Views: 299 Author: Site Editor Publish Time: 2021-03-02 Origin: Site
The electrical converter converts the 0～10mA or 4～20mA DC signal into a 20～100kPa pneumatic signal so as to communicate the electric unit instrument and the pneumatic unit instrument to work together.
The electric converter uses open loop control and small mass magnets to perform precise air pressure control at a relatively economical cost. It is not affected by location and anti-RFI/EMI interference.
The current or voltage input signal is converted into a linear proportional pneumatic output pressure. This universal instrument is designed to provide high reliability and repeatability applications at a relatively economical cost. The small range model is designed for standard process control with 3 to 5 psig output. The extended range model can provide 145psig output for higher pressure industrial pneumatic and process control system operation requirements.
Valve positioners are divided into pneumatic valve positioners, electrical valve positioners and intelligent valve positioners according to their structure. They are the main accessories of regulating valves. According to their energy form, actuators are divided into three categories: air power pneumatic actuators, electric actuators and hydraulic actuators. They have their own characteristics and are suitable for different occasions. This article mainly details the working principle of the electric valve positioner.
Generally, the valves commonly used in valve positioners mainly include motorized ball valve, electric butterfly valve and pneumatic angle seat valve.
A device is hung under each regulating valve, which is the heart of the regulating valve, called a valve positioner. Through this device, the amount of air entering the head (pneumatic membrane) can be adjusted, and the position of the valve can be precisely controlled.
Valve positioners have intelligent positioners and mechanical positioners. This article mainly discusses the mechanical positioner.
The air source comes from compressed air from an air compressor station. There is also an air filter pressure reducing valve in front of the air source inlet of the valve positioner to purify the compressed air. The air source from the outlet of the pressure reducing valve enters from the valve positioner. As for how much air enters the membrane head of the valve, it is determined according to the output signal of the controller.
The electrical signal output by the controller is 4-20mA, the pneumatic signal is 20Kpa-100Kpa, and the electrical signal to the pneumatic signal is carried out by an electrical converter.
When the electrical signal output by the controller is converted into a corresponding air signal, the converted air signal is then applied to the bellows.
The back pressure of the nozzle increases. After being amplified by the pneumatic amplifier, a part of the air source is sent to the air chamber of the pneumatic membrane, and the valve stem takes the valve core downward to automatically gradually reduce the valve opening.
At this time, the feedback rod connected to the valve stem moves down around the fulcrum, so that the front end of the shaft moves downward, the eccentric cam connected to it rotates counterclockwise, and the roller rotates clockwise to move to the left, thereby stretching the feedback spring.
