A three phase microprocessor based firing circuit is a populated printed circuit board primarily designed for incorporating into three phase power control assemblies for the control of thyristors (SCR’s). The unit is available in various supply voltage capabilities. Phase wiring installation is kept to a minimum, with simple gate/cathode outputs and no necessity for external phasing supply transformers.

Auto Phase Rotation correction & Phase-Loss detection
Switch selectable phasing reversal
Control type: Phase angle, Burst fire, or Phase angle and Burst fire combination
Analogue or digital input signal control options (opto isolated)
Load type selection switch, for resistive or inductive applications
Output status LED indication
Current limit facility, switch selectable with LED indication
Over current latching trip to 120% of maximum, with LED indication
Adjustable ramp control 0 to 30 seconds
Applications are universally acceptable for AC, DC, resistive or most inductive loads via thyristor pairs on three phase assemblies
SCR Power handling gives smooth proportional control to all types of industrial processes which includes furnaces, electroplating, controlled rectifiers and transformers

The number of complete mains cycles during fixed repeating periods (typically 1 to 10 seconds) is varied, thus altering the duty cycle or on-/off-time ratio. Trigger pulses coincide with the zero-crossing times of the mains supply thus ensuring no RFI is produced when using resistive loads.