Capacitive pressure measurement involves determining the rate of change of capacity as a result of the movement of a diaphragm. The sensor is electrically excited by a high frequency oscillator. When the diaphragm deforms due to a change in pressure, the relative capacitance is measured by the bridge circuit. The capacitive method was originally developed and used to measure vacuum pressures.
Two types of design of this sensor are common. It is the first type of two-page design that works in both balanced and unbalanced modes. The second type is single capacitor design.
Balanced mode is such that the reference capacitor is placed in such a way that the output rejection, zero voltage is generated. In unbalanced mode, to measure the pressure, it is necessary to measure the output voltage to the excitation voltage.
This type of pressure measurement is quite accurate and has a wide operating range. In addition, capacitive pressure measurement to determine the level of a tank is quite common.
* Accuracy 0.01 to 0.2%
* Temperature sensitivity
* Waste capacitor problems
* Limited ability to withstand pressures outside the work range
* High cost
Application Limitations: Many of the drawbacks mentioned in connection with the capacitive method have been reduced in the new designs. For example, for applications that require high precision, there are temperature-controlled sensors. If tensometers are the most common method of measuring pressure, capacitive sensors are next.
Andres Hauser, Fuji, Vika, Honeywell, Siemens are some of the best brands of pressure transmitters that have capacitive pressure sensors.
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