^ecknlcai rlote 92o. .2.20

SOME MODIFICATIONS IN METHODS OF

CALIBRATION OF UNIVERSAL RATIO SETS

DAVID RAMALEY

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
THE NATIONAL BUREAU OF STANDARDS

National Bureau of Standards is a principal focal point in the Federal Government for maximum application of the physical and engineering sciences to the advancement of technology in industry and commerce. Its responsibilities include development and maintenance of the national stand- ards of measurement, and the provisions of means for making measurements consistent with those standards; determination of physical constants and properties of materials; development of methods

for testing materials, mechanisms, and structures, and making such tests as may be necessary, particularly for government agencies; cooperation in the establishment of standard practices for incorporation in codes and specifications; advisory service to government agencies on scientific and technical problems; invention and development of devices to serve special needs of the Government; assistance

to industry, business, and consumers in the development and acceptance of commercial standards and

simplified trade practice recommendations; administration of programs in cooperation with United

States business groups and standards organizations for the development of international standards of

practice; and maintenance of a clearinghouse for the collection and dissemination of scientific, technical, and engineering information. The scope of the Bureau's activities is suggested in the following

listing of its four Institutes and their organizational units. Institute for Basic Standards. Electricity. Metrology. Heat. Radiation Physics. Mechanics. Applied Mathematics. Atomic Physics. Physical Chemistry. Laboratory Astrophysics.* Radio Standards Laboratory: Radio Standards Physics; Radio Standards Engineering.** Office of Standard Ref- erence Data. Institute for Materials Research. Analytical Chemistry. Polymers. Metallurgy. Inorganic Materials. Reactor Radiations. Cryogenics.** Office of Standard Reference Materials. Central Radio Propagation Laboratory.** Ionosphere Research and Propagation. Troposphere

and Space Telecommunications. Radio Systems. Upper Atmosphere and Space Physics.

Institute for Applied Technology. Textiles and Apparel Technology Center. Building Research.

Industrial Equipment. Information Technology. Performance Test Development. Instrumentation.

Transport Systems. Office of Technical Services. Office of Weights and Measures. Office of Engineering Standards. Office of Industrial Services.

* NBS Group, Joint Institute for Laboratory Astrophysics at the University of Colorado. ** Located at Boulder, Colorado.
NATIONAL BUREAU OF STANDARDS

technical ^ote 220

Issued August 30, 1964

SOME MODIFICATIONS IN METHODS OF

CALIBRATION OF ONIVERSAL RATIO SETS

David Ramaley

Radio Standards Laboratory

National Bureau of Standards

Boulder, Colorado

NBS Technical Notes are designed to supplement the Bureau's regular publications program. They provide a means for making available scientific data that are of transient or limited interest. Technical Notes may be

listed or referred to in the open literature.

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

Price: 25 cents
National Bure?u of Star AUG 5 1965

130,8*10

QCIOO

C:
CONTENTS

PAGE

1. Introduction -------------------------- 1

2. Conventional Method for the Calibration by Means of

Standard Resistors and Direct Reading Ratio Sets ------ 2

3. A Modification of the Calibration of the One Hundred

Ohm-Per-Step Dial by Means of Trimmed Resistors 3

3. 1. Trimmer Adjustments --------------- 3

3. 2. Calibration Arrangement -------------- 4

4. Calibration of the One -Hundred Ohm-Per-Step Decade

with Twenty Untrimmed Resistors -------------- 5

5. Calibration with Ten One-Hundred Ohm Resistors - - — - 6

6. Modified Method of Calibration of the Ten Ohm-Per-Step

and Lower Decades by Means of a Universal Ratio Set or

Resistive Voltage Divider- ------------------ 7

7. Calibration of the One -Hundred Ohm-Per-Step Dial and

Setting X on the Ten Ohm-Per-Step Dial by Means of

Another URS -- 9

8. Conclusions *.------------------------- 11

REFERENCES 12

iii

SOME MODIFICATIONS IN METHODS OF CALIBRATION

OF UNIVERSAL RATIO SETS

David Ramaley

Universal Ratio Sets can be calibrated by a number of different methods. The well established

methods are very briefly outlined and emphasis is

placed on some more recent developments. The

choice of methods will depend upon available laboratory equipment and other considerations.

1. Introduction

Universal Ratio Sets [1,2,3] , commonly abbreviated URS,

are now usually constructed as six dial instruments. Seven dial

instruments probably will be available commercially in the future.

Five dial varieties will not be considered in this paper.

Because the ratio set is a ratio device, it need not be calibrated in terms of any particular unit of resistance. A convenient unit

for calibration is one two -thousandth of the total resistance of the

twenty-step dial. If this unit is used, the settings and 20 on the high

dial will have no corrections. Usually the corrections at other settings

of a URS are small (a few milliohms).

Conventional methods of calibration are mentioned first, followed by a description of several modified methods. Some of these modified calibration methods are applicable to resistive voltage dividers

and other ratio devices.

Figures in brackets indicate the literature references at the end of

this paper.
2. Conventional Method for the Calibration by Means of

Standard Resistors and Direct Reading Ratio Sets

A conventional method of calibration is described in a Department of the Navy Instrument Calibration Technique [4] and also by at

least one manufacturer's instruction manual.

The person performing the calibration should be acquainted

thoroughly with decade calibration methods [2, 3] . Peacock [5] gives

additional information on resistance decade calibration.

The step decades often ohms-per-step and lower are calibrated by conventional step substitution methods. The resistors of the

twenty step dial can be measured by the double substitution method of

comparing four-terminal resistors with two-terminal standards [2, 3] .

It will be necessary to solder in leads to the appropriate points on the

resistance coils to make the connections needed for most commercial

ratio sets now on the market. Total resistance of the twenty-step dial

circuit can be obtained by comparison with two one -thousand ohm

resistors in series. This measurement furnishes the conversion

factor for changing the measured resistances in ohms of all decades

to resistances in terms of the arbitrarily chosen unit.

Another procedure for calibration of the twenty -step dial

involves taking difference readings on the URS across a precision

standard resistor. This is described in the calibration instruction

procedures for the URS first mentioned.

Compensation of the ten ohm-per-step and lower decades needs

to be tested in a suitable bridge circuit to insure adequate stability of

overall URS resistance regardless of dial settings.
3. A Modification of the Calibration of the

One Hundred Ohm-Per -Step Dial by Means of Trimmed Resistors

If one has available either ten or twenty one -hundred ohm,

closely adjusted resistors (± 0. 002 percent) of precision quality, with

low temperature coefficients, this method is convenient.

3. 1. Trimmer Adjustments

Good quality, small adjustable resistors, commonly referred

to as "trim pots" in the radio industry, are connected across the

individual one -hundred ohm resistors. A good trimmer resistor of

one megohm magnitude and low temperature coefficient connected

across the potential terminals of a precision standard resistor constitutes a trimmable standard with good stability for short periods of

time. Combinations of trim resistors of other 'magnitudes can be

utilized for this purpose also, provided the selection offers an appropriate magnitude and does not reduce the overall resistance of the unit

excessively.

A good test to evaluate the suitability of a group of trimmed

resistors is to adjust all the resistors to equality within about a part

per million and then recheck this equality several times over a period

of about two or three hours. After this period of several hours, the

maximum spread in individual resistance should not exceed about four

parts per million.

Adjusting and comparing resistors to about one part per million

can be accomplished by using any appropriate bridge circuit with

adequate stability and resolution. Universal or Direct Reading Ratio

sets may be used for this purpose. In making the comparison of the

precision trimmed resistors the contact variations should be less than

100 microhms, and consequently the resistors should be mounted on

mercury-surfaced stands.
If the trimmed resistor group fails to demonstrate adequate

stability over a two hour period one may resort to better quality trimmer components, closer temperature control or possibly a series of

resistors with lower temperature coefficients.

3.2. Calibration Arrangement

Figure 1 shows an arrangement for calibration of a URS using

twenty trimmed resistors. The resistors are mounted on mercury

contact stands and connected to two resistance boxes and to the URS as shown. These resistance boxes should be of the best quality. The

boxes are connected in parallel so that they may be adjusted in fine

increments. Usually these boxes will be adjusted so that the URS

reading difference corresponding to power application at points and

20 will be exactly 2000. 0000 (interpolating between steps on the 0. 001

ohm-per-step dial on the URS). This arrangement is thus direct reading in terms of the arbitrarily chosen resistance unit, and the corrections to step and step 20 will be 0. 0000.

Bridge balance readings are taken next on the URS corresponding to power supply connections to all points, to 20 inclusive. Because all twenty of the trimmed resistors are considered equal in

resistance, the corrections to all twenty steps on" the URS can be

written down by inspection of the twenty-one URS readings simply by

comparison with the or 20 step reading. The correction to the ten

steps on the 10 ohm-per-step dial should 'be obtained at this time, also,

by taking an additional reading with power applied at point 1 (fig. 1)

and with the 10 ohm-per-step dial set at X. This correction to the 10

ohm-per-step dial in terms of the unit for the 100 ohm-per-step dial

is discussed under topic 6, pages 7 and 8. An example of calibration

data for the 100 ohm-per-step dial and X step on the 10 ohm-per-step

dial is given in table 1.
It is of interest to mention that this same procedure of using a sequence of trimmed resistors can be utilized for calibration of resistive voltage dividers and some types of potentiometers.

4. Calibration of the One -Hundred Ohm-Per-Step Decade

with Twenty Untrimmed Resistors

The same calibration can be performed with untrimmed resistors provided the correction for each resistor is known with respect

to the mean of the group of twenty. The calibration technique is the

same as with the trimmed resistors, but the computation of corrections

is somewhat more complicated. Table 2 gives an example of data for

such a calibration for a group of untrimmed resistors. The zero

reading on the URS should be large enough to accommodate changes

encountered because of differences in corrections to individual resistors of the group. A zero reading of 0. 0300 will probably be adequate

for use with most groups of one-hundred ohm standard resistors. If

standards are closely adjusted, the zero reading can be much less.

To increase the zero reading, the lead resistance from the zero point

on the resistor stand to the URS is increased. The arrangement should

be made direct reading by adjusting the resistance boxes (fig. 1) until

the URS reading difference between balances taken with power applied

to the and 20 points is exactly 2000. 0000. The last place is obtained

by interpolation. If the arrangement is not made direct reading, computations are somewhat more complicated.

Computed readings of column 5 of table 2 are obtained by adding the summation of corrections to the resistors to the zero reading

of the URS plus the step change readings that would have occurred for

perfect 100 ohm resistors. Corrections given in the last column are

obtained by comparing columns 5 and 6. These corrections are identical to those in table 1 for the same URS when calibrated with trimmed

resistors.
5. Calibration with Ten One-Hundred Ohm Resistors

Ten one-hundred ohm resistors, either trimmed or untrimmed,

plus a thousand ohm resistor can be used to calibrate the one hundred

f

ohm-per-step URS dial . The thousand ohm resistor can be trimmed

to equal the resistance of the ten one-hundred ohm resistors, or it can

be left untrimmed. All eleven resistors are placed in a series arrange'

ment as in figure 1. This modification requires only eleven resistor

positions and is represented in the diagram by means of the dashed

line jumper which bypasses and removes from the circuit the unnecessary resistor holders. The one thousand ohm resistor is situated in

location 10-11, and the hundred ohm resistors in locations 1-10.

With power applied to point 0, a URS reading is taken and then

another URS reading taken at point 11. The resistance boxes are

adjusted so that the reading difference between these two balances is

exactly 2000. 0000. The correction to the setting 10, or midpoint, is

obtained by taking a reading with power applied at point 10, then

exchanging resistor 1 with resistor 11 and taking another reading

with power applied at point 1 (fig. 1). The average of these two readings will be that reading which would have been obtained for a midpoint

reading of two perfectly matched 1000 ohm resistors. In fact, if the

thousand ohm resistor has been perfectly trimmed, we should observe

The ten ohm-per-step decade and setting 10 on the one ohm-per

step decade can be calibrated with ten trimmed or untrimmed resistors

in a manner similar to that described in sections 3 and 4. The one

hundred ohm-per-step dial is shorted out by a jumper to eliminate the

unnecessary resistance in the circuit. Likewise the resistance in the

string of ten resistors can be reduced by shunting with a standard

resistor of appropriate magnitude. This same method can be continued for the calibration of the 1 ohm-per-step and even lower decades.
identical readings before and after the resistor exchange. As an example let us suppose that with the ten one -hundred ohm resistors to

the left of the power connection the URS reading is 1000. 0128 and that

with the one -thousand ohm resistor to the left, the URS reading is

1000. 0086. This case would represent an untrimmed thousand ohm

situation. For a trimmed thousand ohm resistor, both readings should

be 1000. 0107 or the average of readings obtained with untrimmed

resistors. Furthermore, let us suppose that we have readings for

connections at position and position 11 which are 0. 0113 and

2000. 0113, respectively. The resulting correction to the 10 step is + 0. 0006.

Corrections to steps 1 thru 9 are obtained next by placing the

one-hundred ohm resistors in the appropriate positions and taking the

necessary step readings. Next, the hundred ohm resistor group is

placed in position to obtain readings for correction computations for

steps 11 thru 19. The corrections of the ends (0. 0000) and midpoint

(+ 0. 0006) of the decade are used for setting up the conditions for

determining corrections to the. other steps.

This method can be further extended to use only five onehundred ohm resistors if a five-hundred ohm or two one-thousand

ohm resistors (in parallel) are available. In fact, there are a number

of other calibration combinations which can be used. However, additional complication of computations make such calibrations more

difficult.

6. Modified Method of Calibration of the Ten Ohm-Per-Step

and Lower Decades by Means of a Universal Ratio Set or

Resistive Voltage Divider

If the 100 ohm-per-step dial is shorted out by a jumper, the

overall resistance of the URS becomes 111. 110 ohms and the maximum

number of possible step changes for a six dial ratio set is 111, 110.
Thus, if we connect a shorted URS directly to an unshorted URS, we

have about twenty times the number of available step changes on the

unshorted ratio set as on the shorted set. This calibration then becomes similar to the typical calibration of common types of potentiometers by means of the URS. Readings can be taken on the unshorted

or standard set corresponding to step changes for each step of all of

the ten step decades of the shorted ratio set. This arrangement gives

excellent resolution and provides a convenient method of calibration.

Corrections to the several dials are obtained by multiplying the URS

reading differences by a factor obtained from the known correction to

setting X of the ten ohm-per-step dial. As an example let us assume

that the actual correction to this dial is + 0. 0014. Let us also suppose

that the standard URS reading difference corresponding to setting and

setting X of the 10 ohm-per-step dial on the URS under calibration is

1890. 007. Thus the multiplying constant desired would be 100. 0014

divided by 1890. 007 or 0. 05291060. When all of the standard URS

reading differences are multiplied by this constant, the actual dial

steps for all of the ten step decades are obtained. The corrections

then can be ascertained by simple inspection.

This method can be modified for even greater convenience if the standard URS is made direct reading by a factor of twenty according to the known correction to setting X on the 10 ohm-per-step dial.

The circuit for this is shown in figure 2. The two resistance boxes

are placed in parallel to permit adjustment of resistance in very fine

increments. Let us assume for example that the correction to setting

X of the 10 ohm-per-step decade is + 0. 0014. The standard URS reading difference would then be made to equal 2000. 028 by adjustment of

the resistance boxes for a twenty times direct reading arrangement.

All URS reading differences divided by 20 would thus give the desired
information for readings taken on all steps of the ten step decades.

Table 3 gives an example of calibration with this arrangement for the

10 ohm-per-step dial and two steps on the 1 ohm-per-step dial.

A resistive voltage divider with a resolution of a part per

million can be used in this same manner to calibrate the ten step URS

decades . However, the high resistance of the divider and the low

resistance of the shorted URS (111. 11 ohms) may require an especiallysensitive galvanometer or null detector in the precise balancing of the

resultant bridge circuit.

7. Calibration of the One -Hundred Ohm-Per-Step Dial and

Setting X on the Ten Ohm-Per-Step Dial by Means of Another URS

The two ratio sets are connected as shown in figure 3. Here

G. and G_ are adjustable clips or other convenient devices which permit connection at any point along the connectors between the two ratio

sets. These adjustable connections enable one to secure the desired

readings for the zero step settings of the ratio sets and also for the

twenty step settings. These adjustments are made so that the balanced

bridge reading differences are equal for both ratio sets when the 100

ohm-per-step dials are set respectively at zero and twenty. For

example, if the standard URS reads 0. 0080 when the URS being calibrated reads 0. 0000, then the standard should read 2000. 0080 when the

other URS reads 2000. 0000. It is well to allow about 0. 008 ohms extra

coverage on the standard URS if one plans to set the URS under calibration on the various steps and take the corresponding reading on the

Although not a part of the subject under consideration, it is interesting to note that the second and lower dials of a Kelvin -Varley type

resistive voltage divider or potentiometer can be calibrated by this

same method by shorting out the proper portion of the first dial circuit.
standard URS. One can do it in reverse manner by setting the standard URS and reading the URS to be calibrated. For this situation the

extra coverage setting of about 0. 008 ohm should be in the URS being

calibrated. Purpose of the extra coverage is to insure that the reading of the lowest dial will be large enough to accommodate corrections

to any of the twenty steps involved in the calibration.

If the standard URS has been calibrated accurately, all steps

on all dials can be quickly compared with the corresponding steps on

the other instrument and corrections assigned accordingly. Readings

should be taken to an interpolated place on the 0. 001 ohm-per-step

dial if possible.

When neither URS has been calibrated, the procedure is somewhat more complicated. For each individual 100 ohm step change on

the unknown URS, two readings are necessary. The first is the reading for the corresponding step on the second URS. The second is the

reading on this same 100 ohm step of the second URS when the URS

being calibrated is set to the next lower 100 ohm step with the 10 ohmper-step dial set on X. Table 4 illustrates an example of this method

for calibration of the 100 ohm-per-step dial and setting X on the 10

ohm-per-step dial. The same method could be applied to work on

down through the lower dials. However, the method outlined previously

for shorting out the twenty step dial is much more convenient if the

standard URS is in fair adjustment even though not recently calibrated.

Errors of 0. 001 or 0. 002 ohms on the standard URS will result in

negligible corrections for the URS being calibrated.

Calibration of the 100 ohm-per-step dial and X step on the 10

ohm-per-step dial also can be accomplished for a single URS by this

method using a string of twenty untrimmed 100 ohm resistors. By

10
making the step by step comparison of the X step on the 10 ohm-perstep with each step on the 100 ohm-per-step dial, corrections need

not be known to any of the twenty resistors arranged in series.

8. Conclusions

The various methods of URS calibration mentioned here indicate

that the user of a URS has available a choice of methods. Still other

methods not described here can be used if one has access to a variety

of resistance boxes and possibly a slide wire. We can conclude that

standards accurately incorporating the unit of resistance are completely unnecessary for accurate URS calibrations. Any moderately

well equipped laboratory is in a position to adequately calibrate a URS.

11
REFERENCES

[1] Wenner, F., and Weibel, E. (1914), BS Bui. 11, 27, S223.

[2] Thomas, J. L. (Oct. 8, 1948), National Bureau of Standards

Circular 470.

[3] Brooks, P. P. B. (March 1, 1962), National Bureau of

Standards Monograph 39.

[4] Standards Laboratory Instrument Calibration Technique DR-03,

Six Dial Universal Ratio Set, issued by Department of the Navy,

Calibration Program. Available for a fee from the Office of

Technical Services, Department of Commerce, Washington,

D. C.

[5] Peacock, L. W. , I. S. A. Proceedings, 1961 Fall InstrumentAutomation Conference and Exhibit, Vol. 16 - Part 1, Paper

No. 22-61.

12
COI

CO

COQ

UJ2

cc

cro

L.Zo<

(JQO

a:o

i-o

UJzzoo

CO

CO

CT>

CO

CO

IO

CD I Q

CD

COQ

CO<HZoo>

CEo

CC

LU5

CO

tro»-CO

CO

UJ

cc

>-

h-z

UJ o O Z z *

CO UJ 3 cr<

hui

CO

CO o o n Ul <

cr

crcrof ) _i< u

CO

orhi CJ > Ul

CO z _) -> Ul < m> U. < O 5 z CO o cr

1-

R < (O

rrm Ul

_i cr <o Q

UJ

rr S o :> u.

cr

hh- z z -> UJ5

Ul ro o rr z o < hcr co

cr< CO

Ul

cr o

tn < Ul S ?

UlX S o cr CO i- o

13
o-O It Q-OAAAAAAAAAAAAAAAAA/VV-

(TWENTY STEP OlAL SHORTED OUT)

URS IN CALIBRATION

POWER SUPPLY

O Q

RESISTANCE BOX

Uaaaaaaaaa/wwwwv

STANDARD URS

RESISTANCE BOX

FIG. 2. CALIBRATION OF THE TEN STEP DECADES OF A URS IN A DIRECT

READING ARRANGEMENT. COMBINED RESISTANCE OF RESISTANCE

BOXES IS ABOUT 110 OHMS FOR URS READING DIFFERENCE OF

2,000,000 FOR THE 10 OHM- PER -STEP DECADE.

14
URS

UNDER

CALIBRATION

POWER SOURCE

Q

SECOND URS

FIG. 3. ARRANGEMENT FOR CALIBRATION OF THE 100 OHM-PER- STEP

DIAL AND THE X STEP ON THE 10 OHM-PER-STEP DIAL OF A

URS BY MEANS OF A SECOND URS.

15
Table 1. Example of calibration data for URS twenty step dial and

X step on 10 ohm-per-step dial using twenty trimmed

resistors

Power

Supply

Connection

Point

URS

Reading Correction

20

11*

2

3

4

5

6

7

8

9

10

11

12

13

14

15

1-6

17

18

19

20

0.

2000.

100.

X0.

200.

300.

400.

500.

600.

700.

800.

900.

1000.

1100.

1200.

1300.

1400.

1500.

1600.

1700.

1800.

1900.

2000.

0032

0032

0037

0018*

0039

0041

0043

0038

0035

0033

0030

0028

0026

0027

0024

0020

0026

0034

0039

0043

0038

0036

0032

0.0000

0. 0000

-0. 0005

+0. 0014*

-0. 0007

-0. 0009

-0. 0011

-0. 0006

-0. 0003

-0. 0001

+0. 0002

+ 0. 0004

+0. 0006

+ 0. 0005

+0. 0008

+0. 0012

+0. 0006

-0. 0002

-0. 0007

-0. 0011

-0. 0006

-0. 0004

0. 0000

* Data for X step on 10 ohm-per-step dial.

16
Table 2. Example of calibration data for URS 100 ohm-per-step dial and X step on

10 ohm-per-step dial using twenty untrimmed resistors. Correction to each

resistor in terms of the mean of the group is known to a part per million.

Correction Power Computed

Resistor

Number

in

CO

to

ppm

mpared

mean of

Summation

of

corrections

supply

connection

point

Reading

for a perfect

Actual

URS

Reading

Correction

to URS

g

r oup in use URS

0. 0113 0. 0113 0. 0000

20 2000. 0113 2000. 0113 0. 0000

1 - 6 - 6 1 100. 0107 100. 0112 -0. 0005

it ti ti 1* X0. 0107* X0. 0093* +0. 0014*

2 + 5 - 1 2 200. 0112 200. 0119 -0. 0007

3 -10 -11 3 300. 0102 300. 0111 -0. 0009

4 + 21 + 10 4 400. 0123 400. 0134 -0. 0011

5 + 1 + 11 5 500. 0124 500. 0130 -0. 0006

6 -17 - 6 6 600. 0107 600. 0110 -0. 0003

7 -14 -20 7 700. 0093 700. 0094 -0. 0001

8 + 13 - 7 8 800. 0106 800. 0104 + 0. 0002

9 -10 -17 9 900. 0096 900. 0092 + 0. 0004

10 + 10 - 7 10 1000. 0106 1000. 0100 + 0. 0006

11 - 5 -12 11 1100. 0101 1100.0096 + 0. 0005

12 + 17 + 5 12 1200. 0118 1200. 0110 + 0. 0008

13 - 3 + 2 13 1300. 0115 1300. 0103 +0. 0012

14 + 2 14 1400. 0115 1400. 0109 + 0. 0006

15 + 10 + 12 15 1500. 012d 1500. 0127 -0. 0002

16 - 9 + 3 16 1600. 0116 1600. 0123 -0. 0007

17 + 2 + 5 17 1700. 0118 1700. 0129 -0. 0011

18 + 4 + 9 18 1800. 0122 1800. 0128 -0. 0006

19 - 1 + 8 19 1900. 0121 1900.0125 -0. 0004

20 - 8 20 2000. 0113 2000. 0113 0. 0000

* Data for X step on ten ohm-per-step dial.

17
Table 3. Calibration data for the ten step decades of a URS

Dial

setting

of URS in

calibration

Reading

of the

standard

URS

Reading

difference

Correctior

to dial

settings

0000.000 0.034

X0. 000 2000. 062 2000. 028 0. 0014

00.000 0. 034 0. 000 0. 0000

10. 000 200.038 200.004 +0. 0002

20. 000 400. 042 400. 008 + 0.0004

30. 000 600. 045 600.011 + 0.0006

40. 000 800. 047 800. 013 +0. 0006

50. 000 1000. 050 1000. 016 +0. 0008

60. 000 1200. 055 1200. 021 +0. 0010

70.000 1400. 056 1400. 022 +0. 0011

80. 000 1600.059 1600. 025 +0. 0012

90. 000 1800.061 1800. 027 + 0. 0014

X0. 000 2000. 062 2000. 028 + 0. 0014

0. 000 0.034 0. 000 0. 0000

1.000 20. 032 19.998 -0. 0001

2.000 40. 036 40. 002 + 0. 0001

etc.

18
Table 4. Example of calibration of the 100 ohm-per10 ohm-per -step dial on a URS with the aid

arrangement shown in Figure 3. )

step dial and X step on the

of a second URS. (Circuit

Reading Reading

of URS " 6

, Reading

of second „..,, undergoing _~„ Differences

... 6. & URS

calibration

Summation

of

Differences

Summation

that would Correction

result if all for the

twenty URS corresponding

steps were URS step

equal

0. 0000 0. 0060

2000. 0000 2000. 0060

100.0000 100. 0063 -0. 0024

X0. 0000 100. 0087

200.0000 200. 0049 -0. 0021

1X0. 0000 200. 0070

300.0000 300. 0054 -0. 0021

2X0. 0000 300. 0075

400. 0000 400. 0043 -0. 0020

3X0. 0000 400. 0063

500.0000 500. 0052 -0. 0018

4X0. 0000 500. 0070

600.0000 600. 0051 -0. 0027

5X0. 0000 600. 0078

700.0000 700. 0059 -0. 0019

6X0. 0000 700. 0078

800.0000 800. 0074 -0. 0015

7X0.0000 800. 0089

900. 0000 900. 0075 -0. 0028

8X0. 0000 900. 0103

1000.0000 1000. 007 3 -0. 0030

9X0. 0000 1000. 0103

-0.0024 -0.002165 -0.0002 1

-0. 0045 -0. 004330 -0. 0002 2

•0.0066 -0.006495 -0.0001 3

-0.0086 -0.008660 +0.0001 4

0.0104 -0.010825 +0.0004 5

-0.0131 -0.012990 -0.0001 6

•0.0150 -0.015155 +0.0002 7

•0.0165 -0.017320 +0.0008 8

•0.0193 -0.019485 +0.0002 9

-0.0223 -0.021650 -0.0006 10

19
1100. 0000

10X0. 0000

1200. 0000

11X0.0000

1300. 0000

12X0. 0000

1400. 0000

13X0. 0000

1500.0000

14X0. 0000

1600.0000

15X0.0000

1700. 0000

16X0.0000

1800. 0000

17X0. 0000

1900. 0000

18X0.0000

2000. 0000

19X0. 0000

0. 0000

1100. 0075

1100. 0098

1200. 0062

1200. 0085

1300. 0076

1300. 0089

1400.0060

1400. 0082

1500. 0062

1500. 0086

1600. 0067

1600. 0092

1700.0050

1700. 0080

1800.0051

1800. 0078

1900.0062

1900. 0073

2000. 0060

2000. 0072

-0. 0023

•0. 0023

-0. 0013

-0. 0022

0. 0024

-0. 0025

-0. 0030

-0. 0027

0. 0011

-0. 0012

Table 4 cont.

-0. 0246

• 0. 0269

-0. 0282

•0.0304

-0.0328

-0. 0353

-0. 0383

-0. 0410

-0.0421

-0. 0433

•0. 023815

-0. 025980

-0. 028145

-0.030310

-0. 032475

0. 034640

-0. 036805

•0. 038970

0. 041135

-0.04330

-0. 0008

-0. 0009

0. 0001

-0. 0001

-0. 0003

-0. 0007

-0. 0015

•0. 0020

-0. 0010

0. 0000

11

12

13

14

15

16

17

18

19

20

'This is the

correction to X

+ 0. 0433 t20 = +0. 00216 < step on 10 ohmper-step dial

* By adjusting G 1 and G in Figure 3 so that the zero and 20 step readings are reversed for the two ratio sets it is possible to calibrate the URS by setting the

second URS on 0. 0000, 100.0000, 200.0000, etc. and reading the first URS at points such as 0.0080, 100.0073, X0. 0049, 200.0091, 1X0.0070, etc. Care

must be exercised to see that the correct signs (+ or -) are applied properly

in making the computations.

GPO 843-630

20