Proximity switch performance characteristics and classification

Proximity switch , also known as non-contact travel switch , can not only complete travel control and limit protection, but also is a non-contact detection device used to detect part size and speed, etc. It can also be used for frequency conversion counter, frequency conversion pulse generator, liquid level control and automatic connection of processing program. Its characteristics include reliable operation, long life, low power consumption, high repositioning accuracy, high operating frequency and adaptability to harsh working environment.

Performance characteristics

Among all kinds of switches, there is a component that has the ability to "sense" objects approaching it - displacement sensor . The purpose of controlling the switch on or off is to use the displacement sensor 's sensitive characteristics to approaching objects. This is the proximity switch.

MICROSONAR series proximity switches: When an object moves toward the proximity switch and approaches a certain distance, the displacement sensor will "sense" it and the switch will operate. This distance is usually called the "detection distance". Different proximity switches have different detection distances.

Sometimes the objects being tested move towards the proximity switch one by one at a certain time interval, and then leave one by one, and this is repeated continuously. Different proximity switches have different response capabilities to the objects being tested. This response characteristic is called "response frequency".

type

Because displacement sensors can be made according to different principles and methods, and different displacement sensors have different ways of "sensing" objects, the common proximity switches are as follows:

1. Eddy current proximity switch

This type of switch is sometimes called an inductive proximity switch. It uses the fact that when a conductive object approaches the proximity switch that generates an electromagnetic field, an eddy current is generated inside the object. This eddy current reacts to the proximity switch, causing the parameters of the switch's internal circuit to change, thereby identifying whether a conductive object is approaching, and then controlling the switch to be on or off. The object that this proximity switch can detect must be a conductor.

2. Capacitive proximity switch

The measurement of this switch usually constitutes one plate of the capacitor, and the other plate is the shell of the switch. This shell is usually grounded or connected to the chassis of the device during the measurement process. When an object moves toward the proximity switch, regardless of whether it is a conductor or not, its proximity will always cause the dielectric constant of the capacitor to change, thereby changing the capacitance, and the circuit state connected to the measuring head will also change accordingly, thereby controlling the switch to be turned on or off. The objects detected by this proximity switch are not limited to conductors, but can also be insulating liquids or powders, etc.

3. Hall proximity switch

The Hall element is a magnetic sensitive element. The switch made of the Hall element is called a Hall switch. When a magnetic object moves close to the Hall switch, the Hall element on the switch detection surface produces the Hall effect, which changes the state of the switch's internal circuit, thereby identifying the presence of a magnetic object nearby and controlling the switch to turn on or off. The detection object of this proximity switch must be a magnetic object.

4. LED /' target='_blank'>Photoelectric proximity switch

A switch made using the photoelectric effect is called a photoelectric switch. The light-emitting device and the photoelectric device are installed in the same detection head in a certain direction. When a reflective surface (the object to be detected) approaches, the photoelectric device receives the reflected light and outputs a signal, thereby "sensing" that an object is approaching.

5. Pyroelectric proximity switch

A switch made of a component that can sense temperature changes is called a pyroelectric proximity switch. This type of switch installs a pyroelectric device on the detection surface of the switch. When an object with a different temperature from the ambient temperature approaches, the output of the pyroelectric device changes, thereby detecting the approach of an object.

6. Other types of proximity switches

When the distance of the observer or system to the wave source changes, the frequency of the approaching wave will shift. This phenomenon is called the Doppler effect. Sonar and radar are made based on the principle of this effect. The Doppler effect can be used to make ultrasonic proximity switches, microwave proximity switches, etc. When an object approaches, the reflected signal received by the proximity switch will produce a Doppler frequency shift, which can be used to identify whether an object is approaching.