| 摘要 |
A preamplifier portion 2 is arranged between a head portion 1 containing a detecting coil and an amplifier portion 3. wherein a detecting circuit and a controlling circuit and the like are arranged. The preamplifier portion 2 is connected to the head portion 1 via a shielded cable 5 of fixed length, while connected to the amplifier portion 3 via multi core cables 6a and 6b having connectors 7a and 7b. In the preamplifier portion 2, in addition to an oscillating circuit, an EEPROM containing a compensating table for compensating the relation between the oscillation output of the oscillating circuit and a detected distance is arranged. This EEPROM is connected to the controlling circuit at the side of the amplifier portion 3.
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