Michael Brown Control Engineering

Email: michael.brown@mweb.co.za
www: www.controlloop.co.za
more information about Michael Brown Control Engineering

Case History 192: Drum pressure cycling.
May 2024, Editor's Choice

I was asked to investigate a problem of a drum pressure control that was cycling badly in a distillation column in a petrochemical refinery. The control team had spent a lot of time trying to stop the cycle by playing with the controller tuning. All to no avail.
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Case History 187 - Integrating or self-regulating or both?
May 2023, Editor's Choice

It is vital, when optimising a control loop, to establish at the outset if the process is self-regulating or integrating, as not only do these two process types behave completely differently, but also they are tuned very differently.
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Loop Signatures 17 - How to make a bad valve into a good valve.
April 2023, Editor's Choice, PLCs, DCSs & Controllers

People often have little realisation as to how badly a faulty valve can affect the performance of the control of the loop. So how can one make a real valve with its problems into a perfect valve? The answer is simple. One makes use of a technique called cascade control, whereby a second controller is used to control the flow of fluid through the valve.
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Case history 186: Don’t always trust valve position feedback signals
March 2023, Editor's Choice, PLCs, DCSs & Controllers

I recently encountered an interesting problem in a minerals recovery processing plant. The loop in question was a gas flow control to a burner. The operators reported that the loop cycled badly in automatic, and was very difficult to control manually. The C&I technicians had tried all sorts of tunings without any improvement.
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Loop Signatures 16 - Digital controllers: Part 8: The full PID controller and response to setpoint or load changes.
February 2023, Editor's Choice, PLCs, DCSs & Controllers

The full PID controller and response to setpoint or load changes.
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Control loop case history 185: Temperature cascade control on boiler desuperheaters.
January 2023, Editor's Choice, System Integration & Control Systems Design

This is a wonderful example of how the use of a cascade flow control still allowed excellent control of the primary temperature control loop to be achieved, in spite of a valve with severe problems.
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Case History 184: Why couldn’t they tune the loops to get good control?
October 2022, Editor's Choice

This month’s article by Michael Brown covers two examples where all the tuning in the world would not have achieved good control.
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Loop Signatures 14: Digital controllers – Part 6: The D term, continued
September 2022, Editor's Choice

Why would a DCS manufacturer set a default value in the system that effectively switches one of the parameters off? It is completely senseless.
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Case History 183: Bad valve split-ranging causing problems
August 2022, Editor's Choice, System Integration & Control Systems Design

Pressure control is one of the processes that can be self-regulating or integrating, and it is sometimes very difficult to determine which type it is.
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Loop Signatures 13: Digital controllers – Part 5: The D term
July 2022, Editor's Choice, System Integration & Control Systems Design

The objective of the derivative term is to speed up the control response in very slow processes, as often encountered in some temperature controls.
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Loop Signatures 12: Digital controllers – Part 4: The I term
June 2022, Editor's Choice, System Integration & Control Systems Design

Generally, as PLCs sometimes do not handle PIDs well, I always do some tests on them to check on the operation of their control loops.
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Control loop: Case History 182 - A temperature cascade control loop that didn’t work
May 2022, Editor's Choice, System Integration & Control Systems Design

The problems encountered in a heater outlet temperature control in a petrochemical refinery were causing considerable difficulties for the operators. Here is another wonderful example of the power of cascade control, even with a really bad control element.
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