NBS Measurement Services:

Solid-State DC Voltage

Standard Calibrations

Bruce F. Field

U.S. Department of Commerce

National Bureau of Standards
Center for Basic Standards

The Center for Basic Standards develops and maintains the scientific competences and laboratory facilities nec- essary to preserve and continue to refine the base physical quantities upon which the Nation's measurement

system is constructed. The Center is responsible for the standards of voltage, current, resistance and

impedance, temperature, vacuum, leak rate, pressure, mass, length, time and frequency. The Center collaborates closely with the standardizing laboratories of other countries to ensure that measures used in international

trade are fully compatible. The Center also performs research at the frontiers of physics in order to improve

measurement capability and quantitative understanding of basic physical processes that underlie measurement

science.

Electricity Division

Maintains and improves the national standards of electrical measurement; conducts experiments to realize the

electrical units in terms of the mechanical units; develops stable electrical standards and improved methods for the dissemination of the units of electrical measurement; determines fundamental physical constants related to

electrical units; develops instrumentation for precise electrical measurements directly referenced to the national

standards; implements techniques for their use and puts them into practical applications; assists in applying scientific and technological development to measurement problems, especially in other areas of NBS research.

Temperature and Pressure Division

Maintains and improves the national standards of temperature and pressure; conducts research towards the development of new concepts for these standards; calibrates practical standards for the U.S. scientific and technical community in terms of the primary standards; develops methods and devices to assist user groups in the

assessment and enhancement of the accuracy of their measurements of temperature and pressure; prepares

and promulgates evaluations and descriptions of temperature and pressure measurement processes; coordi- nates these standards and measurement methods nationally and internationally; and determines the accuracy of

the national standards of temperature and pressure with respect to fundamental thermodynamic relations. Length and Mass Division

Develops and uses the competence necessary to implement a more accurate measurement system for length

and mass; applies research, utilizing the most advanced technology available, to the improvement of our present

standards arid devises new standards and new methods for their transfer. Time and Frequency Division

Maintains, develops and improves the national standards for the unit of time, the unit of frequency, and time

scales based on these standards; carries out research in areas of importance to the further fundamental improvement of frequency standards and their applications focusing on microwave and laser devices, atomic and

molecular resonances, and the measurement of fundamental physical phenomena and constants; adapts time

and frequency standard devices and concepts to special scientific and technological demands; develops time

and frequency measurement methods in the radiofrequency, microwave, infrared, and visible radiation regions;

coordinates the NBS time scales with international time scales and the time scales maintained by the United

States Naval Observatory; collaborates with national and international organizations in the development of improved methods for the measurement of time related quantities; operates time and frequency dissemination services, such as radio stations and broadcasts, for the purpose of traceability to the national standards of time and

frequency.

Quantum Physics Division

Engages in research in atomic and molecular physics at the forefront of the field, and performs basic, highly

accurate measurements and theoretical analyses that help establish a reliable foundation for scientific and technological measurement and data.

Quantum Metrology Division

Engages in forefront research in quantum metrology; contributes to new determinations of the fundamental

physical constants, and the extension and refinement of the electromagnetic scale and devises, where possible,

tests of basic symmetries and invariances.
NBS MEASUREMENT SERVICES:

Solid-State DC Voltage Standard Calibrations

Bruce F. Field

Center for Basic Standards

National Measurement Laboratory

National Bureau of Standards

Gaithersburg, MD 20899

January 1988

U.S. DEPARTMENT OF COMMERCE, C. William Verity, Secretary

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director
Library of Congress Catalog Card Number: 87-619904

National Bureau of Standards Special Publication 250-28

Natl. Bur. Stand. (U.S.), Spec. Publ. 250-28, 39 pages (Jan. 1988)

CODEN: XNBSAV

U.S. GOVERNMENT PRINTING OFFICE

WASHINGTON: 1988

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, DC 20402-9325
PREFACE

Calibrations and related measurement services of the National

Bureau of Standards provide the means for makers and users of

measuring tools to achieve levels of measurement accuracy that

are necessary to attain quality, productivity and competitiveness. These requirements include the highest levels of accuracy

that are possible on the basis of the most modern advances in

science and technology as well as the levels of accuracy that are

necessary in the routine production of goods and services. More

than 300 different calibrations, measurement assurance services

and special tests are available from NBS to support the

activities of public and private organizations. These services

enable users to link their measurements to the reference

standards maintained by NBS and, thereby, to the measurement

systems of other countries throughout the world. NBS Special

Publication 250, NBS Calibration Services Users Guide, describes

the calibrations and related services that are offered, provides

essential information for placing orders for these services and

identifies expert persons to be contacted for technical

assistance

.

NBS Special Publication 250 has recently been expanded by the

addition of supplementary publications that provide detailed

technical descriptions of specific NBS calibration services and,

together with the NBS Calibration Services Users Guide, they

constitute a topical series. Each technical supplement on a

particular calibration service includes:

o specifications for the service

o design philosophy and theory

o description of the NBS measurement system

o NBS operational procedures

o measurement uncertainty assessment

error budget

systematic error

random errors

o NBS internal quality control procedures
The new publications will present more technical detail than the

information that can be included in NBS Reports of Calibration.

In general they will also provide more detail than past

publications in the scientific and technical literature; such

publications, when they exist, tend to focus upon a particular

element of the topic and related elements may have been published

in different places at different times. The new series will

integrate the description of NBS calibration technologies in a

form that is more readily accessible and more useful to the

technical user.

The present publication, SP 250-28, NBS Measurement Services:

Solid-State DC Voltage Standard Calibrations, by Bruce F. Field,

is one of approximately 20 documents in the new series published

or in preparation by the Center for Basic Standards. It

describes calibration technology and procedures utilized in

connection with NBS Service Identification Numbers from 53110 to

53150 listed in the NBS Calibration Services Users Guide.

Inguiries concerning the contents of these documents may be

directed to the author or to one of the technical contact persons

identified in the Users Guide (SP-250).

Suggestions for improving the effectiveness and usefulness of the

new series would be very much appreciated at NBS. Likewise,

suggestions concerning the need for new calibration services,

special tests and measurement assurance programs are always

welcome

.

Joe Simmons, Acting Chief

Office of Physical Measurement Services

Helmut Hellwig, Acting Director

Center for Basic Standards

iv
Table of Contents

page

List of Figures vi

List of Tables vi

Abstract 1

1. Introduction 1

2. Description of Service 2

Types of Standards Accepted for Calibration 2

Shipment of Standards 2

Calibration Procedures 2

3. Calibration Apparatus and Measurement Approach 3

System Description 3

Zener Reference 4

Resistive Divider 4

Scanner 4

Digital Voltmeter 5

Working Group C 5

Measurement Process 5

Measurement Theory 6

4. Operational Procedures 7

Client Standards Handling 7

Daily Procedures 8

Calibration of Working Group C 8

Calibration of Solid-State Standards 8

Analysis of the Daily Data 9

5. Assignment of the Final Value 12

Uncertainty 13

Explanation of Table Items 13

6. Quality Control Procedures 15

Measurement System Verification 15

Client Standard Evaluation 17

7. Bibliography 18

Appendices

A Report of Calibration 19

B Measurement Software 22

V
List of Figures

Figure page

1. Block diagram of the dc voltage measuring system 3

2. Simplified wiring diagram of the measuring system set

up to compare a standard-under-test to the calibrated

resistive divider (Transfer Reference) 6

3a. Page 1 of a typical daily printout from the measurement

program READZEN 10

3b. Page 2 of a typical daily printout from the measurement

program READZEN 11

4. The three voltage outputs of a typical solid-state standard

sent to NBS for calibration 13

5. Ten volt output of a check standard as measured by

the system 16

List ofTables

page

Table I. Uncertainties in the Final Assigned Value 14

vi
NBS MEASUREMENT SERVICES:

SOLID-STATE DC VOLTAGE STANDARD CALIBRATIONS

Bruce F. Field

Abstract: This document describes the procedures used at NBS to calibrate

solid-state dc voltage standards in terms of the U.S. Legal Volt. The process

involves calibrating client standards at NBS approximately 10 times over a

two week period. The operational procedures and apparatus used to compare the client standards to the U.S. Legal Volt are discussed in detail.

L Introduction

DC voltage standards based on solid-state devices are now available with

stabilities approaching 1 ppm/year. Such voltage standards can be used to

maintain and disseminate (transfer) a laboratory unit of voltage with ac- curacies approaching those obtainable with saturated standard cells.

Presently-available voltage standards 'contain at least one (and sometimes

more) Zener diode reference devices which develop a voltage that is scaled

using internal resistive dividers and low-noise amplifiers to produce a

range of output voltages from 1 to 10 V. These standards typically have

their best accuracy at some voltage other than the 1.01-V level of standard

cells. NBS has developed a calibration service based on a specialized measuring system that automatically compares the output of any arbitrary voltage source, within the voltage range of one to ten volts, to a 1.018-V reference standard.

Solid-state voltage standards that are accepted for calibration must be complete instruments, must be powered by the ac line or internal batteries, and

must continuously produce one or more stable voltages. Such standards,

when sent to NBS, are allowed to stabilize, and then are directly compared

to NBS standards which are in turn calibrated in terms of the U.S. Legal

Volt. Typically ten comparisons are made (once each working day) over a

two week period. At the conclusion of the test a report is issued with a

statement of the values of the voltage outputs of the standard and the estimated uncertainties for the values while the standard was at NBS. No additional uncertainty is included for transportation effects, long term drifts

of the outputs, or measurement errors in the client's laboratory.

The calibration of solid-state standards is closely tied to, and dependent on,

the calibration of working groups of standard cells. The reader is thus re- ferred to reference 1, NBS SP250-24, NBS Measurement Services: Standard

Cell Calibrations, for a complete explanation of the apparatus and procedures used for the calibration of standard cells.

1
2. Description of Service

Types of Standards Accepted for Calibration

NBS offers a calibration service for solid-state voltage standards that are complete functioning standards which continuously produce the output

voltages to be measured. We do not accept bare reference devices or modules that require a stabilized power supply for operation. Also not ac- cepted are instruments with multiple outputs that must be manually

switched to one set of output terminals. Each output voltage to be measured

must be continuously available at a set of terminals dedicated to only that

output. A potentiometric (non-loading) method is used for the measurement of the standards so there is no requirement that the standard be capable of delivering current to the measuring system. Standards having output resistances as high as 1 kQ can be accurately measured.

Shipment of Standards

Solid-state standards may be carried to NBS by hand, or shipped to NBS by

common carrier; arrangements can be made with a local delivery service

for pickup and delivery to local airports. Standards may be shipped under

battery power to maintain temperature control and/or to power the reference device, or they may be shipped with all power turned off. If they are shipped with the power turned off we have observed that a short (2-3 days)

settling time is occasionally necessary before high-accuracy measurements

can be started.

Calibration Procedures

Most solid-state standards operate with the reference device in a temperature-controlled oven. The temperature of the oven is recorded when the

standard is first put on test (if the standard contains a temperature measuring device), but unless specially requested, the temperature of the oven

is not measured or recorded during the remainder of the test.

Routine calibrations of solid-state standards typically take 2 to 3 weeks to

complete. The voltages are read daily for a period of ten working days. After ten readings the data are reviewed by NBS personnel and if the stability

and day-to-day scatter of the outputs are within acceptable limits, a calibration report is issued. If the measured voltages fluctuated or drifted unduly

during the measurement period, the report will reflect these circumstances. In some cases additional measurements may be taken to confirm

the existence of a problem. If the standard exhibits an initial drift but later

becomes stable (indicating a transportation problem), additional measurements will be taken until at least ten stable readings have been obtained.

Only in rare circumstances would more than twenty measurements be

taken; if the standard has not stabilized by that time it is likely that it is de2
fective. Only the stable readings are used for the final values in the calibration report.

3. Calibration Apparatus and Measurement Approach

System Description

The system used at NBS to calibrate solid-state voltage standards is specially designed; it employs a potentiometric method to measure the standard which allows voltage measurements to be made without loading the

standard. (This system is also described in reference 2). The system is basically a scaling device for comparing arbitrary voltage standards to 1.018-V

standard cells. It will measure any dc voltage in the range from 0 to 10 V,

and has input channels for up to 54 unknown standards.

The system is also capable of making high-accuracy standard cell comparisons. Standard cells may be connected to the input channels of the scan- ner in place of (or in addition to) solid-state standards and these cells may

be intercompared with one another.

10-step divider

in a temperature

lagged enclosure

10.18 V

Zener

reference

dual floppy

disk drive

80-channel

low-thermal scanner 1

I

desktop

computer

test inputs

0 - 10 Volts

6-1/2 digit

digital

voltmeter

dot matrix

printer

Fig. 1. Block diagram of the dc voltage measuring system.

Figure 1 is a simplified block diagram of the measurement system. It includes a modified 10.18-V Zener reference, a 10-step resistive divider consisting of 10 nominally equal 250-Q. resistors, a low-thermal-emf crossbar

scanner, a 6-1/2 digit digital voltmeter (DVM), and a desktop computer.

The scanner, voltmeter, disk drive, and printer are connected to the computer with an IEEE-488 bus system. Not shown in the figure is an addition3
al connection to a 16 Mbyte hard disk which is common to several measuring systems in the laboratory and which is used for program and data storage. The floppy disk system is used for backup data storage in addition to

the main storage on the hard disk.

Also not shown in Fig. 1 is the group of four saturated standard cells used

as a reference for the system (Working Group C). All solid-state voltage

measurements are expressed as a numerical ratio times the mean emf of

these four cells. These cells in turn are calibrated daily in terms of the U.S.

Legal Volt using standard NBS procedures [1].

Zener Reference

The Zener reference is a commercial Zener standard that has been modified to produce 10.1817 V rather than the 10 V normally supplied. With 16

AWG wire connecting the standard and the resistive divider the voltage at

the divider is very close to 10.181 V, approximately ten times the voltage of a

saturated standard cell at 30 °C. Interactions between the Zener reference

and the other parts of the measuring system (notably the DVM) are

negligible even when the standard is plugged into the ac power lines. The

Zener reference is operated on ac power for all the measurements.

Resistive Divider

The resistive divider driven by the Zener reference consists of 10 nominally

equal, stable 250-Q wire-wound resistors. The 250 Q choice is a compromise between reducing the resistance to minimize the effects of leakage re- sistances and increasing the load current that must be supplied by the Zener reference. The resistors are selected for matched temperature coefficients; all the coefficients are within ±1 ppm/°C of one another. The resistors are mounted in a thick-walled aluminum box for temperature lagging.

During a measurement sequence the individual resistors typically change

value less than 0.03 ppm with respect to the total divider resistance.

Scanner

The scanner used to select the voltage inputs is a modified crossbar switch

identical to the VTP scanner described in reference 1. It has 80 2-wire input channels and uses latching relays to reduce the thermal emfs within

the switches. The scanner is wired so that any two of the 80 channels may

be selected by the computer and connected together in series opposition with

the difference voltage presented to the DVM. By selecting the two channels

in reverse order the voltage difference with opposite polarity is presented to

the DVM. The unresolved thermal emfs of the scanner have been periodically measured and are less than 0.015 uV per switch. Twenty of the

channels are used for the resistive divider, four channels are used for the

reference standard cells, and two channels are reserved for crossbar thermal tests, leaving 54 channels available for unknown standards.

4
Digital Voltmeter

A 6-V2 digit DVM with 0.1 uV resolution on the 0.1 -V range is used as the

system voltmeter. The voltmeter is programmed and read by the computer.

All voltages are measured by the DVM in both the forward and reverse direction to cancel offset voltages in the DVM. The 0.1 -V range is used when

measuring microvolt level voltages associated with standard cell differences, and an integration time of 9 s for each polarity yields a random measurement uncertainty of 0.03 uV (Is) for a single measurement. For all

measurements of solid-state standards, except at the 1.018-V level, the voltmeter is calibrated and used on the 1-V range.

Working Group C

Working Group C consists of four saturated standard cells housed in a

commercial temperature-regulated enclosure. The enclosure contains an

internal thermistor and Wheatstone bridge for measurement of the cell

temperatures with a resolution of 0.001 °C. The enclosure is powered from

a regulated 12 V dc power supply to minimize any effects of a changing ac

line voltage.

Measurement Process

The general measurement procedure is to 1) self-calibrate the system using

Working Group C, 2) compare the unknown solid-state standards to the

calibrated system, and 3) self-calibrate the system again to make sure no

significant drifts have occurred. The exact procedure is controlled by a

measurement procedure file (RUNFILE) which is executed by the computer. The measurement procedure file is created and modified daily by the

operator as necessary.

Figure 2 shows some critical parts of the measuring system in more detail.

The modified 10.18-V Zener reference is permanently connected to the

resistive divider; this combination (the Transfer Reference) is considered to

be a stable voltage source with ten series-connected 1.018 V outputs. The

Transfer Reference is calibrated by comparing the voltage drop across each

resistor to each cell in Working Group C, measuring the microvolt-level

difference voltages with the digital voltmeter. All four Working Group C

cells are compared to the ten Transfer Reference voltages for a total of 40

measurements which results in a redundant set of measurements. [1] By

referencing each output tap to the bottom tap, the Transfer Reference can be

used as a source of ten calibrated voltages from 0 V to 10.18 V in steps of

1.018 V. Then (as shown in Fig. 2) the output voltage developed across N of

the divider resistors is compared to the voltage of the unknown standardunder-test using the DVM. N is chosen to minimize the magnitude of the

DVM reading. All the solid-state standards to be measured are compared

in turn to the divider tap appropriate for that standard. Then the Transfer

Reference voltages are compared a second time to the standard cell voltages

after all the standards-under-test measurements have been completed. The

5
second "calibration" of the Transfer Reference reduces the error caused by

any drift in the Reference during the measurements. The low-thermal

scanner switch is used to connect the standard cells and solid-state

standards to the measurement system.

digital voltmeter

standard

under test

Fig. 2. Simplified wiring diagram of the measuring system set up to compare a standard-under-test to the calibrated resistive divider

(Transfer Reference). Not shown is the low-thermal crossbar se- lector switch.

Measurement Theory

With this system the digital voltmeter is used to read only a fraction of the

voltage of the standard-under-test which reduces the contribution of the

DVM uncertainty to the overall measurement uncertainty. When comparing the standard-under-test to the Transfer Reference (with voltage taps at

1.018 V increments) the maximum reading required of the DVM is 0.509 V.

Thus,

Vz-W1.018 U = C/DVM

where t/DVM is the DVM uncertainty expressed as a percentage of reading,

Vz is the voltage of the solid-state standard, N is the number of resistors,

and U is the final DVM uncertainty as a percentage of Vz. For a worst case

of VZ = 5.6 V, U = 0.09 C/dvm, and for VZ = 10 V, U = 0.02 £/dvm. Therefore,

if the DVM can be calibrated to an accuracy of 1 ppm the worst case error contribution is 0.09 ppm.

6
The linearity of the DVM is checked as necessary, but the gain of the one

volt range of the DVM is calibrated every time measurements are made by

measuring the 1.018 V developed across two of the resistors in the Transfer

Reference; typically resistors Ri and R2 are used (see Fig. 2.). This is done

to evaluate the effect of measuring voltages at ground and above ground.

Gain calibrations from several days can be combined to detect a systematic

bias in the measurements with respect to the particular resistor used.

Such measurement errors can be caused by excessive DVM leakage or bias

currents and will also affect the accuracy of the comparisons between the

Transfer Reference and the standard cell reference group.

Once the Transfer Reference has been calibrated in terms of the reference

standard cells the linearity of the DVM on the 10 V range can be checked by

directly measuring the ten voltages, 1.018 to 10.18 V, developed across the

resistors. Although not a thorough calibration of the DVM linearity, this

test can be used to detect significant changes in the linearity errors.

The DVM is used on the 0.1 -V range to improve the resolution of comparisons of 1.018-V solid-state standards to the Transfer Reference, and of the

comparisons of the Transfer Reference to the reference standard cells. The

gain error of the 0.1-V range is not calibrated daily by the system but, the

largest expected measurement difference for these comparisons is only

200 uV. Thus for an overall measurement error of 0.005 ppm (of 1.018 V)

the gain need only be known to 250 ppm. The gain of the 0.1-V range is

periodically checked using external standards to ensure that it is within

this limit.

The final value for each solid-state standard under test is computed by

correcting the measured difference between the standard and the Transfer

Reference for the gain of the DVM, and adding this to the value of the

appropriate tap of the Transfer Reference. The calibrated values of the

Transfer Reference are determined using a least-squares analysis of the

redundant measurements that compared the 10 outputs of the Reference to

the reference standard cell group. The mean of the "before" and "after"

calibrations is used.

4. Operational Procedures

Client Standards Handling

Standards shipped to NBS under power are hand carried from the Building

301 Receiving Room as soon as Electricity Division personnel are notified.

The temperature is checked by qualified laboratory staff (if the standard has

a temperature measuring device) and the standard is brought to the Volt

Facility Laboratory. All solid-state standards to be calibrated are connected

to the measuring system scanner at the time of their arrival and are left

undisturbed until the test is completed. When the standard is received it is

7
assigned a unique ID number, usually a subset of the serial number, and

this is entered into a log book along with the date and the condition of the

standard. Measurements are begun the day after the arrival of the unit.

After the test is completed, the client is notified and the standard is

repacked in its original shipping material and returned to the client.

Daily Procedures

Calibration of Working Group C

Working Group C is used as the reference for all solid-state measurements

in the Volt Facility Laboratory. Working Group C is compared daily to two

groups of primary cells (Primary Groups A and B) using the automated

standard cell comparison system VTP [1]. These measurements are made

early in the morning before measurements of solid-state standards are begun and the data is immediately reduced to determine the values of the cell

emfs of Working Group C. These values are used for the solid-state

standard measurements done that day.

Calibration of Solid-State Standards

The operator must set up a measurement procedure file (RUNFILE) that

has a list of all the standards to be calibrated. Program EDITA, a general

purpose text editor, is usually used to modify the previous day's file. The

exact format of the file is described in Appendix B, but in general the file

contains the measurement sequence for calibrating the Transfer Reference, a list of identification numbers of the standards-under-test, their

scanner circuit numbers, and the approximate voltage of each of the standards. The operator manually measures the temperature of Working

Group C before the measurements are begun and enters this into the file

along with the cell emf values (from the comparisons with the primary

groups). When the file is complete the measurement program (READZEN)

is started and measurements proceed automatically with the fully corrected

values of the solid-state standards printed out and saved on disk at the con- clusion of the measurements.

READZEN first checks the measurement system apparatus to make sure

everything is functionally working. This includes sending a clear-allchannels command to the scanner and checking to see if it responds, sending an initialization command to the DVM and checking it's response,

checking that the manual front/rear input switch on the DVM is set

properly, checking to see if the hard disk/file server is connected and turned

on (if it is to be used), checking that the printer is turned on and loaded with

paper, and finally, checking that a properly initialized data disk and a program disk containing a RUNFILE are in their respective disk drives. Multiple RUNFILEs may be included on the program disk for different sets of

measurements; the operator selects the desired one at the time the program

READZEN is run.

8
Measurements are started by setting the DVM to the 0.1 -V range and

shorting the DVM input to discharge the input capacitance. Then the ten

1.018-V outputs of the Transfer Reference are compared to the Working

Group C cell emfs using the redundant measurement design discussed in

section 3. Forty measurements are required and the data is saved on disk;

this process takes about 1/2 hour. Measurements of the unknown solidstate standards are preceded by gain calibrations of the DVM 1-V range.

DVM gain calibrations consist of directly measuring (in both forward and

reverse polarity) two of the Transfer Reference voltages (1.018 V) using the

1-V range of the DVM as discussed above.

The solid-state standard voltages are measured by comparing each one in

turn to the tap on the Transfer Reference that is closest in voltage to the

standard's voltage and measuring the difference with the DVM set on the

1-V range (in both forward and reverse polarity). Once all the unknown

standards have been measured the measurement sequence repeats starting

with the DVM calibrations. This measurement sequence (including the

DVM calibrations) is repeated three times and then a final (fourth) DVM

calibration is done. At the conclusion of these measurements, the Transfer

Reference is recalibrated against Working Group C. To summarize, the

measurement sequence is - calibrate the Transfer Reference using Group

C, calibrate the DVM, measure the unknown standards, calibrate the

DVM, measure the unknown standards, calibrate the DVM, measure the

unknown standards, calibrate the DVM, and finally calibrate the Transfer

Reference a second time.

Analysis of the Daily Data

At the conclusion of all the measurements for the day, the READZEN program automatically calculates the emfs of the standards-under-test and

produces a two page printout summarizing the calibration of the Transfer

Reference and listing the emfs of the solid-state standards. The emfs of the

standards (as well as intermediate results) are also saved on two disk files,

one on a floppy disk, and the other on the hard disk. These data are combined with other daily data sets for assigning the final emf values to the

standard.

Figures 3a and 3b are copies of the two pages of a typical daily printout produced by READZEN. At the top of page 1 , below the date and the name of

the RUNFILE that was used, is a summary of the measurements made,

and their starting time. In the example shown the Transfer Reference

(denoted Transfer Zener in Fig. 3a) was compared to Working Group C

(2800) at 8:03 and 10:07 am. The unknown solid-state standards were compared to the Transfer Reference three times: 8:35, 9:05, and 9:35 am. This

part of the log is printed as the measurements are being taken so the operator can track the operation of the program.

9
ZENER MEASUREMENT LOG FOR: 9 SEP 1987 [1.0] WEEK : 8737

RUNFILE: RUNFILEA: , 700,

1

08:03 DESIGN: (2800 - Zener ) Zener = 7970.159 SD = . 022

08:35 Zener measurement completed -- Set 1 09:05 Zener measurement completed -- Set 2 09:35 Zener measurement completed -- Set 3

10:07 DESIGN: (2800 - Zener ) Zener = 7970.155 SD = .017

RFFFRFNCF, PFT.T, STATISTICS

.017 Standard Deviations (uV)

.008 .006 Left-Right Components (uV)

30 .0135 30. 0135 Reference Cell Box Temps (C)

Reference Value at Difference Value at Mean

Cells Res 08 : 03:56 (uV) 10: 07 :02 Values

2801 1 8166 .558 < .003> 8166 .561 8166. 560

2802 1 8164 .409 < -0.000> 8164 .409 8164. 409

2803 1 8165 .602 . uu / ^ ft i ^ . £D 0U Qi7 8165 . 606

2804 1 8166 .147 < -0.010> 8166 . 137 8166. 142

Mean 8165 .679 < 0 .000> 8165 . 679 8165 . 679

Transfer Zener

Zl 7978 .379 < 0.000> 7978 .380 7978 . 379

Z2 7976 .446 < -. 021> 7976 .425 7976. 436

Z3 7932 .627 < -.006> 7932 .621 7932 . 624

Z4 7956 .967 < -. 004> 7956 .963 7956. 965

Z5 8052 .081 < -. 011> 8052 . 071 8052 . 076

Z6 7954 . 107 < -.015> 7954 .092 7954. 099

Z7 7956 .854 < -.006> 7956 .848 7956. 851

Z8 7966 .002 < -.006> 7965 .996 7965. 999

Z9 7958 .452 < .019> 7958 . 471 7958. 461

Z10 7969 . 671 < .015> 7969 . 686 7969. 678

Mean 7969 . 671 < -.004> 7970 155 7970 . 157

DVM CALIBRATION SUMMARY

Number of DVM calibrations = 8 Mean DVM error (ppm) = 2.0

Std. Dev. of mean error = .1

Fig. 3a. Page 1 of a typical daily printout from the measurement program READZEN.

10
page 2

ZENER CALIBRATION SUMMARY FOR: 9 Sep 1987

Zener ID Voltage Std. Dev.

(volts) (ppm)

188/1 9.99999654 .145

188/2 1.01813796 .220

C5950/1 9.99999937 .006

C6015/1 10.00000245 .002

5027/1 10.00002831 .004

5027/2 1.01799749 .011

5027/3 . 99999292 0 .000

5010N/1 10.00003443 0.000

5010N/2 1.01800020 .008

5010N/3 1.00000492 0 .000

5011/1 10.00002566 .031

5011/2 1 .01799755 .028

5011/3 1.00000773 .036

5018/1 9. 99999464 .004

5018/2 1.01799740 .007

5018/3 . 99997592 0.000

BFF1/1 1.01899358 .020

49105/1 9.99987041 .026

49105/2 1.01798278 .010

4*i Q1j -L nU DR / ^ I 3 0.000

49105/4 6.99989104 .052

49111/1 9.99990381 071

49111/2 1.01798826 .017

49111/32 . 99998952 . 042

49111/4 6. 99992458 .047

5035/1 10.00000727 .014

5035/2 1.01799416 .013

5035/3 .99999792 0.000

ALL CALCULATIONS COMPLETED AND SRM UPDATED

Fig. 3b. Page 2 of a typical daily printout from the measurement program READZEN.

11
The comparisons of the Transfer Reference to 2800 (Working Group C) are summarized under the heading REFERENCE CELL STATISTICS. The

standard deviations are the standard deviations of a single observation from

the redundant measurement design [3]. The emfs of the reference cells in

2800 and the 1.018-V outputs of the Transfer Reference (labelled Zl to Z10)

are expressed in microvolts reduced by 1.01 volts. The mean values from

the two calibrations are used as the values of the Transfer Reference for

calculating the values of the solid-state standards under test. The emf differences between two calibrations are calculated and printed in the Difference column to aid the operator in detecting abnormal changes.

At the bottom of Fig. 3a a short summary of the DVM calibrations appears.

In this example the DVM was compared to two different resistors before

and after each set of Zener measurements ([3 sets +I]x2) for a total of 8 calibrations. The mean DVM error on the 1-V range was found to be (2.0 ± 0.1)

ppm.

Fig. 3b, page 2 of the printout, lists the standards under test, their average

measured voltage, and the standard deviation of the measured voltage as determined from the repeated sets of measurements (3 in this case). The

repeated measurements are performed over a relatively short period of time

(1 to 2 hours) to reduce the variability of the final averaged values. The

complete set of measurements described above is considered to be a single

measurement of each standard consisting of the one averaged value for that

standard.

5. Assignment of the Final Value

Client standards are measured in terms of NBS working cells once a day

(using the above procedure) for at least ten working days. The measured

values are plotted and the data are reviewed by laboratory staff to determine

if the outputs exhibit sufficient stability for a report to be issued. If so, the

mean of the all the daily measurements is used as the final assigned value

for the output of the standard. In some rare cases standards have shown

an initial drift for the first few days after arriving at NBS. If this happens

additional measurements are taken so that at least ten stable

measurements are obtained, and the early unstable readings are not used

in determining the final value. Even if the standard behaves properly, the

exact number of measurements used for any calibration is not fixed; it

depends on when the standard was received, when the client requires that

it be returned, etc., but at least ten measurements are always used and

usually not more than fifteen.

Figure 4 shows the measured values of three outputs of a typical Zener

standard. The outputs are all derived from the same Zener reference

device; the 1.018-V and 1-V outputs are obtained from internal resistance

dividers connected to the 10-V output.

12
5007/1 .,

5007/2 .;

5007/3 .

Q O

O

o-o-o--O- u

u

-O-Or-O-

- -

Jo.2 ppm

•

m —

•

-x • I

1.01800012

1.00000345

0 2 4 6 8 10 12 14 16 18 Days

Fig. 4. The three voltage outputs of a typical solid-state standard sent to NBS for calibration. The outputs are plotted in ppm from their

mean voltage. The solid line is drawn at the mean value which is also labelled (in volts) on the right axis.

Uncertainty

The measuring system was designed principally to measure solid-state

standards in the range 5 - 10 V. Table I lists the sources of uncertainty in

the measuring system extrapolated to the worst case unknown voltage in

the 5 - 10 V range. The system may be used over the 1 - 5 V range but with

somewhat reduced accuracy when the unknown voltage is not near a car- dinal value (1.018, 2.036, 3.054,... V).

Explanation of Table Items

By far the most critical component of the system is the digital voltmeter.

The DVM gain is measured during the course of the Zener measurements

and the gain error of the 1-V range is calculated and applied as a correction

to the DVM readings. An allowance is included in the Table for the inaccuracy of this gain measurement.

The DVM linearity was initially checked on the 10-V range using a

calibrated, manual 7-dial Kelvin-Varley divider, and measurements on

similar DVMs indicate little or no change in the linearity with time. The

linearity error is typically a maximum of 0.7 ppm or less at half-scale input

and no correction to the data is made for it. Provision has been made for the

system to calibrate automatically the linearity of the DVM at 10 points on

the 10-V range by measuring the 10 voltages 1.018, 2.036, 10.18 V

although this is not done routinely.

13
TABLE I Uncertainties in the Final Assigned Value

Source of Uncertainty 1 std. dev. estimate

(ppm)

DVM gain uncertainty 0.020

DVM linearity uncertainty 0.062

DVM leakage/bias currents 0.023

Standard cell leakage currents 0.006

Scanner switch thermal emfs 0.013

Random uncertainty in calibrating

the Transfer Reference 0.007

Random uncertainty in calibrating

the client standard (within-day) 0.013

RSS subtotal 0.072

Uncertainty in value of Working Group C 0.040

Change in Working Group C during the day 0.047

Uncertainty of the value assigned to the

client standard

RSS Total 0.095

The DVM leakage and bias currents and standard cell leakage currents

were measured directly with an electrometer and their effects on the measurement calculated.

The crossbar scanner switch thermal emfs were measured with the DVM

by shorting the input leads and measuring the residual voltages.

The random uncertainties in calibrating the Transfer Reference and the

client standards are estimated from the pooled standard deviations of the

measurement designs. Although these uncertainties tend to be reduced by

averaging ten measurements of the client standard we prefer to include

them for completeness.

14
Two sets of DVM readings are taken for every voltage measurement (both

for standard cells and solid-state standards), one with the input voltage

source connected normally and a second with the voltage source polarity

reversed by the crossbar scanner. Subtracting the second reading from the

first and dividing by two yields a measurement free from any error due to a

non-zero DVM offset, thus no allowance has been included in the Table for

DVM offset errors. Ac effects observed in an earlier system were found to be negligible in this

system [2]. The ac effects on the Zener reference of the Transfer Reference

were estimated by monitoring changes in its voltage using a passive measurement circuit referenced to a standard cell while ac was introduced into

the system by connecting the DVM to the Transfer Reference taps.

The RSS subtotal represents the ratio error in comparing an arbitrary voltage source to a group of 1.018-V standard cells. For establishing an uncertainty for the client standards with respect to the U.S. Legal Volt, the

uncertainty of Working Group C must be added. The uncertainty of the

value of Working Group C computed from earlier measurements is

developed in reference 1 and will not be repeated here. An additional

uncertainty is included, however, for temperature instabilities and other

related emf variations in the present standard cell enclosure used for

Working Group C that cause the cell emfs to change during the day.

As far as is known, all systematic errors listed in Table I are independent

of each other. Therefore, they are combined in root- sum-square (RSS) fashion along with the random errors. The final reported uncertainty for a

client standard (Ureported) is three times the root-sum-square of the above

measurement uncertainty and the standard deviation of the mean of the ten

daily measurements (sm), i.e.,

Measurement System Verification

As discussed in Section 5 all major sources of error in the measuring system are evaluated during the measurements and corrections are applied to

the data as necessary. The printout from READZEN is reviewed daily by

laboratory personnel to verify that all the measurements are in statistical

control.

6. Quality Control Procedures

15
Other potential sources of error include uncompensated thermal emfs in

the crossbar switches and in the leads to the standards and circulating

ground currents within the measuring instrument and between the measuring instrument and the client standard. Several quality control procedures are periodically performed to estimate or eliminate these uncertainties.

Thermal emfs in the leads from the standards to the crossbar switch are evaluated regularly. The positive and negative leads are shorted together at

the end where they would normally connect to the standard and a redundant measurement design is done between the two sets of shorted leads us- ing the DVM as the detector. These thermal emf measurements are performed as standards leave the laboratory and leads become free. Experience has shown that the thermal emfs are usually small and fairly con- stant (approximately 15 nV or less).

Leakage resistance and leakage current measurements are made periodically between the different parts of the measuring system using an electrometer to ensure that they are at acceptable levels.

A 10-V standard that is not moved is measured every day as part of the

workload and serves as a check standard to monitor the long term stability

of the measurement system. The 10-V output of the standard is plotted ver- sus time in Fig. 5.

1.2

E

a

o_ >

o

E

o

H—c

o

B

>Q

1.0 -

0.8

((•(• - 0.6

• #

0.4 -

0.2 -

slope = 0.20 ppm/year

standard deviation = 0.067 ppm

0.0 J

1

1 I h

0 50 100 150 200

Time in days

Fig. 5. Ten volt output of a check standard as measured by the system.

16
Client Standard Evaluation

Tests for ac effects are done for each new type of standard received for test. Some models of standards produce a dc shift of the output voltage when an

ac source is connected to the output terminals. Experiments have shown

that for some standards the DVM can produce a significant shift [2]. These

experiments also showed that the effect was model dependent, not standard

dependent; all items of a particular model tested either had the problem or they did not. Any new, unfamiliar model received is tested for ac effects by

applying a small ac signal to the output while observing the dc voltage.

17
7. Bibliography

1. Field, B. F., "NBS Measurement Services: Standard Cell Calibrations," AtaZ. Bwr. Stand. (U.S.), Special Publ. 250-24, 52 pages (1987).

2. Field, B. F., "A Sub-PPM automated 1-10 Volt DC Measuring System," IEEE Trans. Instrum. Meas., Vol. IM-34, No. 2, pp. 327-330

(1985).

3. Eicke, W. G. and Cameron, J. M., "Designs for Intercomparing

Small Groups of Saturated Standard Cells," Natl. Bur. Stand. (U.S.),

Tech. Note 430, 19 pages (1967).

4. Eicke, W. G., "Comments on Zener diodes as voltage standards,"

Comite International des Poids et Mesures, Comite Consultatif

d'Electricite, 10th Session, p. 27 (1963).

5. Eicke, W. G., "Making precision voltage measurement on Zener

diodes," IEEE Trans., Paper CP 63-416 (1963).

6. Eicke, W. G., "The Operating Characteristics of Zener Reference

Diodes and their Measurement," ISA Transactions, Vol. 3, No. 2, pp.

93-99(1964).

7. Huntley, L., "The Fluke direct voltage maintenance program," Proc.

1984 Meas. Sci. Conf., pp. 147-151 (1984).

8. Koep, K. J., "The use of a solid state dc voltage transport standard to

transfer the dc volt in a regional standard cell MAP program," Proc.

1984 Meas. Sci. Conf., pp. 142-146 (1984).

9. Murray, W. and Dencher, P., "High-accuracy voltage transfer using

a modified commercial solid-state reference," J. Phys. E.: Sci. Instrum., Vol. 17, No. 5, pp. 354-356 (1984).

10. Spreadbury, P. J. and Everhart, T. E., "Ultra-stable portable voltage

sources," IEE Conf. Publ, Vol. 174, pp. 117-120.

18
Appendix A - Report of Calibration

UNITED STATES DEPARTMENT OF COMMERCE

National Buraiu af Standardr

G

u

Ith nrxbxjrq.Mziryliind 20833

REPORT OF CALIBRATION

Solid-State Voltage Standard

XXXXX Model YYYY DC Reference Standard

Serial No. 1111111

Submitted by

XXXXXXXX

XXXXXXXXXXXX xxxxxxxxxxxxxxx

This voltage standard was calibrated during the period June 1,

1987 to June 18, 1987, by comparing its output voltages with

those from a calibrated ten step divider driven by a stable ten

volt source. The difference voltages were measured using a calibrated digital voltmeter. This measuring system was standardized by saturated standard cells calibrated in terms of the

U.S. Legal Volt (volts-NBS) using standard NBS procedures. The

solid-state voltage standard was received with the IN CAL light

on and with a thermistor resistance of 3.91 kilohms . The unit

was plugged into the ac power line for all measurements.

The values given in the table below are the mean values of the

results of the individual calibrations summarized in the Appendix. The uncertainties given are three standard deviation

estimates equal to three times the root-sum-square of the estimated 0.095 ppm one standard deviation uncertainty in the measurement system (primarily systematic or type B) , and the one standard deviation random (type A) uncertainty of the mean of

the measurements on the individual voltage standard output.*

Nominal Output Measured Voltage Uncertainty Uncertainty

(volts-NBS) (ppm) (microvolts)

10 volts 10.0000450 0.29 2.86

1.018 volts 1.0180001 0.29 0.29

* The nomenclature 'type A" and 'type B' and the procedure used

to combine them to obtain the total uncertainty has been recom- mended by the International Bureau of Weights and Measures

(BIPM) Working Group on the Statement of Uncertainties, see Metrologia, vol. 17, No. 2, p. 73 (1981)

.

Test No. 521/XXXXXXXXX

19
Appendix A (cont'd) - Report of Calibration

Solid-State Voltage Standard

XXXXX Model YYYY DC Reference Standard

Serial No. 1111111

These uncertainty figures contain no allowance for the effects

of transport of the standard back to the user. Any valid uncertainty statement applying to the above values when the standard

is used other than in this laboratory must contain an additional

uncertainty component . Also not included in the above uncertainties is an allowance for long term drift of the output voltages of this standard. This must be determined from historical

data on a case by case basis.

For the Director

National Measurement Laboratory

Norman B. Belecki, Physicist

Electricity Division

Center for Basic Standards

Test No.: 521/XXXXXXXXX

Reference: XXXXXXXXXXXX

Date: September 8, 1987

20
Appendix A (cont'd) - Report of Calibration

Solid-State Voltage Standard

XXXXX Model YYYY DC Reference Standard

Serial No. 1111111

APPENDIX

(values in volts-NBS)

Date Time 10 volts 1.018 volts

06/01/87 10 :19 10 . 0000448 1 0180001

06/02/87 10 :58 10 .0000452 1 .0180002

06/03/87 09 52 10 .0000451 1 .0180001

06/04/87 12 16 10 .0000454 1 0180001

06/05/87 10 07 10 .0000447 1 0180001

06/08/87 10 27 10 .0000450 1 0180001

06/09/87 09 12 10 .0000450 1 0180001

06/10/87 09 34 10 .0000450 1 0180001

06/11/87 09 33 1C .0000451 1 0180002

06/12/87 11 20 10 .0000448 1 0180001

06/15/87 11 03 10 .0000453 1 0180001

06/16/87 11 03 10 .0000449 1 0180001

06/17/87 09 39 10 .0000448 1 0180001

06/18/87 09 38 10 .0000450 1 0180001

Mean (volts-NBS) 10.0000450 1.0180001

Standard Deviation

of the Mean (ppm) .006 .007

Number of readings 14 14

Test No.: 521/XXXXXXXXX

Reference: XXXXXXXXXXXX

Date: September 8, 1987

21
Appendix B - Measurement Software

The READZEN program is a generalized measurement program that runs

under the direction of an ASCII text file (RUNFILE) and is used to make all

the measurements required for solid-state standard calibrations. Program

EDITA is a general purpose editor program for creating and modifying

RUNFILEs. The following sections describe how to operate the programs

and the purpose of some of the important program variables. It is assumed

that the reader is familiar with the BASIC language environment (Rocky

Mountain BASIC) used with the Hewlett/Packard model 200/300 desktop

computers.*

Program READZEN

READZEN is the main measurement and calculation program. It has the

capability of doing standard cell intercomparisons, least-squares cell data

reduction, Zener-Transfer Reference comparisons, and Zener data re- duction. The operation of the program is controlled by an ASCII text file

named RUNFILExxx that is stored on the program disk. The xxx indicates

a 1 to 3 character suffix of numbers or letters. The suffix is used to differentiate between several Runfiles that may be stored on the same disk but

were created for different measurement procedures, i.e., normal workload

measurements, special tests, etc. At runtime the operator is prompted to

select one.

At the beginning of the program code of READZEN are comments on the

purpose of the program, array variable dimension statements, and a number of variables that define the various defaults of the program. These variables control things like the specification of the program disk and data disk

storage units, the 488 bus addresses of the measuring system instruments,

and other internal variables used to control calculations and data storage.

These variables are described in detail below. Program operations that may

be optionally changed by the user are generally controlled by these variables. No modification to the program code itself should be necessary.

Running the program

When the program is started an informational screen is shown giving the

name, version number, and purpose of the program, and all the scanner

channels are opened. If the scanner is not connected or turned on a message is printed and the program is stopped. Similarly, the printer is

checked and the disk drives are checked for the program and data disks. If

* Specific model names are used for clarification only and their use does not constitute an endorsement by NBS as the best available equipment. Other instruments may be as

suitable, or more suitable, for the applications described.

22
all is in order, the Runfile names on the program disk are displayed along

with an ID number, a 20 character identifying line, and the creation date of

the file. The operator must enter the ID number of one of the Runfiles.

Once this has been done the measurements proceed automatically with no

further operator control. At the conclusion of the measurements the re- sults are printed on the printer and saved on disk.

Program options

Variables to control the data storage and bus addresses of the measuring

instruments are contained in lines 1270 to 1641 of READZEN. A description

of some useful variables follows with their normal values shown in parentheses.

Observer$

Zsets

Dvmcorr

Dk$

Progdk$

Srm$

Dir$

is an identifying name for the system.

(Observer$="Micky")

is a counter for the number of times the

Zener references are compared to the

transfer reference. Under special circumstances more or fewer measurements

may be desired. (Zsets=3)

is a "gain" value that is used to multiply all

DVM readings taken on the 0.1 V scale. If

the 0.1 V scale is known to have a significant gain error this variable can be set to

compensate for it; e.g., if the gain error is

-100 ppm, the DVM reading is lower than

the actual value, set Dvmcorr = 1.00010.

Generally, the DVM is physically adjusted

if the gain is significantly in error. (Dvmcorr=l)

is the data disk specifier. (Dk$=":,700,0")

is the program disk specifier.

(Progdk$=":,700,l M

)

is the suffix for the SRM.

(Srm$=":REMOTE")

is a prefix directory name for the SRM.

This name will preface the data file name,

and Srm$ will be appended to the end to

form a complete filename.

(Dir$="ZENDATA/")

23
Zener_volt$ is the partial filename for result files.

Calculated standard cell results preface

Zener_volt$ with a "D" and Zener reference

results preface it with an "R". For both, the

2 digit year and a 2 digit week number

within the year are appended to the filename. Zener_volt$ should be 4 characters

or less, otherwise the filename will be too

long.

(Zener_volt$=,, ZEN")

Hcopy controls the printing of measurement data,

intermediate results, and final results to

the printer. If Hcopy=0 (normal default)

one line is printed on the printer each time

a measurement set (cells or Zeners) is completed. The printer output becomes a log of

the measurements; the actual measurements are not printed. The results of

the cell calculations and the final Zener re- sults are also printed. If Hcopy = 1 then log

printing is suppressed but cell and Zener

results are printed. If Hcopy = 2 all the

measurement data (cell-pair differences

and Zener differences) are printed to the

printer as well as the results. If Hcopy = -1

nothing is printed to the printer. (Hcopy =

0)

Srm controls whether data is saved on an SRM

in addition to the floppy disks. It should be

set to either Yes or No. If Yes, check to

make sure that Dir$ is correctly set to the

subdirectory desired. (Srm=Yes)

Saveflag controls saving of data on floppy disk and

the SRM. For Saveflag set equal to 1, all

measurement data files and result files are saved on disk. To save space on disk Saveflag may be set equal to 0 so only the cell and

Zener result files are saved. If Saveflag = —1

only the final Zener result files are saved.

(Saveflag = 1)

File use READZEN automatically creates as needed a number of data files. These

are all ASCII files with data stored as strings. Each line in the file is stored as one string and may contain an arbitrary number of items with the items

24
separated by at least one space. All files are read using a free-field format;

only the order of the data is important, not the position on any one line. File

names are generally composed of a unique prefix identifying the type of file

and a suffix based on the date. The date suffix is either of the form

YYMMDD or YYWW where YY is the year, MM is the month, DD is the

day, and WW is the number of the week in the year. WW starts with 1 for

the first week of the year and automatically changes on Sunday for the next

week. The exact style of the date suffix depends on whether the file contains

one day's data or one week's. The exact format of the data stored in the files

is discussed below.

The creation and use of the files is as follows: Intercomparisons between

the reference standard cells and the Transfer Reference produce 40 voltage

difference readings (4 cells by 10 resistors). These difference readings are

stored in an "S" file, i.e., SYYMMDD. All intercomparisons performed in

one day are stored one after the other in the file. READZEN performs a

least-squares calculation on the "S" data and saves the calculated cell values and "resistor-voltages" from the Transfer Reference in a "D" file, i.e.,

DZEN_YYWW. All standard cell and Transfer Reference voltages for the

entire week are stored in this file. The raw difference readings between the

Zener standards under test and the Transfer Reference are stored in "Z"

files, i.e., ZYYMMDD. After calculation the final Zener values are stored

in "R" files, i.e., RZEN_YYWW.

The files are initially created with a specified size and once created cannot

be increased beyond this size. They have generally been made large enough

to handle one or two sets of measurements per day. If the file size is

consistently too small the initial size specification may be increased. "S"

files are created in line 4780 of READZEN and are specified as 68 records of

256 characters/record. "D" files are created in line 11840 and are specified

with a length of 20 records of 256 characters/record. "Z" files are created in

line 8100 with a length of 20 records of 256 characters/record. "R" files are created in line 12980 with a length of 20 records of 256 characters/record.

Program EDITA

EDITA is a general purpose ASCII text file editor for viewing, printing,

and modifying the input and output files generated by READZEN. Prior to

running READZEN a RUNFILE is created using EDITA which details the

measurements to be made for that day. The specific RUNFILE format is

described in the next section on file formats.

Running the program.

When the program is started it asks for a file storage device. This is the

floppy disk or hard disk on which a previously created file is stored or a new

file is to be stored. Enter a standard H/P disk designator without any

quotes, e.g., :, 700,0. The program then prompts for a file name; enter the

25
name of an existing file or a name for the new file to be created. If the

program cannot find the file on the specified disk, it will ask if a new one

should be created. Enter Y or N as appropriate.

Most operations are controlled by the function keys at the top of the keyboard. They are:

£L PREV SCREEN

£2 NEXT SCREEN

f3 FIND CHRS

f4 2ND KEY LEVEL

&

m

f7

Scroll up to display the previous

screen of data.

Scroll down to display the next

screen of data.

Find a string of characters within

the text.

Change the key functions to the

alternate (2nd) set. APPEND ON (OFF) With append on additional lines

may be added to the file, with append off the original length is preserved.

GO TO LINE Go to the specified line number.

MOVE/DEL COPY Move, delete, or copy a block of

lines.

f8 END PROGRAM

2nd Key Level

Stop the program without saving

the file.

fl STORE TEXT

f2 MERGE FILES

f3 NEW STORAGE

f4 1ST KEY LEVEL

f5 NEW PRINTER

Save the file in the previously

specified name.

Append another file to the end of

the existing one in memory.

Specify a new disk designator

Return to the original key

functions

Specify the printer select code

(usually 701). Note: this must be

done before printing the first time.

26
fB PRINT TEXT Print the file on the printer select

code from f5.

f7 CAT Print a catalog of specified disk.

{8 END PROGRAM Stop the program without saving

the file.

In addition all the normal H/P program editing keys may be used — insert

line, delete line, insert character, delete character, and all the arrow keys.

File Formats

All files are ASCII files with data stored as strings. Each line in the file

comprises one string and may contain an arbitrary number of items. All

files are read using a free-field format; only the order of the data is important, not the position on any one line. Each item is separated from its

neighbor by one or more spaces (usually one). For convenience we have

adopted a convention of grouping several items on a line together to make it

easier for the operator to "read" the file. For each file an example of actual

data is given. Line numbers are shown for identification purposes only,

they are not included in the file. The exact number of lines is unimportant;

data may be stored all one line, or one item per line if desired.

Runfiles

Runfiles contain the measurement design data and commands to control

operation of the READZEN program. The exact format will vary depending

on the measurements required but will follow the general pattern of making cell measurements between the reference cell group and the Transfer

Reference (DESIGN), measuring the unknown Zeners (ZMEAS), repeating

the cell measurements (REDESIGN), and calculating the final results

(ZCALC).

Note: The ten resistor voltages of the transfer reference are considered to be equivalent to cells for the purposes of the measurement programs and files. The ten voltages are assigned a

group name of 'Zener' and individual IDs of Zl, Z2, Z3,...,Z10.

Sample data: RUNFILEA

1 2.11 38921 114E11 Zener_workload

2 ! 4x10 design, 1600 vs transfer Zener

3 DESIGN

4 2 1600 4 Zener 10

5 4010 40 8165.455 0.034

27
6 11110000000000

7 1601 1602 1603 1604 Z1 Z2 Z3 Z4 Z5 Z6 Z7 Z8 Z9 Z1

0

8 29 30 31 32 19 20 21 22 23 24 25 26 27 28

9 1517191111132628210212214

10 353739311 3134648410412414

11 13411 49474541431231038363

12 13211 2927252141 121 101 81 61

13 30 30.011 30 30

14 ENDDATA

15 ! 16 ZMEAS

17 5018-1 10 8

18 5018-2 1.018 7

19 5018-3 1 12

20 ENDDATA

21 ! 22 REDESIGN

23 ZCALC

Description:

1 time and date in seconds (standard H/P time as re- turned by TIMEDATE), identifying label (up to 30

characters with no spaces) displayed by READZEN to

identify different Runfiles

2 any line preceded by an exclamation point (!) is ignored

by the program; this is a comment for the operator

3 command to the program to expect DESIGN data for

intercomparing cell groups to follow

4 number of cell groups, group 1 name, number of cells in

group 1, group 2 name, number of cells in group 2

5 a meaningless design number - not used but something

must be there; total number of observations, mean of

reference group, accepted standard deviation (the

mean of the reference group is expressed in microvolts reduced by 1.01 volts, i.e., 8165.455 J 1.018165455

volts)

6 restraint - one number for each cell in each group, 1

identifies the cell as included in the mean of the reference group, 0 the cell is not included

7 cell IDs - group 1 first, group 2 next

8 cell circuit number corresponding to above cell IDs

9-12 measurement design - cells in line 7 are assigned position numbers 1 through N (14 here). Pairs of numbers indicate difference measurements to be made,

i.e., 1-5 indicates to measure cell "1" (1601) minus

cell "5" (Zl). The number of pairs of numbers must

agree with the number of observations specified on

line 5.

28
13 nominal temperature of group 1, actual temperature of

group 1, nominal temperature of group 2, actual

temperature of group 2

14 ENDDATA command to indicate end of DESIGN data set

15 comment

16 ZMEAS command to start accepting Zener measurement data for unknown Zeners to be measured

17-19 Zener ID, nominal voltage (volts), scanner channel

number

20 ENDDATA command to indicate end of ZMEAS data set

21 comment

22 REDESIGN command, repeat previous cell

intercomparison specified by the DESIGN data

23 ZCALC command, calculate standard cell measurement designs and final Zener voltages. ZCALC re- quires that a DESIGN measurement on the transfer

reference be done before and after the ZMEAS measurements.

"S" files

"S" files contain the raw standard cell intercomparison data; only one set is

shown here. A file may contain additional sets taken on the same day. The

similarity between lines 4 through 12 of the Runfile with lines 2 through 10

of the "S" file is no coincidence!

Sample data: S860730

1 07 30 86 13:54:46 Micky

2 2 1600 4 Zener 10

3 40 8165.455 0.034

4 11110000000000

5 1601 1602 1603 1604 Z1 Z2 Z3 Z4 Z5 Z6 Z7 Z8 Z9 Z10

6 1 5 1 7 1 9 1 11 1 13 2 6 2 8 2 10 2 12 2 14

7 3537393 11 3 13 46484 10 4 12 4 14

8 13 4 11 4947454 14 3 12 3 10 38363

9 13 2 11 2 9 2 7 2 5 2 14 1 12 1 10 1 8 1 6 1 10 30 30.011 30 30

11 157.742 199.267 87.808 173.733 173.267 149.658

12 169.544 170.258 159.317 157.133 154.942 196.600

13 84.825 170.825 170.467 151.842 171.758 172.492

14 161.475 159.417 -169.067 -169.608 -83.544 -195.217

15 -153.542 -160.475 -162.833 -173.717 -173.000 -153.217

16 -166.683 -167.267 -81.258 -192.875 -151.333 -163.433

17 -165.633 -176.592 -176.000 -156.083

29
Description:

1 month, day, year, time, observer (system) name

2 number of cell groups, group 1 name, number of cells in

group 1 , group 2 name, number of cells in group 2

3 total number of observations, mean of reference group,

accepted standard deviation

4 restraint - one number for each cell in each group; 1

identifies the cell as included in the mean of the reference group, 0 the cell is not included

5 cell IDs - group 1 first, group 2 next

6-9 measurement design - cells in line 5 are assigned position numbers 1 through N (14 here) pairs of numbers

indicate difference measurements to be made, i.e.,

1-5 indicates to measure cell "1" (1601) minus cell

"5" (Zl). The number of pairs of numbers must

agree with the number specified on line 3.

10 nominal temperature of group 1 , actual temperature of

group 1, nominal temperature of group 2, actual

temperature of group 2

11-17 actual measured cell differences in microvolts

"D" files

"D" files contain the results of the standard cell intercomparison data; only

one set is shown here. A file may contain additional sets of data taken

within the same week.

Sample data: DZEN_8630

1 860730 14 40 26 0.08247 0.0133 NBS-Z 12:15:11 2 -0.596

2 1600 4 30 30.011 -0.6226

3 1601 1602 1603 1604

4 Zener 10 30 30 0

5 Z1 Z2 Z3 Z4 Z5 Z6 Z7 Z8 Z9 Z10

6 1 1601 8103.3617 1 1602 8096.9666 1 1603 8100.4951 1 1604 8099.1765

7 0 Z1 7945.575 0 Z2 7947.2625 0 Z3 7904.0645 0 Z4

7927.444

8 0 Z5 8015.7105 0 Z6 7926.848 0 Z7 7929.7768 0 Z8

7937.7688

9 0 Z9 7930.194 0 Z10 7939.9563

Description:

YYMMDD, total number of cells, number of observations, degrees of freedom, standard deviation, left30
right component, measurement system ID, time,

number of cell groups, average DVM offset

2 group 1 name, number of cells in group 1 , nominal

temperature, actual temperature, temperature cor- rection

3 group 1 cell IDs

4 group 2 name, number of cells in group 2, nominal

temperature, actual temperature, temperature cor- rection

5 group 2 cell IDs

6-9 restraint flag, cell ID, cell emf in \xV reduced by 1.01 V.

The restraint flag=l if the cell is included in the

reference group mean, =0 if not. The restraint, ID,

and emf triplet is repeated for each cell measured.

"Z" files

"Z" files contain the raw Zener measurements taken between the unknown

Zener references and the transfer Zener; only one set is shown here. A file

may contain additional sets taken on the same day.

Sample data: Z860730

1 860730 15:2847 3 2 3

2 DVM 1 1.0181223E+6

3 DVM 2 1.0181238E+6

4 5018-1 10 -179729.8

5 5018-2 1 21.9

6 5018-3 1 -17988.95

7 DVM 1 1.01812225E+6

8 DVM 2 1.01812395E+6

9 5018-1 10 -179730.15

10 5018-2 1 22.05

11 5018-3 1 -17988.8

12 DVM 1 1.0181223E+6

13 DVM 2 1.0181236E+6

14 5018-1 10 -179729.9

15 5018-2 1 21.7

16 5018-3 1 -17988.95

17 DVM 1 1.01812225E+6

18 DVM 2 1.0181237E+6

Description:

1 YYMMDD, time, number of repeated sets of Zener measurements, number of DVM calibrations per Zener

measurement, number of Zeners measured

31
2 - 3 string "DVM" to indicate a direct DVM reading of one of

the resistors of the resistive divider, the number of

the resistor measured (1-10), the reading in uV

4 - 6 Zener ID, tap number of resistive divider to which Zener

was compared (0-10), measured difference in

7 - 18 repeated measurements, stored the same as lines 2 - 6

"R" files

"R" files contain the final calculated results of the Zener data; only one set

is shown here. A file may contain additional sets of data taken within the

same week.

Sample data: RZEN_8632

1 860730 12:53:36 3 3

2 4 8131.1000 1601 1602 1603 1604

3 5018-1 10.0000047045 0.00333333176584

4 5018-2 1.01799810104 0.142727802049

5 5018-3 0.999989513271 0

Description:

1 YYMMDD, time, number of Zeners calibrated, number

of repeated measurements (Zsets)

2 number of reference cells, mean emf of reference cells,

reference cell IDs

3 - 5 Zener ID, calculated voltage (volts), standard deviation of

the mean (ppm) calculated from the repeated measurement sets

System Software Requirements

The measurement software will run satisfactorily on all H/P Basic systems

3.0 and higher. The following BIN files are required for proper operation.

CLOCK CS80

KBD MAT

ERR HPIB

For use with an SRM the following additional BIN files are needed.

SRM DCOMM

32
NBS-114A (rev. 2-80) U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET (See instructions)

1. PUBLICATION OR

REPORT NO.

NBS/SP-250/28

2. Performing Organ. Report No 3. Publication Date January 19 8 8

4. TITLE AND SUBTITLE

NBS Measurement Services: Solid-State DC Voltage Standard Calibrations

5. AUTHOR(S)

Bruce F. Field

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

NATIONAL BUREAU OF STANDARDS

U.S. DEPARTMENT OF COMMERCE

GAITHERSBURG, MD 20899

7. Contract/Grant No.

8. Type of Report & Period Covered

Final

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

Same as item 6

.

10. SUPPLEMENTARY NOTES

Library of Congress Catalog Card Number 87-619904

I ] Document describes a computer program; SF-185, FIPS Software Summary, is attached.

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

bibliography or literature survey, mention it here) This document describes the procedures used at NBS to calibrate solid-state

dc voltage standards in terms of the U.S. Legal Volt. The process involves

calibrating client standards at NBS approximately 10 times over a two week

period. The operational procedures and apparatus used to compare the client

standards to the U.S. Legal Volt are discussed in detail.

12. KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolon s)

calibration services; dc volt; solid-state standards; voltage standards; Zener diodes

13. AVAILABILITY

j^^J Unlimited

| | For Official Distribution. Do Not Release to NTIS

jRF] 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

39

15. Price

USCOMM-DC 6043-P80

*U.S. Government Printing Office : 1988 - 201-597/72497

THE SP 250 SERIES ON NBS MEASUREMENT SERVICES*

SP 250-1 Spectral Radiance Calibrations 003-003-02792 $3.50

SP 250-2 Far Ultraviolet Detector Standards 003-003-0281 0-0 $4.25

SP 250-3 Radiometric Standards In the Vacuum

Ultraviolet 003-003-02806-1 $6.50

SP 250-4 Frtcke Dosimetry in High-Energy Electron Beams

003-003-02816-9 $2.75

SP 250-5 Alpha-Particle Calibrations

SP 250-6 Regular Spectral Transmittance 003-003-02805-3 $3.25

SP 250-7 Radiance Temperature Calibrations 003-003-02827-4 $2.25

SP 250-6 Spectral Reflectance 003-003-02812-6 $7.00

SP 250-9 Calibration of Beta-Particle-Emitting

Ophthalmic Applicators

003-003-02817-7 $2.00

SP 250-15 Photometric Calibrations

SP 250-16 Calibration of X-Ray and Gamma-Ray

Measuring Instruments

SP 250-17 The NBS Photodetector Spectral Response

Calibration Transfer Program

SP 250-18 Neutron Source Strength Calibrations

SP 250-19 Calibration of Gamma-Ray-Emitting

Brachytherapy Sources

SP 250-20 Spectral Irradiance Calibrations 003-003-02829-1 $5.50

SP 250-21 Calibration of Beta- Particle Radiation Instrumentation

SP 250-22 Platinum Resistance Thermometer

Calibrations 003-003-02831-2 $17.00

SP 250-23 Uquid-in-Glass Thermometer

Calibration Service

SP 250-10 Radioactivity Calibrations with the "4ir" Gamma Ionization Chamber, and Other

Radioactivity Calibration Capabilities

003-003-02824-0 $2.25

SP 250-1 1 Dosimetry for High-Dose Applications

SP 250-12 Neutron Personnel Dosimetry

003-003-02811-8 $2.50

SP 250-13 Activation Foil Irradiation with Californium

Fission Sources

SP 250-14 Activation Foil Irradiation by Reactor Cavity

Fission Sources

SP 250-24 Standard Cell Calibrations 003-003-02825-8 $2.75

SP 250-25 Calibration Service for Inductive Voltage Dividers

SP 250-26 Phase Angle Calibrations

SP 250-27 AC-DC Difference Calibrations

SP 250-28 Solid-State DC Voltage Standard Calibrations

SP 250-29 Traceable Frequency Calibrations

SP 250-30 GOES Satellite Time Code Dissemination:

Description and Operation

* Those entries containing a stock number (003-003 ) and price can be purchased from the Superintendent of Documents, U.S. Government Printing Office, Washington, DC 20402. GPO will accept checks, money orders, VISA, and Mastercharge. For more information, or to place an order, call (202)783-3238. Be sure to use the stock number In all orders. Titles without stock numbers are in preparation.
U.S. Department of Commerce

National Bureau of Standards

Gaithersburg, MD 20899

Official Business

Penalty for Private Use $300