RBFU 1.01 ST Field Unit is used for controlling one Belimo 24 V fire damper actuator (BF24..-ST, BFG24..-ST, BLF24..-ST). The unit is connected to the ringbus master controller module via a 4 wire ring bus communication. The Belimo ST actuators are equipped with plug connectors that can be plugged directly into RBFU 1.01 ST unit. The actuator is isolated from mains by a transformer. Each unit has a predefined address and therefore has not to be addressed during the system commissioning. RBFU 1.01 ST Field Unit is able to work without 230 V, but then it is only sending data about actuator position to Ringbus master controller and is not able to turn on/off the actuators.