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Advanced Process Control; Is it the Operatorís Best Friend or Worst Enemy?

NEWSLETTER ARTICLE

Although advanced process control can greatly improve the efficiency of a processing unit, the benefit often comes at a price. Automation can result in operators that are distanced from the detailed operation of a system, i.e., the operator is out of the loop, thereby potentially leading to degraded performance when the operator is required to intervene during an automation failure and retake control.

One recent study (Endsley and Kiris, 1995) examined the effects of automation on operator performance. Subjects were asked to perform an automobile navigation task with varying amounts of computer assistance. The computer assistance ranged from complete computer automation of the task to manual performance of the task, with three levels in-between.

All levels that involved some type of automation experienced a simulated system breakdown halfway through the experiment. The system operators were then required to perform the tasks manually. The subjectsí performances were recorded during the experiment and the subjects were interviewed afterwards.

After reviewing the data, the experimenters found that the operators who were on some type of automated control before the breakdown responded more slowly to the remaining tasks and had a lower degree of understanding of the system status than did the subjects who were completely on manual control. The lack of awareness increased and the response time decreased on the systems with more automation. The authors speculate that this lack of situation awareness is probably due to the fact that the operators on the automated systems performed passive monitoring of the system, whereas the operators on the manual systems actively monitored their systems.

These findings, along with data from other studies and research, indicate that the main consequence of being out of the control loop is that the operator may not know or remember how to take control of the system in case of a computer failure. This has often happened on airplanes when there were system failures and the crew was so dependent upon the system that they were unable to take control of the plane, thus resulting in injuries and death.

Advanced process control can significantly lower the steady state control requirements, as determined from a study performed by Beville which found that processes on advanced control made roughly half as many controller adjustments compared to those not on advanced control. While there is no doubt that advanced control can improve daily operations, it can also make upset response more difficult because the operator is out of the loop.

To keep a processing unit financially competitive and mitigate the negative effects of advanced control, it is necessary to take an approach that involves automation, but still keeps the operator involved and their skills from degrading. Putting the operator in the loop for short periods can help, but this can be expensive as the advanced control can usually run the process more efficiently. Simulators are another option, but are they cost-effective? The best choice for today is to thoroughly plan for an upset and make certain that the displays and alarm systems of your advanced control system are configured in accordance with human factors principles.

REFERENCE: Endsley, M.A., and Kiris, E.O., (1995). The Out-of-the- Loop Performance Problem and Level of Control in Automation. Human Factors 37(2), 381-394.

Copyright © 1997 Beville Engineering, Inc., All Rights Reserved

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