Temperature controller for heating apparatus

摘要

Heating apparatus has at least two electrical heating elements 2, 3 and a temperature controller which responds to a temperature sensor TH1 to vary the duty cycle of each of the elements in a sequential manner. For example, at an upper sensed temperature level, the first element is supplied with power at a first-duty cycle; at a mid-range level the first element is supplied with more power at a second duty cycle; and at a lower level the first element is provided with maximum power whilst the second element is supplied with power at a third duty cycle. The controller may employ zero voltage switches connected to respective triacs T1, T2 in order to control burst firing whereby the first and second duty cycles are controlled at different sensor temperatures within a proportional control band.