| 摘要 |
PURPOSE:To prevent the decrease in detection sensitivity by driving a detection coil and a dummy coil for compensation alternately to prevent the operation of both coils from overlapping with time and detecting the difference in the outputs of both coils with an oscillation system. CONSTITUTION:A detection coil 2 and a dummy coil 3 for temp. compensation are connected respectively to tho two electronic switches 71, 72 of a selector switch 7. The two coils 2, 3 are connected alternately to one oscillation circuit 8 by changing over the switch 7. The signal outputted from the circuit 8 is discriminated to the oscillation signal on the detection coil side and the oscillation signal on the dummy coil side for temp. compensation by using a gate circuit 9, and both signals are fed to a counter part 10. The oscillation frequencies are measured and calculated with an up-down counter 101, and the signal proportional to the difference in the frequency of both coils is obtained. The decrease in detection sensitivity in the detection circuit of a dual coil system is thus prevented. |
