Electro pneumatic valve positioner
The valve positioner is the main attachment of the pneumatic regulating valve, which uses the valve stem displacement signal as the input feedback measurement signal, and the controller output signal is used as a set signal, and when the two have deviation, change the valve positioner to pneumatic The output signal of the body is actuated, enabling the pneumatic actuator, establishes a correspondence between the valve stem displacement signal and the controller output signal, and the composition is used as the measurement signal, and the controller outputs a feedback control system for setting signals. .
Valve positioner classification
The valve positioner is divided into a pneumatic valve positioner and an electro pneumatic valve positioner according to the input signal. There is a clear difference between the two:
1. The input signal of the pneumatic valve positioner is a 20-100 kPa standard gas signal.
2. The input signal of the electro pneumatic valve positioner is a standard current or voltage signal (e.g., 4-20 mA or 1-5V), converts the electrical signal into electromagnetic force inside the electro pneumatic valve positioner, and then outputs the air signal to the pneumatic regulating valve.
3, the pneumatic valve positioner can be used with the pneumatic film regulating valve, and the pneumatic piston adjustment valve is used, which accepts the 20-100 kPa signal given by the pneumatic regulator to control the travel of the pneumatic regulating valve, and the effect of the feedback system, ensuring the spool The pneumatic signal from the regulator is accurately executed, thereby implementing the correct positioning of the spool.
4, electro pneumatic valve positioner and pneumatic adjustment valve is used to form a closed loop control loop. Convert the DC current signal given by the control system into a gas signal that drives the adjustment valve, and controls the operation of the adjustment valve. At the same time, feedback according to the opening degree of the adjustment valve, allowing the valve position to be properly positioned according to the control signal output by the system. After adding the valve positioner, it consists of a secondary circuit with the valve stem displacement amount of the sub-argument. It consists of a cascade control system with the original single loop control system. The controlled variable of the original control system becomes the main cause of the cascade control system. Controlling variables, therefore, adding a valve positioner to improve control system functions. Since the cam is used as the feedback link, the change of the cam shape can effectively change the gain of the secondary circuit, compensate for the nonlinear characteristics of the controlled object. For valves such as butterfly valves with only fixed flow characteristics, the positioner can use a characterized cam to improve the corrected flow characteristics.
Contact: Vison Chan
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Add: EAA Central Industrial Zone,Wenzhou,Zhejiang Province,China