How Do I Tune a Temperature Loop?

Before Tuning that Temperature Loop…Understand the Basics of Continuous Temperature Control

Temperature is one of the more common types of self-regulating – also known as non-integrating – processes used in industry. Like other self-regulating loops, temperature loops tend to naturally settle at a new operating state when adjustments are made to the corresponding Controller Output. What’s more, temperature loops are nonlinear in their behavior and process dynamics can vary considerably from one range of operation to the next. The later attribute, in particular, the nonlinear one – can hamper effective control if the associated PID is tasked with controlling a wide assortment and volume of production inputs. Such a scenario can put even the most experienced practitioner’s skills to the test. In this post the focus is on temperature control of continuous processes.

When tuning temperature control loops, it’s usually best to start with a well-conceived plan for both testing the PID loop’s process dynamics and collecting good data. A good testing protocol aside, certain attributes of temperature control are worth noting:

  • Dynamic Differences

Don’t be fooled – the dynamics associated with heating can be distinctly different from those associated with cooling. What’s more, insulation can amplify the difference between the two by retarding a system’s natural thermodynamics. Be sure to thoroughly test the Design Level of Operation of a temperature process by capturing dynamic process data both above and below Set Point (i.e. heating and cooling).

  • Patience Required

Generally speaking, temperature loops are slow to respond. That’s especially true of arc furnaces, rotary kilns, ovens, and other processes that possess significant mass. Although it may take a while to complete a bump test, the positives of capturing good process data generally outweigh the negatives. Without good data, the process model’s accuracy will be questionable and any tuning parameters that result could be counterproductive.

  • Alternate Application

Consider applying different tunings – aggressive vs. conservative – to the different zones of a multi-zone process. Large processes like ovens and extruders possess highly interactive characteristics. By staggering the tunings from one zone to the next, the tendency of adjacent zones to compete with one another is lessened. Another rule of thumb is to tune the first and last zones aggressively as that allows a process to speed its recovery from the disturbances of material entering and leaving.

  • Derivative Advantage

For practitioners who want to put Derivative to work, here’s your chance. While the limitations of Derivative are widely documented, temperature processes involving significant inertia make the most out of Derivative’s strengths. Since noise is usually minimal in these applications, Derivative will not result in excessive wear and tear on the associated instrumentation. Rather, Derivative prevents overshoot and improves the overall performance of temperature loops.

Again, its important to apply an effective strategy that thoroughly tests a given process’ dynamics and provides quality data for both modeling and PID controller tuning. Controller tuning workshops are available from any number of vendors. If you’re new to controller tuning, then consider enrolling in a training workshop that focuses more on industry best-practices and less on the use of a particular PID tuning software. A little investment in training and skills development can result in significant gains in both PID performance and your facility’s overall control loop optimization effort.

In a future post, we’ll tackle temperature control of batch processes.


These resources offer related content:

How Do I Detect Valve Issues and Prevent Failures?

  Control Loop Monitoring Solutions Provide Valuable Early Detection of Valve Stiction and Valve Deadband It's generally known that the behavior of final control elements (FCEs) (valves, air handlers, etc.) change over time. Like most things the dynamics of FCEs are different from the time...

The Relationship Between Loop Performance Monitoring and Loop Tuning

Imagine that you just purchased software to help with the tuning of your plant’s control loops.  You’re ready to enhance control and to improve production throughput and efficiency, right?  With software successfully installed you consider the 100s if not 1000s of PID controllers regulating your...
osi pi data historian fi

4 Reasons the OSI PI Data Historian is King of the Market

Data historians are a “must have” technology and among the automation market’s options the PI Historian from OSIsoft is the gold standard. OSIsoft has more-or-less led the historian market from its inception in 1980. The reason: OSI has continuously innovated to assure that the PI...

Still looking for more?

Now that you’ve gotten the basics, connect with our team to learn how our people, processes and technologies can help you optimize.