The best of the best, Part 1

Columnists Greg McMillan and Stan Weiner, PE, bring their wits and more than 70 years of process control experience to bear on your questions, comments and problems in this month’s installment of Control Talk.

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Greg: What were your two greatest technical achievements in process control?

    

This Month's Puzzler

What Time’s the Execution?
In a simulation test on the effect of module-execution time, what is the additional dead time from the module for a disturbance added to the measurement input to a PID block in the module with the same execution time as the module?
Send an e-mail with your answer, questions, or comments to The Puzzler.


Terry: The two technical achievements with the most wide-spread applicability to which I contributed were the repeated application and demonstration of the benefits of real-time dynamic simulation for control loop checkout and operator training, and the application of a systematic approach to the design of basic distillation column control strategies.

Greg: What are the two greatest opportunities in process control today?

Terry: In my opinion, the two greatest opportunities in process control today are making intelligent use of all the process data now available with Fieldbus-based digital control systems, and choosing the most appropriate combination of classical and model predictive control methods to achieve the best-performing and most robust control loop strategies.

Greg: We conclude with the Top Twenty Sources of Disturbances


Control Talk


Top Twenty Sources of Disturbances

(20) Limit cycles (split-ranged point discontinuity, resolution and cascade dead band)
(19) Interaction between loops
(18) Slow secondary loops (cascade control)
(17) Design limits (equipment operating limits)
(16) Low residence times (e.g. undersized feed, recycle, surge and waste tanks)
(15) Manual procedures and manual valves
(14) Field switches (e.g. on-off level control)
(13) Activity (catalytic and metabolic)
(12) Ambient conditions
(11) Interlocks and sequences
(10) Raw materials
(9) Recycle streams
(8) Startups, shutdowns and product transitions
(7) Fouling (e.g. process coatings) and frosting (e.g. crystal accumulations)
(6) Parallel trains
(5)  Undersized cooling towers
(4) Bored board operators
(3)  Shift changes
(2) Initiatives
(1)  Goal reviews


  About the Authors

Greg McMillan and Stan Weiner, PE, bring their wits and more than 66 years of process control experience to bear on your questions, comments and problems. Write to them at controltalk@putman.net.
 

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