A thin film gauge for use in measuring distributed convective heat transfer rates occurring along given surfaces, is described. The gauge is particularly suited to measuring test surfaces in the air stream of a wind tunnel. The gauge is characterized by a plurality of painted platinum leads extend across the surface of a substrate; a pair of leads on the surface is adapted to deliver an electric current at a constant amperage through a selected thermally active area. Leads are also coupled at opposite sides of the thermally active area for detecting induced voltage drops occurring in the area so that the active length of the gauge is defined between voltage output leads. Changes in heat transfer to the thermally active area are isolated and determined by detecting induces changes in voltage drop

Mcronald, A. D.

English

NASA Technical Reports Server

NAL AERONAUTICS AND SPACE ADMINISTRATION
WASHINGTON. D.C. 20546
REPLY TO
ATTN OF: GP
TO
MAY 1 0 1974
FROM:
entific & Technical Information Division
Attn: Miss Winnie M. Morgan
GP/Office of Assistant General
Counsel for patent Matters
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.
XThe following information is provided:
U.S. Patent No. : . 5/1
Government or
Corporate Employee
Supplementary Corporate
Source (if applicable)
NASA Patent case No.
, CA
= JfL
jo, (,(7-1
NOTE - If this patent covers an invention made by a corporate
employee of a NASA Contractor, the following is applicable:
YES NO
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
inventor (author) appears at the heading of column No. 1 of
the Specification, following the words "...with respect to
an invention of ..."
Bonnie L. Woerner
Enclosure
https://ntrs.nasa.gov/search.jsp?R=19740013982 2020-03-17T14:42:26+00:00Z
United States Patent
Paine
( i s ) 3,648,516
[45J Mar. 14, 1972
[54] THIN-FILM GAUGE
[72] Inventor: T. O. Paine, Administrator of the National
Aeronautics and Space Administrator with ,
respect to an invention of Angus D. Mc-
Ronald, 2363 Mountain Avenue. La
Crescenta, Calif. 91214
[22] Filed: May 29, 1969
[21] Appl. No.: 828,920
[52] U.S.CI 73/190H
[51] IntCl GOlk 17/00
[58] Field of Search .73/15, 190,204
[56] References Cited
UNITED STATES PATENTS
2,412,471 12/1946 Olson 73/204
3,068,693 12/1962 Ferranetal 73/204
3,367,182 2/1968 Baxter 73/15
OTHER PUBLICATIONS
Brown et al.," Steady-State Heat Flux Guage" In the Review
of Scientific Instruments 32(8) pg. 984- 985, August 1961
Primary Examiner—Richard C. Oueisser
Assistant Examiner—Herbert Goldstein
Attorney—J. H. Warden, Monte F. Mott and G. T. McCoy
[57] ABSTRACT
A thin-film gauge for use in measuring distributed, convective
heat transfer rates occurring along given surfaces, particularly
surfaces of test specimens disposed in the air stream of a wind
tunnel, characterized by the utilization of a thin-film substrate
and a plurality of painted platinum leads extending across the
surface of the substrate including a pair of leads adapted to
.deliver an electrical current at a constant amperage through a
selected thermally active area and a pair of leads coupled
therewith at opposite sides of the thermally active area for de-
tecting heat induced voltage drops occurring in the thermally
active area so that the active length of the gauge is defined
between the voltage output leads, whereby changes in heat
transferred to the thermally active area are isolated and deter-
mined by detecting induced changes in voltage drop occurring
therein.
1 Claim, 3 Drawing Figures
(BlSli-Case-IPO-10617-1).
patent (Has A) u p
FILM GAUGE
cscL 14B
H74-22095
Dnclas
_OAX.1-».
\
Patented March 14, 1972 3,648,516
;8
ANGUS D. MC RONALD
INVENTOR
ATTORNEYS
3,648,516
1 2
• ' • • • * " THIN-FILM GAUGE DESCRIPTION OF THE PREFERRED EMBODIMENT
ORIGIN OF INVENTION Referring now : to FIG. 1, therein is illustrated a test
specimen, generally designated 10. The specimen is supported
The invention described herein was made in the per-
 in an ^t stream by means including a convenient mount 12
formance of work under a NASA contract and is subject to the
 While not specifically illustrated, the mount 12 is of a type
provisions of Section 305 of the National Aeronautics and adapted to be arranged and supported within a wind tunnel of
Space Act of 1958, Public Law 85-568 (72 Slat. 435; 42 USC known design for purposes of supporting test specimens dur-
2457).
 mg investigation of effects of changing thermal conditions
BACKGROUND OF THE INVENTION '« established incident to the direction of an accelerated or high
velocity stream of air across the surface thereof. The shape of
1. Field of the Invention the test specimen is varied, as desired. However, it is intended
This invention relates to temperature measuring devices that initiated temperature changes occurring at selected ther-
and more particularly to a thin-film gauge including an electri- mally active areas be detected with resulting electrical readout
cal resistance adapted to be mounted on a test specimen 15 signals being provided and applied to convenient recording
disposed within a wind tunnel and employed for determining mechanisms, also not shown. Since the structure, function and
heat transfer rates by detecting changes in voltage drops oc- purposes of wind tunnels, as well as the normally associated
curring across the resistance. recording devices, are well understood, a detailed description
2. Description of the Prior Art thereof is omitted in the interest of brevity.
It is known that the electrical resistance of various types of 20 As illustrated, the specimen 10 to be examined is generally
metal varies in accordance with an occurrence of changes in of a wedge-shaped configuration having a knife-edge leading
temperature. This phenomenon has long been exploited in portion 14 disposed in a flow-interrupting disposition within
various types of temperature measuring gauges, since by sup- an air stream: Mounted on the surface of the specimen, ad-
plying a constant current through the device, changes in volt- jacent to its knife-edge portion, there is arranged a thin-film
age drop are proportional to temperature changes in the re- 2^ gauge 16. While the gauge 16 is illustrated as a planar
sistance of the device. However, where attempts have been member, it is to "be understood that it may be of any con-
made to employ this phenomenon in temperature gauges for venient configuration found desirable for various purposes, in-
acquiring measurements of distributed, convective heat eluding the mounting thereof.
transfer rates along the surface of test specimens mounted As best illustrated in FIG. 2, the gauge 16 includes a thin-
within wind tunnels, difficulty has been experienced in obtain- 30 film substrate 18 formed of any convenient dielectric material,
ing accurate readings, primarily because the gauges and their such as, for example, commercially available material corn-
associated electrical leads tend to disturb the flow of the air monly referred to as Pyrex. If desired, the substrate may be
stream, as the stream is directed across the surface of the formed of flexible material whereby the mounting thereof is
specimen. Furthermore, the exposed portions of the leads ab- -, enhanced. Across the surface of the substrate 18 there is pro-
sorb heat and therefore induce a detectable change in the total v'ded in physical parallelism a plurality of electrical conductor
electrical resistance of the gauge circuit and consequently leads 20,22,24 and 26. The leads are applied to the substrate
cause an erroneous reading to be provided at the output for bX employing convenient painted circuit fabrication
the gauge. techniques. In practice, the leads preferably are formed from
._ platinum although other metallic materials may function quite
OBJECTS AND SUMMARY OF THE INVENTION 4U satisfactorily. Since the painting of platinum leads to thin-film
_, . . . . , . . ..„. . substrates involves well-known techniques, a detailed descrip-Th,s invention overcomes the aforementioned difficulty
 tionthereof isomitted.
 P
through the use of a circuit painted on the surface of a thin-
 Neaf Qne C|id of ^ subs(rate ,g adjacent tQ ^ |e
film, dielectric substrate adapted to be mounted on a test
 of ^ j^. cimen 10, there is provided an electrical
specimen and including constant current electrical leads inter- 45
 conductor 28 wfijch interconnects the |eads 20 th h 26.
connected through a thermal detecting resistance, across ^
 condudor & formed in a manner simi)ar to that in
6
which
which a voltage measuring device is connected so that an mex-
 the conductoVieads 20 through 26 were formed. However, it
pensive and nonperturbating temperature gauge is provided
 js tQ ^  rticular, noted that ^em tne |eads 22 ^ ^
for reporting an accurate readout corresponding.*, tempera- ^ ^ ,ead 2g ^^ g segmen, designated 3,, ,t is intended
ture changes . . . . . . , that this segment be extended through the thermally activeAn object of die instant invention is to provide an improved
 afea rf ^ surface tQ be ,ed for determini convective
thm-film gauge for measuring convective heat transfer rates.
 heat transfer>ates while the leads 20 ^ h 26 aK a|ug.
Another object is to provide a convective heat transfer rate
 tfated n ^ „ ed |t js to ^ understood that u js
measuring device for use in detecting and measuring changes
 not ftt a,| necessary that th te „ d and ,hat the
,n surface temperatures .mparted to test specimens mounted
 mem 3Q bg of ^ ,ength desired ^ provjding the desired £
in wind tunnels. . . . ' _ , • , . tection and indication of heat transfer. However, it is impor-Another object is to provide an improved thm-film, electn- ^
 w note ^ ^ resolutjon of the fa ennancJ b
cal circuit adapted to employ an electrical current at constant shortening this segment
amperages to indicate temperature changes occurring within
 6Q The ^^^ ^ ^ inustrated in FiG. 3, at ^y given in.
selected, thermally active areas by detecting and providing
 stam has M eiectrica, resistance of m ohmic va,ue deter.
output signals indicative of heat induced changes in circuit re-
 mined by ^-^^^^y of heat delivered thereto. Therefore, as
sistance as the changes occur within an electrical circuit com- ,he temperature of tne segment is varied, in response to a
ponent extended through the thermally active areas. transfer of heat thereto, its resistance is varied. Consequently,
BRIEF DESCRIPTION OF THE DRAWING 65 by determiningthe value of ^e electrical resistance of the seg-
ment, its temperature becomes a known quantity, since for
FIG. 1 is a perspective view of a test specimen mounted each value of resistance there is a corresponding temperature,
within a wind tunnel having a thin-film gauge of a type em- The leads 20~and 26, in effect, provide a path of relatively
bodying the principles of the instant invention mounted along low resistance for a current of a constant amperage. The re-
a surface thereof. 70 sistance of the leads schematically is represented, FIG. 3, by
FIG. 2 is a fragmentary cross section taken generally along resistors 32 and 34. In practice, these leads are extended along
line 2—2 of FIG. 1. the substrate 18 and terminate at points removed from the
FIG. 3 is a circuit diagram of an electrical circuit of a type path of the stream of air flowing over the surface of the test
within which the gauge of FIGS. 1 and 2 may electrically be specimen. This arrangement permits electrical connections to
connected. '5 tie made without disturbing the flow of air across the
3,648,516
4
specimen. As shown, the conductor leads 20 through 26 are
coupled with the electrical leads 36,38,40 and 42 at terminals
44. 46, 48 and 50, respectively. The leads 36 through 42 ex-
tend to a convenient terminal board 52 having mounted
thereon a plurality of convenient electrical connectors, such 5
as, for example, binding posts 54,56,58 and 60.
While a DC (Direct Current) source 62 of electrical poten-
tial serves-to provide an electrical current at a constant am-
perage through the circuit of the gauge 16, various types of
constant current sources are available and may be employed 10
quite satisfactorily. Such sources include transistorized cir-
cuits of various and known types capable of delivering DC
currents at given amperages. However, for purposes of ex-
planation, the source 62 is a DC battery of a predetermined
voltage rating. 15
With particular reference to FIG. 3, it will be noted that
when the gauge 16 is activated, a current flow is established
through the resistance 30, between the terminals 44 and 50,
while a voltage pickoff is provided for the terminals 46 and 48.
These terminals are connected with the lead 28 at the opposite 20
sides<of the resistance segment 30. A pair of terminals 49 dia-
grammatically represents the point of connection for the ter-
minals 46 and 48.
The terminals 46 and 48 are, in turn, connected to opposite
sides of a convenient voltage detecting device 64, illustrated 25
as a conventional voltmeter. However, it should be fully ap-
preciated that the function of the device 64 is to detect
changes in voltage drop occurring across the resistance 30
and, therefore, various types of readily available voltage mea-
suring devices, including oscilloscopes, may be employed. 30
The electrical resistance of the leads 22 and 24 are, for the
sake of simplicity, illustrated as resistances 66 and 68, FIG. 3.
Therefore, since the circuit of the gauge 16 includes a plurali-
ty of electrical resistances, a convenient variable, high-re-
sistance resistor 70 is connected in the circuit in series with 35
the circuit of the gauge for thereby assuring that a constant
amperage is provided for the flow of current delivered through
the gauge, in accordance with well-known principles of circuit
design. In order to achieve an electrical balance for the volt-
meter 64, as it is connected at the opposite sides of the seg- ^0
ment 30, another variable resistance resistor 72 is provided
and employed in coupling the voltmeter between the terminals
46 and 48.
Therefore, it should be apparent that as the source of DC
potential 62, connected with the terminals 44 and 50, applies ^5
a voltage across the segment 30 a detectable voltage drop
across the segment 30 occurs. However, this voltage drop is, in
effect, isolated from the voltage drop occurring across the re-
sistances 32 and 34 since the voltmeter will detect only the
voltage drop occurring across the resistance of the segment ^0
30.
Referring particularly to FIG. 2, it will be noted that the
substrate 18 is illustrated as being inserted into a relief,
designated 74, formed in the surface of the specimen 10. The
purpose of inserting the substrate 74 to establish a coplanar "
relationship with the surface of the test specimen is to avoid
perturbation of the flow of air across the specimen. Since the
leads employed are relatively thin, perturbation is minimized.
It should, of course, be understood that the substrate 18
may be mounted on the surface of the test specimen 10 at any °°
desired location and, due to the relatively small dimension of
the thickness of the substrate, perturbation is for practical
purposes often deemed negligible.
65
It is believed that in view of the foregoing description..the
operation of the device will be readily understood and it will
be briefly reviewed at this point. With the thin-film gauge 16
seated on or alternatively within a relief at a selected area to
be investigated along the surface of a test specimen, in a
manner such that the segment 30 extends through the ther-
mally active area, the source of electrical potential 62 is con-
nected across the segment at the terminals 44 and 50. The
voltmeter 64 then is connected at opposite sides of the seg-
ment. The specimen 10 mounted on the support 12 operative-
ly is arranged within a wind tunnel of a selected capability. As
a high velocity stream of air is forced across the leading por-
tion of the specimen, the temperature thereof is elevated. As
the temperature of the specimen is elevated, a transfer of heat
to the gauge 16 occurs, which heat is transmitted to the lead
28. As the temperature of the lead is elevated, the resistance
of the segment 30 is increased. At various points in the testing
cycle a reading is taken at the voltmeter to determine the volt-
age drop then occurring across the segment. This reading nor-
mally is taken by closing a convenient switch, such as switch
80, for a period of only a few milliseconds. The ohmic.value of
the voltage drop continues to increase as the temperature in-
creases. For each change in the value of the voltage drop ex-
perienced, a known temperature value is assigned so that for
any detected voltage drop, the temperature of the segment 30
is provided, whereby heat transfer rates are determined.
Although the invention has been herein shown and
described in what is conceived to be the most practical and
preferred embodiment, it is recognized that departures may be
made therefrom within the scope of the invention.
What is claimed is:
1. In a heat transfer measuring system for use in measuring
distributed, convective heat transfer rates at a selected surface
of an aerodynamic body operatively supported within an air
stream, a thin-film gauge comprising:
A. a substrate-including a planar portion formed of a thin-
film dielectric material and including a thermally active
region configured to be seated in a recess formed in a
selected surface of an aerodynamic body;
B. a pair of spaced electrical energy leads deposited on the
substrate and extending along opposite edge portions
thereof in spaced relationship with said thermally active
region;
C. means remote from said thermally active region for con-
necting the leads across a source of electrical potential;
D. an electrical lead including a segment deposited on said
planar portion and extending through the thermally ac-
tive region of the gauge and electrically interconnecting
the spaced input leads for conducting an electrical cur-
rent through said thermally active region of the gauge;
E. a pair of voltage pickup leads deposited on said substrate,
electrically connected with the segment adjacent op-
posite sides of said thermally active region and terminat-
ing at points remote therefrom;
F. a pair of voltage output terminals remotely related to said
segment and electrically coupled with a voltage measur-
ing device; and
G. means electrically connecting the voltage pickup leads
with the voltage output terminals, whereby as the tem-
perature of the thermally active region is varied a change
in electrical resistance is imparted to the segment, so that
the resulting change in the voltage drop occurring across
said segment is detected by said voltage measuring device
in order that changes in the convective heat transfer rate
may be determined. <-
OPERATION
70
75


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