| 摘要 |
<p>The encircling detector (1) is transmitter-receiver type. A magnetic field is created round the product to be controlled, by adding magnetic loss fields due to a part of the transmitter, consisting of three winding pairs arranged on a ferrite core (1). The ends of each winding (2-2',3-3',4-4',5-5',6-6',7-7') exit from the ferrite core at diametrically opposite positions to each other. Some ends (2,3,4,2',4',6') exit near to the other ends (3,5,7, 3'5',7'). The windings of the same pair are electrically mounted in phase opposition with respect to the other. The assembly formed by a pair of windings (2-2',3-3') is angularly shifted on the ferrite by 120 degrees with respect to the other two winding pairs (4-4',5-5') and (6- 6',7-7'), which are fed by currents of the same frequency and phase shifted by 120 degrees . They induce in the product to be controlled Foucault currents whose distribution is influenced by the presence of faults, such as discontinuities that appear by changes in voltage at the terminals (9-9',10-10') of the opposed windings forming part of the receiver (8) surrounding the product to be controlled. The amplitude and phase of the induced voltage in the receiver windings represents the nature and importance of the discontinuity.</p> |
