Chemical Processing - December 2007 - (Page 22)

2007 Software improveS controller performance >> Simple but powerful oop-Pro Product Suite Version 4.5 provides plants with an easy-to-use tool to check and enhance the performance of controllers. While the software incorporates highly sophisticated process modeling and tuning routines, it follows a simplified recipe-based procedure that suits it for use by operators as well as technicians. Most plants heavily rely on proportional-integral-derivative (PID) control. Getting proper performance from such control loops plays a crucial role in achieving smooth, safe L plants usually have far more operators than engineers and they are an untapped resource. and efficient operation. This usually requires the efforts of control engineers or other specialists. However, such staff often are in short supply and have lots to do, hampering their ability to give adequate attention to many control loops. Other engineers on site generally can’t pick up part of the burden because they learned little about control theory in college. There is an untapped resource, though. Plants usually have far more operators than engineers — one estimate is that there’re 25 operators for every engineer at a typical petrochemical plant. But most operators typically only have a high-school education and so can’t use conventional control loop diagnostic and tuning tools. The Loop-Pro Product Suite provides a simplified way to apply PID diagnostics and tuning best-practices. It enables operators to conduct thorough analyses of underperforming PID loops, compare potential changes to tuning parameters, and quickly and consistently optimize loops based on simulated PID controller performance and the associated process stability, while validating each step involved in the tuning (Figure 5). Moreover, tuning is tailored to the plant’s particular setup — operators customize the controller parameters based on the site’s distributed control system (DCS) or programmable logic controller (PLC) and unique control objective. The recipe-based procedure involves 5 steps: 1. Open a data file; 2. Select and edit data; 3. Choose a model; 4. Fit the model to the data; and 5. Specify a controller. 22 • December 2007 Figure 5. Graphical representations make it easier for operators to understand control loop performance. A lot of effort has been directed at making the software easy to use. For instance, just by moving a slide bar, an operator can alter the balance between controller robustness and speed of response, with the corresponding change in simulated performance visible in real time. Stability is represented graphically, easing interpretation of data and the handling of non-linearity and time-variant systems. Color-coded alerts draw attention to potential stability issues. Descriptive statistics and robustness values are updated and displayed automatically. Just by moving a slide bar, an operator can alter the balance between controller robustness and speed of response seeing the results in real time. The software provides a complete matrix of PID controller configurations, including P-only, PI, PID and PID with filter. An extensive library of pre-programmed DCS and PLC algorithms reduces the chance of miscalculation and eases the customizing of controller parameters. Automated PID tuning reports simplify the documentation of analysis and recommendations, and can include user’s observations and other details. CP www.chemicalprocessing.com http://www.chemicalprocessing.com

Table of Contents Feed for the Digital Edition of Chemical Processing - December 2007

Chemical Processing - December 2007 Contents From the Editor ChemicalProcessing.com Field Notes In Process Energy Saver Compliance Advisor 2007 Vaaler Award - The Quest Ends Take Equipment Diagnostics to a New Level Better Bellows Boosts Blending Process Puzzler Plant InSites Equipment & Services Product Spotlight/Classifieds Ad Index End Point

Chemical Processing - December 2007

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