THE ERRORS OF COPPER-CONSTANTAN THERMOCOUPLE CAUSED BY THERMO IMPACTS

Abstract

Investigations on improving the controllability of the operating engineering units, nuclear power plants in particular, have become of great importance especially after the repeated explosions in the reactor halls in Japan, which are likely to be caused by the decrease of the reactors hardware maintenance system control, thermoshock damages in the thermo-electrode wires in particular.

The effect of cyclic temperature changes on thermal electromotive of the thermocouple materials copper and constantan (TCC), as well as on the stability of thermocouple copper – constantan when heated to 400 ... 800 K and cooled at a rate 10⁴ K/s to the room temperature is investigated.

The dependencies of the deviations of thermal electromotive force of the thermal electrodes on the number of cycles in the environment (argon, air) during calibration in the range of 293 ... 800 K are presented. According to the results, an alloy constantan (-100 mV) is more sensitive to thermal cycling (heating in argon 50 cycles), for pure copper complex dependencies are observed: up to 20 cycles electronegative deviations that with the increase to 50 cycles are transformed into electropositive (+12 mV), are recorded. Thermal cycling of thermal electrodes in the air causes deviation of thermal electromotive force in 2 – 4 times higher than after heating in argon.

It is shown that thermal cycling (50 cycles, heating in argon) will cause the deviation of copper – constantan values in minus 1,6º C, similar number of cycles while heating in the air will change copper – constantan values relatively NSC in minus 4º C.