There was a time when driving a car meant you needed to know how a car worked. If something went wrong, you needed to figure it out and fix it. You needed to be able to detect conditions and understand what they meant.
By the time I was born, cars had a dashboard full of gauges. You could see the vehicle speed, engine speed, oil pressure, engine temperature, and numerous other indicators. By monitoring these gauges, a driver could determine if something was wrong and perhaps fix it.
Last week I had a Lyft drive in a Tesla. The only dashboard component was a flat computer screen. With this screen, the driver could navigate as well as get any diagnostic information from the car. If something was wrong, a notification would appear on the screen.
This evolution in cars mirrors that that we have seen in industry. There was a time when we had to walk around and put our hands on equipment to know if something was wrong. Then we had instrumentation that gave us the information we needed to monitor. Today we have computer displays showing everything we need to know from the comfort of a control room or a remote office.
Our computer displays of the process are called Human Machine Interface (HMI). Another common acronym is User Interface (UI).
Our first industrial HMIs were obviously more rudimentary than today. They commonly consisted of a panel connected to an individual PLC or a mainframe host driving several displays. The displays were monochrome and data intensive. Any graphical capabilities were primitive.
As control systems evolved, fancy graphics became possible in an HMI. It was common to see very colorful displays with process renderings of equipment and piping, as well as trends and graphs. The HMIs were networked with the processing distributed, so that each HMI was a computer with its own processor and memory. This eliminated a single point of failure.
This was indeed an improvement, but over time some drawbacks were observed. First, the distributed processing meant that each HMI computer needed to be individually maintained. Any time new software or configuration was required, it required maintenance on every single HMI computer. This can be tedious, inefficient, and error prone. The other issue was the fatigue experienced by operators subjected to a kaleidoscope view of colors and objects on multiple HMIs. This approach to HMI overwhelmed the user with sensory inputs that may be distracting, misleading, and confusing.
Todays’ modern HMI has now evolved to systems that can be much more easily maintained and effectively used.
The ISA 101 standard is now widely adopted throughout industry for HMI design. Gone are overwhelming colors, and in come grayscale displays that only show color when there is something abnormal for the operator to notice. Commonly, the colors refer to alarm conditions. The ISA 18.2 standard addresses proper alarm management so that operators are not overwhelmed and can focus on the most critical alarm conditions. These standards have gone a long way toward operating industrial processes more effectively.
For maintenance, the system design has in some ways gone backwards. Instead of having each HMI with its own processor and memory, industry has widely adopted thin clients. This allows low-cost displays to be deployed that individually require little to no maintenance. The processing occurs in a server that can centrally manage displays. Software upgrades and configuration can easily be performed at the server without having to do anything at the thin client. If a thin client has a hardware failure, it can be replaced with another thin client at low cost and with little effort. It seems a bit odd that the old idea of a mainframe driving every HMI seems to be the new standard, but in this case the processing at the field level is distributed while it is only the HMI that is being centralized. Redundant servers address the reliability of a thin client system.
Another maintenance enhancement is the use of virtual machines. This prevents a software application being held hostage by an antiquated piece of hardware and operating system. A virtual machine has all the attributes of an actual computer and operating system other than a hardware dependency. The machine runs in a virtual environment on an actual piece of hardware. The advantage is that when that hardware needs to be replaced, the virtual machine is just moved and redeployed to the new hardware. It is also very helpful for system redundancy, in which a virtual machine can be automatically switched over to another piece of hardware when there is a failure.
One aspect of HMI that seems to have gone backwards is the concept of a single window. When I began in industry, there was a clear separation between a Distributed Control System (DCS) and a Quality Control System (QCS). This meant that an operator used the DCS HMI for everything in the mill except for the final quality measurement and control. The operator had to view and interact with the QCS HMI to ensure the basis weight, moisture, and other quality measurements were on target in the machine direction and cross direction. The DCS and QCS displays looked, operated, and behaved differently, so the operator had to be trained on each one. There was a demand in the paper industry to have the DCS be the single window to the process. I was very involved in the development of this, and we had several mills adopt this single window. This allowed the operator to do everything from the DCS HMI. Today, it appears most mills have independent DCS and QCS systems again.
A consideration in today’s HMI is whether we have lost connection with the process. In the days of walking around and putting our hands on equipment and piping, we may have had a better understanding of how to fix what is wrong. Like the cars we drive today that we typically do not have the skill or tools to maintain on our own, processes have become more remote. However, in many ways we know much more about our processes than ever before. A modern HMI can provide much more insight about the process, not only on specific equipment or unit operations but on the entire operation. It can be argued that we are much more connected today because we have insight that could not be detected through manual inspection.
In the Industry 4.0 era we can become enraptured with technology and esoteric concepts. However, the way we view and interact with the process cannot be overlooked. The HMI is our eyes on the process.
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