signaling information the evaluation and control unit detects that the light emitting diode 70 associated with channel k1 is to be actuated according to one advantageous embodiment the light emitting diode 70 blinks at a predetermined blinking frequency bus subscriber 30 may be designed in such a way that replacement of the sensor 50 at the terminal contacts 31 may be detected as soon as the removal of the sensor 50 and or the connection of a new sensor at the terminal contacts 31 has been detected the evaluation and control unit causes the light emitting diode 70 to again be deactivated alternatively the programmable control unit 20 may transmit additional signaling information containing deactivation instructions to bus subscriber 30 the evaluation and control unit causes led 70 to be switched off in response to this signaling information in a second scenario bus subscriber 30 of the programmable control unit 20 is able to signal errors regarding channels k3 and k4 for example this causes the programmable control unit 20 to generate signaling information containing the addresses or numbers of channels k3 and k4 as well as an identification of bus subscriber 30 the signaling information in turn is detected in the evaluation and control unit of the bus subscriber in response to the received signaling information the evaluation and control.