| 摘要 |
PURPOSE:To prevent erroneous detection caused with variations in electrostatic capacitance due to the effect of relatively gentle temperature and humidity, by detecting whether a crew exists of not while paying attentions only to a sharp variation alone in the electrostatic capacitance between a first and second electrodes. CONSTITUTION:A microcomputer MPU 1 samples the number of pulses outputted from an oscillator OSC through a counter CTR and a P/S register PSR each time being interrupted by a 0.1sec timer 3 to set a frequency data corresponding to the number of pulses while a variation data is set corresponding to hourly changes in the oscillation frequency (f) of the OSC from the frequency data and the previous frequency data. When the set variation data shows changes within a specified range of the oscillation frequency (f) of the OSC, 'no crew' is detected while the frequency data is updated and set as reference data Ref. When the variation data shows a decrease beyond a specified range of the frequency (f), 'existence of a crew ' is detected. |
