| 摘要 |
PURPOSE:To adjust automatically phase so as to minimize material effect by providing a circuit which controls the phase adjustment in the direction where the peak value of the unbalance detection signal when an object to be inspected passes between two receiving coils and a transmission coil decreases. CONSTITUTION:An alternating magnetic field is generated from a transmission coil P by the oscillation signal of an oscillator 11. A differential voltage signal from a tuning circuit 13 is outputted when objects W to be inspected pass successively by each piece between the coil P and receiving coils S1, S2. The signal is inputted through an AC amplifier 14, a detecting circuit 16, a DC amplifier circuit 17, an AD converter 18 and a peak holding circuit 20 receiving the detection signal from an object detector 19 to a metal detecting circuit 21 which compares the signal with the reference signal from a reference setter 22 and outputs a metal detection signal when the signal exceeds the reference value. A decision circuit 23 makes relational decision of the peak value held in the circuit 20 and the stored peak value when the metal detection circuit is not inputted to said circuit. A change-over control circuit 24 controls the circuit 13 in the direction where the peak value decreases according to the decision circuit of said circuit. |
