The Siemens 6ES7231-7PB22-0XA0 is a 2-channel analog input module for resistance thermometers (RTD) and resistive sensors. It uses a sigma-delta measurement principle.
Two analog inputs per module allow up to four channels per slot when using two modules. The sigma-delta converter provides noise immunity for long cable runs — max shielded cable length 100 m to the sensor, loop resistance limit 20 Ω (2.7 Ω max for Cu10 loops). Group error and external fault indicators (red SF and EXTF LEDs) signal broken sensor or wiring issues without needing the diagnostic buffer. The module uses non-pluggable I/O terminals — wiring direct to the front terminal block, and the 80 mm height matches standard enclosure cutouts.