| 摘要 |
PURPOSE:To enable a highly sensitive detection of both ferrous and non-ferrous metal by driving a transmission coil with the time division of two frequencies. CONSTITUTION:When an object W to be inspected containing iron passes as shown by the arrow, the balance of induced voltage of a receiving coil 14, particularly the balance of the amplitude breaks and a differential signal of a waveform C is outputted. A synchronous detection signal of a waveform D is supplied to a synchronous detector 16 through a switch 21 and a differential signal C' is detected synchronously by synchronous detection signals eF and eS varied in the phase at each Tl during the period Th to obtain a synchronous detection signal of a waveform E. The waveform E is time divided with a switch 22 to be inputted separately into BPF17a and 17b and the input waveform gives a detection signal having frequency fh and fl components as shown by F and G. The signal F is zero in the mean value and a discriminator circuit 18a fails to operate while the signal G is Ef in the mean value and the discriminator 18b operates to output a signal indicating mixing-in of iron. |
