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Oct
12

Dead Time Compensator Myth Buster

Deadtime is the deadliest attribute of a control loop. Without deadtime I would be out of a job. Perfect control would be possible. The integrated error is proportional to the deadtime squared. The controller gain could be infinite since the maximum controller gain is inversely proportional to deadtime. Fortunately, for process control engineers there is always deadtime in a loop. Even if the process deadtime was zero, the automation of the system by the use of valves, measurements, and a DCS controller introduces deadtime into the loop since these devices do not have an instantaneous response. The only loop I have seen with zero deadtime was in a simulation in a university paper. The model had a single process time constant. The researcher was proud of performance he could attain by his special tuning not realizing there was no limit to controller gain and loop performance. I could have doubled his gain and got double the performance. I could have quadrupled his gain and gotten quadruple the performance.

The consequences of deadtime naturally have lead to various attempts to eliminate the effect on control loops. Again fortunately for me it would take Scotty with warp drive to accelerate the control system to the speed of light altering space and time to eliminate deadtime. The quest has been the subject of over 1000 papers and articles. A lot of wishful thinking has lead to a lot of myths. Since I have no research or product to sell, my goal is to sort fact from fiction and to learn and share some concepts.

Deminar #10 at 10:00 am CDT on Oct 13 shows a simple deadtime compensator and the opportunities and limits to increasing control loop performance. The results are surprising.

To join us live, visit 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

Like the rest of the deminar series, there will be a recorded video available as well as the PowerPoint slides from the session. I’ll post a review with the embedded versions of these once they’ve been produced and uploaded. We look forward to having you join us!