foerfarande foer oevervakning av funktionen av i kontaktrets i hiss

摘要

The invention relates to a procedure for supervising the operation of contact circuits in an elevator, which contact circuit (7) comprises safety contacts (6) connected in series with a contactor (8). The contactor (8) is energised when the safety contacts (6) are closed. The arithmetic mean (U(i)) of an alternating voltage (U(t)) in a voltage measuring circuit (3) during a measuring period (i) is monitored and, when a voltage change exceeding a given threshold value occurs, the number of measuring periods (N) elapsing from the time of the change from the stable state preceding the change until reaching the stable state again is counted, and when the number of measuring periods exceeds a predetermined value, an abnormal switching event is indicated.