| 摘要 |
<p>A device for detecting and measuring capacitance variations which are small in relation to the capacitance of a capacitive measuring body, preferably for measuring the concentration of a gas or liquid. The device includes a measuring cell (1) with a measuring capacitor (3) the capacitance variations of which are to be measured, and a detector unit (2) which converts the capacitance of the measuring capacitor into an electric signal. The device is characterized by an astable multivibrator (5) the output of which is connected, on the one hand, to the input of an inverter (6) and, on the other hand, to one input of an EXCLUSIVE-OR circuit (7), and by a monostable multivibrator (11) connected to the output of the inverter. The components of said multivibrator determining its pulse length includes said measuring capacitor. The output of the multivibrator is connected to a second input of the EXCLUSIVE-OR circuit which thereby at its output produces a pulse signal, called difference pulse signal, which is the difference in pulse length between the output signal of the monostable multivibrator and that of the astable multivibrator. </p> |
