Patent GB-784582-A (GB)
Title: Improvements in or relating to electrical phasemeters and torque meters
Inventor: MAY LEONARD GEORGE
IPC: G01R25/00
Filed: 1954-06-15
Abstract: 784,582. Electric indicating systems. BRISTOL AIRCRAFT, Ltd. Aug. 25, 1955 [June 15, 1954], No. 17612/54. Class 40 (1). [Also in Group XL (c)] An electric phasemeter applicable to measure torque by phase comparison between alternating signals of equal frequency derived from two axially spaced generators on a rotatory shaft, comprises means converting the signals into trains of pulses having corresponding frequency and phase which are respectively applied to a bi-stable circuit comprising two transistors one of which is conductive and the other non-conductive, so that the pulses of one train change the circuit from the first stable state to the second stable state and the intervening pulses of the other train change it from the second to the first stable state; the average value of the difference between the transistor outputs representing the phase difference between the input signals. In Fig. 1 a shaft transmitting torque carries two axially separated toothed wheels of ferromagnetic material each modulating the flux in a stationary magnetically cored pick-up coil 11, 12 to develop trains of alternating pulses of equal frequency which are co-phased for rotation transmitting zero torque and are displaced in phase proportionally to the shaft torsional strain and to the transmitted torque stress producing it. Negative pulses are suppressed by half-wave crystal diodes D1, D 10, and the remaining positive pulse trains are capacitance coupled through half-wave crystal diodes D2, D8 to the emitters of point contact transistors G1, G4, whose base electrodes are earthed over resistance-capacitance circuits R1, C2 and C7, R19. Capacitors C1, C8 discharge during pulse intervals over crystal diodes D3, D9 oppositely poled to diodes D2, D3 and connected to the base electrodes of the respective transistors, whose collectors are connected to source 30 of a 45-volt negative supply overload resistances R2, R18 across which are developed rectangular pulses synchronous with the respective input pulse trains, which are resistancecapacitance coupled over positive pulse transmitting crystal diodes D4, D6 to the base electrodes of point contact junction transistors G2, G3, whose base and collector electrodes are mutually interconnected over parallel resistancecapacitance circuits C4, R7, C5, R13 while the collector electrodes are also connected to supply source 30 over resistances R4, R16 and R9, R11 ; the latter being shunted by milliammeter M. The emitter electrodes are earthed over common resistance R10, while the bases are connected to earth over resistances R5, R6 and R14, R15 respectively in series; the junctions of R5, R6 and R14, R15 being connected over resistances R8, R12 to a positive 45 V. bias source 25. Resistances R6, R15 are shunted by crystal diodes D5, D7 so that points 26, 27 are clamped to a small positive bias value, and the base electrodes are held to a small negative value. In operation (Figs. 2,'3, 4, not shown), assuming transistor G2 to pass a high collector current (" on ") and transistor G3 to pass a lowcollector current (" off "), the arrival of a positive pulse on the base of G2 develops a similar pulse at the emitter of transistor G2 in common with that of G3, so that the latter is triggered into its " on " condition. A large positive pulse developed at the collector electrode thereof is transmitted over C5, R13 to the base electrode of transistor G2, which then cuts off, while G3 conducts; these conditions remaining stable until a positive pulse arrives on the base of transistor G3, so that transistor G2 conducts and G3 is cut off according to a similar mechanism. Resistance R10 is chosen to ensure that at least one transistor is always held conductive, while diodes D4, D6 by admitting only positive pulses ensure that one transistor at least is always held non-conductive in response to a positive pulse; no negative pulse such as to drive a transistor to cut-off being admitted. Meter M indicates the average of the difference between the collector currents of the transistors over a period determined by the meter inertia and large compared with a complete triggering cycle of the transistors; the reading being zero for zero transmission torque when the transistors are each on and off for equal times. Torsional strain of the shaft causes a corresponding phase difference between the s ignal inputs so that one transistor conducts for a longer period of each cycle than the other, and the meter reads in correspondence with the torque magnitude and sense. In a modification (Figs. 5, 6) a torque transmitting shaft 47 rotates two axially spaced phonic wheels 43 of magnetic material in the fields of the permanently magnetized cores 46 of stationary pick-up coils 41, 42 which develop sinusoidal voltages whose phase difference is proportional to the torsional strain in the shaft and the transmitted torque and which are directly supplied to the base electrodes of junction transistors G11, G14 whose emitters are earthed and whose collectors are connected over resistances R22, R32 to a 6.5 V. negative potential source 53. The sinusoidal inputs are transformed (Figs. 7, 8, not shown) into trains of voltage square waves, with sides coincidental with the zero points of the sinusoids, appearing across resistances R22, R32, which are differentiated by series capacitance-resistance circuits C11, R23, C12, R31 to alternate sharp positive and negative pulses, of which the former are suppressed by germanium diodes D11, D12 while the latter trigger the base electrodes of junction transistors G12, G13. In the latter the emitter electrodes are earthed and the base electrodes are oppositely interconnected over resistances R26, R29 with the collector electrodes, which are connected over equal load resistances R24, R30 to opposite ends of balancing potentiometer P1, whose slider is connected to source 53. The collector electrodes are also interconnected through meter M. and series resistance R25. Operation is analogous to that of the Eccles-Jordan thermionic valve circuit. With the transistor G12 cut-off, its collector is at the negative source potential together with the base of transistor G13 which is conducting, so that its collector holds the base of transistor G12 at earth potential to maintain cut-off. A negative pulse at base 74 triggers the transistors to interchange their, positions to G12 conducting, G13 cut-off, which condition is stable until arrival of a negative pulse at the base of transistor G13 interchanging their positions once more. If the shaft 47 transmits no torque during its rotation, the input signals are in phase and each transistor conducts for an equal time so that the centre zero microammeter M measuring the average total collector current is undeflected. When torque is transmitted the input signals are correspondingly out of phase, so that one transistor conducts for a time greater than that of the other in each cycle and the meter is deflected proportionally to the torque in magnitude and sense.