| 摘要 |
An externally modulated oscillator (10), a switch amplifier connected to the output side of the oscillator (10) and an electronic switch, for instance a transistor, thyristor or triac, controllable by the oscillator (10) via the switch amplifier is shown and described, the oscillator (10) having a oscillator amplifier (15) and a feedback (16). The invention is capable of detecting ferromagnetic modulating elements through paramagnetic material, in that a second feedback (17) is provided, the second feedback (17) has two externally modulatable coils (18, 19) connected in series in opposite directions, the series circuit of the two coils (18, 19) is located in the output circuit of the oscillator amplifier (15) and the junction point of the two coils (18, 19) is connected to the input (21) of the oscillator amplifier (15).
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