Lew Gordon

AT A GLANCE

• Machine control
• Robots
• Machine vision
• Open architecture
• Signal conditioners

Using language rules to address control issues was borne of the need to deal with problems that resisted precise mathematical definition for one reason or another. Also, the traditional control technologies of basic regulatory control (BRC) and advanced regulatory control (ARC) discussed in the previous installments assume the availability of robust signals from field transmitters to provide the needed measurement values. But these signals are not always available, and the information they provide may be insufficient.

In addition, the absolute values of process variables are not the only key issue that must be considered. Rates of measurement change can be more important. SometimesCONTROL ENGINEERING China版权所有, the value or measurements have to be considered in relation to other conditions. Boolean logic states that conditionswww.cechina.cn, such as whether process equipment is running or not, can be important. Proper control system operation also can depend on time of day, cleaning and maintenance控制工程网版权所有, and other activities. Also, not all errors are equally important. Deviations in one direction may call for a weak or slow response, while deviations in another direction may require a strong or rapid response.

The bottom line is that a control problem can require several conditions to be considered in logical combinations. And all issues mentioned above can be difficult to express mathematically. In such casesCONTROL ENGINEERING China版权所有, rule-based control can sometimes provide an advantage.

Rules, algorithms

At their core, dist