Capacitive appts. to measure concn. of gas or liq. - uses astable and monostable multivibrators in differential circuit that detects small changes in capacitance

摘要

The appts. measures small variations in the capacitance of a capacitor (3) in a measurement cell (1). The output of an astable multivibrator (5) is coupled directly (8-10) to one input of an exclusive or circuit (7), and is coupled to the other input via an inverter (6) and a monostable multivibrator (11) whose pulse length is determined by the capacitor (3). The exclusive or circuit generates a pulse signal which represents the difference in pulse length between the output of the monostable multivibrator and the output of the astable multivibrator.