HMI Philosophy | Development of High-Performance HMI

Welcome back to our series of High-Performance HMI. In the previous installments, we covered the current state of HMI’s and justification of change to High-Performance HMI as well as the Fundamentals of High-Performance HMI and High-Performance HMI standards. In this installment of the series, we are going to talk about the basic High-Performance HMI working principles and the Development of High-Performance HMI Philosophy.

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Main principles of HMI philosophy

HMI analog indicators

When developing a High-Performance HMI, one of the main principles is the use of moving analog indicators with a moving pointer instead of only a numerical display.

The analog indicators display the range of the instrument being displayed, and in that range will be an indicator of the normal process limits.

Above and below the indicator will be white bands indicating abnormally high and low process values respectively.

Above and below the white bands are dark gray bands which indicate High High and Low Low process values.

At a quick glance of a second or two, the operator will see the pointer position and will be able to determine the operating status of the process and be able to move on to the next process.

HMI trends

A High-Performance HMI uses another very powerful and useful tool which is the trend. Making trends available in all HMI applications is important, but in High-Performance HMI, making access to trend data should be a top priority in your design.

Remember, a High-Performance HMI is designed for the operator, and all available information should be easy to access for every operator.

When developing trends for display, they should be implemented with certain characteristics and capabilities. For instance, when a trend graphic is called by an operator, the Y-axis of the trend should be automatically ranged to a predetermined scale which is often not the full scale of the value.

Having a tight scale will make any meaningful change immediately detected by the operator. The trend screen should give the operator the capability to alter the timebase and ranges without the requirement of keystrokes, making use of dragging the cursor to re-range.

HMI colors

The proper use of color in a High-Performance HMI is fundamental to its design. In many industrial HMIs, color was improperly used or overused. In a High-Performance HMI, color is strategically used and applied consistently across the entire project.

Starting with the background color, a High-Performance HMI utilizes a light gray. The use of light gray will address the problems with glare, contrast, color interference, and operator fatigue. Generally speaking, the ideal background color is Gray 3 or Gray 4.

These are the hex and RGB codes for these background colors:

Gray 3 => Hex: #dddddd  => RGB: 221, 221, 221

Gray 4 => Hex: #c0c0c0  => RGB: 192, 192, 192

We’ll create a new video about the high-performance HMI color codes in the near future and discuss the exact color codes you need to use in designing your HMI.  

Foreground colors should be kept to a minimum and used sparingly. For instance, process lines and tanks should be black, with more attention to line thickness.

Color should not be used to indicate process material, such as using white for steam, green for demineralized water, and pale blue for ethylene. Using color to depict processes usually cannot be consistently applied in practice and proves to be a distraction.

Remember, color is used in High-Performance HMI to indicate an abnormal situation, and is meant to draw the operator’s attention quickly. If the process is running normally, then the screen should display little or no color at all.

HMI process lines

When creating lines, vessels, and static equipment it is important to show them correctly. For instance, process lines should be dark gray or black, with line thickness or weight used to differentiate their significance. The main process lines should be 3 pixels in width and secondary lines should be 1 pixel in width.

The use of arrows to depict process flow direction should be kept to a minimum, and primarily used where lines intersect or tee off from each other.

When you are using different line styles such as solid, dotted, and dashed, they should be limited to a maximum of three styles with the same line thickness.

HMI process vessels

Process vessels should be two-dimensional and not three. The vessel exterior should be outlined in a thin black or dark gray line and the vessel interior should be shaded without gradients and should be uniform in color.

You can depict an overall vessel shape, but not get into too much detail. The vessel size should be relative and in proportion to the other vessels around it.

Any internal components of a vessel should not be animated and there should not be any cut-away drawings showing vessel internals.

HMI process flow and navigation

The process flow is very important when it is depicted on High-Performance HMI. The process flow should be consistent in layout across all screens of a High-Performance HMI.

General considerations for process flow are that it should flow from left to right, vapors should flow up and liquids should flow down.

In some instances, pumps and compressors can affect the depiction of vapor and liquid flow.

Process lines should enter and exit the screen consistently as well. Entry and exit points are also navigation targets and should be shown as a different object than a non-navigation link label.

Static texts and live data

Static text on displays should be minimized, but not eliminated. Some general rules for displayed static text are that the text should be dark gray and a simple font that is easily displayed on an LCD screen.

When you are using abbreviations, the abbreviations must be consistent across the entire project.

Use larger text to identify duplicated equipment like multiple pumps

And when you have isolated words, titles, and equipment designations the text should all be uppercase.

Live data should be depicted differently than static text. The use of a bold dark blue for live data is a good choice against the gray background and the dark gray static text.

If live data is shown in a table, align the numbers on the decimal point and do not display leading zeros.

When required, the units of measurement are displayed in lower contrast and adjacent to the live data value.

While there are more details in developing a High-Performance HMI, the information we presented here should give you a very good idea of how a High-Performance HMI should look and how it gives information to the operators.

By following these guidelines, you will be more efficient and productive in your design, and give the operators the best information available to them.

Summary

Ok… let’s review what we have learned in this article:

– Use analog indicators with a moving pointer instead of a numerical display

– Access to trend data should be a top priority in your design

– Grayscale is preferred over multiple colors

– Screens should display correct process flow, left to right

– Text should be consistent across the entire HMI project

– Line weight or thickness is more important than color

We recommend checking the following related articles, if you haven’t already, to have a better understanding of High-Performance HMI Philosophy:

What is High-Performance HMI? (Part 1 of 4)

High-Performance HMI Design Basics (Part 2 of 4)

▶ Development of High-Performance HMI Philosophy (Part 3 of 4)

Detailed Design Principles of High-Performance HMI Display (Part 4 of 4)

If you have any questions about High-Performance HMI Philosophy or about HMI working principles in general, add them in the comments below and we will get back to you in less than 24 hours.

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