Working principle and main characteristics of capacitive sensor

Capacitive sensor is a conversion device that uses various types of capacitors as sensing elements to change the measured physical or mechanical quantities into capacitance changes. In fact, it is a capacitor with variable parameters. The following mainly introduces the working principle and main characteristics of capacitive sensor. Let's have a look!

Working principle of capacitive sensor

The capacitance detection element of the capacitive sensor works according to 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 π 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 practical 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: pole distance change type, area change type and medium change type. The pole distance change type is generally used to measure the small linear displacement or the pole distance change caused by force, pressure, vibration, etc. Area change type is generally used to measure angular displacement or large linear displacement. Medium change type is often used for level measurement and measurement of temperature, density and humidity of various media.

Working principle and main characteristics of capacitive sensor

Main characteristics of capacitive sensor

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, but also has little impact on the stability due to its small heat. The resistance sensor has copper loss, which is easy to generate zero drift due to heating.

2. Simple structure

Inductive sensor is simple in structure, easy to manufacture and ensure high accuracy, and can be made very small to achieve some special measurements; It can work in harsh environments such as high temperature, strong radiation and strong magnetic field, and can withstand large temperature changes, high pressure, high impact, overload, etc; It can measure the ultra-high temperature and low pressure difference, and can also measure the magnetic work.

3. Good dynamic response

Due to the small electrostatic attraction between the charged plates, the inductive sensor requires very little action energy, and because its movable part can be made very small and thin, that is, its mass is very light, so its natural frequency is very high, its dynamic response time is short, and it can work at a frequency of several megahertz, especially suitable for dynamic measurement. Because of its low dielectric loss, the system can be powered by a higher frequency, so the system operates at a high frequency. It can be used to measure parameters with high speed changes.

4. Non-contact measurement and high sensitivity

It can non-contact measure the vibration or eccentricity of the rotating shaft, the radial clearance of the small ball bearing, etc. When non-contact measurement is adopted, capacitive sensor has average effect, which can reduce the influence of workpiece surface roughness on measurement.