1, 3. 2. 4. 3-1, and 3.2.4. 3-2.

[5]

EQUATE ATLAS Programming Manual for AN/USM-41 0( )

( V)

,

Electronic

Equipment Test Station, Volume 1, Change 3, RCA, January 1982,

p. 9-1 07 and p. 9-11 5.

[6]

B. A. Bell and 0. Petersons, ATE Calibration by Means of Dynamic

Transport Standards, Proceedings of AUT0TESTC0N '81, Oct. 19-21, 1981,

pp. 280-287.
ALL

OUTPUTS

OF

DC

SOURCE

AT

VARIOUS

TEMPERATURES

Q_ CL n I cr Ld Li_ <M K) Q Ld CJ QC Ld Id CO

17

Figure

1.

The

limits

in

the

changes

of

the

output

voltage

of

the

source

over

the

temperature

range

0°

to

40°C.
DC

VOLTAGE

STABILITY

WITH TI

HE

18

Figure

2.

The

change

of

the

dc

voltage

output

at

four

selected

voltages

over a

period

of

approximately

seven

months.
DEVIATION

OF

DC

VOLTAGE

SOURCE

FROM

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STANDARD

K)S

CMS

<3 I <3

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—' 00

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19

Figure

3.

The

difference,

on

two

occasions,

between

the

dc

output

voltage

of

the

source

and

the

NBS

Legal

Volt

as

maintained

by

the

Electrical

Measurements

and

Standards

Division

of

NBS.
TEMPERATURE

SENSITIVITY

OF

AC

CALIBRATOR

Figure

4.

The

change

in

ac

output

voltage

asa

function

of

ambient

temperature.
AC

VOLTAGE

STABILITY

WITH

TIME

21

Figure

5.

The

change

of

the

ac

voltage

output

of

the

source

at

four

selected

voltage

and

frequency

combinations

over

period

of

approximately

seven

months.
DC

TRANSFER —8

TO

20

22

Figure

6a.

The

results

of

the

ac-dc

intercomparison

over

the

range

of8

to

20V

ac

and

over

the

frequency

range

of

50

Hz

to

50

kHz.
DC

TRANSFER 8

TO

20

23

Figure

6b.

The

same

intercomparison

as

shown

in

figure

6a

performed

three

months

later.
DU-4-

0.078

UERT. -

49.9999MU/0IU.

YHIN -

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MU

Figure

7.

NBS

pulse

source

50

ns

pulse

direct

to

APMS

sampler

with 5

ns

NBS

filter

(HISTOGRAM

definition).
25

Fiqure

8.

NBS

pulse

source

50

ns

pulse

direct

to

ARMS

sampler

with

5

ns

NBS

filter

(MIN-MAX

definition).
50

ft

aouopaduii aAj|D|ay

26

Figure

9.

A

time

domain

reflectometry

signature

of

the

50«

DIU

BNC

connector

port

to

EQUATE.
27

Time

/

Distance

Figure

10.

The

time

domain

reflectometry

signature

of

pin-pair

IS

of

the

PIU

input

in

the

unbuffered

mode.
<DOCo

to Q©E

i28

Figure

11.

The

time

domain

ref

lectometry

signature

of

pin-pair

and

IS

of

the

PIU

input

in

the

buffered

mode.
Figure 12. A Dynamic Transport Standard concept and support strategy.

Dashed lines indicate that the transport standard is physically

moved from one location to another.

29
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U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET (See instructions)

1. PUBLICATION OR

PARTS I S II

2. Performing Organ. Report No. 3. Publication Date

December 1982

' ]\uf(MWC TESt IqU I PMENT CALIBRATION/PERFORMANCE

VERIFICATION EVALUATION AND RESEARCH PROGRAM

(JLC/DdD Subtask 30702)

EXECUTIVE SUMMARY PART I

5. author(S) Barry A. Bell, Thomas F. Leedy, William L. Gans, Paul S. Lederer,

Robert E. Nelson

6. PERFORMING ORGANIZATION (If joint or other than NBS, see instructions)

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

7. Contract/Grant No.

8 . Type of Report & Period Covered

Final

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City. State, ZIP)

Prepared for

Joiht Logistics Commanders Panel on Automatic Testing

DoD Joint Technical Coordination Group for Metrology

DoD Calibration Coordination Group

USAF ASD/AEGB Mate Program Office

10. SUPPLEMENTARY NOTES

jJJ Document describes a computer program; SF-185, FiPS Software Summary, is attached.

li. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bi bliography or literature survey, mention it here)

This work describes an experimental approach to verify the

performance of selected third generation automatic test systems.

The approach consisted of careful laboratory characteri zation

of two types of signal sources. One was a dc and low frequency

ac voltage source covering the range of approximately 100 mV to

200 V dc, and 300 mV to 1 40 V ac rms over a frequency range of

100 Hz to 10 MHz. The second source was a precision time

synthesizer used to generate pulses of known durations from 50 to

1000 ns. Both of these sources were used to verify the ability of

two automatic test systems to measure ac and dc voltages and time

intervals. The methods used to characterize these sources and the

measurement results of applying the sources to the two automatic

test systems are discussed in detail. Recommendations for future

efforts to improve the measurement capabilities and traceability of

automatic test systems are also presented.

12. KE Y WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolon s) ATE; automatic test systems; cal i brat ion ; characterization; dynamic transport

standard; evaluation; field calibration; performance test; third generation system.

13. AVAILABILITY

Unlimited For Official Distribution. Do Not Release to NTIS

T I Order From Superintendent of Documents, U.S. Government Printing Office, Washington, D.C.

20402.

] Order From National Technical Information Service (NTIS), Springfield, VA. 22161

14. NO. OF

PRINTED PAGES

15. Price

USCOMM-DC 6043-P80