Capacitive sensors are a type of sensor that can convert measured physical quantities (such as size, pressure, etc.) into changes in capacitance. Its working principle is based on the capacitance formula of a parallel-plate capacitor, which is C=εS/δ, where ε is the relative dielectric constant between the plates, S is the area of the plates, and δ is the distance between the plates. When one of the measured parameters changes, the capacitance also changes. The change in capacitance can be converted into an electrical signal output through a matching measurement circuit.

According to the characteristics of the capacitance parameters, capacitive sensors can be divided into three types: polar distance change type, area change type, and dielectric change type. Among them, the polar distance change type and area change type are widely used. The sensitivity of the polar distance change type capacitive sensor is inversely proportional to the square of the polar distance, so the sensitivity increases as the polar distance decreases. In order to reduce non-linear errors, the measurement range is usually specified, and the polar distance change range is taken as the sensitivity of the sensor at this time is approximately constant.

In order to improve the sensitivity of the sensor, increase the linear working range, and overcome the effects of external conditions (such as power supply voltage, ambient temperature, etc.) on measurement accuracy, differential capacitive sensors are often used.