I am new to the world of tuning and may not be familiar with all the technical jargon. However, I am currently working on tuning a 3" Fisher sliding stem PCV for a flow control valve in an amine plant. The goal is to ensure that when the set pressure is exceeded, the valve will gradually shut to divert gas flow to a PRV without disrupting the plant's operations. Unfortunately, the valve is behaving erratically, opening and closing too quickly and sometimes even shutting off completely despite my attempts to set a minimum output limit of 10%. My target pressure is 11,500 mcf with a setpoint of 11,750. The current tuning parameters are: Kc - 0.8, Ti - 0.4, Td - 0.0, Time mode - Timed, Deadband - 5 (unclear if this is in percentage), Feed Forward Bias - 5 (unclear what this means). I would greatly appreciate any advice or guidance on how to properly tune this system for optimal performance.
To optimize your system performance, consider adjusting the Td parameter to 0.2 and monitoring the outcome. This tweak could greatly impact your results!
Are you measuring your Ti in seconds or minutes? Whichever it is, it appears to be short. Consider recalibrating using the lambda tuning method, a straightforward and reliable technique for optimizing loops with a single CV step adjustment. You can easily find detailed explanations and calculation methods by searching for it on Google. It is unusual that your feedforward remains constant, as it is typically used to react quickly to significant disturbances. The PID instruction uses the scaled measurement of the disturbance to adjust the output CV accordingly.
jhutto expressed concern about their lack of expertise in tuning, particularly when it comes to a 3" fisher sliding stem PCV within an amine plant's flow control valve system. The goal is to ensure that when the desired PV is surpassed, the valve gradually redirects gas flow to a PRV rather than overwhelming the plant. However, the valve is currently behaving erratically, opening and closing rapidly and occasionally dropping to 0% output. They are making adjustments to prevent this, with a desired PV of 11,500 mcf and a scaled setpoint of 11,750. The current tuning settings include Kc - 0.8, Ti - 0.4, Td - 0.0, Time mode - Timed, Deadband - 5, and Feed Forward Bias - 5. Seeking guidance on how to improve the tuning process, jhutto is open to suggestions for a beginner-friendly approach. For those unfamiliar with PIDE autotune, it is recommended as a helpful tool for optimizing control systems. A standardized set of ladders can be used with direct-acting control systems like this one, particularly for flow and pressure control. However, it may not be as effective for level control. To utilize PIDE autotune effectively, ensure it is in ProgAuto mode when active and ProgManual mode with PVTracking on when not in use. Adjust the PID_TON.PRE based on system response and set the CVProg (% between min and max set in PIDE FBD) to achieve a steady response before initiating autotuning. Begin the autotuning process in manual mode at the steady CVProg value, adjusting the autotune tag, CV step size, and initiating the autotune (optional PV change limit). Once the desired tune is applied, return to normal operation by toggling Temp_Prog_Man_Req and conducting testing to validate the adjustments.
What is the loop update time set in the PID instruction and how can you guarantee that the PID instruction runs at that specified loop update time? It's important to remember that PIDs revolve around timing. It's essential to note that you aren't tuning the PID itself, but rather the system, which is composed of the process and the PID controller. System tuning can be a complex task, especially for beginners. If you're new to this, consider using the auto-tune feature of PIDE as suggested by @AMarks95.
Inquiring for guidance on tuning a system? Unfortunately, providing a solid starting point without knowing crucial details like PV/SP and CV scalings, process gain, response time, control valve speed, and type of PV (possibly flow). Ambiguities like PCV (Pressure Control Valve) or PRV (Pressure Relief Valve) further complicate matters. Additionally, mismatched loop update times can lead to poorly tuned systems. One approach could be manually adjusting the valve to a desired CV position, monitoring PV and CV trends as the system stabilizes. Make sure to display trends in PID scaled percentages with labeled time units for accuracy.
From your description, it sounds like you could be dealing with an oscillation issue often associated with over-tuning. By reducing the Kc value (which is essentially the controller gain), the response might potentially be smoothed out. Similarly, for a system behaving in a fast and erratic manner, increasing the Ti value (which stands for Integral Time) could be of help. This essentially increases the time the controller takes to respond, which could help in avoiding abrupt behavior. The Deadband value you've mentioned is generally given in the same units as the input and output of the controller, in your case probably a percentage. It's typically used to avoid system instability brought on by small errors, so increasing this value might help. Lastly, the Feed Forward Bias you asked about is a baseline setting that is applied even when no error is present between the set point and the control point. This is used for systems where the stable position is not 0% or where load disturbances can be anticipated. Make sure to adjust and test these settings incrementally, checking plant's responses after each adjustment.
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Answer: - PID loop tuning is the process of adjusting the parameters of a PID (Proportional-Integral-Derivative) controller to achieve optimal system performance. In the context of high pressure gas flow control, proper PID loop tuning ensures that the control valve responds appropriately to changes in pressure, maintaining stability and accuracy in the system.
Answer: - Erratic behavior in a control valve could be a result of improper PID tuning parameters. Check and adjust the proportional gain (Kc), integral time (Ti), and derivative time (Td) values to better suit the characteristics of the system. Additionally, ensure that the deadband setting is appropriate to prevent rapid opening and closing of the valve.
Answer: - The Feed Forward Bias parameter in PID loop tuning is a feature that allows the controller to anticipate and compensate for disturbances in the system before they occur. A positive bias value adds an offset to the controller output, helping to preemptively adjust for changes in setpoint or process conditions.
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