Alarm contact monitoring circuit - uses short duration external interrogation signal for interrogating alarm switches for e.g. machine tool surveillance

摘要

The monitoring circuit for the alarm contacts, e.g. in a machine tool surveillance system employs a short duration external interrogation signal, for interrogating several alarm switches, each comprising a rest contact and a working contact, connected in one or more closed loops. An anti-valence signal is supplied to a first timing element and an equi-valence signal is supplied to a second timing element, in the case of anti- or equi-valence of the alarm contacts. The outputs of the two timing elements are coupled via logic gates to means for initiating the next interrogation signal.