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Safety Critical

Flame Detector / Scanner

The "eyes" of the burner system. Flame detectors continuously monitor the combustion chamber to verify the presence of a flame, preventing fuel accumulation and explosion hazards.

How Flame Detectors Work

A Flame Detector (or Flame Scanner) is a sensor designed to detect and respond to the presence of a flame or fire. In industrial burners, they are the primary input to the Burner Controller (BMS).

If the flame detector fails to "see" a flame while the fuel valve is open, it signals the BMS to immediately cut off the fuel supply (usually within 1-3 seconds) to prevent the accumulation of unburned fuel in the combustion chamber, which could lead to an explosion.

Types of Detection Technology

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Ionization Electrode (Flame Rod)

Gas Only

Uses the principle of flame rectification. A flame conducts electricity and rectifies AC current to DC. The rod is placed in the flame edge.

Pros: Simple, low cost, fast response, fail-safe.
Cons: Contact with flame wears out the rod; ceramic insulator can crack; not suitable for oil.
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UV Sensor (Ultraviolet)

Gas & Oil

Detects UV radiation emitted by the combustion of fossil fuels. Uses a gas-filled tube that becomes conductive when exposed to UV.

Pros: High sensitivity, works with both gas and oil, compact.
Cons: Can be fooled by ignition spark (requires proper positioning); UV tube degrades over time; sensitive to background radiation (e.g. welding).
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IR Sensor (Infrared)

Oil & Coal

Detects infrared radiation (heat flickering). Modern IR sensors filter for the specific flicker frequency of a flame (10-200Hz) to distinguish it from hot refractory walls.

Pros: Can 'see' through smoke/dust/steam; distinguishes flame from hot walls.
Cons: More expensive; complex setup; requires stable flame flicker.

Common Issues & Troubleshooting

SymptomPossible CauseSolution
False Flame Signal (Flame detected when none exists)UV tube aging, external light source, hot refractory (IR)Replace UV tube; Shield sensor from sunlight/spark; Check sensitivity settings.
Flame Failure during operationDirty lens, poor ground (ionization), unstable flameClean lens; Check burner grounding; Adjust air/fuel ratio.
Weak SignalSensor misalignment, soot buildup, old sensorRe-align sensor to flame root; Clean sensor; Replace unit.

Industry Leaders

  • SiemensQRA (UV), QRB (Photoresistive), QRI (IR)
  • HoneywellC7027, C7012, C7061 (UV)
  • FireyeUV1A, 45UV5, Insight Scanners
  • DuragHigh-end industrial flame scanners
  • BrahmaCompact UV/Photocells

Related Components

Burner ControllerIgnition Transformer

Maintenance Tip

A dirty lens is the #1 cause of nuisance shutdowns. Wipe the UV/IR scanner lens with a soft, clean cloth during every service interval. Do not use abrasive cleaners.