The working principle of capacitive proximity switch

Generally speaking, there are three common types of proximity switches: capacitive, inductive and Hall proximity switches. Capacitive sensors can detect any object in a non-contact manner. Compared with inductive sensors that can only detect metal objects, capacitive sensors can also detect non-metallic materials, and inductive proximity switches must detect metallic materials. The Hall proximity switch is composed of Hall elements, which has the characteristics of low energy consumption, non-destructive and long life. Proximity switches have a technical index for the detection distance or the action distance of the switch. This parameter can be selected according to different applications. If the detection distance is uncertain and needs-an approximate range, it is recommended to use a proximity sensor

The measuring terminal of the capacitive proximity switch is a plate that constitutes the capacitor, and the other plate is the shell of the switch. When an object moves to the capacitive proximity switch, no matter whether the object is conductive or not, because its dielectric constant will always be different from the original environmental medium (air, water, oil, etc.), the capacitance changes, which makes the inside of the switch The circuit parameters change, which can identify whether there is an object approaching, and then control the on or off of the switch. Capacitive proximity switches can detect any medium, including conductors, semiconductors, insulators, and can even be used to detect liquid and powdery materials.

In the actual measurement process, the housing mentioned later is generally grounded or connected to the machine housing. When an object approaches the switch, whether it is a conductor or not, the dielectric constant of the capacitor will change more or less at this time. Of course, the capacitance will also change as a result, which leads to the state of the circuit and the measurement. The connection of the head has a certain change, and finally it controls the opening or closing of the capacitive proximity switch.

Capacitive proximity switches can not only detect metals, but also non-metallic substances such as plastic, glass, water, oil and other substances. When detecting non-metallic objects, the corresponding detection distance is affected by the conductivity, dielectric constant, volumetric water absorption and other parameters of the detection body. The corresponding detection distance is different, and there is the largest detection distance for grounded metal conductors.

In practical applications, capacitive proximity switches are mainly used to detect non-metallic substances.

The working principle of the capacitive proximity switch is that when the power is turned on, the RC oscillator does not oscillate. When a target approaches the power of the capacitor, the capacity of the capacitor increases and the oscillator starts to oscillate. Through the processing of the subsequent circuit, the two signals of vibration and oscillation are converted into switching signals. The sensing surface of the capacitive proximity switch is composed of two coaxial metal electrodes, much like an "open" capacitor electrode. The two electrodes form one by one. A capacitor is connected in series in the RC oscillating circuit, so as to detect the existence of objects. The sensor can detect metal objects as well as non-metal objects. The maximum movement distance can be obtained for metal objects. The movement distance for non-metal objects is determined by the dielectric constant of the material. The greater the dielectric constant of the material, the obtainable action The greater the distance.

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