GB967639A - Improvements in or relating to electrical signal generators - Google Patents

Abstract

967,639. Measuring speed electrically. DECCA Ltd. Dec. 4,1962 [Dec. 13, 1961], No. 44576/61. Heading G1N. [Also in Division H2] A signal generator for generating an output whose frequency is proportional to a rotational speed comprises a rotatable ferromagnetic annular member 35 having radially inwardly directed teeth 36 and within which extends in a diametral direction a fixed core 14 bearing a coil 16 through which is passed a field-producing direct current, and an output circuit from the coil including a D.C. blocking capacitor 45 to permit the passage of only A.C. signals. The member 35 is secured in a light alloy cylinder 30 drivable by e.g. a magnetic tape and carried by integral apertured flanges 32 of a spindle 31 mounted in bearings 34. The core 14 has at each end two or more teeth 15 and is mounted in a non-ferromagnetic stator 10, 11 slotted and resin filled at 19 to prevent eddy current losses. A further stator slot 22 houses the-winding leads 20, 21,and flanges 37, 39 form dust-excluding labyrinths. In Fig. 6, the direct current applied to terminals 42, 43 is smoothed by a capacitor 44, and rotation of the teeth 36 modulates the magnetic flux to develop across a resistor 40 an alternating voltage which is fed via a transistor 46 to an output lead 49. A rectifier 50 improves the squaring action of the transistor. In another circuit Fig. 7 not shown the transistor is of the PNP type.