1,Adopt to second-wire system 2,Non-contact 3, The long transmission distance, square wave output. <1>Smith- ... ,II,III<2>Feature1,Adopt to second-wire system 2,Non-contact 3, The long transmission distance, square wave output. 4,Explosion ... the signal line and the power line and ground).2, non-contact, sending letters and reliable.3, the long transmission distance, square ...