Spare-part EM 231 for S7-200 CN racks
The Siemens 6ES7231-0HC22-0XA8 is the EM 231 analog input expansion module for the SIMATIC S7-200 CN series, explicitly designated as a spare part and restricted to S7-22X CPUs only. It provides 4 differential analog inputs with a 0-10 V DC range and a 12-bit converter, delivering a resolution of 12 bit including sign over the full-scale span.
What the 12-bit, 4-channel differential input means for your BOM
Four differential inputs reject common-mode noise between the sensor ground and the PLC reference — critical when the analog signals share a cable tray with motor drives or contactors in a panel. The 12-bit converter quantises the 0-10 V span into 4096 counts, giving a theoretical resolution of about 2.44 mV per LSB. For a 4-20 mA shunt resistor this is adequate for process monitoring; it will not resolve microvolt-level thermocouple signals without external amplification. Typical power loss is 2 W — the module draws this from the S7-200 backplane, so the total rack power budget must include this draw alongside the CPU and any other expansion modules.
Panel fit and mounting dimensions
The module measures 71.2 mm wide, 80 mm high, and 62 mm deep — it snaps onto the standard DIN rail alongside the S7-200 CN CPU and occupies one expansion slot. Depth of 62 mm means the module protrudes that far from the DIN rail face; allow clearance for the field-wiring connector and any cable bend radius inside the enclosure.
Lifecycle and compliance — spare-part status
The manufacturer lists this as a current spare part for the S7-200 CN platform, carrying only CE approval — no UL, CSA, or other agency markings are noted on the product record.