GB699036A - Improvements in or relating to apparatus for measuring the frequency of alternating currents or speed - Google Patents

Abstract

699,036. Electric correspondence control system. GENERAL ELECTRIC CO., Ltd., ANTRICH, D., and GARDINER, H. W. B. April 9, 1952 [April 24, 1951], No. 9532/51. Class 40 (i) [Also in Group XXXVI] Apparatus for'measuring the speed of a rotating shaft comprises a tachometer generator whose output voltage is fed to a frequency sensitive circuit which indicates the difference between the frequency of the test voltage and a standard frequency obtainable at a standard speed; at low speeds the magnitude of the test voltage is measured directly. The A.C. output from the tachometer generator 10 is taken to a transformer 15, with one secondary winding 17 feeding two relays 20, 22 via a bridge rectifier 18, relay 20 operating at approximately 10 per cent. below normal speed and controlling the energization of a further relay 31 via contacts 21, and relay 22 operating at approximately 10 per cent. above normal speed and controlling the energization of a relay 47 via contacts 23. Another secondary winding 16 of transformer 15 feeds the generator output to one of three circuits determined by the condition of relays 31, 47. At low speeds, when both relays 20, 22 are unenergized, relay 31 is energized via unoperated contacts 21, and connects an indicating voltmeter 44 and recording voltmeter 45 to the secondary winding 16 via rectifier bridge 40. At approximately normal speeds relay 20 is energized to operate contacts 21, relay 31 falls, and the output from winding 16 is fed to the meters 44, 45 via two resonant circuits 52, 53 and 54, 55 in parallel, resonating at different frequencies, the voltages across the condensers 53, 55 being rectified at 56, 57, and their difference, appearing across resistors 58, 59, being measured on meters 44, 45 and indicating the magnitude and direction of the difference between the test frequency and the normal frequency, and hence the difference between the measured speed and normal speed. At high speeds relay 22 is also energized, followed by relay 47, when resonant circuits 52, 53 and 54, 55 are changed by contacts 50 to circuits 72, 73 and 74, 75 and indicating voltmeter 44 is disconnected. The recording voltmeter 45 now indicates the magnitude and direction of the difference between the test frequency and another higher normal frequency. The condition of relay 20 is indicated by lamps 33, 34 controlled by contact 21.