The TM172ODM42R is a Modicon M172 programmable controller built specifically for HVAC control — that's its intended application, not a general-purpose PLC. It carries 42 I/O points on board: 12 digital inputs (24 V AC/DC sink/source), 12 relay outputs rated 3 A per channel, 12 analog inputs configurable by pair, and 6 analog outputs (4 voltage, 2 selectable as voltage/current/PWM). The analog inputs accept NTC 103AT-2 and NK103 thermistors, PTC probes, Pt1000 RTDs, plus 0–10 V, 0–5 V, and 4–20 mA current loops. That covers most HVAC sensors — duct temperature, return air, coil temperature, humidity with a 0–10 V transmitter — without external signal conditioners.
I/O configuration and integration
Twelve digital inputs are grouped four per common, sink or source wiring. The twelve relay outputs are split into groups: two SPDT with independent common, three and five SPST sharing a common, and two SPST with independent common — you get both isolated and common-return channels without adding interposing relays. The analog outputs include four dedicated 0–10 V channels and two that can be jumpered for 0–10 V, 4–20 mA, or PWM at 2 kHz. That PWM output is handy for triac-driven actuators or modulating burner controls. On the communications side: one CAN port on a screw terminal block, two RS-485 ports for Modbus serial or BACnet MS/TP, and a USB mini-B for programming and data logging. The real-time clock drifts under 30 seconds per month at -20 to 65 °C, so schedule-based time-of-day sequences stay accurate through the seasons.
Physical mounting and environment
The controller measures 5.7 x 4.3 x 2.4 inches (144 x 110 x 60.5 mm) and mounts on a DIN rail using the optional clip, or directly to a panel. IP20 front, so install it inside an enclosure. Operates from 24 V AC/DC, draws 14 W, and handles -20 to 65 °C ambient (derated to 60 °C for UL 60730-1 horizontal mount). Altitude rating: 0–2000 m, pollution degree 2, overvoltage category II. Material flammability meets UL94 V0.