Method for detecting and monitoring the trolley-bus chassis-contact voltage and a device for carrying out the method

The method involves using a voltage measuring device connected between the earthed pole of the tram overhead line and the chassis. The measured voltage and its time are compared with known voltage-time curves, for a high voltage dropping quickly and a low voltage dropping slowly. If the measured voltage is bigger than the corresponding value on one of the curves, an alarm signal or switch is released. Independent claims are included for a unit for implementing the method and for a method for testing the unit.