2023-07-06
First of all, limit switches, proximity switches and photoelectric switches are three different principles of sensors, but the role of the same, are used to detect the position.
Limit switch: can also be called travel switch; can be installed on relatively stationary objects (such as fixed frames, door frames, etc., referred to as stationary objects) or moving objects (such as traveling cars, doors, etc.). When the object is close to the static object, the switch linkage drive switch contacts cause the closed contacts to break or open contacts to close. The change of the open and closed state of the switch contact controls the action of the circuit and mechanism.
Limit switches can also be divided into rotary limit switches and in-line limit switches. The limit switch is mainly mechanical contact inside, the contact can be normally open or normally closed. The contact is passive, so it does not distinguish between NPN and PNP, and the incoming line is 24V and the outgoing line is also 24V; therefore, it is not picky about PLC.
Proximity switch: a sensor that detects position without mechanical direct contact with moving parts and can be operated, proximity switch is also called contactless travel switch, which can complete travel control and limit protection, etc.
The sensor does not need to be in contact with the detection material, but the material of the detection material needs to be metal, because it does not need to be in contact with the detection, so it is characterized by reliable work, long life, low power consumption, high repositioning accuracy, high operating frequency and adaptation to harsh working environment. Proximity switches are divided into PNP and NPN, so you need to confirm the PLC connection when choosing a sensor.
Photoelectric switch: It is used to detect the presence or absence of an object by using the masking or reflection of the light beam by the detected object, and the circuit is turned on by the synchronous circuit. The object is not limited to metal, but all objects that reflect light (or have an obscuring effect on light) can be detected.
There are diffuse reflection type, opposite type, etc. Diffuse reflection type only needs one sensor to complete the transmission and reception, while opposite type needs two sensors, one transmitting and one receiving.
Photoelectric switches also have NPN and PNP models, but in addition there are also dry junction photoelectric switches, which can be connected to any kind of PLC.
Let's look at their differences.
First, appearance
Limit switches are generally made of an obvious action part, and the part can move back and forth, with different movement angles, some can be 180 degrees, some can only 90 degrees.
Proximity switch is relatively simple, just a separate sensor.
Some photoelectric switches have the same appearance as the proximity switch, but some are completely different and need to have two parts: transmitting and receiving.
Second, the detection distance
Limit switches require direct contact with the detection substance.
Proximity switches are closer, and the general detection range is generally 3-20mm, depending on the sensor. The detection distance of a proximity switch is largely related to the diameter of the detection head, i.e. the larger the detection distance, the larger the diameter required.
The detection distance of photoelectric switches is generally very long, and some can even reach several meters. This is an obvious superiority over proximity switches, but the principle of photoelectric switch is related to light, then it has an obvious defect, that is, it is susceptible to water vapor dust and other effects, once the water vapor dust will detect the route blocked, the sensor will fail, while the proximity switch detects the metal without this problem.
Third, the function and application occasions
1.limit switch for the mechanical switch, the trial is not very use frequency is not very frequent occasions, in addition, some mechanical switches can be made of all-metal, you can work in high temperature occasions, which other sensors can not do.
2.proximity switch life is longer, suitable for "through the signal". The position detection on the cylinder is generally proximity switch. But because the proximity switch also has internal circuit, so it can not be applied in the place of strong magnetic interference.
3.photoelectric switch is the most widely used, only need objects to block the light source can be triggered, so can not be applied in dusty places and strong magnetic interference.
