8 analog inputs, universal range
The Siemens 6ES7331-1KF00-0AB0 SM 331 analog input module provides 8 analog inputs configurable for Pt100 resistance thermometers (standard/climate), voltage ranges from -10 V to +10 V down to -50 mV to +50 mV, and current ranges including 0 to 20 mA, 4 to 20 mA, and -20 mA to +20 mA. It also handles resistance measurements from 0 to 600 ohms and 0 to 6000 ohms, making it a versatile choice for mixed-signal field wiring in a single slot.
Integration and wiring constraints
The module occupies a 40 mm wide slot in the S7-300 DIN-rail rack and requires a 40-pin front connector (sold separately) for field wiring. Shielded cable runs are limited to 200 m for most signals, but drop to 50 m for the 50 mV range — a real constraint when pulling low-level thermocouple or mV signals across a plant floor. Power draw from the backplane bus is 90 mA at 5 V DC, with a typical power loss of 0.4 W.