6ES7421-7DH00-0AB0 SIMATIC S7-400, SM 421 SIMATIC S7-400, SM421 digital input modules, optical isolation, 16 DI, 24 - 60V UC, alarms, diagnostics, the number of digital inputs 16 digital inputs can be simultaneously controlled inputs number up to 40 ℃, the maximum value of 16 up to 60 ℃, the maximum input voltage of 16 types of input voltage AC / DC ratings, UC 24 V; UC 24 至 60 V for signal "0" DC -6 to +6 V; AC 0 to 5 V for signal "1" DC 15 至 72 V; DC -15 to -72 V; AC 15 至 60 V Frequency range AC / DC 47 to 63 Hz Input current for signal "1", typ 4 mA; 4 至 10 mA Cable length Cable length unshielded, max 1000 m unshielded wire length, maximum 600 m; 600m: 3,10,20 ms; 100m: 0.5ms sensors can be connected sensors