ELECTRICAL SENSING APPARATUS FOR SENSING THE PRESENCE OF A CONDUCTIVE OR MAGNETIC OBJECT WITH COMPENSATION FOR SUPPLY VOLTAGE FLUCTUATIONS

摘要

1,102,701. Locating conductors. TATEISI ELECTRONICS CO. June 16, 1965 [June 24, 1964], No. 25467/65. Heading G1N. To compensate for the effect of supply voltage fluctuations on an electromagnetic detector, the output amplifier has a D. C. reference voltage varying with the mains supply. As shown the sensing head comprises a primary 2 and opposed secondaries 3, 4 (for detecting a conductor 9). The output is applied through an amplifier 14 to a common emitter trigger comprising transistors 17, 18 to operate a switching circuit 23. The switching circuit and transistors are energized from constant voltage supplies, but the emitter "reference" bias is derived from the current through a resistor 28 in series with a Zener diode 29 and hence varies with the A. C. supply to the sensing head.