GB904689A - Improvements relating to electric gauging apparatus - Google Patents

Abstract

904,689. Measuring electrically. ASSOCIATED ELECTRICAL INDUSTRIES Ltd. Jan. 19, 1959 [Jan. 17, 1958], No. 1738/58. Class 40 (1). [Also in Group XXXVI] In apparatus for determining the clearance between two ferromagnetic members, a winding 2 on one of the members is connected in series with an inductor or transformer 5 across an alternating voltage source 6 and the rectified voltage developed across the winding 2 is compared with the rectified supply voltage using a self-balancing potentiometer which indicates clearance between the two members. Fig. 4 shows apparatus for determining linear expansion of the shaft of a turbine by measuring variations in the distance d between a ferromagnetic collar mounted on the shaft and the polepieces 1 of an iron-cored coil 2 secured to a bearing housing. Variation in distance d affects the inductance of coil 2 and hence varies the alternating voltage across it. The residual voltage across the coil 2 is reduced by subtracting an antiphased voltage from the secondary of a transformer 5 as described in Specification 900,388. The resultant voltage is rectified and drives a current through a resistor 11. A servomotor 19, controlled by a polarized relay 15, drives the variable resistor 22 until the voltage across the relay 15 falls to zero. The motor 19 also drives a potentiometer 24 which controls a voltmeter 25 to provide an indication of the distance d. In Fig. 3 (not shown), the transformer 5 is replaced by an inductor and the potentiometer 24 and voltmeter 25 are respectively replaced by a variable resistor and an ammeter.