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Operator Interface Terminals (OITs)

What is an OIT?

An Operator Interface Terminal (OIT) is a special type of HMI. It is a panel-mount display which is usually smallish (4-10") and is often installed outdoors at an equipment location rather than in a control room.

This presents problems that other HMIs don't face.


  • Extreme Weather
    • Heat, cold, rain, snow and dust

  • Direct Sunlight
    • Sunlight washes out colors and dulls contrast
    • Screens degrade over time and colors fade

  • Small Display Size
    • Small text is very difficult to read outdoors
    • Differences in color are hard to detect
    • Operators in the field rarely have reading glasses!


  • Purchase Equipment Rated for Outdoor Locations
    • NEMA 4X, minimum

  • Protect Display from Sunlight
    • Mount External Cover over OIT
      • Protects display from degradation
      • Creates more contrast

  • Optimize Application for Small Size
    • Where possible, use a minimum 10" screen size and 12 point font
    • Use high-contrast colors, e.g. white on black, dark blue on light grey
    • Test the application outside before deploying it
      • Screens that look fine indoors may be completely unreadable outdoors
    • Mount the terminal below head height so the reflected sky is not visible in the display