Equipment including at least one plug-in unit (102) and a body device (101) for receiving the plug-in unit is presented. The equipment includes a circuit (124) including a test signal generator for supplying a test signal to a measurement circuit including galvanic contacts provided by electrical connectors between the body device and a plug-in unit so that the test signal belongs at least partly to a frequency band used in data transfer between the plug-in unit and the body device. The equipment includes a monitoring circuit for generating a signal indicative of a difference between a quantity responsive to the test signal and a reference. As the test signal belongs at least partly to the frequency band used in the data transfer, the quality of the galvanic contacts between the body device and the plug-in unit can be monitored concerning the behavior on the data transfer frequency band.