FLOWX Engineer 86-21-54150349
Actuator is one of the industrial automation equipment and is the terminal execution instrument automatic control system, whose function is to change the input medium flow of controlled process object in order to achieve the goal of regulation of controlled process parameters according to the output control signal of the pneumatic actuators. Actuator action replaced the manual operation, so people often compared the actuator to the "hands" of production process automation system. Pneumatic actuator quality determines its popularity to some extent.
Pneumatic actuators consist of three parts, actuator, regulating mechanism and control unit. The actuator, as a purely mechanical part, refers to the device that drives the mechanical mechanism of thrust or displacement according to the attachment of control actuator output signal. Electric actuators and pneumatic actuators are so common. Adjusting mechanism, also a purely mechanical part, is to change the process medium flow of the device based on the movement of the actuator, and common adjusting mechanism is the regulator. Control unit is the core of the actuator, which computes the drive actuator control signal based on DCS system (or controller) of the output control signal and sampling the actual valve position opening, making the actuator as a whole to form a closed loop feedback control system. The common control units are valve positioner used in pneumatic actuator and servo amplifier or controller for electric actuators.
According to different work energy, actuators can be divided into three categories: pneumatic actuators, electric actuators, and other actuators. They have different characteristics and are suitable for different occasions. Among them, the pneumatic technology became an independent technical category by evolution and development of hydraulic and pneumatic technology. The strong vitality in the field of automation has been fully shown through pneumatic actuator quality. The main characteristics of pneumatic actuator are simple structure, stable performance, reliable operation, low failure rate, convenient maintenance, cheap price, nature of explosion-proof, high pneumatic actuator quality, being easy to make high power and so on. Compared with the electric actuator, its price is more superior, so it is widely used in chemical industry, steel, oil refining, petrochemical, metallurgy, power, light, building materials and papermaking industries, etc.
Pneumatic actuators are composed of actuator, valve locator and the regulator, which use compressed air as power source. Although electric actuators quality is very high, the electric - pneumatic valve positioner is usually used since there is a large lag and the pneumatic signal is not suitable for far transferring. The transmit signals are electrical signals, and it is pneumatic operation on the site, which is the best form of electrical combination and is currently the main way of application. Knowing the high pneumatic actuator quality, let’s have a look at its working principle.
Pneumatic diaphragm actuator is an actuator that is most commonly used, which has high pneumatic actuator quality. Under the condition of not considering nonlinear valve, the relationship between the valve stem displacement of pneumatic diaphragm valve head and the air pressures should be determined by the Hooke’s law, which has the nature of proportion. But because there is packing friction, there must be some dead zone and variation. This is the most important reason for causing overshoot and oscillation, which is very harmful for automatic adjustment. Thus, pneumatic actuators nonlinear should not be ignored.