R
I have been experimenting for quite some time trying to learn more about PID control. Most of my lab experiments are performed on a small heater application (basically a soldering iron) whose temperature I can control with an Allen-Bradley PLC-5/20. For the experiments covered in this post I am using the Dependent Gains (ISA standard) equation.
Lately I have become interested in a procedure known as the “lambda” or “setpoint” tuning method. My understanding is that this particular tuning method provides PID control which will neither oscillate nor overshoot whenever a step change is made to the system setpoint. I recently used Rockwell’s RSTune software to automatically come up with a set of lambda tuning values for my little experimental heater system. I have posted the results of using RSTune’s suggested values as Figure 1 at:
http://www.plctalk.net/qanda/showthread.php?postid=23744#post23744
After applying the lambda tuning values, my system responded to a setpoint change without oscillation or overshoot – exactly as desired. Note that in setting up RSTune, I specified a “lambda” time of four minutes. My understanding is that after four lambda time periods (in other words, after 4*4 minutes=16 minutes) the process should be approximately (98%) “on target” at the new setpoint. As shown in Figure 1, RSTune was successful in achieving this level of control.
Based on the successful results of using the RSTune software, I know that lambda tuning is possible with my system. My next objective is to learn how to calculate the lambda tuning values manually – as opposed to relying on a software package. My main purpose for doing this is for my own personal education. Even though I presently have access to products such as RSTune, I’ve found that working through the steps of manual calculations (such as the Ziegler-Nichols method) has helped me visually analyze how various systems respond to different control strategies. I hope that learning how to manually make the lambda calculations will also prove helpful.
Several years ago a local engineer was kind enough to help me by explaining the procedures required to manually calculate the proper values for the proportional, integral, and derivative settings to obtain a lambda tuning response. Unfortunately since that time I have moved (twice) and can no longer find my notes on this subject. I’m hoping that someone will respond to this post and point me in the right direction.
If I remember correctly, the manual calculations necessary for lambda tuning are based on a set of simple formulas which are very similar to those used for the Ziegler-Nichols “Process-Reaction Curve” method. Recently I placed my experimental heater in the manual mode and made a step change to the CV (Control Variable) setting and graphed the system’s response. I have posted the results as Figure 2 on the same forum as linked above.
This figure includes all of the measurements that I think might be of interest – but again, since I’m working from memory here, some of the values included are probably not required. On the other hand, if I’ve left some necessary stone unturned, I will be glad to provide more detail in response to any posted or emailed questions.
I would truly appreciate any information on how to manually calculate the proper settings for lambda tuning - and also any links which you might consider helpful. Nothing which I have been able to find on the web has been specific enough to answer my questions.
Thank you in advance, Ron
[email protected]
Lately I have become interested in a procedure known as the “lambda” or “setpoint” tuning method. My understanding is that this particular tuning method provides PID control which will neither oscillate nor overshoot whenever a step change is made to the system setpoint. I recently used Rockwell’s RSTune software to automatically come up with a set of lambda tuning values for my little experimental heater system. I have posted the results of using RSTune’s suggested values as Figure 1 at:
http://www.plctalk.net/qanda/showthread.php?postid=23744#post23744
After applying the lambda tuning values, my system responded to a setpoint change without oscillation or overshoot – exactly as desired. Note that in setting up RSTune, I specified a “lambda” time of four minutes. My understanding is that after four lambda time periods (in other words, after 4*4 minutes=16 minutes) the process should be approximately (98%) “on target” at the new setpoint. As shown in Figure 1, RSTune was successful in achieving this level of control.
Based on the successful results of using the RSTune software, I know that lambda tuning is possible with my system. My next objective is to learn how to calculate the lambda tuning values manually – as opposed to relying on a software package. My main purpose for doing this is for my own personal education. Even though I presently have access to products such as RSTune, I’ve found that working through the steps of manual calculations (such as the Ziegler-Nichols method) has helped me visually analyze how various systems respond to different control strategies. I hope that learning how to manually make the lambda calculations will also prove helpful.
Several years ago a local engineer was kind enough to help me by explaining the procedures required to manually calculate the proper values for the proportional, integral, and derivative settings to obtain a lambda tuning response. Unfortunately since that time I have moved (twice) and can no longer find my notes on this subject. I’m hoping that someone will respond to this post and point me in the right direction.
If I remember correctly, the manual calculations necessary for lambda tuning are based on a set of simple formulas which are very similar to those used for the Ziegler-Nichols “Process-Reaction Curve” method. Recently I placed my experimental heater in the manual mode and made a step change to the CV (Control Variable) setting and graphed the system’s response. I have posted the results as Figure 2 on the same forum as linked above.
This figure includes all of the measurements that I think might be of interest – but again, since I’m working from memory here, some of the values included are probably not required. On the other hand, if I’ve left some necessary stone unturned, I will be glad to provide more detail in response to any posted or emailed questions.
I would truly appreciate any information on how to manually calculate the proper settings for lambda tuning - and also any links which you might consider helpful. Nothing which I have been able to find on the web has been specific enough to answer my questions.
Thank you in advance, Ron
[email protected]