Flame Detectors

A Flame Detector is a sensor designed to detect and respond to the presence of a flame or fire, allowing flame detection. Most fire detection focuses on detecting heat, smoke (particle matter) or flame (light) – the three major characteristics of fire. All these characteristics also have benign sources other than fire, such as heat from steam pipes, particle matter from aerosols, and light from the sun. Other factors further confound the process of fire detection by masking the characteristic of interest, such as air temperature, and air movement. In some circumstances smoke and heat from fires can dissipate too rapidly or accumulate too slowly for effective detection. In these instances, because flame detectors are optical devices, they can respond to flames in less than a second. This optical quality also limits the flame detector as not all fires have a flame. As with any type of detection method its use must match the environment and the risk within the environment.

There are currently three types of flame detectors available.
These are Infrared (IR), Ultraviolet (UV), and a combination of UV and IR.

Infrared Flame Detectors

Infrared detectors have been available for many years; however, it has only been in recent times that technology has allowed for stable, accurate detection to occur. There are two types of Infrared detectors, single frequency and multi spectrum.

Ultraviolet Flame Detectors

A UV detector uses a sensor tube that detects radiation emitted in the 1000 to 3000 angstrom (one ten billionth of a metre) range. Virtually all fires emit radiation in this band, while the sun’s radiation at this band is absorbed by the earth’s atmosphere. The result is that the UV flame detector is solar blind. The implication of this feature is that the detector can be used indoors and outdoors. In response to UV radiation from a flame that falls within the narrow band, the sensor generates a series of pulses that are converted by the detector electronics into an alarm output.

Ultraviolet / Infrared Flame Detectors

A UV/IR detector consists of an UV and single frequency IR sensor paired to form one unit. The two sensors individually operate the same as previously described, but additional circuitry processes signals from both sensors. This means the combined detector has better false alarm rejection capabilities than the individual UV or IR detectors.

Typical applications are;

• Petrol transport loading terminals
• Pipeline pumping stations
• Refineries
• Aircraft hangers
• Paint spray booths
• Munitions production facilities
• Offshore drilling and production platforms