Patent GB-753579-A (GB)
Abstract: 753,579. Measuring rotor unbalance electrically. GENERAL ELECTRIC CO. Aug. 18, 1953 [Aug. 19 1952], No. 22762/53. Class 40(1) [Also in Group XL(b) Apparatus for determining the unbalance masses of a rotor in two predetermined balance planes comprises means for supporting the rotor 11 (Fig. 1), in two bearings 12, 12a having pressure gauges 13, 13a in the bearings whereby the outputs from the gauges indicate the rotor unbalance forces in the planes of the bearings, and, by means of an electronic circuit described and claimed in co-pending Specification 753,580, these are converted into signals representing the rotor unbalance forces in the two predetermined balance planes, the circuitry including means for integraing the force voltages, representing mass X acceleration to obtain mass X velocity signals which would vary the variation in rotational speed and are therefore corrected in accordance with the speed of the rotor determined photoelectrically, the force signals being compared, before and after integration. with the speed signals to determine the magnitude and angular position of the unbalance masses. The output signals from the pressure gauges 13, 13a which may for example comprise a pair of piezoelectric crystal slabs having one common terminal and two interconnected outer terminals, are fed to a balance plane converter 20 (Figs. 1, 4) where they are converted in accordance with a mathematical relationship given in the Specification, into voltages at the cathodes of valves 57, 58, representing the unbalance forces at the bredetermined balance planes. These voltages are integrated by a pentode valve 84 to represent massvelocity values and a proportion determined by potentiometer 85, adjusted in 'accordance with velocity as described below, is fed via amplifier 23 to a valve 117. The rotational speed of the rotor 11 is measured by a photocell 43 picking out the black and white halves of a disc 37 attached to the rotor shaft by the reflection of the light from a lamp 40 from the surface of disc 37 and a mirror 42 whose angular position can be adjusted by a knob 45 to give a predetermined angular reference relative to the rotor 11. The photo cell output, consisting of alternate square pulses and blanks at the rotational frequency, having a phase position determined by the mirror 42, is amplified at 30 and phase split at 31. Each of the two phases is differentiated to give alternate positive and negative pulses, the latter being by-passed by rectifiers 96 and 103, and the positive pulses being fed to the control grids of a bi-stable multivibrator circuit 92 and a mono-stable multivibrator circuit 107. The bi-stable circuit 92 comprises two valves 99, 105 whose control grids are fed with the positive pulses, thereby producing a square wave output whose two halves are equal and opposite. The mono-stable circuit 107 comprises two valves 106, 109, the control grid of valve 106 being fed with one set of positive pulses from the phase splitter 31, thereby producing a square wave output the duration of half cycle being determined by the frequency of the positive pulses, and the duration of the other half being determined by a condenser 108 and potentiometer 88 and therefore adjustably constant. The output from circuit 92 or 107, i.e. balanced or unbalanced square wave output respectively, is fed via switch 34 to a further phase splitter 35, which feeds the two square out-of-phase voltages to two valves 113, 114 connected in a bridge circuit with resistors 118, 119 and a meter 120. The valves 113, 114 are thus alternately gated by the positive halves of the two square wave voltages, the magnitude of the currents through each valve being determined by the phase relationship between the square wave voltages and the anode current of valve 17, which is determined by the angular position of the unbalance mass of the rotor, and is indicated by meter 120. In operation, a speed adjustment is first made with switches 21, 22, 24, 25 all open, i.e. with no A.C. input to valve 117, by feeding the unbalanced square wave of circuit 107 to the meter 102 and adjusting potentiometer 88 to give zero reading, thus automatically adjusting mechanically coupled potentiometer 85. The values of potentiometer 85 and associated series resistor 85a are such as to provide correct compensation to the mass-velocity voltages for velocity variation. To determine the angle of the unbalance force in the one balance plane, switches 21, 34 are operated to compare the phases of the square wave output of circuit 92 and the unbalance force voltage at the cathode of valve 57. By rotating the mirror 42 until meter 120 reads zero, the associated dial 39a is made to show the position of the unbalance force relative to the fixed black/white demarkation line on disc 37. To determine the magnitude of the unbalance mass in this balance plane, switch 21 is released and switch 24 is operated, the magnitude being shown by meter 120. The angle and magnitude of the unbalance mass in the second balance plane is similarly determined by operating switches 22 and 25 consecutively,