GB854648A - Tachometers - Google Patents

Abstract

854,648. Electrical measuring systems. SPERRY GYROSCOPE CO. Ltd. July 25, 1958 [July 25, 1957; Dec. 24, 1957], Nos. 23538/57 and 40056/57. Class 40 (1). In a tachometer an alternating voltage of frequency dependent on the rotational speed is fed via a limiting amplifier, differentiating circuit and rectifier to one winding of a ratiometer, the other winding being fed with current dependent on the power supply voltage of the limiting amplifier. As shown, the output of the tachogenerator 1, coupled to the rotor of a helicopter, is converted into a square wave by transistor 2 before being fed by a differentiating capacitor 6 and full-wave rectifier 7 to winding 8 of a ratiometer. The second winding 9 is fed with adjustable current from the source 4, 5. The permanent magnet armature 12 is geared to a pointer 15 which moves over a scale calibrated in rotor speed. A stop 17 is positioned so that speeds below 200 r.p.m. are suppressed. The second Provisional Specification -refers to coupling of the armature 12 to a transducer in a speed control circuit so that the rotor speed is governed to a value corresponding to a setting of the variable resistor 10. In Fig. 2 (not shown), two transistors are used in a transformer coupled push-pull arrangement. The first Provisional Specification refers to a tachometer in which the limiting amplifier is omitted and the tachogenerator 1 is replaced by a printed circuit commutator fed by a D.C. supply.