Basic knowledge of the control logic for control valves
Thread Content
Basic knowledge of the control logic for control valves 1. Definition: A control valve is a throttling element whose local resistance can be changed. As the valve core moves within the valve body, it changes the flow area between the valve core and the valve seat, and as a result, the flow rate of the medium being regulated also changes, thereby achieving the purpose of adjusting the process parameters. 2. Flow characteristics of control valves: Generally referred to as ideal flow characteristics, they are the properties in which the pressure difference before and after the valve remains constant. There are typically four types: quick opening, linear, proportional (logarithmic), and parabolic. Introduction to the control system: 1. Cascade control: It consists of a primary regulator and a secondary regulator, with the output of the primary regulator serving as the setpoint for the secondary regulator. Features: 1. It can improve the characteristics of the controlled object, reducing its lag ； 2. Reduce deviation and shorten the adjustment cycle. 2. Ratio control: A control method that maintains a constant ratio between the two materials. For ratio adjustment, it is first necessary to understand which is the main material and which material should be proportioned according to that main material. 3. Override control: also known as selective control or replacement control. It is a control method that applies the logical relationships resulting from the constraints in the manufacturing process to an automatic control system; it features two or more transmitters, and a selector is used to choose one that can meet the requirements of the signals in the manufacturing process. 4. Split-range control: It is the output of a controller that simultaneously controls two or more control valves. “Split-range” refers to dividing the controller’s output signal into different range segments in order to drive various control valves. Notes: SP: Set value; MV: Measured value; OP: Signal value (different from valve opening). RAM: Cascade LOC: Single-loop MAN: Manual AUTO: Automatic
If it is not original, it is best to indicate the source
May I ask the original poster, what do HV, PV, FV, and TV mean in control valves?
It’s quite abstract. A control valve consists of a valve body, transmitters (for pressure, pressure difference, etc.), a positioner, and an actuator. The transmitter sends 4–20mA signals to the DCS, while the actuator and positioner are used to adjust the position of the valve element in order to meet the set parameters. Those who work with instruments are really skilled; this is just my understanding based on my mechanical engineering background
HV – Manual controller valve; PV – Pressure-controlled valve; FV – Flow-controlled valve; TV – Temperature-controlled valve
It would be even better if the original poster could describe the cascade comparison in a more vivid way~!
Could you explain it in more detail? . . Thank you!
Can it be transferred completely? Only a part has been transferred
I thought a control valve consisted of 3 parts: the valve body assembly + actuator + accessories. I need to learn more in the future*. This post was last edited by jfwzf on 2008-11-23 17:29]