WADC TECHNICAL REPORT 59-510

Part IV

NATIONAL BUREAU OF STANDARDS REPORT

7806

STANDARDIZATION OF THERMAL EMITTANCE MEASUREMENTS

PART IV. NORMAL SPECTRAL EMITTANCE, 800 - 1400°K

William N. Harrison

Joseph C. Richmond

Frederick J. Shorten

Horace S. Joseph

National Bureau of Standards

December 1962

AERONAUTICAL SYSTEMS DIVISION

U. 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

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Miscellaneous Publications, and Technical Notes. A complete listing of the Bureau’s publications can be found in National Bureau of Standards Circular 400, 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.
WADC TECHNICAL REPORT 59-510

Part IV

c

780jT

STANDARDIZATION OF THERMAL EMITTANCE MEASUREMENT §

PART IV. NORMAL SPECTRAL EMITTANCE, 800 - 1400 K

William N. Harrison

Joseph C. Richmond

Frederick J. Shorten

Horace S. Joseph

National Bureau of Standards

December 1962

Directorate of Materials & Processes

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

Project No. 7360

AERONAUTICAL SYSTEMS DIVISION

AIR FORCE SYSTEMS COMMAND

UNITED STATES AIR FORCE

WRIGHT -PATTERSON AIR FORCE BASE, OHIO

NOTICE'S

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.

Qualified requesters may obtain copies of this report from the

Armed Services Technical Information Agency, (ASTIA), Arlington Hall

Station, Arlington 12, Virginia.

This report has been released to the Office of Technical Services,

U. S. Department of Commerce, Washington 25, D. C. for sale to the general

public

.

Copies of WADC or ASD Technical Reports and Technical Notes should

not be returned to the Aeronautical Systems Division unless return is re- quired by security considerations, contractual obligations, or notice on a specific document.
FOREWORD

This report was prepared by the National Bureau of Standards under

USAF Contracts No. AF (33~616)-58-2Q, Amendment 1 to that contract. No, AF

(33-616)-61-Q2, and Amendments 1, 2, 3 to that contract. The work was initiated under Project No. 7360, "Materials Analysis and Evaluation Techniques

Task No. 73603 "Thermodynamics and Heat Transfer." The contracts were administered under the direction of the Materials Laboratory, Directorate of

Laboratories, Wright Air Development Center, with Capt. F. V. Zaleski acting

as project engineer, and later under the direction of Materials Central,

Directorate of Advanced Systems Technology, Wright Air Development Division,

with Mr. R, A. Winn acting as project engineer, and still later under the

direction of the Directorate of Materials and Processes, Deputy for Technology, Aeronautical Systems Division, again with Mr. R. A. Winn as project

engineer

.

This report covers work performed during the period 1 July 1958 through

31 October, 1962.

ACKNOWLEDGEMENTS

The authors are pleased to acknowledge the contributions of the following individuals, who have participated in various phases of the project as indicated

:

Earl K. Plyler, Ralph Stair, R. F. Johnson and Arthur G. Maki, of the

Atomic and Radiation Physics Division, for check calibrations of working

standards.

Harold K. Skramstad and L. Tabak, of the Data Processing Systems Division, for work on the design of the data-processing attachment.

Seymour Haber, and other members of the Applied Mathematics Division,

for application of electronic data processing procedures to evaluation of

parameters in the equations relating electronic structure of metals to

spectral emittance.

Warren D. Hayes, for making many of the measurements on the working

standards

.

Grateful acknowledgement is also made to Deane B. Judd and William F.

Roeser of the N.B.S. staff and Thomas R. Harrison, of the Brown Instrument

Division, Minneapolis-Honeywell Regulator Co., for their generous consultative contributions upon several occasions.

WADC TR 59-510 Pt IV
ABSTRACT

Equipment and procedures were developed to measure normal spectral

emittance of specimens that can be heated by passing a current through

them, at temperatures in the range of 800 to 1400°K, and over the wavelength range of 1 to 15 microns.

A data-processi ng attachment for the normal spectral emittance equipment was designed to (1) automatically correct the measured emittance for

"10070 line" and "zero line" errors on the basis of previously-recorded

calibration tests; (?) record the corrected spectral emittance values and

wavelengths at preselected wavelength intervals on punched paper tape in

form suitable for direct entry into an electronic digital computer; and

(3) to compute during a spectral emittance test on a specimen the total

normal emittance, or absorptance for radiant energy of any known spectra.5 distribution of flux, of the specimen.

Working standards of normal spectral emittance having low, intermediate and high emittance values, respectively, were prepared and calibrated

for use in other laboratories to check the operation of equipment and procedures used for. measuring normal spectral emittance.

This report has been rev:

//

'J. I. WITTEB0RT

Chief, Thermophysics Branch

Physics Laboratory

Directorate of Materials and Processes

WADC TR 59-510 Pt IV iii
TABLE OF CONTENTS

PAGE

I OBJECTIVES. .......................... 1

II DEFINITIONS 1

III FUNDAMENTAL CONSIDERATIONS 4

IV COMPONENT PARTS OF THE INVESTIGATION AND ORDER OF PRIORITIES. . 7

V CONSIDERATIONS IN SELECTION OF EQUIPMENT AND PROCEDURES .... 8

VI DEVELOPMENT OF EQUIPMENT FOR NORMAL SPECTRAL EMITTANCE

MEASUREMENTS. ..... 9

VII CALIBRATION OF EMITTANCE EQUIPMENT. .............. 16

VIII EXPERIMENTAL PROCEDURE. .................... 20

IX SELECTION AND CALIBRATION OF WORKING STANDARDS. ........ 22

X PRINCIPLES OF DATA REDUCTION. ...... 44

XI DEVELOPMENT OF DATA-PROCESSING EQUIPMENT. ........... 48

XII EQUATIONS RELATING SPECTRAL EMISSIVITY OF METALS TO OTHER

PROPERTIES .......................... 60

XIII REFERENCES .......................... 62

WADC TR 59-510 Pt IV iv
LIST OF ILLUSTRATIONS

Figure Page

1. Sketch of the Optical Path in the Modified Spectroradiometer . . . 10

2. Photograph of the External Optical System of the Spectroradiometer 11

3. Sectional Drawing of a Blackbody Furnace 12

4. Sketch of the Specimen Enclosure. . 14

5. Wiring Diagram of Power Supply to Comparison Blackbody Furnace. . 15

6. Block Diagram of Temperature Control Equipment 16

7. Spectral "Emittance" of the Combination of the Reference Blackbody Furnace and Sector-disc Attenuator with Various Attenuator

Discs 20

8. A Section of Recorder Chart Showing "100% Line", "Specimen Line"

and "Zero Line." 21

9. Normal Spectral Emittance at 800°K of Platinum Working Standards. 25

10. Normal Spectral Emittance at 1100°K of Platinum Working Standards 26

11. Normal Spectral Emittance at 1400°K of Platinum Working Standards 27

12. Spectral Distribution of Two Categories of Standard Deviations

Obtained on Platinum Working Standards at 800°K 29

13. Spectral Distribution of Two Categories of Standard Deviations

Obtained on Platinum Working Standards at 1100°K 30

14. Spectral Distribution of Two Categories of Standard Deviations

Obtained on Platinum Working Standards at 1400°K 31

15. Normal Spectral Emittance at 800°K of Oxidized Kanthal Working

Standards 33

16. Normal Spectral Emittance at 1100°K of Oxidized Kanthal Working

Standards 34

17. Normal Spectral Emittance at 1300°K of Oxidized Kanthal Working

Standards 35

18. Spectral Distribution of Two Categories of Standard Deviations

Obtained on Oxidized Kanthal Working Standards at 800 K 36

WADC TR 59-510 Pt IV v
LIST OF ILLUSTRATIONS

Figure Page

19. Spectral Distribution of Two Categories of Standard Deviations

Obtained on Oxidized Kanthal Working Standards at 1100 K„ . . 37

20. Spectral Distribution of Two Categories of Standard Deviations

Obtained on Oxidized Kanthal Working Standards at 1300 K. , » 38

21. Normal Spectral Emittance at 800°K of Oxidized Inconel Working

Standards t ...» t ...» • 39

22. Normal Spectral Emittance at 1100 °K of Oxidized Inconel Working

Standards . 40

23. Normal Spectral Emittance at 1300°K of Oxidized Inconel Working

Standards 41

24. Spectral Distribution of Two Categories of Standard Dgviations

Obtained on Oxidized Inconel Working Standards at 800 K. . . . 42

25. Spectral Distribution of Two Categories of Standard Deviations

Obtained on Oxidized Inconel Working Standards at 1100 K . . . 43

26. Spectral Distribution of Two Categories of Standard Deviations

Obtained on Oxidized Inconel Working Standards at 1300 K , „ . 44

27. Graphical Form of Data and Derived Values Used in Computing

From the Spectral Emittance of a Specimen its Total Emittance,

its Total Absorptance, or its Total Emissive Power ...... 45

28. Schematic Wiring Diagram Showing Connections Through Function

Selector Switch of Data-Processing Attachment in "Bypass" and

"Record 100%," or "Record Zero" Positions ........... 48

29. Block Diagram of Data-Processing Attachment During Reading of

"100% Line" and "Zero Line" Deviations ....... 50

30. Schematic Wiring Diagram of Potentiometer Circuits During

Playback of "100% Line” Deviations ........ „ 51

31. Schematic Wiring Diagram of Potentiometer Circuits During

Playback of Both "100% Line" and "Zero Line" Deviations, ... 52

32. Block Diagram of Data-Processing Attachment During a Specimen

Run 52

WADC TR 59-510 Pt IV vi
I. OBJECTIVES

The broad objective of this project is to develop standard procedures,

and to select or design suitable equipment, for the measurement of spectral

emittance and/or spectral reflectance of materials, particularly those used

in aircraft, missiles and space vehicles, at temperatures from below room

temperature to near the melting pbint of refractory materials of interest,

and over the wavelength range from the visible range into the infrared to

15 microns and beyond. The specific objectives include (1) the selection

of suitable materials and the preparation and calibration of specimens as working standards of normal spectral emittance, to be used for calibration

of spectral emittance equipment in other laboratories, and (2) the design

or selection of suitable data-processing equipment (a) to automatically

correct the emittance data for calibration errors of the equipment, (b) to

record the corrected data in form suitable for direct entry into an electronic digital computer, and (3) to compute, concurrently with a spectral

emittance measurement, a single value of total emittance, solar absorptance

or absorptance for radiant energy having any other known spectral distribution of flux.

II. DEFINITIONS

Several important items of nomenclature in the field of electromagnetic radiation have not been firmly established. Different meanings are as- cribed to the same words by different individuals, and some of the con- flicting definitions have been adopted by different technical and scientific organizations of national scope. The terminology used in this investigation follows that advocated by Jones [l], Worthing [2] and others, including American Standards Association [3], in that the word-ending "ivity" is

reserved for the properties of materials, and "ance" for the properties of

specimens. The word-ending "ion", as in reflection, absorption and transmission, is applied to acts or processes; radiation is a process, and some- times denotes that which has been radiated.

All bodies are constantly emitting electromagnetic energy as a result

of the thermal vibration of the particles, atoms and molecules comprising

the body; this process is known as thermal emission , and the rate of such

emission per unit area is often referred to as thermal emissive power .

Note: Bracketed numbers are references. See Section XIII of this report.

Manuscript released by authors November 1962 for publication as a WADC

Technical Report.

WADC TR 59-510 Pt IV 1
Radiant flux is the rate of flow of radiant energy.

Emittance is a property of a specimen; it is the ratio of the emitted

radiant flux per unit area to that of a blackbody radiator at the same temperature and under the same conditions.

A blackb ody absorbs all radiant energy incident upon it and at any

given temperature has the maximum possible emissive power for the temperature. An ideal blackbody is a complete enclosure with opaque walls at a uniform temperature. The amount , and also the geometric and spectral

(or wavelength) distribution of radiant flux per unit area, from a blackbody

at a given temperature can be computed from the Stefan-Boltzmann relationship, Lambert's cosine law and the Planck radiation law, respectively.

Laboratory blackbody furnaces which radiate energy are only approximate

blackbodies, because the opening through which the radiant energy is emitted constitutes a deviation from the ideal. The extent to which they deviate from the ideal depends upon such factors as the relative size of the

opening, the emittance of the inside surface, and the thermal gradients

that may be present in the cavity walls. The rate of thermal emission of

any real specimen is less than that of a blackbody at the same temperature .

Etriissivity is a special case of emittance; it is a fundamental property of a material, and is measured as the emittance of a specimen of the

material which has an optically smooth surface!/ and is sufficiently thick

to be completely opaque (non transmitting).

Reflection is the process by which radiant flux incident upon a sur- face is reflected.

Reflectance is a property of a specimen; it is the ratio of reflected

radiant flux' to incident radiant flux.

Reflectivity is a special case of reflectance; it is a fundamental

property of a material, and is measured as the reflectance of a specimen of

the material that has an optically smooth surface, and is sufficiently

thick to be completely opaque.

Transmission is the process whereby radiant flux is transmitted through

a body.

Transmittance is a property of a specimen; it is the ratio of transmitted radiant flux to incident radiant flux.

Absorption is the process by which radiant energy is absorbed and

converted into other forms of energy.

U Any surface contamination may alter the thermal radiation properties

hence a contaminat ion- free surface is also essential.

WADC TR 59-510 Pt IV 2
Absorptance is a property of a specimen; it is the ratio of absorbed

radiant flux to incident radiant flux.

Absorptivity is a special case of absorptance; it is a fundamental

property of a material and is measured as the absorptance of a specimen of

the material that has an optically smooth surface and is sufficiently thick

to be completely opaque.

Absorption Coefficient is a fundamental property of a material; it is

a quantitative expression of the rate of decrease of radiant flux density

in the direction of propagation of radiant energy through a material due m

absorption. Expressed mathematically

I = I e < .O o in which "i "is the f lux density after passing tnrough a thickness '!x"of a non- scattering material, "l0 "is the flux density at zero thickness, just

after penetration of the surface (thus not including the reflected portions

of the incident radiation) "a "is the absorption coefficient, and"e"is the

base of natural logarithms.

In a light- scattering material, some of the reduction in unidirectional flux density results from internal scattering. Equation (1) is also

used to express the rate of decrease in flux density due to scattering; in

this case the letter"a"symbolizes the scattering coefficient . In lightscattering materials the reduction in flux density is due to both absorption and scattering, in which case the 1 etter "a:i represents the extinction

coefficient

A specimen is opaque when none of the radiant energy incident upon it

is transmitted through it. All materials theoretically require infinite

thickness to become opaque, as illustrated by equation (1). In practice,

a specimen is considered to be opaque when the transmitted radiant flux is

too small to be detected, a condition which occurs at a very small thick- ness for some materials, and at great thicknesses for others. The thick- ness required for a specimen to be opaque also varies with the wavelength

of the incident flux, for any one material.

All of the properties that are defined above vary with the spectral

(or wavelength) distribution of the radiant flux. All are temperature dependent, some strongly so, and others only moderately. All of the properties except the coefficients are influenced by the angular distribution of

flux in the radiant energy. All of the properties that pertain to speci- mens are influenced by the surface texture of the specimen, and by the

thickness, unless the specimen is opaque.

i-A i Ft IV
Since the emission, reflection and absorption characteristics of a specimen are influenced by the direction of propagation, relative to the

surface, of the emitted, incident, or reflected energy, and by the spectral

distribution of radiant flux, most of the terms defined above must be qualified in order to convey precise meanings. For reflection, the direction

of propagation of both the incident and reflected radiation must be specified. Specular , referring to reflection, means in the direction of mirror

reflection. Diffuse , referring to reflection, means in all possible directions. Emission in all possible directions is referred to as hetni_-

spherical . When limited directions of propagation are involved, the word

directional may be used. Normal is a special case of directional, and means a direction normal to the surface. For other directions, the angle

of deviation from the normal is stated. The terms normal and directional

apply strictly to beams of parallel radiation, but are also used for beams

contained within a small solid angle, in which case the direction of propagation is taken as that of the axial ray. Since all laboratory sources,

specimens and receptors are of finite size, significant deviations from

parallelism exist in all laboratory instruments. Hence the source and

field apertures should be specified to define the extent of such deviations

from parallelism.

Radiant energy having a stated wavelength, or more precisely, that is

within a narrow wavelength interval centered on a specified wavelength, is

referred to as spectral . Spectral emittance at a stated temperature is

frequently plotted as a function of wavelength to produce a spectral emittance curve. The word total as used to modify terms describing thermal

emission characteristics, means that the modified term pertains to the integral of rates of spectral emission at all wavelengths.

Some examples of the qualified expressions that are required to convey

precise meanings are: "'total hemispherical emittance at 500 K", "normal

spectral emittance at 1400 K in the wavelength interval 1 to 15 microns",

and "spectral diffuse reflectance for normal illumination over the wavelength interval 0.3 to 3.0 microns."

III. FUNDAMENTAL CONSIDERATIONS

Thermal emission is frequently referred to as a surface phenomenon.

Actually all of the radiant energy that is emitted originates within the

body of the specimen (solid, liquid or gas). The function of the surface,

or interface, in this respect is to fix the fraction c£ the radiant energy

incident upon it from inside the specimen that is internally reflected,

the remainder being refracted and allowed to radiate from the specimen.

The same function is performed with respect to radiant energy incident on the interface from outside the specimen. The fraction of incident radiant

energy that passes through the interface (the remainder being reflected)

is determined by (a) its wavelength, (b) the angle of incidence (internal

or external), and (c) the indices of refraction of the two materials (such

as glass and air) that share the interface. For a material such as metal,

WADC TR 59-510 Pt IV 4
that has a high extinction coefficient, radiant energy that reaches the

surface from the interior must be emitted by particles very close to the

surface. As the extinction coefficient (see equation 1) of the specimen

decreases, there is a corresponding increase in the depth within the specimen from which a significant fraction of the internally emitted energy

reaches the surface by radiation through the material of the specimen without being absorbed. For some materials, and within some wavelength intervals, the maximum such depth may be quite large, as for example in the case

of optical glass and visible light. Gardon [4] presents a detailed mathematical treatment of emission by optically homogeneous materials having

relatively low absorption coefficients. In dealing with ceramic materials

the fact that all emitted radiant energy originates internally cannot be

safely ignored.

The emittance of a specimen that consists of a partially transmitting

coating on a substrate is influenced by the emittance and reflectance of

the substrate. If the coating is completely opaque, it controls the emittance of the specimen. Emittance, reflectance, and transmittance, under

equilibrium conditions, when all heat transfer is by radiation, and when

other conditions, specified below, are fulfilled, are related by the following equations:

E + R + T -

E + R_ co E

E_

1

1A

A

( 2 ) (3)

(4)

(5)

in which: E = emittance

Eoo = emissivity

R - reflectance

Rco = reflectivity

T = transmittance

A = absorptance

Ak, = absorptivity

These equations are valid for the entire span of the spectrum considered as a whole, and likewise for any given wavelength interval within the

spectrum, provided that consistent and pertinent geometric and spectral con- ditions of illumination and viewing are used. If hemispherical emissivity

is specified, the corresponding reflectivity is the value that applies to

diffuse illumination and hemispherical viewing, a condition not readily

achieved experimentally. Likewise, for hemispherical emittance the corres- ponding transmittance value is for conditions of uniformly diffused illumination and hemispherical viewing. For normal emittance the corresponding

reflectance and transmittance values are for uniformly diffused illumination

and normal viewing, or the optical equivalent, normal illumination and

hemispherical viewing.

WADC TR 59-510 Pt IV 5
In addition to these considerations involving the angular distribution

of radiant flux, there are certain aspects of the spectral distribution

that must not be overlooked in applying equations (2) t© (5). Since by

definition emittance is the ratio of radiant flux from the specimen to that

from a comparable blackbody, it follows that one of the conditions ior val«*

idity of these equations which pertain to equilibrium conditions (equal

rates of absorption and emission), is that the radiant energy impinging

upon the specimen must have the characteristics of blackbody radiation at

the temperature of the specimen* ' If total emittance is under consideration

the whole spectrum is involved. If spectral emittance within any specified

wavelength Increment is under consideration, then the radiant energy impinging upon the specimen- must have, within the same limits of wavelength,

the characteristics of blackbody radiation at the temperature of the sped*

men. For extremely narrow wavelength intervals the spectral distribution

-

of flux from any source that would be used is sufficiently close to blackbody distribution (just as a sufficiently short segment of a circle approximates a straight line).-!/

Furthermore, in considering applicable spectral conditions for equations (2) to (5) a clear distinction must be made between emittance (®r

emissivity), on the one hand, and the rate of emission of radiant energy,

on the other. For the latter case the counterpart of equation (2) is

, e + p + t = (jo (6)

in which:

e = rate of emission of radiant energy by the specimen

p = rate at which radiant energy is reflected from the specimen

t = rate at which radiant energy is transmitted through the specimen

uo = rate at which radiant energy, of any wavelength distribution, is _____ impinging upon the specimen. —/ At first glance these conditions for validity of the equations might

appear to preclude their use in the computation of eaiittance from reflectance data obtained with incident flux at a higher level than could be produced by a blackbody of the same size and temperature as the specimen.

Fortunately, however, even though the reflectance of the specimen be measured for incident radiant flux much greater than that required to maintain

the desired temperature of the specimen under equilibrium conditions, with

radiative transfer alone, properly measured reflectance values are val id

for substitution in equation (2); the test temperature is maintained in

this case by dissipating part of the energy absorbed in the specimen by means of refrigeration; often conduction and convection losses are sufficient without special apparatus, when the specimen is at room temperature.

The use in equation (2) of reflectance values determined under these conditions is permissible because the spectral reflectance of the specimen is a function of its temperature regardless of how this temperature is maintained. Equation (2), as stated in the text, is applicable to either total

emittance or spectral emittance when corresponding values of R and T are

used. Thus a spectral reflectance curve for an opaque specimen yields a spectral emittance curve, since T = 0, E = 1-R, and E\ = 1-R^. The conversion of spectral to total emittance is described in the immediately following pages

.

WADC TR 59-510 Pt IV 6
Equation (6), in which the rate of flow of energy is being considered

rather than the relative rate as compared to that of a blackbody as in

equations (2) to (5), is not necessarily valid for limited portions of the

spectrum. Thus a specimen in thermal equilibrium that is heated solely by

solar radiation will be emitting energy with a spectral distribution of

flux that is characteristic of the specimen at the equilibrium temperature,

which may reach a peak at, say, 10 microns. Hence it would be fallacious

to assume that equation (6), or the analagous counterparts of equations ( 3 ). (4), and (5), rewritten to apply to rates of flow of energy, would always

be applicable to wavelength intervals of limited width.

IV. COMPONENT PARTS OF THE INVESTIGATION AND ORDER OF PRIORITIES

The objectives outlined in Section I of this report cover such a wide

range of wavelengths and temperatures, that significant progress on some phases could not be made in the time and with the facilities available, and

work on. the remaining phases is being continued. The temperature range of

interest can be divided into four smaller ranges, as follows: (1) below room temperature, (2) room temperature to 800 K, (3) 800° to 1400 V and (4 ) above 1400 K. In general, different equipment or techniques are required

for each of these temperature ranges. The wavelength range, of interest was

also, for convenience , divided into three smaller ranges, as follows: (1)

from about 0.3 micron to about 1.5 microns; (2) from about 1.5 microns to

15 microns; and (3) from 15 to 35 microns. Again different items of equip"

merit, such as prisms and detectors, are needed in the different wavelength

ranges. A third subdivision can be made on the basis of the type of speci- men to be evaluated, as follows: (1) metals and other materials that can

be heated by passing a current through them, and (2) dielectric materials,

such as ceramics, that cannot conveniently be heated by passing a current

through them.

Top priority was given to the development of instrumentation and procedures for the measurement of normal spectral etnittance of specimens that can be heated by passing a current through them, at temperatures in the

range of 800' to 1400 K, and over the wavelength range of 1.5 to 15 microns.

The selection was made on the basis of: the greatest current interest: of the

Air Force.

The selection and calibration of physical working standards of normal

spectral emittance were undertaken after equipment and procedures for their

measurement had been developed.

The design and construction of automatic data-processing equipment also

followed the design and construction of the measuring equipment.

WADC TR 59" 510 Pt IV 7
V. CONSIDERATIONS IN SELECTION OF EQUIPMENT AND PROCEDURES

In general, accurate absolute measurements of radiant energy are not

easy to make., Comparative measurements of radiant energy can be made much

more readily. For this reason it appears logical to base emittance d@terminations on direct comparison of the radiant flux from a specimen at a given temperature to that from a comparison standard.

Since any comparison standard, other than a blackbody furnace, that

is used for emittance determinations must be calibrated against a blackbody

furnace at each temperature of test, and even then may change with continued use, it is desirable to use a blackbody furnace as the comparison

standard

.

The total emissive power of a blackbody varies as the fourth power of

its absolute temperature. Thus even a small error in temperature measurement can lead to a large error in an emittance measurement. The emittance

of a given material, however, and particularly spectral emittance, usually

varies only slightly with small changes in temperature. The critical re- quirements with respect to temperature control in the determination of

emittance are (a) that the thermal gradients over the surface of the speci- men and comparison standard be minimized, and (b) that the specimen and

standard be kept at the same temperature within acceptable tolerance. Very

small temperature differences can be measured accurately by means of a differential thermocouple, while if the two temperatures are measured separately and the difference computed, the error in the difference may be much

larger. Thus it is desirable to use a differential thermocouple with suitable instrumentation to maintain the specimen and the comparison standard

at the same temperature.

The spectral emittance curve of a solid material heated to a temperature below its melting point does not show the sharp peaks and valleys that are characteristic of the emission and absorption curves of solutions and

gaseous materials. Hence prism monochromators with relatively wide slits

are suitable for use in spectral emittance determinations, in spite of

their rather poor wavelength resolution, because they pass relatively large

amounts of radiant flux for measurement over a wide spectral range. The

use of a variable-width slit is desirable so that in wavelength regions of

low radiant flux the amount passed can be increased by broadening the wavelength band accepted for measurement. Thus the available radiant flux in

the comparison beam can be maintained at a level commensurate with the

sensitivity of the detector.

WADC TR 59-510 Pt IV 8
VI. DEVELOPMENT OF EQUIPMENT FOR NORMAL SPECTRAL EMJTTANCE MEASUREMENTS

The general plan that was followed in developing equipment for determination of normal spectral emittance was to use a double-beam ratio-record

ing infrared spectrometer with a laboratory blackbody furnace and a heated

specimen as the respective sources for the two beams. With this arrangement the instrument will record directly the normal spectral emittance of

the specimen, if the following conditions are met within acceptable tolerances: 1) The temperature of the specimen must be the same as that of the

blackbody furnace; 2) the optical path length in the two beams must be

equal or, preferably, the instrument must operate in a non-absorbing atmosphere or a vacuum, in order to eliminate the effects of differential atmospheric absorption in the two beams; 3) front-surface mirror optics must be

used throughout, except for the prism, and equivalent optical elements must- be used in the two beams in order to reduce attenuation of the beams by absorption in the optical elements; 4) the source and field apertures of the

two beams must be equal in order to ensure that radiant flux in the two

beams compared by the apparatus will pertain to equal areas of the sources

and equal solid angles of emission, and 5) the response of the detectoramplifier system must vary linearly with the incident radiant flux.

Early in the investigation it became apparent that the conditions spec

ified under 2, 3 and 4 above were not being met within sufficiently close

tolerances to permit direct recording of normal spectral emittance to the

desired accuracy. It was necessary to use a second, or reference, laboratory blackbody furnace, identical to the first, or comparison blackbody

furnace, in order to correct for these errors.

A. Description of Spectrometer

The Perkin-Elmer Model 13 spectrometer used for the measurements is

equipped with a wavelength drive that provides automatic scanning of the

spectrum of radiant flux, and a slit servomechanism that automatically

opens and closes the slits to minimize the variations of radiant flux in

the comparison beam. Three prisms were available, 1) fused silica, to cover the spectral range of 0.25 to 3.5 microns, 2) sodium chloride to cover the spectral range 0.7 to 15 microns, and 3) cesium bromide, to cover

the spectral range of 15 to 38 microns. Several photomultiplier detectors were available for use in the spectral range of 0.25 to 1.0 micron, a lead

sulfide detector for use in the spectral range 1.0 to 2.0 microns, a vacuum

thermocouple with sodium chloride window for use in the spectral range 1 to

15 microns, and a vacuum thermocouple with cesium bromide window for use in

the spectral range 1 to 40 microns.

WADC TR 59-510
The source optics of the instrument were modified by incorporation of

an external optical system, which is the standard Perkin-Elmer transfer op°

tical system, used with the hohlraum ref lectrometer . Two 90 folds in a vertical plane were introduced in the specimen beam, to raise the axial ray

of the beam 9 inches above the optical plane of the spectrometer. The com”

parison blackbody furnace was mounted in a fixed position to act as the

source for the comparison beam, and the specimen furnace and reference

blackbody furnace were mounted side by side on a movable plate attached to

a slide in positions such that they could be brought alternately into position to serve as source for the specimen beam, by sliding the plate against

fixed stops on the slide. A sketch of the complete optical path is

shown in figure 1, and a photograph of the external optical system with

furnaces in place and cover removed is shown in figure 2.

Fig. 1 Sketch of the optical path in the modified spectroradiometer

.

It was found by experience that when the two blackbody furnaces were

used as sources for the respective beams of the spectrometer, deviations of

the recorded "100% curve" occurred at the wavelength intervals within which

there is significant absorption of padiant energy by water vapor and carbon

dioxide in the atmosphere. Such absorption should be identical in both

beams if the spectral distribution of flux and path lengths are identical.

However, the two beams are separated in time, passing through the monochromator alternately at a frequency of 13 cycles per second. Since the spectrum is being traversed continuously, one energy pulse is displaced relative to the other on the wavelength scale, by a very small amount. The effect of this displacement is negligible over most of the range, where the

slope of the energy-wavelength curve is not large. But at the wavelengths

near those of maximum absorption, the energy-wavelength curves become very

steep, and the slight spectral displacement of the successive energy pulses

can produce significant deviations in the ratios which are continuously re- corded by the instrument.

WADC TR 59-510 Pt IV IQ
WADC TR 59TM 510 Pt IV 11

Fig.

2

A

photograph

of

the

external

optical

system

of

the

spectroradiometer

.

The

comparison

blackbody

furnace

remains

in

position

to

act

as

source

for

the

specimen

beam.,

but

can

be

replaced

by

the

reference

blackbody

furnace

by

shifting

the

movable

table

on

the

slide.
In order to reduce the effects of absorption by atomospheric water

vapor and carbon dioxide, the entire external optical system of the normal

spectral emittance equipment, including the blackbody furnaces and specimen

furnace, was enclosed in a lucite box. Gas-tight connecting passages were

designed to join 1) the lucite box enclosing the external optics, 2) the

metal cover for the chopper assembly, 3) the metal cover for the combining

optics, and 4) the metal cover for the monochromator. Thus the entire

length of both optical paths in the instrument was enclosed in a single

system of interconnecting housings that was nearly gas-tight. Humidity in

the enclosure was monitored and recorded by means of a humidigraph which

records temperature and humidity. Immediately before a test the enclosure

was purged with "super-dry’* nitrogen, free from carbon dioxide, which was

fed into the enclosure through several inlets, at a slow, constant rate, so that the enclosure was maintained at a slight positive pressure relative to

the surrounding atmosphere. Tests were not started until the recorded humid*

ity was less than 5%.

B. Blackbody Furnace and Specimen Enclosure

Two small laboratory blackbody furnaces were designed and built.

Figure 3 is a sectional drawing of a furnace. The core was a casting of

80 nickel-20 chromium alloy 1 3/16 inches in diameter and 4 inches long.

The cavity was 3/4 inch in diameter and 3 3/8 inches deep, threaded with 13

threads to the inch. The threads were cast in place. The 80 nickel-20

chromium alloy oxidizes to produce a high-emittance surface in the cavity.

Fig. 3 Sectional drawing of a blackbody furnace.

WADC TR 59-510 Pt IV 12
The furnace was heated by means of a platinum-20% rhodium winding. There were two taps on the heating coil approximately one inch from each end.

Shunts across the taps and leads were used to reduce thermal gradients in

the cavity, as shown in figure 5. The aperture in the cavity was reduced

to a slit approximately 1/4 by 3/4 inches in size by means of a Nichrome

cover plate.

The temperature of the blackbody furnace was measured by means of a platinum, platinum- 10% rhodium thermocouple, the bare bead of which extended about 1/4 inch into the cavity from the rear. The thermocouple leads were insulated from the core by high-alumina refractory tubing, which was surrounded by a platinum tube that was grounded, in order to prevent pickup

by the thermocouple of spurious signals due to electrical leakage from the

winding

.

The effective emittance of the blackbody furnace, computed from the

Gouffe^ [5] equation, assuming that the interior of the cavity is at uniform temperature, and is a completely diffuse reflector, was better than

0.999. Both of these assumptions are known to be only approximations, so that the actual effective emittance was somewhat less than the computed

value. The thermocouple bead in the back of the cavity cannot be seen, even with an optical pyrometer, when the furnace is in operation, which in-,

dicates that the effective emittance is very high.

The specimens were strips of metal, 1/4 inch wide by 8 inches long, of

any convenient thickness in the range of approximately 0,010 to 0.050 inch.

They ware heated by passing a current through them. A sketch of the speci- men enclosure is shown in figure 4. The outer shell was water cooled, and

its inner surface was of a nickel - chromium -iron alloy that had been

threaded with a No. 80 thread and then oxidized in air at a temperature

above 1350 K for 6 hours to produce a surface having a reflectance of less

than 0.05 at the operating temperature of the water-cooled walls. The specimen was positioned off-center in the cylindrical enclosure, so that any

radiant flux specularly reflected from the walls would be reflected twice

before hitting the specimen.

The electrodes were of water-cooled copper, and were insulated from the

brass end caps of the furnace by means of bakelite sleeves. The lower electrode fitted loosely in the hole through the end cap to permit the specimen

to expand without buckling when heated. The specimen was viewed through a window about 3/4 by 1 inch in size. A viewing window insert reduced the

opening to about 1/4 by 3/4 inch.

Adjustable baffles above and below the viewing window were used to re- duce convection and the resulting temperature fluctuations and thermal gradients. Adjustable telescoping cylindrical platinum reflectors surrounded

the specimen at each end. These were used to reduce heat loss at the ends

of the specimen, and hence the thermal gradient along the specimen.

WADC TR 59-510 Pt IV 13
Fig. 4 Sketch of

the specimen

enclosure

.

C. Temperature Control Equipment

The power input to the comparison blackbody furnace was adjusted manually by means of an autotransformer. The heater winding of the furnace had

two taps, located approximately one inch from each end of the winding. Variable resistors were connected as shunts across the taps and from the taps

to the input leads, as indicated in the wiring diagram, figure 5. Adjustment of these resistors permitted variation of the power distribution along

the cavity of the furnace by means of which thermal gradients in the cavity

could be minimized. It was found by experience that the heat capacity of

the blackbody furnace was large enough to practically eliminate temperature

fluctuations due to momentary voltage fluctuations in the power supply. A

cold furnace could be brought to 1400°K and stabilized at that temperature

in about six hours, and only about 30 minutes was required to achieve stability after a temperature change of up to about 30 K. Normally the blackbody

furnaces were heated overnight before use.

WADC TR 59-310 Pt IV 14
\

-FURNACE WINDING

Fig. 5 Wiring diagram of power supply to comparison

blackbody furnace.

The power supply for the reference blackbody furnace was identical to

that shown in figure 5, except that when the temperature was to be con- trolled a saturable-core reactor was substituted for the autotransformer,

as is described below.

The temperature of the specimen (or reference blackbody furnace) was controlled to that of the comparison blackbody furnace, within narrow limits

by means of a differential thermocouple. One bead of the differential thermocouple was in the cavity of the comparison blackbody furnace, and the

other was attached to the back of the specimen, in the center of the are being viewed, as described later in this report. The signal from the di

ferential thermocouple was amplified by a d.c. amplifier and fed to a ce r zero recorder-controller. The output of the recorder-controller is prop

tional to the distance between the control pointer and the recorder pointer

on the scale, which is in turn proportional to the temperature difference

between blackbody furnace and specimen. The output of the recorder-control

ler was fed to a current -actuat ing-type controller, the output of which was

separated into three portions, each of which could be varied as desired

One portion was proportional to the input signal, one was proportional t. the first time derivative of the input signal, and one was proportional < the second time derivative of the input signal. The output of the curreiu

actuat ing-type control was fed to the coil of a saturable core reactor w.iri

varied the power input to the specimen. It was possible to reduce undershoot and overshoot of the controlled temperature by proper adjustment of

the three components in the output of the current-actuat ing-type control.

A block diagram of the temperature control equipment is shown in figure 6,

WADC TR 59-510 Pt IV 15

CO
LINE

BLACK BODY furnace

_jL

-

VARIABLF

RAN'.I ORMI H

CENTER- ZERO

RECORDER- CONTROLLER

LINE

Fig. 6 Block diagram of temperature control equipment.

The controller operates

from a signal produced

from a differential

thermocouple

.

With the described control equipment it has been possible to

temperature of a specimen as indicated by the welded thermocouple

within ± 1 K of that of the comparison blackbody furnace, and the

ture of the reference blackbody furnace to within ± 0.5°K of that

comparison blackbody furnace.

hold the

to well

temperaof the

VII. CALIBRATION OF EMITTANCE EQUIPMENT

A. Wavelength Calibration of Monochromator

A complete wavelength calibration was made of the spectrometer with

the fused silica and sodium chloride prisms, respectively, mounted in the

monochromator. In calibrating the equipment with the fused silica prism,

emission spectra of a helium arc and a mercury arc, and absorption spectra

of a didymium glass and a polystyrene film were recorded. The emission and

absorption peaks having known wavelengths were identified in the respective

curves, and for each peak the observed wavelength drum position at which

the peak occurred was plotted as a function of the known wavelength of the

peak r 6 ]. A total of 66 such points, at wavelengths in the range 0.24 to

2.2 microns, was plotted, and a smooth curve was drawn between the points

to produce a calibration curve.

1

1

W:\ur n; vj-'.hi n iv .
A similar procedure was followed in calibrating the equipment with the

sodium chloride prism mounted in the monochromator. In this case, the atmospheric absorption curve replaced the absorption curve for didymium

glass. A total of 52 points, at wavelengths from 0.4 to 15 microns, was plotted to produce the calibration curve.

B. Calibration for Linearity of Response

All of the work done with the spectrometer had been based on the as- sumption that the response of the instrument (the height of the recorded

emittance curve above the recorded "zero curve") was linear with (1) the

radiant flux (within the varying wavelength interval encompassed by the

exit slit) passing through the monochromator, when the instrument is operated in single-beam mode, or (2) the ratio of the fluxes (within the varying wavelength interval encompassed by the exit slit) in the respective

beams that pass through the monochromator when the instrument is operated

double-beam in ratio mode. This assumption had not been checked, and a confirmation of (1) and (2) above was considered desirable.

Linearity Calibration by Varying Slit Width

The entrance and exit slits of the monochromator open and close simultaneously, and both are controlled at the same width by the slit micrometer.

Because of this construction, when a true image of a source is formed at

the entrance slit of the monochromator, somewhat larger than the slit at

its maximum width, the radiant flux reaching the detector from the mono- chromator varies as the square of the slit width. This relationship was used to check the linearity of detector response when the instrument is

used single-beam in direct mode (item (1) above). A single blackbody

furnace, at 1400 K, was used as a source, and each series of measurements

was made at a number of central wavelengths throughout the sensitive range

of the thermocouple detector. Experimental results were in conformity with

the theoretical relationship. In every case, when the height of the re- corder curve was plotted against the square of the slit width, the points

obtained with the sodium chloride prism and thermocouple detector fell on a straight line intersecting the origin, within the error of measurement.

Similar measurements were also made at several wavelengths when the

spectrometer was operated with the fused silica prism and the lead sulfide

detector. Again experimental results were in conformity with the theoretical relationship.

When the spectrometer was used with the fused silica prism and 1P21 detector. appreciable deviations from the theoretical relationship were found

at first, but after careful realignment of the monochromator optics, all of

the points again fell on a straight line, within experimental error.

WADC TR 59-510 Pt IV 17
Calibrations with Sector-Disc Attenuator

A sector-disc attenuator for use in calibrating the normal spectral

emittance equipment was designed and built. The attenuator consists of a variable speed motor, 0 to 4000 rpm, with an attenuator disc mounted on its

shaft

Five interchangeable attenuator discs were prepared, having nominal

transmissions of 75, 50, 25, 12.5 and 5.0 percent, respectively. The discs were machined from sheet aluminum 0.065 inch thick. The 57> disc is 10

inches in diameter, and has four equally spaced radial notches, each 4.5

wide, extending inward from the rim for 3 inches. The other discs are 9

inches in diameter, and have eight notches each, extending inward from the

rim for 2 1/2 inches. The notches are 33 3/4° wide in the 75% disc, 22 1/2

wide for the 507. disc, 11 1/4° wide for the 25% disc, and 5 5/8° wide for

the 12.5% disc

The attenuator is normally operated at about 1300 rpm, and the direction of rotation is opposite to that of the chopper of the spectrometer.

At this speed the beam is interrupted at a frequency of more than 85 cycles

per second by the 5% disc, and more than 170 cycles per second by the other

discs. The chopper in the spectrometer interrupts the beam at a frequency

of 13 cycles per second. No coupling has been observed between the attenuator and chopper frequencies.

The attenuator discs were calibrated in the Engineering Metrology

Section of NBS by measuring the angular width of the notches and blades on each disc, at two positions corresponding to the radial positions at which

the top and bottom, respectively, of the interrupted beam strike the discs

when in use. The unobstructed area of the disc between the two circles was computed as a percentage of the total area between the circles, with the

results shown below:

The measured values were assigned to the respective sector-disc attenuators

Nominal Transmittance

%

Measured Unobstructed Area

%

75

50

25

75.10 ± 0.02

50.00 ± 0.02

25.28 ± 0.14

12.73 ± 0.14

5.07 ± 0.03

12.5

5

WADC TR 59-510 Pt IV 18
\

In the next group of experiments, made for additional check of item

(1) above, the sector-disc attenuator was introduced into the beam near

the blackbody furnace. Each series of measurements was made at a single

wavelength, a single slit width, and a single gain setting. In each

case the gain was adjusted to give a reading of slightly less than 100

units on the strip chart without the attenuator. The attenuator was then

introduced into the. beam, and operated with each of the discs in turn.

The height of the recorder curve was plotted against the previously measured fraction of the beam passed by the attenuator. In every case the

points fell on a straight line passing through the origin, indicating

linear detector response for every combination of slit width and wavelength

tested, with both the sodium chloride and fused silica prisms, and with

the thermocouple, as well as the lead sulfide and photomultiplier detectors .

In the preceding experiments for which the instrument was being used

in direct mode, with single beam, the height of the recorder curve varied

linearly with the signal produced by the detector. This signal was proportional to the radiant flux passing through the monochromator. Normally,

however, the instrument is used in ratio mode, with double beam. In this case the height of the recorder curve should vary linearly with the ratio

of the two signals produced by the detector when it is receiving flux alternately from the respective beams.

In order to check item (2) above, the two blackbody furnaces, con- trolled very closely to the same temperature (about 1400 K), were used as sources for the two beams. The instrument was adjusted so that the

"100% curve" would actually fall between 90 and 100 on the chart, after

which such a curve was obtained over the wavelength range of interest. The

sector-disc attenuator was then introduced into the specimen beam near the

blackbody furnace, and operated with each of the discs in turn, to obtain

"75%, 50%, 257o, 12.5% and 5% curves", each over the wavelength range of interest. The heights of the respective curves were then measured at 100 se- lected wavelengths, and the height of each curve above the experimentally

obtained zero for the pertinent wavelength was plotted against the percentage of the flux in the specimen beam that was passed by the attenuator. In

every case the points fell on a straight line intersecting the origin,

within the error of measurement. No significant departures from linearity

of response were detected for any combination of prism and detector, at any

point within the wavelength range at which they could be used.

The data for the thermocouple detector and sodium chloride prism are shown in figure 7. In this case, the "apparent emittance" of the combination of the reference blackbody furnace and each attenuator disc is plotted

as a function of wavelength. Every value of apparent emittance was within

± 0.01 of the measured transmittance of the respective disc.

WADC TR 59-510 Pt IV 19
80

1 1 1

1 1 —i—i r~—i—i r - 75 % ATTENUATOR /

~1 1

70 - -

60 - -50% ATTENUATOR -

50

40 -

30 /- 25 % ATTENUATOR X

-

20

s—12.5 % ATTENUATOR -

10 y

- 5 % ATTENUATOR —

1 L 1 J 1 . 1 1 1 1 1 1 1 2 3 4 5 6 7 8 9 10 II 12 WAVELENGTH IN MICRONS

13 14 1!

Fig. 7 Spectral "emittance" of the combination of

the reference blackbody furnace and sectordisc attenuator when using the 757,, 50%,

257,, 12.5% and 57, attenuator discs. Data

are for the spectrometer with the sodium

chloride prism and thermocouple detector.

VIII. EXPERIMENTAL PROCEDURE

It was found by experience that the H iOQ% curve", obtained when the two

blackbody furnaces at the same temperature served as sources for the re- spective beams of the spectrometer, deviated appreciably from flatness.

These deviations may be due to either (1) variations in spectral absorption

or other losses along the respective optical paths from source to detector,

or (2) variations in spectral sensitivity of the detector to radiant flux

from the two beams. There are two more mirrors in the specimen beam than

in the comparison beam, as is shown in figure 1. The two beams follow different paths from the sources to the spherical mirror in the combining optics, and are reflected by different mirrors in this portion of the path.

From the spherical mirror in the combining optics to the detector, the two

beams follow the same general path and are reflected by the same mirrors.

However, the paths are not identical, and the beams are reflected by

slightly different areas of each mirror, and are transmitted by different

areas of the prism and the detector window. These differences could ac- count for spectral differences in losses in the two beams, due to absorption, and to scattering, for instance by dust particles on the mirrors.

The two beams are also focused on slightly different areas of the sensitive

surface of the detector. No detector is completely black, and variations

in spectral absorptance over the sensitive surface of the detector could be

responsible for part of the observed effect.

WADC TR 59-510 Pt IV 20
It was also found by experience that the zero curve, obtained when . specimen beam was blocked near the specimen furnace, deviated from flat- ness. These deviations are undoubtedly due to stray radiation in the mono

chromator, which produces a spurious signal when there is in fact no radiant energy being supplied by the specimen.

A test procedure was developed to correct for the errors which result

in the deviations of the "100% Line" and "zero Line" referred to above.

The procedure is as follows:

(1) The two blackbody furnaces are placed in position to act as sources for the respective beams of the spectrometer, and are brought to

the same temperature. The "Full Scale" control of the spectrometer is adjusted to bring the "100%, Line" to a position between 90 and 100 on the

chart. The specimen beam is blocked, and the "Ratio Zero" control on the

spectrometer is adjusted to bring the "Zero Line" to a position between 1 and 3 on the chart. The specimen beam is unblocked, and the position of

the "1007o Line" is checked. These instrument settings then remain fixed

throughout the emittance determinations on the specimen being tested,

(2) The 100% Line", over the wavelength range of interest, is obtained by automatic recording on the strip chart, after which the chart pa

per is rerolled.

Fig. 8 A section of recorde

chart, showing segments of a "1007o Lin

"Specimen Line" and

'Zero Line . " The

normal spectral emit

tance at each wave- length is the rati. aVaebb

•

WADC TR 59-510 Pt IV 21
(3) The specimen beam is blocked near the source, and the Zero Line

is similarly obtained over the wavelength range of interest, after which

the chart paper is again rerolled.

(4) The specimen enclosure is next substituted for the reference

blackbody furnace, in position to act as source for the specimen beam of

the spectrometer. The temperature of the specimen is brought to and held

at the temperature of the comparison blackbody furnace. The specimen beam

is unblocked, and the "Specimen Line" is obtained over the wavelength range

of interest. A section of the completed recorder chart is shown in figure

8 .

The heights of the respective curves are measured at preselected posttions of the wavelength drum (corresponding to known wavelengths), and the

normal spectral emittance is computed for each such wavelength. If Z^ is

the height of the "Zero Line", the height of the "Specimen Line", and

the height of the "100% Line", at some wavelength X, the normal spectral

emittance, , is given by

E = (7)

Values of E^ are computed for each of 100 wavelengths in the range of

1 to 15 microns, and E^ is plotted as a function of wavelength. A curve is

drawn through the plotted points to represent the spectral emittance curve

of the specimen.

IX. SELECTION AND CALIBRATION OF WORKING STANDARDS

The selection and calibration of suitable working standards of normal

spectral emittance, to be used for the comparison of results in several

different laboratories, was one of the objectives of this program.

Working standards having high, intermediate and low emittance, re- spectively, were desired. In addition to having the desired normal spectral emittances, the working standards, to be useful, should be stable on heating in air at temperatures up to the maximum temperature at which they

can be used, for times of several hundred hours. They should also be of a material that is not easily damaged in use. In order to be suitable for

measurement with the equipment described in this report, the specimens are required to have electrical properties that will permit them to be heated

by passing a current through them.

Specimens machined from sheet material of uniform thickness, three of

each material in each of several different sizes and shapes were desired,

suitable for measurement in the equipment used by different laboratories,

as follows:

WADC TR 59-510 Pt IV 22
Strips, 1/4 x 8, 3/4 x 10 and 1 x 10 inches in size

Squares, 2x2 inches in size

Discs, 7/8, 1, 1 1/8 and 1 1/4 inches in diameter.

Because it was not possible to measure the normal spectral emittance

of specimens of all of the above shapes and sizes with the equipment described in this report, it was decided that the measurements would be con- fined to six 1/4 x 8 inch strip specimens of each material. All of the

specimens of a single material were cut from a single sheet of metal, and

all were treated as nearly alike as possible during surface preparation.

After an extensive series of tests, the following materials were se- lected on the basis of the above criteria, for use in preparing the working

standards

:

1. For standards of low normal spectral emittance, 0.035-inch plati- num sheet that had been polished and then annealed.

2. For standards of intermediate normal spectral emittance, 0.043-

inch Kanthal sheet that had been sandblasted and then oxidized.

3. For standards of high normal spectral emittance, 0.053-inch

Inconel sheet that had been sandblasted and then oxidized.

The tests indicated that specimens of these three materials, when prepared as outlined below, were stable in total hemispherical emittance to

better than 0.02 on heating in air at the maximum temperature at which they were calibrated for periods of 200 hours.

A. Platinum Working Standards

The platinum specimens were received from the fabricator as 0.035-inch

sheet, six l/4-x-8-inch strips and three each in the following shapes and

sizes: discs 7/8, 1, 1 1/8 and 1 1/4 inches in diameter. 2-x-2-inch squares,

and strips 1 x 10 and 3/4 x 10 inches in size. It had been specified that

the specimens were to be supplied with highly polished surfaces. The finish actually supplied was not as smooth as had been desired, but it was decided to use the finish supplied, rather than send the specimens back for

reworking. A 1/8- inch hole was drilled in one end of each strip specimen,

to facilitate hanging during annealing.

Each specimen was washed in hot tap water to which a commercial detergent had been added, rinsed in running hot tap water, then in distilled

water, and finally in ethyl alcohol. Rubber surgical gloves were worn at

all times while handling the specimens, and the central portion, observed

for emittance determinations, was not touched after cleaning. The speci- mens were dried in air and placed in a closed container, supported by the

ends or edges only, for storage prior to annealing.

WADC TR 59-510 Pt IV 23
All specimens were annealed in an electrically-heated, silicon-carbideelement furnace. The strip specimens were hung by means of platinum hooks

suspended from aluminum oxide rods in the furnace; the square and disc specimens were supported by the edges only on ceramic forms resting on a flat

ceramic slab. All of the specimens were then enclosed in a ceramic muffle.

Starting with a cold furnace, the temperature of the furnace was raised to

1523°K (125G°C) over a period of six hours, and held at that temperature

for one hour. The power was then turned off, and the specimens were allowed

to cool in the furnace, which required two days.

The specimens were removed from the furnace by means of cleaned platinum-tipped tongs and were placed in individual plastic holders, in which

they were supported only by the ends or edges. Each plastic holder, con- taining a specimen, was then placed in an individual cardboard box, to protect the specimen from contamination.

The six 1/4-x- 8-inch strips were prepared for measurement by welding a platinum-platinum, 107o rhodium thermocouple to each specimen. A shallow

groove was scratched in each specimen, normal to its axis and located at the

mid- length. The 10-mil thermocouple wires were separately welded to the

specimen by means of a condenser-discharge type of electronic spot welder.

Each wire was laid in the shallow groove to position it for welding, and the

welding operation was observed through a low-power microscope.

Precautions were taken at all times to avoid contamination of the specimens. They were handled as little as possible, and when handling was un- avoidable the use of rubber gloves was continued, and even then the center

portion of the specimen was not touched.

Three sets o:f curves

Qwere made for each strip specimen at each of three

temperatures, 800 K, 1100 K, and 1400 K. Each set of curves consisted of

(1) a "100% curve", obtained when the two blackbody furnaces at the test

temperature were the sources for the respective beams, (2) a "zero curve",

obtained when the specimen beam was blocked near the specimen furnace, and

(3) a "specimen curve", obtained with the comparison blackbody at the test

temperature as one source and the specimen at the same temperature as the

other. Each curve was recorded over the range of wavelength drum settings

corresponding to a wavelength range of approximately 1.0 to 15.0 microns.

The normal spectral emittance was computed at wavelengths approximately uniformly spaced, from 1 to 15 microns.

WADC TR 59-510 Pt IV 24
The 18 values (3 each on 6 specimens) at each temperature and wavelength drum setting were tabulated, and the following values were computed:

(1) E, the arithmetic average of the 18 measured values, (2) <j the total

standard deviation-^ of the 18 values about the average of the 18 values,

(3) e, the 95% confidence error of E, (4) am , the average of six standard

deviations, each computed from the three measured values on one of the

six specimens, and (5) as , the standard deviation of the six average values

one for each of the six specimens, about the grand average for all six.

The values for platinum at the respective temperatures are given in Table I

1 T I I

1 T

— oo

°

° o

PLATINUM AT 800°K- MEAN. OF 3 DETERMINATIONS ON EACH OF 6 SPECIMENS

,0CD%,'^oooo00000 o

0 q=ooq>,

2 -

95 % -CONFIDENCE ERRORS OF ABOVE MEAN VALUES

O o Q Qpoooopo QOOOCOOOOOqxP^CPCSCCgPO OOOOOQpOoc 6 7 8 9 10 WAVELENGTH IN MICRONS

I I 12 13 14

Fig. 9 Normal spectral emittance at 800°K of platinum

working standards. The points on the upper curve represent averages of 18 measured values, three

each on six specimens. The points on the lower curve represent the 95%. confidence errors of the

average values in the upper curve.

1_/ All standard deviations computed in this study are precisely defined as "estimates of the standard deviation of the parent population from which

the measurements were drawn." This quantity is assigned the symbol ct, to

distinguish it from the root-mean-square standard deviation, S.D., of individual values from the mean of a given sample.

WADC TR 59-510 Pt IV 25
The average normal spectral emittance, E, of the six plat inurn bpe^. i- mens is plotted as a function of wavelength for readings at 800 K m figure

9, at 1100°K in figure 10 and at 1400°K in figure 11. The 95% confidence

errors—^ associated with the plotted average emittance values are aiso

plotted in the same figures.

Fig. 10 Normal spectral emittance at 1100°K of platinum

working standards. The points on the upper curve

represent averages of 18 measured values, three

each on six specimens. The points on the lower curve represent the 95% confidence errors of the

average values in the upper curve.

\_j The 95% confidence error lias the following statistical significance.

If the measurements were repeated a large number of times, say 1000 times

and the average and 957o confidence error was computed for each group of

18 measurements, then the limits of the group average ± the 95% confidence- error would bracket the overall average of the 1000 groups of measurements

about 19 times out of 20.

WADC TR 59-510 Pt IV 26
26

I I I I I

PLATINUM AT 1400 °K - MEAN OF 3 DETERMINATIONS —

ON EACH OF 6 SPECIMANS.

o0 o° 00°lP °o,

95% CONFIDENCE ERRORS OF ABOVE MEAN VALUES __

i^r^oooiooooh°oHocoHcaxlca4tf^i00oo4^OQf ^

2 3 4 5 6 7 8 9 10 II 12 13 14 15 WAVE LENGTH IN MICRONS

Fig. 11 Normal spectral emittance at 1400°K of platinum

working standards. The points on the upper curve represent averages of 18 measured values, three

each on six specimens. The points on the lower curve represent the 95% confidence errors of the

average values in the upper curve.

It is apparent that the normal spectral emittance of the platinum

specimens at each wavelength increases with an increase in temperature.

The average values for emittance X100 at the 100 wavelengths were 7.49 at

80Q°K, 9«.69 at 1100°K and 11.60 at 1400°K. This effect would be predicted

from the Hagen-Rubens equation on the basis of the known variation in elec

trical resistivity of platinum with temperature.

A pronounced maximum in the spectral emittance curve occurs at a wave

length of about 1.8 microns at 800®K. This peak shifts to shorter wavelengths with an increase .in temperature. This maximum is attributed to

resonance of bound electrons, as discussed in more detail in a later sec- tion of this report.

WADC TR 59-510 Pt IV 27
A second, less prominent, maximum occurred at a wavelength of about

9.5 microns. In this case the wavelength of the peak did not change appreciably with temperature, but the peak became less prominent with increasing

temperature. This peak has been observed by other workers in the field- f 7]

There is evidence in the curves at 1100 and 1400 K of a third maximum at a wavelength of 15 microns or beyond. The observed increasing upward sweep,

with increasing temperature, of the spectral emittance curve near 15 microns

could be caused by a maximum beyond 15 microns that moves to shorter wavelengths at increasing temperatures, or to a peak at or near 15 microns that

does not change wavelength, but becomes more prominent with increasing

temperature

.

The peaks at about 9.5 microns and at 15 microns or beyond are probably caused by resonance effects, but the frequencies are below those that

would be expected for bound electrons. The fact that the peaks are found

on heating in air, but are not reported by other investigators who heated

samples in vacuum, suggests that they may be due to an impurity, such as an adsorbed layer of gas on the surface of the specimen.

The value CTm (the average of the six standard deviations, each computed

from the three measured emittance values on one of the six specimens) is a measure of the overall reproducibility of the test procedure, or the precision of measurement. The average value of am at the 100 wavelengths at

800°K was 0.35, at 1100°K, 0.45, and at 1400°K, 0.39, expressed as emittance

X100. Thus the overall precision of a single measurement of normal spectral emittance of platinum is better than 0.005 in emittance, expressed as a standard deviation.

The value a£ (the standard deviation of the six average values, one for

each of the six specimens, about the grand average for all six) is a measure

of the differences in emittance of the specimens that were measured. The

average value of rrs at the 100 wavelengths at 800 K was 1.22, at 1100 °K,

1.28, and at 1400°K was 1.19, in units of emittance X100. A comparison of

the average values of as and am at each temperature indicates that the

measured differences between specimens are real. Such differences were

regularly observed, but could not occur through chance fluctuations in the error of measurement as frequently as one time in 10,000.

In order to show any trend of am

and as with wavelength, the moving

averages at 5 adjacent wavelengths were computed and plotted as a function

of the central wavelength to produce the curves in figure 12 at 800°K

figure 13 at 1100°K and figure 14 at 1400°K. There appears to be significant

variation in as with wavelength at each temperature. The variation in am with wavelength is much smaller. The value of am

is smaller than the cor- responding value of as at each wavelength at each temperature.

WADC TR 59-510 Pt IV 28
STANDARD

DEVIATION

OF

EMITTANCE

VALUES,

X

IOO

\

2.5 H I 1 T 1 I i I

'

I r“ 1 "T I i .STANDARD DEVIATIONS OF EMITTANCE DETERMINATIONS ON PLATINUM AT 800 ’K

2 0

DUE TO DIFFERENCES 8ETWEEN SPECIMENS

1.5

«

* O®®,, *

1.0 —

0.5 — DUE TO ERROR OF MEASUREMENT

R^jxjo ° °°° °°° 0o 00ooocPoc»c, oo°q. -o':° c<V0

^cPC'-'-h , _ ^ ^OdXQx^f° C0oO°

O ^OCbrf.cP W

_J 1 L_ 1 ...A J L J L.

2 3 4 5 6 7 8 9 10 II 12 13 14 15 WAVELENGTH IN MICRONS

Fig. 12 Spectral distribution of two categories of standard

deviations, each computed from 18 measured omittance

values obtained at 800 K, three each on six platinum

working standards. The tipper curve represents

standard deviations dtie co real differences in emittance between specimens, identified as rr s in the

text. The lower curve represents standard deviations due to random errQr, identified as am in the

text. In both curves each point represents the

moving average of five adjacent values.

WADC TR 59-510 Pt IV 29
STANDARD

DEVIATION

OF

EMITTANCE

VALUES,

X

IOO 2.1

1.9

1.7

i t

1 1 — t r i i \" t i r ' r* r~ STANDARD DEVIATIONS OF EMITTANCE DETERMINATIONS ON PLATINUM AT 1100 “K

1.5

1.3

l.l

09

07

0.5

C.3|-

0.

DUE TO DIFFERENCES

BETWEEN SPECIMENS

J

oo°ooo axpo'^0c«R» ,

* •*. . . N *

oo °oooo0o

DUE TO ERROR OF MEASUREMENT

J L L

I J 1.. 6 7

.1 L.

8 9

:,e0~co0

_l10

j u O, n

°Oo

ocO°^'3CCOO

<_^

.1 L I

II 12 I

***">'* J

14 15 WAVELENGTH IN MICRONS

Fig. 13 Spectral distribution of two categories of standard

deviations, each computed from 18 measured emittance

values obtained at 1100°K, three each on six platinum

working standards. The upper curve represents

standard deviations due to real differences in emittance between specimens, identified as rrg in the

text. The lower curve represents standard deviations due to random error, identified as ctTM in the

text. In both curves each point represents the

moving average of five adjacent values.

WADC TR 59-510 Pt IV 30
Fig. 14 Spectral distribution of two categories of standard

deviations, each computed from 18 measured emittance

values obtained at 1400 K, three each on six platinum

working standards. The upper curve represents

standard deviations due to real differences in emittance between specimens, identified as as in the

text. The lower curve represents standard deviations due to random error, identified as rrm

in the

text. In both curves each point represents the

moving average of five adjacent values.

B. Oxidized Kanthal Working Standards

Specimens of the sizes and shapes referred to above were machined from

0.043-inch Kanthal sheet, marked for identification, and then cleaned with

acetone to remove any oil or grease from the machining operation. They were

sandblasted with 60-mesh fused alumina grit at an air pressure of approximately 70 psi. The sandblasted specimens were cleaned ultrasonically in

acetone, passivated for one minute in 10% nitric acid at 316°K (43°C),

rinsed in distilled water and then in freshly distilled acetone. The

cleaned specimens were subjected to a minimum of handling. When handling

was unavoidable, surgical rubber gloves were worn to eliminate fingerprints,

and the specimens were touched only by the ends or edges. The strip speci- mens were suspended from a metal rack by means of oxidation-resistant metal

hooks, and the rack was inserted into a cold furnace. The disc specimens

were supported by the edges only on special ceramic supports placed on the

hearth of the furnace. The 2 x 2-inch square specimens were also supported

WADC TR 59-510 Pt IV 31
by the special ceramic supports, which made line contact with the^ specimen

in a 1 3/4-inch diameter circle. The furnace was brought to 1340 K and held

at that temperature for 400 hours, after which the power was cut off, and

the specimens were allowed to cool in the furnace.

The specimens were removed from the furnace by means of cleaned stainless-steel tongs, and were placed in individual plastic holders, in which

they were supported by the ends or edges. Each plastic holder, containing a specimen, was then placed in an individual cardboard box, to protect the

specimen from contamination.

The six 1/4 x 8-inch strips were prepared for measurement by welding a platinum-platinum 10% rhodium thermocouple to each specimen. The oxide layer was removed in a narrow strip and a shallow groove was scratched in each

specimen near its mid-length and normal to its axis. The oxide was also re- moved by grinding for a distance of approximately one inch at each end, to ensure good electrical contact with the electrodes. The thermocouples were

welded by means of a condenser-discharge type of electronic spot welder, as described for the platinum specimens. Surgical rubber gloves were worn at

all times while handling the specimens, and care was taken to prevent con- tamination of the center four inches of each specimen.

The normal spectral emittance of each of the six^pecimens^was measured

three times at each of three temperatures, 800°, 1100 and 1300 K, and the

data were reduced and analyzed statistically, as is described in more detail

for the platinum specimen.

The values at each wavelength and temperature are given in Table II for

E, at, e, rrin and crs , as previously defined.

The normal spectral emittance, E, is plotted as a function of wavelength for measurements at 800°K in figure 15, 1100°K in figure 16 and 1300°K

in figure 17. The 9 5% confidence errors associated with the plotted emittances are also plotted in the same figures. Again the emittance increased

at all wavelengths with an increase in temperature. The average values at

the 100 wavelengths are 60.7 at 800°K, 65.2 at 1100°K and 66.9 at 1300°K

expressed as emittance X100.

There is no pronounced maximum or minimum in the spectral emittance

curve. Two broad maxima occur at about 1.25 and 11 microns, respectively,

and there is a shallow minimum at about 7 microns. The oxidized Kanthal

specimens are comprised of a transmitting oxide layer over a rough metal

substrate. The thickness of the oxide layer is such that on a polished substrate, interference effects due to multiple reflections within the layer

produce maxima at several wavelengths in the 1 to 15 micron range. Such

effects do not appear with the sandblasted substrate.

WADC TR 59-510 Pt IV 32
100

90 o

- 80 X

UJo 70 <

h

I- 60

u 40

UJ 30

"t i i i f i i t r~

OXIDIZED KANTHAL AT 800 °K

•Ad r

T ' 1 1 T"

3 °0 °oooot P°

CO°OocP;y„. 0

< ,°v

SojjrC- “

MEAN OF THREE DETERMINATIONS ON EACH OF SIX SPECIMENS

20

10 95 % CONFIDENCE ERRORS OF ABOVE MEAN VALUES

logaptb orOofcooor.loooocA-xt^.rrPcQjajjrrcxn diPOjcipLooocciriOOO.ocbaOQ-CiJr.ccc> oJuPPTP^MPCcra^D_

I 2 3 4 5 6 7 8 9 10 II 12 13 14 15 WAVELENGTH, MICRONS

Fig. 15 Normal spectral emittance at 300 K of oxidized

Kanthal working standards. The points in the

upper curve represent averages of 18 measured

values, three each on six specimens. The points

in the lower curve represent the 95% confidence

errors of the average values in the upper curve.

The average

ovalues for the gtandard deviation crm

for the 100 wavelength

were 0.53 at 800°K, 0.85 at 1100 K and 0.70 at 1300°K, expressed in units

of emittance X100. Thus the overall precision of measurement, aspressed as

a standard deviation, is better than 0.009 in emittance. The corresponding

average values for as were 2.80 at 800°K, 3.62 at 1100°K and 4.01 at 13Q0~K.

This indicates that the differences in emittance between specimens of oxi=

dized Kanthal were more than twice as great as the corresponding differences

with the platinum specimens. Again the differences are real, and could not occur due to chance fluctuations of the error of measurement as frequently

as one time in 10,000.

The moving averages of a and <r at five adjacent wavelength were com- puted and plotted as a function of the central wavelength to produtce the curves shown in figure 18 for values at 800°K, figure 19 at 1100 K and

figure 20 at 1300°K. There appears to be significant fluctuations of cr s with wavelength at each temperature. The variations of crm

with wrvelength

are much smaller.

WADC TR 59-510 Pt IV 33
NORMAL

SPECTRAL

EMITTANCE

X

IOO

Fig. 16 Normal spectral emittance at 1100°K of oxidized

Kanthal working standards. The points in the

upper curve represent averages of 18 measured

values, three each on six specimens. The points

in the lower curve represent the 95% confidence

errors of the average values in the upper curve.

WADC TR 59-510 Pt IV 34
NORMAL

SPECTRAL

EM

IT

TAN

CE

X

IOO

Fig. 17 Normal spectral emittance at 1300°K of oxidized

Kanthal working standards . The points in the

upper curve represent averages of 18 measured

values, three each on six specimens. The points

in the lower curve represent the 95% confidence

errors of the average values in the upper curve.

WADC TR 59-510 Pt IV 35
STANDARD

DEVIATION

OF

EMITTANCE

MEASUREMENTS

X

IOO T

5.5

5.0

4.5

40

3.5

3.0

2.5

2.0

1.5

1.0

0.5

0

i r i—

r

OXIDIZED KANTHAL AT 800 *K

o

-

DUE TO DIFFERENCES BETWEEN SPECIMENS

O

0o

o

o

O O Oo

O Q & o

0

o

cP

°cP ° 0 °0 0

CCD

DUE TO RANDOM ERROR OF MEASUREMENTS

bo© o

2

o°ooo ®

0o o0OO0^O<,0C^«*^^

.1 . J __1 L L J l__f _l L 1 1 L

3 4 5 6 7 8 9 10 II 12 13 14 15 WAVELENGTH, MICRONS

Fig. 18 Spectral distribution of two categories of standard deviations, each computed from 18 measured

emittance values obtained at 800 K, three each on six oxidized Kanthal working standards. The upper

curve represents standard deviations due to real

differences in emittance between specimens, identified as <7 in the text. The lower curve represents standard deviations due to random error,

identified as <j in the text. In both curves

each point represents the moving average of five

adjacent values.

WADC 59-510 Pt IV 36
STANDARD

DEVIATIONS

OF

EMITTANCE

MEASUREMENTS

X

IOO

Fig. 19 Spectral distribution of two categories of standard deviations, each computed from 18 measured

emittance values obtained at 1100 K, three each

o«n six oxidized Kanthal working Standards. The

upper curve represents standard deviations due to

real differences in emittance between specimens,

identified as as in the text. The lower curve represents standard deviations due to random

error, identified as in the text. In both

curves each point represents the moving average

of five adjacent values.

WADC TR 59-510 Pt IV 37
STANDARD

DEVIATION

OF

EMITTANCE

MEASUREMENTS

X

IOO

Fig. 20 Spectral distribution of two categories of stand

ard deviations, each computed from 18 measured

emittance values obtained at 1300 K, three each

on six oxidized Kanthal working standards. The

upper curve represents standard deviations due t real differences in emittance between specimens,

identified as crs in the text. The lower curve represents standard deviations due to random

error, identified as in the text , In both

curves each point represents the moving average

of five adjacent values.

W&DC TR 59-510 Pt XV 38
C. Oxidized Inconel Working Standards

Specimens of the same sizes and shapes referred to above were machined

from 0.053-in. Inconel sheet, and were cleaned and sandblasted as described

above for the Kanthal specimens. The cleaned specimens were placed in a cold furnace, following the procedure previously described. The temperature of the furnace was brought to 1340 K (1067 C) and held for 24 hours,

then dropped to 1100 K (827°C) and held for an additional 24 hours. The

specimens were then allowed to cool in the furnace.

The normal spectral emittance of the six 1/4 x 8-in. specimens was

measured, following the procedure described above for the oxidized Kanthal

specimens, and the data were reduced and analyzed statistically as before.

The values at each wavelength and temperature are given in Table III for E, a , e, ry and rr , as previously defined,

t m s

’ J

The normal spectral emittance, E, is plotted as a

Q

function of wave- length for measurements at 800 K in- figure 21, at 1100 K in figure 22 and

at 1300 K in figure 23. The 95% confidence errors associated with the

WAVELENGTH, MICRONS

O

Fig. 21 Normal spectral emittance at 800 K of oxidized

Inconel working standards. The points in the upper

curve represent averages of 18 measured values,

three each on six specimens. The points in the

lower curve represent the 957, confidence errors of

the average values in the upper curve.

WADC TR 59-510 Pt IV 39
plotted values are also included in the same figure. Again emittance increased with an increase in temperature, at all wavelengths. The average

values at the 100 wavelengths were 80.3 at 800 K, 83.2 at 1100 K and 84.9

at 1300 K, expressed as emittance X100. The spectral emittance curve is

relatively flat, with a small maximum at about 1.4 microns and a second very

broad maximum at about 13.5 microns. The oxide layer on the Inconel speci- men was thick enough to be opaque. The oxide layer is a complex mixture of

the oxides of nickel, chromium and iron, including some spinels, for which

it would be very difficult to predict the occurrence of emission and absorption peaks

.

o Fig. 22 Normal spectral emittance at 1100 K of oxidized

Inconel working standards. The points in the upper

curve represent averages of 18 measured values,

three each on six specimens. The points in the

lower curve represent the 957, confidence errors of

the average values in the upper curve.

The average values for the standard deviations am

for the 100 wavelengths were 0.74 at 800°K. 0.74 at 1100°K and 0.89 at 1300°K. expressed

in units of emittance X100. Thus the overall precision of measurement,

expressed as a standard deviation, is better than 0.009 in emittance.

The corresponding average values for ag were 4.73 at 800°K, 4.56 at HOO^K

and 3.88 at 1300 K, again expressed in units of emittance X100. The differences are real, and could not occur due to chance fluctuations in the error

of measurement as frequently as one time in 10,000.

WADC TR 59-510 40
The moving averages of rrm

and as at five adjacent wavelengths were com- puted and plotted as a function of the central wavelength to produce the' curves shown above in figure 24 for values at 800 K, 25 at 1100°K and 26 at

1300°K. There appears to be significant fluctuation of as with wavelength

at each temperature. The fluctuations of rrm

with wavelength are much

smaller

.

Fig. 23 Normal spectral emittance at 1300 K of oxidized

Inconel working standards. The points in the upper curve represent averages of 18 measured values,

three each on six specimens. The points in the

lower curve represent the 95% confidence errors of

the average values in the upper curve.

WADC TR 59-510 Pt IV 41
STANDARD

DEVIATION

OF

EMITTANCE

MEASUREMENTS

X

IOO

WAVELENGTH IN MICRONS

Fig. 24 Spectral distribution of two categories of standard

deviations, each computed from 18 measured emittance

values obtained at 800 K, three each on six oxidized

Inconel working standards. The upper curve represents standard deviations due to real differences in

emittance between specimens, identified as cs in the

text. The lower curve represents standard deviations

due to random error, identified as in the text.

In both curves each point represents the moving average of five adjacent values.

WADC TR 59-510 Pt IV 42
STANDARD

DEVIATION

OF

EMITTANCE

MEASUREMENTS

X

IOO 10 r

9 j8

:U

7

[

6 !~

•

i 5 -

4

-

3 r

r i i ' r

• "r—i i

r~

OXIDIZED INCONEL AT 1100 °K

°o°o r

DUE TO DIFFERENCES BETWEEN SPECIMENS

oocoo^Sh^ ...

-I

osnfcb- °OD( ,'

. , o°

J J. 1 2 3 4

DUE TO RANDOM t

xfc

Of MEASUREMENT

cP'-‘

i ! I i ! i 5 6 7 8 9 10 II WAV EL l- NOTH IN MICRONS

12 13 14 i;

Fig. 25 Spectral distribution of two categories of standard

deviations, each computed from 18 measured emittance

values obtained at 1100 K, three each on six oxidized

Inconel working standards. The upper curve represents standard deviations due to real differences in

emittance between spec J mens, identified as - in the

text. The lower curve represents standard deviations

due to random error, identified as -

IT] in the text.

In both curves each point represents the moving aver- age of five adjacent values.

WA.DC TR 59-510 Pt IV 43
o2 10 wh

2

%

D

v><

LLl 5wo

2

<

o 3 <

u 2 o

I

WAVELENGTH IN MICRONS

Fig. 26 Spectral distribution of two categories of standard

deviations, each computed from 18 measured emittance values obtained at 1300 K, three each on six

oxidized Inconel working standards. The upper

curve represents standard deviations due to real

differences in emittance between specimens, identified as as in the text. The lower curve represents

standard deviations due to random error, identified

as in the text. In both curves each point re- presents the moving average of five adjacent values.

X. PRINCIPLES OF DATA REDUCTION

A. Computation by the Weighted-ordinate Method

Two steps are necessary in order to compute the total normal emittance or absorptance of a specimen for radiant flux having a specified

spectral distribution from its spectral emittance curve. These steps

are described in relation to figure 27, which represents an actual case.

The first step is to weight a series of ordinates chosen at uniform

wavelength intervals along the spectral emittance curve for the specimen

(Curve A) according to the spectral distribution of flux from a blackbody

at the temperature of the specimen, which can be represented by a second

Curve, B. The weighted ordinates, which are the products of ordinates at

identical wavelengths for Curves A and B, provide points for Curve C, which

WADC TR 59-510 Pt IV 44
Fig. 27 Graphical form of data and derived values used in com- puting from the spectral emittance of a specimen its

total emittance, its total absorptance, or its total

emissive power. Curve A represents spectral emittance

values obtained on a specimen at 650°K(about 1200°F)

Curve B represents the spectral distribution of radiant flux from a blackbody at the same temperature.

The ordinates of Curve C are in each case the product

of the ordinates of Curves A and B at the same wavelength. Curve C represents the spectral distribution

of flux emitted by the specimen having the spectral

emittance indicated by Curve A.

indicates the spectral distribution and amount of radiant energy emitted by

the specimen in unit time. In the case of absorptance, Curve B represents

the spectral distribution and amount of incident flux, and Curve C represents the spectral distribution and amount of absorbed flux.

The second step in computing the total emittance or absorptance of a specimen consists of determining the ratio of the area under Curve C to that

under Curve B. A rig’orous mathematical expression of the quantity sought is as follows:

f e b\ E s\ dk

_Q

CO e b\ dk

o

( 8 )

WADC TR 59-510 Pt IV 45
where: E = total Emittance of specimen

t s —

€

bA. rate of energy emission per unit wavelength interval, c£ a blackbody, for the increment A. to (A. + dA.)

Emittance of the specimen, between A. and (A. 4- dA.) .

In practice, with a sufficient number of uniformly- spaced ordinates (which

are taken at the same set of wavelengths for all the curves) this ratio ct areas is approximated with the required precision by dividing the sum of

the ordinates for Curve C by the sum of the ordinates for Curve B. The

mathematical expression of this operation is given below.

Since all values

as dimensionally.

E

ts

of A A. are

\ , £b\ E sA. A A. (9)

t-

) e bA. A A, L \x equal, they cancel out numerically as well

The units in which the ordinates of Curve A are expressed are pure numbers, representing spectral-emittance values. The units in which the ordinates for Curve B are expressed occur in both the numerator and denominator

of the final ratio; hence it is of no consequence what units are used, provided they are the same for the numerator and denominator, or whether the

ordinates for Curve B are expressed simply as numbers of the correct relative magnitudes. The final answer in either case is a number signifying the

total absorptance of the specimen for radiant flux of the specified spectral

distribution

.

The procedure is identical for computing either total emittance of the

specimen, or its absorptance for radiant energy from any source of known

spectral distribution. To compute total emittance, Curve B represents the

spectral distribution of a blackbody at the temperature of the specimen (as was done for figure 15). To compute absorptance, Curve B represents the

spectral distribution of flux from the source.

When it is desired to compute the total amount of radiant energy, for

unit time and area, emitted by the specimen at a given temperature then

Curve B will represent blackbody radiation and its ordinates will be ex- pressed in energy per unit time and area; hence those of Curve C will also.

In this case the quantity sought is represented by the area under Curve C

which can be obtained by integration. The equation that rigorously describes this relationship for all possible wavelengths is:

f* 05 = 1 E s A. dA. (10) L o Q

'\. a = total emissive power of the specimen.

the

In practice the value can be computed with the required precision by

following approximation:

€ v

ts ~

/ ^

e sA. s bA. AA. q

WADC TR 59-510 Pt IV 46
Since E s ^

is a ratio, and e b ^ represents radiant flux per unit area and

wavelength interval . the X cancels out, dimensionally. Numerically, the

fraction of the span between Xi and Xg, that is occupied by a single interval, AX is the reciprocal of the number of ordinates, n, (each ordinate

representing one interval); hence equation (11) may be written:

This equation states that the total radiant flux per unit area is obtained by simply adding all the ordinates of the points from which Curve C was constructed (each of which represents radiant flux per unit area), and

dividing by the number of such ordinates. Any required accuracy of the approximation can be attained by using a sufficient number of ordinates.

As in the case of emittance and absorptance, the procedure is the same whether the object is to compute the total radiant flux emitted by unit area

of the specimen or the total radiant flux absorbed upon exposure to a specified source. In the former instance, Curve B represents blackbody radiation; in the latter case it represents radiant flux from the specified

source that is incident upon the specimen.

Regardless of what method of computation is chosen, the objects remain

(1) to obtain the ratio of areas under two Curves, B and C, for total emittance or total absorptance, and (2) to evaluate the area under one Curve, C. for total radiant flux per unit area of the specimen, absorbed from a specified source, or emitted. Such values characterize the specimen at a given

temperature only.

Ordinarily it is preferable to use no more ordinates for the calculations than are needed to give the required accuracy. The optimum number of

ordinates can be chosen by spacing them to represent equal areas under Curve

B, a device which results in unequal values of AX. When this method is

used, the first step is to choose ordinates for Curve B at increments of X

such that the areas between all adjacent pairs of these ordinates correspond

to a constant amount, k, of radiant flux per unit area. Then the median

wavelengths within the respective intervals between these adjacent pairs of

ordinates determine the locations of the selected ordinates. When the ordinates of Curve A are read at these specified values of X , the rate at which

energy is emitted per unit area of the specimen can be obtained with the re- quired accuracy simply by adding up these ordinates and multiplying the sum

by the constant, k. The basic equation is:

( 12 ) € ts

n

B. Computation by the Selected Ordinate Method

2

c ts

(13)

^ Xi

WADC TR 59-510 Pt IV 47
But since AX) has

equation becomes:

the constant value k,

k Lx E ^

independent of wavelength, the

(14)

Often, for convenience, ordinates are selected at intervals such that

k = 1.

The economy in number of ordinates required for a given precision makes

this method especially advantageous in the absence of electronic computers.

Like the weighted- ordinate method, it is applicable to calculation of total

emittance or total absorptance from the spectral data, as well as to calculation of rate of emission or absorption of energy by unit area of the speci- men . XI. DEVELOPMENT OF DATA-PROCESSING EQUIPMENT

A. Design of Equipment

The data-processing attachment was designed to perform the following

functions: (1) to produce a corrected graphical record of the normal spectral emittance of a specimen as a function of wavelength, (2) to record in digital form on punched paper tape the corrected spectral emittance values, for

possible use in a separate electronic digital computer, and (3) to accumulate

the digitized emittances at wavelengths which have been pre-selected to yield

specific information as described in this section of the report.

The direct input to the data-processing attachment, in the form of electrical potential, is proportional to the apparent emittance of the specimen;

that is, the emittance that would be recorded by the spectrometer without benefit of the data-processing attachment. This signal is corrected for systematic instrumental deviations on the basis of previous calibration tests.

The resulting record tends to be systematically correct

instrumentation and digitization errors remaining.

Fig. 28 Schematic wiring

diagram, shoeing

connections through

Function Selector

Switch of dataprocessing attachment in "Bypass"

and "Record 100%"

or "Record Zero"

position

.

RECORDING POTENTIOMETER

BLACK BODY | SUDE WIRE

INPUT | 468 Cl k

, with only random

(a) (b)

BYPASS RECORD "|00%"AND "ZERO'

WADC TR 59-510 Pt IV 48
The spectrometer generates two d.c. potentials, one, I

c , proportional

to the flux reaching the detector by way of the comparison (blackbody) beam,

and the other, I s , proportional to the flux reaching the detector by way of

the specimen beam. The apparent emittance is the ratio of the latter potential to the former. When the attachment is operated with the Function

Selector Switch in the "Bypass" position (see figure 28), thus bypassing the

data-processing attachment, the ratio is measured by applying I c potential

to the slidewire of a potentiometer recorder, and balancing I s potential

against the potential of the potentiometer arm. The I s potential is re- corded on the chart as a decimal fraction of the I

c potential, representing

the apparent (uncorrected) emittance as a function of wavelength. However,

the optical paths of the two beams in the spectrometer are not perfectly

matched, and this condition introduces some error into the measurement of

flux ratio in the two beams. This error is compensated by the data-processing attachment, as described below.

The position of the recording potentiometer arm is digitized by an en- coder which is actuated by the arm shaft. The encoder comprises two axially

centered discs, one stationary and one shaft-mounted. Each disc is made of

transparent material, to which curved, but nearly radial, opaque stripes of

a black coating have been applied. A source supplies light which is alternately passed and blocked as the movable disc rotates. This light is sensed

by photoelectric cells, so placed that one cell receives light first when

the movable disc is rotated in the clockwise or "upward" direction, and the

other cell receives light first when the direction of rotation is reversed.

A directional flip-flop is operated by the pulse from the cell first detecting light. A pulse is produced for each increment of rotation corresponding

to 0.1 scale division on the chart, or 0.001 in emittance. The pulses are counted in a reversible counter that is gated so that it increases in count

when actuated by pulses received in the forward direction of the flip-flop,

and decreases in count when actuated by pulses received in the opposite

direction.

The drum dial is driven by a synchronous motor. Its position, which

determines the position of the Littrow mirror and hence the wavelength of

the radiant flux being measured, is digitized in the same manner, and the

resulting pulses are counted. Since the magnetic tape in the tape recorder

is likewise driven by a synchronous motor, the two speeds also are synchronous. The tape is a 16-mm wide, four-channel type, perforated along one side and driven by a sprocketed capstan to prevent slippage.

One source of error in the apparent emittance values is deviations in

the "1007o line", which result from differences in loss of effective flux

along the two optical paths. A second source is deviations in the

"zero line", resulting from stray radiation in the monochromator, which produces a spurious I signal when there is no flux in the specimen beam.

WADC TR 59-510 Pt IV 49
To correct deviations in the 100% line, the reference blackbody furnace

is substituted for the specimen, and its apparent spectral emittance is re- corded with the equipment connected as indicated by the block diagram, figure

29. The data-processing attachment records the pulses from the potentiometer

shaft encoder on two channels of the magnetic tape, the pulses in the

"upward" direction on one channel, and those in the "downward" direction on the other. Only the change in position on the potentiometer, not the position itself, is recorded. For this reason it is necessary to note and record

the reading on the potentiometer at the start of the 100%-line calibration.

9 Fig. 29 Block diagram of data-processing attachment during

recording of "100% line" and "zero line" deviations.

WADC TR 59-510 Pt IV 50
The same procedure is used to record the zero- line deviations on another pair of magnetic tape channels, except that the specimen beam is

blocked near, the specimen furnace. The initial value must also be noted

and recorded, as in the case of the "1007o line."

When a specimen is under test, each digitized value of apparent

emittance is corrected automatically for deviations in the 100% line and

the zero line, respectively. The correction for the former is made as follows: The I

c potential is fed to the 100%-line potentiometer, connected

as indicated in figure 30. The arm of this potentiometer is driven by a ratchet motor, actuated by two monostable multivibrator circuits, one for

each direction of rotation. During the determination the previouslyrecorded magnetic calibration tape is played back synchronously with the

wavelength drive, the pulses from the upward channel driving the arm of

the potentiometer upward, by increments of 0.1%, and the pulses from the

downward channel driving it downward an equal amount. The 1007»-line potentiometer has the same overall resistance as the recorder potentiometer

(468ft). At the start of a measurement of spectral emittance, the 100%-line

potentiometer is set to the value that was recorded at the start of the

100%-line calibration. During the measurement the magnetic tape playback

continually modifies the I c signal, in the amount and direction determined

by the deviation from ideal value of the I r signal from the reference

blackbody furnace, that was recorded during the .100%-line calibration.

This modified I c potential is applied to the high-voltage end of the slide

wire of the recorder potentiometer. The effect is to introduce into the I c signal the same systematic errors that are in the I s signal, in order to

correct the recorded ratio of the two.

Fig. 30 Schematic wiring diagram

of potentiometer circuits

during playback of

"100% line" deviations.

The zero-line correction is made through a similar zero-line potentiometer, connected as shown in figure 31, and driven by a similar ratchet

motor and multivibrator circuits, actuated by pulses from the zero- line chan

nels on the magnetic tape. The zero-line potentiometer also is set at the

value that was recorded at the start of the zero-line calibration before

starting the spectrometer. The zero-line potentiometer, as controlled by

the magnetic tape during playback, produces a signal representing the I Q

signal at the same wavelength that was recorded during the zero-line calibration. This signal is applied to the low-voltage end of the slidewire of

WADC TR 59-510 Pt IV 51
VSArBLACK BODY INPUT SIGNAL

Fig. 31 Schematic wiring

diagram of

potentiometer

circuits during

playback of both

”100% line” and

"zero line”

deviations

.

Fig. 32 Block diagram of data-processing attachment during

a specimen run.

WADC TR 59-510 Pt IV 52
the recorder potentiometer, maintaining it above ground potential. The net

effect of this adjustment is to subtract this zero-line potential, thus com- pensating for the zero- line error.

The potentials from the 1007o -line and zero-line potentiometers are applied to the recorder potentiometer through isolating unity-gain amplifiers,

to prevent reduction in potential due to load. A block diagram of the equipment during a specimen run is shown in figure 32.

B. Mathematical Analysis of Operation

The operation of the data-processing equipment may be analyzed mathematically as follows:

Let I =

c

I

r

I o

I

s

W

s

Note:

comparison blackbody signal

reference blackbody signal

zero signal (spurious signal received when specimen beam is

blocked)

specimen signal

radiant flux from blackbody entering the optical system to

produce I or I • (The flux from the reference and the

comparison blacSbody furnaces are equal since they are at the same temperature.)

radiant flux from specimen entering the optical system to

produce I . s All of the signals, I c , I r , I Q and I s , appear as potentials in the output of the spectrometer amplifier, before entry into the potentiometer-recorder

or data-processing attachment.

a = proportionality factor between flux entering specimen beam

of spectrometer and signal produced. W = al , W = al . B IT s s There is a second proportionality factor between flux entering comparison beam of the spectrometer and the signal produced. However, this factor

is not required in the mathematical analysis, because I c is maintained con- stant by the slit servomechanism.

Note: All of the above terms are functions of wavelength, and

all are referred to at specific values of \, but for simplicity the subscript X is omitted in the mathematical

treatment that follows.

Let us first consider what is needed, in terms of signals, to give the

true emittance of the specimen. The zero signal, I Q , is measured only in

the specimen beam of the spectrometer and is assumed to have the same spectral distribution whether the reference blackbody is substituted for

the specimen or the specimen itself radiates the beam, since in either case any spurious deviations occur when the beam is blocked from entering the

spectrometer. Therefore, for each wavelength of the specimen beam

WADC TR 59-510 Pt IV 53
a 11(1

W = a(I - I ) B r o

( 15 )

W - a(I - I ) s s o 06)

Since the spectral e.mittance, E, is defined as Vw

b

the desired equation, in terms of signals, becomes

(17)

E

a (I

s

- I ° ) «Or

- V

The factor a cancels out, and need not be considered further.

(18)

However, the spectrometer is used as a double-beam instrument, which

measures the ratio of the signal from the specimen beam to that in the com- parison blackbody beam, and we must work with these instrumental ly obtained

ratios to obtain the desired corrected emittance values.

First, assume that I q = 0. Then, from equation (18)

E = l

s /l

r (19)

The output of the spectrometer is the position of the recording potentiometer arm, which represents the ratio of the signals from the respective

beams in terms of the fraction, f, of the total range of the arm. This

fraction, f, may also be recorded on a strip chart as a decimal fraction.

During calibration, see figure 29, the two signals are I in the com- parison beam and I in the specimen beam. Consequently,

rs

;

This ratio, is recorded as the "100% line." on the magnetic tape, and may

also be recorded on the chart, during the 100% calibration. During the

testing of a specimen, in which the automatic data-processing attachment:

functions to make automatic corrections, the playback from the magnetic tape

controls the position of the arm on the 100%- line potentiometer to the position representing the fraction f of its range, while the potential applied

to its slidewire is the signal I c

. Hence the output of the 100%-line potentiometer is

l

which is applied to the recording potentiometer slidewire by the amplifier.

The signal input is l

g

, and for this condition

WADC TR 59-510 Pt TV >4
( 22 ) f"j. -- IJ-s/J-r /I

the corrected spectral emittance,’ for I =0.

o The situation is more complex when I q

> 0, as it usually is. In figure

31, the potential from the 1007o-line potentiometer, which was shown in

equation (21) to be equal to Ir , is applied to the top end of the recording

potentiometer slidewire. The potential from the zero-line potentiometer is

applied to the bottom end of the slidewire. This potential is equal to I as is shown by the following treatment.

Daring zero-line calibration, the position, f' 11

, of the arm on the re- cording potentiometer is

f"' = I 0 /I

c (23)

During playback, the position of the arm on the zero-line potentiometer is

controlled by the signals from the magnetic tape to the fraction, f

1 ' 1 , of

its range, while the potential applied to its slidewire is a constant voltage, K, representing I

c

. It should be noted that the slit se’rvomechanism

of the spectrometer automatically opens and closes the slits of the mono- chromator to keep I

c constant during a test.

The potential drop across the recording potentiometer slidewire is thus

(I r

- I Q

) . The potential, I s ^ is balanced against the arm potential:

i 0 + £""(ir

- i 0 ) = i

s .i-i

consequently f

1 ' 1 = —S = e ^r ” J o the spectral emittance corrected for both absorption and stray radiation,

see equation (18).

Since equation (25) involves signals from a blackbody furnace and a specimen at the same temperature and at the same source position (the effect

of the signal I c from the comparison blackbody having been cancelled out in

derivation of the expression) the proportionality factor, a, is in both

a-umerator and denominator, hence cancels out, as shown in equation (18).

The emittance, or f ,,,,

, appears as a shaft position of the recording

^irm and pen, which is encoded as before. The results are counted in the re- versible counter. The positions of the counter are punched in Friden Programmatic Single Case Code on paper tape at preset intervals of drum rotation. The counter numbers are also accumulated in the electronic accumulator, at other preset intervals. The results shown by the recording pen

counter, the digitized drum dial counter, or the accumulator can be selected

for display as decimal digits. These digits are punched in a word group

whose first four characters are the drum dial division numbers. The latter

three are the pen position digits. The most significant digits are first.

The eighth character is always a "Carriage Return."

(24)

(25)

WADC TR 59-510 Pt IV 55
The preset wavelengths for punching and addition are selected separately. These intervals for punching are each

1/2 drum dial division,

1 drum dial division,

2 drum dial divisions,

5 drum dial divisions,

or 10 drum dial divisions, as desired

The increments between successive wavelengths at which spectral emittance values are to be accumulated are pre-recorded on punched paper tape.

The tape is read into the data-processing equipment during a determination

by the tape reader. The method of coding the tape is explained below in the

next section.

C. Preparing Punched Paper Tape

The Tape Input Pleader utilizes a 12-bit binary register and counter,

set up so that its "zero" state produces an output pulse that actuates the

Tape Punch Readout and/or the accumulator (when switched to those positions).

The register is composed of three 4-bit sub-registers, which receive the

first three 4-bit characters from the read-in tape. The fourth character

on the tape, a Carriage Return, is used as a "Stop" pulse. (Any other characters on the tape between the third character and the Carriage Return are ignored.) The registers are thus set in one of the 4096 possible sequences

or states. After the "Stop" pulse, pulses from one side of the least significant drum dial binary counter are fed into a capacitative gate which

causes the register to cycle through successive states in its counter mode,

starting with the number previously read in from the tape. When the number

of binary counts plus the starting number reaches 4096, the register is in

the "zero" state, and the output pulse occurs.

The operation can be described by stating that 4096 (= 163 ) counts produce a complete cycle, in three sexa-decimal groups of four binary digits

each. Since the counts are produced by pulses from one side of the drum

dial binary counter, this counter produces a pulse for every two pulses it

receives; the result is a pulse for each 0.002 revolution of the wavelength

drum. The increment of counts required to complete a cycle is thus the

complement of (1000)x 6 in sexa-tdecimal notation. The method of computing

these increments and preparing the punched paper tape is described below.

In preparing the punched paper tape it is first necessary to select the

wavelengths at which the accumulation is to be performed, and then to record

these values on punched paper tape in the proper manner. The method of se- lecting the wavelengths was outlined in Section IX, Principles of Data Reduction .

After the proper wavelengths have been selected, they are processed as follows

:

WADC TR 59-510 Pt IV 56
1. Convert the selected wavelengths into wavelength drum positions, by means of a calibration curve, to the nearest 0.2 division on the scale

(1/500 drum revolution).

2. Compute the increments between successive wavelength drum positions,

in units of scale divisions and fractions.

3. Multiply the increments by 5. to convert into integral numbers.

Note: • The first increment is that between the starting position of the

wavelength drum and the position corresponding to the first preselected

wavelength

4. Convert the integral decimal numbers obtained in step 3 to threedigit sexa-decimal numbers, i.e., base 16 numbers. The digits in this system are 0, 1, 2, 3, 4, 5, 6 , 7, 8 , 9, A, B, C, D, E and F. The number 108io

then becomes 06C1S > or 311810 becomes C2E16 .

5. Form the complement of these numbers, i. e., subtract the number

from 1000i6 • Thus 108xo = 06Cx S becomes F94xe, and 3118io = C2E16 becomes

3D2x 6* (An alternative procedure is to subtract the original decimal number

from* 4096 and convert the difference to sexa-decimal numbers. Thus for

108i O , 4Q96io - IQ 810 = 3988x 0 = F9416 , and for 311810 , 409610 -• 3118x 0 = 978io = 3D2i6 •

)

6 . Prepare an 8 -channel punched paper tape in word groups of four

characters each. The first character of the word is the most significant

digit of the sexa-decimal number, the next is the middle digit that is followed by the least significant digit, and the last character in the word is

the Carriage Return. For the two examples cited above, one would type

for 108xo " F94R

Q and for 3118xo ~ 3D2 R

For use, the punched paper tape is inserted into the paper tape reader,

and the wavelength drum is set at the starting position. The accumulator

selector switch is set to the tape reader position, arid the tape reader is

turned on. As the spectrometer traverses the spectrum, the tape reader will

trigger the accumulator circuit each time the wavelength drum has advanced

an amount equal to the increment that was punched into the tape. The paper

tape reader automatically advances the tape one position after each accumulation.

WADC TR 59-510 Pt IV 57
D. Current Status of Data-Processing Equipment

The electronic data-processing equipment was installed by the manu- facturer during the month of February, 1962. A number of the functions

were checked and found to operate properly, particularly the digital functions of the pen position and drum dial counters, as well as the accumulator.

Several paper tapes were made, but intermittant troubles soon appeared.

These apparently were caused by transistors that were somewhat weak. They

were replaced. Also the original 300-foot tape would record for only about

8 minutes, instead of the 32 minutes required to traverse the spectral range

from 1 to 15 microns at the intermediate speed. The tape and reels were re- placed with larger reels and a thinner tape 1200 feet long. In addition,

the speed of the tape drive was reduced by one half.

When the equipment was checked it became evident that the 100% line

Potential Isolating Amplifier had excessive drift - about 0.2 mv in potential in a 10 mv circuit. The zero line Potential Isolating Amplifier

drifted by the same amount, but because of the lower potential in the circuit, 0.5 mv, the effect was more pronounced. This situation was remedied

by moving the 100% line Potential Isolating Amplifier to a higher voltage,

300 mv, but less filtered, position in the circuit. The voltage drift was now negligible compared to the higher voltage of the circuit at this point.

Calculations of the impedance relationships indicated that the effect of

drift was negligible. The zero line Potential Isolating Amplifier was re- moved, and the zero line potentiometer was changed to a lower impedance,

10 ohm, unit. This made the analog conversion more stable.

After these changes were made, effects due to recorder pen motion be- came apparent. The pen position counter produced extra counts during re- versals. Diode gates were installed to prevent this. The 1007, line potentiometer correction circuit continued to make larger changes than were

called for by the number of pulses recorded during the calibration. This

was the result of unintended positive feedback in the stepping motor drive

amplifier. When this was corrected, the drive motor could not keep up with

the rapid pen position changes.

The rapid pen motion, or jitter, was examined more closely, and was

found to be the result of noise in the spectrometer, and hence noise in the

output. Such random errors appear in I s , I Q , I c and I r , as previously defined in Section IX B . As was shown in that section, the spectrometer outputs used for calibration and measurement are all ratios of two of these

four signals. If the random error term is d with an appropriate subscript, we can see from the following analysis how many times it appears in the

final result. The recorded 100% line deviations are the ratio f

!

I + di

f r

( 26 )

The output of the 100%- line potentiometer is f'l c.

WADC TR 59-510 Pt IV 58
f'Vdo + Sa) lf4lr ( 27 ) which is applied to the top of the recording potentiometer slidewire.

The recorded "zero line" deviations are the ratio f

' *

'

f’ ' ' Ip +

Ic + S5 (28)

The output of the zero-line potentiometer is f

' * 1 times a constant

voltage, K. This output is applied to the bottom of the recording potentiometer slidewire.

The potential drop across the slidewire is thus

(I c + d3 ) I r + hi _ I 0 + d4 I c +

* I c Tlfe

The potential I s is balanced against the arm potential to produce the

ratio f

1 ’ *

'

Is + S6 = k-10 + ^4 I t I (

f

' 1 t

Ic + ^5

= (Iq + 96 > " K

lo + ^

C + ^5/

( t _i_ ^ \ Ir "b Si _vIo"b S4

(Ic + S3 ) ic + 5a *?- + &

(29)

It can be seen that d, the random error due to noise, appears in the

final ratio f six times.

Obviously it would not be a satisfactory solution to record the random

error S. Ideally it should be reduced to zero; practically it must be re- duced to a tolerable level.

A critical examination of the spectrometer indicated that some of the

noise was due to deterioration of components in the amplifier, and a higher

than normal noise-to-signal ratio was due to deterioration of the vacuum

thermocouple detector. The defective parts were replaced, and all optical

elements were removed and cleaned, after which the entire optical system was realigned

When these changes had been completed, it was possible to determine

that the stepping motor was following most, but not all, of the correction

signals. This was traced to two conditions, binding in the mechanical gears

between the motor and stepping switch, and borderline gain of the tape output amplifier. The gears were readjusted to eliminate binding.

The gain of the tape output amplifier had been ample to drive the stepping switch motor when the original high tape speed was used. At the lower

speed, operation was marginal. The gain of the amplifier was increased, and

WADC TR 59-510 Pt IV 59
the stepping motor speed is now appreciably higher than before. In addition,

the manufacturer has supplied a higher-speed motor for the tape drive, that can be installed if needed.

The data-processing equipment now appears to be operating satisfactorily. A series of tests has been started to evaluate the stability of the

system over a period of several weeks.

The fact that one malfunction would mask several others, and the fact

that the effect of a malfunction appeared only in the final output of the

system, rather than as a change in some intermediate voltage, has made the

malfunctions difficult to locate, and hence to remedy. The manufacturer has

cooperated fully in eliminating malfunctions and changing components where

required

.

The experience to date has revealed several ways in which the spectrometer can be improved to increase accuracy. For instance, the amplifier

noise was found to be above the theoretical lower limit, and some of the

electrical components can be replaced by currently available units of greater stability. However, the spectrometer is now operating with an overall

accuracy and precision that is better by about an order of magnitude than

the ‘Standard performance tolerance the manufacturer calls for,

A separate paper is being prepared, describing in detail the design and

operation of the data-processing attachment.

XII. EQUATIONS RELATING SPECTRAL EMISSIVITY

OF METALS TO OTHER PROPERTIES

Simple equations relating the emissivity of metals to their electrical

resistivities have been available for more than half a century. The contributions of Drude and of Hagen and Rubens were classic, and a series of refinements of the Hagen-Rubens equation led to the Schmidt and Eckert modification of Davisson and Weeks' version of the equation. The Schmidt and Eckert

equation is quite useful and applies especially well to platinum. The known

temperature dependency of the electrical resistivity of platinum made it

possible to compute the spectral thermal emissivity of platinum (or its

spectral reflectance) with reasonably good accuracy over a wide range of

wavelengths, but the lower limit of the wavelength range in which this accuracy prevails is strictly limited, and may be taken roughly as about 2p for

temperatures of incandescence and about 7p for room temperature.

This entire family of equations gives smooth, uninflected curves that

conform in a general way with the drastic increase in emissivity (decrease

in reflectivity) of metals that occurs within or near the range of visible

radiation (0.4 to 0.7p). But it does not take into account the inflections

in experimentally obtained spectral emissivity (reflectivity) curves, mostly

at wavelengths shorter than 2 p and to a significant extent at longer wavelengths. The opinion has repeatedly been expressed that these inflections

at the shorter wavelengths are controlled by bound electrons, whereas the

WADC TR 59-510 Pt IV 60
electrical resistivity of a metal, upon which the conventional calculation

is based, is controlled by free electrons. Nevertheless it was not until

recent years that the literature has recorded attempts to combine the effects of both free and bound electrons in equations relating the spectral

emissivity (reflectivity) of metals to other properties.

Notable among recent attempts are those of S. Roberts r s] and T. R.

Harrison [9], who proposed an extension of the Drude model, based on classical electron theory. The formulas they propose contain, as parameters,

several quantities which measure certain physical properties of the various

families of bound and free electrons in the metal. In the present state of our knowledge, these parameters must be obtained empirically, from the ex- perimentally observed reflectivity (emissivity) values, by a curve fitting

procedure. In this way Roberts was able to obtain spectral emittance curves

that accord fairly well with observed data on metals at wavelengths significantly shorter than those for which the Hagen-Rubens equation provides any

useful results. However his curves left considerable room for improvement.

Harrison also gives curves (figure 16 of his book) using assumed values of

the parameters to show how the new bound-electron terms introduced enable

the curves to better fit the experimental data than was possible with the

Drude theory; but does not attempt to fit the observed curves in detail.

The equations suggested by T. R. Harrison have terms to provide for the

effects of different categories of free electrons and also different categories of bound electrons. They are based upon classical electron theory.

A sol ution of these equations, based upon assumed parameters that are applicable to typical metals, was given graphically in Harrison's book (figure 6).

The results illustrated the effect of bound electrons in producing inflections of a magnitude, and at a wavelength interval, that closely resembled

curves of observed spectral reflectivity (emissivity) within and near the

wavelength limits of visible radiation.

Attempts were made in this study to compute good values of the parameters from experimentally obtained spectral reflectivity (emissivity) curves. The metal rhodium was chosen as the subject of the study because of the

availability of accurate reflectance data at room temperature. First only

one category of free electrons and one of bound were used. Within the wavelength range of visible radiation a curve obtained in- this way gave a very

creditable fit, and followed the inflection corresponding to a maximum in

emittance at about 0.45 micron. In the attempt to extend the range of good

fit out to about 10p, it became evident that additional parameters, making

at least 10 in all, would be required, for insertion into more than one term for free electrons and more than one for bound electrons.

with the fraction of total effort on this study that could be devoted

to this aspect, no set of parameters was found that will produce a spectral

reflectance (emittance) curve that fits the observed data both generally and

in detail. However the findings were not negative since they gave promise

that further exploration would probably produce one. The work completed

indicates that a satisfactory fit throughout the wavelength range of interest would involve an equation with one or two terms for free electrons and

two or three for bound electrons.

WADC IR 53-510 Pt IV 61

U-COMM-N BS-DC
XIII. REFERENCES

1 1 I Jones, L. A. J. Opt. Soc. of America, Vol . 27, p. 207 (1937).

[2] Worthing, A. G. Temperature Radiation Emissivities and Emittances.

Temperature, Its Measurement and Control in Science and Industry.

Amer. Inst, of Phys . Reinhold Publishing Corp., N. Y. 1941,

pp. 1164-1187.

T 3

"1 Report on Letter Symbols for Heat and Thermodynamics. Amer. Standards

Bull. ASA Z10. 4-1943.

f”4 1 Gardon, Robert. The Emissivity of Transparent Materials. J. Amer.

Ceram. Soc., 39 Ts], pp . 278-287 (Aug. 1956).

[ 5 ] Gouffe", Andre Corrections d'Ouverture des Corps-noirs Artificiels

Compte Tenu des Diffusions Multiples Internes. Revue d'Optique 24

[l-3], pp. 1-8 (Jan. - Mar. 1945).

! 6 ] t Table of Wavenumbers. International Union of Pure and Applied

Chemistry. Butterworth (1961).

*"7] Gaumer,R. E. and Plyler, E. K, Private communication.

[ 8 ] Roberts, S. Phys. Rev. 100, 1667, (1955); U4, 104, (1959); 118, 1509

(1960).

[9] Harrison, T, R. Radiant Heat Transfer, pp. 28-62 and Appendix IV.

John Wiley & Sons (1960)

.

WADC TR 59-510 Pt IV 62
TABLE I

NORMAL SPECTRAL EMITTANCE OF

PLATINUM WORKING STANDARDS AT 800°K

Wav«l. eugth”^ 2 / Emittance'" 3/ nl~

4/ 5/

°tn 6 / o's“ Microns X100 XI 00 xToo xioo xfori

1 . 04

1.09

1.15 13.5 1.47 .75 ,71 2.48

I • 2 / 14,3 1,40 . 72 , 38 .2 . 52

1.28 15.2 1 ,47 ,75 ,7( 4 2 , 60

1.36 16.2 1.40 .71 .31 2.52

1.44 17.0 1.39 .71 .36 2,49

1.52 17.6 1.31 .67 ,36 2 . 34

1.63 18.0 1.23 .63 34

i . 74 18.3 1.24 .63 c 3 j

')

pi ^

1.88 17.7 1.14 .58 .37 2,02

. 2.10 16.9 .96 .49 , 39 1.65

2.36 15.5 .95 .49 , 34 1.67

2.60 14.0 .78 .40 ,34 1.33

2.81 12.5 .90 .46 .48 1.44

3.02 11.5 .90 .46 .46 1 : 51

3,25 10.7 .93 .47 > p 1

i: Q

3.45 10.1 .82 .42 .36 1.31

3.65 9.5 .86 .44 .35 1.49

3.87 9.2 .95 .48 .37 1.65

4.09 8.9 .09 .50 .44 1 .68

4.30 8.9 .93 .47 .43 1.58

4.50 8.1 .78 .40 .29 1.35

4.67 8.2 .92 .47 .38 1.58

4,83 7.9 .95 .48 .37 1 . 6 5

4.99 7.8 .93 .48 .37 1.62

5.13 7.7 . .94 .48 .36 1.63

5.27 7.6 .93 .47 .33 1.63

5.40 7.5 .90 .46 .38 1,54

5.54 7.3 .97 .49 .43 1 , 6 6

5.69 7.3 .89 .46 .34 1,56

5.83 7.1 .93 .47 .34 1.63

5.97 7.0 .76 .39 .28 1.34

6.10 6.9 .79 .40 .30 1.38

6.22 6.9 .80 .41 .31 1 .40

1/, 1/, 3/, 4/, 5/, 6J - See footnotes on page 66.

WADC TR 59-510 Pt IV 63
TABLE I cont 'd

.

NORMAL SPECTRAL EMITTAMCE OF

PLATINUM WORKING STANDARDS AT 800 K

Wavelength"7

^ 2/ Emittance— 3/

°t

4/ 6~“ O

-'5 m

6/ o -

s Microns xio'o X10Q xToo X100 XI00

6 .35 6.8 .91 .46 .29 1.61

6.47 6.8 .89 .45 .29 1,57

6.58 6 .

6

,77 .39 ,36 1.31

6.70 6.4 .73 ,37 .30 1.27

6 , 80 6.5 .72 .37 .25 1.28

6.91 6.5 .79 .40 .29 1.38

7.01 6.4 .84 .43 .28 1.50

7.13 6.4 .82 .42 .27 1.45

7.25 6.4 .85 .43 .42 1 .42

7.37 6.3 .93 ,47 .31 1.64

7.49 6.3 .94 .48 .34 1.64

7.60 6 o 3 .86 .44 .28 1.53

7.71 6.2 .90 .46 .26 1,62

7.94 6.2 .94 .48 .26 1,68

8,12 6.2 .91 .46 .23 1.63

8.32 6.3 .86 .44 .33 1.50

8.50 6.5 .85 .43 .36 1.46

8 <70 6.5 .96 .49 .38 1.66

8.88 6.5 .84 ,43 .31 1.46

9.05 6.4 .84 .43 .40 1.42

9.22 6 „ 6 .85 .43 .34 1.41

9.38 7.4 .76 .39 .41 1,26

9.55 7.4 .80 .41 ,29 1.40

9.71 6.7 .80 ,41 ,23 1,42

9.87 6.3 ,80 .41 .29 1.41

10.03 5.9 o 74 .38 ,33 1.26

10.18 5.8 ,72 .37 .31 1,24

10.34 5.6 .66 .34 .33 1.00

10.50 5.6 .59 .30 .31 .97

10,64 5.5 .61 .31 .32 1 .01

10.80 5.4 ,65 .33 ,41 .98

10.94 5.4 .55 .28 .38 ,82

11.08 5.4 .56 .28 .36 .85

11.22 5.3 .62 .32 .42 .94

11.35 5.3 .49 .25 .30 .76

WADC TR 59“ 510 Pt IV 54
TABLE I cont'd.

NORMAL SPECTRAL EMITTANCE OF

PLATINUM WORKING STANDARDS AT 800 °K

- .1/

•;.ve length- _ . 2/ Emittance- 4/ e~

5/

(7

ra s Microns X100 X100 X100 X100 xioo

11.49 5.3 .47 .24 .28 .75

11 o 62 5.2 .48 .24 .33 .72

11.74 5.3 ,42 .21 .29 .63

11.87 5.2 .35 .18 .26 .50

12.00 5.1 .46 .23 .34 .66

12.13 5.1 .42 .21 .36 .53

12.26 5.1 .51 .26 .36 .77

12.38 5.1 .44 .22 .31 .65

12.50 5.0 .44 .23 .39 .55

12,63 5.1 .46 . 23 .41 .51

12.75 5.0 .37 .19 .33 .42

12.88 5.0 .40 .20 .35 .51

13.00 5.0 .47 .24 .32 .71

13.12 4.9 .43 .22 .29 .66

13.24 4.9 .42 .22 .28 .65

13.36 4.9 .41 .21 .25 .65

13.48 4.8 .44 .22 .38 .55

13.60 4.9 .40 .20 .28 .60

13.72 4.9 .40 .20 .40 .38

13.84 4.8 .39 ,20 .39 .36

13.95 4.9 .44 .22 .43 .46

14.06 4.9 .41 .21 .36 .52

14.17 4.8 .35 .13 .33 .38

14.28 4.7 .42 .22 .42 .42

14.38 4.8 .42 .21 .45 .34

14.49 4.8 .36 .18 .29 .47

14.60 4.8 .30

' .15 .27 .35

14.71 4.8 .46 .24 .42 .55

14.82 4.8 .45 .23 .45 .44

14.92 4.8 .35 .18 .32 .40

WADC TR 59 -510 Pt IV 65
TABLE I cont'd.

NORMAL SPECTRAL EMITTANCE OF Q

PLATINUM WORKING STANDARDS AT 800 K

Wavelength^"

2/ Emittance” 3/

a “

t Jtf 5/

rrm

6/

cr “

s Microns XI 00 X100 X100 X100 X100

15.03 4.8 144 ,22 .46 .38

15.14 4.7 .49 .25 .39 ,66

1/ Emittance was computed at uniform increments of wavelength drum

position^ which are not uniform increments of wavelength.

2/ Average of 18 measurements^ 3 each on 6 specimens.

3_/ Standard deviation of the 18 measured values about the average.

4/ 95% confidence error of the average of 18 measurements.

5/ Average standard deviation of the 3 measured values for each,

specimen about the average for that specimen.

6/ Standard deviation of the 6 average values for the 6 specimens

about the overall average.

WADC TR 59-510 Pt IV 66
TABLE I cont'd

NORMAL SPECTRAL EMITTANCE OF

PLATINUM WORKING STANDARDS AT 1100°K

Wavelength”^ 2/ Emittance— 3/ a

t~

ay 5/ 6/ as"

Microns X100 X100 X100 X100 X100

1.04 18.9 .76 .39 .82 .60

1.09 20.0 .86 .44 .48 1.41

1.15 20.8 .99 .51 .53 1.64

1.22 21.4 1.05 .54 .49 1.78

1.28 21.6 1.05 .54 .51 1.77

1.36 21.8 .95 .48 .48 1.58

1.44 21.6 1.03 .53 .52 1.72

1.52 21.4 .99 .50 .50 1.65

1.63 20.8 .91 .46 .52 1.47

1.74 20.4 .85 .43 .54 1.32

1.88 19.4 .77 .39 .53 1.15

2.10 18.1 .81 .41 .51 1.27

2.36 16^8 .83 .42 .55 1.28

2.60 15.5 .81 .41 .55 1.23

2.81 14.2 .80 .41 .59 1.15

3.02 13.2 .74 .38 .51 1.11

3.25 12.5 .85 .44 .49 1.38

3.45 11.9 .92 .47 .50 1.50

3.65 11.3 .93 .47 .46 1.56

3.87 11.1 .91 .47 .50 1.50

4.09 10.8 1.00 .51 .48 1.70

4.30 11.0 1.03 .53 .59 1.67

4.50 10.0 .89 .45 .45 1.48

4.67 10.1 1.02 .52 .47 1.73

4.83 9.9 .99 .50 .47 1.67

4.99 9.7 1.07 .54 .47 1.82

5.13 9.5 1.12 .57 .53 1.90

5.27 9.4 1.13 .58 .53 1.92

5.40 9.3 1.09 .55 .52 1.84

5.54 9.2 1.03 .53 .49 1.75

5.69 9.0 1.12 .57 .57 1.87

5.83 8.9 1.06 .54 .46 1.82

5.97 8.8 1.04 .53 .50 1.75

6.10 8.7 1.05 .53 .47 1.79

6.22 8.6 1.03 .53 .48 1.75

\/, 2/, 3/, 4/, 5/, 6/ See footnotes on page 70.

WADC TR 59-510 Pt IV 67
TABLE I cont'd

NORMAL SPECTRAL EMITTANCE OF

PLATINUM WORKING STANDARDS AT 110() UK

, ; 1/ Wavelength— 2 / Emlttattee— a

t~

4/

e*“ m

0

6/

8 Microns XI 00 X100 XI 00 XI 00 X100

6 .35 8.6 1.07 .54 .53 1.79

6.47 8.5 .97 .49 .46 1,64

6 . 58 8.4 .95 .49 .56 1.53

6.70 8.3 .98 .50 .58 1.56

6.80 8.2 1.09 .55 .57 1,80

6.91 8.2 1.00 .51 .44 1,72

7.01 8.2 1.12 .57 .49 1.92

7.13 8.1 1.10 .56 ,52 1.86

7.25 8.1 1.08 .55 .54 1,80

7 o 37 8.0 1.09 ,55 .50 1,85

7.49 8.0 1.12 .57 .58 1.85

7.60 8.0 1.14 .58 .56 1.91

7.71 7.9 1.10 .56 .52 1.86

7 .94 7.9 1.14 .58 .52 1.94

8.12 7.9 1.13 .58 .43 1,97

8.32 7.9 1.10 .56 .48 1.89

8.50 8.0 1.11 .57 .50 1,90

8.70 8,2 1.06 .54 .51 1.80

8.88 8.1 1.03 ,53 .55 1.70

9.05 8.1 1.01 .52 .45 1.73

9.22 . 8,1 1.04 ,53 ,46 1.77

9.38 8,6 ,96 .49 .38 1,67

9.55 8,9 .96 .49 ,48 1.61

9.71 8.6 .96 ,49 .47 1.61

9.87 8.0 .89 .46 .48 1.47

10.03 7.7 ' .97 .50 .49 1.62

10.15 7.4 .79 .40 ,42 1.30

10.34 7.3 o 78' .40 .39 1,30

10.50 7.2 ,70 .36 ,43 1.10

10.64 7.1 .72 .37 .42 1.16

10.80 7.1 .76 .39 ,33 1.30

10.94 6.9 .79 .40 .45 1.28

11.08 6.9 .72 .37 .43 1.22

11.22 6.8 .73 .37 .36 1.22

11.35 6,8 .69 .35 ,32 1.16

WADC TR 59“ 510 Pt IV 68
TABLE I cont 1 d

NORMAL SPECTRAL EMITTANCE OF

PLATINUM WORKING

Wavelength—^ Emittance—

/

Microns X100

11.49 6.7

11.62 6.7

11.74 6.7

11.87 6.6

12.00 6.4

12.13 6.4

12.26 6.5

12.38 6.4

12.50 6.4

12.63 6.4

12.75 6.4

12.88 6.4

13.00 6.3

13.12 6.2

13.24 6.3

13.36 6.3

13.48 6.3

13.60 6.3

13.72 6.2

13.84 6.3

13.95 6.3

14.06 6.2

14.17 6.3

14.28 6.3

14.38 6.4

14.49 6.5

14.60 6 .

14.71 6.7

14.82 6.8

14.92 7.0

STANDARDS AT 1100°K

3/ & m

6/

<7 ~

S X100 X100 X100 X100

.61 .31 .33 1.01

.68 .35 .35 1.12

.58 .29 .30 .96

.58 .30 .47 .79

.53 .27 .35 .82

.55 .29 .39 .82

.44 .23 .36 .60

.48 .24 .37 .68

.43 .22 .39 .52

.43 .22 .35 .57

.45 .23 .38 .58

.43 .22 .32 .62

.38 .19 .35 .44

.36 .18 .26 .52

.36 .18 .33 .43

.36 .18 .33 .41

.44 .22 .32 . 64

.48 .25 .34 .71

.38 .19 .26 .56

.41 .21 .26 . 64

.44 .22 .35 .60

.45 .23 .42 .51

.46 .23 .33 .66

.46 .23 .39 .59

.39 .20 .32 .53

.40 .20 .37 .47

.44 .22 .34 .62

.42 .22 .35 .57

.42 .21 .34 .56

.50 .25 .45 .59

WADC TR 59-510 Pt IV
TABLE I cont'd.

NORMAL SPECTRAL EMITTANCE OF

PLATINUM WORKING STANDARDS AT 1100 K

Wavelength

2/ EMITTANCE- 3/

rr ~

t 4/ e—

5/ n —

m

6/

rT s Microns X100 XI 00 X100 X100 X100

15.03 7.0 .40 .20 .34 .50

15/14 7.0 .51 .26 .44 .65

1/ Emittance was computed at uniform increments of wavelength drum

position,, which are not uniform increments of wavelength.

2/ Average of 18 measurements, 3 each on 6 specimens.

3/ Standard deviation of the 18 measured values about the average.

4/ 957o confidence error of the average of 18 measurements.

5J Average standard deviation of the 3 measured values for each

specimen about the average for that specimen.

6/ Standard deviation of the 6 average values for the 6 specimens

about the overall average.

WADC TR 59-510 Pt IV 70
TABLE 1 cont'd.

NORMAL SPECTRAL EMITTANCE OE

PLATINUM WORKING STANDARDS AT 1400 °K

, 1 / Wavelength—

2/ Emittance— 3/

<y

t 4/

e 5/ a ~

tn 6/ a —

s Microns X100 X100 X100 • X10O XI 00

1 „04 24.9 1.57 .80 .68 2.69

1 .09 24.9 1.55 .79 .70 2.64

1.15 24.8 1.41 .72 .59 2.44

1.22 24.7 1.33 .68 .44 2 o 35

1 . 28 24.4 1.31 ,67 .41 2,33

1 ,36 24.3 1.13 .58 .49 1 . 94

1.44 23.8 1.07 .54 o 38 1.88

1.52 23.3 o 87 .45 ,51 1.41

1.63 22.4 .87 .44 .55 1.35

1.74 21.8 .71 .36 ,48 1 .05

1.88 20.7 ,66 .34 ,52 91

2.10 19.5 .69 .35 .53 , 96

2.36 18.3 .54 .28 .42 .75

2.60 17.1 .64 .32 .45 .93

2.81 16.0 .58 .30 .41 ,87

3 .02 15.2 .57 .29 ,37 .88

3.25 14.6 .58 .30 ,42 .86

3.45 13.9 .69 .35 .42 1.09

3.65 13.2 .77 ,39 .41 1.27

3.87 13.0 .81 .42 .47 1.31

4.09 12.6 .84 .43 ,40 1.42

4.30 12,4 .85 .44 .31 1.51

4.50 11.7 .76 .39 ,26 1.34

4.67 11.8 .79 .40 ,36 1.35

4.83 11.6 .92 .47 .33 1,62

4 .99 11.5 .93 ,48 .39 1,61

5.13 11.3 ,93 .47 .40 1.60

5.27 11.2 .92 .47 .43 1.56

5.40 11.0 .93 ,48 .34 1 . 64

5.54 10.8 .97 .50 .40 1.68

j .69 10.6 1.03 .52 .36 1.49

5,83 10.5 .96 .49 .40 1.67

5,97 10.4 .34 ,43 .34 1,46

£.10 10.3 ,81 ,42 . 36 1.39

6 . 22 10.1 .82 .42 .37 1,40

y, it, y, 4/ } 5/, 6/ See footnotes on page 74

WADC TR 59-510 Pt IV 71
TABLE I eont'd

NORMAL SPECTRAL EMXTTANCE OF

PLATINUM WORKING STANDARDS AT 1400 °K '

Wavelength—^

1/ Emittance— 3/ V

4/

a—

5/

°ra 6/

a

s Microns X100 X100 X100 X100 X100

6.35

' 10.1 ‘ .90 .46 ,33 1.59

6.4? 10.0 .90 .46 .34 1.57

6.58 9.9 .82 .42 .33 1.42

6.70 9.7 .81 .41 .35 1.38

6.80 9.7 .85 .44 .32 1.50

6.91 9.6 .81 .41 .33 1.40

7.01 9.5 .81 .41 .34 1.37

7.13 9.5 .77 .39 .35 1.46

- 7.25 9.6 .88 .45 .31 1.54

7.37 9.6 .94 .48 .38 1.64

7.49 9.5 .89 .45 .36 1.53

7.60 9.5 .85 .44 .39 1.45

7.71 9.4 .90 .46 .45 1,50

7.94 9.3 .88 .45 .37 1,51

8.12 9.2 .92 .47 .39 1,58

8.32 9.4 .85 .44 .40 1.45

8.50 9.4 .81 .41 .41 1.35

8.70 9.5 .80 .41 .36 1.35

8.88 9.5 .79 .40 .37 1.34

9.05 9.5 .74 .38 .34 1.25

9.22 9.4 .78 .40 .34 1.34

9.38 9.5 .80 .41 .35 1.37

9.55 10.0 .84 .43 .41 1,41

9.71 10.2 .75 .38 .31 1.29

9.87 10.0 .81 .41 .46 1.31

10.03 9.6 .75 .38 .34 1.29

10.18 9.3 .67 .34 .25 1.17

10.34 9.1 .62 .32 .35 1.00

10.50 9.0 .60 .31 .32 1.00

10.64 8.9 .68 .35 .42 1.08

10.80 8.8 .60 .30 .36 ,94

10.94 8.7 .59 .30 .32 .*98

11.08 8.6 .63 .32 .42 -.95

11.22 8.6 .57 .29 .34 ..91

11.35 8.5 .56 .29 .38 .85

WADC TR 59-510 Pt IV 72
TABLE I cont'd.

NORMAL SPECTRAL EMITTANCE OF

PLATINUM WORKING STANDARDS AT 1400°K

Wavelength^ ^ , 2/ Emittance- 3/

0\.

iL. 4/

e 5/

CTm

6/

Microns X100 X100 X100 X100 X100

11.49 8.5 .54 .28 .38 .80

11.62 8.4 .53 .27 .31 .85

11.74 8.4 .52 .26 .32 .82

11.87 8.4 .45 .23 .27 .71

12.00 8,4 .50 .26 .31 .79

12.13 8.4 .45 .23 .24 .74

12.26 8.4 .42 .22 .29 .64

12.38 8.4 .44 .23 .27 .70

12.50 8.4 .40 .20 .29 .58

12,.63 8.4 .40 .20 .28 .59

12.75 8.4 .34 .18 .18 .57

12.88 8.4 .39 .20 .21 .64

13.00 8.5 .41 .21 .28 .63

13.12 8.4 .39 .20 .26 .59

13.-24 8.5 .37 .19 .32 .47

13.36 8.5 .31 .16 .17 .50

13.48 8.6 .36 .18 .26 .54

13.60 8.6 .41 .21 .28 .61

13.72 8.6 .35 .18 .30 .47

13,84 8.7 .38 .20 .27 .57

13.95 8.8 .37 .19 ,22 .59

14.06 8.9 .41 .21 .21 .68

14.17 9.0 .44 .23 .26 .71

14.28 9.1 .46 .23 .18 .79

14<,38 9.2 .50 .25 .30 .79

14.49 9.4 .40 .20 .14 .70

14.60 9.6 • .49 .25 .25 .81

14.71 9.9 .55 .28 .23 .94

14.82 10.0 .46 .24 .26 .75

14.92 10.3 .51 .26 .34 -.77

WADC TR 59-510 Pt IV 73
TABLE I cont'd.

NORMAL SPECTRAL EMITTANCE OF

PLATINUM WORKING STANDARDS AT 1400 '"K

, , 1 / Wavelength— „ • 2/ Emittance3/ a

t 4/ e~

5/ n ~

m

6/ V

Microns XI 00 X100 XI 00 XI 00 XI 00

15.03 10.6 .51 .26 .40 .71

15.14 10.5 .51 .26 .29 ,82

!_/ Emittance was computed at uniform increments of wavelength drum

positions, which are not uniform increments of wavelength.

2/ Average of 18 measurements, 3 each on 6 specimens.

3 / Standard deviation of the 18 measured values

4/ 95% confidence error of the average of 18 measurements.

5/ Average standard deviation of the 3 measured values for each

specimen about the average for that specimen.

5/ Standard deviation of the 6 average values for the 6 specimens

about the overall average.

WADC TR 59-510 Pt IV
TABLE II

NORMAL SPECTRAL EMITTANCE OF

KANTHAL WORKING STANDARDS AT 800 °K

Wavelength—^ 2/ Emittance— 3/

CTt"

4/ e~

5/ c —

m

6/

cr —

s Microns X100 xioo X100 X100 X100

1.15 65.8 1.98 1.01

1.22 66.5 1.93 .98

1.28 68.4 2.22 1.13 .96 3.56

1.36 70.7 2.24 1.14 .86 3.55

1.44 72.7 2.13 1.09 .81 3.50

1.52 74.1 1.75 .89 .76 3.34

1.63 74.8 1.75 .89 .72 3.09

1.74 75.0 1.73 .88 .69 2.85

1.88 74.3 1.56 .74 .68 2.75

2.10 73.5 1.47 .75 .72 2.64

2.36 72.7 1.48 .76 .70 2.65

2.60 71.0 1.55 .79 .66 2.66

2.81 69.4 1.72 .88 .63 2.64

3.02 68.2 1.48 .76 .60 2.56

3.25 67.2 1.39 .71 .55 2.44

3.45 66.0 1.22 .62 .55 2.31

3.65 64.8 1.18 .60 .57 2 . 30

3.87 64.0 1.38 .70 .65 2.43

4.09 63.3 1.53 .78 .66 2.65

4.30 63.1 1.82 .93 .62 2.90

4.50 62.5 1.82 .93 .61 3.02

4.67 62.8 1.77 .90 .61 2.98

4.83 62.5 1.68 .86 .51 2.75

4.99 62.2 1.41 .72 .50 2.42

5.13 61.8 1.09 .56 .50 2.11

5.27 61.1 .97 .49 .46 1 . 85

5.40 60.3 • .98 .50 .44 1.68

5.54 59.6 .94 .48 .42 1.62

5.69 58.8 .95 .48 .42 1.63

5.83 57.8 .95 .48 .45 1.76

5.97 56.7 .97 .50 .49 1.84

6.10 55.7 1.35 .69 .49 1.95

6.22 54.8 1.18 .60 .51 2.09

6.35 54.4 1.24 .63 .53 2.24

6.47 54.2 1.31 .67 .51 2.26

6.58 53 .

5

1.37 .70 .53 2.38

WADC TR 59-510 Pt IV
TABLE II c ont 1 d

.

NORMAL SPECTRAL EKITTANCE OF

KANTHAI, WORKING STANDARDS AT 800 °K

Wavelength^ „ . 2/

Ermttance- 3/ 4/e“

5/ n —

m

6/

°s

Microns XI 00 XiOO X100 X100 X100

6 o 70 53.2 1.38 .71 .53 2.44

6.80 53.4 1.52 . 77 .55 2.53

6.91 53.1 1.39 .71 .55 2.65

7.01 53.4 1.57 .80 .53 2.74

7.13 53.6 1.65 .84 .50 2.82

7.25 53.7 1.60 .82 .48 2.96

7.37 53.9 1.67 .85 .45 3.02

7.49 54.3 1.75 .89 .43 3.05

7.60 54.8 1.70 .86 .44 3.05

7.71 55.4 1.75 .89 .45 2,99

7.94 56.5 1.63 .83 .43 2.95

8.12 57.5 1.52 .77 .44 2.96

8.32 58.6 1.64 .84 .40 2,88

8 . 50 60.1 1.72 .88 .38 2.78

8.70 61.2 1.51 .77 .39 2,69

8.88 62.1 1.31 .67 .40 2.51

9.05 63.0 1.30 . 66 ,40 2.35

9.22 63.7 1.16 .59 .45 2.17

9.38 63.8 1.33 .68 ,48 2 , 06

9.55 63.3 1.12 .57 .45 1.97

9.71 62.8 1 .05 .54 ,44 1.96

9.87 62.2 1.02 .52 .45 1 . 86

10.03 61.8 1.14 .58 ,45 1 . 86

10.18 61.5 1.06 ,54 .45 1,85

10.34 61.0 1.12 .57 ,46 1,86

10.50 60.5 1.04 .53 .47 1,78

10.64 60 .

6

1.05 ,54 .47 1,67

10 . 80 61.5 .96 .49 .47 1.57

10.94 62.9 .79 .40 .46 1.48

11.08 64.3 .89 .45 . 46 1.48

11.22 64 .

5

.82 .42 .46 1.48

11.35 63.2 1.05 . 54 .45 1.61

11.49 61.5 .93 .47 .42 1.77

11.62 59.9 1.09 .56 ,40 1.98

11.74 59.0 1.25 . 64 .39 2,09

WADC TR 59-510 Pt IV 76
TABLE II cont'd.

NORMAL SPECTRAL EMITTANCE OF

KANTHAL WORKING STANDARDS AT 800 °K

Wavelength—^ _ , 2/ Emittance- 4/

e- 5/rr —

t m s Microns X100 • X100 X100 X100 X100

11.87 58.6 1.32 .68 .39 2.25

12.00 58.4 1.32 .67 .38 2.38

12.13 58.4 1.34 .68 .38 2.51

12.26 58.7 1.43 .73 .39 2.62

12.38 59.0 1.58 .80 .38 2.72

12.50 59.3 1.64 .83 .38 2.78

12.63 59.5 1.57 .80 .39 2.83

12.75 59.8 1.50 .77 .39 2.90

12.88 59.9 1.57 .80 .38 2.95

13.00 59.9 1.74 .89 .39 3.04

13.12 59.8 1.78 .91 .39 3.14

13.24 59.7 1.82 .93 .40 3.32

13.36 59.6 1.75 .89 .42 3.45

13.48 59.5 2.06 1.05 .45 3.60

13.60 59.3 2.13 1.08 .47 3.76

13.72 59.1 2.19 1 . 12 .48 3.92

13.84 58.6 2.25 1.15 .49 4.07

13.95 58.2 2.21 1.13 .49 4.30

14.06 57.9 2.47 1.26 .48 4.48

14.17 57.4 2.71 1.38 .47 4.70

14.28 56.7 2.69 1.37 .48 4.93

14.38 56.0 2.82 1.44 .53 4.99

14.49 55.6 2.83 1.44 .65 5.09

14.60 55.5 2.66 1.36 .76 4.95

14.71 54.4 3.10 1.58 .82 4.97

14.82 54.6 2.42 1.24 .88 4.69

14.92 53.7 2.92 1.49 .90 4.54

15.03 53.7 2.16 1.10

15.14 54.2 2.28 1.16

y, y, i/. 4/, L/

6/ See footnotes at end of Table I(pag e 74)

WADC TR 59-510 Pt IV 77
TABLE II cont’d.

NORMAL SPECTRAL EMITTANCE OF

KANTHAL WORKING STANDARDS AT 1100°K

Wavelength"^ . 2/ Emit tan ce—

3/ a ~

t

CD 5/ a ~

m

6/ a

s Microns X100 X100 X100 X100 X100

1.09 79.40 2.134 1.09

1.15 80.87 2.002 1.02

1.22 81.83 1.882 .96 1.19 2.99

1.28 82.20 1.864 .95 1.12 2.86

1.36 81.94 1.659 .85 1.09 2.79

1.44 81.23 1.686 .86 1.11 2.73

1.52 80.65 1.467 .75 1.10 3.00

1.63 79.69 1.439 .73 1.14 3.11

1.74 78.66 2.534 1.29 1.16 3.25

1.88 77.43 2.013 1.03 1.17 3.44

2.10 75.92 2.062 1.05 1.13 3.56

2.36 74.31 2.209 1.13 1.09 3.53

2.60 72.89 1.983 1.01 .99 3.73

2.81 71.64 2.361 1.20 .92 3.80

3.02 70.14 2.361 1.20 .84 3.80

3.25 68.94 2.113 1.08 .78 3.86

3.45 67.68 2.088 1.06 .77 3.89

3.65 66.30 2.058 1.05 .80 4.00

3.87 65.57 2.424 1.24 .86 4.28

4.09 65.16 2.677 1.37 .88 4 . 64

4.30 64.78 2.903 1.48 .89 5.00

4.50 64.65 3.065 1.56 .90 5.13

4.67 64.78 3.009 1.53 .87 5.11

4.83 64 . 54 2.771 1.41 .83 4.85

4.99 64.18 2.587 1.32 .80 4.42

5.13 63.72 2.185 1.11 .77 3. 99

5.27 63.07 1.913 .97 .74 3.60

5.40 62.26 1.837 .94 .75 3.26

5 . 54 61.43 1.713 .87 .72 3.15

5.69 60.61 1.743 .89 .73 3.08

5.83 59.85 1.850 .94 .74 3.09

5.97 59.01 1.762 .90 .75 3.16

6.10 58.20 1.865 .95 .72 3.33

6.22 57.41 1.912 .97 .72 3.41

6.35 56.89 2.142 1.09 .67 3.60

6.47 56.49 2.053 1.05 .66 3.82

6.58 56.34 2.219 1.13 .66 4.04

I/, 2/, 3/, 4 /, 5/, 6/ See footnotes at end of Table I(page 74)

WADC TR 59-510 Pt IV 78
\

TABLE II c on t

1 d

.

NORMAL SPECTRAL EMITTANCE OF

KANTHAL WORKING standards AT 1 1.00°K

Wavelength—^ ^ . 2/

Emttance""' _ 3/

rjt 4/ e~ ,5/

m

6/

a ~

s Microns XI 00 XI 00 X100 X100 X100

6.70 55.97 2.400 1.22 .64 4.13

6.80 56.07 2 . 500 1.27 .61 4.28

6.91 55.83 2.360 1.20 .65 4.43

7.01 5 6 . 04 2.428 1.24 .65 4.51

7.13 56.32 2.627 1.34 . 66 4.56

7.25 56.58 2.639 1.35 .71 4.66

7.37 56.88 2.648 1.35 .72 4.75

7.49 57.19 2.674 1.36 .72 4.86

7.60 57.61 2.681 1.37 .73 4.82

7.71 53.16 2.754 1.40 ,70 4.80

7 . 94 59.39 2.658 1 .36 .70 4.81

8.12 60.68 2.578 1.31 .73 4.78

8.32 62.04 2.698 1.36 .78 4.69

8 . 50 63.28 2.623 1.34 .80 4.61

8 . 70 64 . 53 2.584 1.32 ,84 4.52

8.88 6 5.59 2.469 1,26 ,84 4 „ 32

9.05 66.52 2.378 1.21 .87 4.13

9.22 67.53 2.182 1.11 ,90 3.9 5 9.33 68.27 2.166 1.10 .93 3. 80

9.55 68.37 2.182 1.11 ,92 3.69

9.71 68.05 2.132 1.09 .95 3.69

9.87 67.64 2.067 1.05 .95 2.65

10.03 67.51 2.237 1.14 .96 3.56

10.18 67.26 2.046 1.04 .95 3.51

10.34 67.23 1.980 1.01 .96 3.50

10.50 66 . 86 2.011 1.03 .94 3.41

10.64 66.68 2.046 1.04 .95 3.31

10.80 66.99 1.991 1.02 .92 3.26

10.94 67.74 1.809 .92 .91 3.18

11.08 68.78 1.816 .93 ,91 3,11

11.22 69.13 1.772 .90 .94 3.08

11.35 68.54 1.891 .96 .95 3.07

11 .49 67.26 1.950 .99 .98 3.12

11.62 66.15 1.812 .92 ,98 3.18

11.74 65.12 1,973 1.00 .97 3.24

WADC TR 59-510 Pt IV 79
TABLE II cont'd.

NORMAL SPECTRAL EMITTANCE OF

KANTHAL WORKING STANDARDS AT 1100°K

Wavelength—^ _ . 2/ Emittance— Qrt

(UJ 4/ e~

K / m

o /

'T s Microns X100 X100 X100 X100 X100

11.87 64.36 1.944 .99 . 9 5 3.13

12.00 63.84 2.019 1.03 ,95 3.48

12.13 63.43 2.156 1.10 .92 3.56

12.26 63.41 2.149 1.10 .91 3,61

12.38 63.59 2.118 1,03 .90 : . 56

12.50 63.68 2.053 1.05 .88 3.52

12.63 63.84 1.900 .97 ,87 3.54

12.75 64.00 2.012 1.03 .86 3.55

12.88 64.30 2.194 1.12 .86 3 . 54

13.00 64 . 53 2.110 1.08 .86 3.59

13.12 64.43 2.023 1.03 .85 3.59

13.24 64.35 2.036 1.04 . 81 3.58

13.36 63.93 1.989 1 .01 .80 3.56

13.48 64.07 2.144 1 .09 • / / 3.57

13.60 63.92 2.020 1.03 1 "1 3.50

13.72 63.77 2. 012 1,03 ,77 3.47

13.84 63.37 1.872 .95 .75 3.40

13.95 63.00 1.907 .97 .73 3.35

14.06 62.84 1,918 .98 .68 3 , 29

14.17 62,49 1 . 886 .96 , 64 3.26

14.28 52.22 1 . 780 .91 .62 3 . 22

14.38 61.55 1.735 .88 .65 3.22

14.49 61.02 1.782 .91 .66 3.32

14.60 60.66 1.967 1.00 .72 3.43

14.71 60.27 2.173 1.11 .74 3.57

WADC TR 59-510 Pt IV 80
TABLE II cont'd.

NORMAL SPECTRAL EMTTTANCE OF

KANTHAL WORICING STANDARDS AT 1100°K

Wavelength”^

2/ Emittance— 3/ a —

t & 5/ a "m

6/ a ~

s Microns X100 X100 X100 X100 X100

14.82 59.78 2.121 1.08 .79 3.72

14.92 59.07 2.112 1.08 .82 3.83

15.03 59.32 2.263 1.15

15.14 59.33 2.285 1.17

y, y, y, y, 5/, 6/ See footnot es at end of Table I (page 74).

WADC TR 59-510 Fl IV 31
TABLE II cont 'd

NORMAL SPECTRAL EMITTANCE OF

KANTHAL WORKING STANDARDS AT 1300°K

Wavelength—^ w . 2/ Emittance 3/ a

t 4/ e~ ^

5/ m6/

ry S Microns X100 XI 00 XI 00 X100 X100

1.01 83.9 2.16 1.10

1.04 84 .

4

2.25 1.15

1.09 84.7 1.99 1.01 1.05 3.30

1.15 84.7 1.83 .93 .93 3.23

1.22 84.6 1.78 .91 . 89 3 , 09

1.28 84.0 1.77 ,90 .86 3 . 10

1.36 83.4 1.82 .93 .83 3,22

1.44 82.6 1.96 1.00 .82 3.31

1.52 81.6 2.07 1.06 .81 3.44

1.63 80.4 2.01 1.03 .77 3,65

1.74 79.1 2.08 1.06 .73 3.78

1.88 77.6 2.30 1.17 .73 3.87

2.10 76.0 2.25 1.15 .72 4.02

2.36 74.4 2,31 1.18 .72 4.18

2.60 72.8 2.31 1.18 .70 4.30

2.81 71.5 2.48 1.27 .69 4.38

3.02 69.9 2.58 1.32 ,66 4.44

3.25 68.8 2.49 1 .27 ,66 4 . 50

3.45 67.6 2.44 1.24 ,66 4 , 63

3.65 66.5 2.54 1.30 ,65 4 , 80

3.87 65 .

6

2.81 1 .44 .66 5

,

1-. 4.09 65.1 3.04 1.55 . 6

1

5 . 3 / 4.30 65.0 3.21 1.64 .58 5.61

4.50 64.6 3.06 1.56 .54 5.68

4.67 64.8 3.15 1.61 .55 5 . 5'6 4.83 64.5 2.97 1.51 .54 5.30

4.99 64.1 2,80 1.43 .60 5.07

5.13 63.7 2.58 1.32 ,67 4.75

5.27 63.1 2.49 1,27 .69 4 .46

5.40 62.5 2.36 1.20 .71 4.20

5.54 61.8 2.21 1.13 .69 4.07

5.69 61.1 2,15 1.10 .65 3.99

5.83 60.2 2.22 1.13 .65 3.93

5.97 59.5 2.26 1.15 .65 3.96

6*10 58.6 2.18 1.11 .63 4.09

6.22 57.9 2.30 1.17 . 66 4.15

6.35 57.4 2,46 1.26 ,74 4.20

6.47 57.1 2.41 1.23 .76 4.31

6.58 56.8 2.46 1.25 .78 4.40

WADC TR 59-510 Pt IV 82
TABLE II cont'd

NORMAL SPECTRAL EMITTANCE OF

KANTHAL WORKING STANDARDS AT 1300°K

Wavelength—^ 2/ Emittance— 3/ V

5/ 6/ a

s“

Microns X100 X100 X100 X100 X100

6.70 56.5 2.50 1.27 .77 4.47

6.80 56.8 2.56 1.30 .73 4.60

6.91 56.6 2.64 1.34 .64 4.71

7.01 56.8 2.71 1.38 .56 4.83

7.13 57.1 2.68 1.36 .51 4.90

7.25 57.3 2.73 1.39 .51 4.98

7.37 57.8 2.72 1.39 .54 5.04

7.49 58.0 2.85 1.45 .58 5.10

7.60 58.4 2.89 1.48 .62 5.13

7.71 59.0 2.87 1.46 .61 5.15

7.94 60.4 2.82 1.44 .61 5.10

8.12 61.7 2.77 1.41 .61 5.05

8.32 62.9 2.73 1.39 .60 4.99

8.50 64.2 2.74 1.40 .59 4.93

8.70 65.4 2.72 1.38 .60 4.79

8.88 66.7 2.65 1.35 .62 4.64

9.05 67.6 2.40 1.22 .63 4.47

9.22 68.6 2.36 1.21 .65 4.33

9.38 69.4 2.29 1.17 .65 4.18

9.55 69.8 2.36 1.20 .70 4.06

9.71 69.9 2.27 1.16 .72 3.98

9.87 70.0 2.13 1.08 .71 3.93

10.03 69.8 2.17 1.11 .67 3.87

10.18 69.6 2.15 1.09 .59 3.83

10.34 69.5 2.18 1.11 .57 3.81

10.50 69.5 2.16 1.10 .55 3.79

10.64 69.3 2.06 1.05 .54 3.81

10.80 69.4 2.00 1.02 .55 3.76

10.94 69.7 2.17 1.11 .62 3.74

11.08 70.2 2.06 1 .05 .63 3.70

11.22 70.5 2.10 1.07 .62 3.66

11.35 70.4 1.96 1.00 .62 3.62

11 .49 69.5 1.98 1.01 .63 3.59

11.62 68.5 2.07 1.06 .66 3.58

11.74 67.5 2.00 1 .02 .64 3.66

W&DC TR 59-510 Pt IV 83
TABLE II cont’d.

NORMAL SPECTRAL EMITTANCE OF

KANTHAL WORKING STANDARDS AT 1300°K

Wave 1 ength~ , 2/ Emit tance— 3/ a

t 4/ e~ „ 5/ m

6/ ,-T s Microns XI 00 X100 X100 XI 00 X100

11.87 66.6 2,01 1 .03 .64 3.63

12.00 66.0 2.00 1.02 .64 3.61

12.13 65.6 2.04 1.04 .62 3.68

12.26 65.4 2.00 1.02 .61 3.72

12.38 65.3 2.18 1.11 .62 3.76

12.50 65.3 2.19 1.12 .61 3.74

12.63 65.5 2.12 1.08 .63 3.75

12.75 65.6 1 .98 1 .01 .64 3.71

12.88 65 .

9

2.04 1.04 .65 3.72

13.00 65.9 2.02 1 .03 .64 3.67

13.12 66.0 2.20 1.12 ,62 3.66

13.24 66.0 2.00 1.02 ,62 3.61

13.36 66.0 1.93 .98 .62 3.56

13.48 65.9 1.89 .97 .62 3.50

13.60 65.8 1.98 1.01 .63 3.46

13.72 65.6 2.04 1.04 .64 3.41

13.84 65.5 1.90 .97 .64 3.34

13.95 65.3 1.81 .92 .69 3.24

14.06 65.0 1.75 .89 .70 3.15

14.17 64.9 1.80 .92 .70 3.11

14.28 64 .

5

1.81 .92 .68 3.06

14.38 64.2 1.80 .92 .71 3.04

14.49 63.9 1.68 .86 .70 3.06

14.60 63.5 1.73 .88 , 78 3.09

14.71 63.2 1 . 84 ,94 .84 3.17

14.82 63.0 2.01 1 .02 1.05 3,32

14.92 62,4 2.09 1.07 1.17 3.43

15.03 62.4 2.40 1.22

15.14 62.3 2.22 1.13

1/, 2/, 3/, 4/, 5/ , 6/ See footnotes at end of Table I (page 74 ) .

WADC TR 59-510 Pt IV 84
TABLE III

NORMAL SPECTRAL EMITTANCE OF

INCONEL WORKING STANDARDS AT 800°K

Wavelength—^ 2/ Emittance” 3/

CT t~

4/ e~

5/ a “

m

6/

Microns X100 X100 X100 X100 X100

1.22 71.8 6.10 3.11

1.28 73.4 6.47 3.30

1.36 75.7 6.11 3.12 1.64 10.73

1.44 77.6 5.81 2.96 1.42 10.43

1.52 79.0 5.40 2.76 1.28 10.35

1.63 79.6 5.12 2.61 1.19 9.74

1.74 79.7 6.15 3.14 1.13 9.13

1.88 79.2 4.40 2.24 1.03 8.60

2.10 79.1 4.15 2.12 .99 7.98

2.36 78.8 3.90 1.99 1.00 6.99

2.60 78.7 3.46 1.77 .97 6.52

2.81 78.1 3.51 1.79 .93 6.05

3.02 77.7 3.13 1.60 .88 5.67

3.25 77.3 2.85 1.46 .78 5.45

3.45 76.9 2.86 1.46 .72 5.17

3.65 76.5 2.78 1.42 .67 5.02

3.87 76.2 2.71 1.38 .62 4.96

4.09 75.8 2.70 1.38 .67 5.17

4.30 76.1 2.66 1.36 .72 5.14

4.50 75.2 3.45 1.76 .77 5.06

4.67 75.5 2.77 1.41 .83 4.98

4.83 75.3 2.55 1.30 .85 4.91

4.99 75.3 2.54 1.30 .79 4.55

5.13 75.4 2.48 1.26 .75 4.47

5.27 75.3 2.45 1.25 .70 4.53

5.40 75.2 2.51 1.28 .61 4.62

5.54 75.0 2.66 1.36 .63 4.72

5.69 74.9 2.70 1.38 .70 4.90

5.83 74.6 2.75 1.40 .74 5.02

5.97 74.6 3.00 1.53 .77 5.02

6.10 74.8 2.88 1.47 .87 4.92

6.22 74.5 2.68 1.37 .89 4.76

6.35 74.7 2.53 1.29 .88 4.55

6.47 74.8 2.34 1.19 .87 4.52

6.58 74.7 2.44 1.25 .84 4.52

WADC TR 59-510 Pt IV 85
TABLE III c on t

1 d

.

NORMAL SPECTRAL EMITTANCE OF

INCONEL WORKING STANDARDS AT 800 K

, 1 / Wavelength” 2/ Emittance” 3/

rr ““ t 4/

e~

5/

rr "

m

6/

rr

' s Microns X100 X100 X100 XI 00 XI 00

6 . 70 74,6 2,83 1 .44 ,81 4.63

6,80 75,0 2,64 1 . 34 .78 4 . 75

6.91 74,7 2,79 1 .42 ,72 4.81

7.01 75.0 2.64 1.34 ,69 4.68

7,13 75.1 2,53 1.29 .73 4,54

7,25 75.3 2.42 1,24 .73 4.31

7,37 75.5 2.34 1.19 .71 4.11

7,49 75.9 2.17 1.11 .70 3.93

7,60 76.2 2,08 1 .06 .72 3,87

7,71 76.4 2.05 1.05 . 66 3.92

7,94 77,5 2,30 1 .17 .67 3.88

8.12 79.4 2.40 1,22 .67 3.80

8,32 81.4 2,07 1.05 .70 3.73

8.50 82.5 1.86 .95 ,69 3.72

8.70 83,0 1.91 .98 ,72 3.68

8.88 83.9 2,28 1.16 .75 3 , 74

9,65 84 .

3

2.30 1.17 .75 3,78

9.22 84.8 2.27 1.16 .75 3.94

9.38 84.8 1 .98 1 .01 ,75 4,01

9.55 84.7 2.32 1.18 .80 3.99

9.71 84,6 2.47 1,26 .76 3.96

9.87 84 ,4 2,31 1.18 .72 4.01

10.03 83.9 2.13 1.09 .72 3.98

10.18 84.0 2.09 1.07 .67 3.83

10.34 84,2 2.23 1.14 .63 3,75

10.50 84,4 2.02 1 ,03 .65 3.69

10.64 84.8 2.06 1,05 ,64 3 . 70

10.80 84.7 1.99 1.01 ,57 3.65

10.94 84.6 2.13 1.09 .59 3,60

11.08 84 ,

6

2.02 1 .03 .59 3.53

11.22 85.0 1 .91 .98 .60 3.51

11.35 85.2 1,86 ,95 ,63 3,50

11.49 85,5 1.97 1 .00 .67 3.46

11.62 85,5 2.12 1 .08 .65 3,46

1 1 , 74 85.3 1.98 1 .01 .64 3.39

WADC TR 59“510 Pt IV 86
TABLE III cont'd.

NORMAL SPECTRAL EMITTANCE OF

INCONEL WORKING STANDARDS AT 800°K

Wavelength-^ 2/ Emittance—

t 4/

e“

5/

rr —

m

6/

O' —

s Microns X100 X1O0 X100 X100 X100

11.87 85.6 1.89 .96 .60 3.38

12.00 85.9 1.65 .84 .65 3.34

12.13 86.1 1.91 .97 .63 3.37

12.26 86.3 2.06 1.05 .63 3.36

12.38 86.3 2.02 1.03 .61 3.45

12.50 86.5 1.88 .96 .50 3.55

12.63 86.6 1.85 .94 .51 3.62

12.75 86.9 2.14 1.09 .45 3.67

12.88 86.9 2.24 1.14 .42 3.78

13.00 86.8 2.18 1.11 .44 3.95

13.12 86,9 2.15 1.10 .52 4.11

13.24 87.0 2.31 1.18 .48 4.23

13.36 86.9 2.57 1.31 .55 4.38

13.48 86.6 2.58 1.32 .58 4.50

13.60 86.2 2.57 1.31 .55 4.58

13.72 85.9 2.48 1.27 .52 4.63

13.84 85.5 2.52 1.28 .50 4.65

13.95 84.8 2.66 1.36 .47 4.61

14.06 84.2 2.56 1.31 .48 4.63

14.17 84.0 2.46 1.25 .46 4.65

14.28 82.4 2.55 1.30 .44 4.61

14.38 81.1 2.53 1.29 .46 4.50

14.49 80.0 2.35 1.20 .53 4.28

14.60 79.3 2.27 1.16 .57 3.94

14.71 78.6 1.94 .99 .70 3.42

14.82 78.2 1.74 .89 .SO 2.80

14.92 76.7 1.41 .72 .81 2.46

15.03 76.8 1.09 .56

15.14 77.2 1.39 .71

If, 2/. 3/, 4/, 5/, 6/ See footnotes at end of Table I (page

WADC TR 59-510 Pt IV 87
I'A !<[.,!• 1 1 1 con l: ' d ,

NORMAL SPEC TEAL EMIT'PAN CIS or INCONEL WORKING ; TANKARDS AT IlOO' ’k

1

; 4 /

i- t

i , 6 /

'

1 nngth'

'

Ernie t ;i i c (' - 3 /

i 6 m s Lev m s v 1 00 X. 1 00 : l oo XI 00 X 1.00

1 ,09 83 .

5

4.73 2 .41 .80 8.64

1 . 1 5 84 .

5

4.81 2 .45 1 .06 8 , 84

t .22 85.6 4 . 69 2.39 1 .09 8.49

1 .28 86.2 4 . 3 8 2.23 . 70 8.01

1 .36 86.4 4 . 30 2.19 .79 7 . 83

1 . 44 86 .

3

4.04 2.06 .96 7 . 30

1 . 52 86.0 3.96 2.02 1 . 06 2.25

1 .63 85.3 3.79 1 .93 1 .08 6.79

1.74 84.4 3.74 1.91 .81 6.79

1.88 83.2 3.53 1.80 .75 6 .40

2,10 82.3 3.34 1 ,70 .71 6.07

2.36 81.5 3 .01 1 . 53 .62 5.48

2 . 60 81 .2 2.84 1.45 .78 5.10

2.81 80.5 2.79 1 .42 .67 5.03

3.02 79.9 2.53 1.29 .52 4.59

3.25 79.6 2 .44 1.24 . 55 4.41

3 .4 5 79.2 2.33 1.18 . 59 4.19

3 . 6 5 79.0 2.41 1.23 .67 4.30

3.37 73.8 2.43 1.24 .73 4 . 34

4.09 73.6 2.22 1.13 .49 4 . 0 3 4.30 7 8 .

5

2.16 1.10 .85 3.75

4 . 50 7 8.4 2.81 1 .43 1 .48 4 . 64

4.67 7 8.2 2.19 1.12 .73 3 . 88

4.83 78.2 2.21 1.13 .68 3.94

4.99 78.2 2.16 1.10 .66 3 . 84

5 . 1

9

73.3 2.16 1.10 .46 3.92

5.27 78.1 2.06 1 .05 / r «

• T / 3.72

5.40 78.0 2.08 1 .06 .49 3.75

5 » 54 77.9 2 . 1

2

1 .08 . 56 3,81

5.69 77.8 2 . 0 5 1.05 .61 3.66

5.83 77.6 2.12 1 .08 .66 3.77*

5,07 7 7.5 2.16 1.10 .85 3,77

6 . 1 0 78.0 2 . 39 1 . 2 2 .82 4.22

6

.

2

1 7 7 . 8 2.26 1 . 1 5 v 7 b 3.99

6 . 3 5 77.7 2 . 00 1 .07 . 58 3 . 58

6.47 7 7 . 7 2 . 1 5 1 . 1 0 o / / 3.78

6 . 58 78.0 2 . 3 8 i . :> i 99 4 . 1 7

I V

\i,, tp 59-51.0
table III coat 'd

,

NORMAL SPECTRAL EMITTANCE OF

INCONEL WORKING STANDARDS AT 1100°K

Wavelength-^ 2 / Emtttance—

3 / a

t 4/

e— 5 /

cr ~

m

6/

CT —

s Microns X100 X100 X100 X100 X100

6.70 77.6 2.13 1.09 .75 3.76

6.80 78.2 2.25 1.15 .88 3.92

6.91 77.4 2.17 1.11 .87 3.77

7 .01 78.0 2.03 1 .04 .73 3 . 56

7.13 78.3 2.10 1.07 .66 3.73

7.25 78.4 2.10 .107 .62 3.75

7.37 78.5 1.99 1.01 .47 3.59

7.49 78.8 2.15 1.10 .75 3.79

7.60 79.2 1.97 1 .00 .51 3.55

7.71 79.5 2.04 1.04 .52 3.68

7.94 80.2 2.09 1 .07 .73 3.69

8.12 81.0 1.99 1.01 .61 3.55

8.32 82.4 1.84 .94 .70 3.22

8.50 83.5 1.96 1.00 .72 3.45

8.70 84 . 3 1.90 .97 .50 3.42

8.88 84.9 2.03 1.04 .64 3.62

9.05 85.2 1.83 .93 .66 3.22

9 .22 85.6 1.97 1.00 .63 3.49

9.38 85.9 1.93 .98 .77 3.36

9.55 86.2 2.02 1 .03 .60 3.60

9.71 86.3 1.99 1.01 .52 3.58

9.87 85.9 2.03 1.04 .58 3.63

10.03 85.7 1.95 .99 .58 3.48

10.18 85.8 2.01 1.03 .89 3.45

10.34 86.1 2.00 1.02 .88 3.43

10.50 86.3 1.94 .99 .76 3.38

10.64 86.4 1.86 .95 .74 3.24

10.80 86.4 1.90 .97 .62 3.37

10.94 86.5 1.82 .93 .72 3.18

11.08 86.7 1.90 .97 .87 3.20.

11.22 87.0 1.99 1.01 1.03 3.29

11.35 87.1 1.82 .93 .86 3.08

11.49 87.1 1.87 .95 .69 3.27

11.62 87.2 1.82 .93 .70 3.17

11.74 87.4 1.77 .90 .77 3.04

WADC TR 59-510 Pt IV 89
TABLE III cent *d

N ORMAL SPECTRAL EMITTANCE OF

INCONEL WORKING STANDARDS AT U00°K

. 1/

Wave 1 ervgth- 2/ Emittance~

3/

rrt 4/

e“

5/

rr —

m

6/ a ~

9 Microns XI 00 X100 X100 X100 X100

11.87 87.6 1.74 .89 .91 2.88

12.00 87.6 1.83 .93 .71 3.20

12.13 87.7 1.89 .96 .78 3.27

12.26 87.9 2.03 1.03 .77 3.55

12.38 87.9 1.88 .96 .84 3.22

12.50 88.1 2.02 1.03 .68 3.57

12.63 88.3 2.19 1.11 .74 3.87

12.75 83.4 2.39 1.22 .77 4.25

12.88 88.6 2.23 1.14 .71 3.96

13.00 38.6 2.15 1.10 .81 3.77

1 3.12 83.7 2.29 1.17 .64 4.12

13.24 83.7 2.58 1.32 .58 4.66

13.36 88.9 2.74 1.42 .72 4.93

13.48 83.8 2.82 1.44 .76 5.07

13.60 88.5 2.92 1.49 .77 5.25

13.72 88.4 3.05 1.56 .73 5,51

13.84 83.4 3.21 1 . 64 ,59 5.36

13.95 88.0 3.31 1.69 .57 6 » 04

14.06 87.8 3.46 1.76 .58 6.32

14.17 87.1 3 . 50 1.78 .59 6.38

14.28 83.3 3.57 1.82 .65 6.51

14.38 85.5 3.52 1.79 .63 6.42

14.49 84.3 3.78 1.93 .55 6.91

14.60 83.4 4.09 2.09 .73 7.45

14.71 82.3 4- . 1

5

2.12 .61 7.58

TP. 59-510 Pc IV
TABLE III cont’d

NORMAL SPECTRAL EMITTANCE OF

INCONEL WORKING STANDARDS AT 11 00°K

Wavelength”^ v 4 2/ Emittance” 3/

CTt"

4/

e 5/

am

6/ a

s Microns X100 X100 X100 XI 00 X100

14.82 81.2 4.38 2.23 .74 8.00

14.92 79.3 5.06 2.58 .81 9.25

15.03 78.3 4.39 2.24. 1.85 7.57

15.14 78.4 4.73 2.41 1.63 8.35

I/, V, 3/, 4 /, 5/, 6/ See footnotes at end of Table I (page 74).

WADC TR 59-510 Pt IV 91
TABLE III cont'd

NORMAL SPECTRAL EMITTANCE OF

INCONEL WORKING STANDARDS AT 1300°K

1/ Wavelength- . 2/ Emittance— 3/

r? t 4/ e~

5/

rr

~“* m

6/ a ~

s Microns X100 X100 X100 X100 X100

1.01 88.7 3.65 1.86

1.04 88.1 3.72 1.90

1.09 88.3 3.64 1.86 1.67 6.23

1.15 88.0 3.90 1.99 1.34 6.44

1.22 88.6 3.70 1.88 1.27 6.33

1.28 88.4 3.41 1.74 1.22 6.14

1.36 88.4 3.32 1.69 1.21 5.84

1.44 88.0 3.16 1.61 1.12 5.47

1.52 87.6 3.11 1.59 1.02 5.11

1.63 86.9 2.61 1.33 .96 4.75

1.74 86.0 2.36 1.20 .97 4.47

1.88 84.8 2.32 1.18 .95 4.24

2.10 83.8 2.39 1.22 .94 4.07

2.36 83.0 2.48 1.26 .99 4.04

2.60 82,3 2.19 1.08 1 . 00 3.92

2.81 81.7 2.34 1.19 .96 3.75

3.02 81.1 2.02 1.03 .88 3.55

3.25 80.8 1.92 .98 .86 3.42

3.45 80.7 1.84 .94 ,78 3.25

3.65 80.5 1.85 .94 .76 3.18

3.87 80.5 1.79 .91 .73 3.13

4.09 80.4 1.81 .92 .84 3.24

4.30 80.4 1.73 .88 .86 3.24

4.50 79.9 2.32 1.18 .90 3.26

4.67 80.3 1.86 .95 .90 3.29

4.83 30.2 1 .90 .97 .96 3.38

4.99 30.3 1.89 .96 .87 3.29

5.13 80.2 2.04 1.04 .84 3.28

5.27 80.0 1.96 1.00 .86 3.27

5.40 80.0 1.80 .92 .87 3.27

5.54 79.9 1.90 .97 .84 3.37

5.69 79.9 1.90 .97 .85 3.53

5.83 80.0 2.24 1.14 .86 3.62

5.97 79.7 2.38 1.22 .82 3.76

6.10 80.1 2.05 1 .04 .81 3.80

6.22 ^9.8 2.19 1.12 , 79 3.80

6.35 30.0 2.00 1.02 .82 3.78

6.47 79.8 2.20 1.12 .90 3.91

6.58 80.0 2.37 1.21 .95 3.89

WADC TR 59-510 Pt IV 92
TABLE III cont'd.

NORMAL SPECTRAL EMITTANCE OF

INCONEL WORKING STANDARDS AT 1300°R

Wave 1 eng t h“ ? / Emitiance— <r3/

t 4/

e — 5/

ry —

m

6/

ry ““ S Microns X100 X100 X100 X100 X100

6.70 79.8 2.50 1.27 1.03 3.94

6.80 80.1 2.21 1.13 1.07 3.88

6.91 79.8 2.28 1.16 1.03 3.75

7.01 80.1 2.10 1.07 .93 3.66

7.13 80.3 1.99 1 .02 .89 3.63

7.25 80.4 2.12 1.08 .84 3.55

7.37 80.7 2.08 1.06 .88 3.59

7.49 80.9 1.98 1.01 .88 3.61

7.60 80.9 2.27 1.16 .92 3.46

7.71 81.3 2.04 1 .04 .91 3.39

7.94 81.8 1.81 .92 .85 3.34

8.12 82.1 1.88 .96 .77 3.23

8.32 83.2 1.76 .90 .75 3.11

8.50 84.5 1.86 .95 .78 3.10

8.70 85.1 1.71 .87 .80 2.98

8.88 85.4 1.84 .94 .80 2.97

9.05 85.5 1.62 .83 .79 2.90

9.22 86.0 1.72 .88 .86 2.94

9.38 86.6 1.66 .85 .84 2.93

9.55 86.5 1 .93 .99 .83 2.97

9.71 86.7 1.78 .91 .84 2.95

9.87 86.6 1.71 .87 .85 2.94

10.03 86.4 1.68 .85 .73 2.95

10.18 86.8 1.64 .83 .69 2.96

10.34 87.2 1.79 .91 .68 2.96

10.50 87.2 1.74 .89 .68 2.91

10.64 87.0 1.67 .85 .65 2.88

10.80 86.8 1.54 .79 .70 2.82

10.94 87.2 1.54 .78 .69 2.79

11.08 87.6 1.69 .86 .69 2.77

11.22 87.9 1.64 .84 .68 2.77

11.35 87.9 1.63 .83 .68 2.76

11.49 87.6 1.54 .78 .70 2.73

11.62 87.8 1.52 .77 .70 2.72

11.74 88.3 1.64 .84 .73 2.71

WADC TR 59-510 Pt IV 93
TABLE III cont'd.

NORMAL SPECTRAL EMITTANCE OF

INCONEL WORKING STANDARDS AT 1300°K

Wavel ength~^ n , 2/ Emit tance- 3/ a ~

t 4/ e~

5/

rr —

m

6/

ry ~

s Microns X100 X100 X100 X100 X100

11.87 88.4 1.64 .84 .74 2.74

12.00 88.4 1.63 .83 .79 2.77

12.13 88.2 1.64 .84 .78 2.80

12.26 88.2 1.66 .84 .76 2.82

12.38 88.6 1.71 .87 .74 2.89

12.50 88.9 1.65 .84 .75 2.94

12.63 89.0 1.78 .91 .69 2.98

12.75 89.0 1.80 .92 .66 3.03

12.88 88.9 1.67 .85 .72 3.13

13.00 89.3 1.79 .91 .73 3.24

13.12 89.4 1.98 1.01 .77 3.38

13.24 89.7 2.08 1.06 .80 3.56

13.36 89.5 2.21 1.13 .80 3.76

13.48 89.1 2.18 1.11 .78 3.93

13.60 89.2 2.31 1 . 18 .80 4.07

13.72 89 .2 2.38 1.21 .81 4.27

13.84 89.3 2.45 1.25 .84 4.48

13.95 88.9 2.74 1 .40 .86 4 . 64

14.06 88.7 2.78 1.42 .87 4.83

14.17 88.2 2.73 1.39 .90 5.09

14.28 88.0 2.89 1 .47 .92 5.30

14.38 87 . 3 3.16 1.61 .86 5.48

14.49 86.5 3.31 1.69 .88 5.72

14.60 85 .

5

3.21 1.64 .88 5.94

14.71 84.8 3.38 1.72 .84 6.26

14.82 84.1 3.49 1.78 .93 6.25

14.92 83.0 3.96 2.02 1.01 6.55

15.03 81.2 3.42 1.75

15.14 81 .7 4.07 2.08

y, 2/, 3/, 4/, 5/. 6/ See footnotes at end of Table I (page 74)

WA DC TR 59-510 PL [V 94
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U. 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., and

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

In general, each section carries cut specialized research, develonment, and engineering) in the field indicated by

its title. A brief description of the activities, and of the resultant publications, appears on the inside of the

front cover.

W ASHINGTON, 0. C.

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Office of Weights and Measures. BOULDER, COLO.

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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. I Hgh Frequency

Impedance Standards. Microwave Calibration Services. Microwave Circuit Standards. Low requency t “°

Services.

USCOMM-NBS-DC