GB1257299A - - Google Patents

Abstract

1,257,299. Inductive signalling; leakage signalling. CONTINENTAL OIL CO. 23 Feb., 1970 [25 April, 1969], No. 8499/70. Heading H4U. A transmission system comprises means for generating an audio frequency voltage, means for conductively coupling the voltage into the earth at a first location, and means for inductively sensing said voltage from the earth at a second location. As shown in Fig. 6, the audiofrequency transmitter 66 and receiver 68 are situated in a mine shaft and co-operate with a transmitter 62 and receiver 64 on the surface. The output of transmitter 62 is supplied via conductors 72, 74, the ends of the conductors being spaced apart and connected to earth by metal anchor pins 76, 78. The co-operating receiver 68 in the mine is provided with a sensing coil 102 inductively coupled to the tunnel roof 100. Similarly, the output of transmitter 66 is conductively connected to ground via the spaced ends of conductors 90, 92 and conductive anchors such as an existing roof bolt 96 or a pin 98 and the receiver 64 is inductively coupled via coil 80 to the earth's surface. The system may serve for speech communication or for locating the position of the underground transmitter, e.g. in the event of parts of the mine becoming isolated. For the latter, the coil 80 is moved along a path 88 until a position of maximum signal is reached and for the final determination the axis of coil 80 is re-orientated to a vertical direction and the coil moved to produce a null output. The input signal may be swept through a band of audiofrequencies.