US2445874A - Radiation thermopile and method of making the same - Google Patents

Description

y 1948- D. R. DE BOISBLANC ETAL 2,445,874

RADIATION THERMOPILE AND METHOD OF MAKING THE SAME Filed June 1, 1944 2 Sheets-Sheet 1 /8 (HOT Jl/NL'T/OMS) /7 (com Ju/vcrlo/vs) l9 27, 194. D R. DE BOISBLANC EI'AL 2,445,874

RADIATION THERMOPILE AND METHOD OF MAKING THE SAME Filed June 1, 1944 2 Sheets-Sheet 2 5 MW B Gk 1 8 WM H, m m n m m m J m. T D 0 M [W Patented July 27, 1948 it Ari.

RADIATION THERMOPILE AND METHOD OF MAKING THE SAME Application June 1, 1944, Serial No. 538,320

14 Claims.

This invention relates to improvements in electric thermopiles or thermocouples, and a method of manufacturing them.

The main object of this invention is the provision of a novel thermopile construction and method of producing it whereby a plurality of thermo-electric junctions are readily provided in a simple and inexpensive manner.

A more specific object of this invention is the construction of a thermopile having a plurality of alternately occurring hot and cold thermoelectric junctions formed by the superposition of a plurality of pieces of one metal. upon a suitable dissimilar metal in the form of a spiral strip prepared and assembled in accordance with the novel process herein disclosed.

Another object of the invention involves a simple method of forming a basic metal into a spiral strip having superposed thereon units of dissimilar metal extending substantially in a diametral direction with respect to the spiral strip and transversely disposed with respect to a diameter whereby a series of alternate hot and cold thermo-electric junctions are provided when suitably shielded by a slotted mask.

Other and more detailed objects of this invention will be apparent from the following description when taken in connection with the attached drawings.

This invention resides substantially in the combination. construction, arrangement, steps and combination of steps, as will be described in detail below.

In the accompanying drawings,

Figure l is an end elevational view of a thermopile constructed in accordance with this invention;

Figure 2 is a cross-sectional view taken on the line 2-4 of Figure 1;

Figure 3 is an end elevational view of a modifled thermopile construction in accordance with this invention; and

Figure 4 is a cross-sectional view taken on the line 4-4 of Figure 3.

Figure 5 is an end elevational view of the mask which is used in constructing the device and can be used when the device is in operation; and

Figure 6 is a side elevational view thereof.

The general construction of thermopiles or thermocouples is well known. Briefly, however, they consist of a plurality of physical contact junctions between two dissimilar metals, which junctions are arranged in pairs. One series of pairs is adapted to be subjected to heat radiated from the source the temperature of which is to be measured, while the other series of pairs is arranged to be exposed to ambient temperature conditions. The voltages generated at the junction pairs are algebraically added by reason of the construction provided so as to generate an electrical voltage proportional to the temperature of the source compensated for ambient temperature conditions.

The thermop'lle of this invention is basically similar in these respects but its physical construction and the method of producing it is believed to be novel.

Referring to the drawings, a body it] of suitable insulating material is molded or formed in any suitable manner, for example a rod of insulating material is placed in a lathe and an annular recess ii of suitable axial depth is formed thereon, A center hole is drilled through the body ID and tapped at one end, as shown in Fi ure 2, to receive the terminal screws 2 1. If the body I!) is molded it can, of course, be molded with a central bore and a tap at one end, as is well known in the molding arts. A metal sleeve i2 is then seated in the recess, so that its free end projects a suitable distance beyond the end of the insulating body ID, as illustrated in Figure 2. The sleeve and support are secured together in any suitable manner as by a forced fit, set screws, threads and the like. The sleeve i2 is provided with a series of holes i3 around its periphery in the region beyond the end of the supporting body it), and a soluble plastic, not shown, is filled into the space S, Figure 2, flush with the end of the sleeve. The screw is seated in place before the space S is filled with the plastic. The filled end of the unit is then faced off square with the axis thereof and the plastic is recessed out to form a very shallow space in which a thin disc of insulating material i l is seated so as to be flush with the end of the sleeve, as is clear from Figure 2. The shallow recess need not necessarily be formed since the disc it! can have the same diameter as the outside diameter of sleeve l2, and rest against the end of the sleeve. In this case the screw M will project beyond the plane of the end of the sleeve a distance equal to the sleeve i2 so that it may be threaded there into in the same manner as shown in Figure A thin film of metal i5 is then deposited. on the exposed face of the disc i i, so as to overlap the end edge of the sleeve ii in the form of structure illustrated in the drawings. This thin film may be deposited in any suitable manner but preferably in accordance with known practice it can be evaporated thereon in a vacuum so as to metal film having a pair of radial slots lying substantially on the same diameter but displaced slightly on opposite sides thereof. These slots terminate short of the center of the mask so that in effect the mask will look like the end of the thermopile as it appears in Figure 1, the-body of the mask comprisin the entire disc except for the slots corresponding to the superposed strips of metal it which are deposited on the metal film It through the slots in the disc, again by vaporization in a vacuum, by a metal spray gun, or any other suitable method. The thermopile herein disclosed is adapted to respond to faint radiations of the order found in spectrographs, and it is preferable therefore, that the strips It be extremely thin as in the case of the film I'B. When the mask is removed there will appear the radially extending slightly transversely shifted metal strips it, as is clear from Figure 1.

A mask of the type generally referred to above is illustrated in Figures 5 and 6. In the case of a cylindrical thermocouple the mask comprises a thimble of any suitable material of circular crosssection and composed of the end wall 50 and the cylindrical side wall 5!. Disposed in the end Wall Eli are a pair of rectangular openings 52 and 53 extending in a radial direction but transversely shifted with respect to the diameter of the end wall so as to provide oflfset openings through which the metal is sprayed to form the strips [6 as previously explained. Upon consideration it will be seen also that a mask of this type can be used with the finished device to mask off the opposite edge of each of the strips It to provide the cold junctions by shielding them from the radiations. This would be especially useful in the case of a source of heat radiations which could not readily be focused as explained herein so as to produce the same effect, all as hereinafter explained.

At this point it may be noted that the metal of the "film l5 and the metal of the strips iii are dissimilar metals suitable for thermocouples of this type. There are a number of metal pairs well known for this purpose, and it is contemplated that it is within the scope of this invention to use any oi these known metal pairs. For example a pair of preferred metals for the thermocouple comprises for the film It the metal bismuth and for the strips IS the metal antimony. The unit is replaced in a lathe and a spiral cut representedby the line I! in Figure 1 and the fine slot I'i in Figure 2 is cut, preferably from the center of the disc to the outside and of a depth so as to completely out through the metal film l5 and form it into a spiral strip, as is well illustrated in the drawings. At the same time the continuous metal strips it are cut into enough sections, as is apparent from Figure 2,- so that these units are arranged along the length of the spiral strip at intervals determined by the shape of the mask. Proceeding in either clockwise or counterclockwise direction along the spiral strip it will be seen that the thermo-electric junctions l8 occur alternately with the thermo-electric junctions I 9, The electric circuit connections are made to the sleeve i2 and the screw 24 as diagrammatically illustrated in Figure 2. The soluble plastic in the space S is then dissolved out with a solvent suitable for the purpose which acts thereon through the holes l3, with the result that iihe thermocouple metals and the disc I 4 are separated on the end of the sleeve in spaced relation to the more massive support "I. The result is a thermopile of relatively low mass, and therefore low heat inertia.

By way of example it may be noted that the thermopile herein disclosed is particularly adapted for the measurement of extremely weak or faint radiations, and is therefore adapted for use in spectrophotometry. In use this thermopile will be mounted behind a mask having a slit, as indicated at 20 in Figure 1, which it will be seen exposes the opposite edges of the units, that is the hot junctions'lfl to the heat source while shielding the cold Junctions l9. Alternately an image of the spectrograph exit slit may be focussed on junctions ill by a lens or mirror system. The result is that ambient temperature conditions are completely compensated.

An important feature of this invention is found in the resultant structure by means of which a large number of alternate hot and cold junctions are provided within a limited space so that a resultant voltage is produced, even under faint radiation conditions, which is of suflicient magnitude so that the output thereof can be applied to a vacuum tube amplifier. Devices of this type as commonly used for the measurement of faint radiations are of necessity used in conjunction with sensitive galvanometers because the voltage output is so low as to be within the noise level of the best designed amplifiers. However, by means of this invention a sufliciently high voltage is generated to make it possible to use a vacuum tube amplifier with the thermopile, with the resultant advantages over the use of very delicate galvanometers.

It may be noted, although it is clear by inference, that the insulating bodies l0 and I4 should be made of materials which are not attacked by the solvent for the plastic which temporarily fllls the space S, so that it can easily be removed without detrimental effects on the permanent structure.

In the modified construction of Figures 3 and 4 the insulating support. III with the attached metal sleeve i2 is employed as before. In this case the insulating disc aross the open end of the tube I2, as shown at 44, extends so as to overlap the annular end edge of the tube which represents one structural difference from that of the first modification. In addition the insulating disc 44 is made considerably thicker in view of the fact that a centrally disposed diametral band is cut away from the under side of the disc as shown at 48 so that the disc is made quite thin in this region. The conducting coating i5 is applied as before, and made to overlap the edge of the disc as indicated at 41 so as to electrically connect this coating with the sleeve [2. The end of the screw 24 is drilled out, as is the adjacent portion of the disc 44, so that when the coating [5 is applied by spraying for example, the metal thereof will spray down into the hole in the end of the screw 24 to provide a connecting conductive tip 46 as is clearly shown in Figure 4. The upper coatings l8, as is clear from Figure 3, are disposed in parallel relation to and overlying the cutaway portion 45 so that at the region of the hot and cold junctions the thermal inertia of the structure by reason of the thinness of the disc 44 at that region is held to. a. low value. An advantage of making the disc 44 thicker while keeping it thin in the region of the coatings I6 is that in cutting the spiral groove II in the coating IE it does not matter if the cutting tool cuts into the disc 44 a short distance. It is nevertheless strong enough to withstand this action and the thicker portions provide adequate support for the thin central band portion.

Since in the actual device the disc 44 is considerably thinner than illustrated in the drawings, a method of forming this disc with the cutout portion 45 will be suggested. For example, the space S which in this construction will be filled as before with a soluble or meltable material, can be filled in fiush with the end edge of the tube l2 except at the central diametral portion at which the cutout in the disc 44 is to be formed. An extension of the filling having a cross-sectional outline corresponding to the cross-sectional outline of the cutaway portion 45 will be formed. The disc 44 can then be coated, sprayed or otherwise applied to the end of the structure resulting so that when the material filling the space S is dissolved or melted out the finished disc will take the form clearly illustrated in Figure 4. There are, of course, other ways of forming the disc, as for example making it from a thin sheet of rigid insulating material of some type and milling out or otherwise removing the central diametral band to form the cutaway portion or channel 45. Another way of describing this cutaway portion is to state that it is a central diametral channel running across the rear face of the disc 44 as shown by the dotted lines 45 in Figure 3, making the central portion of the disc as thin as might be desired and as will be permitted by considerations of strength.

From the above description it will be apparent to those skilled in the art that the subject matter of this invention will find application in other physical forms and in other methods of procedure while employing the novel features thereof. We do not, therefore, desire to be strictly limited to the disclosure given herein in an illustrative sense, but rather by the full scope of the appended claims.

What is claimed is:

1. A thermopile comprising an insulating support, a metal film mounted on said support cut to form a spiral strip, and a plurality of metal plates thermoelectrically dissimilar from said film and diametrically arranged on said strip to provide a plurality of alternate hot and cold thermo-electric junctions.

2. In the structure of claim 1, said metal plates being arranged so as to extend substantially radially of the spiral strip.

3. In the combination of claim 1, said metal plates arranged substantially diametrically of the spiral strip but transversely shifted slightly with respect to the common diameter.

4. A thermopile comprising an insulating support having a metal sleeve thereon, said sleeve projecting at one end beyond the support, an insulating plate attached to said support at the projecting end of said sleeve, a thin metal film mounted on said plate, and a pair of radially extending metal strips on said film thermoelectrically dissimilar from said film, said film and strips being subdivided by a spiral groove to form a plurality of thermo-electric junctions.

5. In the combination of claim 4, said plate being spaced from the end of said support.

6. In the combination of claim 4, said support. sleeve and plate being circular in cross section.

'7. In the combination of claim 4, said metal strips being substantially diametrically arranged but transversely shifted a short distance with respect to each other.

8. A method of manufacturing a thermopile comprising attaching a thin metal layer to an insulating support, forming a pair of radially spaced and substantially radially aligned metal strips thermoelectrically dissimilar from said metal layer on the surface of said metal layer, and cutting a spiral groove in said assembly extending through the metal strips and layers to form the metal layer into a continuous spiral strip.

9. A method of manufacturing a thermopile comprising mounting a metal sleeve on an insulating support so that the sleeve projects beyond the end thereof, filling the recess formed by the projecting end with a removable material, mounting an insulating support on the end of the sleeve, depositing a metal film on the exposed face of the support, forming radially spaced strips of metal thermoelectrically dissimilar from said film on the exposed face of said film, cutting a spiral groove through the metal layers to form a spiral strip, and removing said material to form a space behind said support.

10. In the method of claim 9, said material being soluble and being removed by means of a suitable solvent.

11. A thermopile comprising an insulating support having a metal sleeve mounted thereon, said sleeve projecting at one end beyond the support, a thin plate of insulating material extending across the end of said sleeve having a central diametral portion of reduced thickness, a thin metal film overlying the outer face of said coating having a spiral slit forming it into a continuous conductor from the center to the periphery, and a pair of metal strips thermoelectrically dissimilar from said film overlying said film above said diametral band, said strips being subdivided at said slit.

12. In the combination of claim 11, a connection to the central end of said conductor and a connection to the terminal end.

13. In the combination of claim 11, a connection to the central end of said conductor and a connection from the terminal end to said sleeve.

14. A method of manufacturing a thermopile comprising mounting a metal sleeve on an insulating support so that the sleeve projects beyond the end thereof, filling the recess formed by the projecting end with a removable material having a central diametral extension, forming an insulating support over the end of said sleeve and filling, depositing a film on the exposed face thereof, forming radially spaced metal strips thermoelectrically dissimilar from said film on the exposed face of the film parallel to said diametral extension and overlying it, forming a spiral slit through the metal layers to form a spiral strip and removing the said material in the space behind said insulating support.

DESLONDE R. on BOISBLANC. HUGH M. BARTON, Jn.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 813,682 wilderman et al. Feb. 27, 1906 1,502,562 Hausrath July 22, 1924 1,664,720 Woodrutl Apr. 3, 1928

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