Overview
The 3RK3121-2AC00 is a Siemens 3RK31 central unit combining fail-safe and standard I/O in a single IP20 enclosure: 1/2 fail-safe digital input, 6 standard digital inputs, 1 fail-safe relay output, and 1 fail-safe digital output. It is rated for 15g / 11 ms shock and mounts via snap-on DIN rail or screw-mount with an additional push-in lug.
Function & operation
This unit integrates safety-related and standard I/O on one module. The fail-safe inputs (1/2 F-DI) support 2-channel wiring for safety functions such as emergency stop (has_emergency_stop: True) and safety circuits (has_safety_circuits: True). The six standard digital inputs handle non-safety signals. The fail-safe relay output (1 F-RO) and fail-safe digital output (1 F-DO) provide switched outputs up to 1.5 A switching current, with a conditional short-circuit rating of 1 ms at 24 V. Protocol support is available via an optional DP interface module, enabling 64-bit cyclical data exchange on PROFIBUS-DP. The unit operates at up to 1000 switching cycles per hour and is rated for pollution degree 3 environments.
Lifecycle & compliance
The 3RK3121-2AC00 carries a RoHS compliance date of 28-05-09. It is classified for Class A EMC environments only; in residential settings it may cause radio interference, requiring mitigation. Finger-safe touch protection is provided, and the unit is rated for altitudes up to 2000 m.
Integration & mounting
Dimensions are 133.00 x 52.5 x 133.00 mm (width 45 mm, height 111 mm, depth 124 mm). Weight is 450 g. Power draw is 4.5 W. Terminals are spring-loaded, accepting wire sizes 24...16 AWG. Mounting options: snap onto DIN rail or screw-mount with an additional push-in lug.