“There is no such thing as information overload.
There is only bad design.”
This article aims to describe modern techniques for designing and developing human-machine interfaces (HMIs), in order to obtain improvements in the results of the process operation. The concepts apply to any SCADA system in any type of industry.
The concepts presented here are based on the research and recommendations on User-Centered Interfaces in SCADA systems made by the ASM Consortium, in the book “The High Performance HMI Handbook” by Hollifield et al. (ISBN-10: 0977896919), in the guidelines of the ANSI / ISA101.01-2015 standard (Human-Machine Interfaces for Process Automation Systems), in my investigation of the fundamentals of user interfaces area and in the practical experience of adapting this methodology to the remote control operation of Power Transmission Substations.
What you and your company can gain from this? According to a scientific test developed by the ASM Consortium, a User-Centered Interface compared to a traditional interface achieved the following results:
- Problems were detected by the operators 5 times more, before the first alarm.
- 36% Gain in success rate in completing the proposed operations.
- Operators completed the tasks 41% faster.
These are extraordinary gains that translate directly into financial benefits, safety and quality of operation, please note that these results are obtainable just by redesigning the HMI, there are no other investments.
Of course the results can vary greatly from case to case, but the benefits are quite obvious once conceived, implemented, tested and put into practice the new interface. In the practical case that I implanted, the new interface obtained an index of more than 80% of approval from the operators, which is extremely significant for the environment of the electric sector where the resistance to the change is notorious.
The importance of the subject is such and the results so concrete that it has motivated the creation of the ISA101 standard. The standard sets out recommendations and best practices that cover the entire lifecycle of the HMIs. The ISA101 standard aims to:
- Provide guidance on the design, implementation, operation and proper maintenance of HMIs that result in a safest, most effective and most efficient process control under all operating conditions.
- Improve the operator’s ability to detect, diagnose and respond appropriately to abnormal situations.
According to ISA101, Situational Awareness is classified into three levels:
- Level 1 – Be aware of what is happening in the process.
- Level 2 – Understand the current state of the process.
- Level 3 – Understand what should be the probable state of the process in the future.
One of the fundamental characteristics of User-Centered Interfaces is to empower the operator to precisely understand the present situation and to be in a good position to predict the state of the process in the near future and, thus, to have a more preventive action on the process and no longer simply respond to alarms. This is only possible by providing information, in the form of suitable visualizations, in context to the operators, when they need it, and not simply reproducing on the screen the P & ID or single-line diagrams with scattered numbers representing process measurements (traditional methodology allows reaching only Level 1 of Situational Awareness).
Structure and navigation
It is essential that the HMI be always designed with the tasks performed by the operators in mind. So there is no magic formula to create an HMI, but rather a course to pursue using some directions and guidelines as provided here or in the ISA101 standard. For each case, the list of tasks that the operators perform must be elaborated and studied and from this point on, to think about the structure and then the visualizations. For this, some methodology can be used, for example GDTA (Goal Directed Task Analysis).
Two very important aspects for the efficiency of the HMI are the hierarchical structuring of the screens and the consistency of navigation.
It is recommended that an organization be developed at levels:
- Level 1 – Overview or Area Wide Display: This display presents an overview of the general state of the system, and should include the visualization of the main functions that must be monitored by the operator, specifically the main indicators of the situation, quality, production and safety, as well as systemic alarms. This high level display is usually shown on the video wall when available. For example, in the case of the substation remote control it could be the display with the systemic view, that is, with the situation of the interconnection lines between the substations. If there is load and / or voltage control, bar graphs of the largest deviations and trend graphs built into the screen could be shown so that the future condition can be glimpsed and preventive action can be taken to avoid violations of the established limits.
- Level 2 – Process Unit or Facility Control Displays: are the set of displays, one for each control unit. For example, in the case of the electric sector, they would be the displays of each substation. In this it should be shown the situation of the main processes of the unit, also with the main measurements in visualization in the analog form and graphs of tendencies. These should be the displays that should be created first.
- Level 3 – Process Detail or Detailed Information Displays: For each unit, it shows in detail the operation of each process in the unit. It can also represent the state of the equipment that makes up the process or facilitate the execution of specific tasks. In the case of substations it could be a detailed transformer screen, ancillary services or to support the restoration process.
- Level 4 – Process Unit Support or Auxiliary Information Displays: displays that presents detailed information for equipment status and instrumentation, as well as help screens, operating instructions, diagnostics, etc. E.g.: supervisory and control architecture screens, showing the health and status of equipment and the status of communications links.
Navigation must be consistent so that the operator is never left without guidance. There must be a clear and fast way to navigate the four hierarchical levels, the links should be positioned consistently and be shown at what level you are at the moment. As a reference, you should be able to reach any screen in up to three clicks in at most 5 seconds.
The use of colors
The proper usage of colors in HMIs is one of the most important factors that define the high performance graphics recommended by ANSI / ISA101.01-2015 and several other authors.
The use of colors should be limited, because too much color makes the visualization confusing to the operator, especially in stressful situations. Alarm colors should be reserved for this function only to make it easier to identify what is most important at the right time.
The normal operating situation should be represented serenely, basically with 2D, with limited contrast and few colors. The use of 3D, complex textures, shading, gradients and excessive contrast should be avoided as they overload the visual processing of the brain, causing fatigue and slowness in understanding the situation. Bright colors and animations should also be avoided except for alarm situations.
Colors should not be the only way to represent information. This is necessary because of the fact that about 10% of men have some visual impairment for color identification. For example: it is not recommended to differentiate the type of the measurements only by the colors, it is advisable to place the unit next to the measurement. The open and closed circuit breaker representation (in the case of substation control systems) should not only be made by color: the open circuit breaker should be hollow, for example, and the closed circuit breaker should be filled to facilitate differentiation.
The background color recommended by the vast majority of authors is light gray (close to RGB 200, 200, 200). This color is considered to provide adequate contrast and causes little visual fatigue when harmonized with a well-lit environment. However, I believe it is possible, while not ideal, to also apply many of the high-performance graphics concepts even using other backgrounds, such as black, dark blue, and white.
The forehead color should provide an adequate contrast to the background, but not excessive, it can usually be in dark gray shades, with variations in the thickness for the lines and size for the texts according to the importance of the represented objects. Other colors may also be used, but restricted to a single hue, for example, in a pastel (not bright) shade of green or blue.
For alarms, it is suggested to use red, yellow, orange and violet according to priorities. Also for alarms, color should not be the only form of representation, and should be combined with shape (form) and text (triple coding).
The use of colors should be efficient, consistent and documented for all functions, across all displays. In this way the operators’ learning curve becomes quite smooth, that is, in a short time the operators learn to use the system properly. On the other hand, graphs made without criterion, require the operators to take months or even years to get accustomed and to be able to process minimally the data presented in the displays, and even after this time they will have their working memory overloaded, which can cause delay and error in decision making.
To illustrate the wrong and correct use of colors see the following pictures (source of the images: https://tinyurl.com/isa101hawrylo):
The form of representation of measurements in the HMIs is an aspect that almost always presents opportunities for significant improvements.
A measured value represented only by the number on the screen causes the need for the operator to mentally process the value to know if the value is high / low, erroneous, increasing / decreasing, or if it is close to entering the alarm range. Notice that it is common that established limits can only be checked by accessing the point data by opening the faceplate info dialog. This will burden the working memory and reduce the cognitive ability of operators. With experience, operators can become more efficient at this kind of task, but will always be overloaded in some way. Note that this overcharge is multiplied by the number of measurements presented on the screen.
To facilitate the rapid identification of the quality of measurements, it is recommended that at least the most critical measurements of the process be represented in the analog form.
See the figure below of the Star Trek series and compare with the numerical representation:
Temp = 36.5 :: Brain = 70 :: Lungs = 1.8 :: CELL RATE = 5.5 :: BLOOD = 20.0 :: BLOOD T = 8.0
Dashboards allow for a much faster identification of the health of a process, and are especially recommended in the charts belonging to levels 1 and 2 of the navigation hierarchy.
Some useful types of representation are:
- Vertical bar graph;
- Horizontal bar graph;
- Bullet chart;
- Box plot;
- Web or radar graph.
Pizza and donut graphics are not recommended for more than 2 measurements on the same chart as they do not easily allow comparison of quantities.
Gauge graphics are also not ideal because they take up a lot of space. They are often marketed because they mimic reality (skeumorphism), with the unnecessary use of shading, reflections and bright colors.
Another highly recommended form of representation is trend charts. These are very useful as they allow to identify whether the measurement is stable, or is approaching the alarm range and how quickly. Thus, the operator can act preventively in order to avoid violations and to make the process more optimized, economical and safe. These graphs should be plotted directly on the screen. A plot utility is not a substitute for this functionality.
For purely numerical representation, it is important:
- A not too prominent text color (reserve bright colors only to represent failures or alarms);
- A sans serif font, with monospaced numbers that renders anti-aliased;
- A size and contrast adequate for good readability;
- The representation of the unit of measurement next to the value in a faded color;
- That positioning be made in a coherent order;
- To avoid showing unnecessary decimal places;
- To use symbols to represent flow direction and increase / decrease in value.
Life Cycle and Documentation
Establishing a Life Cycle for HMIs is an important definition of the ISA101 standard. The Life Cycle aims to regulate all aspects of HMIs from the creation, implantation, operation and even maintenance. The Life Cycle comprises:
- System Standards: contains the rationale for the elaboration of the HMIs.
- Design: definition of functional, hardware and software aspects of HMIs.
- Implementation: creation of the HMI in the target platform and put into action.
- Operation: production phase, including maintenance and change management.
- Continuous Work Process: audit procedures and maintenance of HMIs.
The System Standards are composed of the HMI Philosophy Document, the HMI Style Guide, and the Toolkit. These components should be elaborated or revised whenever a new system is created or when significant changes in processes or systems occur.
- The HMI Philosophy Document should contain the considerations and principles to be followed in the HMI projects, bearing in mind the human aspects, best practices and functional requirements, all independently of the supplier’s software platform.
- The Style Guide goes into the functional details of the implementation and operation of the HMI, showing how the interface components should be created and how they work, and taking into account the specificities of the controlled process. This document should also be independent of the target platform. Note that this part of documentation can be reused in case of change of supplier or exchange / upgrade of the system platform. It can also be used to elaborate the specification of the HMI system in new projects.
- The Toolkit is the implementation of the basic elements, objects and templates, already on the target platform, that will serve to compose the HMI displays.
A well-grounded, thoughtful and detailed System Standards will be the foundation that can avoid many problems and save a lot of time in the remaining phases of the HMI life cycle.
In the HMI Design stage the following tasks must be performed:
- Functional, user and task requirements. It aims to identify the activities that will be carried out through the HMI.
- HMI System Design. Its objective is to define the HMI platform, interfaces, communication and controls to be performed.
- Console Design. Defines all hardware, software, and furniture to use in the solution.
- Display Design. Identifies the required displays, their content, and the navigation and hierarchy schemes.
The Implementation stage is divided into the following activities:
- Build of displays, databases, alarms and configurations.
- Build Consoles: physical construction of the operating consoles.
- Tests: tests of the displays and systems before deploying in production environment.
- Commissioning: tests in operation in the production environment.
- Training and certification of users. It is important that users are presented with the philosophical and standardization documents so that they understand the foundations of the HMI construction.
The Operation stage of the HMI comprises:
- In Service: the HMI system in operation.
- Maintenance: keeping the HMI always functional, correct, updated and optimized.
- Decommission: management of partial or total deactivation of HMIs.
The Continuous Work Process is composed of:
- Management of Change: considers the impacts of changes to be introduced in processes, tasks and functional requirements. It must guarantee the safety and effectiveness of the operation of the process.
- Audit: verification that the HMIs are being managed and maintained according to established standards.
- Validation: conference that the HMI’s meet the functional requirements, the effective accomplishment of operational tasks and the conformity of human / ergonomic aspects.
With this article I hope to have contributed to spread the modern methodology of HMI design, which can bring enormous benefits in safety, productivity and cost savings in the operation of processes in all types of industries.
Ricardo Olsen, MEng
Electrical Engineer, Masters Degree in Engineering (Federal University of Rio Grande do Sul – UFRGS/Brazil).
Areas of expertise: SCADA/EMS systems, historian systems, communication protocols, High Performance HMI, substation automation, control centers, cloud systems, information integration and visualization.
Company: DSC Systems – https://dscsys.com
XPlain SCADA@cloud service.
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