US2021491A - Electrical pyrometer resistance - Google Patents

Description

Nov. 19, 1935. RUBEN 2,021,491

ELECTRICAL PYROMETER RES I STANCE Filed March 18; 1930 I VENTOR BY ATTORNEY Patented Nov. 19, 1935 PATENT OFFICE ELECTRICAL PYBOMETEE RESISTANCE Samuel Ruben, New Rochelle, N. Y., assigninto Vega Manufacturing Corporation, Wilmington, Del.,. a corporation of Delaware Application March 18, 1930, Serial No. 430,668

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This invention relates to an electrical pyrometer and specifically to one utilizing the resistance change of a metallic compound with heat to indicate temperature changes. The characteristic .3 property of the material employed for the tem-* perature indicating resistance element is one having a high negative resistance coeflicient.

The general object of the invention is to produce an accurate and durable pyrometer. The

device may also be used as a relay and to directly control other devices. It may be used for electromagnetically operating valves or switches.

Broadly, the invention consists in utilizing the eflect of heat to vary the electrical contact resistance of an electrode having a layer of a negative resistance compound containing one or more elements of the oxygen series of the sixth periodic group. An integrally formed layer of cuprous oxide on a copper body is most desirable for the purposes of this invention, although other compounds of the series also produce fairly satisfactory results.

In the art, various materials have heretofore been utilized for indicating temperature conditions by virtue of their negative temperature resistance coeflicients. Usually, have been oxides or sulphides in pressed or sintered form. And they have been subject to various limitations relating to their composition,

among which are 1. Chemical instability such as decomposition, oxidation, etc.

2. Physical instability, such as cracking, chipping, peeling, etc. Y

3. Electrical instability, such as change in electrical resistance during operation cycles, continuous drift and lack of consistency in operating characteristics.

4. Limited current capacity and difliculty of reproducing the resistance device within necessary commercial limitations.

5. Electrolytic or decomposition effects due to passage of indicating or controlled current.

I' have found that the resistance of cuprous oxide, when made in the manner to be described, decreases with heat, and the change in resistance can be used 'to indicate the heat in an atmosphere or liquid. If a copper element be oxidized so as to form an integral oxide layer on its surface, this layer being fused to form a hard, dense and homogeneous layer of cuprous oxide, it is possible to construct an accurately responsive electrical pyrometer eliminating the limitations cited for the prior art.

65 The oxide is formed by heating the copper base these materials to 1000" C. for a period of approximately thirty minutes in an oxidizing atmosphere until a glazed and melted layer of cuprous oxide is integrally formed on the copper base. The element is then quenched in a solution of hydrochloric acid which 5 reduces and dissolves the cupric oxide formed on the surface. It is then cleaned in concentrated nitric acid which dissolves the reduced cupric oxide, also some of the cuprous oxide, leaving a clear, ruby red glass-like surface of low electrical l0 resistance 'and having the desired chemical and physical stability. This oxide layer is used as the resistance element responsive to the changes in temperature and the resultant resistance changes are used to control an indicating cur- 5 rent or device. Another method is to quench the element in oil as soon as it is taken from the furnace. This has the effect of reducing the cupric oxide and a small part of the cuprous oxide formed on the surface, to copper, thus allowing a 20 good contact. The remainder of the cuprous oxide layer is underneath the superficial layer of copper which may itself be removed by immersion of the element in nitric acid. The quenching may also take place in other atmospheres. 25

In order to more completely describe the invention, reference is made to the accompanying drawing in which Fig. 1 shows a cross sectional view of a pyrometer element. Figures 2 and 3 show circuits in 30 which these pyrometer elements can be operated.

Referring to Fig. 1, copper element (2) drawn into thimble shape has integrally formed oxide layers (4) and (4a) on its exterior and interior surfaces. Contact with the interiorsurface (4a) 35 is made by means of graphite powder (6) pressed into the tube and held in place by plug (l0). (Other conductive means could be used in place of the graphite.) Lead (i8) makes contact with the pressed graphite through rod (8) which ex- 40 tends into the powder and lead (20) makes contact with the copper shell (2) through soldered connection (l2). End plug (ll) holds the leads in place. 40

Fig. 2 shows the leads (I0) and (20) as the line wires with source of potential (22) and indicating meter (24).

Fig. 3 shows the invention in the form of a device adapted to automatically compensate 50 against room temperature and voltage changes.

A Wheatstone bridge circuit is used with two cuprous oxide resistances in conventional a1- rangement. Resistances (26) and (28) are used to balance the circuit so that any variation in resistance of one of the cuprous oxide resistances unbalances the bridge circuit, the differential being indicated by meter (24) In operation of the device, the resistance or the cuprous oxide layer decreases with temperature and the extent of this decrease is indicated either by the series current as registered on the meter (Fig. 2) or by the unbalancing of the bridge circuit (Fig. 3) due to the change of potential across the resistor, the differential being registered on the meter (24). Due to the stable form of this oxide, when produced in the manner described, the readings are accurately duplicated.

Where, in the manufacture or use of the device, it is desired to substitute a solid conductive material for the cuprous oxide layer described, I have found that a mixture of cuprous sulphide and cuprous oxide, when melted together and cast, has a negative temperature resistance coeflicient, and for some uses, is desirable. Another mixture, which may be mentioned for the same purpose, is cuprous sulphide melted with antimony sulphide.

In all cases, the fundamental requirement for chemical and physical stability and practicability, is that in the formation of the element, the crystalline material must be melted or fused so as to give a thermally interlocked and homogeneous structure.

It is not that the devices of the invention be constructed in the form shown in the drawing. The exterior cuprous oxide layer of the shell for instance, may be omitted. Other modifications, without departing from the scope 5 of the invention, will undoubtedly suggest themselves, as will particular uses for the adaptation of the device, for instance, as a heat indicator for automobile and other motors, or for use in fire alarm systems, etc.

What is claimed is:

1. An electrical pyrometer comprising a copper shell having integrally formed on its interior surface a layer of cuprous oxide, said shell being substantially filled with graphite powder, two electrodes, one of which contacts with an unoxidized portion of said copper shell and one of which contacts with said cuprous oxide layer by virtue of being imbedded in the said graphite powder.

2. An electrical pyrometer comprising a copper shell having integrally formed on its interior surface a layer of cuprous oxide, said shell being substantially filled with electrically conducting powder, two electrodes, one of which contacts with an unoxidized portion of said copper shell and one of which contacts with said cuprous oxide layer by virtue of being imbedded in the said powder.

SAMUEL RUBEN.

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