Which distance is the maximum for an ultraviolet scanner from the flame?

Which distance is the maximum for an ultraviolet scanner from the flame?

• A. 12 inches
• B. 10 inches
• C. 15 inches
• D. 18 inches

Answer: (D)

The key idea is how far a UV flame scanner can still reliably detect a flame. The scanner needs to receive enough UV photons from the flame to exceed its detection threshold. As distance increases, the flame’s UV signal at the sensor drops, so there’s a practical limit where detection becomes unreliable. For typical UV scanners used in burner safety, that maximum reliable distance is around 18 inches. At distances shorter than that, the flame is easily detected, but 18 inches represents the farthest distance at which the detector can still reliably trigger in normal conditions.

The key idea is how far a UV flame scanner can still reliably detect a flame. The scanner needs to receive enough UV photons from the flame to exceed its detection threshold. As distance increases, the flame’s UV signal at the sensor drops, so there’s a practical limit where detection becomes unreliable. For typical UV scanners used in burner safety, that maximum reliable distance is around 18 inches. At distances shorter than that, the flame is easily detected, but 18 inches represents the farthest distance at which the detector can still reliably trigger in normal conditions.