| 摘要 |
PURPOSE: To determine surely that a terminal to be measured has touched a liquid level by determining the variation rate of capacitance being applied to a measuring terminal to be detected from a capacitance detector using a differentiation circuit and then making a decision based on the determination results from the differentiation circuit using a comparator. CONSTITUTION: When a stray capacity 114 (Cp) of a probe 121 is detected, the probe 323 is floated electrically and the voltage being fed to a two-input exclusive OR gate 115 has a waveform integrated through a resistor 112 (R) and the stray capacity 114 (Cp). An integration circuit 116 integrates the output waveform having pulse width corresponding to the phase difference between two inputs obtained from the gate 115 through exclusive OR operation and transforms the phase difference into a voltage value. Subsequently, a variable gain amplifier 102 amplifies the output from the circuit 116 with a gain being set variably and programmably and the integrated voltage waveform is differentiated by a differentiation circuit 103. Finally, a comparator 104 decides whether the differentiated voltage exceeds a predetermined reference voltage. |
