rgive
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R
Application: PID Loop to control the flow in a large water line. Analog 4-20ma output feeding a large motor driven valve actuator. Input 4-20ma from a DP cell which is converted to flow.
Goal: Achieve a slow modulating output that will maintain a position. For example if a flow is achieved, then keep the valve at that %open position.
Issues: First of all, I have tried tuning the loop via PID parameters and the loop never seems to settle down. For example, if the Set point is 5 MGD, then the PV fluctuates quite a bit due to the valve constantly changing. It appears that the Analog Output is constantly changing with the PID. With this large motor driven actuator, I need the output to the valve to modulate slow and maintain position. In the past, I have tuned loops but they have been air actuated valves and it didn’t really matter how many times the valve actuated to achieve flow. This valve cannot actuate constantly due to the motor driven actuator and the size of the valve. It doesn’t appear that the adjustment of the PID parameters will allow me to achieve the slow modulating output and keep the valve in a maintained %open position. Note: The valve actuates extremely slow so there may be timing issues with the PID. I can set the loop in manual and adjust the output to maintain a steady flow rate.
There are items in the PID Loop that I’m not familiar with. What are the following items: Bias, High/Low Integral Windup, Initialization flag, Loop timer, error summation byte, Pointer to loop counter, max # loops scanned. Can any of these items help me achieve my goal? Do I have the PID setup correctly?
Is this not the right application for a PID?
Goal: Achieve a slow modulating output that will maintain a position. For example if a flow is achieved, then keep the valve at that %open position.
Issues: First of all, I have tried tuning the loop via PID parameters and the loop never seems to settle down. For example, if the Set point is 5 MGD, then the PV fluctuates quite a bit due to the valve constantly changing. It appears that the Analog Output is constantly changing with the PID. With this large motor driven actuator, I need the output to the valve to modulate slow and maintain position. In the past, I have tuned loops but they have been air actuated valves and it didn’t really matter how many times the valve actuated to achieve flow. This valve cannot actuate constantly due to the motor driven actuator and the size of the valve. It doesn’t appear that the adjustment of the PID parameters will allow me to achieve the slow modulating output and keep the valve in a maintained %open position. Note: The valve actuates extremely slow so there may be timing issues with the PID. I can set the loop in manual and adjust the output to maintain a steady flow rate.
There are items in the PID Loop that I’m not familiar with. What are the following items: Bias, High/Low Integral Windup, Initialization flag, Loop timer, error summation byte, Pointer to loop counter, max # loops scanned. Can any of these items help me achieve my goal? Do I have the PID setup correctly?
Is this not the right application for a PID?