GB192749A - Improvements in or relating to measuring instruments and indicators - Google Patents

Abstract

192,749. Moullin, E. B. Nov. 1, 1921. Tell-tale apparatus.-Torsion or other angular movement of a shaft is measured by the variation in the reluctance of a. magnetic circuit, two elements of which are supported at positions between which the relative angular movement takes place. Two saddle pieces 11, 12 are fixed to the shaft 10 at points some distance apart. The saddle piece 11 supports a U-shaped laminated magnet 13 on which is mounted a coil 14. The saddle piece 12 carries an arm 15 extending longitudinally of the shaft to the piece 11. A laminated armature 16 separated from the magnet 13 'by a small air-gap 17 is carried .on a rod 18 passing through a bracket 19 carried on the saddle piece 11, the rod being pressed to the right, Fig. 2, by a spring 20. The end of the rod engages a coned screw passing through the arm 15. An alternating current is supplied to the coil 14 from an alternator 22 through slip-rings 24. When the shaft is transmitting power, the air-gap 17 is reduced and the variation in the current through the coil 14 which is indicated at the ammeter 23 is a measure of the relative angular rotation between the points at which the saddle-pieces are secured. The ammeter 23 may give direct readings of the length of airgap and consequently of torsion angle. When required to indicate power, an alternator excited by a direct current permanent magnet generator driven by the shaft may be used. Instead of modifying the generator, a current measuring device may be used which gives indications proportional to the product of the current in the winding 14 and the speed of the shaft. The ammeter may measure the root-mean-square value of the current, or an instrument of the oscillograph type may be used. The magnet core and. armature may be mounted in saddles of different sizes for fitting to shafts of different sizes. For measuring large angles, the pole faces of the magnet core may be arranged coaxially with the axis of rotation of the moving part, the armature in this case being tapered to obtain variation in the size of air gap.