This imbalance increases the current i1 and decreases i2.
Therefore, the working points of the two thermocouples change: the thermocouple polarized by the current i1 operates at A, and the other thermocouple operates at B (Figure 3.6(b)).
In this situation, with the above hypotheses, the voltmeter measures the voltage imbalance De proportional to the active power absorbed by the load (except for the surplus given by the powers dissipated in R, S, r1, and r2):