ddeshi2
Member
Hi all, I have two PID loops in the program: flow loop and pressure loop.
Flow loop: We have a flow meter (magnetic flow meter for water), a positive displacement pump, a VFD to control the speed of pump thereby controlling the flow.
Pressure loop (To create Backpressure with the water flow): We have a control valve (Fail Open)and a Pressure Transmitter.
I'm using a timer to trigger the PIDs (250ms) and loop update times for both PIDs (250ms) and they seem fighting with each other. I read somewhere here that the pressure loop update time should very fast compared to the flow loop and they cannot have same loop update times. Is it true? Can someone please elaborate on this or give me a link to the article about pressure and flow loops.
Also, My flow and pressure loops have the following PV and CV:
Flow loop: PV-- FLOWMETER READING
CV-- VFD SPEED
Pressure loop: PV-- Pressure Transmitter
CV-- Control valve (Back pressre)
I need to get a back pressure of 50 PSI with 3 GPM of water. I'm using two PIDs now and they are not cascaded. Am I thinking in the right direction or should they be cascaded or something? Please help.
Thanks in advance,
Ding
Flow loop: We have a flow meter (magnetic flow meter for water), a positive displacement pump, a VFD to control the speed of pump thereby controlling the flow.
Pressure loop (To create Backpressure with the water flow): We have a control valve (Fail Open)and a Pressure Transmitter.
I'm using a timer to trigger the PIDs (250ms) and loop update times for both PIDs (250ms) and they seem fighting with each other. I read somewhere here that the pressure loop update time should very fast compared to the flow loop and they cannot have same loop update times. Is it true? Can someone please elaborate on this or give me a link to the article about pressure and flow loops.
Also, My flow and pressure loops have the following PV and CV:
Flow loop: PV-- FLOWMETER READING
CV-- VFD SPEED
Pressure loop: PV-- Pressure Transmitter
CV-- Control valve (Back pressre)
I need to get a back pressure of 50 PSI with 3 GPM of water. I'm using two PIDs now and they are not cascaded. Am I thinking in the right direction or should they be cascaded or something? Please help.
Thanks in advance,
Ding