GB382292A - Methods and apparatus for analysis and measurement of noise and other mechanical vibrations associated with running machinery - Google Patents

Abstract

382,292. Locating sounds. CARPENTER, R. E. H., 35, Croham Valley Road, Croydon, and STANSFIELD, R., 16, Avenue Road, Teddington, Middlesex. June 22, 1931. No. 18018. [Class 118 (ii).] A method of investigating noises and other mechanical vibrations associated with running machinery consists in causing the vibrations to actuate a visual indicating device only during uniformly spaced time periods. The apparatus for use in carrying out the method comprises a microphone 1, Fig. 1, associated with the input transformer 2 of a two-stage thermionic valve amplifier of known type in which the grid-bias voltage is dependent upon the mean value of the space current. The secondary winding of the output transformer 11 is connected to the diagonally opposite points of a rectifying unit 12 which may be of the dry plate type and serves to rectify the amplified oscillations. The other diagonal points which form a wheatstone bridge arrangement are connected to a direct current type of indicating device such as a voltmeter 15 which is shunted by a condenser 16 and resistance 17. Across the output transformer is connected a selector device 18 comprising a metal disc 19 with a sector 21 of insulating material and cooperating contacts 22, 23, the disc being mounted on a rotatable shaft 20 so as to shortcircuit the amplifier during the greater part of a revolution. In utilizing the apparatus for investigating the noises associated with a fourstroke internal-combustion engine the microphone is placed at a suitable position near the engine and the shaft 20 is coupled to the engine cam shaft and the brush 23 is adjustable around the spindle. The diaphragm of the microphone may be coupled mechanically as by means of a rod to the member whose vibrations are being measured. A preferred form of selector device is shown in Figs. 2 and 3 ; it comprises two shafts 25, 26 which may be coupled to the cam, and crank shafts respectively. The shafts are connected by a 2: 1 gearing and the shaft 26 carries an insulating drum with conducting sleeves 30, 31. A brush 32 in continuous contact with the sleeve 30 is connected to one terminal of the output transformer, and two brushes 33, 34 arranged in parallel are connected to the other terminal. The brushes 32, 33 are mounted on a member 35 rotatable relatively to the casing 28 and having an index 36 co-operating with a scale 37. The brush 34 is mounted on a member 39 rotatable relatively to the member 35 and its setting is indicated by an index 41 and scale 42. A stop 44 fastened to a part of the engine prevents rotation of the selector device. A separate synchronously driven selector may be provided for use in conjunction with a stroboscope or oscilloscope.