NAMUR-rated input module for hazardous-area sensing
The Siemens 6ES7321-7TH00-0AB0 is a 16-channel digital input module for the S7-300 family, specifically designed for NAMUR proximity sensors (2.1 to 7 mA signal range) and 2-/3-/4-wire BEROs, with an 8.2 V or 18 V sensor supply voltage selectable per group. Each channel provides wire-break and short-circuit detection (electronic), diagnostic alarms, and hardware interrupt capability — essential for monitoring sensor health in safety-instrumented or remote I/O applications where a broken wire must be flagged immediately. The module draws up to 190 mA from the 18 V sensor supply at 60 °C (110 mA at 40 °C) and 60 mA from the 8.2 V supply, plus 100 mA from the backplane bus via the 40-pin front connector.
End-of-life sourcing reality
Availability is limited to existing stock or surplus channels. No official Siemens successor order code is on record for this module. For a replacement, evaluate the S7-1200 or S7-1500 NAMUR-capable input modules, which require a different form factor and backplane.
Sensor wiring and cable length limits
Shielded cable length is limited to 400 m when using the 18 V sensor supply, and 200 m with the 8.2 V supply. Unshielded cable is not permitted — a critical detail for field wiring in electrically noisy environments. Input filtering is symmetrical: 2.5 to 3.5 ms on both rising and falling edges, which sets the minimum detectable pulse width for the downstream PLC logic. The module occupies a single slot (40 mm wide, 125 mm high, 120 mm deep) and requires a 40-pin front connector — verify the mating connector is on hand before installation.
Operating temperature envelope
Rated for 0 °C to 60 °C ambient, with full 16-channel operation sustained across the entire range — no derating above 40 °C. Typical power dissipation is 11 W, which must be considered in enclosure thermal calculations, especially when the module is grouped in a dense rack near other heat sources.