4 analog inputs, 1 analog output — the EM 235 combo module for S7-200
The Siemens 6ES7235-0KD22-0XA0 is the EM 235 analog combination module for the S7-200 PLC family, packing 4 differential analog inputs and 1 analog output into a single expansion unit. The four inputs accept differential signals across a wide range: ±10 V, ±5 V, ±2.5 V, 0–10 V, 0–5 V, 0–1 V, ±1 V, ±500 mV, ±250 mV, ±100 mV, ±50 mV, ±25 mV, 0–500 mV, 0–100 mV, 0–50 mV, and 0–20 mA, with a bipolar resolution of ±32,000 counts and unipolar 0–32,000 counts. The single analog output provides voltage (0–10 V, ±10 V) or current (0–20 mA) signals, with a 100 µs conversion time for voltage outputs and 2 ms for current outputs — fast enough for most process loops on an S7-200 rack.
Conversion speed and signal range — what the specs mean for the scan cycle
Basic conversion time is under 0.25 ms per channel, so reading all four inputs adds roughly 1 ms to the PLC scan cycle. The module draws 2 W typical power from the backplane bus; that thermal budget is manageable in a standard S7-200 rack but matters if you are loading the 5 V rail near its limit with multiple expansion modules. Maximum common-mode voltage is 12 V between the differential pairs — keep the signal sources within that window to avoid clipping the input front-end.
Panel fit — footprint and mounting
No plug-in I/O terminals; wiring connects to the fixed screw terminals on the module face.