Measuring circuit is the capacitive sensor capacitive sensor as a capacitor and converted into a voltage or other power circuits. Therefore, the common measurement circuit main bridge circuit, FM circuit, pulse width circuit, an operational amplifier circuit, the diode bridge and double T-shaped ring diode AC discharge method. Frequency modulation circuit is actually part of the capacitive sensor is used as the resonant circuit of the oscillator, when the input lead to changes in capacitance, oscillator frequency is changed. Although available as an output of the frequency measurement system to determine the size of the measured non-electricity, but this time the system is nonlinear and difficult to correct, and therefore have to join a frequency discriminator, the change in frequency is converted to a voltage amplitude variation, amplified instruments can be recorded instructions or recorder. In practical applications, often using differential structure, even if the sensitivity is increased by 1, and also allows non-linear error is greatly reduced, enhanced anti-jamming capability. Capacitive sensors are used to measure the linear displacement, angular displacement, vibration amplitude (measured to 0.05μm small amplitude), particularly suitable for measuring high-frequency vibration amplitude, precision shaft rotary precision, acceleration and other mechanical quantity, can also be used to measure the pressure difference pressure, level, material surface, the moisture content of the grain, non-metallic materials, coatings, film thickness, humidity measuring dielectric, density and thickness. In the automatic detection and control systems are often used as a position signal generator. From the point of view of energy conversion, the capacitance transducer is a passive converter is necessary to convert the measured mechanical quantity into a voltage or current is amplified and processed. Mechanics amount of linear displacement, angular displacement, spacing, distance, thickness, tensile, compression, expansion and deformation are all closely related to the amount and length; they are for mass volume is measured by the length or the length ratio, and the relationship between the measurement method is also very close. Further, in some conditions, these mechanical quantity changes rather slow, and very small range, have a high resolution required to measure very small distances or if displaced, the other sensors is very difficult to achieve high resolution requirements, Precise measurement of differential transformer sensors commonly used in the resolution of only 1 ~ 5μm magnitude; but there is a capacitance micrometer, his resolution of 0.01μm, the former two orders of magnitude increase, the maximum range of 100 ± 5μm, so he favored in small precision displacement measurement.

keywords: Sensors, pressure sensors, capacitive pressure sensor,