Patent GB-1145502-A (GB)
Title: Unbalance analyser
IPC: G01M1/24
Filed: 1966-04-21
Abstract: 1,145,502. Measuring dynamic unbalance electrically. ABEX CORP. April 21, 1966 [April 21, 1965], No.17540/66. Heading G1N. In order to test the balance of a petrol engine 12 running under its own power within a predetermined measured speed range, accelerometers 15, 16 are affixed to the engine casing adjacent the front and rear main bearings and a synchronizing signal is taken from one sparking plug 14. Alternatively a photo-electric pick-up may be used. From these inputs, signals are obtained indicative of the amplitude and phase of only the components of the vibration signals which are at synchronous frequency so as to eliminate unwanted signals due to the vibration of auxiliary equipment e. g. water pumps. The desired signals are displayed only whilst the engine speed is within the test range, and subject to the engine not running roughly. As the front and rear accelerometer signal circuits are identical, only one will be described. An A. C. signal having an amplitude proportional to velocity is obtained from the accelerometer and passed to a low pass filter 24 to eliminate the third and higher harmonics. The velocity signal may be attenuated by a potential divider 56 for calibration purposes before being integrated to provide a displacement signal which is applied in parallel to two synchronous detectors shown as item 26. Two squarewave demodulating signals of synchronous frequency, one of reference phase, the other lagging 90 degrees, are developed from the sparking plug signal at 14 by shaping and frequency doubling circuits 28, 31, 32, 30, and applied to the two detectors 26 to provide two D. C. output signals proportional to the components of the displacement signal resolved about two axes at right-angles. The two D.C. signals are chopped at 1KHz to provide two A. C. signals, by two parallel choppers (shown as 36) before being applied to the stator windings of a resolver 58 the rotor windings of which are linked by an R. C. network to provide a single-phase A. C. output having an amplitude proportional to the original displacement signal and a phase relative to the 1KHz signal proportional to the engine unbalance position. The resolver 58 may be adjusted for calibration purposes. The signal is passed through a sharply tuned circuit 40 and mixed with an adjustable portion of the signal from the rear accelerometer channel to compensate for rear-to-front cross-effects before being amplitude demodulated to provide an "amount" signal on meter 20 and phase demodulated to provide a "position" signal on meter 18. The meters have coils which, when energized, lock the pointers. These are released by a signal from a speed responsive circuit 48 (energized from the sparking plug circuit) when the engine speed is between predetermined limits (1, 200 to 1, 800 R.P.M.). The meters are not however unlocked if the engine is misfiring or otherwise running roughly. To this end, the outputs of both accelerometers 15, 16 are added at 50, components having a frequency higher than half synchronous frequency are removed by a low pass filter 52 and the resultant energizes a relay 54 if above a predetermined amplitude. Relay contacts disable the meter unlocking circuit and energize a warning lamp.