A variable-capacitor transducer is shown in Fig. 14.14(a).It is very similar in op- eration to the capacitor microphone(to be described later). The reference pressure of the transducer of this example can be atmospheric pressure(for relative pressure mea surement), a vacuum(for absolute measurements), or a fluid from the second pressure of interest(for differential pressure measurements)
A metal diaphragm within the capacitor transducer moves closer or farther away from a rigid plate and thereby causes a change in the capacitance of the structure the capacitance value is made part of an oscillator circuit, the frequency of the will change as the capacitance changes. The frequency changes can be monitored value to indicate the pressure change.
The capacitor pressure transducer is one of the most rugged to a wide range of ducers available for measuring pressure. It can be built to respond pressure values as well as to high-frequency pressure changes.