Electric discharge machine current cutoff control

Abstract From the Canadian patent

A control system for electronic discharge machine includes an automatic relay control in which machining pulses are a step function of machining cycle period and higher frequency pulses are held to a lower current level to avoid power transistor overload. The relay control circuit also includes a threshold responsive circuit which senses any change in relay controlling output signals and acts to interrupt machining pulses briefly to allow time for relay operation. A current cutoff control circuit detects abnormally low voltage across the machining gap and reduces gap discharge energy level. Pulses referred to as "probe pulses" replace the normal master pulses to control gap discharge time …