S7-1200 SM1231 Analog Inputs

S7-1200 SM1231 Analog Inputs is the Siemens S7-1200 signal-module branch for adding analog measurement channels when the controller platform is already S7-1200 and the project needs process values instead of only discrete field points. Compared with SM1221 and SM1222, SM1231 is the branch for analog sensing, scaling, and measured-value acquisition rather than simple on/off inputs or switched outputs. It is usually the right family when the station has to read transmitters, analog sensors, or process signals that do not belong in the digital I/O path. Keep this family in scope when the PLC already sits in the S7-1200 range and the remaining decision is how many analog channels and which signal types the panel needs to support. Read the product list by channel count and analog signal support first, then narrow by resolution, wiring fit, and the intended process-variable mix.