GB1052383A - - Google Patents

Abstract

1, 052,383. Measuring electrically. FERRANTI Ltd. Dec.17, 1964 [Oct. 26, 1963; July 22, 1964], No.42397/63 and No. 29614/64. Heading G1N. A device producing pulses at a frequency dependent on a quantity to be measured, e.g. shaft speed, or a quantity which can be represented by a shaft speed, consists of two discs 15, 16, Fig. 2, mounted on the same shaft 14, having teeth and gaps around their edges with the gaps of one disc offset from those of the other disc by half the distance between two adjacent gaps; an A. C. energized winding 17' the signal from which is detected by coils 21', 22' whenever a gap occurs in the plate separating the respective coil from the generating winding 17'; and a bistable circuit, 27 which is triggered into one state by the rectified signal from coil 21' and into the other state by the rectified signal from coil 22'. To ensure that no erroneous output is obtained, should the shaft rotate in the opposite direction to that required, a second A. C. field-generating winding 51 with associated pickup coils 52', 53', is provided at a point on the disc circumference spaced from the first mentioned pickup assemblies by (2n + 1)/2 times the space between a slot S1 on one disc and the next adjacent slot S2 on the other disc. The outputs of these coils 52', 53', drive a second bistable circuit 56, and the output pulses of the bistable 56 control gates 43, 47 to which the pulses from the first bistable 27 are fed after being differentiated at 41, 45. The gates 43, 47, pass the pulses from the first bistable, 27, to a third bistable 44, only when the shaft is rotating in a predetermined direction. Reciprocating linear movement rather than rotary movement of the magnetic shield members may be employed.