Thermocouple Input Module for S7-200
The Siemens 6ES7231-7PD20-0XA0 is an EM 231 thermocouple input module that mates exclusively with S7-22X CPUs. It provides four analog inputs configurable for +/-80 mV or direct thermocouple connection across types J, K, S, T, R, E, and N, with 15-bit plus sign resolution.
Mounting and Signal Integrity
Thermocouple signals are low-level and noise-sensitive. Keep unshielded runs short; for longer distances, use shielded twisted-pair thermocouple extension wire with the shield grounded at the panel end only. The 15-bit plus sign resolution provides enough granularity for most process loops, but expect to filter readings in software if VFDs or contactors are nearby. Ground-loop currents on thermocouple wiring can produce offset errors — check the shield continuity before chasing phantom temperature drift.