1,Adopt to second-wire system 2,Non-contact 3, The long transmission distance, square wave output. <1>Smith-I (two-wire, 5 V supply), Smith-II (two-line system, 12 V power supply), Smith-III (two-line system, 24 V power supply), Smith-IV(three-line system , power supply 5 V) , Smith –V (three –wire , 12 V power supply), Smith-VI(three –wire, 24 V power supply) is a type of letter angular ...