During an infrared survey of overhead power components, the insulator is about 7 inches in diameter and the closest you can get to the disconnect is 100 feet. Which detector resolution and lens are recommended?

• A. 320x256 detector with a 9mm lens
• B. 1280x1024 detector with a 35mm lens
• C. 640x512 detector with a 19mm lens
• D. 640x480 detector with a 12mm lens

Answer: (C)

In infrared surveying, you must match detector resolution and lens focal length to the target size and distance so the object is sampled with enough pixels to read temperatures and notice defects. The insulator is 7 inches across and you’re 100 feet away, so the image of that insulator will be relatively small in the frame. You want enough pixel detail across the insulator to see temperature variations and surface features, but you also need a field of view that keeps the whole object in frame without zooming in so much that you lose context or framing flexibility.

A 640x512 detector with a moderately sized lens like 19 mm hits that balance well. It provides enough pixels across the insulator at that distance to discern temperature differences and possible hotspots, while the 19 mm focal length gives a practical field of view to frame the insulator and adjacent components without requiring you to get closer than allowed. The other options either sacrifice detail (low-resolution detector) or over-zoom or under-zoom (very long or very short focal lengths) in this working setup, making it harder to reliably evaluate the component from 100 feet.