Switching appts. for recognising intrusive conductive media in switching amplifier input - has component which changes electrical parameter of input circuit, changes over input terminal polarity, and prevents switch=on w.r.t. parameter

摘要

The switching appts. includes a switching amplifier (10) with input terminals (28). A signal detector (14,42) is connected e.g to a high pressure pump, and a connector (12) couples the signal to the input terminals of the switching amplifier. With reversal of current flow, an electrical parameter of the input circuit is changed. A changeover device (32) switches the poles of the input terminals with a present clock frequency. An evaluation circuit (34) measures the electrical parameter, e.g the current, compares the measured values, and generates a signal preventing the switch-on of the appts. if a preset criterion is fulfilled. USE/ADVANTAGE - In explosive environments or high pressure cleaning equipment. High reliability, simple mfr.