HMIs and the growing importance of operator interaction

Every design starts with a concept. From that concept, a set of considerations are spelled out by the end user.

There will be a list of functions that we want the machine to perform. From there, we might turn the mechanical designer loose on defining the assemblies that will make up those listed functions, and, from there, a frame will be designed to mount all the sub-assemblies.

Out of that work comes a list of physical devices that comprise the various sub-assemblies and, in that list, is the components that make up the controls on the system.

When we set out to design a control system, a great deal of time and effort goes into the physical devices themselves. We might start by listing all the inputs and outputs. We might further divide those into digital and analog devices because the connection to the controller will vary based on that distinction.

For modern control design, we must also consider networked devices vs. physically wired. That distinction can even be subdivided into panel- and field-mounted network devices. Suffice it to say that our control designs are complicated.

For machines and processes, the interaction between the operator and the control system has taken on a role far greater than ever before. As a result, what have evolved over time are the form and function of human-machine interfaces (HMIs).

Early in my career, the HMI was little more than a graphical mimic panel. For those who don’t remember, the mimic panel of those days was often a large panel where a picture of the process was painted on it.

Lights of various colors and sizes were used to represent the various control stations along the path of the production line. These were in great use in the automotive industry, where I spent some of my early years learning about control systems. But I also saw them in large processing plants such as petrochemical and water treatment.

As I recall, some of these mimic panels were huge, taking up an entire wall in a control room. Intermixed with all the lights, there would be pushbuttons, selectors and rotary switches, which the operator could use to remotely interact with the process.

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With the advent of graphical interface technology, the interaction with the process could be broken down into logical focus areas. While a main screen might show the whole process with colored lines to represent simple status—red for stopped, yellow for manual, green for automatic—areas of that overall screen could function as buttons to navigate into a particular section of the operation where a closer view of that focus area could be displayed in greater detail with more information and interaction available. The use of zoom and focus navigation can present the entire machine or process in great detail.

The next logical steps in the evolution and implementation of an HMI have turned it into a control, maintenance and connectivity platform. Features can now include advanced functionality, such as localized control, sliders and setpoints; high-resolution graphics and user-interface capabilities; diagnostics and maintenance tools; document storage and connectivity; VPN access and mobile troubleshooting; virtual-reality applications; distributed HMIs; and PLC-HMI combination devices.