GB701412A - Improvements in or relating to testing apparatus for short circuited turns - Google Patents

Abstract

701,412. Testing for faults. FORTIPHONE, Ltd. Sept. 25,1952 [Oct. 3, 1951], No. 23049/51. Class 37 A coil to be tested for short-circuited turns and number of turns is linked with the field threading a pair of coils in a magnetic bridge, which coils are coupled to a local oscillator, the signals :from the pair of coils being rectified and fed to a D.C. bridge circuit. A magnetic core 1 carries three coils 2, 3, 4 forming a magnetic bridge. The central coil 2 is fed from a local oscillator 5, and the coils 3, 4 are connected together and earthed at their junction. The coils 3, 4 are connected to similar valve amplifiers 6, 7 followed by rectifiers 9, 10. The rectified outputs are passed to a D.C. bridge balance circuit 11, the output of which is fed to an indicating meter 12. The apparatus is first balanced, so that the indicator 12 reads zero. A coil 15 to be tested is then slipped over one end of the core 1 and an indication is given if the coil contains short-circuited turns. The magnetic bridge portion 1, 2, 3, 4 is preferably made as a separate unit enclosed in a casing from which projects the end of the core over which coils 15 are to be placed for testing. This unit is made with plug-in terminals so that it can be plugged into a second unit containing the parts 6, 7, 9, 10, 11, 12. To test a coil for correct number of turns the apparatus is given a predetermined degree of unbalance, and the coil to be tested is shortcircuited and placed over the end of the core. Balance is restored if the number of turns is correct. The predetermined degree of unbalance may be introduced by means of an adjustable attenuator in the output circuit of one of the coils 3, 4. Alternatively, a standard coil of the correct number of turns is shortcircuited and placed on one end of the core. The coil to be tested is shortcircuited and placed on the other end of the core. Balance is restored if the number of turns is correct. Instead of a straight core in the magnetic bridge, a T-shaped core may be employed, the central limb carrying the coil 2.