Fire Detectors – Optical Flame Detectors

Optical flame detectors are sophisticated devices that use optics to see a small or a large fire far away without the heat or the smoke getting to it first. Unlike smoke or heat detectors that can only trigger an alarm when there is a smoke or intense heat, optical flame detectors are programmed to trigger an alarm or a fire suppression system when they identify a flame through its wavelength.

In this article, we are going to be looking at the various types of optical detectors and their features and application.

Types of optical flame detectors

Basically, there are four primary types of optical fire-sensing technologies. There are- Infrared detectors (IR), ultraviolet (UV), Ultraviolet and Infrared (dual), and visual flame imaging. Their operation is based on the line of sight detection of radiation that is given off by red flames and heat as shown in the visible light, IR spectral bands and UV.

Optical fire detectors are more effective than other flame detectors because they use optical sensors, working in specific ranges and accurately recording radiation at the wavelength at the chosen wavelength. The signal that is recorded by each sensor is carefully analyzed with some special techniques.

Below are a few of them:

• Flickering frequency analysis.
• Mathematical correlation and ratios between different signals.
• Correlation of stored spectral analysis.
• Threshold energy signal comparison.
• Comparator techniques.

It is important to give careful consideration to the following flame detector performance criteria’s when configuring a flame detector device.

These include:

• Self-diagnostics.
• Detection range.
• False alarm immunity.
• Response time.
• Field of view.

UV flame detectors

Ultraviolet flame detectors are special devices that effectively identifies with the use of advanced ultraviolet sensory technology. Ultraviolet detectors respond rapidly to radiation in the spectral range of 200 to 260nm at high speeds of 3.4 milliseconds. They offer quick response and sensitivity at short ranges.

Ultraviolet flame detectors can accurately detect gas fires and hydrocarbon-based fuel, silane, invisible hydrogen and ammonia. This type of detector is commonly used for indoor application and should never be exposed to ultraviolet sources like sparks, electric arcs, and welding so as to reduce false alarms.

Application

Below are some areas that UV flame detectors can be installed:

• Explosive and munitions.
• Aerospace.
• Hydrogen fuel industry.
• Warehouses.
• Hydrogen vehicle parking and refuelling.
• Pharmaceutical industry.
• Refinery.
• Power generation facilities.
• Battery charging areas.
• Paint and solvent processing factories.
• Space industry hydroxyl propellant.
• Static fuel cell systems.

Features of UV flamed detectors

Detection range for some fuel can be up to 15 meters.

Infrared flame detectors

An infrared optical detector can effectively locate flame by deploying infrared sensors to pinpoint or identify radiation with their specific spectra pattern given off by the fire.

Infrared fire detectors are perfect for locations where combustion can cause foggy or smoky fires. They can operate within the range of 60meters from a fire source with moderate speeds. They can be used in both indoor and outdoor environment. Unlike other detectors, infrared detectors are immune to radiation produced by sunlight, arc welding, lightning, and other hot materials that may be present in an industrial environment.

UV/ IR flame detectors

A dual-band flame detector is basically a combination of infrared sensors and Ultraviolet sensors sensitive to the IR and UV radiation emitted by a raging flame. IR sensors operate at a unique wavelength of 2.5 to 3.0µm and can accurately detect hydrocarbon-related fires, hydrogen, hydroxyl, as well as, the infrared portion of the EM (electromagnetic) spectrum. Continuous detection of radiant energy in the infrared and ultraviolet sensors triggers an alarm.

Infrared and ultraviolet detectors have become not only useful for detecting different types of fires but also contributing to the minimization of false alarms. UV/IR detectors use both IR and UV sensors to detect inorganic fire, hydrocarbon-related fires, and gas fires. To accurately verify the reliability of the fire signal, the Infrared threshold signal, the Ultraviolet radiation threshold signal and their flickering mode is compared. The fire alarm will be triggered only when all parameters satisfy the programmed detection mathematical algorithm. Since they are sensitive to IR and UV radiation they are somewhat immune to false alarms and can operate at moderate speeds. They are suitable for indoor and outdoor use.

Application of UV/IR detectors

Below are some areas that UV/IR detectors can be installed:

• Power generation facilities.
• Explosives and munitions.
• Aircraft hangers.
• Petrochemical plants.
• Storage tank farm.
• Pharmaceutical industry.
• Warehouses.
• Onshore oil and gas installations.
• Automotive industries.
• Offshore oil and gas installations.

Features of the UV/IR flame detectors

• UV/IR dual sensor.
• Programmable RS-485 and via HART.
• Manual and automatic built-in-test to assure continued operation.
• Quick response-200 milliseconds.

CCTV Flame detectors

Certain facilities cannot be protected alone with radiation technologies; IR3 flame detection devices can be utilized to increase the protection of such application. The reason why they are so effective is that they utilize a color video image to quickly confirm the location of a flammable threat.

Triple-spectrum optical detector utilizes a special video camera and a combination of triple infrared sensor technology to identify flames quickly. The device is immune to false alarms and it is a reliable video that gives users the window to quickly verify and react to a situation.

CCTV fire detectors use an IR3 Sensor technology designed only to respond to flickering radiation signals within the spectral bands of 4.0 to 5.0 micron, making it less prone to false alarms. The colored video camera creates a room for the operator to accurately investigate a monitored area, accurately identify the location of a fire and help select the best response to the fire situation.

Application of CCTV Flame detectors

Below are some areas that CCTV Flame detectors can be installed:

• Storage plants.
• Aircraft hangers.
• Automotive industry.
• Waste disposal facilities.
• Offshore and onshore oil and gas facilities.
• Petrochemical plants.
• Explosive and munitions.
• Printing industry.

Features of CCTV Flame detectors

• Live color video image.
• Manual and automatic built-in test.
• Sensitivity selection.
• 43,000 operational hours.
• Programmable HART and RS-485.

Final note

The various optical flame detectors that are available are designed to respond to a fire or flames within seconds. Granted, all of them are effective, but their response to flame depends on the way and manner they were installed. Since all-optical detectors are not made the same, there is a need for you to learn about their working principle and the application of each of them. While doing this might be tasking, it will help you determine the best optical detection device for your facility.

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