The working principle and main characteristics of capacitive sensor

Capacitive sensors use various types of capacitors as sensing elements to convert the measured physical or mechanical quantity into a conversion device for capacitance changes, which is actually a capacitor with variable parameters. The following mainly introduces the working principle and main characteristics of capacitive sensors, let's take a look!

The working principle of capacitive sensor

The capacitor detection element of the capacitive sensor is based on the principle of cylindrical capacitor, the capacitor is composed of two insulated coaxial cylindrical plate inner electrode and outer electrode, when the electrolyte with dielectric constant e is filled between the two cylinders, the capacitance between the two cylinders is C=2 PI eL/lnD/d, where L is the length of the overlapping part of the two cylinders; D is the diameter of the outer cylinder electrode; d is the diameter of the inner cylinder electrode; e is the dielectric constant of the intermediate medium. In the actual measurement, D, d and e are basically unchanged, so the capacitive sensor has the characteristics of convenient use, simple structure and high sensitivity.

Capacitive sensors can be divided into three types: polar distance variation type, area variation type and medium variation type. The polar distance variation type is generally used to measure the small line displacement or the polar distance change caused by force, pressure, vibration, etc. The area variation type is generally used to measure angular displacement or large linear displacement. Medium variation type is often used for level measurement and measurement of temperature, density and humidity of various media.

The main characteristics of capacitive sensors

1, good temperature stability

The capacitance value of the capacitive sensor is generally independent of the electrode material, which is conducive to the selection of materials with low temperature coefficient, and because of the minimal heating itself, the stability is little affected. The resistance sensor has copper loss, easy to heat and produce zero drift.

2. Simple structure

Inductive sensors are simple in structure, easy to manufacture and guarantee high accuracy, and can be made very small to achieve some special measurements; Can work in high temperature, strong radiation and strong magnetic field and other harsh environment, can withstand great temperature changes, withstand high pressure, high impact, overload and so on; Can measure ultra-high temperature and low pressure difference, can also be measured with magnetic work.

3. Good dynamic response

Because the electrostatic attraction between the charged plates is very small, the action energy is very small, and because its moving part can be made very small and thin, that is, the mass is very light, its natural frequency is very high, the dynamic response time is short, and it can work at a frequency of several megahertz, especially suitable for dynamic measurement. And because of its small dielectric loss can use a higher frequency of power supply, so the system operating frequency is high. It can be used to measure fast-changing parameters.

4, can be non-contact measurement and high sensitivity

The vibration or eccentricity of the rotating shaft and radial clearance of small ball bearings can be measured without contact. When non-contact measurement is used, capacitive sensor has average effect, which can reduce the influence of workpiece surface roughness on measurement.