Plant operators have a more demanding job than ever before. Operators are now responsible for reducing costs and improving production while still keeping the plant operating safely, efficiently and profitably. They perform the bulk of these critical tasks through the “eyes” of the plant – HMIs.
HMIs (Human-Machine Interfaces) play a large role in a successful operation. However, HMIs have traditionally been overlooked or ignored as a possible area for operational improvement. Implementation of an effective HMI must consider all factors of the operator’s work environment. Poor HMIs have repeatedly been identified in the past as contributors to major industrial accidents or ongoing poor plant performance. A poorly designed HMI can put the safety of the personnel and the plant at risk and hinder rather than help the operator during abnormal conditions.
For example, in the image above, the operator has too different many interfaces (e.g. push-buttons, multiple keyboards, displays) to contend with. Situational awareness is hampered by mixture of pilot lights, freestanding monitors, panel-mount displays, and wall-mount monitors, and by poorly laid-out HMI screens. The operator is not ergonomically situated with the HMI since he is standing but monitors are not angled correctly for ease of viewing from that position. The keyboard and mouse are not easily accessible, and attempting to reach for them may cause inadvertent operation of the push-buttons. For anyone seated or of shorter stature, their view of the wall-mounted CCTV displays would be blocked by the HMI monitors. In addition, there is not enough use of effective and informative encoding of information such as sparklines, trends and other analog indicators. These Human Factors issues should be corrected in order to achieve a more effective HMI.
Studies have proven that a good HMI built with the right design principles can enable all operators, no matter what skill level, to improve plant performance by more accurately assessing situations and more quickly taking action. The key is that effective HMIs are able to transform volumes of raw data produced on the plant floor into actionable information without overwhelming the operator. Highly effective HMIs assist operators in dealing with normal and abnormal conditions by improving their situational awareness (i.e. the acute understanding of operational conditions). Thus, having a good HMI that leverages Human Factors Engineering and Abnormal Situation Management is important. Slowly companies are beginning to realize the need for more effective HMIs and the benefits this has on improving performance and reducing safety risks.
Basic HMI Design Principles
One of the primary mistakes made in the design of an effective HMI is the engineers overlook the main purpose of an HMI which is to support the operator. HMIs should always be designed with the operator’s viewpoint in mind and not to purely satisfy usage requirements of secondary audiences like managers or engineers (although these usages are important).
What are some basic design principles to ensure a good HMI? HMIs need to be:
- Intuitive: Natural and easy to use by the operator
- Concise: Brief in form but comprehensive in information
- Actionable: Operators can make changes quickly and safely
HMIs are what connect operational personnel to plant assets; therefore HMIs should be easy to use and understand. For one, HMIs should always be standardized in terms of functionality and look and feel. For example, commands and objects on a screen should act the same way in all situations. The same colours and symbols should be used to indicate the same things consistently. For ease of use, the HMI screen should have a layout and navigation that is logical and hierarchical (i.e. monitor at a higher level with aggregate information, and drill down for more detail only when needed). Operators should be able to perform functions with minimal workflows and it should be easy for them to distinguish between different processes. HMIs should look plain with dull backgrounds and minimal colour usage and animation. Only during abnormal situations should colours and animations be used to get the attention of operators. The idea is that personnel can clearly understand what is going on in far less time.
From an effective HMI, the operator should be able to get a lot of information clearly at a glance or with just a few manipulations. A good HMI should be brief in form but comprehensive in scope. All (and only) relevant information should be displayed, with the most important information being emphasized and prominent. Graphical indicators can help to condense and provide the information at a glance, without sacrificing simplicity or clarity. HMIs should also include trends, since trends communicate a lot more information than just current values. With a more concise HMI that is embedded with trends, decision making and response time can be improved.
HMIs provide a very useful function for operator command and control. Not only do they help operators visualize and understand processes, they provide current information in an interpretable format allowing a decision to be made or an action to be taken. For instance, rather than displaying hundreds of numeric values, an effective HMI will provide the information in context to indicate whether these values are good, normal or bad; whether they are getting better or worse, and how quickly. The operator can then make an interpretation quickly and provide an immediate and well-informed response to remedy or even prevent abnormal situations. With actionable information, operators become more forward-looking, taking action to reduce any negative impact before it happens.
The above mentioned are just a few pointers among a host of best practices involving HMI design. Ultimately, the outcomes of a better designed HMI are that operators have greater situational awareness, less fatigue/mistakes and faster/safer response times. All of this adds up to improved operator effectiveness and a better-running plant.
This post was written by Jonathan Long. Jonathan is the Technical Director at Cogent Industrial Technologies, a recognized leader in IT/OT solutions and project management.