How are the split points for split-control determined?
Thread Content
Hello, experts in instrumentation: I would like to ask you a question. In petrochemical production facilities, cascade control schemes are often used to control two or more control valves simultaneously. I would like to know how the cascade points for such cascade control are determined! I would be very grateful if you could share your insights. Thank you so much!
Regarding the determination of the split points for control valves in a split-control system, it is first necessary to identify the problems that such a system needs to address (increasing the adjustability of the control valve, controlling different fluids to meet production requirements, implementing certain safety measures), the direction of operation of the two control valves (in the same direction or opposite directions), and the flow capacity of the control valves. There are three types of split points for control valves: split at one point, split with overlapping coverage areas between the two valves, and split with dead zones between the two valves. For a split in the same direction for two valves, the selection of the split point also takes into account the issue of smoothness in the characteristics of the equivalent valve.
In my opinion, the determination of the intermediate points needs to be based on the actual process requirements; there is no one-size-fits-all approach. For example, regarding the split points of two control valves, in some cases the split is at 50%, meaning the two valves do not operate simultaneously; but in other cases there are two split points, resulting in an overlapping area where both valves have an open degree.
This is usually determined by the process engineering team, rather than the instrumentation team.
Split-control was proposed by the process engineering team; the split points vary from place to place, and it must be implemented in conjunction with the process requirements. On-site debugging is being carried out at the split point
The last edit to this post was made by yunrun on 2020-5-27 at 11:24. Regarding the calculation of split points, I read an article titled “If you can’t calculate and determine split points, don’t claim to understand split-point control”; it contained calculations that were quite complex