The hysteresis adjustment principle of vacuum pressure switches

The hysteresis regulation principle of vacuum pressure switches is based on the displacement characteristics of the internal elastic elements and the mechanical structure design. By adjusting the hysteresis value, the frequent operation of the switch during pressure fluctuations can be avoided. The core mechanism and regulation method are as follows:

First, the physical basis of hysteresis adjustment

When the measured pressure exceeds the set value, the elastic element (such as diaphragm, bellows) deforms, pushing the switch element (such as microswitch) to change its on-off state. Hysteresis refers to the difference between the reset pressure when the pressure changes from high to low and the action pressure when it changes from low to high. For example, when the set value is -80 kpa, if the hysteresis is 5kPa, the switch will act when the pressure rises to -80 kpa and reset when the pressure drops to -85 kpa.

Second, the implementation method of hysteresis adjustment

Mechanical structure adjustment

Change the preload or lever ratio of the elastic element by adjusting the screw. For example, rotating the adjusting screw clockwise can increase the initial deformation of the elastic element, thereby increasing the difference (hysteresis) between the operating pressure and the reset pressure. Some switches adopt a double-spring design, and the hysteresis regulation is achieved by adjusting the relative positions of the two springs.

Electronic circuit regulation

The electronic vacuum pressure switch regulates the threshold voltage or current through the built-in circuit. For example, switches with programmable chips can set hysteresis values through buttons or software, and the circuit automatically calculates the electrical signal thresholds corresponding to the action and reset pressure.

Third, the role of hysteresis regulation

Prevent frequent actions

In pressure fluctuation scenarios (such as the start-up and shutdown of vacuum pumps), hysteresis can prevent the switch from frequently turning on and off near the threshold. For example, if the hysteresis is 2kPa and the pressure fluctuates between -79 kpa and -81 kpa, the switch operates only once.

Improve the stability of the system

Reduce equipment wear and false alarms caused by frequent switch actions. For instance, in semiconductor equipment, too small a hysteresis may cause process interruption, while an appropriate hysteresis can ensure continuous production.

Fourth, hysteresis Settings in typical applications

Vacuum packaging machine

It is necessary to respond quickly to changes in vacuum degree, but it is necessary to avoid interruptions in the packaging process caused by minor fluctuations in pressure. The hysteresis is usually set at 3 to 5kPa, for example, the action pressure is -90 kpa and the reset pressure is -95 kpa.

Chemical reactor

High pressure stability is required, and a large hysteresis needs to be set. For example, the action pressure is -50 kpa and the reset pressure is -60 kpa to prevent the false triggering of the safety interlock due to pressure fluctuations.

Fifth, precautions for adjustment

The hysteresis matches the range

The hysteresis value should be less than 10% of the range. For instance, for switches with a range from -100 kpa to 0kPa, the hysteresis should not exceed 10kPa; otherwise, it may affect the control accuracy.

Environmental impact

Under high-temperature or vibration conditions, the deformation characteristics of elastic elements may change, and the hysteresis needs to be recalibrated. For example, in an environment of 120℃, the hysteresis needs to be increased to compensate for the threshold drift caused by the thermal expansion of the material.

Long-term stability

Regularly check whether the hysteresis value has drifted. For example, the hysteresis is verified through a standard pressure source every six months. If the difference between the action pressure and the reset pressure exceeds ±10% of the set value, it needs to be readjugated.