DISPLAYS FOR COMPLEX SYSTEMS - KNOWING A FEW CONCEPTS CAN IMPROVE THEIR QUALITY

NEWSLETTER ARTICLE

Creating displays for complex systems, such as chemical processing units, can be a perplexing task. The quality of the displays created is largely dependent on the designer's awareness of underlying concepts and principles of display design. Knowing some of the underlying concepts will help prevent bad displays from being created. A concept which is unknown by many display designers is the concept of lapping. Simply stated, lapping refers to the correspondence between two sets of objects.

The "goodness" of a control display is largely determined by the closeness of the lapping between the controller operation and the machine's functions. Take, for example, the steering wheel of an automobile. Turning the steering wheel to the right causes the car to veer to the right. There is a direct relationship between the controller's and the machine's actions, which is reflected in a high degree of lapping. The direction of the controller movement (steering wheel turned to the right) laps directly onto the machine's movement (car veering to the right). If there is a high degree of lapping between the controller's action and the machine's output, then it is easy for a person to construct a conceptual model and correctly control the machine.

In Norman's example cited in a separate article ("Can a Control System be Operated Correctly if the User Has an Incorrect Conceptual Model?"), he could not figure out how to set the controls of his refrigerator because there was poor lapping between the controller operations and the refrigerator's functions.

A better design for the refrigerator's controls might lap the basic functioning of the refrigerator (cold air production and direction) as well as the system constraints (minimum, and maximum cooling and direction) onto the operation of the controller.

The concept of lapping can be extended to displays for advanced control systems. Just as a car driver does not need to be shown the entire steering mechanism to develop a conceptual model which will allow him to steer the car, displays for advanced control systems do not have to show the operator exact wiring schematics for him to use the control system. With the limitations of current display systems, the display representation would probably be far from exact. However, the displays do have to be done correctly. With an advanced control display, the relationships between the advanced control program and the system's constraints need to be mapped onto the display.

Copyright 1993 Beville Operator Performance Specialists, Inc., All Rights Reserved