Abstract: A monitoring device for a system for measuring process variables, in particular in liquid analysis, which measuring system comprises a sensor (2) for recording a process variable and a contactless, inductive plug-in connection (5) between the sensor (2) and a cable (6) for preferably bidirectional transfer of digital signals between the sensor (2) and a remote transducer (7), the monitoring system comprising: a coupling device (17) that can be placed on the plug-in connection (5) and operates without contact to record the signals transferred via the plug-in connection (5), an evaluation device (21) for evaluating the recorded signals, and a display device (22) for presenting the evaluated signals.