Simple bar graph displays for control variables and alarm status

Graphic displays and descriptive alarm messages are useful in complex systems. However, for applications which are operated daily, hourly, and in real-time, simple and intuitive techniques are needed to maintain user attention, and reduce operator errors and fatigue. Although bar graphs have been used with process control and machine operations for a long time, the number of elements and colors have not been effectively utilized because of technology limitations and costs. This paper evaluates several man-machine interface and human behavior studies. The paper illustrates tricolor LED bar graph displays useful for representing process control variables in instruments and control systems. Various colored bar graph displays and suitable applications are described. Simple bar graphs can be more useful to represent process variables, and they can also increase operator efficiency by reducing the difficulty of digital data interpretation. They are useful to show the dynamic characteristics of process variables, such as relative change, direction of change, rate of change, frequency of change, etc, in a concise and intuitive display. In this paper an integrated bar graph display device is described which can directly interface with sensors, actuators, and micro-controllers with independent circuits, increasing the system modularity and reliability. It can provide complex bar graph display implementation functions in a small size and at a low cost