Look up. I'm confident that if you're in a public space, you'll see at least one person looking at their mobile computing device (phone, tablet, computer), which means a human machine interface (HMI). The pandemic has only increased the expectation that we should be able to access any information we need to “do our work” from anywhere at any time.
Some of the HMI design challenges include:
- Screen size or display “real estate,”
- Form factor,
- Operating system and
- Cybersecurity.
Let’s look at how each of these affects not only your user experience but some of the challenges they present to developers.
Screen size can range from a wall panel of multiple displays integrated together down to the other end of the spectrum—a smartphone with a 4-inch display. There are different types of targeted usage and information to be displayed in either case, but how much information can be shown at one time is obviously different. The more complex part of the user interface is managing the expectation that whatever I can see on my desktop PC should also be available on my handheld device.
Form factor in this instance refers to the device itself. Whether a server or a handheld, both CPU and graphics card will affect the rate at which the interface can be updated and hence, indirectly, how much information can be displayed.
Processing power and memory also affect the available operating system options. Within the normal control system environment, the supplier can normally contain this set of options to Linux and Windows. However, if we start needing to include handhelds, then other systems such as Android, iOS and “light” versions of Linux and Windows enter the equation.
Though not a direct cybersecurity issue, securing the range of devices that will likely exist within and outside the formal operational technology (OT) system infrastructure needs to be considered. At a minimum, user authentication needs to be embedded in any user interface. Zero Trust and similar cybersecurity methods can help manage the distributed cybersecurity requirements of this and other Industrial IoT use cases.
Custom themes and dark modes
The other challenge faced by interface developers is the user expectation that features they enjoy on their personal devices should also be deployed in the OT space.
Examples of some of these capabilities that in some cases are “automatically enabled”—particularly for handhelds—are dark mode and customizable themes. Therefore, if you deploy an HMI to such a device, how the interface will look in dark mode is one new item to consider. If the user views your data during an abnormal situation in the middle of the night, will they quickly understand what's going on?
When it comes to best practices in HMI development, there's more assistance available in the standards developed by the ISA 101 committee. ISA 101 has developed two standards to help with the specification, design, implementation and management of HMIs. The original standard is being adopted as an IEC standard.
The areas covered within ISA 101's work include menu hierarchies, screen navigation conventions, graphics and color conventions, dynamic elements, alarming conventions, security methods and electronic signature attributes, interfaces with background programming and historical databases, popup conventions, help screens and methods used to work with alarms, program object interfaces, and configuration interfaces to databases, servers and networks. In other words, all aspects of HMI design.
Yes, we do have HMIs everywhere. However, the OT space has particular requirements. Fortunately, in addition to our direct experience, we have standards that we can rely on when making the difficult decisions about if or how to extend functionalities beyond their originally intended use.
