Thermolec Application &Technical Notes - Manual (Page 66)

THERMO-AIR & THERMO-ZONE
Graphic for proportional control
Proportional Control Diagram - Principle of the Pulse With Modulation
By comparing the input signal with an internally generated reference signal (triangle wave), the controller activates the SCR
output in a range of 0 to 100%.
On this graphic, every time the horizontal line corresponding to the input (in this example, 10 %, 50 % and 80 %), crosses
the reference signal, the heating elements are switched ON or OFF. The total heat output is an average between the ON
and OFF periods. For low heat demand, the heater is not "dimmed" but switched ON for very short periods.
Note: All Thermolec controllers are equipped with a zero-cross thyristor switching circuitry that virtually eliminates all
electro-magnetic interference (EMI) and radio frequency interference (RFI). The light emitting diode (LED) on the controller
indicates when the heating element is on.