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May
11

The Most Underutilized Component in Nearly Every Control Loop

If you look at all the features and options of a PID controller that are sitting idle, you realize only a small fraction of the power of the PID is used even if you make the big assumption that the controller is tuned. How many loops use integral deadband, nonlinear gains, dynamic reset limits, setpoint velocity limits, or anything but the default PID structure?

The Deminar series started in April and continuing through July provides dynamic examples of how PID power can be used to reduce process variability and make batches and startups faster. In particular, the demanding and critical role of integrating processes is being revealed. We normally think of level as the primary integrating process and may dismiss the tightness of control as not important. Also statistics would say most of the loops are self-regulating. If you look closer you realize that the main reason for the large number of self-regulating loops is that the fact there are more flow loops than any other type of loop. Sure flow loops can be screwed up but auto tuners can find the right settings in matter of minutes and process control improvements can be quickly tested. What we often do not realize is that the really difficult and important loops have either a true integrating response (e.g. gas pressure and batch temperature and composition loops) or are so slow they are best treated as having a near integrating response (e.g. continuous temperature and composition loops). Furthermore, few realize that integrating processes are more sensitive to secondary lags, less than ideal valves, and have counter intuitive tuning rules. I would maintain that 90% of the loops with integrating processes are not tuned correctly and probably have too small of a reset time. The Deminar series and access to the web labs online should provide a source of exploring the opportunity to do better with these loops that matter the most. Check out the Deminar May 12 at 1:00 CDT to see how integrating loops suffer from slow valves and slow secondary loops.

To attend the event, go to http://bit.ly/JC-LiveMeeting

Use the information below to connect (if you’re not using the available computer audio):

• Toll-free: +1 (877) 771-7176

• Toll: +1 (225) 383-1099

• Participant code: 264679

(1) PID Control of Sampled Measurements (How to Eliminate Oscillations from Analyzers and Wireless Measurements with a PID Enhancement) – April 7, Wed 1:00 pm CDT

(2) PID Control of Valve Sticktion and Backlash (How to Eliminate Continual Oscillations with the “Integral Deadband” PID option) – April 21, Wed 1:00 pm CDT

(3) PID Control of Slow Valves and Secondary Loops (How to Eliminate Bursts of Oscillations with the “Dynamic Reset Limit” PID option) – May 12, Wed 1:00 pm CDT

(4) Web Lab Access and Use Instructions (How to Use Free Online Process Control Labs for Fun and Profit and Become Famous by Friday or at Least Saturday) – May 27, Thurs* 1:00 pm CDT (* – Thursday date is to avoid conflict with the World Batch Forum)

(5) PID Tuning for Self-Regulating Processes (How to Compensate for Nonlinearities in Flow and Liquid Pressure Loops) – June 9, Wed 10:00 am CDT

(6) PID Tuning for Near-Integrating Processes (How to Reduce the Tuning Time for Column and Vessel Temperature and Pressure Loops by 90%) – June 23, 10:00 am CDT

(7) PID Control of True Integrating Processes (How to Reduce the Batch Cycle Time for Temperature and pH Loops by 25%) – July 14, 10:00 am CDT

(8) PID Control of Runaway Processes (How to Improve the Performance of Exothermic Reactor Temperature Loops) – July 21, Wed 10:00 am CDT