Monthly Archive: December 2007

Dec
28

Biggest Opportunities for Process Control Improvement – The Operator (Online Metrics)

Who is living with the process every minute? Who changes the feed rates or charges? Who changes the modes and set points of the control system? Who starts or stops batches or unit operations? In most plants, it is the operator, yet the displays and education of the operator haven’t changed much in the last …

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Dec
21

Biggest Opportunities for Process Control Improvement – Controller Tuning – Part 4

Tools are now available to identify the process dynamics and calculate tuning settings. The tools can indicate a relative speed (faster or slower) of the new tuning versus the old tuning. However, the new tuning settings depend upon the lambda factor or the desired speed chosen. Thus it is still up to the user or …

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Dec
15

Biggest Opportunities for Process Control Improvement – Controller Tuning – Part 3

The integrated error for a given unmeasured disturbance is inversely proportional to the controller gain. If you double the controller gain, you halve the integrated error. However, you need to keep the controller gain below a maximum that prevents oscillations from adverse changes in the process dynamics. The maximum controller gain corresponds to Lambda equal …

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Dec
14

Biggest Opportunities for Process Control Improvement – Controller Tuning – Part 2

Oscillations are indicative of a controller that is tuned too fast unless the oscillations are very slow or are limit cycles caused by valve stick-slip for any type of process or valve dead band for an integrating process (e.g. level). The amplitude of fast oscillations that are not limit cycles can be reduced by decreasing …

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