PID and digital control efficiencies

Most proportional-integral-derivative (PID) applications use digital controllers, though some still use analog. Digital control can offer additional process control system efficiencies.

By CFE Media November 14, 2016

Digital controllers have some advantages over analog controllers for proportional-integral-derivative (PID) applications. James F. Beall, principal process control consultant, Industry Solutions Group, Emerson Process Management, explained how digital control may offer additional process control system efficiencies by answering five questions. 

Digital PID controllers

Q: For PID applications, about how much analog control is still in place?

Beall: Based on looking around in the plants where I have control projects and asking a few customers, I would say there are less than 5% analog controllers in plants.

Q: What are the main advantages of using digital controllers over analog in PID applications?

Beall: There are many useful options in digital controllers that are unavailable in analog controllers, such as variable tuning; selectable PID structure [P and D on process variable (PV) or error] and form; gap control; error squared; tuning algorithms; accurate tuning settings; and others.

Q: Are there PID applications where analog has advantages over digital?

Beall: I have heard that a digital control controller must have input to output response time less than 100 milliseconds to match the speed of an analog controller. So, for loops that require a very fast response, the analog controller is faster than most digital controllers.

Q: When transitioning from analog to digital PID-type controllers, what are the special considerations, if any, for selection, setup, operation, optimization, or modifications over time?

Beall: The first step is to make sure you PROPERLY convert the current tuning in the analog controller to the digital controller.

Also, ensure you don’t configure a lot of new alarms just because it is easy to do so.

Finally, investigate the new features of the digital controller to find better ways to duplicate or improve previous functionality.

Q: Beyond performance, what are some other advantages of digital controllers for PID applications?

Beall: Other advantages include ease of collecting data from the controller and easier troubleshooting the controller action.

Edited by Mark T. Hoske, content manager, CFE Media, Control Engineering,


Go Online for more on PID Other Control Engineering PID-related coverage including:

  • The PID and Advanced Control page on Control Engineering’s website
  • Process and Advanced Control eNewsletter–Click on the newsletter image to see the latest. Click on the newsletter name to subscribe for free. 
  • PID Tuning Best Practices Digital Report–This PID article collection contains five of the most-referenced Control Engineering articles delivering practical advice on improving the use of PID, examining the important third factor in PID, and matching the control technique to process. 

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More information about Emerson Automation Solutions.

Article links

The velocity of PID

Inside Process: Proportional-integral-derivative (PID) theory is best introduced as the familiar second order differential equation via the velocity form instead of the more traditional positional form. 

Understanding PID control and loop-tuning fundamentals

PID loop tuning may not be a hard science, but it’s not magic either. Here are some tuning tips that work. 

Advanced process control and real-time optimization

Advanced process control and real-time optimization are techniques that can improve a plant’s profitability and efficiency by maintaining a process at desired operating conditions while taking process constraints into account. 

Author Bio: Since its founding in 2010, CFE Media and Technology has provided engineers in manufacturing, commercial and industrial buildings, and manufacturing control systems with the knowledge they need to improve their operational efficiency. CFE delivers the right information at the right time around the world through a variety of platforms.