What are the types and advantages of capacitive sensors

A device or device that uses the principle of capacitors to convert non electrical energy into capacity and then convert non electrical energy into electricity is called a capacitive sensor. Capacitive sensors should use various types of capacitors as sensing elements to convert measured physical or mechanical quantities into capacity conversion devices, which are actually capacitors with variable parameters. This article has collected and organized some materials, hoping to have greater reference value for readers.

Types of capacitive sensors

Capacitive sensors can be divided into variable electrode distance type, variable area type, and variable material type according to the working principle of the sensor.

1. Variable electrode distance capacitive sensor

Taking a parallel plate capacitor as an example, the upper electrode plate is fixed, the lower electrode plate is a moving electrode plate, and the distance between the original two electrode plates is d0. When the spacing decreases Δ When d, the capacitance increases accordingly, and the capacitance is relatively converted to

It can be seen that the relative variation and offset of capacitors are non-linear. Within the allowable deviation range, the static sensitivity of the capacitive sensor is. If only the quadratic nonlinear term is considered and other higher terms are ignored, the nonlinear error is:

As the pole distance decreases, the nonlinear error increases, and the general range of variation of the pole distance is Δ D/d0 ≈ Therefore, this capacitive sensor is only suitable for small offset measurements (0.01 μ m～1 mm)。

Differential capacitance sensors are commonly used in practical applications to improve sensitivity, reduce nonlinear errors, and overcome the impact of external conditions such as power supply currents, operating temperature changes, and so on. The total capacitance of the differential capacitor is converted to:

Therefore, after the capacitive sensor is made into a differential structure, when the same offset changes relative to each other, the non-linear error is greatly reduced, and the sensitivity is twice as high as that of a single polar distance capacitive sensor.

2. Variable area capacitive sensor

When the sensor of a variable area capacitor, taking a parallel plate capacitor as an example, changes the relative coverage between the two electrode plates, resulting in changes in the capacitor. This sensor can be used for displacement measurement. According to application regulations, there are parallel plate plates, barrel plates, and serrated plates, which have strong linear characteristics.

When a linear displacement occurs on the moving electrode piece, the corresponding capacitance is converted to, where K is the sensitivity, and its output is linearly related to the input, with the sensitivity being constant. However, parallel plate structures are more sensitive to pole distance conversion, and detection accuracy may be affected. However, cylindrical structures are less affected by pole axial conversion, making them the most commonly used structures in practice. When the moving cylinder moves and the overlapping length of the two cylinders changes, the capacitance is converted to: K is sensitivity.

3. Variable material capacitance sensor

The variant capacitor sensor should insert different substances between the two electrode plates of the capacitor, causing the capacitor to switch. Sensors based on this principle are typically used to measure liquid level (i.e., capacitive water level sensors) and material thickness.

The original capacitor for a coaxial cylindrical capacitor is. During the measurement process, part of the material in the capacitor is liquid at the level to be measured, and part is gas. C1 is a capacitor formed when the liquid height is hx, and C2 is a capacitor formed when the gas height is h-hx. Because C1 and C2 can be considered as two parallel capacitors, the total capacitor is:

In theory, capacitance is linearly related to the level height, and the level height can be obtained by measuring the capacitance.

Another capacitive sensor that measures changes in the dielectric constant of a material has a structure similar to that of a parallel plate capacitor. When there is a material with unknown thickness but known relative dielectric constant based on the electrode gap, the material thickness can be obtained by changing the capacitor.

Advantages of capacitive sensors

1. Good temperature stability

The capacitance value of capacitive sensors is generally independent of the battery material, making it advantageous to select materials with low temperature coefficients. Due to its small heat content, it has little impact on stability. The resistance sensor has copper damage, which is prone to burns and zero drift.

2. Compact structure

Inductive sensors have a compact structure, convenient manufacturing, and strong guaranteed accuracy, which can achieve some special measurements; Able to work in harsh environments such as high temperature, strong radiation, and magnetic fields, and able to withstand large temperature changes, high pressures, high shocks, and loads; It can measure ultra-high temperature, low pressure differential, and also measure magnetic work.

3. Good dynamic response

Due to the small electrostatic attraction between the charged electrode plates (about 10 ^ (- 5) N), the necessary functional kinetic energy of the inductive sensor is very small. Because its moving part can be very small and thin, that is, its mass is very light, so its resonance frequency is very high, and its dynamic response time is very short. It can work at a number of megahertz, especially suitable for dynamic measurement. Due to low dielectric loss, the system operates at a high frequency. It can be used to measure rapidly changing parameters.

4. Non contact measurement, high sensitivity

Non contact measurement of vibration or eccentricity of rotating shafts, radial clearance of small rolling bearings, etc. When using non-contact measurement, capacitive sensors have an average effect, which can reduce the impact of workpiece appearance roughness on the detection.

If you have any purchase requirements for electronic components, please contact Chengyexing

Shenzhen electronic component IC chip supplier, one-stop BOM distribution company, 5000+standing stock inventory, million level original factory material number data

Can provide integrated circuit IC chips, memory IC chips, analog signal switches, interface IC chips, clock drive IC, audio amplifier IC, photocouplers, etc

Various electronic components (resistors, capacitors, inductors, switch connectors)

Spot materials are shipped on the same day, and the BOM quotation can be completed within one day. Service hotline: 134-3440-1267, 155-2178-1275