Troubleshooting Gas Hot Plate with PID Control and Ball Valve Issues

25-01-2025
ian.smith7
17 comments
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Question:

Greetings, We are currently encountering an issue with a gas hot plate that is controlled by a PID system. The hot plate consists of six gas burners connected to a shared forced air manifold, with air flow and flame level regulated by a PID controlled ball valve. During the initial startup process, the ball valve is controlled by a PLC to manage the purge and ignition cycles successfully. Once all six burners are ignited, control is then transferred to the temperature controller. However, there are instances when the PID controller, set at a setpoint (SP) of 220 deg C and with a process value (PV) of 30 to 40 deg C, causes the ball valve to reduce the flame level below the desired limit. This results in the burners operating at a lower flame, slowly heating the hot plate to only 100 deg C, while the controller continues to adjust the ball valve to its minimum limit. To address this issue, the PID controller needs to be reset, the burners relit, and the controller can then resume normal operation by regulating the ball valve as intended. Despite changing the Controller, ball valve, and sensor Loop interface, the problem persists, indicating that the issue lies in the setup of the controller. The controller is currently in PI mode with specific parameters set, and the temperature sensor is located around 1.5 meters away from the flame. If anyone has any insights or advice on how to rectify this issue, it would be greatly appreciated. Warm regards, Ian

Top Replies

Could you provide more detail on whether the PI control is managed by separate dedicated controllers instead of being integrated within the PLC? If that's the case, how does the PLC adjust the controllers' output? I want to make sure I'm understanding the setup correctly.

26-01-2025
parky

parky inquired about the nature of PI control in relation to dedicated controllers and PLCs. Is the PI control conducted by separate controllers, or is it integrated within the PLC itself? During Purge and ignition processes, the PLC takes precedence over an external controller (such as a West 4170) by utilizing relays to bypass the controller's output. Following ignition, the external temperature controller resumes control as the PLC disengages the override relays. Observations have shown that the ball valve gradually adjusts to the Low Limit as the temperature controller outputs pulses. Ian provided this insight while on a job assignment, showcasing the intricate process of PLC and controller interactions.

26-01-2025
ian.smith7

Does the PID algorithm run continuously, even when control is taken over by the PLC? Do you observe the measured temperature exceeding the setpoint before any issues arise? Additionally, do you have access to information or data regarding the PID output?

26-01-2025
MaxK

Are you sure the controller is not set to adaptive tune or self-tune mode? Has this issue been present since the initial installation or has it recently appeared? It is not optimal to have a controller attempting to make adjustments while another process is interfering. This type of control is not typically seen, but when using standalone controllers, it is common to have a startup profile with incremental output adjustments. Check for these settings to ensure optimal performance.

27-01-2025
parky

ian.smith7 mentioned the transition of control from the PLC to the temperature controller when all 6 burners are ignited. This handoff can sometimes lead to complications. Can you elaborate on what is meant by "the PLC then releases control to the temperature controller?" Is the temperature controller referring to the PID system? Is the PID system set to automatic or manual mode before and after the PLC hands over control? How does the PID system handle changes in mode, such as transitioning from auto to manual? What are the setpoint (SP) and process variable (PV) values of the PID system before, during, and after the PLC releases control? For more insights, consider the concept of Rubber Duck Debugging.

27-01-2025
drbitboy

Hi Ian, it sounds like a frustrating situation! One thing to consider is the positioning of your temperature sensor; being 1.5 meters away from the flame might be causing a lag in the readings, leading to the controller reacting too slowly. You might also want to look at tuning your PID parameters further—sometimes a bit of overshoot can help compensate for the delay in heating. If you haven’t already, experimenting with a feedforward control strategy in conjunction with the PID could improve responsiveness as well. Good luck, and I hope you get it sorted out soon!

01-03-2025
Olivia Evans

Hi Ian, it sounds like you're dealing with quite a tricky situation! One thing you might want to consider is the placement of your temperature sensor; being 1.5 meters away from the flame could be causing delays in responding to actual temperature changes, contributing to the PID overshoot or undershoot. Additionally, have you tried tuning the PID parameters? Sometimes, relatively small adjustments in the integral or proportional gain can make a big difference in how the system reacts under varying load conditions. You might also want to check for any potential lag in the system due to the airflow dynamics that could affect the measurements. Good luck, and I hope you find a solution soon!

01-03-2025
Evelyn Bell

More Replies →

It appears that the external PID controller is becoming overactive during the initial stages of low flame ignition. By temporarily bypassing the controller's CV without switching it to manual mode, this issue can arise. It is important to configure the controller for PV tracking to ensure a smooth transition, as recommended by others.

28-01-2025
robertmee

Is the west controller adaptive if its auto tune function is disabled? I tried to find a Boost function to ensure the output reaches 100% when the process value (PV) is below the Boost value, but it seems that the West controller does not have this feature. The controller continually operates in auto mode, but the PLC disconnects the control outputs from the valve during purge and ignition sequences. All control is managed through the West 4170, as there is no PID control in the PLC. The input sensor remains connected to the West controller at all times, ensuring it operates in auto mode without interfacing with the PLC. This issue has persisted for several years.

29-01-2025
ian.smith7

Based on my understanding, the programmable logic controller (PLC) activates relays that switch between the controller and outputs during purge and ignition processes. The controller remains inactive while the PLC takes control. To ensure a smooth transition, it is essential to establish connections to the controller, such as a manual setpoint (SP) and digital inputs that can force the controller into manual mode without disrupting operations.

30-01-2025
parky

During the low flame ignition process, it appears that the external PID controller is experiencing windup. But what exactly is windup and how does it affect the system's performance? Let's dive into the details.

30-01-2025
ian.smith7

ian.smith7 asked the question: "What is windup?" As Parky detailed in the previous post, it is not possible to simply bypass the output of the PID controller. During this time, the controller must be instructed not to run the PID in order to prevent windup. With an integral KI coefficient, the PID will continue to integrate the error, causing windup, because it keeps trying to make adjustments even when the output is bypassed.

30-01-2025
robertmee

Robertmee and Parky both emphasized the importance of not simply bypassing the output of the PID controller. Instead, it is crucial to instruct the controller to temporarily suspend PID operation to prevent error integration or windup. This is especially critical with an integral KI coefficient, as the PID will continue to integrate the error even when the output is bypassed. Hi Rob, if the controller is driving the output to a minimum when the PV is well below the setpoint of 220 degrees Celsius, it may be due to the generated error being negative. In this case, the output should be driven to maximum as per the reverse output action setting. As a novice, I am seeking clarity on this matter. Ian

30-01-2025
ian.smith7

If occurrences are consistent every time, there may be a system issue. If specific settings of PV, SP, and time always result in a problem, there may be a system issue. If issues occur sporadically, the system may seem fine, but it's important to identify any discrepancies. Check for consistent values during successful operations and when issues arise. Take note of the SP and PV values when problems occur. Monitor how long the PLC takes to initiate the system. Pay attention to the West controller display when issues arise. Consider if the problem is more prevalent on hot or cold days or if weather conditions play a role. Collecting data is essential to pinpointing the cause of the issue. You can manually take notes or have the PLC log the data. Alternatively, consider recording a video to review the operation later. If the issue occurs sporadically, set up a video camera to start recording when the PLC triggers the system.

30-01-2025
BryanG

If your equipment is in reverse, attempt switching it to direct mode. It's important to comply with current European regulations, which require a burner controller approved for the purge and ignition cycle. Alternatively, a hardwired circuit with pressure switches and timers is also typically accepted. Stick to approved devices to ensure safety and adherence to regulations.

30-01-2025
lfe

Hello everyone, I appreciate your responses and assistance. Recently, I observed a situation with the Hot Plate where the burners were manually switched off and the plate's temperature was decreasing. However, the West controller continued to try to raise the temperature, resulting in significant errors as the temperature dropped. This led to a buildup of errors that persisted even when the burners were eventually turned back on. Typically, I would reset the controller by powering it down. To address this issue, my solution involves adding a second contact to the burner control switch. This way, the West controller can be powered off whenever the burners are switched off. This will allow the controller to reboot during the Purge cycle. Thank you, Ian

30-01-2025
ian.smith7

Execute the system's lighting process while setting the West 4170+ controller to manual mode with bumpless transfer configuration. Adjust the 4170+ output manually to match the PLC's designated 15% low-flame value during the lighting procedure. Once the transfer is completed, switch the 4170+ PID to automatic mode. If this method proves successful, task the PLC with automating the manual adjustments. However, a more straightforward solution has been discovered.

30-01-2025
drbitboy

Hello everyone, I want to thank you all for your responses and assistance. Recently, I observed an issue with the Hot Plate where, despite the burners being turned off manually and the plate temperature decreasing, the West controller continued to try and raise the temperature. This resulted in significant errors accumulating as the temperature dropped. When we eventually turned the burners back on, the controller still retained these errors. Typically, I would reset the controller by powering it down. However, I have devised a solution by adding a second contact to the burner control switch. This way, we can power off the West controller whenever the burners are switched off. This gives the controller time to boot up during the Purge cycle. This adjustment addresses the windup issue I mentioned, specifically during the cooldown event, rather than during ignition. Thank you, Ian

30-01-2025
robertmee

Hello everyone, I would like to express my gratitude for the support provided. The issue at hand is the "Wind Up" problem, a term that was unfamiliar to me due to my limited experience with instrumentation. After conducting some research, I was able to grasp the concept. Additionally, there was a secondary issue causing confusion, as the valve would occasionally drop to minimum flame before quickly returning to full flame. This was a result of a slow Setpoint Ramp setting, which took time to adjust the SP past the initial cold temperature of the Hot Plate during startup. To address this, a new instrument with digital input has been ordered to allow for manual steady state operation when the burners are turned off. I appreciate everyone's input, as it helped me understand the explanations provided. Thank you all for your valuable contributions.

30-01-2025
ian.smith7

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Frequently Asked Questions (FAQ)

FAQ: 1. Why is the PID controller causing the ball valve to reduce the flame level below the desired limit?

Answer: - The PID controller may be incorrectly configured, causing it to adjust the ball valve in a way that hinders reaching the desired temperature setpoint.

FAQ: 2. What troubleshooting steps have been taken to address the issue of the burners operating at a lower flame and slowly heating the hot plate?

Answer: - The thread mentions attempts to change the controller, ball valve, and sensor loop interface, indicating a systematic approach to resolving the issue.

FAQ: 3. What could be causing the persistent problem despite changing the controller, ball valve, and sensor loop interface?

Answer: - The issue may be related to the setup of the PID controller itself rather than the individual components, as indicated in the discussion.

FAQ: 4. What is the current mode of operation of the PID controller and the distance of the temperature sensor from the flame?

Answer: - The PID controller is in PI mode with specific parameters set, and the temperature sensor is located approximately 1.5 meters away from the flame, providing insight into the system configuration.

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