What is the classification and working principle of valve limit switchbox?

1. Mechanical limit switchbox

Usually this type of switch is used to limit the position or stroke of the mechanical movement, so that the moving machinery can automatically stop, reverse movement, variable speed movement or automatic reciprocating movement according to a certain position or stroke. It consists of an operating head, a contact system and a housing. Divided into direct-action (button), rolling (rotary), micro-action and combination.

Direct-acting limit switch: the action principle is similar to that of the button, the difference is that one is manual, and the other is collided by the bumper of the moving part. When the impact block on the external moving part presses the button to make the contact move, when the moving part leaves, the contact automatically resets under the action of the spring.

Rolling limit switch: When the stop iron (collision block) of the moving machine is pressed on the roller of the limit switch, the transmission rod rotates together with the rotating shaft, so that the cam pushes the impact block, and when the impact block hits a certain position, it pushes the micro movement The switch operates quickly. When the stop iron on the roller is removed, the return spring resets the travel switch. This is a single-wheel automatic recovery limit switch. And the two-wheel rotary type travel switch can not recover automatically, and when it relies on the moving machine to move in the opposite direction, the iron stopper bumps into another roller to restore it.

A micro switch is a snap switch actuated by pressure. Its working principle is that the external mechanical force acts on the action reed through the transmission element (press pin, button, lever, roller, etc.), and after the energy is accumulated to the critical point, an instantaneous action is generated, so that the moving contact at the end of the action reed The point and the fixed contact are quickly connected or disconnected. When the force on the transmission element is removed, the action reed produces a reverse action force, and when the reverse stroke of the transmission element reaches the critical point of the action of the reed, the reverse action is completed instantaneously. The contact distance of the micro switch is small, the action stroke is short, the pressing force is small, and the on-off is rapid. The action speed of its moving contact has nothing to do with the action speed of the transmission element. The basic type of micro switch is push pin type, which can be derived from button short stroke type, button large stroke type, button extra large stroke type, roller button type, reed roller type, lever roller type, short arm type, long arm type etc.

The mechanical valve limit switch usually adopts the micro switch of the passive contact, and the switch form can be divided into: single pole double throw SPDT, single pole single throw SPST, double pole double throw DPDT.

2. Proximity limit switchbox

Proximity switch, also known as non-contact travel switch, can not only replace travel switch with contact to complete travel control and limit protection, but also be used for high counting, speed measurement, liquid level control, part size detection, automatic connection of processing procedures wait. Because it has the characteristics of non-contact trigger, fast action speed, action within different detection distances, stable and pulse-free signal, stable and reliable work, long life, high repeat positioning accuracy and adaptability to harsh working environments, etc., so It is widely used in industrial production such as machine tools, textiles, printing, and plastics.

Proximity switches are divided according to the working principle: mainly high-frequency oscillation type, Hall type, ultrasonic type, capacitive type, differential coil type, permanent magnet type, etc. Permanent magnet type: It uses the suction force of the permanent magnet to drive the reed switch to output the signal.

Differential coil type:

It uses the change of eddy current and magnetic field generated when the detected object approaches, and operates through the difference between the detection coil and the comparison coil. Capacitive proximity switch: It is mainly composed of a capacitive oscillator and an electronic circuit. Its capacitance is located on the sensing interface. When an object approaches, it will oscillate due to changing its coupling capacitance value, thereby generating oscillation or stopping the oscillation to generate an output signal. more and more change. Hall proximity switch: It works by converting magnetic signals into electrical signal output, and its output has a memory retention function. The internal magnetic sensitive device is only sensitive to the magnetic field perpendicular to the end face of the sensor. When the magnetic pole S is facing the proximity switch, the output of the proximity switch has a positive jump, and the output is high. If the magnetic pole N is facing the proximity switch, the output is low. level.

Ultrasonic proximity switch: It is mainly composed of piezoelectric ceramic sensors, electronic devices for transmitting ultrasonic waves and receiving reflected waves, and program-controlled bridge switches for adjusting the detection range. It is suitable for detecting objects that cannot or cannot be touched. Its control function is not disturbed by factors such as sound, electricity, and light. The detection target can be an object in a solid, liquid or powder state, as long as it can reflect ultrasonic waves.

High frequency oscillating proximity switch: 

It is triggered by metal, mainly composed of high frequency oscillator, integrated circuit or transistor amplifier and output device. Its working principle is: the coil of the oscillator generates an alternating magnetic field on the active surface of the switch , when a metal object approaches the active surface, the eddy current generated inside the metal object will absorb the energy of the oscillator, causing the oscillator to stop vibrating. The two signals of oscillation and vibration stop of the oscillator are transformed into binary switching signals after being shaped and amplified, and the switching control signals are output.

The magnetic induction valve limit switch generally adopts the electromagnetic induction proximity switch of the passive contact, and the switch form can be divided into: single pole double throw SPDT, single pole single throw SPSr, but no double pole double throw DPDT. The magnetic induction is generally divided into 2-wire normally open or normally closed, and the 3-wire is similar to single-pole double-throw SPDT, without normally open and normally closed.

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