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Flame Detection

Flame Detection

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Flame Detection

Types Of Burner Flame Detectors

Flame detectors range from simple ionisation probes designed to sit at the root of the flame, through to complex microprocessor solid state flame scanners that can be ‘tuned’ to select an individual flame from several visible flames.

The radiation emitted is determined by the fuel used. As a general rule-of-thumb, gaseous fuels produce UV radiation and liquid/solid fuels produce IR. However, most fuels produce a range of emissions across both the UV & IR spectrum meaning there is crossover when deciding on which type of flame detector to use.

Maintaining Your Flame Safety System

Contamination of the detector’s lens with dust or oil also affects performance. This can be alleviated with the addition of Quartz lenses in front of the sensor or with compressed air being fired over the lens to keep it clear of contaminants. More regular servicing is also required in these environments.

Do I Need a Self Checking Flame Detector

Systems can be classed as either non-continuous or continuous operation. Non-continuous operation requires that the burner be switched off at least once every 24 hours to confirm the flame detector is able to detect both states i.e. flame in/flame out.

Some flame detectors, for example, a UV tube, may have a non-failsafe failure mode, meaning their operation needs to be verified periodically. Continuous operation can be achieved by using a device containing a mechanical shutter that allows the detector to self-check by simulation of a no flame condition.

More modern flame detectors use more sophisticated methods for self-checking. A characteristic of nearly all flames is that they flicker. This is a product of the fuel type, combustion process and mechanical design of the burner. Flicker frequency tends to increase with firing rate as a result of higher air velocity and fuel mixing at the burner head or nozzle. Flicker frequency varies along the flame path dropping off significantly towards the end of the flame. This characteristic can be used to ‘tune’ a flame detector to discriminate one flame from another in multi-burner systems or to discriminate the flame from other background radiation. These more intelligent flame detectors monitor the flicker and the self-check using software rather than mechanical operation. 

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