In the specific application of processing plant, many people can not distinguish the difference between limit switch, photoelectric switch and proximity switch in the middle.
Once limit switch, proximity switch and photoelectric switch are three kinds of sensors with different basic principles, but the actual effect is the same. They are all used to detect the directional angle.
Limit switch: can also be called a stroke power switch; can be installed on a relativity terminated objects (such as fixed immobile architecture, door sets, etc., commonly known as still life sketch) or fitness movement objects (such as safety driving, doors, etc.). When the object is close to the stationary motionless life, the power switch crankshaft pushes the contacts of the power switch to make the closed contacts break or break the contacts close. The behavior of the power circuit and organization is manipulated by the power switch contacts and turn off the change of situation. Limit switch can also be divided into rotation limit switch and immediate limit switch. The internal of the limit switch is mainly mechanical equipment contacts, so that the contacts open and close or normally closed. The contact is passive, thus there is no NPN or NPP, the key-in line is 24 volts and the export line is 24 volts, thus it is not important for PLC.
Proximity switch: A sensor that verifies orientation without direct contact with the fitness motion member. Proximity switches are also called contactless limit switches. It is possible to perform travel arrangement manipulation and limit maintenance. The sensor does not have to touch the raw material being inspected, but the raw material being inspected must be metallic material. Because it does not touch the raw material being inspected, it has the characteristics of reliable actual operation, long service life, low functional loss, high multi-precision level, high output power, and integration into extreme office environments. The proximity switch is divided into PNP and NPN, so when selecting the sensor, it is important to carry out identification of the PLC connection.
Photoelectric switch: It uses the object to be inspected to block or reflect the surface of the light, opens the power circuit according to the same control circuit, and then inspects whether the object exists. The object is not only limited to metal materials, but all objects that refract light (or are likely to block light) can be detected. The photoelectric switch is equipped with spreading types, reverse photo types, etc. For diffuse light, only one sensor is required to send and receive, while for the spreading type, two sensors are required, one to send and one to receive.
There are also two types of photoelectric switches, NPN and PNP, but in addition, photoelectric switches also have dry connection points, in other words, they can be connected to a PLC at will.
