SA Instrumentation & Control - Control Loop

Control Loop

Flow loops behaving badly: case history 70
April 2003, Michael Brown Control Engineering, System Integration & Control Systems Design
I have lost count of the number of times I have been told that flow loops are very simple things, that they are easy to tune, that you do not need a tuning package to tune them, that they can be tuned ...

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Filters - the great deceivers
March 2003, Michael Brown Control Engineering, System Integration & Control Systems Design
Noise on the PV signal was discussed in the previous loop signature article, and it was mentioned that it is generally better to live with the noise rather than filtering it out; provided it does not ...

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Some unusual integrating processes
February 2003, Michael Brown Control Engineering, System Integration & Control Systems Design
As mentioned in previous articles, all industrial processes fall into one of two classes of dynamics, known as self-regulating and integrating. In particular refer to Loop Signature No. 2 for a full description ...

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Control loop case history 68: control mayhem on a mine
December 2002, Michael Brown Control Engineering, System Integration & Control Systems Design
I have often written about the dearth of understanding of practical control, which is largely due to the generally purely theoretical teaching of process control at educational institutions. I have also ...

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Problems encountered in level controls
October 2002, Michael Brown Control Engineering, System Integration & Control Systems Design
This month's article deals with a few of the more difficult problems encountered in level controls. Before going into them it would be appropriate to summarise a few important points on integrating processes ...

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A depressing day in a plant with no miracles
August 2002, Michael Brown Control Engineering, System Integration & Control Systems Design
I was recently asked to optimise some loops in a petrochemical plant. Most of the time when doing this sort of work, improvements are the order of the day, and I normally go home at the end of the day ...

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Digital controllers - Part 8: The full PID controller and response to setpoint or load changes
July 2002, Michael Brown Control Engineering, System Integration & Control Systems Design
Earlier articles in this series discussed the roles played by the P, I and D sections of controllers used in industry. In this article Michael Brown talks about the manner in which these blocks may be ...

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The only magic: understanding what you are doing
June 2002, Michael Brown Control Engineering, System Integration & Control Systems Design
Optimisation of regulatory control systems is not easy. It is also time consuming and hard work. There are generally no short cuts. Many people often do not realise this, and are always seeking for a ...

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Control problem in an ammonium nitrate prilling plant
April 2002, Michael Brown Control Engineering, System Integration & Control Systems Design
In this issue Michael Brown has forwarded an interesting article submitted by Melvin Jones who graduated from the University of Pretoria as a chemical engineer. He has a keen interest in process control ...

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Problems in a plant with no positioners on valves
February 2002, Michael Brown Control Engineering, System Integration & Control Systems Design
During the two-day practical part of a course held recently in a large South African chemical plant, it was found that none of the valves had positioners on them. This is very unusual these days. The ...

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Are there problems in the control loops?
December 2001, Michael Brown Control Engineering, System Integration & Control Systems Design
Although this is appearing in the middle of the current series of loop signatures on digital controllers, I felt that it would be nice to have a change and write another article on some of the more interesting ...

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Digital controllers: Part 4 - the I term
November 2001, Michael Brown Control Engineering, System Integration & Control Systems Design
In the previous article in this series, it was shown that the main problem with the P only controller is the fact that it is not capable of eliminating offset between setpoint and process variable (PV) ...

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The case of the mysterious cycle on a paper machine
July 2001, System Integration & Control Systems Design
I, personally, find the control of paper machines extremely interesting. As in many other plants, we generally find the vast majority of the regulatory controls on the paper machines are working extremely ...

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Regulatory controls in most plants do not work properly
May 2001, System Integration & Control Systems Design
As mentioned many times in previous articles, most people's perceptions are that the basic regulatory controls are operating reasonably well in their plants. Our experience has proved time and time again ...

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