SA Instrumentation & Control - Control Loop

Control Loop

Loop Signatures 10: Digital controllers – Part 2: Testing controller operation
January 2022, Michael Brown Control Engineering, Editor's Choice
There is a commonly held belief in control circles that all PID controllers are similar and relatively simple. This is a dangerous fallacy.

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Case History 180: Fuel gas pressure control problem
November 2021, Michael Brown Control Engineering, Editor's Choice
The problem with the pressure control was that it seemed to work intermittently and seldom got to setpoint, resulting in large and unacceptable variance on the control.

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Case History 179: Some unusual measurement and control problems
September 2021, Michael Brown Control Engineering, Editor's Choice
The example given in this article illustrates some mistakes made by the system integrators and control engineers at a metals extraction plant that used a well-known make of PLC and scada for its controls.

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Loop Signatures 8: Final control elements – Part 4: the infamous stick-slip cycle
August 2021, Michael Brown Control Engineering, Editor's Choice
An inherent phenomenon occurring in most control valves that few people are aware of is ‘stick-slip’.

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Case History 178: An over-filtered hydrogen flow loop
July 2021, Michael Brown Control Engineering, Editor's Choice
A good example that shows how lack of knowledge of the practicalities of control can result in terrible control characteristics.

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Loop Signatures 7: Final control elements – Part 3 hysteresis and deadband
June 2021, Michael Brown Control Engineering, Editor's Choice
Some of the biggest problems associated with the final control element are hysteresis and backlash.

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Loop Signatures 1: Introduction to the Loop Problem Signatures series
May 2020, Michael Brown Control Engineering, Editor's Choice
Over the years I have had many requests to write a book giving more detailed explanations of some of the problems I have encountered in my work on practical loop optimisation. I am by nature and inclination ...

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Case History 177 - Valves, valves, valves!
May 2021, Michael Brown Control Engineering, Editor's Choice
75-85% of all industrial control loop problems are caused by valve issues.

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Loop Signatures 6: Final control elements – Part 2: characteristics.
April 2021, Michael Brown Control Engineering, Editor's Choice
Feedback theory generally assumes that the process has a linear transfer function, which means that equal changes on the input will result in equal changes on the output.

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Control Loop: Case History 176 The importance of programming PLC control modules correctly.
March 2021, Michael Brown Control Engineering, Editor's Choice
Every time I work on a plant that is using a PLC and scada system for feedback control, I always first do a test on a controller module to ensure that the controllers have been configured correctly.

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Control Loop: Loop Signatures 5
February 2021, Michael Brown Control Engineering, Editor's Choice
This article outlines some of the practical problems and rules of thumb relating to final control elements, which can affect control in the real world.

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Control loop: Case History 175 Oversized valve disrupts good control
January 2021, Michael Brown Control Engineering, Editor's Choice
This article provides good insight into the dangers of using largely oversized valves, and into the importance of understanding practical control, and how your controllers work.

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Loop Signatures 4: Process dynamics – deadtime and simple lags
November 2020, Michael Brown Control Engineering, Editor's Choice
Two important dynamic factors occurring in the majority of process responses are deadtime, and the first order lag.

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Case History 174: The importance of setting up your controller properly
October 2020, Michael Brown Control Engineering, Editor's Choice
It always amazes me that so few people really understand the workings of their feedback controllers. I have met only a few who really understand the practicalities of control blocks.

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