What it is and what it does
The Siemens 3RK1903-0CH10 is a control module that slots into an ET200S station, providing two 24 V DC digital inputs for local functions tied to High Feature or Failsafe starters. It includes a COM interface for direct connection to a PC programming cable (6ED1057-1 AA00-0BA0), so you can commission or diagnose the starter without pulling a separate fieldbus gateway.
Where you'll find it in the panel
This module lives on the ET200S rail — it's not a standalone DIN-rail device. You're adding it to an existing ET200S slice, typically alongside the power module and the starter itself. The COM port is a handy diagnostic hook for a field tech who needs to read fault logs or adjust parameters on the starter without a laptop connected to the PROFIBUS/PROFINET network.
Temperature range and field reality
It's rated for operation from -40 °C up to +80 °C, which covers most outdoor cabinet scenarios in northern climates or near ovens. The storage range is narrower at 0 °C to 60 °C — so if you're warehousing spares, keep them in a conditioned space, not a freezing warehouse or a hot shipping container.
Compliance note
The substance prohibitance date is 05/01/2012, which aligns with the RoHS compliance timeline for this generation of Siemens automation components. No UL or CSA marks appear in the spec record, so if your panel requires those approvals, verify against the nameplate on delivery.