Input specs that govern the fit
The 6ES7321-1CH80-0AA0: 16 digital inputs, optically isolated from the backplane bus and grouped in two banks of 8 with channel-to-channel isolation between groups. Rated for 48 VDC nominal, with a permissible range of 48 VDC to 125 VDC — covers nominal 48 V and 110 VDC control circuits common in industrial and utility plants. Signal thresholds are non-standard for a 24 V system: a logic '0' spans -146 VDC to +15 VDC, and a logic '1' requires 30 VDC to 146 VDC. This module is designed for higher-voltage DC buses, not standard 24 V PLC I/O. Typical input current at signal '1' is 3.5 mA; the module draws 40 mA max from the 5 VDC backplane bus. Power loss is 4.3 W typical — within the S7-300 rack's thermal budget for a 16-channel card.
Switching response and wiring reach
Input filter times: 0.1 ms to 3.5 ms on rising edge, 0.7 ms to 3 ms on falling edge. Fast enough for discrete sensing and limit-switch monitoring; not intended for high-speed encoder or pulse-train capture. Supports 2-wire proximity sensors with a max permissible quiescent current of 1 mA. Unshielded cable runs up to 600 m; shielded runs up to 1000 m — adequate for distributed field wiring in a plant.
Green LED per channel for status indication. No diagnostics function and no alarms — a basic input module for straightforward discrete sensing.