8 AC inputs with channel isolation
The Siemens 6ES7321-1FF10-0AA0 is a SIMATIC S7-300 SM 321 digital input module providing 8 isolated AC inputs rated for 120/230 V AC (47–63 Hz). Each input is individually isolated in groups of 1 via optocoupler, with a tested isolation of 1500 V AC between channels and the backplane bus — meaning a fault on one channel stays contained and won't pull down the rack's 5 V DC logic supply.
Signal thresholds and wiring
The module reads a signal "1" between 79 V and 264 V AC, drawing typically 7.5 mA at 120 V and 17.3 mA at 230 V. Signal "0" is 0 to 40 V AC. The 25 ms max transition time (both 0→1 and 1→0) is fixed — no parameterisable filter — so the PLC scan cycle must accommodate this latency for fast AC line monitoring. Wiring uses a 40-pin front connector (required, not included). Shielded cable runs up to 1000 m; unshielded up to 600 m. The module accepts 2-wire sensors with a permissible quiescent current up to 2 mA. Status indicators (green LEDs) per channel give immediate visual feedback during commissioning.