The Roadmap to Thoughtful, User-Centered Screen Design to Facilitate Productive, Safe and Profitable Industrial Operations.
For a long time, it has appeared that touch panel and SCADA screen design was almost an afterthought in automation projects. Many man-hours could be spent on the process design and PLC/DCS code and then be let down by a poor operator interface that didn’t maximise the system’s potential.
At the end of the day, the primary function of a HMI is to enable the operator to run a plant with maximum safety and efficiency. The HMI should be a mechanism for providing the operator accurate information, assisting normal plant operations, as well as detecting and correcting problems BEFORE they happen, especially in plants where safety is critical.
Upon walking into a plant, you would typically find a plant mimic closely based on P&IDs using fancy 3-D pipes, tanks and valves with many process variables inundating the user with too much information. You will find many SCADA systems with 20 or 30 process variables on one screen and only a highly trained operator would know how far out of spec those values are. Fancy graphics and colour palettes that delight the development team only serve to distract the operator from the important tasks at hand.
Simple, minimalistic graphics with critical information displayed in a manner that allows operators to quickly identify potential problems should be the aim of every HMI.
Delivering the right information to the right operator at the right time for their appropriate action requires the use of user-centred design principles. For example consider:
- Instead of just placing a value on a screen, try using graphical indicators that show how far the process values are from their alarm limits. This allows the operator to immediately identify a problem before process is shutdown by an alarm.
- Small, embedded trend windows (Sparklines) for critical process values can give a snapshot into the rate of change, transforming raw data into meaningful information to assist operators’ decision making.
- Colours should be clearly defined at the start of the project with no more than 3-7 typically used. Plant objects such tanks, pumps, valves, etc. should not be the prominent focus of the operator’s attention and photo realistic representation is unnecessary.
- Simple, plain coloured objects are all that is required to avoid drawing attention away from the really important information.
- Light grey backgrounds with black text give the best clarity and enable operators to focus on the information more quickly than dark backgrounds and bright text.
- Simple, intuitive navigation. Avoiding a top down structure where many clicks are required to reach a desired screen.
Instigating change to HMI systems can be difficult with operators and management often entrenched in doing things the way that they have been used to for many years but the benefits of a successful HMI system can be numerous: increased productivity, better quality, improved safety, fewer plant incidents that may damage equipment, to name a few.
The High Performance HMI Handbook by Bill Hollifield, Dana Oliver, Ian Nimmo and Eddie Habibi (PAS, Houston, 2008) is an easy read. It is also a comprehensive and detailed reference work covering the background, the principles and best practices for display design. We recommend this handbook as a great introduction to thoughtful, user-centred screen design for productive, safe and profitable industrial operations.