Design and characteristics of thermocouples consisting of flexible tape for improved attachment to temperature sourc

Turner, R. C.

English

NASA Technical Reports Server

8 J A M E S  E. W E B B  
A D M I N I S T R A T O R  OF THE N A T I O N A L  A E R O N A U T I C S  
A N D  S P A C E  A D M I N I S T R A T I O N  
THERMOCOUPLE ASSEMBLY 
Filed Nov. 10. 1964 
I 23 I 14 
FIG. 
Fi G. 
14 
TO TEMPERATURE 
REGISTERING 
CIRCUITRY 
I 
2 
2 
6. 
ATTORNEYS ‘x’k.-.-’ 
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aten 
3,377,208 
T ~ ~ M ~ ~ ~ ~ ~ ~ E  ASSEMBLY 
James E. Webb, A ~ ~ i ~ ~ s ~ a t o r  of the National Aeronau- 
tics and §pace A ~ ~ ~ ~ ~ s ~ a ~ i o ~ ~  with respect to an in- 
vention ~f Richard 631. Turner, Levittown, Pa. 
Filed NQB. BO, 1964, Ser. NO. 410,332 
5 Claims. (CH. 3136-23Q) 
ABSTRACT OF THE ~ ~ ~ ~ L ~ $ ~ ~  
A thermocouple assembly which consists of a flexible 
strip of tape, such as nylon. One or a first side of the 
tape, having adhesive prqperties, is used to adhesively sup- 
port a junction of a thermocouple, as well as for ad- 
hesively attaching the assembly to  the surface of matter 
whose temperature is to be sensed. The opposite or a 
second side of the tape has heat-reflecting properties, 
achieved by means of a metallic coating, in order to 
miizimjze heat which is directed to the junction through the 
tzpe. A pair of terminals, electrically insulated from one 
another, are supported on the second side of :he tape 
to provide means for electrically connecting the thermo- 
couple junction to appropriate circuitry. 
Origin of invention 
The invention described herein was made in the per- 
formance of work under a NASA contract and is subject 
to the provisions of Section 305 of the National Aero- 
nautics and Space Act of 1958, Public Law 85-568 (72 
Stat. 435; 42 USC 2457). 
This invention relates to a thermocouple and more par- 
ticularly to an improved assembly thereof. 
The use of thermocouples as temperature sensing de- 
vices is quite widespread in both military and civilian 
applications. 
In designing thermocouples, designers strive to reduce 
the size of the thermocouple bead or junction point of 
the two thermocouple leads, since the smaller the bead's 
surface, the smaller is the undesired heat radiation there- 
from. Further, a smaller bead is less affected by incident 
heat radiation or by the rate of change of surface tem- 
perature. In addition, the response time of the thermo- 
couple to temperature changes is related to its thermal 
mass. Thus, a smaller bead having less mass produces less 
time delay in the signals supplied to indicate the tem- 
perature which is sensed. Designers also strive to use 
relatively short and small leads to connect the bead to  
the rest of the circuitry, since the effects of conduction 
along the leads is directly related to their size and, ap- 
preciable conduction loss along the leads reduces the 
surface temperature being measured, thereby giving false 
rezdings. However, irrespective of the desired to reduce 
the size of the bead and its leads, the entire thermocouple 
assembly must be suEciently rigid so that the thermo- 
couple may be fastened to the surface, the temperature of 
which is to be sensed, as well as be coupled to the leads 
connecting the thermocouple to the additional circuitry 
used to register the sensed temperature. 
An optimized thermocouple assembly is one which, be- 
sides being small but rigid, can be easily installed on 
the surface to be measured as well as easily removed 
therefrom. Such characteristics are especially important 
where thermocouples are only temporarily attached to 
surfaces of systems or devices which are tested during 
their development stages, as for example, the many tests 
performed on systems and vehicles to be used for space 
exploration. 
Additional requirements are imposed in temperature 
measurements of spacecraft where heat exchange by ra- 
diation is appreciable and in some cases predominant. 
In such cases, it is necessary to shield the back of a 
therriocouple with a material having a low emissivity, 
namely, a material which is a good heat reflector. This 
insures that the thermocouple is measuring the surface to 
5 which it is attached rather than that of a body elsewhere 
in the spacecraft which is radiating to it or receiving 
radiation from the thermocouple. 
Accordingly, an object of this invention is the provision 
of an improved thermocouple assembly. 
Another object of the present invention is the provision 
of a novel thermocouple assembly which, due to its 
small size, produces accurate temperature information. 
Yet another object of the present invsntion is the 
provision of a novel thermocouple assembly incorporating 
15 a small thermocouple bead which is substantially un- 
affected by extraneous undesired heat inputs by thermal 
radiation of a nearby radiating body or by the rate of 
change of the temperature being sensed. 
Yet another object of this invention is to  provide a 
20 small therniocouple assembly which is easily attachable 
to, and removable from, the surface whose temperature 
is to be sensed. 
A Eurther object of the present invention is to  provide 
a thermocouple that will give accurate surface tempera- 
25 ture measurements in a total vacuum, such as space 
environmental conditions, without altering the tempera- 
ture distribtuion that would have existed had the thermo- 
couple not been there. 
These and other objects of this invention are achieved 
30 by a thermocouple assembly in which a small thermo- 
couple bead formed at the junction point of two small 
thermocouple leads is taped to a good heat reflecting 
pressure sensitive tape such as aluminized pressure sensi- 
tive nylon tape. The tape is conveniently used to  attach 
35 the thermocouple bead to the desired surface. The two 
open ends of the two small thermocouple leads are con- 
nected to two contact points such as soldering pins pro- 
vided on a small glass epoxy board, the other side of the 
board being taped to the aluminized nylon tape by means 
40 of a double face pressure sensitive Mylar tape. The contact 
points on the board are used to connect the open ends 
of the thermocouple leads to interconnecting leads for 
transmitting signals indicative of the temperature sensed 
by the thermocouple bead to temperature registering cir- 
45 cuitry. Since such circuitry is in general a distance away 
from the surface, the temperature of which is to be 
measured, the intexonnecting leads are generally quite 
long and therefore of significant weight. The weight of 
such interconnecting leads generally produce tensile 
strains which, in a conventional thermocouple assembly, 
are directly transmitted to the thermocouple leads. Thus, 
conventional thermocouple leads must be of sufficient size 
to withstand the tensile strains without breaking. How- 
ever, in the present invention, the tensile strains produced 
65 by the interconnecting leads are transmitted to the con- 
tact joints mounted on the epoxy board rather than to 
the thermocouple leads. Therefore, in the present inven- 
tion, small sized thermocouple leads are used without 
excessive tensile strains being produced by interconnect- 
s" ing leads which can strain and break either or both 
thermocouple leads and thus damage the thermocouple. 
The novel features that are considered characteristic of 
this invention are set forth with particularity in the ap- 
pended claims. The invention itself both as to its organiza- 
s5 tion and method of operation, as well as additional ob- 
jects and advantages thereof, will best be understood from 
the folIowing description when read in connection with 
the accompanying drawings, in which: 
FIGURE 1 is a bottom elevational view of one embodi- 
ment of the invention; 
FIGUIRE 2 is a side elevational view of the thermo- 
couple assembly of the invention; 
I,) 
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FIGURE 3 is an isometric view of the embodiment of in the shape of a bead of approximately .02 inch in diame- 
the invention shown in FIGURE 1; and ter. The bead and the thermocouple leads extending there- 
FIGURE 4 is an isometric view of another embodi- from were adhesively fastened to the adhesive surface of 
ment of the present invention. the aluminized pressure sensitive nylon tape. The entire 
Reference is EOW made to FIGURE 1 which is a bot- 5 thermocouple assembly was then tested and found to pes- 
tom elevational view of the novel thermocouple assembly form most satisfactorily, due largely to the small size of 
of the invention. As shown therein, the assembly includes both the bead and the leads connected thereto which, as 
two small size thermocouple leads 11 and 12, joined at  previousily explained, greatly affect the performance of the 
one end to form a welded bead 13 which serves as the thermccouple. In addition, the aluminized pressure sensi- 
uple junction. The bead 13, together with the tive nylon tape was found to  be a most convenient means 
and 12, are fastened to  an adhesive heat re- for attaching the thermocouple, or removing it from, the 
flecting surface of a high temperature pressure sensitive surface whose temperature is to be sensed. 
tape 24, such as aluminized pressure sensitive nylon tape. There h a  been described and shown hereinabove a 
The tape is aluminized on the non-adhesive surface so novel, useful and practical thermocouple assembly. The 
that as the bead is held by the adhesive side, any external 15 foregoing description, including the specific values recited 
heat exchanged by radiation is reflected by the aluminized in connection with the assembly which had actually been 
surface, thereby insuring that the thermocouple measures reduced to practice, has been presented for exemdary 
only the temperature of the surface to  which it is attached. Purposes only, the invention not intended to be limited 
The tape 14, in addition to supporting the bead 13 so that thereto. 
the tensile strain produced by the bead on the leads 11 20 The assembly, as disclosed herein, is particularly adapt- 
and 12 is greatly minimized so that smaller size leads may able for use in measuring the temperature of vehicles sub- 
also serves as the means of attaching jected to space environment conditions. The aluminized 
to the surface, &e temperature of tape, because of its low emissivity, is particularly respon- 
d. Attaching is conveniently accom- sible for shielding the thermocouple from extraneous 
plished ,by adhesively fastening the tape to the desired 25 radiation inputs. The aluminum also acts as an excellent 
surface. shield from radio frequency (R.F.) signals that may bom- 
Referring now to MGURES 2 and 3 which are respec- bard the thermocouple and induce an undesired electro- 
tively side elevational views and an isometric view of the motive force (E.M.F.1 therein. 
thermocouple assembly of the invention, therein, the rest The proper choice of materials, all of wlhich should 
e assembly is shown comprising a 30 Preferably have WrY low VaWT Pressure Gharacteristics, 
ich is connected to, along one side insures that the thermocouple assembly Will function 
y means of a double-faced adhesive properly in high vacuum Space envirmmenh. The use Of 
terial 18. me board 17, which is a silicone adhesive on the two tapes aforementioned, in- 
made of electrically non-conducting material such as glass sures that the thermocouple assembly will stay securely 
epoxy, has a pair of contact points such as pins 35 attaohed to the surface being measured even when main- 
21 and 22 mounted on the top face thereof. ne open ends tained in a space environment for extended durations. 
of the thermocouple leads 11 and 12 are joined to inter- It is understood that suitable modifications may be 
connecting leads 23 and 24 respectively at the soldering made in bhe assembly as disclosed by those familiar with 
pins 21 and 22. shown in ~ G U R , ~  2 and 3, the other the art without departing from the spirit of the invention. 
ends of the interconnecting leads are connected to  con- 40 Accordin&, all suitable modification6 and equivalents 
ventional temperature circuitry (not shown) are intended to  fall within the scope of the invention 
which is energized by the signals transmitted through as 
leads 11, 12, 23, and 2 , the signals being indicative of What is claimed is: 
the temperature sensed by the welded bead 13. 1. A thermocouple assembly for adhesively fastening 
I [ ~  another preferred embodiment of the invention 45. a thermocouple to be in direct contact with a surface 
leads 18 and 12 are connected to leads 23 and 24 re- a strip of tape having first and second sides; 
spectively by means of solder points 27 and 28 respec- a thermocouple including first ‘and second thermo- 
tively, soldered on separate copper surfaces 31 and 32 coupIe leads joined at  one end to form a thermo- 
ich are coated on the top side of the mounting block coulY1e junction; 
On copper surfaces is an adhesive layer means on said first side of said strip 
an alternative to  the use of soldering pins as the means of tape for adhering said thermocouple to said first 
of connecting the thermocouple leads 11 and 22 to the side and to a surface whose temperature is to be 
interconnecting leads 23 and 24 respectively. sensed; a heat reflecting coating on said second side of said 
embodiment of the invention, a piece of mounting board strip of tape; 
baving dimensions d .312 by .125 by .030 inch was ad- an electrically &dated mounting blmk; 
sensitive tape, to a $strip of aluminized pressure sensitive block to said second side of said strip of tape; 
nylon tape .312 inch wide and about .5o0 inch. long. 60 first and second electrically conducting contact 
Each of the two small areas on the tap side of the block, members; 
is copper coated to a thickness of .oo5 inch, was means mounting said first and second electrically con- 
ducting contaot members on said electrically insulat- used t o  solder thereon the open end of one of two 36 g a u g  ing mounting block; and 
‘OpFr and means electrically connecting said first ,and second 
thermocouple leads to said first and second electrical- two interconnecting deads of 26 gauge C O ~ T  and cm- 
ly conducting contact members respectively. stantan wires. It is apparent, however, that the assembly 
materials such as iron-constantan, chromel-alumel, and in tape is of a synthetic material and said first and 
others. The choice Of materia! depends Won the 70 second electrically conducting contact members comprise 
one chooses to  measure the signal and the temperature first and second solder pins. 
range and accuracy required. The other open en& of the 3. A thermocouple assembly as recited in claim 1 where- 
two 35 gauge copper-constantan thermocouple leads in said tape is of a synthetic material and said first and 
which were cut to  a length of approximately SO0 inch, second electrically conducting contact members com,pl.ise 
were welded together to form a thermocouple junction 15 first and second areas coated with electrically conducting 
shown in FIGURE 4 in isometric view, the thermocouple whose t ~ ~ P e r a t u r e  is to be .%XMed comprising 
Such a soldering 
In an actual Teduction to practice of the latter described 55 
hesiveay fastened, by means of a dottble-face presswe meanS fastening said electrically insulating mounting 
leads’ to One Of the 65 
of the invention can be made using any tl’ermmude 2. A the!rmocoup1e assembly as recited in claim 1 where- 
3,377,208 
material, said first and se d areas being electrically first and second elec ally conducting contact 
insulated from one another. members; 
4. A thermocouple assembly as recited in claim 1 where- means mounting said first and second electrically con- 
in said tape is of nylon ,and said electrically insulating ducting contact members on said electrically insulat- 
mounting block is adhesively fastened to said second side ing mounting block; and 
of said strip of tape. means electrically connecting said first and second 
5. A thermocouple assembly comprising a strip of nylon thermocouple leads to said first and second electrical- 
tape having first and second sides; ly conducting contact members respectively, 
a nhermocouple including first and second thermocouple 
leads joined at one end to  farm a thermocouple eferences Cited 
1u 
UNITED STATES PATENTS 
3,279,956 10/1966 Ekstrom _ _ _ _ _ _ _ _ _ _  136-233 X 
junction; 
an adhesive layer means on said first side of said strip 
of tape for adihering said thermocouple to said fir& 3,075,386 1/1963 DalY. 
side and to a surface whose temperature is to be 
FOREIGN PATENTS 15 
sensed; 
a heat reflecting metallic layer on said second side; 
an electrically insulating mounting block; 410,572 5/1934 Great Britain. 
means fastening said dectricdly insulating mounting 
block to said second side of said strip of tape; ALLEN B. CURTIS. Primam Examiner. 


Thermocouple assembly Patent

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