The Role of Humans in Control Systems

Humans can play a variety of roles in a control system. In the simplest cases, they create the control commands and apply them directly to the controlled process. For a variety of reasons, particularly speed and efficiency, the system may be designed with a computer between the human controller and the system. The computer may exist only in the feedback loop to process and present data to the human operator. In other systems, the computer actually issues the control instructions with the human operator either providing high-level supervision of the computer or simply monitoring the computer to detect errors or problems. 

An unanswered question is what is the best role for humans in safety-critical process control. There are three choices beyond direct control the human can monitor an automated control system, the human can act as a backup to the automation, or the human and automation can both participate in the control through some type of partnership. These choices are discussed in depth in Safeware and are only summarized here. 

Unfortunately for the first option, humans make very poor monitors. They cannot sit and watch something without active control duties for any length of time and maintain vigilance. Tasks that require little active operator behavior may result in lowered alertness and can lead to complacency and overreUance on the automation. Complacency and lowered vigilance are exacerbated by the high reliability and low failure rate of automated systems. 

The human monitor needs to know what the correct behavior of the controlled or monitored process should be however, in complex modes of operation—for example, where the variables in the process have to follow a particular trajectory over time—evaluating whether the automated control system is performing correctly requires special displays and information that may only be available from the automated system being monitored. How will human monitors know when the computer is wrong if the only information they have comes from that computer In addition, the information provided by an automated controller is more indirect, which may make it harder for humans to get a clear picture of the system Failures may be silent or masked by the automation. 

If the decisions can be specified fully, then a computer can make them more quickly and accurately than a human. How can humans monitor such a system Whitfield and Ord found that, for example, air traffic controllers appreciation of the traffic situation was reduced at the high traffic levels made feasible by using computers [198]. In such circumstances, humans must monitor the automated controller at some metalevel, deciding whether the computer s decisions are acceptable rather than completely correct. In case of a disagreement, should the human or the computer be the final arbiter  

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