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Decreasing the Cost of Control
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Автор:  san [ 13 вересня 2014, 11:45 ]
Тема повідомлення:  Decreasing the Cost of Control

Decreasing the Cost of Control
One of the most basic ways to reduce the cost of control is to reduce the number of variables. Using APC can cut down the number of loops required to run a given process, which can make every aspect of control simpler.
http://e-ditionsbyfry.com/Olive/ODE/CTL ... w=document
Цитата:
One common challenge when designing or upgrading an installation is determining how to reduce costs. There are a number of factors to be considered, including development, deployment, and maintenance costs. Although many ideas may come to mind, the possibility of using advanced process control (APC) is more easily attainable due to the power of computers and new strategies that are now feasible. But what if we reduce the number of variables to be controlled? With fewer variables, less hardware is needed, the process is simpler, and it is easier to teach to others. So, how can users reduce the number of loops to control?
Often, process control systems are composed of a number of variables coupled together . Not only is effort spent on controlling variables, but also on using “fake” controllers to decouple the variables so that single-input and single-output algorithms, like the ever-present PID, can be implemented. APC now adds the strategy to control several variables simultaneously, so there is no need for decoupling. While PID is the workhorse of the control algorithms used in industry, it has limitations. First, it is a single-input, single-output system, so control engineers have to figure out how to take information from several measuring devices and combine them into a single value that makes sense for the controller. The reverse is also a challenge: how can a controller make decisions on several control variables based on the combined inputs? The most typical approach is to design several PID controllers in parallel, but this option is not without its own challenges. Since some variables are coupled, more controllers are put in place to try to isolate those variables. The challenge that comes now is tuning all those controllers that have been placed in the plant. Although there are rules to tune PID control algorithms, it is not an exact science. In the case of multivariable controllers, it is more challenging since changing one gain will affect the behavior of not only the PID loop that is being tuned, but also all the different controllers and variables that are coupled.

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