GB772190A - A method of and apparatus for the indication and measurement of displacements of a point with respect to a system of co-ordinate axes - Google Patents

Abstract

772,190. Measuring rotary unbalance electrically. BUISSON, P. Sept. 16, 1954 [Sept. 22, 1953], No. 26903/54. Class 40 (1). Apparatus for determining the movement of a body O (Fig. 1) in space comprises three differential condensers 1, 2, 3, &e., each consisting of two fixed plates 2, 3, 2<SP>1</SP>, 3<SP>1</SP>, 2<SP>11</SP>, 3<SP>11</SP> and a central movable plate 1, 1<SP>1</SP>, 111 attached to the body O, each condenser unit having its axis located in one of three mutually perpendicular planes OX, OY, OZ, the fixed plates being supplied with an A.C. voltage, whereby the ratio of the P.D.'s between the movable plate and each of the associated fixed plates identifies the movement of the body O in each of the three planes. For determining the vibration of a rotating shaft 6 (Fig. 6), two pairs of fixed, curved plates 2<SP>1</SP>, 3<SP>1</SP>, 2<SP>11</SP>, 3<SP>11</SP> are located on perpendicular diameters of a cylinder 7 keyed to the shaft, and fixed washers 2, 3 opposite the end faces of the cylinder, to form the three mutually perpendicular differential condensers in association with the surface of the cylinder 7. The fixed plates 2<SP>1</SP>, 3<SP>1</SP> and the earthed cylinder 7 form two arms of an A.C. bridge incorporated in unit 14<SP>1</SP> together with an amplifier and rectifier to provide a D.C. voltage signal indicative of the vibration of the shaft 6 along the OY axis. Similarly, the fixed plates 2<SP>11</SP>, 3<SP>11</SP> produce a signal indicative of vibration along the OZ axis, and these signals may be fed to the plates 15<SP>1</SP>, 16<SP>1</SP> and 15<SP>11</SP>, 16<SP>11</SP> of a C.R.O. A cam, not shown, may be mounted on the shaft 6 to close a contact once per revolution to produce a bright spot on the C.R.O. trace to identify the phase position of the vibrations. To enable the axial movements to be indicated at the same time, the signal derived from plates 2<SP>1</SP>, 3<SP>1</SP> multiplied by cos α is added to the signal derived from plates 2, 3 by axial movement multiplied by sin a, before being applied to the horizontal plates 15<SP>1</SP>, 16<SP>1</SP> of the C.R.O. The multiplication is obtained by two ganged, sine-cosine potentiometers, whereby the angle α can be manually adjusted. The unbalance can be measured by duplicating the condenser units, the second set being associated with an eccentric cylinder driven at the same speed, the further condenser plates being rotatable and axially displaceable. The unbalance of the auxiliary plates can be made exactly identical with that of the shaft, and can, therefore, be located and eliminated. In another embodiment, the moving body is not a shaft but a cube 4 (Fig. 2), whose movements in three mutually perpendicular directions may be similarly determined.