| 摘要 |
<p>PURPOSE:To dispense with the adjustment of a coil interval, to facilitate preparation and to stabilize a detection sensitivity temp. characteristic, by providing a resonance circuit, an oscillator and an voltage detection part. CONSTITUTION:A resonance circuit wherein a coil 1 of a single winding empty core and a resonance frequency adjusting condenser 3 are connected in parallel is connected to the wiring of an oscillator 5 containing a current control resistor 2 and a voltage detector 6 detects the voltage between the terminal of the coil 1 and that of the condenser 3. A curve A shows the frequency characteristic of a magnetic sensor when a magnetic material 4 is absent within a detection distance range and the resonance frequency thereof is f0. A curve B shows a characteristic when the magnetic material 4 enters the detection distance range of the sensor and the resonance frequency f0' at that time becomes lower than f0. A curve C shows a frequency characteristic when iron being a soft magnetic material similar to the magnetic material 4 enters the detection distance range and the resonance f0'' at that time becomes higher than f0. Further, the voltage level of the whole of the curve C is lowered. By utilizing the frequency characteristic changing as mentioned above, the magnetic material and the soft magnetic material can be discriminated.</p> |
