NATIONAL BUREAU OF STANDARDS REPORT

7834

STANDARDIZATION OF THERMAL EMITTANCE MEASUREMENTS

PROGRESS REPORT No. 17

October 1 - December 31, 1962

Contract No. DO (33-616) 61-02

Task No. 73603

AERONAUTICAL SYSTEMS DIVISION

AIR FORCE SYSTEMS COMMAND

UNITED STATES AIR FORCE

WRIGHT-PATTERSON AIR FORCE BASE, OHIO

II. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
THE NATIONAL BUREAU OF STANDARDS

Functions and Activities

The functions of the National Bureau of Standards are set forth in the Act of Congress,

March 3, 1901, as amended by Congress in Public Law 619, 1950. These include the development and maintenance of the national standards of measurement and the provision of means

and methods for making measurements consistent with these standards; the determination of

physical constants and properties of materials; the development of methods and instruments

for testing materials, devices, and structures; advisory services to government agencies on

scientific and technical problems; invention and development of devices to serve special needs

of the Government; and the development of standard practices, codes, and specifications. The

work includes basic and applied research, development, engineering, instrumentation, testing,

evaluation, calibration services, and various consultation and information services. Research

projects are also performed for other government agencies when the work relates to and supplements the basic program of the Bureau or when the Bureau’s unique competence is required.

The scope of activities is suggested by the listing of divisions and sections on the inside of

the back cover.

Publications

The results of the Bureau’s research are published either in the Bureau’s own series of

publications or in the journals of professional and scientific societies. The Bureau publishes

three periodicals available from the Government Printing Office: The Journal of Research,

published in four separate sections, presents complete scientific and technical papers; the Technical News Bulletin presents summary and preliminary reports on work in progress; and the

Central Radio Propagation Laboratory Ionospheric Predictions provides data for determining

the best frequencies to use for radio communications throughout the world. There are also

five series of nonperiodical publications: Monographs, Applied Mathematics Series, Handbooks,

Miscellaneous Publications, and Technical Notes.

A complete listing of the Bureau’s publications can be found in National Bureau of Standards Circular 460, Publications of the National Bureau of Standards, 1901 to June 1947 ($1.25),

and the Supplement to National Bureau of Standards Circular 460, July 1947 to June 1957

($1.50), and Miscellaneous Publication 240, July 1957 to June 1960 (includes Titles of Papers

Published in Outside Journals 1950 to 1959) ($2.25); available from the Superintendent of

Documents, Government Printihg Office, Washington 25, D.C.
NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT NBS REPORT

1009-11-10491 7834

STANDARDIZATION OF THERMAL EMITTANCE MEASUREMENTS

PROGRESS REPORT No. 17*

October 1 - December 31, 1962

Contract No. DO 33(616)61-02

Task No. 73603

The two phases of this project are conducted under the supervision of

the following persons, who have approved this report.

race M. Joseph

Electronic Engineei^Pata^rocessing Systems Division

William N. Harrison - Coordinator

dhief, Metallic Building Materials Section, Building Research Division

to

AERONAUTICAL SYSTEMS DIVISION

AIR FORCE SYSTEMS COMP&ND

UNITED STATES AIR FORCE

WRIGHT-PATTERSON AIR FORCE BASE, OHIO

IMPORTANT NOTICE NATIONAL BUREAU OF STAND/

for use within the Government. Befor and review. For this reason, the publ whole or in part, is not authorized i Bureau of Standards, Washington 25, the Report has been specifically preps

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST)

on October 9, 2015.

counting documents intended

>cted to additional evaluation ng of this Report, either in ice of the Director, National Government agency for which

for its own use. <3jb|>

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

*See footnote on page 1

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NOTICES

When Government drawings, specifications, or other data are used for

any purpose other than in connection with a definitely related Government

procurement operation, the United States Government thereby incurs no

responsibility nor any obligation whatsoever; and the fact that the

Government may have formulated, furnished, or in any way supplied the

said drawings, specifications, or other data, is not to be regarded by

implication or otherwise as in any manner licensing the holder or any

other person or corporation, or conveying any rights or permission to

manufacture, use, or sell any patented invention that may in any way be

related thereto.

This document may not be reproduced or published in any form in whole

or in part without prior approval of the Government. Since this is a progress report, the information herein is tentative and subject to

changes, corrections, and modifications.
* % '
I

.

SUMMARY *

Most of the work during the report period was concentrated on improvement and overhaul of the data-processing attachment. By the end of the

period most of the malfunctions had been corrected, but the equipment was

still not functioning correctly in all respects.

A computer code was written to facilitate checking of the performance

of the data-processing attachment.

II. INSTRUMENTATION

Spectrometer Maintenance

In order to ensure operation of the spectrometer at peak efficiency,

all of the mirrors were removed, carefully cleaned and replaced. The en- tire optical system was then realigned. After this had been done, it

became apparent that a diminution in sensitivity of the vacuum thermocouple detector required its replacement. A new detector was installed,

and the removed detector returned to the factory for repair.

As a preliminary step to extending the wavelength range of experimental work to 38 microns, a new thermocouple detector having approximately four times the sensitivity of the one now used was ordered.

III. DATA-PROCESSING ATTACHMENT

The manufacturer had been informed of the deficiencies in the dataprocessing attachment, and sent an engineer to the Bureau to correct them.

In the main, the difficulties consisted of unstable circuits which resulted

in drift from the calibration settings of potentiometers controlling corrections of the zero and 100-percent lines. The trouble was found to be in

the digital portions of the circuits. A number of changes were made to

improve these functions. A mechanical difficulty, binding of the gears in

in the correcting potentiometer drive mechanism, was also found and corrected . Following these adjustments, the data-processing equipment operated

satisfactorily for a time, after which intermittent trouble developed, which

was manifested as unequal response of the stepping motors, to signals calling for change in one direction as compared to the other. This effect was

found in both correcting circuits, and was traced to overheating of the

motor-drive transistor, indicating excessive current through it. Normally

the transistor should be kept at cutoff when it is not in operation, but

continuous overheating indicated the cutoff was not effective. The difficulty could arise from leakage, from a defect in the power transistor, incorrect bias in the preceding driver stage, improper circuit design, or a combination of causes. Each of these possibilities is being checked. * The fifteenth quarterly progress report covered the period Jan. 1 - Mar. 31, 1962. Work done during the period April 1 - December 31, 1962 was

covered and included in the summary report for the period July 1, 1958

through Oct. 31, 1962, WADC TR 59-510 Pt IV, which constitutes the sixteenth progress report.
2

Some of the difficulties with the data-processing equipment were aggravated by noise in the spectrometer amplifier. Efforts to find a preamplifier with a lower noise level than that now used, have not so far been successful.

During a period of satisfactory operation the equipment was checked by

use of the reference blackbody furnace and sector-disc attenuator simulating

a graybody specimen having an emittance equal to the known transmission factor of 0.75. Curves were obtained which represented a graybody spectral

distribution within ± 0.01 of the known correct value over the spectral range

of 1 to 15 microns.

The data-processing attachment has provision also for making punched-tape

records that can be fed into separate computers to obtain various types of

information. Use can be made of the punched-tape records to test the functioning of the equipment as follows: In addition to digitized records of the

"zero line", the "1007c line" and the uncorrected spectral emittance curve of

the specimen, a fourth set of values is recorded on the punched tape, representing the emittance curve of the specimen as corrected concurrently with

the test, by use of the magnetic tape, and recorded on the strip chart. This

operation requires separate tests on the specimen, with and without correction.

During the report period a computer program was designed so that, from

the four-channel punched-tape, the computer would: (1) apply corrections to

the uncorrected emittance data, based on the "1007. line" and "zero line"

records, (2) compare the resulting corrected emittance values with the corresponding corrected values recorded on the punched tape during test

through functioning of the magnetic tape, and (3) record the algebraic differences between the two sets of independently corrected data.

The computer program was tried, and was found to function, so that it

could be used for the intended purpose. Several tapes had been recorded,

ready for processing, at the end of the report period.

IV. WORKING STANDARDS OF NORMAL SPECTRAL EMITTANCE

Working standards of normal spectral emittance having low, intermediate

and high emittance, respectively, were prepared, calibrated and transmitted

to the Physics Laboratory, A.S.D., prior to the start of the current report

period.

Detailed instructions for the handling and use of these standards were

prepared and transmitted to the Applications Laboratory, A. S. D., during the

current report period.
3

V. EQUATIONS

The formulas for reflectivity were rewritten using new parameters which

are combinations of the original parameters. An analysis of the equations

indicated that the new parameters are more directly related to the geometric

properties of the calculated reflectivity curve, and it is hoped that their

use will facilitate the fitting of the observed reflectivity data. Existing programs were modified to permit use of the new parameters, and exploratory calculations were continued.

VI. WAVELENGTHS FOR 100 SELECTED ORDINATE COMPUTATIONS

The rigorous method of computing total normal emittance from spectral

data may be expressed mathematically as follows:

i* 00 E d\

E

ts = -J2-- (1)

00

r g b\ dx

o where E

tg = total normal emittance of specimen

= *ate of energy emission (radiant flux), per unit area, from a blackbody at the temperature of the specimen, within the wavelength interval \ to (X. + d\)

.

E . = normal spectral emittance of the specimen at wavelength

SA

All computations from data are based upon finite intervals of wavelength, A\.

The following equation applies:

^3

E

ts

2 e bX£sX,A^

Xa

*•1

( 2 )

X1 and Xg being selected to include substantially all of the flux emitted by

a blackbody radiator at the test temperature.
- 4 -

In the weighted ordinate method, uniform values of A X are used, and

each value of Es \ must be weighted by a factor proportional to « b\- This

value of ejjX. represents the area, within the wavelength interval X to

(X + AM, irnder the spectral distribution curve of radiant flux, from

unit area of a blackbody radiator, at the test temperature.

In the 100“ selected- ordinate method, the area under the spectral distribution curve for the radiant flux from a blackbody radiator at the test

temperature is divided into 100 equal slices. The 100 selected ordinates

are then the 100 median wavelengths for the 100 areas. In this case AX

varies, but the quantity eb\AX is held constant at 0.01. Under these

conditions equation (2) can be rewritten:

X ~ ioo

E

ts

= 0,01 * EsK (3)

In practice, any desired degree of precision in the computation of Ets

can be attained by either method by taking a sufficient number of ordinates.

With any given number of ordinates, the computation error will be less by

the selected ordinate method than by the weighted ordinate method. With

solids, whose spectral emittance curves do not normally have sharp peaks or

valleys, the 100 selected ordinate method gives values that have no significant computation error from this source.

The wavelengths representing the 100 selected ordinates were computed

for temperatures of 600, 700, 800, 900, 1000, 1100, 1200, 1300 and 1400°K,

and are given in Table I.

The 100 selected ordinates for temperatures of 800°, 1100°, 1300° and

1400 K were converted to digital form and punched on paper tape for use

with the data-processing attachment to the normal spectral emittance equipment .
WAVELENGTHS

FOR

COMPUTATION

OF

TOTAL

EMITTANCE

FROM

SPECTRAL

DATA

BY

THE

100-

SELECTED

ORDINATE

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11. S. DEPARTMENT OF COMMERCE

Luther H. Hodges, Secretary

NATIONAL BUREAU OF STANDARDS

A. V. Astin, Director THE NATIONAL BUREAU OF STANDARDS

The scope of activities of the National Bureau of Standards at its major laboratories in Washington, D.C., aad

Boulder, Colorado, is suggested in the following listing of the divisions and sections engaged in technical work.

In general, each section carries out specialized research, development, and engineering in the field indicated fey its title. A brief description of the activities, and of the resultant publications, appears on the inside of the

front cover.

W ASHINGTON, l). C.

Electricity. Resistance and Reactance. Electrochemistry. Electrical Instruments. Magnetic Measurements

Dielectrics. High Voltage.

Metrology. Photometry and Colorimetry. Refractometry. Photographic Research. Length. Engineering Metrology.

Mass and Scale. Volumetry and Densimetry.

Heat. Temperature Physics. Heat Measurements. Cryogenic Physics. Equation of State. Statistical Physics.

Radiation Physics. X>ray. Radioactivity. Radiation Theory. High Energy Radiation. Radiological Equipment.

Nucleonic Instrumentation. Neutron Physics.

Analytical and Inorganic Chemistry. Pure Substances. Spectrochemistry. Solution Chemistry. Standard Refer- ence Materials. Applied Analytical Research. Crystal Chemistry.

Mechanics. Sound. Pressure and Vacuum. Fluid Mechanics. Engineering Mechanics. Rheology. Combustion

Controls.

Polymers. Macromolecules: Synthesis and Structure. Polymer Chemistry. Polymer Physics. Polymer Characterization. Polymer Evaluation and Testing. Applied Polymer Standards and Research. Dental Research.

Metalliffgy. Engineering Metallurgy. Microscopy and Diffraction. Metal Reactions. Metal Physics. Electrolysis

and Metal Deposition.

Inorganic Solids. Engineering Ceramics. Glass. Solid State Chemistry. Crystal Growth. Physical Properties.

Crystallography.

Building Research. Structural Engineering. Fire Research. Mechanical Systems. Organic Building Materials.

Codesand Safety Standards. Heat Transfer. Inorganic Building Materials. Metallic Building Materials.

Applied Mathematics. Numerical Analysis. Computation. Statistical Engineering. Mathematical Physics. Operations Research.

Data Processing Systems. Components and Techniques. Computer Technology. Measurements Automation.

Engineering Applications. Systems Analysis.

Atomic Physics. Spectroscopy. Infrared Spectroscopy. Far Ultraviolet Physics. Solid State Physics. Electron

Physics. Atomic Physics. Plasma Spectroscopy.

Instrumentation. Engineering Electronics. Electron Devices. Electronic Instrumentation. Mechanical Instru- ments. Basic Instrumentation.

Physical Chemistry. Thermochemistry. Surface Chemistry. Organic Chemistry. Molecular Spectroscopy. Elementary Processes. Mass Spectrometry. Photochemistry and Radiation Chemistry.

Office of Weights and Measures. BOULDER, COLO.

Cryogenic Engineering Laboratory. Cryogenic Equipment. Cryogenic Processes. Properties of Materials. Cryogenic Technical Services.

CENTRAL RADIO PROPAGATION LABORATORY

Ionosphere Research and Propagation. Low Frequency and Very Low Frequency Research. Ionosphere Research. Prediction Services. Sun-Earth Relationships. Field Engineering. Radio Warning Services. Vertical

Soundings Research. t

. Radio Propagation Engineering. Data Reduction Instrumentation. Radio Noise. Tropospheric Measurements.

Tropospheric Analysis. Propagation-Terrain Effects. Radio-Meteorology. Lower Atmosphere Physics.

Radio Systems. Applied Electromagnetic Theory. High Frequency and Very High Frequency Research. Fre- quency Utilization. Modulation Research. Antenna Research. Radiodetermination.

Upper Atmosphere and Space Physics. Upper Atmosphere and Plasma Physics. High Latitude Ionosphere

Physics. Ionosphere and Exosphere Scatter. Airglow and Aurora. Ionospheric Radio Astronomy.

RADIO STANDARDS LABORATORY

Radio Physics. Radio Broadcast Service. Radio and Microwave Materials. Atomic Frequency and Time-Interval

Standards. Radio Plasma. Millimeter-Wave Research.

Circuit Standards. High Frequency Electrical Standards. High Frequency Calibration Services. High Frequency

Impedance Standards. Microwave Calibration Services. Microwave Circuit Standards. Low Frequency Calibration

Services.

USCOMM—NBS— DC
NBS