A monitoring device comprising a monitoring pattern signal generating module, a calibration pattern signal generating module, a mixer module for mixing an input signal with the monitoring pattern signal and the calibration pattern signals, a recognition module configured to recognize the monitoring pattern signal, at least one calculation module for calculating at least one offset error and at least one gain error, a transmission module for transmitting a signal of proper operation or of faulty operation to a user device depending on whether the monitoring pattern signal is recognized or not recognized by the recognition module and a transmission module for transmitting a signal representative of the offset error and a signal representative of the gain error.