Non-reactive monitor for switchgear contacts - has series connection of HF relay, oscillator and filter in parallel with switch contact for potential-free signalling

摘要

The monitor system provides a simple, low-cost method of detecting the position of series-connected switch contacts, without interactive effects. It comprises a detector (1) which is connected in parallel across the switch (2) being monitored. The detector consists of a filter (6), which prevents 50 Hz voltage being shunted by the detector, a self-contained 10 kHz AC source (5) and a relay (7) with output contacts for signalling, interlock or control purposes. When the contact under consideration is closed, the detector is driven from the high-frequency signal and the relay output signal is available. This provides a potential-free indication of series-connected switch contacts in a switchgear installation used, for example, in a processing plant.