unity gain amplifier the output of amplifier 227a is coupled to the input of amplifier 227c through an isolation circuit 227b the output of amplifier 227c is connected by conductor 226 to the anode of diode 225 the reference terminal of amplifier 227c is connected to conductor 39 a 12 14 volt dc power supply 234 is connected by conductors 235 and 236 to the internal power supply 227d of isolation amplifier 227 regulator 220 provides operating power for comparator 204 zener diode 206 provides a reference voltage for comparator 204 resistors 221 and 223 and potentiometer 224 allow for the adjustment of the signal input voltage to comparator 204 so that before the arc is struck the voltage at the non inverting input of comparator 204 is greater than the reference voltage provided by zener diode 206 this causes comparator 204 to energize relay 211 which thereby makes the connection between conductors 38 and 214 once the arc is struck the voltage at terminal 28 will drop to a lower voltage and cause the signal input voltage to comparator 204 to be less than the reference voltage comparator 204 will then de energize relay 211 which in turn causes conductors 38 and 213 to be connected therefore 80 volts is applied to conductor 214 before the arc is struck and once.