Can anyone provide guidance on the optimal use of Siemens PID_Temp versus PID_Compact (Temperature)? I am facing challenges in tuning these instructions for heating a 3/4" stainless steel plate with a 7 sq ft area using a large resistive heater. Despite multiple attempts, I struggled to pretune the PID_Temp correctly. The required delta between the PV and setpoint exceeded 100°C, with the output fluctuating between 25% and 100% during the tuning process. The temperature even rose above 220°C, prompting me to abort the tuning to prevent equipment damage. Switching to PID_Compact did not fully resolve the issue, as the PV still overshot by nearly 60%. Fine-tuning also proved challenging, with slow progress and high output temperatures. If anyone has encountered similar problems or has insights on tuning these PID instructions effectively, any assistance would be appreciated.
Search for "hot rod" discussions in this forum. Inquiring about the nature of PV measurement, is it conducted by a single temperature sensor/transducer positioned above, inside, or below the 7 sq ft metal (assuming a vertical dimension of 3/4")? What is the temporal behavior of the measurement - is it noisy or smooth? How does the PV measurement change when the heating element is activated (e.g., slope)? What happens to the PV measurement when the metal is hot but the heating element is off? How and where does the heating element apply heat to the metal - at a single point or distributed across the entire surface? Is the heating element exposed to ambient conditions or enclosed in a chamber with the metal? How is the metal positioned vertically? Can you recall and share the discrete form of the PID algorithm? In a recent experiment with the PID_Compact set to Temperature, the initial tuning session lasted around 5 hours without reaching the setpoint. After adjusting the PID parameters and setting it to auto mode with a new setpoint, the PV overshot by nearly 60%, deemed unacceptable. During the transition to the second setpoint, was a new metal piece introduced or did the original metal cool down? And when the PID was switched to auto with the second setpoint, was it above or below the current PV of the metal?
There is no specific trend at the moment. I have an auto tune code available here at https://deltamotion.com/peter/py/SOPDT.zip. Currently, I am assisting someone with their heater system. While my code worked for them, it encountered issues with their .csv file for some unknown reason. I am investigating this further. It is crucial to ensure that the units for the two PIDs controller gains match. Rockwell's approach can be challenging as they use counts for everything, making it essential to pay attention to scaling and timing. Personally, I prefer using the ISA standard, which includes a gain, integrator, and derivative time constant in minutes. The data in the .csv file is sourced from Ron Beaufort's hotrod from 2005, where he recorded it in seconds. Therefore, I had to divide the times by 60 to convert them into minutes. I frequently use Ron's hotrod data for testing various system identification methods. Over time, I have realized that many individuals and companies claiming to have autotuning capabilities do not execute it correctly. In the past, I collaborated with Doug Cooper, a professor at UCONN, who recommended the best algorithm for autotuning. More information can be found on his website at www.controlguru.com.
When selecting a PID controller for temperature control, it is important to consider the differences between the two temperature PIDs. If you have separate outputs for heating and cooling, such as a system with a heater to increase the temperature and a fan to reduce it, it is recommended to use the pid_temp. However, if you only have one output, you can use either PID controller. The pid_compact is a preferred choice for many. To optimize your temperature control, various factors need to be considered. Is your system's inertia large? Is the heater located close to the sensor? Is there an air gap between the heater and the plate? These questions can impact the performance of your temperature control system. Timing is also crucial in temperature control. How quickly does the sensor detect a temperature rise after manually starting the heater? How long does the temperature continue to rise after turning off the heater? Additionally, it is important to know the maximum temperature tolerance of your machine and the setpoint value you will use. Fine-tuning a controller can be time-consuming, typically taking around 4 hours to achieve the desired results. It is recommended to request fine-tuning with a setpoint value that your system can handle without overloading. It is worth noting that conducting tuning when the system is empty and later adding loads may not yield accurate results. For a quicker solution, try using a higher gain like 10 and set the I and D values to 0. For more personalized assistance, please provide additional information and pictures of your system. This will enable us to provide more specific guidance and support.
In a forum post, user drbitboy recommended searching for "hot rod" to find relevant information. The post in question raised several important questions about the PV measurement process. These questions included the nature of the measurement, the temporal characteristics, and the heating element's impact on the metal. The PV measurement is conducted using a single Thermocouple with a ring terminal mounted at the center of a plate with a 10-32 bolt. The temporal characteristics are described as smooth, with a slow but steady slope. Even after the plate is heated and the heater turned off, the PV continues to rise for several hours before returning to ambient conditions. As for the heating element, it consists of 480v 2700w insulated disk heaters mounted at both ends of a large cylindrical tank oriented horizontally. The heaters cover the entire surface of the plate and are secured by 1/4-20 bolts. The tank housing the heating element and metal plate is located in a climate-controlled building maintained at a temperature of 75 F. The metal plate's orientation was not specified in the post. In terms of the PID system, the user was unable to provide the discrete form from memory. When changing to a new setpoint during the exercise, the same plate was used, with the first attempt not allowing it to cool to ambient conditions. Both attempts resulted in similar overshooting, with the setpoint consistently lower than the PV reading. The user expressed gratitude for the response and mentioned the intention to provide trend data in the future.
Peter Nachtwey shared a helpful auto-tune code for PID controller on his website https://deltamotion.com/peter/py/SOPDT.zip, although he mentioned that he is currently assisting someone with their heater system which is facing issues with the code when applied to a .csv file. He highlighted the importance of ensuring that the units for the PID controller gains are consistent, especially when dealing with Rockwell systems that operate in counts. Nachtwey emphasized using the ISA standard with specific gain, integrator, and derivative time constants in minutes for accurate system identification. He mentioned utilizing Ron Beaufort's hotrod data from 2005, converted from seconds to minutes for testing different techniques. Nachtwey also pointed out that many people and companies claiming to have autotuning capabilities often do not implement it correctly, citing collaboration with Doug Cooper from www.controlguru.com, a UCONN professor, for guidance on the best algorithm. Expressing gratitude for the code and assistance provided by Nachtwey, the individual acknowledged transitioning from a Rockwell to a Siemens shop, with plans to ensure consistent units and tune the PID loops accordingly. They appreciated the code provided in Python, expressing excitement for the opportunity to work with it.
It sounds like you're having a tough time, and I can relate to the difficulties of tuning these PID instructions. One suggestion I have is to utilize autotuning if you haven't done so already. Siemens controllers often have built-in autotuning capabilities, and these can be utilized to determine optimal PID parameters. However, if you have already done this and the autotuning failed or did not yield satisfactory results, you may want to consider manual tuning. Start with proportional control and gradually increase the gain until you see consistent oscillations in temperature. Then apply the integral control to get rid of steady state error and lastly, apply derivative control to foresee the error trend. And importantly, make sure to establish safe operation protocols, such as setting maximum temperature limit to not to burn your heater. Remember, PID tuning requires trial, error, and patience. Hope this helps!
It sounds like you're dealing with some pretty tricky PID tuning! One thing that helped me in the past was tweaking the proportional and integral settings separately to see how they impact the system's response. You might also want to consider implementing some form of anti-windup to prevent that output from overstressing your heater. Additionally, if you haven’t already, try starting with a simpler or smaller heating element for initial tuning before scaling up to the larger setup. Sometimes, doing a more gradual ramp-up can help you get a clearer picture of how the PID is responding without overshooting. Good luck!
It sounds like you're dealing with quite a challenging setup! Have you considered using a slower tuning method, like the Ziegler-Nichols or a modified version of it, which might give you more stability before you push it into active tuning? Also, tweaking the PID parameters one step at a time while monitoring system response closely can really help—maybe start with the P gain and see how that affects the output before adjusting I and D. Sometimes even small changes can lead to better control, especially with a system as sensitive as yours. Additionally, ensuring that your sensor response time is adequate can help with those overshoots. Best of luck, and don’t hesitate to share your results!
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Answer: - Siemens PID_Temp is designed for temperature control applications, while PID_Compact offers a more simplified version of the PID controller for the same purpose.
Answer: - Tuning PID controllers for heating a stainless steel plate can be challenging due to the material's thermal properties. It is recommended to start with lower setpoint values and gradually increase them while monitoring the system response.
Answer: - Common issues include overshooting the setpoint, slow response times, and difficulty in achieving stable control. These challenges can be addressed by adjusting the tuning parameters incrementally and analyzing the system's behavior.
Answer: - To prevent equipment damage, it is essential to closely monitor the system during the tuning process and intervene if the temperature exceeds safe limits. Additionally, implementing safety measures such as temperature limits and emergency shutdown procedures can help mitigate risks.
Answer: - Best practices for tuning PID controllers in high-temperature applications include starting with conservative tuning parameters, monitoring the system closely during the tuning process, and making small adjustments to the parameters to achieve stable control. Consulting with experts
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