The output channel isolation and protection measures on the one hand prevent the transmission of the minimum system interference signal along the forward path, and also isolate the influence of the interference pulse generated during the operation of the drive circuit on the original forward channel, so the isolation protection function is bidirectional . The maximum output current of the photocoupler is 15mA, and the working current of the solenoid valve is 1.5 ~~ 3A, so each output control signal can only drive the corresponding solenoid valve after power amplification. Considering the influence in practical application, the selection is 1.5 times, then the magnification of the current of the triode of the solenoid valve is: