GB575495A - Improvements in or relating to devices for testing coils of insulated wire - Google Patents

Abstract

575,495. Indicating faults ; impedance measurements. FROGLEY, G. J. March 15, 1944, No. 4805. [Class 37] A device for detecting faults in inductance coils comprises a balanced A.C. bridge, one arm of which contains an inductance with an extended iron core, over which may be placed the coil under test. Short circuited turns in the latter will cause the balance of the bridge to be disturbed, while if the ends of the coil be connected together, open circuit will then show by causing the bridge balance to remain undisturbed. The two secondary windings 2, 3 of the step-down transformer 1 comprise two arms of the bridge, the other arms being the preset adjustable resistance 16 and the series resonant circuit formed by the condenser 8 and inductance 9. The iron core 10 of the latter is extended to project outside the apparatus so that coils under test may be placed over it. The balance of the bridge may be adjusted by means of a potentiometer 13 and is detected by the bridge-connected rectifier 12 and the meter 15. A switch 17 is arranged so that in position (1) the transformer 1 is disconnected from the A.C. supply 7 and the meter 15 short-circuited in position (2) the meter 15 remains short circuited while the A.C. supply 7 is connected to the apparatus, and in position (3) the short-circuit across the meter is removed and the apparatus ready for use.