GB596983A - Improvements in or relating to electromagnetic apparatus for measuring torque - Google Patents

Abstract

596,983. Dynamometers. WESTING- HOUSE ELECTRIC INTERNATIONAL CO. March 20, 1945, No. 7000. Convention date, Nov. 19, 1942. [Class 106 (ii)] Apparatus for continuously measuring torque comprises a stationary member, subject to the torque output and comprising relatively angularly displaceable sections, at least one electromagnetic member and a co-operating magnetic member mounted respectively on the two relatively displaceable sections of the stationary member, means for producing a voltage varying with changes in relation of the two magnetic members and means for measuring the voltage to indicate the torque. To measure the torque of an aero-engine, the latter is mounted in the usual manner on a ring 1 connected to a ring 4 by means of a framework 3. The ring 4 is not, however, mounted directly upon a firewall 2, but is carried by spacing members 6 secured to a further ring 5 which is itself secured to the firewall. In this manner, the engine torque produces a counter torque which results in a relative angular displacement of the rings 4 and 5. Such displacement is measured by means of a pair of diametrically opposed magnetic strain gauges, each of which comprises a pair of E-shaped core members 18, 19, each having a coil wound about its central leg, secured to the ring 4 and an armature 25 carried by the ring 5 and disposed between the confronting core members. A relative angular displacement of the rings 4 and 5 thus varies the magnetic flux path associated with each coil and increases the impedance of one of each pair of coils and decreases the impedance of the other coil of each pair. The coils are connected to form a bridge, Fig. 8, the output of which is fed through a bridge rectifier 41 to a coil 40 of a cross-coil indicating instrument. A bridge rectifier 42 is also connected across the source of alternating potential of the bridge and has its positive and negative terminals connected to the other coil 39 of the indicating instrument which therefore indicates changes in voltage across the bridge circuit independently of fluctuations in the alternating potential. The instrument may be calibrated to read torque directly and may be set to zero by means of a small biassing battery and rheostat. In an alternative circuit, Fig. 5, the two pairs of coils respectively form two arms of a bridge, the other arms being formed by a potentiometer 28 which may be used for zero adjustments. The output of the bridge is fed to an indicating instrument 31 via a bridge rectifier. If it is desired to measure the power output of the prime mover, a tachometer generator 32 is provided to produce a voltage proportional to the speed of operation of the prime mover. This voltage is multiplied by that due to the bridge unbalance in an indicating instrument 43 which may be calibrated to read horsepower directly. The magnetic strain gauges may alternatively be mounted to measure the torsional deflections of a sun gear in the planetary gear reduction unit of the aircraft engine itself.