Triggering of the thyristors controlling the loads is by comparing the error signal resulting from the difference between quantities proportional to desired temp. and actual load power with a fixed frequency sawtooth voltage. To prevent coincidence of switching of several controllers the sawtooth waveform generators are controlled to reach their peak values at different times. The interval between peak values is determined by the number of controlled loads. The sawtooth frequency is lower than the mains frequency. The pulse timing controller is, in turn, controlled by a fixed frequency generator. The distribution of trigger instants assists in reducing the magnitude of voltage transients on the supply system which helps in the elimination of light flicker. The principle application is for electrical heating installations where a number of controlled loads are operated in parallel from a common distribution system line.
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