SU30327A1 - Thermocouple - Google Patents

Description

The present invention consists in the fact that in a thermocouple of nickel alloys, in order to obtain an electromotive force that is independent of the temperature of the cold spa at about -j-200 ° C, an alloy containing from 5 to 20% copper is used as a negative electrode.

In FIG. 1 schematically depicts a thermocouple; FIG. 2 shows the electromotive force curve of conventional thermocouples, and FIG. 3-curve of the electromotive force of the proposed thermocouple. (

The thermocouple thermocouple strength depends on the difference in contact potentials in its heated and cold spaces. The introduction of a third, uniform in length, conductor into the thermocouple circuit does not change the position expressed, if the ends of this conductor are at the same temperature, taken as the temperature of the hot tub. Thermoelectromotive force E in a circuit consisting of three dissimilar conductors A, B and C, with equal temperatures of the spa 2 (A with C) and 3 (B with C) (Fig. 1), is equal to

(t) -yAB (to),, where the symbol indicates the potential difference between conductors A and B,

241

a sign of the functional dependence (t) shows that this potential difference depends on the temperature of the spa. Typically, thermocouples have a continuously increasing potential difference with increasing contact temperature, and therefore the dependence of the developed thermoelectromotive force on the temperature of the hot junction (at a constant temperature of cold junction) has the form shown in FIG. 2. The values of the thermoelectromotive force are plotted along the ordinate E, and the hot spa along the abscissa is the temperature. The temperature of cold junctions is assumed constant, equal, for example, to - If the temperature of cold junctions changes and becomes equal to, then the electromotive force developed by the thermocouple will decrease by an amount E equal to

(t} -VAB (U)

The last expression formulates a correction for the temperature of cold junctions, introducing a significant misunderstanding in the practical use of all currently used thermocouples.

From the foregoing it can be seen that the correction for the temperature of cold junctions could be eliminated if function 1 had the form shown in Fig. 2 for the dependence of the contact potential difference of the thermocouple. 3. As can be seen from FIG. 3, the thermocouple would be made of such materials in which the contact potential difference maintains a constant value in the temperature range from ti to 4- At the same time, practically possible temperatures of cold junctions should not exceed the specified range from ti to fg. those. the temperature should be below 0 °, and the temperature / 2 should be in the range of up to about - | - 200 ° and higher, but of course, below the lowest temperature that it is desirable to measure with a thermocouple.

When the contact potential difference is constant in the range from / i to tz, the correction for the temperature U of the cold junctions is:

 ,

if a

 and

The contact potential of the temperature range from –50 ° to –– –200 ° is typical of thermocouples composed of nickel alloys, with alloys with 10–20% Fe or with the same cobalt content being most suitable for the positive electrode, while as a negative electrode contains

5-20% C The combination also gives good results: 20% Fe (10% Cu or 15% Fe) 17% Cu. 8 to improve the machinability of these alloys, to impart greater heat resistance (non-acidity and no recrystallization at high temperatures), as well as for deoxidation and desulphurisation required during smelting, small amounts of manganese, silicon, magnesium, aluminum can be included in these alloys. , chromium, vanadium, molybdenum.

According to the inventors, the alloys of the above composition actually showed the constancy of the contact potential within the limits indicated as the extreme possible temperatures of cold junctions (from –50 ° to –f 200 °).

The subject matter of the invention.

Claims (2)

1. A thermocouple made of nickel alloys, characterized in that, in order to obtain an electromotive force independent of a change in the temperature of the cold spa to approximately - {- 200 ° C, a alloy containing from 5 to 20% copper is used as a negative electrode. 2. In the thermocouple according to claim 1, use for improving the technological and operational properties of nickel alloys, minor additions of manganese, silicon, magnesium and other metals. Fig1 D 2 t 1 t B 3 t E Figure 2 tTtr