What is a Proximity Sensor
The proximity sensor is a general term for sensors that replace the contact detection methods such as limit switches and aim to detect without touching the detection object. It can detect the movement information and presence information of objects and convert them into electrical signals. Among the detection methods of electrical signals, there are methods that utilize eddy currents generated in a metal object to be detected by electromagnetic induction, methods that capture changes in the capacity of electrical signals due to the proximity of the object to be detected, and methods that use sharp stones and guide switches. The proximity sensor is a device with the ability to sense the proximity of objects. It uses the sensitive characteristics of displacement sensors to approach objects to identify the proximity of objects and output corresponding switch signals. Therefore, proximity sensors are usually called proximity switches.
In the JIS standard, the JIS standard (JIS C 8201-5-2 Low-voltage switchgear and control device, fifth control circuit device and switching element, second section proximity switch) was established based on IEC60947-5-2 non-contact position detection switch. In the definition of JIS, products that can also detect the proximity of an object in a non-contact manner and the presence or absence of a nearby detection object are collectively referred to as "proximity switches". It is composed of induction type, electrostatic capacitance type, ultrasonic type, photoelectric type, magnetic type, and so on. In this technical guide, inductive proximity sensors that detect the presence of metals, capacitive proximity sensors that detect the presence of metallic and non-metallic objects, and switches that utilize a DC magnetic field generated by magnetic force are defined as "proximity sensors".
Proximity Sensor Types and Working Principle
Capacitive Proximity Sensor
The capacitive proximity sensor is an electric capacitance proximity switch with electrodes as detection terminals. It consists of a high-frequency oscillation circuit, detection circuit, amplifier circuit, shaping circuit, and output circuit.
Usually, there is a certain capacitance between the detection electrode and the ground, which becomes an integral part of the oscillation circuit. When the detected object is close to the detection electrode, due to the voltage applied to the detection electrode being C=Q/V, the detection electrode will be subjected to electrostatic induction to generate polarization. The closer the detected object is to the detection electrode, the more induced charges on the detection electrode. Since the electrostatic capacitance exits on the detection electrode, the capacitance C of the detection electrode increases as the number of charges increases. Since the oscillation frequency of the oscillation circuit is inversely proportional to the capacitance, when the capacitance C increases, the oscillation of the oscillation circuit weakens or even stops the oscillation. The two states of oscillation and stop of the oscillation circuit are converted into switching signals by the detection circuit and then output to the outside.
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