Siemens 6ES7131-4BD01-0AA0 is a SIMATIC ET 200S digital input module that provides four DC 24 V inputs for distributed I/O in automation systems. The ST variant (4DI DC24V ST) is a compact, 15 mm-wide module designed to mount alongside other ET 200S devices in the distributed I/O network. Siemens lists this part as a spare for ET 200S, commonly sold in multi-pack quantities of five units, to expand the controller’s digital input capabilities while maintaining standard 24 VDC sensing compatibility.
