A radiometer is described operating in a vacuum under steady state conditions. The front element is an aluminum sheet painted on the outer side with black or other absorptive material of selected characteristics. A thermocouple is bonded to the inner side of the aluminum sheet. That is backed by highly insulative layers of glass fiber and crinkled, aluminized Mylar polyester. Those layers are backed with a sturdy, polyester sheet, and the entire lamination is laced together by nylon cords. The device is highly reliable in that it does not drift out of calibration, and is significantly inexpensive

Loose, J. D.

English

NASA Technical Reports Server

REPLY TO
ATTN OF: GP
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
WASHINGTON. D.C. 20546
JUL 3 1974
TO: KSI/Scientific & Technical Information Division
Attn: Miss Winnie M. Morgan
FROM: GP/Office of Assistant General
Counsel for Patent Matters
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SUBJECT; Announcement of NASA-Owned U.S. Patents in STAR
In accordance with the procedures agreed upon by Code GP
and Code KSI, the attached NASA-owned U.S. Patent is being
forwarded for abstracting and announcement in NASA STAR.
The following information is provided:
U.S. Patent No.
Government or
Corporate Employee
Supplementary Corporate
Source (if applicable)
NASA Patent Case No.
3,%iyiT
\)«15. cr o oer/\ t/fr e^\^
NOTE - If this patent covers an invention made by a corporate
employee of a NASA Contractor, the following is applicable:
YES /—7 NO /y7
Pursuant to Section 305(a) of the National Aeronautics and
Space Act, the name of the Administrator of NASA appears on
the first page of the patent; however, the name of the actual
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an invention of ..."
Bonnie L. Woerner
Enclosure
https://ntrs.nasa.gov/search.jsp?R=19740019748 2020-03-17T15:01:27+00:00Z
United States Patent
Loose
[in 3,819,419
[45] June 25, 1974
[ 54 ] STEADY STATE THERMAL RADIOMETERS
[75] Inventor: Jack D. Loose, Huntsville, Ala.
[73] Assignee: The United States of America as
represented by the Administrator of
the National Aeronautics and Space
Administration, Washington, D.C.
[22] Filed: Nov. 17, 1972
[21] Appl. No.: 307,728
[52] U.S. Cl 136/213, 136/230, 136/233
[51] Int. Cl HOlv 1/02
[58] Field of Search 136/213, 216, 230, 233,
136/225; 73/355 R
[56] References Cited
UNITED STATES PATENTS
3,427,209 2/1969 Hager 136/225
3,431,149 3/1969 Webb 136/213
3,511,991 5/1970 Beerman 136/213 UX
3,607,445 9/1971 Mines 136/225
OTHER PUBLICATIONS
'Leighton et al., J. Phys. Chem., 36, 1822-1824 (1932)
Primary Examiner—Benjamin R. Padgett
Assistant Examiner—E. A. Miller
Attorney, Agent, or Firm—L. D. Wofford, Jr.; G. J.
Porter; J. R. Manning
[57] ABSTRACT
A radiometer operative in a vacuum under steady-
state conditions. The front element is an aluminum
sheet painted on the outer side with black or other ab-
sorptive material of selected characteristics. A ther-
mocouple is bonded to the inner side of the aluminum
sheet. That is backed by highly insulative layers of
glass fiber and crinkled, aluminized Mylar polyester.
Those layers are backed with a sturdy, polyester sheet,
and the entire lamination is laced together by nylon
cords. The device is effective for the purposes de-
signed, is highly reliable in that it does not drift out of
calibration, and is significantly inexpensive.
12 Claims, 2 Drawing Figures
V
PATENTED JUN251914 3,819,419
.FIG. I. FIG.2.
A7
3,819,419
1 2
STEADY STATE THERMAL RADIOMETERS for fabrication, precluding fabrication by the relatively
• /-VT-.I.T-.IVI f\r -T-TII- ixi\/r:Krri/~»xt unskilled user.ORIGIN OF THE INVENTION
 g ^ ^.^ & Bulky Mounting_Many of the
The invention described herein was made by an em- commeriial sensors are relatively heavy, requiring
ployee of the United States Government and may be 5 bulky mounting fixtures which block part of the mount-
manufactured and used by or for the Government for jng surface from the incoming flux,
governmental purposes without the payment of any None of the known prior art employs an uncompli-
royalties thereon or therfor.
 cated sensing assembly isolated by a pad of insulation
BACKGROUND OF THE INVENTION m tne manner °f this invention. The radiometer in ac-10
 cordance with this invention is designed for use for
This invention relates to radiometers, and in particu- steady-state applications in a vacuum,
lar to devices to observe and measure thermal radiation
in a vacuum or other environment in which convection SUMMARY OF THE INVENTION
and heat transfer influences are not significant factors.
 It is a prirnary object of this invention to provide a ra-
diometer which is inexpensive and practical.
Many variations of thermal radiation flux sensors are
 It is> sirniiariy> an object of this invention to provide
commercially available. Those which measure only ra-
 a radiometer which is uncomplicated and may be fabri-
diation effects are properly denominated radiometers.
 cated without Spedaiize(i equipment, facilities, or per-
Other sensors respond to a range of heat transfer condi- sonnel
tions, including conduction and convection, and are 20
 It is ^ ^ object of this invention to proivde a radi.
denominated calorimeters ometer which is relatively sturdy and not notably sub-
Radiometers are typically sophisticated and expen- .
 t tQ jm d £
sive, monitoring both steady state and transient fluxes ,t fe ^ ^ objecfof ^ invemion ,o idg a radj,
and bemg capable of operation ma vacuum an atmo-
 25 Qmeter which is easi, fabricated and ma be built to
sphere, or both. Such sensors generally employ one of
 custom irement/b the user.
three principles. The Gardon type sensor works on
 I{. ano*eT object f ^  . ^ ^ rad[
the principle that the heat absorbed by an exposed cir-
 Qmeter whjch do
J
es jre periodic
H
calibration.
cular disk ,s a funct.on of the resul ing radial tempera-
 ft an ^ f £ . ^
ture gradient across the disk. The Schmidt-Voltaire
 lfl ,' ,. ,
 J
, . . .. ,0
 . ., • • , ., . .. , . , w a radiometer which does not require complicatedtype sensor works on the principle that the heat ab- „ . . . . . ., , ,.cJr
, ,, ,
 f • .. ,. ., . matermatical manipulation or other such modificationsorbed by an exposed wafer is proportional to the tern-
 f , A t
perature gradient through the wafer. The "capaci- ° ,ine oulp.ut a^ , ,. . -A A-
tance" type gage works on the principle that the heat It is another object of this mvenuon to prov,de a radi-
absorbecI by an isolated slug is a function of the slug
 35
 ometer wh
'
ch| ls not ^ubJe^ to sPe^trum filtenng'
temperature and temperature-time derivative. . J1S' similarly, another object of this invention to pro-
The prior art devices are limited by a number of dis- v'de/ "diometer which has no inherent limitation in
advantageous characteristics, in particular the follow- thf frequency range observed.
: It is also an object of this invention to provide a radi-
L Expensive-Commerical sensors are manufac- 40 ometer which is H8ht in we'8nt and easi'y mounted-
tured in small lots or to customer requirements and If 1S> similarly, an object of this invention to provide
generally exceed $100.00 per unit in cost to the cus- a radiometer which is small and minimizes blockage of
tomer any surface to which it is mounted.
2. Fragile-Most sensors contain delicate internal It is another object of this invention to provide a radi-
mounting strands and fine wiring, requiring care in han- 45 ometer which has an unimpaired (180°) field of view in
dling to avoid damage. one direction.
3. Require Temperature Correction—Many sensors In accordance with this invention a radiation-
require relatively inaccurate temperature correction responsive, temperature-measuring radiometer has a
factors or special temperature conditioning (such as metal sheet painted on the outer side with an absorp-
water cooling of the sensor), making their use difficult, 50 live material of desired characteristics. A thermocou-
particularly in enclosed vacuum chambers. P'e is attached to the inner side. That assembly is
4. Require Correction for Spectrum Filtering—Se- backed by an insulating pad of high performance, made
veral sensors employ a window over the sensing ele- up of layers of glass fiber and aluminized polyester in
ment which filters part of the incident energy spectrum. the preferred embodiment. The far layer may be a
Such systems require a precise knowledge of the inci- 55 heavy, polymer sheet, and the entire assembly is laced
dent spectrum and an approximate calculation after the together by cords of heat insulation material, such as
measurement to determine the energy level received. nylon.
5. Limited Range-Few of the sensors are capable of DESCRIPTION OF THE DRAWINGS
accurately monitoring radiation fluxes in the low range
(0 - ¥2 solar constant). These and other objects, features, characteristics,
6. Require Recalibration—To maintain accuracy, the and advantages of the invention will be apparent by
complex or delicate sensors require recalibration after consideration of the following description of preferred
extended use. Recalibration is usually performed at a embodiments, as illustrated by the accompanying
fee by the manufacturer, as it usually entails the use of
 65 drawings.
specialized and expensive calibration equipment. FIG. 1 is a perspective view of a preferred device,
7. Difficult to Fabricate—Commercially available round in external configuration, with the parts sepa-
sensors require specialized tooling, skills, and materials rated for better illustration.
3,819,419
FIG. 2 illustrates two of the devices completed, one
round and one square, but otherwise essentially identi-
cal.
DESCRIPTION OF THE PREFERRED
EMBODIMENTS
The preferred'embodiment comprises one of circular
form, 1 % inch in diameter, and one of square form, 2
inches wide, which are otherwise essentially identical.
FIG. 1 shows the circular embodiment, but is equally
descriptive in other respects of the device when built
square externally or of .other external configurations.
As will be evident, the outer configuration defines the
area of ratiation intercepted and thereby observed by
the radiometer.
A thin, aluminum alloy plate 1 serves as the sensing
head. The outer side of the plate 1 is painted com-
pletely with a surface 3 (FIG. 2) of a material absor-
bent to selected spectral bands of heat radiation. Such
materials are available conventionally and may be
black if the entire spectrum is of interest, or may be of
a nature absorbent to only the frequencies of interest.
On the inner side of plate 1, a conventional, copper-
constantan, two-wire thermocouple 5 is attached. In
the preferred embodiment it is attached to the surface
with strips of adhesive tape 7. The leads from thermo-
couple 5 which extend from the body of the radiometer
are wrapped with a metal shield to substantially elimi-
nate inaccuracies which might be caused by radiation
loss from those leads.
Plate 1 contains four, 0.025 inch diameter holes
symetrically located near its outer edges.
Behind thermocouple 5 are alternate layers which
make up a high-performance thermal insulation pad.
The comprises alternate layers of paper-like fiber glass
9, followed by layers of crinkled (a rumpled condition)
aluminum coated (aluminized) Mylar polyester 11.
(The glass fiber laminations 9 in the preferred embodi-
ments are of borosilicate glass fibers, nominally 14
pounds per cubic foot, with each lamination being
0.006 inch thick.) The laminations 9 and 11 have four
holes punched through them matching and aligned with
the holes in the plate 1.
At the inner side is a strong, polyester sheet 13,
which provides rigidity to the assembly. In the pre-
ferred embodiment sheet 13 is Mylar polyester 0.014
inch thick. It is also has holes matching and aligned
with those in plate 1 and the pad elements 9 and 11.
• The plate 1 and its attachments, the insulation pad 9
and 11, and the backing sheet 13 are held in contact by
low-thermal-conductivity nylon cords 15. A single cord
is threaded through each of the aligned holes of the as-
sembly and is heated at each end to form a bead 17 at
each end which will not then pass through the holes.
The radiometer may be suspended in place for mea-
surement by threads 19 (FIG. 2, square.embodiment)
attached to the backing sheet 13 or may be fastened to
the test article surface. A conventional Velcro fastener
21 is shown on the back of the circular embodiment in
FIG. 2 as illustrative of the use of such fasteners.
The devices can be fabricated inexpensively and
without special facilites. The cost of materials may be
quite small. Technicians without extensive training or
exceptional skills have fabricated the devices in quani-
tites of more than four hundred at an average time ex-
pendature of 1.04 hours per device. This compares
with an approximate purchase cost of $300.00 for each
commerical sensor which would otherwise be used for
the same measurement operation.
THEORY OF DESIGN AND SELECTION OF PARTS
5
In the absence of convective heat transfer (i.e., in a
vacuum) the outer, steady-state flux absorbed by the
absorbent surface equals the sum of re-radiation and
conduction losses, which is stated by formula as fol-
10 lows:
15
20
where:
Qate = Absorbed heat flux (BTU/hr-ft2)
e + Emissivity of surface
a- = Stefan-Boltzmann Constant (0.1714 X lO'8
BTU/hr-ft2)
T = Surface temperature (° R)
QL = Conductive heat loss from surface
Emissivity, e, is a known characteristic, or measurable.
Temperature, T, is monitored directly by the thermo-
couple 5.
QL occurs by conductivity through the .attached
parts, which in the device are the pad insulation 9 and
25 11, the leads of the thermocouple 5, and the nylon
cords 15. The design in accordance with this invention
makes QL negligibly small.
. Since QL is negligible, Q,,te = ewT4.
When the absorbtive coating of the device (numeral
30 3 in FIG. 2) is of known absorptance, a, the incident
flux is directly established mathematically by the fol-
lowing: Qnte = aQiac
where:
Qinc = Incident flux
35 By straightforward substitution and manipulation:
If incident flux is to be monitored, a spectrally insen-
sitive coating, such as a flat black paint, is used. Where
40 the radiant flux absorbed by a surface is to be mea-
sured, and the absorptance of the surface to the incom-
ing radiation spectrum is unknown or not known to the
desired degree of precision, the sensor is coated identi-
cally as the surface; flux absorbed by the surface is then
45 monitored virtually directly without knowledge re-
quired of the surface absorptance.
IN OPERATION
Operation of the device is, of course, inherent in the
50
 design and takes place without human intervention or
movement of parts. Voltage readings at the output
leads of the thermocouple 5 may be directly transposed
into values representing the heat intensity of incident
radiation. The device itself need not be calibrated, and
^ maintenance and other continuing supervision is
largely unnecessary. The device is simple and rugged.
It may be constructed at the site of use in desired form
by relatively untrained personnel.
Since the device has so little tendency to change or
'drift" in output values or to develop other inaccura-
cies, it is quite useful for calibration purposes. The radi-
ometer may be employed to calibrate thermal radiation
simulators, and, of course, used for general monitoring
,. of environments under test for steady-state heat radia-
tion.
The radiometers may be suspended by threads 19 at-
tached to the back sheet 13, or the radiometers may be
3,819,419
attached to an object by a fastener 21 attached to the
back 13.
The very low cost of fabrication and use of the de-
vices is exploited by the use of greately increased num-
bers of the sensors over a given external surface area 5
to be observed or tested. The reliability of the devices
is exploited by using them as redundant measuring ele-
ments with more sophisticated sensors, to thereby indi-
cate inaccurate operation of the more sophisticated de-
vices. The value of the radiometer in accordance with 10
this invention has been established by various actual
performances including the successful use of as many
as three hundred eighty-nine of the sensors to map
steady-state geometric distribution of flux during flux
simulator calibration, and the use of the sensors as 15
backup for commercial sensors in test operations.
The radiometer is suited to be built to the require-
ments of particular applications. Refinements of the in-
vention and other variations will be apparent, and vari-
ations may well be developed which employ more than 20
ordinary skill in this art, but nevertheless employ the
basic contribution and elements of this invention. Ac-
cordingly, patent protection should not be essentially
limited by the preferred embodiments disclosed, but
should be as provided by law, with particular reference 25
to the accompanying claims.
What is claimed is:
1. A radiometer comprising a heat conductive ele-
ment having heat absorptive characteristics on one
side, a thermocouple in contact with the side of said el- 30
ement obverse to said one side, and a pad having high
heat insulating characteristics positioned on said ob-
verse side covering said thermocouple.
2. The radiometer as in claim 1 in which said element
is a metal plate having a layer of absorptive paint on 35
said one side.
3. The radiometer as in claim 1 in which said pad
comprises alternate layers of a fiber material and an
aluminum coated polymer.
4. The radiometer as in claim 3 in which said element
is a metal plate having a layer of absorptive paint on
said one side.
5. The radiometer as in claim 4 in which said plate
and said alternate layer are held in contact by cords of
heat insulative material which pass through aligned
holes through said plate and said alternate layers.
6. The radiometer as in claim 5 in which the material
of said cord is nylon.
7. The radiometer as in claim 5 also comprising a
layer of a strong polymer positioned in contact with the
side of said alternate layers opposite said plate and held
in contact by said cord which passes through holes in
said strong polymer aligned with holes in said plate and
said alternate layers.
8. The radiometer as in claim 7 also having means to
support said radiometer attached to said layer of strong
polymer. •
9. The radiometer as in claim 7 in which said plate is
an aluminum alloy sheet, said fiber material is fiber
glass,-and said aluminum coated polymer is crinkled
aluminum coated polyester.
10. The radiometer as in claim 9 in which said fiber
glass is borosilicate glass and the material of said cord
is nylon.
11. The radiometer as in claim 10 in which said
strong polymer is a polyester and means to support said
radiometer are attached to said layer of strong poly-
mer.
12. The radiometer as in claim 11 in which ends of
said nylon cords have been melted into beads which
will not pass through the aligned holes, thereby holding
the radiometer elements together.
40
45
50
55
60
65


Steady state thermal radiometers

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