Supervision system for monitoring the integrity of a transmission line

Abstract

The integrity of a two-conductor transmission line, over which d-c energizing voltage is supplied to a series of shunt-connected detectors (such as fire and/or smoke detectors) and which line is terminated by an end-of-line capacitor, is monitored and repetitively tested by periodically and momentarily interrupting the application of the d-c energizing voltage to the transmission line or conductor pair, while at the same time connecting a resistive load across the line's input end to provide a discharge path for the capacitor. If the integrity is normal, meaning that the line is continuous and not open, and has no excessively high series resistance or excessively low shunt resistance, and also meaning that the capacitor is functioning normally and is not deteriorated, the capacitor will discharge very little during each test and will maintain a relatively high voltage across the resistive load. On the other hand, if there is any trouble on the line giving rise to abnormal integrity, a relatively low voltage will be developed across the resistive load during each test. By sensing the resistive load voltage, the integrity can therefore be determined. When the integrity is found to be abnormal, a trouble indicator provides an appropriate visual and/or audible signal signifying that a trouble condition exists on the conductor pair.