GB566227A - Improvements in electromagnetic gauges - Google Patents

Abstract

566,227. Electric gauges. BRITISH THOMSON-HOUSTON CO., Ltd., and LUDBROOK, L. C. July 13, 1943, No. 11340. [Class 40 (i)] [Also in Group XXXVI] In an electromagnetic gauge the output from the A.C. winding on the core is applied to the ammeter through a phase-sensitive demodulator bridge which is biassed by A.C. in phase with the supply. The gauge head comprises an E-shaped core 1 having a pivoted armature 2 which carries a feeler 3 adapted to be brought into engagement with a standard part or part to be tested 4. The outer limbs of the core 1 carry windings 5 energized in series from the secondary winding 6 of a transformer 7. The central limb of the core 1 carries a winding 9. The windings 5 are so connected that with equal air gaps between the outer limbs of the core and the armature 2 no voltage is induced in the winding 9, but with unequal gaps an A.C. voltage is induced therein having a magnitude depending on the discrepancy in the air gaps and a phase which is either forward or reversed according to which air gap is the greater. The output from the winding 9 is supplied to a phase - sensitive demodulator bridge circuit 10 which produces in the ammeter 11 a D.C. proportional to the A.C. voltage in the winding 9 and a polarity which reverses with reversal of phase in the A.C. voltage. The bridge circuit comprises four rectifiers connected in bridge formation with resistances connected across the diagonals. An A.C. biassing voltage from a secondary winding of the transformer 7 is applied to the mid-points of these resistances, the A.C. from the coil 9 being applied to one of the diagonals of the bridge and the ammeter 11 being connected across the other diameter.