Fundamentals of HMI Design and Best Practices
In the last post of this series we went through a brief history and the current status of the HMI. We broke down the best practices of HMI design and the 7 steps to creating a High Performance HMI. In this post we will start applying those into how to assess HMI performance, creating a High Performance HMI design philosophy, the basic principles of the High Performance HMI, and detailed design of the High Performance Displays.
Assessing HMI Performance
When looking to apply High Performance HMI design styles to your current system the first thing you must do is assess the current status of your HMI. To do this the book presents a method adapted from the United Kingdom’s Health and Safety Executive consisting of six criteria.
- The operators find it easy to keep track of the process in normal conditions.
- Information about the process and plant conditions is adequate for operators to be confident they can effectively monitor abnormal or upset conditions. The critical measure of an operator information system is how well it performs when the demands are greatest – in an abnormal situation.
- During a abnormal, upset, or emergency condition, the operators can keep track of the process using only the HMI, without a burdensome and distracting need to gather relevant information from multiple control room displays, logbooks, procedure manuals, etc.
- During abnormal situations, the unit’s managers, engineers, and supervisors must not interrupt the operator by manipulating the operator’s displays, or even worse, making their own adjustments to the process.
- Non-operating tasks are not required of the operator during upset or abnormal conditions. Whenever there are critical process activities demanding the operator’s attention, there must be no unnecessary tasks, duties, or disturbances.
- The HMI must meet all of the major criteria contained in the assessment checklist in Appendix 2 regarding:
- General graphic factors
- Navigation factors
- Workstation factors
- Control room and work practice factors
- Alarm management factors
These six criteria are used to grade the display on a A-F scale. Meeting criteria one, two, and three allows you to move beyond an “F” to “D”. Criteria Four must be met to achieve a “C”. Criteria five to achieve a “B” and criteria six to achieve an “A”. I highly suggest if you want to assess your HMI to pick up a copy of the book as it would be unfair for me to list everything here. Lastly you would want to periodically reassess your HMI to make sure it continues to meet the standard you want to achieve.
The Development of a High Performance HMI Philosophy and Style Guide
The best thing to get started is to create a living document that defines your design philosophy and style guide. Here at Corso we have both our own internal principles that we try to use for each project we do along with adapting those to fit that of our client’s needs. So one of the first things we do as we get started is to create an agreed upon design and style philosophy with our clients.
Sometimes this is just simple as their desired color scheme or can be as complex as creating a standardized symbol system for each piece of machinery, alarm notifications, and layout structure. It becomes a case by case basis but overall by setting out with an agreed upon standard you can produce a guide with which you can judge your designs from and apply to any desired changes or additions.
The book addresses this by saying the document must create a standard that should apply to all DCS systems of HMI that are being used. Knowing that the difficulty of getting everything to meet this in an existing system it is expected to be implemented slowly but any new screens must be created to its standards. Knowing that there may be different systems each one can be addressed separately but overall the general High Performance HMI philosophy setup within must apply to all.
It should be, simply put, a document that cover how to properly create a High Performance HMI. A guide to doing things correctly so that no designer or engineer, with the best intentions, should have an issue following it. This document should also cover the life cycle of the HMI from design, implementation, performance monitoring, ongoing modification, and management of change. Applicable both in-house and for use of any contractors hired to work on the system.
The style guide be highly detailed and include all display design aspects including layout, hierarchy, backgrounds, lines, text, objects, trends, navigation, and anything else to be involved in the display of information. Since multiple systems may be in use with differing design capabilities this must be addressed to so that each ones capabilities and limitations can be accounted for and adhere to the style principles as best possible. The best way to do this is to create HMI Object Libraries and code-repositories so that it easier to have standardized elements for each specific system that can accessed and used for any redesigns or creations. Also make sure that regular offsite backups are taken to prevent the horror of lost HMI source code.
Lastly one of the most important pieces of this document would be the Management-of-Change practices. Setting a standard of who is allowed to implement changes to what objects in what systems along with a process of how this should be done should prevent any undesirable alterations. This should specifically be considered to prevent the modification of elements that are in the process of being incorporated into displays so that the standard is uniform across all of them.
Basic Principles for High Performance HMIs
Over time more has been learned about what creates a good industrial HMI design versus bad. A lot of this comes from deficiencies made apparent through accidents and in-depth analysis, academic research, research from other industries including software design and avionics, and advances in the technology and capabilities of modem HMI systems. Overall this has been shown to be three basic principles: clarity, consistency, and feedback.
Clarity can be found in graphics that are easy to read and intuitive to understand. Ones that clearly show the process state and conditions. The elements that are used to manipulate the process are clearly distinguishable and consistently implemented. No unneeded clutter and detail. They convey the relevant information and not just data. Information has a prominence based upon relative important and that alarms and indications of abnormal situations are clear, prominent, an consistently distinguishable.
Consistency found through graphic functions that are standardized, intuitive, straight forward, and involve the minimum number of keystrokes or pointer manipulations. The HMI is set up for navigation in a logical, hierarchical, and performance-oriented manner.
Feedback in graphic elements, controls, and objects is consistent with all graphics and all situations. Important actions with significant consequences will have confirmation mechanisms to avoid inadvertent activation. Design principles are used to minimize user fatigue since operational personnel will be using the screens constantly.
Ultimately the goal is simply to provider the operators with the information they need in a clear and easily understood way to minimize the possibility of mistakes. To keep their attention drawn to the most critical information. Confusion and mistakes can be eliminated through consistent, easy to read, intuitive design elements with proper feedback. This ultimately helps optimize the reaction time by providing the operator information in simple, logically progressive, and performance-oriented HMI display structure.
Good HMI vs Bad HMI – The Showdown
One of the hallmarks of bad HMI design is the process pictorial. The P&ID was never meant to be the basis for an HMI. More often than not you will find overly complex screens with unnecessary symbols littered with live values that don’t help operate know whats going on and how to address abnormal situations. Sometimes, when done well, it will have proper places and uses. More often than not a P&ID display screen can help maintenance debug issues that can’t be solved through digging into ladder logic alone. But in general it has severe deficiencies in many areas and there are more effective methods of displaying information to the operator.
The book states that High Performance graphics should look boring. It should optimally designed for running a process and handling abnormal conditions effectively. It shouldn’t be showing off the latest in 3D shadowing, flashing animations, and whatever cool new feature was added in for the heck of it.
“Bad” Graphic At A Glance:
- No trends
- Big flashing flames or other animated graphics
- Brightly colored vessels with 3D shadowing and 3D process lines and pumps
- Spinning agitators and pumps, moving conveyors, splashing liquids
- Detailed depictions of non-changing internal elements of equipment
- Attempted color coding of process piping with their contents.
- Measurement units spelled out in bright, big text
- Liquid levels in bright colors displaying the full width of the vessel
- An exact representation of the P&ID with minor connections and valves
- Lots of crossing lines
- Process flow from left to right, right to left, top to bottom, and bottom to top.
- Alarm-related colors on non-alarm related elements
- Limited, haphazard navigation from screen to screen
- Inconsistent color coding
High Performance Graphics:
- Depiction of process status and values are made in the context of information
- Important information and Key Performance Indicators have embedded trends
- Animation is only used to highlight abnormal situations.
- Gray backgrounds used to minimize glare along with generally low contrast depiction
- Limited use of color and alarm colors are restricted to display alarms and nothing else (No red means off and green means on)
- Equipment is depicted in a simple 2D low contrast manner without 3d-shadowing or highlights
- Layout is consistent with the operators mental model of the process
- Logical and consistent navigation methods utilize are hierarchy for the progressive exposure of detail
- Display access requires the minimum number of keystroke or pointer manipulations
- Techniques are used to minimize the potential of operator mistakes including confirmations/validation popups and security measures
- Display elements have consistent visual and color coding
Some of the key features in achieving High Performance Graphics is knowing that data is not information. Data must be conveyed in the context with which is makes sense. It doesn’t matter if the furnace is 1200 ˚F if you don’t know the operating range should be 900 – 1100 ˚F. The best way this can be shown is with is using graphics like a moving analog indicator showing where the optimum range is and when it is abnormal. Trends, sparklines, and radar charts can help show these operational statuses and help predict when a process may be moving into an abnormal range by creeping out of the optimum operating level. When the value is nearing out of range or has hit a high or low limit alarm indicators and colors can be used to highlight this and quickly bring it to the operators attention.
The book goes into a lot more detail about various situations, color schemes, and layouts. It is really worth reading because I cannot provide all the information here in a way that would do it justice without making this long blog post much longer. Also the short and sweet page on the Ignition documents page is worth checking out. So as part of the next post we will really dive into Detailed Design of High Performance Displays and touch more on some of those subjects and lead into Design and Implementation of a High Performance HMI.
What more HMI Basics? Check out the Acronyms Are Hard: HMI and PLC post