Siemens AG 6ES5-421-8MA12 Digital Input Module

Siemens 6ES5-421-8MA12 Digital Input Module is an 8-channel, 24 V DC digital input block designed for SIMATIC S5 control systems. It accepts eight 24 V DC signals from sensors or switches and interfaces with S5 CPUs such as the S5-90U, S5-95U, and S5-100U, as well as ET 100U and ET 200U distributed I/O rails. This module is identified by the part number 6ES5-421-8MA12 and is used to add digital input points in legacy automation projects, enabling binary sensor information to be read by the PLC for sequencing, interlocks, and process conditions. In typical installations, the module is integrated into an S5 system and wired according to its channel wiring diagram, which shows eight input channels and terminals for the 24 V supply (L+) and common return (M). As a member of Siemens' SIMATIC S5 family, it pairs with compatible adapters and racks to expand control architectures without upgrading the controller. The 8x24 V DC input format makes it suitable for direct connection to common industrial sensors and switch gear, delivering reliable state information to the PLC for real-time control loops and alarm logic.