| 摘要 |
The sensor has a sensing electrode, a shield grid electrode, which is spaced at a fixed distance from the sensing electrode, and an evaluating circuit. The evaluating circuit has a current-voltage converter connected between the sensing electrode and the shield grid electrode. A first transistor is connected between the current-voltage converter and the sensing electrode in such way, as to minimize a voltage difference between the electrodes. The sensing electrode and the shield grid electrode are connected to the evaluating circuit and the shield grid electrode is subjected to an alternating voltage. The current-voltage converter converts the current flowing from the sensing electrode to earth into a proportionate voltage.
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