I often publish articles showing valve problems. One of the reasons is that I do not think many people understand that valves are generally responsible for 75-80% of all control loop problems. When it ...
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I was recently asked to conduct a control loop audit on a mineral extraction processing plant which was fairly old and had been acquired by new owners. A new and very modern control system had been installed ...
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I have often written about the huge advantages of using cascade control on processes with very slow dynamics. It is particularly useful when it comes to most temperature related processes, which are normally ...
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Eliakim Musikiti read one of my articles in SA Instrumentation and Control and emailed me to ask what the differences are between PLCs and DCSs. I started replying to him and then thought that it would ...
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In a recent assignment to sort out problems being experienced in a petrochemical refinery, I came across the following two examples:       Drum pressure misbehaving The first was with the control of an ...
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It still fascinates me that so many control problems are caused by poor operation of control valves. I have encountered and recorded hundreds of cases of such problems. What is amazing is that many plant ...
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I was recently asked to help with a client who treats a product in an autoclave and was complaining that they always got overshoot on a step setpoint change to holding temperature. The following is taken ...
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Control loop optimisation has always fascinated me. In most cases when I am called into a plant to sort out a problem, it is something that they have been trying to fix for a long time without success. ...
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People often battle for long periods trying to tune a controller to eliminate problems. As I have often said, one of the biggest fallacies found in plants when it comes to control is that “all problems ...
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I have come across quite a few control loops that were doing a reasonable job of control and which were in fact completely unstable, and in some cases were working much better than if the loop had been ...
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I recently wrote a Case History about control problems in a minerals extraction plant in Portugal, which was experiencing great difficulty with the control on their flotation banks. I have also written ...
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I was recently asked to advise on a bad pH control problem in a water treatment plant. A new carbonisation bay had been installed at the plant: Figure 1 shows the layout of the bay and controls. Raw water ...
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