| 摘要 |
A liquid level detector circuit includes a capacitive probe, a reference capacitor and two further capacitors connected as a capacitor bridge, with one terminal of each of the probe and the reference capacitor earthed and a common terminal of the further capacitors providing an output to a warning circuit. An oscillator is provided by two transistors connected so as alternately to interconnect the other terminals of each of the probe and the reference capacitor and to connect these to two different fixed potentials. The further capacitors charge slowly but discharge rapidly so that when there is any imbalance there is an excursion of the mean voltage at the common terminal during discharge which, depending on the polarity of the excursion can trigger the warning circuit. |
