What is the max distance an ultraviolet scanner may be placed from the flame?

• A. 24 inches
• B. 6 inches
• C. 18 inches
• D. 12 inches

Answer: (C)

Ultraviolet flame detectors rely on picking up UV emissions from the flame, and the strength of that signal drops as distance increases. To ensure reliable sensing and a fast, safe response, installers keep the detector within a limited range of the flame. The commonly specified maximum is 18 inches, which places the flame well within the detector’s sensing field and maintains a strong, detectable UV signal under typical operating conditions. If you go beyond this distance, the UV energy reaching the sensor may be too weak or obscured by ambient light, making flame detection less dependable and potentially delaying shutdown if the flame goes out or a fault occurs. For best results, the detector should have a clear line of sight to the flame and be positioned so the flame stays within its view.