Improvements in or relating to mine roof supports and the operation thereof

摘要

1,085,274. Photo-electric control arrangements. GULLICK Ltd. Jan.18, 1965 [Feb. 7, 1964], No.5273/64. Heading G1A. [Also in Division F1] An hydraulically actuated electrically controlled mine roof support system (see Division F1) comprises a series of advanceable roof supports each provided with a photo-electric cell arranged to detect the passage past the support of a fluorescent lamp carried by a mineral cutting machine, the advance of a support being prevented unless it has received a signal from its associated cell indicating that the cutter has passed. To prevent inadvertent energization of the photoelectric cell, each cell is formed of a phototransistor 37 incorporated in a circuit which gives a maximum A. C. output when excited with modulated light but zero output when illuminated with unmodulated light from e.g. a miner's lamp. The circuit includes a transistor 38 the ball of which receives a D. C. signal via a rectifier 39 when the modulated light of a predetermined frequency acts on the photo-transistor 37. The output from the transistor 38 operates a relay 11a forming part of the electro-hydraulic control of the support.