How to determine the split points for step control
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In a venting system, there are two control valves, A and B. The transmitter has a measurement range of 0~0.4 MPa, and the setpoint of the controller is 0.25 MPa. Valve A is to be opened when the pressure reaches 0.25 MPa; if the pressure continues to rise and reaches 0.3 MPa, Valve B is to be opened. So where should the split point set by the controller be located? I hope the experts here can give me some advice.
It is difficult to determine this split point, as there are several possible scenarios: 1) After valve A is fully opened, the pressure still continues to rise to 0.3 MPa; at this point, valve B needs to be opened. 2) If valve A is not fully open yet but the pressure has already reached 0.3 MPa, then valve B must be opened. So I think it’s hard to determine where the split point is. However, the original poster can try doing it at 50% of the output; as long as the requirements are met, there’s no need to worry about exactly which point to use.
The split point set by the controller’s output is at 0.28 Mpa: valve A is opened and valve B is closed when the pressure is below 0.28 Mpa； Above 0.28 Mpa, open valve B and close valve A.
So how is 50% determined? It has nothing to do with the PV value, right?
Isn’t the controller’s output 0~100%? Can it be set using the PV value?
PV needs to be combined with SP; the valve opens only when PV exceeds SP. Once the configuration is set up and in use, fill it with some nitrogen and give it a try.
You can set the digital signal ranging from 0 to 0.3 Mpa to correspond to an output of 0 to 100%, enabling step control. For specific details, consult the instrumentation engineer.
I'm terrible at it. If two valves are set at 50%, then are the three cooling control valves spaced out, with each set at 33.3%? 66.7%?
This is not mandatory; the selection of the stage points is determined based on requirements. In some operating conditions, it is necessary for the two control valves to operate within an overlapping range, while in other cases no overlap is required, and there may even be a dead zone between the stages.
The question is not clear enough: it asks whether valve A should be fully opened when the pressure reaches 0.25 MPa. It also asks whether valve A will operate when the pressure is below 0.25 MPa, and whether valve B should be fully opened when the pressure rises to 0.3 MPa
It can be designed such that 0–50 degrees correspond to the opening degree of valve A, while 50–100 degrees correspond to the opening degree of valve B (when valve B is open, valve A is in its fully open state)~~