During a project for a pulp and paper mill client, we were tasked with optimizing the water usage on a wash line. This entails feeding material into the wash line and spraying it with water to wash out undesired materials to promote a uniform consistency. There are a number of measurements used throughout the line to monitor key variables to identify the "quality of wash", etc. This process requires a complex control scheme.
This particular control scheme attempted to automate many of the things an Operator might do to actively manage the system in question. Still, there remained as always, factors outside of the control system's visibility. For such items, an effective interface for the Operator or Engineer to enter these factors into the system is required. This may be as simple as high and low limits, or as complex as the maximum rate of change for the trim ratio of a cascade loop. Our job as the enabling engineer is to design a way to present this data concisely and accurately as an integral part of the control scheme.
Take for example the following data entry section:
The basic design was made to allow the Operator the ability to check the enable box to turn the Dilution factor On or Off. Then, the Operator has two spots (the yellow numbers) where desired set points could be entered. In addition, the current mode of the controller is shown in a compact form. (For this screenshot we are in manual.) Finally, a few additional values were calculated and displayed in grey to indicate the Operator cannot enter any data.
There are a few key takeaways to point out.
At the end of the day, you need to keep two guiding principles in mind when it comes to HMI design. First, the Operator has enough on their plate already. Adding complexity and distraction with your HMI just makes things worse. Second, and most important, the Operator is the primary customer. With that in mind, do not design an interface only an engineer could love. If you will keep these goals at the forefront of your project when designing the HMI's you will end up with a happy customer... your Operator.