Response of a Thermocouple Circuit to Nonsteady Currents

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Abstract
The response of a thermocouple circuit functioning as a Peltier cooler to time‐varying currents was determined by assuming that the current density could be represented by the sum of a dc and a time‐varying component. The time‐varying component took the form of either an impulse applied at time t 0>0, a square pulse lasting from t 0 to t 1, a step increase in the current at time t 0, or a sinusoidal ripple superposed on the dc current. The increased current results in an initial thermal cold spike at the cold junction but the time‐average temperature difference between the junctions is reduced unless the dc current is well below the optimum value. The possibility of using such thermal spikes in a very long wavelength infrared communications system or in synchronous detection is discussed. In the case of a sinusoidal ripple the temperature difference between the junctions may either follow the fluctuations in current or may not, depending on the time constant of the couple and the frequency of the ac signal. In the latter case the only effect is a reduction in the temperature difference between junctions by the additional Joule heating due to the ac component.

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