| 摘要 |
The invention concerns an arrangement when detecting metal objects by means of a transmission coil 5 which generates an electromagnetic field to maintain the amplitude of the generated field constant. The transmission coil 5 is designed to interact with a receiving coil which is arranged so that an electromotive force is induced in the coil under the influence of the field generated by the metal object and the field generated directly by the transmitter coil 5. The transmitter unit contains an oscillator 1 which generates a sinusoidal signal which is sent to the transmitter coil 5. A negative feedback loop of the oscillator 1 includes a variable attenuation or amplification circuit 2 for regulating the amplitude of the oscillator signal. Said circuit 2 is controlled by a feedback circuit for feeding back the voltage across the transmitter coil 5. <IMAGE> |
