According to the different capacitor change parameters, what are the different types of capacitive s

The common ones are variable intercept type, convenient area type, and variable dielectric constant type.

However, the variable intercept principle is usually used for displacement measurements. That is, the measured object (which needs to be conductive) is used as one plate of the capacitance, and the sensor is used as the other plate of the capacitance. The factors that affect the capacitance value of this capacitor are the distance, the area facing and the gap medium.

If you want to measure displacement with a capacitive sensor, you need to make sure that the latter two do not change.

In the case of the German Mi-iridium CapanCDT, it is possible to measure both conductor and non-conductor materials (the variable permittivity principle is used when measuring non-conductor materials). Absolute errors can reach microns and resolution can reach nanometers. However, it is required that there should be no influencing factors such as oil pollution and water (constant oil pollution and water can also be compensated, and there will be problems if it is not constant), otherwise it will affect the dielectric constant of the capacitor.

A capacitive sensor is a capacitance with variable capacitance, and a capacitor is a capacitance with a relatively fixed capacitance.

Capacitance: Also known as "capacitance". refers to the amount of charge stored at a given potential difference; refers to the ability to contain an electric field; It is a physical quantity that expresses the ability of a capacitor to hold an electric charge.

Capacitor: A device that holds an electric charge. Any two conductors (including wires) that are insulated from each other and in close proximity to each other constitute a capacitor. Without being confused with capacitance, capacitors are also referred to as "capacitors".

Capacitors are not the same as capacitors. Capacitance is a fundamental physical quantity, symbol c, and the unit is f (farad). A capacitor is a device with capacitance, which is usually used as the main indicator for the capacitance it has.

The basic formula for explaining the capacitance of a capacitor is: c = q u, that is, the charge of the object q divided by its potential u; Specific to the capacitor device itself, there is a capacitance determinant.

c=εs/4πkd。where: is the dielectric constant, s is the positive surface area, k

Electrostatic force, d-plate distance.

While. c=εs/4πkd

. 4πk

When it is constant, the dielectric constant, the plate (effective) area s, and the plate distance d

Determines the capacitance of the capacitor.

In general, capacitors are manufactured with the goal of stabilizing capacitance. Make the dielectric constant, plate area, plate distance.

The change in capacitance caused by the environment and use is so small that it can be ignored (under certain conditions) compared to the nominal capacitance of the capacitor.

Sensor: It is a detection device that can feel the measured information, and can transform the felt information into an electrical signal or other required form of information output according to a certain law.

Capacitive sensors use dielectric constant, plate area, and plate distance.

The relationship between the three and the capacitance is to achieve the purpose of measurement by allowing one or several of the items to change in relation to the measured parameter, and then obtaining the change in the measured parameter through the capacitance change caused by this change. For example:

A level sensor that measures the liquid level by changing the medium between the plates (dielectric constant);

A pressure sensor that measures pressure by acting on the plates and affecting the distance between the plates;

A displacement sensor that changes the plate area.

According to the working principle of the sensor, the capacitive sensor can be divided into three types: variable pole distance type, variable area type and variable medium type.

According to the structure of the sensor, capacitive sensors can be divided into three types of structural forms. They can be divided into two kinds according to the form of displacement: linear displacement and angular displacement, each of which is divided into flat (circular) plate shape and cylindrical (cylindrical) shape according to the shape of the sensor plate, although there are other shapes such as spherical shape and zigzag shape, but generally rarely used. Among them, the differential type is generally better than the single-group (single-sided) sensor, which has the characteristics of high sensitivity, wide linear range and high stability.

The capacitive sensor has the advantages of simple structure, high temperature resistance, radiation resistance, high resolution, and good dynamic response characteristics, and is widely used in the measurement of pressure, displacement, acceleration, thickness, vibration, liquid level, etc.

However, in use, it is necessary to pay attention to the influence of the following aspects on the measurement results: reduce the changes in ambient temperature and humidity (which may cause changes in the dielectric constant of some media or the geometric size and relative position of the plates); Reducing edge effects; Reduction of parasitic capacitance; Use shielded electrodes and ground them (protect the electric field of the sensitive electrode and isolate it from the external electric field); Pay attention to the leakage resistance, excitation frequency, and insulation of the plate bracket material.

Capacitive sensors can be divided into three types: pole distance change type, area change type, and medium change type.

According to the change of the measured parameters:

1) Pole Variable Distance Capacitive Sensor (D).

2) Variable area capacitive sensor (a).

3) Variable dielectric capacitive sensor ( ).

Summary. 1. The pole pitch type of pole change plate spacing.

Characteristics of variable plate spacing capacitive sensors: The capacitance is inversely proportional to the plate spacing. It is mainly used to measure the amount of displacement.

What are the types of capacitive sensors depending on the change in parameters? Briefly describe the working principles of various types of capacitive sensors.

1. The characteristics of the variable pole distance type variable plate spacing capacitive sensor Qiaohong or: the amount of capacitance filial piety is inversely proportional to the plate spacing. It is mainly used to measure the amount of displacement.

2. The characteristics of the variable area type variable plate coverage area difference type capacitive sensor of the substation plate coverage area: the capacitance withering amount is proportional to the area change. The main hole is to be used to measure the line displacement and angular displacement.

3. The characteristics of the variable dielectric constant of the variable dielectric constant of the variable dielectric variable dust type capacitive sensor are as follows: the dielectric constant of different media is different, and the measured detection is realized by changing the dielectric constant of the orange mode medium, and it is reflected by the change of the capacitance of the capacitive sensor. It is mainly used when the dielectric constant of the medium changes.

Capacitive sensors can be divided into three types as follows:

1. Parallel plate capacitive sensor: The parallel plate capacitive sensor is composed of two parallel metal plates, separated by a medium. When the target object approaches or moves away from the capacitive sensor, the capacitance between the media changes, which in turn reflects the change in the distance between the target object and the sensor.

2. Rolling capacitive sensor: The rolling capacitive sensor consists of a fixed metal shaft and an annular metal wheel. When the target object approaches or touches the sensor, the position of the annular metal wheel changes, which changes the capacitance between the metal wheel and the metal shaft, and then detects the approach or touch of the target object.

3. Proximity capacitive sensor: Proximity capacitive sensor is usually used to detect the approach or touch of high-standard objects without direct contact with the target object. They detect the presence of a target object by sensing changes in the electric field around the target object.

When the target object approaches the sensor, the capacitance of the target object affects the distribution of the sensor's electric field and is thus detected by the sensor.

The role of capacitive sensors

1. Proximity detection: Capacitive sensors can detect the change in the distance between the target object and the sensor, so as to achieve proximity detection. When the target object approaches the sensor, its capacitance value changes, and the sensor can detect the proximity of the target object by measuring the change in capacitance.

2. Touch sensing: Capacitive sensors can detect the contact of the human body or other objects, so as to achieve touch sensing. For example, the capacitive sensors used in touch sensing technology can detect the touch position and force of the finger to respond to touch operations.

3. Non-contact measurement: Capacitive sensors can be used for non-contact distance or displacement measurement. By measuring the change in capacitance between the target object and the sensor, the position or displacement information of the target object can be inferred.

Capacitive sensors are a commonly used type of sensor that can measure the capacitance change of a capacitor to achieve the measurement of physical quantities such as displacement, weight, etc. Capacitive sensors can be divided into three types according to different sensitization principles: the first is a planar capacitive sensor, the second is a miniature capacitive sensor, and the third is a capacitive weight sensor.

Planar capacitive sensors.

It consists of two parallel metal plates sandwiched between a layer of insulating material. When the measuring object is close to the metal plate, the capacitance of the capacitor is changed due to its dielectric constant, which is different from that of air. By measuring the change in capacitance, the distance between the object and the metal plate can be obtained.

Miniature capacitive sensors.

It usually consists of a miniature capacitor and a circuit. Miniature capacitors consist of micron-sized electrodes and an insulating layer that can measure small displacements and vibrations. By connecting a miniature capacitor to a circuit, a small change in capacitance can be converted into an electrical signal output.

Capacitive weight sensor.

It measures the weight of an object by measuring how much it squeezes the metal plate. When the object is stressed, the metal plate will undergo a slight deformation, which will be transported to change the capacitance of the bridge mold capacitor. By measuring the change in capacitance, the weight of the object can be calculated.

In short, capacitive sensors have the advantages of high accuracy, fast response, and good stability. In practical applications, we can choose different types of capacitive sensors according to our needs to meet different measurement requirements.

1.Variable pole distance capacitive sensor.

to parallel plate capacitors.

For example, the upper plate is fixed, the lower plate is moved, and the initial distance between the two plates is d0. When the distance decreases δd, the capacitance increases accordingly, and the relative change in capacitance is .

It can be seen that the relationship between the relative change of capacitance and the displacement is nonlinear. Within the limits of the allowable error, omitting the higher-order term gives an approximate linear relationship, i.e., the static sensitivity of a capacitive sensor is 0. If only the quadratic nonlinear term is considered and the other higher-order terms are ignored, the nonlinear error can be derived from the following equation:

The nonlinearity error increases as the pole distance decreases, and the range of the pole distance is usually δd d0. Therefore, this capacitive sensor is only suitable for measuring small displacements (1 mm in microns).

In order to improve sensitivity, reduce nonlinearity errors, and overcome the influence of external conditions, such as supply voltage and ambient temperature, differential capacitive sensors are often used in practical applications. Difference.

The total capacitance of the capacitors varies as follows:

Therefore, when the capacitive sensor is made into a differential structure, the nonlinear error when the displacement changes relative to each other is greatly reduced, and the sensitivity is twice that of the unipolar capacitive sensor.

2.Variable area capacitive sensors.

When the upper plates move, the relative coverage area between the two plates changes, resulting in a change in capacitance. This sensor can be used for displacement measurement. According to the application requirements, there are parallel plate plates, cylindrical plates and serrated plates.

These sensors have good linearity.

When the plate is moved linearly displaced, the corresponding capacitance changes as follows, where k is the sensitivity and its output is linearly related to its input.

Sensitivity is constant. The parallel plate structure is particularly sensitive to the change of pole distance, and the measurement accuracy will be affected, while the cylindrical structure is less affected by the radial change of the plate, so it has become the most commonly used buried structure in practice. When moving the cylinder.

When the overlapping length of the two cylinders changes after moving, the capacitance changes as follows: where k is the sensitivity.

3.Variable dielectric capacitive sensors.

Variable dielectric capacitance sensors are the insertion of different media between the two plates of a capacitor to cause a change in capacitance. Sensors made using this principle are often used to measure the level (i.e. capacitive level sensors) and the thickness of the material.

The initial capacitance of a coaxial cylindrical capacitor is . When measuring, the medium of the capacitor is part liquid and part air at the level of the capacitor. C1 is the capacitance formed when the liquid height is Hx, and C2 is the capacitance formed when the air height is H-Hx.

Since C1 and C2 can be considered as two capacitors connected in parallel, the total capacitance is:

It can be seen that theoretically, the capacitance has a linear relationship with the liquid level height, and Dong Yusun can obtain the liquid level height by measuring the capacitance.

Another capacitive sensor used to measure the change in dielectric constant is similar in structure to parallel plate capacitors. When the thickness is unknown but the relative permittivity.

When a known dielectric nanochain passes through the gap between the plates, the thickness of the dielectric can be obtained by changing the capacitance.