Patent GB-585469-A (GB)
Title: Vibration analyser and indicator
IPC: G01H1/00
Filed: 1944-05-13
Abstract: 585,469. Valve amplifier circuits. METALASTIK, Ltd., MOYAL, J. E., and MAY, S. May 13, 1944, No. 9203. [Class 40 (v)] [Also in Group XXXVI] Electric wave-forms to be analysed are passed through an amplifier comprising a positive feedback path variable under the control. of an operator to discriminate between frequencies so that various frequency components of the wave-form may be studied successively. Negative feedback is also provided to prevent self oscillation at any selected frequency range. The electric impulses under study derived e.g. from an engine crankshaft, are applied to an input amplifier or buffer stage VI, Fig. 1, and then successively through (1) a selective amplifier V2 which passes only the frequency band required, (2) an integrating amplifier V3, V4 wherein compensating effects may be introduced dependent on the type of pickup used for converting the mechanical vibrations into electrical oscillations, and finally, (3) an output amplifier V5, V6. The output therefrom is fed over a condenser C38, to the vertical deflecting plates of a cathode 'ray oscillograph CRO, Fig. 3, the horizontal deflecting plates of which are fed from a standard time base circuit V10, or with periodic electric impulses derived from the rotation of the crankshaft over resistances R53, R54 so that a stationary picture of the oscillation under study is obtained. The output from V6 is also rectified at V7, W1 to actuate an output meter MA1, Fig. 3, indicating the average amplitude of the wave-form. The input amplifier V1 functions as a triode, and overloading thereof is prevented by tapping off, by switch S1, an appropriate proportion of the input voltage connected across attenuator R1, R2, R3. The frequency selection is effected by a manually operated three-position switch AS having wiper contacts AS1... AS7. In the FO (filter out) position shown the whole frequency range is accepted ; the output from V1 is connected over condensers C4, C18 to the grid of V2, and the output therefrom is connected over condenser C2, and paralled resistances R23, R24 to the next stage. The wiper AS6 connects the byepass capacity C14 in the cathode circuit and the stage V2 thus acts as a normal amplifier. A condenser C17 connected across the anode and cathode of V1 byepass oscillations of frequency above the range with which the apparatus is to deal. In the next position LR (low range)-of switch AS, the wipers AS 1... AS7, thereof, contact with the next lower fixed contacts shown. The input circuit to the buffer valve V1 is unaltered, but the output therefrom is now coupled over condensers C4 and C5 to the grid of V2. The anode of V2, is now coupled over wipers AS3, 4, 5, to inject positive feed back to the grid by way of the phase shifting net-work C6, C7, C8, R19, R20, R21, VR10, VR11, VR12. This regenerative arrangement is designed to select and amplify only the frequency band desired, e.g. 720 to 6000 cycles per minute depending on the setting of the adjustable ganged resistances VR10, 11, 12, which may be calibrated to read the frequency direct. To limit the regenerative feed back to a value just less than the selfoscillation value, negative feedback is introduced by means of condenser C12, and preset resistance VR6, shunted across the V2 cathode bias resistance R16, R18. Owing to the enhanced sensitivity of V2, the output therefrom is reduced by R23 before being applied to the next stage. In the HR (high range) position of switch AS the input to valve V1 is tapped off resistance VR4. V2 is coupled only by C4 wipers AS3 ... AS5, connect condensers C9, 10, 11 in the phase shifting feedback circuit and wiper AS6 connects up condenser C13 and resistance VR22 to introduce negative feedback, whereby only frequencies within the high range e.g. 4,500 to 35,000 cycles per minute are selected and amplified. The integrating amplifier V3, V4, Fig. 2, includes a three-position manually operated switch MS having five ganged wipers MS1 ... MS5, which varies the amplifier characteristics to compensate for variations in the conversion of the mechanical vibrations being analysed into electrical vibrations dependent on the pick-up used. In the position of switch MS shown valve V3 only is operative ; this valve gives linear amplification characteristics and is therefore suitable for pick-ups in which output is directly proportional to displacement. In the second position of switch MS, the integrating valve V4 is connected in cascade with V3, its modifying effect causing the amplifier to have a linear characteristic falling with frequency which compensates for the rising characteristic of pick-ups wherein output is proportional to velocity. In the third position of MS1 ... MS5, the amplifier valve V3 is converted by the insertion of resistance R28 and condenser C21 into an integrating valve which further modifies the combined amplifying effect of V3, V4, to compensate for pick-ups in which the rising output is proportional to acceleration. The output amplifier V5, V6 is of normal construction. To prevent overloading thereof the input thereto is taken from the appropriate tapping of the input resistance R37 ... R40. A voltage checking and calibrating unit, Fig. 4 (not shown), is provided which by a series of push buttons enables the working voltages at the various supply points in the system to be selected and checked on a meter. In a modified input and analyser amplifier stage, Fig. 5 (not shown), five frequency ranges are provided for and enhanced selectivity and sensitivity obtained by using an additional valve in the analyser.