What it is and where it fits
The Siemens 3RK1903-0CH20 is a control module for the ET200S High Feature Starter and ET200S Failsafe Starter systems. It provides 2 digital inputs at 24 V DC for local input functions or manual operation, and includes a COM interface for connection to a PC cable. This module snaps onto a 35 mm DIN rail per EN 50022 within the ET200S distributed I/O station, typically mounted in a control cabinet alongside the starter and safety relay slices. It handles the local pushbutton and selector switch inputs that feed the failsafe logic.
Environmental ratings and what they mean
Operating temperature range of -40 to +80 °C means this module can be deployed in unheated enclosures, cold storage areas, or near hot machinery — it will function from deep-freeze conditions up to hot cabinet interiors without derating. Storage temperature range of 0 to 60 °C is narrower than the operating range — the module should be kept in conditioned storage between those limits before installation. This is typical for electronics with electrolytic capacitors or LCD components that degrade outside that band.
Integration notes
The COM interface on this module connects directly to a Siemens PC cable for configuration and diagnostics via the ET200S backplane. No additional gateway or bus coupler is needed for the local I/O functions. The 2 DI 24 V DC inputs are intended for local pushbuttons, selector switches, or sensor feedback that must be read by the failsafe starter logic. They are not general-purpose ET200S input slices — they are specific to the starter control function.