2 AI / 2 AO with 4-20 mA and ±20 mA ranges
The Siemens 6ES7144-1GB31-0XB0 is an EM 144 analog I/O module for the SIMATIC ET 200X distributed I/O family, providing 2 analog inputs and 2 analog outputs in a single unit. Inputs accept both 4 mA to 20 mA and -20 mA to +20 mA current signals, with an input resistance of 25 Ω for either range — the 4-20 mA range is the standard for process transmitters, while the ±20 mA range covers bipolar signals from actuators or flow meters. The module draws 0.9 W typical power loss, with a maximum current draw of 40 mA from the supply voltage L+.
Channel-by-channel diagnostics and alarms
Each input channel independently monitors for wire-break, short-circuit, overflow/underflow, and limit value alarms — the diagnostics are parameterizable and report via a group error SF (red) LED. Hardware interrupts are supported, and the module can generate a diagnostic alarm on fault conditions, making it suitable for safety-monitored loops where the PLC needs immediate notification of a broken sensor wire or a shorted loop. The integrating measurement principle with a parameterizable integration time of 16.7 ms or 20 ms matches the 50 Hz or 60 Hz line frequency for noise rejection — common mode interference is suppressed by at least 60 dB, and crosstalk between inputs by at least 45 dB.