Circuit arrangement for monitoring short circuits to earth and frame

摘要

A circuit arrangement for detecting short circuits to earth and/or frame for use in a control system which has a non-earthed direct-voltage supply network is specified. A test voltage (Uo) is applied via high-resistance sensing resistors (RM1, RM2) to both terminals (U+, U-) of the direct-voltage supply network. This test voltage is an alternating squarewave voltage of very low frequency and is balanced with respect to earth potential. The response of the network which forms the direct-voltage supply network with its earth-fault resistors (RE1, RE2), is detected by multiple measurement of the voltage (U1, U2) present at the terminals of the direct-voltage supply network with respect to earth potential, and evaluated in an evaluating circuit. If an earth-fault resistor drops below a predetermined limit value, an earth-fault message is initiated. If a more elaborate evaluating circuit containing a microcomputer is used, the values of the earth-fault resistors can be calculated and indicated. The measured earth-fault resistors can also be recorded over a particular time. <IMAGE>