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.

Problems

• 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!
    
  
  

Solutions

• 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