Use of Color
Colors are an important consideration when designing a high performance HMI where gray-scale colors are used instead of the traditional bright red, green, and blue colors.
The person that designs the HMI must understand the diverse audience that may view the HMI. For example, an operator may look at a motor on a traditional HMI. If it the HMI has colored the motor green, the operator may conclude that the motor is running. However, if a maintenance technician looks at the same motor, he may conclude that the motor is not faulted. These are logical conclusions. They reflect the respective interest of the person viewing the HMI where the operator wants the motor to run and the maintenance technician wants it to be working.
In reality, the motor is simply "scheduled" to run, meaning when it runs depends on its control mechanism. For example, the motor may run when there is product on the line or boxes on the conveyor. In other words, the motor may be periodically starting and stopping automatically.
A high performance HMI can eliminate this confusion by introducing a color that signifies a state of "scheduled." A common high performance HMI practice is to use a dark gray to signify a "scheduled" state for equipment. This color should never compete with more alerting colors that "pop" from the HMI resulting in the viewer's eye's being drawn to the portion of the HMI where the problem may be occurring.
Colors and Alarm Indicators
Color can play an important role in how an operator responds when problems do occur. High performance HMI design refrains from coloring equipment when the equipment is in a state of fault. For example, some equipment may still run when faulted. Instead, an optimized solution is to place an alarm indicator near the equipment in such a way that when the equipment is undergoing some fault, the alarm indicator renders with the appropriate color and shape. The object and the consequential color should signify the most important alarm state occurring for the equipment at that current time.
Technical Considerations with Colors
Some HMIs in industrial settings may temporarily lose their ability to render color because of various environmental factors. High performance HMI design incorporates this possibility by encouraging the use of descriptive text with color. For example, motors of two different colors may look the same on a color deficient HMI resulting in confusion for the viewer. Even worse, the viewer may misinterpret the motor state and assume everything is fine. However, if each motor has a descriptive text such as "Motor 1 is Faulted" and "Motor 2 is Running", the problem associated with a faulty HMI failing to display color is largely reduced by the HMI's high performance design.
Accommodating Color Blind Viewers
Common color combinations such as red and green and blue and purple cannot adequately be distinguished by those with color blindness. High performance HMI design accommodates color blind uses by combining colors with descriptive text as well as incorporating alarm indicators in unique shapes.