US2063097A - Thermocouple - Google Patents

Description

Patented Dec. 8, 1936 UNITED STATES PATENT OFFICE No'Drawing. Application February 21, 1935,

Serial No. 7,569

4 Claims.

This invention relates to a thermocouple and has specific reference to a novel alloy thermocouple.

I have found by experimentation that a thermocouple formed from an alloy composed of nickel, copper and molybdenum as one element and a copper-nickel alloy as the other element has in addition to a high thermoelectric power a low ohmic resistance, this effecting a large flow of current essential to obtain a high ratio of input to output.

The current produced by this thermocouple flows from the Ni-Cu element over the hot junction to the Ni-Cu-Mo element, so that in conformity with the rule generally applied, the Ni-Cu' alloy is hereafter termed the positive element and the Ni-Cu-Mo alloy the negative element of the thermocouple.

, I have made a number of melts of the negative metal and subjected each of these melts to a test to determine the composition having the most pronounced thermoelectric properties. In this way, I have found that a thermocouple consisting of an alloy composed of 74% to 80% of nickel, 10% to 11% of copper and 10% to 16% -of molybdenum as the negative element, and an alloy of 55% of copper and 45% of nickel as the positive element possesses the highest thermoelectric power and the lowest ohmic resistance. The thermo-electromotive force produced by this thermocouple is in excess of 0.037 volt at a difi'erence of temperature as low as 425 0., and the ohmic resistance of the negative element of the couple ranges between 1 m and ohms with reference to centimeter cube. While I have determined that the thermal conductance.

of the metal is less than that of the positive element composed of 55% copper and 45% nickel, the exact value of this conductance has not yet been established.

The small ohmic resistance of the thermocouple permits a correspondingly small cross section for the elements, so that the temperature of the thermocouple can be raised quickly to the point at which it will produce the flow of current desired.

In producing the negative element metal, I first melt the predetermined quantity of nickel and copper and add thereto the predetermined quantity of molybdenum which dissolves in the melted nickel and copper.

The negative element alloy is very ductile, far more ductile than a nickel-molybdenum alloy, and it can easily be drawn into wire and ribbon and rolled into sheet form. Moreover, this negative element resists oxidation at temperatures up to 500 C. or more. This is the case when the alloy is prepared from the most efiective composition in a thermoelectric sense hereinbefore referred to, and it is also the case when the metal is made up from 55% of nickel, 30% of copper and of molybdenum.

I claim:

1. A thermocouple element formed from an alloy composed entirely of nickel, copper and molybdenum.

2. A thermocouple element consisting of an alloy composed entirely of 74% to 80% of nickel, 10% to 11% of copper and 10% to 16% of molybdenum.

3. A thermocouple of which one element is an alloy composed entirely of 74% to 80% of nickel, 10% to 11% of copper and 10% to 16% of molybdenum and the other element is composed of approximately 55% of copper and 45% of nickel.

4. A thermocouple having an average electromotive force per centigrade degree difference of temperature of about 0.00009 volt, the negative element of said thermocouple consisting of an alloy composed entirely of approximately 74% of nickel, 10% of copper and 16% of molybdenum, any variations in the percentages of the elements bringing the sum thereof to 100%, and the positive element being formed from an alloy composed of 55% of copper and 45% of nickel.

OTTO HERMANN.