Lost in our age of microprocessors is the importance and need to still operate equipment using hardwired switches mounted in panels. In some cases, these are critical controls related to safety systems that serve as a backup to microprocessor-based control. Improper operation of these panels can have significant safety, environmental and equipment integrity consequences.
Despite their importance, hardwired panels usually get very little review from a human-factors perspective. While the panel should be designed reflecting its intended use, there are some basics in panel-layout design that enhance usability. These basics involve how we humans are wired to process information. By matching the layout to our inherent processing characteristics better, an easier-to-use design is created.
Two basic techniques for improving panel layout are demarcation and hierarchical labeling. Demarcation aids information processing by breaking the interface into chunks, so that it becomes easier to process. Human short-term memory, our conscious processing, is a capacity-limited system. We can handle about seven chunks of information. Demarcation, placing boxes or lines around related items, reduces the information processing demands by allowing all of the controls and displays with the lines or box to be processed as a chunk. Hierarchical labeling aids information processing by matching the hierarchical manner in which we humans store information. Once a major section has been identified and labeled, that information need not be repeated on labels within that section or subsection. Creating master labels that eliminate the need for repetition on individual labels enables use of larger fonts to increase legibility. Information transfer, bits per square inch, is increased. Operator scan time is reduced as each label need not be inspected to place the switch or light into context as to its function and use.
Consider the case of an emergency isolation panel for a process with a highly toxic catalyst. The original design was an 8-by-16 array of push buttons. The same controls were used, even though different functions were being performed: (1) initiation of a program and (2) opening/closing of a valve. There was some minor demarcation, with the panel broken into three, albeit oddly shaped areas. Making sense of the panel requires considerable inspection to understand the controls and indicators.
