| 摘要 |
A humidity sensing circuit uses a humidity sensing film variable capacitor as a circuit element in the RC control network for a timer circuit. As the voltage at one terminal of the capacitive sensing element swings between charge and discharge points for the timer/multivibrator, the other electrode of the capacitance is held at a voltage which is the approximate midpoint of the charge/discharge point to thereby cancel out any time averaged net DC component on the sensing element, to reduce stress thereon and extend its life. A power-down technique may also be used between sensing intervals, to remove all potential across the capacitance.
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