Session Type: Paper
Paths(s): Technician Marketing Engineer Academia/R&D/Scientist
Will your control system respond correctly when an instrument fails or goes out of range? Are you using sound practices to determine and manage Bad PV settings? For many companies, there is significant room for improvement in this area. Learn about potential consequences resulting from improper Bad PV settings along with commonly made errors. Proper threshold settings, shed mode and extended range will be explained along with recommended practices to allow your control system to function as intended during Bad PV situations. This presentation is recommended for anyone involved with the determination, implementation or management of Bad PV settings in any control system.
As more and more emphasis is placed on supporting operator performance in the process industries, it is important to understand how concepts from outside process control can be used to inform improvement efforts. Developed primarily in the context of aviation and military applications, Situation Awareness (SA) is becoming a popular term when discussing monitoring in process control settings. In everyday terms, having good situation awareness (SA) just means “knowing what’s going on” around you. Based on this simple definition it's easy to agree that having good SA is (or certainly ought to be!) very important to someone operating a complex, dynamic and potentially hazardous process. But what does SA really mean? What makes it difficult to build and maintain SA in the context of process operations? What design strategies can we use to support it? This article provides some background on the concept of situation awareness and takes a critical look at how it can be used to provide a new perspective on improving process operations.
It is often said that for a cascade control system to be stable, the outer loop should be tuned for a significantly slower response than the inner loop. However, the minimum ratio of outer to inner loop response time required for stability is subject to some dispute. This paper explores the minimum response-time ratio required for cascade control systems to be stable, and the effect that process characteristics and tuning methods have on this minimum. Some surprising results regarding response-time ratios and loop stability are presented.
It has also been recommended that for cascade control to be beneficial, the inner loop in a cascade control system must respond at least five times faster than the outer loop. This paper analyzes some typical, but distinctly different, cascade control applications and evaluates their benefits. It shows that in practice, cascade control is not always applied for improving control performance and explains how cascade control is sometimes applied solely to simplify a control strategy.
The paper makes recommendations about the type of tuning methods that should be used to obtain stable, responsive cascade control systems. It also provides guidance about predicting the benefits that may be reaped from implementing cascade control on different process types.