S w % \

^a

*TN NBS TECHNICAL NOTE 1024
NATIONAL BUREAU OF STANDARDS

The National Bureau of Standards' was established by an act of Congress on March 3, 1901

The Bureau's overall goal is to strengthen and advance the Nation's science and technology

and facilitate their effective application for public benefit. To this end, the Bureau conducts

research and provides: (1) a basis for the Nation's physical measurement system, (2) scientific and technological services for industry and government, (3) a technical basis for equity in trade, and (4) technical services to promote public safety. The Bureau's technical work is per- formed by the National Measurement Laboratory, the National Engineering Laboratory, and

the Institute for Computer Sciences and Technology.

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physical and chemical and materials measurement; coordinates the system with measurement

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agencies; develops, produces, and distributes Standard Reference Materials; and provides

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guidelines, and managing Federal participation in ADP voluntary standardization activities; provides scientific and technological advisory services and assistance to Federal agencies; and

provides the technical foundation for computer-related policies of the Federal Government.

The Institute consists of the following centers:

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'Headquarters and Laboratories at Gaithersburg, MD, unless otherwise noted; mailing address Washington, DC 20234.

: Some divisions within the center are located at Boulder, CO 80303.

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402
EVALUATION OF THREE-TERMINAL AND

FOUR-TERMINAL PAIR CAPACITORS

AT HIGH FREQUENCIES %TT^*%*

OCT 2 4 1980

QCIOQ

- VU51SZ

R.N. Jones /q fo

Electromagnetic Fields Division

National Engineering Laboratory

National Bureau of Standards

Boulder, Colorado 80303

4? Vj/ \

^^y "*tM Of '

U.S. DEPARTMENT OF COMMERCE, Philip M. Klutznick, Secretary

Luther H. Hodges, Jr., Deputy Secretary

Jordan J. Baruch, Assistant Secretary for Productivity, Technology and Innovation

U/. NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

Issued September 1980
NATIONAL BUREAU OF STANDARDS TECHNICAL NOTE 1024

Nat. Bur. Stand. (U.S.), Tech. Note 1024, 20 pages (Sept. 1980)

CODEN: NBTNAE

U.S. GOVERNMENT PRINTING OFFICE

WASHINGTON: 1980

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

Price $1.50 (Add 25 percent additional for other than U.S. mailing)
CONTENTS

Page

List of Figures and Tables iii

1. Introduction 1

2. Background 1

3. Determination of High Frequency Effective Capacitance 2

4. The Resonance Method for Three-Terminal Capacitors 3

5. The Resonance Method for Four-Terminal Pair Capacitors 6

6

.

The Shorti ng El ements 9

7. Sources of Error 11

8

.

Summary 13

9. References 15

LIST OF FIGURES AND TABLES

Page

Figure 1. Simplified high frequency equivalent circuit for a capacitor 3

Figure 2. Circuit arrangement for measuring the residual series inductance

of a three-terminal capacitor 4

Figure 3. The capacitances comprising the total resonating capacitance, Cj 5

Figure 4. A block diagram showing a typical arrangement for measuring the resonant

frequency of a short circuited capacitor 6

Figure 5. Photograph of instrumentation setup for determining capacitor

sel f-resonance 7

Figure 6. The four-terminal pair concept 8

Figure 7. Circuit model for four-terminal pair capacitor 8

Figure 8. From top to bottom: One 4TP capacitor and two three-terminal capacitors

fi tted wi th shorti ng el ements 10

Figure 9. Various types of shorting elements for use with three-terminal and fourterminal pair capacitors 12

Figure 10. Percent correction to C

Q versus frequency for a lOOOpF capacitor having a residual series inductance of 0.050 microhenry 14

i n

Evaluation of Three-Terminal and Four-Terminal

Pair Capacitors at High Frequencies

R. N. Jones

Electromagnetic Fields Division

National Engineering Laboratory

National Bureau of Standards

Boulder, Colorado 80303

The low frequency (1 kHz) capacitance values of three-terminal

and four-terminal pair air dielectric capacitors can be extrapolated

to higher frequencies if the residual series inductance is known. A resonance method for evaluating the residual series inductance of

these capacitor types, together with the extrapolation procedure, is described. For the region where the product of capacitance in

farads and frequency in hertz is 10" 2 or less, uncertainties of one percent or less may be obtained.

Key words: Calibration; capacitance; immittance standards;

inductance; four-terminal pair capacitance; residual series

inductance; three-terminal capacitance; resonance techniques.

1. Introduction

Manufacturers of capacitance standards usually provide the buyer with the capacitance

value at 1 kHz. However, many such standards are useful for calibrating immittance

measuring instruments well into the high frequency range, provided that appropriate

allowance is made for changes resulting from residual series inductance in the capacitor.

The techniques described are used at the National Bureau of Standards to establish standards

for high frequency use. The procedure was previously described [1] for use with two- terminal capacitors fitted with unshielded connectors. It is described again here, but with

modifications for use with three- terminal and four-terminal pair (4TP) standards. The

method is useful for both fixed and variable air capacitors.

2. Background

A resonance technique for evaluating residual series inductance, together with an accompanying procedure for mathematically extrapolating low frequency (1 kHz) capacitance

values to higher frequencies is described in reference [1]. This procedure was specifically

intended for use with two-terminal air-dielectric capacitors equipped with unshielded

connectors of the binding post or banana plug type. In the ensuing years, three-terminal

1 Figures in brackets indicate the literature references at the end of this paper.
capacitance measuring instruments have appeared which cover the range from 0.001 to 1000 pF

at frequencies up to 1 MHz and capacitance standards have been established at NBS to provide

supporting calibration services. More recently, immittance measuring instruments have been

introduced which utilize an active measurement principle [2] and a four-terminal pair

arrangement for connecting the device under test to the instrument. These instruments,

often called LCR meters, 2 operate at frequencies well above 1 MHz and utilize 4TP capacitors

as calibration standards.

To establish the high frequency values for both the three-terminal capacitance

standards as well as the 4TP capacitance standards, NBS has again employed resonance methods

combined with a mathematical extrapolation similar to that used for two-terminal types.

Thus the procedures to be described are essentially only adaptions in the procedure in

reference [1] modified for use with three-terminal capacitors and 4TP capacitors.

It is to be emphasized that the procedures described in this technical note are applicable only to air dielectric capacitors or capacitors having dielectrics whosp

dielectric coeffic.: .... does not change with frequency. Due to interfacial polarization, the

dielectric coefficient of some materials, such as silvered mica, decreases as frequency

increases. This occurs in the audio region and above. Hence, a simple linear extrapolation

from 1 kHz based solely on the residual series inductance, does not yield an accurate

result. A second limitation to this procedure is that it should not be employed at frequencies approaching self-resonance of the capacitor where the reactance of the residual

series inductance approaches that of the capacitance. In this region the effective

capacitance increases rapidly and approaches infinity, and the uncertainty becomes

unacceptably large due to inaccuracies in the residual series inductance as determined by

the resonance technique.

3. Determination of High Frequency Effective Capacitance

The procedure for using the residual series inductance of a capacitor to calculate its

effective capacitance value at higher frequencies is basically the same for two-terminal,

three-terminal and 4TP capacitors. It is not an exact method because it includes a number

of approximations and assumptions, but if its use is confined to a reasonable range of

frequencies and capacitance values, it will yield accuracies that are adequate to provide

excellent calibration support for instruments in the 0.1 to 1.0 percent uncertainty range.

Because most of the capacitors used as high frequency immittance standards are of comparable

physical size and configuration, they are usually found to have residual series inductances

in the range of 10 to 50 nanohenries. This being true, it may be assumed that as long as the product of the nominal (1 kHz) value of capacitance in farads and the frequency in hertz

is equal to or less than 10 , the uncertainty of the extrapolated value of effective

p Inductance, capacitance and resistance
capacitance will be one percent or less. This criteria roughly defines the frequency and

capacitance ranges where the technique is used by NBS. Briefly, the extrapolation principle

is illustrated by the following diagram and derivation:

o-nnjiTH

Figure 1. Simplified high frequency equivalent circuit for a capacitor

For any two-terminal, three-terminal or 4TP capacitor, the effective capacitance, Ce

, at any

frequency above 1 kHz is obtained by equating the reactances:

1 =l - <oL idC u)C r e o

and

C e

= T ^w (1)

where Ce is the capacitance in farads, l_ r is the residual series inductance in henries, C Q

is the low frequency (1 kHz) value of the capacitance in farads, and, u, is the angular

frequency in radians per second. This simple derivation assumes that any contribution from

series resistance or shunt conductance in the equivalent circuit of figure 1 is negligible,

which is true of high quality capacitors having dissipation factors of 10~° or less.

4. The Resonance Method for Three-Terminal Capacitors

The diagram in figure 2 is a representation of the circuit elements which are of

significance in the determination of residual series inductance, L r. The main capacitance

element, represented by C , is enclosed in a conducting shield. The two coaxial connectors,

"H" and "L", provide the means of connection to an external circuit. C

H and CL are the

stray capacitances from each side of C Q

to ground. The residual inductance, l_ r

, is a property of the internal leads to the capacitance element and, to some extent, the

capacitance structure. To indicate the distributed nature of L

r

, it is represented as two equal halves, L

r /2, shown on each side of CQ

. It is this residual inductance that causes a

3
significant change in the effective value of the capacitance standard as the frequency is increased. To evaluate l_ r

, The capacitor is fitted with a shorting element having a selfinductance L , and is shown connected between the center conductors of "H" and "L", but not contacting the outer conductors of the two coaxial connectors. A grid-dip meter is shown

coupled inductively to L

$

. By varying the frequency of the grid-dip meter oscillator, a sharp dip will be observed when the series resonant frequency of the circuit is reached.

This circuit includes the capacitances CQ

, C

H and CL

, plus the inductances L r and l_ s

.

Assuming that the mutual inductance between the shorting element, L

s

, and the grid-dip

meter coil is negligible, the series resonance relationship may be written as:

X

L = XC

or

a) (L + L ) r r s \^J

(2!

Grid Dip Meter

Antenna

Frequency Sensing Coil

Figure 2. Circuit arrangement for measuring the residual series inductance of a threeterminal capacitor.
where u> is the angular resonant frequency in radians per second, (L r + L ) is the sum of

the inductances in henries, and the total circuit capacitance, Cj, is in farads. The

circuit configuration of figure 3 shows the arrangement of the capacitance elements, C , C

H and Ci which comprise Cj. The value of Cj is given by the expression

C C C + ?

L

„ (3)

'H

The value of C is usually given to satisfactory accuracy by the manufacturer or may be

determined by a three-terminal capacitance measurement at 1 kHz. The values of Cm and C

L are obtained by two-terminal capacitance measurements at 1 kHz. Placing a coaxial short on terminal "L" and measuring the two-terminal capacitance of "H" (see figure 2) yields the sum of CQ

and C

H

. Then, by similarly shorting terminal "H" and measuring the two-terminal

capacitance at "L", the sum of CQ and C

L is obtained. With C

Q previously determined, the

values of C

H and C^ may be found and the value of Cj calculated by eq (3). Rearranging eq

(2), the residual series inductance, L r, is given by:

(4)

o 1

1

o — o

CH •= C L

Figure 3. The capacitances comprising the total resonating capacitance, CT

.
Figure 4 is a block diagram showing an arrangement of instrumentation that has proven

convenient for measuring the self-resonant frequency of the short circuited capacitor. The

resonant frequency may be read directly from the grid-dip meter to about three significant

figures, but the use of an rf amplifier and a frequency counter yields better resolution,

thereby allowing a much better determination of the precision of the resonant frequency. A typical measurement setup is illustrated in the photograph of figure 5.

Grid Dip Meter ^2h

O^

Coaxial

Lead

r^A X

Capacitor

Antenna

or Sensing Coil

RF

Amplifier

10-500 MHz

J7

Frequency

Counter

Figure 4. A block diagram showing a typical arrangement for measuring the resonant

frequency of a short circuited capacitor.

5. The Resonance Method for Four-Terminal Pair Capacitors

Although the same basic resonance approach is used for 4TP capacitors as that just

described for three-terminal capacitors, there are some necessary modifications which arise

because of differences in capacitor construction. Also, the 4TP measurement principle is

different from the three-terminal method. A complete explanation of 4TP LCR meter operation

is provided in ref [2], but the principle will be briefly discussed here in order that the

modifications referred to above may be better understood. The diagram of figure 6 illustrates the 4TP measurement principle and figure 7 is a diagram of a 4TP capacitance

standard of the type used to calibrate 4TP immittance (LCR) meters. In figure 6, a current

is passed through the device under test (DUT) and also through a reference standard

resistor, R$. The complex impedance of the DUT is then determined by taking the product of

the complex ratio of the voltages V

x and Vs

, and the value of R$. This measurement

principle makes it necessary to use separate pairs of coaxial connectors on the DUT as shown

in figure 7. One pair is used for current injection and is labeled H and L cur -cur

1 The

other pair is used to detect the voltage (or potential), V

x

, across the DUT and these are labeled H ot and L ot . The use of H and L designates the input (High) and output (Low)

sides of the DUT. It is this external connector arrangement together with the

inaccessability of the points "H" and "L" (fig. 7) for connecting the shorting element that

require the modification of the procedure used for three-terminal capacitors.
CUo

e

itco

</) <D

SI

cu

S-O

o

Cl

<o

(_> 0>c

S-

<D

-t-> cu T3

s.o

Q.

+J

cuto

4->

4->

CUE

Q.

A3

i_

CT> O

CU

S-CD
Referring to figure 7 the main capacitor, C , is usually an air dielectric parallel

plate capacitor, and the other elements are the residuals shown as lumped inductors and

capacitors. Loss components are omitted because they are not of first order significance in

this discussion, assuming the capacitance standard is of good quality. A shorting element

for use in determining the residual series inductance is shown as L

$

. Examination of figure

7 will reveal that below the points "H" and "L" the equivalent circuit is identical to the

three-terminal equivalent circuit of figure 2. In fact, it is only the capacitance between

points "H" and "L" that is measured by a 4TP instrument. The inductances L^, l_2, Lo and L^

i ^^^ * ^^^

DUT

< v —* *—V,

Figure 6. The four- terminal pair concept.

. rn . u

Figure 7. Circuit model for four-terminal pair capacitor.
are the residuals associated with the internal leads connecting the points "H" and "L" to the external coaxial connectors, and do not effect the high frequency effective value of the

main capacitor, C

Q

. Because the internal points "H" and "L" are not readily accessible the

shorting element must be connected externally. As a result, two of the four lead

inductances (usually L

2 and L3) will be part of the circuit whose resonant frequency is determined by the grid-dip meter. Otherwise, the procedure for determining the residual

inductance of a 4TP capacitor by the resonance method is essentially the same as that

already described for three-terminal capacitors. Thus the residual inductance of the 4TP

capacitor is given by:

L r

= * - (L

s +L2+ L

3

), (5)

r T

if the shorting element is connected between the H t and L t terminals as shown in figures

5 and 7. In the case of one particular type of 4TP capacitor, L

2 and L3 amounted to the

inductance of two BNC type panel feed through connectors, or approximately 14 nH. This

value was derived by measuring panel feed through connectors of an identical type on an inductance bridge. In most instances, it will probably be found that the internal portions

of the inductance paths between "H" and "L" and the external connectors are not directly

accessible and some indirect method for determining the inductances L2 and L3 is required.

However, with care it should be possible to achieve accuracies to within one or two nH,

thereby preserving the accuracy of L to within +10 percent. Of course, if other terminal

combinations are used such as Hcurand L ot , or H t and L cur , or Hcurand L cur , then other

inductances would replace L 2 and L3 in eq (5). Having found the residual inductance, L r

, for the 4TP capacitor, the extrapolation represented by eq (1) is used to determine the

effective capacitance at a given frequency.

6. The Shorting Elements

Of utmost importance to the accuracy of this procedure is the value used for the

inductance, l_ s

, of the shorting element. Because it may be nearly as large as the residual

series inductance to be measured, it is necessary to determine l_ s as accurately as possible. Figure 8 is a close-up photograph of several shorting elements in use with threeterminal and 4TP capacitors. Using a high frequency impedance bridge, some attempts at measuring the inductances of these shorting devices have been made; however, more accurate

results are probably realized through computation using various inductance formulas for

conductors of round or rectangular cross section. These formulas were originally derived by

NBS [3] and have been more recently published by Terman [4], For convenience the

expressions for the self-inductances of a straight round rod and a straight rectangular

bar of materials whose permeability, u = 1 are given here.
I^HHI ^^K^^^^^^^^^^^^H HHH

Figure 8. From top to bottom: One 4TP capacitor and two three-terminal capacitors fitted

with shorting elements.

10
For a straight round rod of length, £<100d, where d is the diameter, the self

inductance at high frequencies is:

4?. L

s = 0.00200* (2.303 log

1Q -J

- 0.75 + ^-) microhenry (6)

For a straight rectangular bar, the expression for self-inductance is:

2 P. b+c.

I_ s = 0.00200£ (2.303 log

1Q -^~ + 0.5 + 0.2235 —) microhenry (7)

where b, c and i are the width, thickness and length in cm respectively. If the dimensions

are in inches as in ref [4], the constant, 0.00508, must be used in place of, 0.00200, in

eqs (6) and (7).

In order to minimize the uncertainty in the inductance value calculated for the

shorting element, L

s

, it is helpful if it is configured so that the inductance is as small

as possible. This will make the error in the calculated value of L

$

less significant in relation to L r

. Three shorting elements are pictured in figure 9. Note especially the one made of a cylindrical rod, and the one made of A.W.G.#18 copper wire. Each is 2.25 cm

long. For least uncertainty in the calculated value, the larger diameter rod is better

because its inductance as calculated from eq (6) is only 6.6 x 10" 9 henry as compared to

q 14.6 x 10 henry for the wire element. Thus the final result will be more accurate where

the larger diameter shorting element is used.

7. Sources of Error

Three sources of error associated with this measurement procedure are as follows: (a)

inaccuracy in the determination of the resonant frequency of the short-circuited capacitor,

(b) mutual coupling between the shorting element and the grid-dip meter coil, and (c) the

inductance of the shorting element. In examining these sources of error it is necessary to generalize in a number of instances because of the absence of a suitable geometrical

arrangement upon which to base a rigorous analysis.

In measuring the resonant frequency of the short circuited capacitor, the grid-dip

meter indication is very distinct because the capacitor and shorting element constitute a high Q circuit. This condition makes it possible to achieve repeatability which is beyond

the resolution of the frequency scale on the grid-dip meter oscillator. Either of two methods may be employed to improve this resolution. The frequency of the radiated signal of

the oscillator may be measured with a heterodyne frequency meter, or the signal may be

amplified and fed into a frequency counter. In this manner, it is possible to achieve

11
Figure 9. Various types of shorting elements for use with three- erminal and fourterminal pair capacitors.

repeatability well within one percent. Assuming that the accuracy is also of this order,

the effect on the value of the total circuit inductance would be approximately two percent. For frequency accuracies within a few percent, the accuracy in inductance is given

by the expression:

AL Aw

(8)

where aL and Aco represent the errors in inductance and angular frequency respectively.

The error due to mutual coupling between the shorting element and the grid-dip meter

coil is evidently ^ery small because no distinct change in the resonant frequency is caused

12
by varying the distance between them. Any change in the resonant frequency resulting from

an increase or decrease in the separation is probably of the same order as the stability and

setability of the grid-dip meter oscillator. In any event, the coupling error may be

minimized by maintaining a separation of two or three centimeters between them.

Probably the largest source of error is in the value used to represent the selfinductance of the shorting element. As already mentioned, it is possible to improve the

overall accuracy of the procedure by optimizing the configuration of the shorting element to obtain the minimum self-inductance. At best, however, eqs (6) and (7) provide only

approximations of the inductance of shorting elements because of the assumptions made in the course of their derivations. These assumptions include a free space environment, a perfectly straight current path and the absence of end effects, all of which are violated to some degreee in this application.

Because of the sources of error, it is estimated that the reliability of the value

obtained for the residual series inductance by the method described is of the order of ten percent. Referring to figure 10, the broken lines indicate the upper and lower limits of

the corrections which result from this ten percent uncertainty in the inductance value. In general, the effective capacitance may be determined by this method to accuracies of one percent or better up to frequencies where the correction amounts to ten percent of the 1 kHz

value.

8. Summary

Procedures have been described for evaluating the residual series inductance of airdielectric three-terminal and 4TP capacitors and for extrapolating the low frequency (1 kHz)

values of these capacitors to higher frequencies. The procedures require only what is considered to be commonly available equipment. A high degree of skill or experience is not required, and the measurements and calculations can be performed in a short time.

Uncertainties in effective capacitance of one percent or less are obtainable in the region

where the product of capacitance in farads and frequency in hertz is 10 or less.

13
100

LUD

_l<

>

LUO

2

<

O

<

<

o

NI

o

Z

o

I-o

LUDC

CCo

O

\-z

LUo

DC

LU

CLIO

l»

1.0

0.1

T—I I I I I I T—I I I I I U

9.7%

L

r = 0.050 juh

10.8%

L

r = 0.055 mTT

L

r = Residual Series Inductance

J I III/,

8.6%

L

r = 0.045 juh

i_L

100 kHz 1 MHz 10 MHz

PERCENT CORRECTION FOR CQ VERSUS FREQUENCY FOR A 1000 pf

CAPACITOR HAVING A RESIDUAL INDUCTANCE OF 0.050 MICROHENRY

Figure 10. Percent correction to CQ versus frequency for a 1000 pF capacitor having a residual series inductance of 0.050 microhenry.

14
9. References

[1] Jones, R. N., A technique for extrapolating the 1 KC values of secondary capacitance

standards to higher frequencies, Nat. Bur. Stand. (U. S.) Tech. Note 201, 16 pages (Nov.

5, 1963).

[2] Maeda, K. and Narimatsu, Y., Multi frequency LCR Meters Test Components Under Realistic

Conditions, Hewlett-Packard Journal, 24-31 (Feb. 1979).

[3] Rosa, E. B., and Grover, F. W. , Formulas and tables for the calculation of mutual and

self-inductances, Nat. Bur. Stand. (U.S.) Bull. 8, [1], 1-237 (Jan. 1912).

[4] Terman, F. E., Radio Engineers Handbook, 1st ed., 48-51, (McGraw-Hill Book Co., Inc., New York, 1943).

15
NBS-114A (REV. 9-78)

U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO. NBS TN-1024

4. TITLE AND SUBTITLE

Evaluation of Three-Terminal and Four-Terminal Pair

Capacitors at High Frequencies

3. Jtecipteflt's Ac-c*$5ioft No.

5. Publication Date September 1980

6. Performing Organization Code

7. AUTHOR(S)

R. N. Jones

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, DC 20234

10. Project/Task/Work Unit No.

11. Contract/Grant No.

12. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street, City, State, ZIP) 13. Type of Report & Period Coverec

iVS^onsoTiflg Agel^CSoM:

15. SUPPLEMENTARY NOTES

|

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

16. ABSTRACT (A 200-word or less (actual summary ol most significant information. If document includes a significant bibliography or

literature survey, mention it here.)

The low frequency (1 kHz) capacitance values of three-terminal and fourterminal pair air dielectric capacitors can be extrapolated to higher frequencies

if the residual series inductance is known. A resonance method for evaluating

the residual series inductance of these capacitor types, together with the

extrapolation procedure, is described. For the region where the product of

capacitance in farads and frequency in hertz is 10~2 or less, uncertainties of one percent or less may be obtained.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name;

separated by semicolons)

Calibration; capacitance; immittance standards; inductance; four-terminal pair

capacitance; residual series inductance; three-terminal capacitance; resonance

techniques.

18. AVAILABILITY ^Unlimited

I | For Official Distribution. Do Not Release to NTIS

fXI Order From Sup. of Doc, U.S. Government Printing Office, Washington, DC

20402.

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

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(THIS REPORT)

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various subjects related to the Bureau's scientific and technical activities. Handbooks—Recommended codes of engineering and industrial practice (including safety codes) developed in cooperation with in- terested industries, professional organizations, and regulatory

bodies. Special Publications—Include proceedings of conferences sponsored by NBS, NBS annual reports, and other special publications

appropriate to this grouping such as wall charts, pocket cards, and

bibliographies. Applied Mathematics Series— Mathematical tables, manuals, and

studies of special interest to physicists, engineers, chemists,

biologists, mathematicians, computer programmers, and others engaged in scientific and technical work.

National Standard Reference Data Series—Provides quantitative data on the physical and chemical properties of materials, compiled from the world's literature and critically evaluated. Developed under a worldwide program coordinated by NBS under

the authority of the National Standard Data Act (Public Law

90-396).

NOTE: The principal publication outlet for the foregoing data is the Journal of Physical and Chemical Reference Data (JPCRD)

published quarterly for NBS by the American Chemical Society

(ACS) and the American Institute of Physics (AIP). Subscriptions,

reprints, and supplements available from ACS, 1 155 Sixteenth St., NW, Washington, DC 20056.

Building Science Series—Disseminates technical information developed at the Bureau on building materials, components,

systems, and whole structures. The series presents research results,

test methods, and performance criteria related to the structural and

environmental functions and the durability and safety characteristics of building elements and systems.

Technical Notes—Studies or reports which are complete in themselves but restrictive in their treatment of a subject. Analogous to monographs but not so comprehensive in scope or definitive in treatment of the subject area. Often serve as a vehicle for final reports of work performed at NBS under the sponsorship of other government agencies.

Voluntary Product Standards—Developed under procedures

published by the Department of Commerce in Part 10, Title 15, of

the Code of Federal Regulations. The standards establish nationally recognized requirements for products, and provide all concerned interests with a basis for common understanding of the

characteristics of the products. NBS administers this program as a supplement to the activities of the private sector standardizing

organizations. Consumer Information Series—Practical information, based on N BS research and experience, covering areas of interest to the con- sumer. Easily understandable language and illustrations provide

useful background knowledge for shopping in today's tech- nological marketplace. Order the above NBS publications from: Superintendent of Documents, Government Printing Office. Washington, DC 20402. Order the following NBS publications— Fl PS and NBSlR's—from

the National Technical Information Services. Springfield, VA 22161

.

Federal Information Processing Standards Publications (F1PS

PUB)—Publications in this series collectively constitute the Federal Information Processing Standards Register. The Register

serves as the official source of information in the Federal Govern- ment regarding standards issued by NBS pursuant to the Federal Property and Administrative Services Act of 1949 as amended,

Public Law 89-306 (79 Stat. 1127), and as implemented by Executive Order 11717(38 FR 12315, dated May II, 1973)and Part 6 of Title 15 CFR (Code of Federal Regulations).

NBS Interagency Reports (NBSIR)—A special series of interim or

final reports on work performed by NBS for outside sponsors

(both government and non-government). In general, initial dis- tribution is handled by the sponsor; public distribution is by the National Technical Information Services, Springfield, VA 22161,

in paper copy or microfiche form.

BIBLIOGRAPHIC SUBSCRIPTION SERVICES

The following current-awareness and literature-survey bibliographies are issued periodically by the Bureau:

Cryogenic Data Center Current Awareness Service. A literature sur- vey issued biweekly. Annual subscription: domestic $35; foreign

$45. Liquefied Natural Cas. A literature survey issued quarterly. Annual

subscription: $30.

Superconducting Devices and Materials. A literature survey issued

quarterly. Annual subscription: $45. Please send subscription or- ders and remittances for the preceding bibliographic services to the National Bureau of Standards, Cryogenic Data Center (736) Boulder, CO 80303.
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