GB813261A - Improvements in or relating to torque measuring apparatus - Google Patents

Abstract

813,261. Electric torsion meters. WAYNE KERR LABORATORIES Ltd., and WILMOT BREEDEN Ltd. Sept. 21, 1956 [June 24, 1955], No. 18384/55. Class 40 (1). Relative displacement of the electrodes of a capacitor measures the strain between two points of a shaft, one electrode being mounted on the shaft at one point and the other electrode being carried by a member which is mounted at the other point, the variable capacitor being connected into a transformer bridge circuit where it is balanced against a standard capacitor. As shown in Fig. 1, a shaft 10 rotating in bearings 11 and 12 has a reduced portion 20 at one end of which an inner electrode 13 having projecting teeth 15 is secured. Surrounding the teeth 15 are an equal number of teeth 30 on an outer electrode 29 mounted between insulating plates 31 and 32 and'secured to a tube 21 which is anchored to the other end of the reduced portion of the shaft 10. Strain in the shaft 20 alters the relative angular positions of the teeth on the electrodes. On each side of the outer electrode 29 are guard electrodes 25 and 33. Electrical connection to the outer electrode 29 and guard electrodes 25 and 33 is made over brushes 35, 37 and 38 mounted on the fixed bearing block 37. If the shaft is not rotatable, as in a weighing machine, the brushes are not necessary. As shown in Fig. 2, to measure the torque a source of 10 kc/s. energizes a bridge circuit in which limbs of a tapped transformer are connected over coaxial lines to the torque capacitor and a standard capacitor 44, respectively. The guard electrodes are connected to the transformer tap over the outer conductor of the coaxial line connecting the torque capacitor to the transformer. The out of balance signal in the transformer is amplified and applied to an indicator 52. In place of the torque capacitor electrodes lying radially opposite each other, as shown in Fig. 1; they may overlap radially with an axial spacing; or they may comprise interleaving cylindrical surfaces coaxial with the shaft.