Siemens SIMATIC S7 System Manual page 716

553BTechnical specifications
A.7 Thermocouple and RTD signal modules (SMs)
The SM 1231 RTD analog signal module measures the value of resistance connected to the
module inputs. The measurement type can be selected as either "Resistor" or "Thermal
resistor".
● "Resistor": The nominal range full scale value will be decimal 27648.
● "Thermal resistor": The value will be reported in degrees multiplied by ten (for example,
The SM 1231 RTD module supports measurements with 2-wire, 3-wire and 4-wire
connections to the sensor resistor.
Table A- 103 Wiring diagrams for the RTD SMs
SM 1231 RTD 4 x 16 bit (6ES7 231-5PD30-0XB)
①
Loop-back unused RTD inputs
② ③
2-wire RTD 3-wire RTD
Note
The RTD unused channels can be deactivated. No error will occur if an unused channel is
deactivated.
The RTD module needs to have the current loop continuous to eliminate extra stabilization
time which is automatically added to an unused channel that is not deactivated. For
consistency the RTD module should have a resistor connected (like the 2-wire RTD
connection).
716
25.3 degrees will be reported as decimal 253).
④
4-wire RTD
SM 1231 RTD 8 x 16 bit (6ES7 231-5PF30-0XB0)
System Manual, 11/2011, A5E02486680-05
S7-1200 Programmable controller