Remote switch monitoring circuit for mining

A monitoring system for a gate remotely located from said monitoring system in a mine for indicating whether said gate is closed, open, or whether a fault exist in the monitoring system, said system comprising:

• signalling means for generating a signal;
• electrical circuit means and receiving means for conducting and receiving, respectively, electrical signals;
• said signalling means generating a signal having a predetermined wave form and transmitting said signal to said electrical circuit means and to said receiving means, said electrical circuit means conducting said signal to said gate and conducting return signals from said gate to said receiving means;
• said electrical circuit means also including signal inverting means for inverting said signal and switching means for routing said signal over respective paths;
• said inverting means, when energized, producing a first return signal from said gate which is the inverse of said signal received by said gate;
• said switching means energizing said inverter when said gate is closed and deenergizing said inverter when said gate is open and producing a second return signal from said gate being the same as said signal from said electrical circuit means when said inverter is deenergized;
• said receiving means comprising comparator means and indicating means for respectively comparing said signal and indicating the status of said mine gate and monitoring system;
• said comparator means comparing said signal transmitted from said signalling means with said return signals conducted from said electrical circuit means;
• and
• said indicating means indicating when said gate is closed and open when said first and second return signals are received, respectively, and also indicating a fault in said monitoring system when a return signal is not one of said first and second return signals.