Instrument issue
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Gentlemen, I would like to ask: in a proportional control system, do the valves operate simultaneously or one after another? In other words, does one valve need to reach its limit value before another valve operates, or do both valves act at the same time – for example, one valve opens while another closes? Thank you! ! !
Check how the controllers and valves are configured. For proportional control, it is defined that two valves are controlled within one signal range, but it does not specify how this control is carried out. I have seen scenarios where from 0-45% of the signal, valve A moves from open to closed; from 45-55% no action occurs; and from 55-100%, valve B moves from closed to open. There have also been cases where from 0-80% of the signal, valve A moves from closed to open, while from 20-100% valve B moves from open to closed. In other words, depending on the process requirements, the two valves can operate simultaneously or separately
Reply to 2# zccchunchen: That’s how our unit with heat exchangers works. I originally thought that one valve would open while the other remained closed – that is, when the temperature rises, the valve in the bypass route opens while the valve in the main route stays closed. When the process parameters aren’t met even with the bypass valve fully open, then the valve in the main route is reduced in size. But recently, a colleague of mine told me that she observed on-site that two valves operate simultaneously – one opens while the other closes. I’m not sure what the difference is between this and what I described earlier, where each valve operates individually. But if both valves operate at the same time (one opening and one closing), then wouldn’t there be dead zones during shutdown and cleaning?
One action at a time, not actions simultaneously. The two valves operate in different valve position ranges; of course, each range for proportional control varies depending on the process.
One controller, two control valves, with proportional control; when the regulator output is between 45% and 55%, both valves 2406A/B operate simultaneously. For this as well, it’s between 20%-80%; both valves operate in that range. As for the cases where they operate at 0-50%A and 50-100%B, those are relatively simple. There is also another scenario where they operate at 0-40%A, do not operate at 40-60%, and then operate at 60-100%B; no examples have been found yet
Reply to 5# zccchunchen: Thank you!
Split control is a system in which one regulator controls two control valves, adjusting one of them as needed
There are many different forms of split-range control, and the specific design should be determined based on the requirements of the process. The annotation section of a typical PID diagram will specify the control scheme. The control patterns I have seen include cross-shaped, parallel lines, and V-shaped. Generally, the split point for 2 control valves is at 50% of the valve position, while for 3 control valves, it is usually divided at 50%, 25%, and 25% – for your reference