The High Performance HMI Handbook and You – Part 2
Fundamentals of HMI Design and Best Practices
In the first post of this series, we went through a brief history and the current status of the industrial HMI. We broke down the best practices of HMI design and the 7 steps for creating a High Performance HMI design. In this post, we will assess HMI design, create a High Performance HMI design philosophy—including the basic principles of the High Performance HMI Handbook—and conduct a detailed design review of some High Performance Displays.
Assessing HMI Performance
When looking to apply High Performance HMI design styles to your current system, first assess the current status of your HMI. For this process, the book presents a method adapted from the United Kingdom's Health and Safety Executive consisting of six criteria.
High Performance HMI Review Criteria:
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 confidently and 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 is required for a "B" and criteria six to achieve an "A". We highly suggest if you want to assess your HMI to pick up a copy of the book as it would be unfair for us to list everything here. Lastly, periodically reassess your HMI to make sure it continues to meet the standard you want to achieve.
Developing a High Performance HMI Philosophy and Style Guide
The best starting point is to create a living document defining your design philosophy and style guide. Here at Corso Systems, we have both our own internal principles we use for each project and adapt them to fit each of our client's needs. One of the first things we do on a project is create an agreed-upon design and style philosophy with our clients. Sometimes this is as simple determining their desired color scheme, or it can be as complex as a standardized symbol system for each piece of machinery, alarm notifications, and layout structure. We work on a case-by-case basis before setting out on an agreed upon standard. We can produce a style guide, then our project team will generate the screen designs, apply to any desired changes, or create additions to existing systems.
Creating HP HMI Standards
The book states that a standards document should apply to all DCS systems or HMIs that are being used. Since we know how difficult it can be to get everything in an existing system to meet the standard, the expectation is that the standard will be implemented slowly. Any new screens will be created in accordance to the standard. Different systems at the same facility can be addressed separately, but overall, the general High Performance HMI philosophy standard must apply to all of them. The standard will include how to properly create a High Performance HMI for the given customer. And the standard must be detailed and clear so that every designer and engineer on the project can follow it. This document should also cover the lifecycle of the HMI from design, implementation, performance monitoring, ongoing modification, and management of change. The HP HMI standards document will be applicable for both in-house developers and any contractors hired to work on the system.
Creating an HP HMI Style Guide
An HP HMI style guide should be highly detailed and include all display design aspects including layout, hierarchy, backgrounds, lines, text, objects, trends, navigation—and anything else involved with the display of information. Since multiple systems with different design capabilities may be in use, this must be addressed to so that the capabilities and limitations of each can be accounted for to adhere to the style principles as best possible. The best way to do this is to create HMI object libraries and code repositories for standardized elements on each specific system—so that they can accessed and used for any redesigns or creations. Also make sure to take regular offsite backups 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. Prevent undesirable alterations by setting a standard of who is allowed to implement changes to what objects in what systems along with a process of how to do it. This should be specifically 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. Deficiencies became apparent through accidents and in-depth analysis, academic research, research from other industries including software design and avionics. The principles have also evolved along with advances in technology and the capabilities of modem HMI systems. Overall this knowledge can be understood within three basic principles: clarity, consistency, and feedback.
Clarity
Graphics that are easy to read and intuitive to understand have clarity. HMI graphics should clearly show the process state and conditions. The elements used to manipulate the process will be clearly distinguishable and consistently implemented. The overall design is free of clutter and unnecessary detail. The graphics convey relevant information—not just data. Alarms and indications of abnormal situations are clear, prominent, and consistently distinguishable.
Consistency
Consistency is required for graphics and 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
Feedback in graphic elements, controls, and objects is consistent across all graphics and situations. Important actions with significant consequences will have confirmation mechanisms to avoid inadvertent activation. Design principles minimize user fatigue since operational personnel will be working with the screens constantly. Ultimately, the goal is simply to provide operators with the information they need in a clear and easily understood way to minimize the possibility of mistakes. The screens must 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 reaction time by providing the operator information in a 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 operators know what’s going on or 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 by through digging into ladder logic alone. But in general, these displays have severe deficiencies, and there are more effective methods of displaying information to an operator. The book states that High Performance graphics should look boring. They should optimally designed for running a process and handling abnormal conditions effectively. The graphics shouldn't be about showing off the latest in 3D shadowing, flashing animations, and whatever cool new feature was added in for the heck of it.
"Bad" Graphics 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 (KPIs) 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 a hierarchy for progressive exposure of detail
Display access requires the minimum number of keystroke or pointer manipulations
Techniques such as confirmations, validation pop-ups, and security measures are used to minimize the potential of operator mistakes
Display elements have consistent visual and color coding
Key Features of High Performance HMI Design
Some of the key features in achieving High Performance HMI graphics is knowing that data is not information. Data must be conveyed in the context where it 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.
What Else?
The High Performance HMI Handbook 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 reviewing.
What more HMI Basics? Check out the Acronyms Are Hard: HMI and PLC post
Updated - 7/7/2022