This unit sets the RMS value of the voltage on the load by cutting the leading edge of the sinus waveform by means of a Triac.
Inductive and capacitive filters are provided to get rid of possible noise signals fed back to the supply line.
The unit allows a fine setting of the speed of one-phase a.c. motors, but can be used also with other resistive-inductive loads. It cannot be used for purely capacitive loads.
There is no protection against electrical overloading.
With the potmeter fully rotated c.c.w. the load is off.
By slowly increasing the c.w. rotation of the potmeter, the load will be fed with a progressively increasing voltage.
The trimmer resistor on one side of the box adjusts the minimum voltage value on the load.