The operating method measures changes in inlet temp., throughput and supply voltage to derive compensating signals that attempt to keep the outlet temp. constant despite the changes. Heated electrical risistors lie one after the other along the water channel and are connected via switches to the outer conductors of a three-phase supply network. The switches adjust the power and are controlled by the compensating signals.All changes are detected as temp. changes before and after a constantly-heated risistor (R4) at the inlet (2) of the channel (1).The effects of throughput and voltage changes are compensated together
