How to apply limit switch, photoelectric switch and close switch? Automatic control of the itinerary switch!

In the actual application of the factory, many people do not clearly distinguish the limit switch, the difference between the photoelectric switch and the close switch, and it will be popular today.

First of all, the limiting switch, close to the switch and the photoelectric switch are different sensors with different principles, but the effect is the same.


Limited switch:


It can also be called a stroke switch; it can be installed on a relatively static object (such as fixed racks, door frames, etc., referred to as static objects) or moving objects (such as driving, doors, etc.). When the object is close to the static object, the connection to the connecting rod driver of the switch is closed or disconnected from closed or disconnected. Control the actions of the circuit and the mechanism from the change of the switching contact and the change of the state. The limit switch can also be divided into rotating limit switches and straight -line limit switches. The interior of the limit switch is mainly mechanical contacts, and the contacts can be frequent or normal. The contact is not the source, so regardless of NPN and PNP, the line is 24V, and the line is 24V; therefore is not picky PLC.

Limited switch internal wiring diagram

A variety of ways of limit switch

Near the switch:

A sensor that does not need to perform directly contact with the motion component and can operate the position that can be operated. It is close to the switch, which is also called a non -contact itinerary switch. It can complete the itinerary control and limit protection.

This sensor does not need to be in contact with the detection substance, but the material of the detection material needs to be metal because there is no need to contact the detection. Therefore, it is characterized by its reliable work, long life, low power consumption, high re -positioning accuracy, high operating frequency, and harsh adaptation. Working environment, etc. Near the switch is divided into two types: PNP and NPN, so you need to confirm the PLC connection when choosing a sensor.


Three -line system is close to switch

Metal tested

Photoelectric switch;

It uses the obstruction or reflection of the detected object to the beam, which is connected to the circuit from the synchronous circuit to detect the object. Objects are not limited to metals, and all objects that can reflect light (or have a cover effect on light) can be tested. The photoelectric switch has a man -reflex type. For shooting types, etc., the drill reflection only requires one sensor to complete the launch receiving. Two sensors are required for the shooting type, and one is launched.

The photoelectric switch also has the NPN and PNP models, but in addition to this, the optoelectronics switch also has a dry node, which can be followed by any PLC.


Let’s take a look at their differences;

One shape

The limit switch is generally a obvious action site, and the part can be moved back and forth. The angle of movement is different. Some can only be 180 degrees, and some can only be 90 degrees.

It is relatively simple to close the switch, just a separate sensor.

Some photoelectric switches are consistent with the close switch, but some are completely different. There are two parts of launch and receiving.

Two detection distance

The limit switch needs to be directly contacting the detection substance.

Near the switch is relatively close. Generally, the detection range is generally 3-20mm. It is dedicated to the sensor. The detection distance close to the switch is largely related to the diameter of the detection head. The larger the detection distance, the larger the diameter required.

The left side detection distance is 8mm, and the right test distance is 15mm

The detection distance of the photoelectric switch is generally long, and some can even reach a few meters. This is a significantly better than close to the switch, but the principle of the photoelectric switch is related to light, then it has an obvious flaw, that is, it is easy to be affected by water vapor and dust. Once water vapor and dust will be obstructed And close to the switch to detect metals without this problem.


Three functions and applications

The 1 -limit switch is a mechanical switch. It is tried not to use the frequency or frequent occasions. In addition, some mechanical switches can be made into all metals and can work at high temperature occasions. This is not available by other sensors.

2 close to the switching life long, suitable for “through signal”. The location detection on the cylinder is generally close to the switch. However, because there are also circuits near the switch, it cannot be applied to a strong magnetic interference.

3 The optoelectronic switch is the most widely used. It only needs to have an object to block the light source to trigger, so it cannot be applied to a large dusty place and a strong magnetic interference place.


The following will bring you the automatic control of the itinerary switch

The advancement of the car, the automatic control of the backward movement, and the automatic reciprocating cycle control of the motor, the content:


1. Manual control: The asynchronous motors introduced before, stop, and positive control are all issued by people through the button.

2. Automatic control of switching: In modern production, some switches that can automatically release commands are used to implement various automatic control.

3. Switch automatic control type: By converting different physical quantities into switching commands.


When the motion component reaches a certain itinerary position, the itinerary is used to control its operating conditions. Due to process and safety requirements in production, it is often necessary to control the itinerary and location of certain machinery. For example, the workbench of the Longmen plane requires the reciprocating motion processing product. When reaching the limit position at the workbench, it must be stopped automatically. Travel control like this can be implemented with a itinerary switch.

Itinerary control is usually implemented with a itinerary switch.

(1) Itinerary switch


1. What is a itinerary switch?

The itinerary switch is also called the location switch or the limit switch. It is an automatic electrical appliance that switches the circuit according to the movement of the motion component, which can achieve the protection of the limited position of the motion component. Mechanical signals can be converted to electrical signals to achieve control of mechanical movements.

2. The structure and classification of the itinerary

It is mainly composed of the contact system, operating agency and shell. According to its structure, it can be divided into three types: direct, roller, and micro -movement. After the itinerary switch moves, there are two types: automatic reset and non -automatic reset.


3. The working principle of the itinerary switch

Its working principle is similar to the buttons, but it is just a crash. When the crash is installed on the workbench of the mechanical parts, when the iron block of the sports machine is pressed on the roller, the lever is rotated together with the rotation shaft, and the collision block is pushed. When the collision block is pressed to a certain position, the micro -switch movement is pushed to make the frequent tentacles break, and the normal closed contact is closed. After the transmission of the motorized machine, the reset spring allows the components of each part of the itinerary to restore the normal state.

4. The graphic symbol of the itinerary switch

(2) Automatic round -trip control line Original


Circuit structure analysis:

1. The main circuit is the same as the positive and reverse circuit.

2. The control circuit is similar to the forward and negative circuit of the electrical interoperability, but there are 4 more itinerary switches.

3. The itinerary of the SQ 1 and SQ 2 of the itinerary switch, respectively.


4. The stroke switch SQ 3 and SQ 4 control the limits of the left and right movements of the workbench.

5. These itinerary switches are implemented by hitting these strokes on the side of the workbench.

Circuit work process

The motor can be manually controlled by the button SB1, SB2, SB3, or automatic control through the itinerary switch SQ1 and SQ2.

The itinerary switch is removed to control the positive and backward rotation of the motor, and it can also achieve various requirements such as terminal protection, automatic circulation, braking, and transmission.


Electric automatic reciprocity control

Universal milling machine requires the workbench to move automatically within a certain distance.

1. Structure: connect SQF’s dynamic contact contacts with the reverse button SBR, and connect the SQR dynamic contact contact with the positive rotation button SBF.

2. Working principle: When the motor drives the workbench to the right to the limit position: hit the block A and hit the SQF, which not only makes it disconnecting the contact, the motor stops Press the reversal button SQR to drive the motor reversal to the workbone to move left.

Leaving the SQF of the Block A, the contacts are automatically reset, the contactor KMR locks, and the motor continues to drive the workben to move left.

When moving to the limit position on the left: hit the block B and touch the SQR, which not only breaks the contact of the contact, the motor stops, and the dynamic contact contact is closed, which is equivalent to pressing the front button SBF to make the motor positive. Rotate the workbench to the right.

This is not stopped until the stop button sbstop is pressed.

1 Follow the switch QS and press the start button sb2

2 M1 to power the self -lock, the motor is rotating, dragging the motion component to the left movement

3 When the component moves to the SQ2 of the collision block B down the stroke switch, the SQ2 breaks off the contact, KM1 is released from power, the SQ2 dynamic contacts are closed, the KM2 gets the electric self -lock, and the motor is transformed into the motor. Reverse, dragging motion components to move to the right


4 When the hit A press down the itinerary switch SQ1, the motor changes from the reverse to the rotation. In this way, the movement components are performed within the scope of the restricted itinerary.

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