Siemens 6ES7 131-4BD01-0AA0 is a four-channel digital input module for the SIMATIC ET 200S distributed I/O system, designed to read 24 V DC signals from sensors and switches on a DIN-rail mounted ET 200S rack. The module provides four independent 24 V DC digital inputs and is the standard-feature version (order code suffix -0AA0). Siemens documentation describes it as a "Digital input module 4 DI; 24 V DC; standard," confirming its core function and voltage rating, and it integrates into the ET 200S family to feed the PLC with input states in a compact 4-channel form factor.
