Industrial Automation

Ultraviolet Flame Detectors

Flame detector

  • A flame detector is a fire prevention device that detects flames in the area where it is installed and sounds an alarm to warn persons nearby of the threat of fire. 
  • Furnace flame detectors are utilized in the majority of manufacturing organizations to find and stop fires. 
  • Flame detectors can react to radiant energy that is visible to the human eye or that is invisible to the human eye. Some flame detectors use a combination of both optical flame detector and flame ionization detectors
  • Flame detectors operate within certain ranges and use optical sensors to capture the incoming radiation at a specific wavelength.
  •  The flame emits electromagnetic radiation, which may be recognized at different spectral ranges like UV, IR, and VIS. 
  • There are several types of flame detectors available, including infrared flame detectors, ultra violet flame detectors, UV/IR, IR/IR, and tripe IR spectral band detectors, depending on the sensor being utilised. A cone of vision of a flame detector indicates how effectively it can detect fire. It responds more quickly to rapidly emerging fires like flammable gas and liquid but is ineffective for sluggish fires. 

Types of flame detectors

Depending on the sensing mechanism and power source, there are various types of flame detectors. The primary category of a flame detector is 

  • Based on Optics 
  • Detection of ionization current flow
  • Thermocouple Flame detection 

Because of its great accuracy, optical type flame detectors are utilized the most frequently among these three types. 

Optical type flame detectors

  1. Ultra violet flame detector 
  2. IR flame detector 
  3. IR and UV flame detector 
  4. IR/IR flame detector 
  5. Flame detector (IR/IR/IR) 
  6. Visible flame detector

Ultraviolet Flame Detector

  • One ten billionth of a meter (1000–3000 angstrom) of radiation is detected by a sensor tube in a UV detector. 
  • It is significant to remember that the sun’s UV light begins to reach Earth at 2800 angstrom. If the detector’s sensor has a broad range, the sun’s rays will cause it to activate, making it only useful indoors. 
  • Sensors having a range of 1800 to 2500 angstroms are readily accessible. Almost all flames emit radiation in this range, but the earth’s atmosphere absorbs solar radiation in this range. 
  • The UV flame detector is as a result solar blind. This feature implies that the detector can be utilized both indoors and outside. 
  • The sensor produces a series of pulses in reaction to UV light from a flame that falls within the restricted band, and the detector electronics translate these pulses into an alert output. 
  • When the wavelength is less than 300 nm, UV detectors can work. These detectors can recognize fires and explosions within 3 to 4 milliseconds thanks to the UV radiation that is produced as soon as a fire or explosion occurs.
  • False alarms can be generated by UV sources such as lightning, arc welding, radiation, and sunlight. To reduce false alarms, UV Flame detector systems usually incorporate a two- to three-second time delay. 
Ultraviolet Flame Detector
  • It is quicker and can find fires that generate light in the UV range. 
  • Although accurate, it can be affected by UV sources like the sun, welding, lightning, and solar radiation. 
  • Flame detector testers are available to assist users in securely testing the flame detector, and they should be chosen with UV flame detectors in mind. In potentially dangerous and explosive environments, UV flame detectors are utilized. 
  • In the majority of furnaces, a UV flame detector is used with a furnace flame detector to detect flames. The sensor cell typically consists of a cylindrical chamber with an I.D. of about 1 mm and a length of a few mm, with a capacity of between two and eight microliters. 
  • UV light from a source enters the sensor and travels to a photoelectric cell, where it is processed electronically before being shown on a potentiometric recorder, a computer screen, or a printer. 
  • The selectivity of the detector can be increased by placing a monochrometer between the light source and the cell to choose only light with a particular wavelength for detection. 
  • An alternative is to use a broad band light source, and after passing through the cell, let the light fall onto a diode array after being optically dispersed by a prism or grating. 
  • The detector can be tailored to only pick up chemicals that absorb light at that certain wavelength by keeping an eye on a particular diode. 
  • A UV absorption spectrum can be obtained to help identify solutes if the output from every diode is scanned. At a signal-to-noise ratio of two, the fixed wavelength UV detector has a sensitivity of approximately 1 x 10-8 g per ml. 

How does Ultraviolet Flame Detector work?

An UV flame detector is able to function because it is able to detect UV radiation that is present at the moment of ignition. The vast majority of fires give out UV radiations; hence, in the event that a flame was present, the sensor would become aware of it and produce a sequence of the pulses. These pulses would then be transformed by the detector electronics into an alarm output.  

UV Sensing: The detector contains a UV-sensitive sensor that detects ultraviolet radiation in the wavelength range of 180 to 260 nanometers (nm). Flames emit UV radiation during combustion, primarily in the UV-C range (200 to 280 nm) and partially in the UV-B range (280 to 320 nm).

Filter: To ensure the detector responds specifically to UV radiation emitted by flames, it is equipped with a filter that blocks out most visible light and only allows UV radiation to pass through. This filter helps to reduce false alarms triggered by non-flame sources of UV radiation.

Sensor Activation: When a flame is present in the vicinity, the UV detector senses the UV radiation emitted by the flames. The sensor is designed to be highly responsive to UV radiation within the specified wavelength range.

Flame Recognition: The UV detector’s electronic circuitry analyzes the UV radiation levels detected by the sensor. It distinguishes between background UV radiation and the UV radiation emitted by flames. The detector’s sensitivity and threshold settings are configured to ensure reliable flame detection while minimizing false alarms.

Alarm Triggering: If the UV detector detects a flame based on the specific UV radiation signature, it triggers an alarm signal. This alarm signal can be used to activate safety systems, such as fire suppression systems, sound alarms, or initiate emergency protocols to mitigate potential hazards.

Safety Features: UV Flame Detectors often include safety features to enhance their reliability and performance. For example, they may incorporate self-check mechanisms to verify the functionality of the sensor and internal circuitry periodically. They may also have built-in fail-safe mechanisms to ensure continued operation even in the event of power loss or component failure.

It is essential to maintain that UV flame detectors work best for spotting flames that release a lot of UV light, such hydrocarbon fires. They might not be effective in finding fires with diverse spectral compositions or low UV radiation emissions.

Advantages of the UV Flame Detectors

  • Responds to fires involving hydrocarbons, hydrogen, and metals 
  • Fast response time
  • Insensitive to solar

Disadvantages of the UV Flame Detectors

  • Will react to welding at a distance 
  • Could react to corona, X-rays, sparks, and lightning some gases and vapors will make it difficult to detect them. 
  • A large detection range in some UV sensors causes solar false alarms. 
  • The most adaptable all-purpose optical fire detector is the UV detector
  • Have ability to recognize the majority of flames which includes hydrocarbons (liquids, gases, and solids), metals (magnesium), sulphur, hydrogen, hydrazine, and ammonia.

Frequently asked Questions:

What is the difference between IR and UV flame detector?

The IR sensors monitor the infrared emission spectral band between 4.3 and 4.4 microns, which is the major radiant emission band for fires fueled by hydrocarbons, while the UV sensors detect flames produced by UV radiation.

What is meant by UV/IR Flame Detector?

In order to confirm the fire signal and reduce false alarms, UV and IR flame detectors compare the threshold signal in two ranges in a “AND” setup.

Where are UV flame detectors used?

  • Gas-powered stoves and ovens.
  • Hydrogen stations 
  • Stoves that are fueled by gas.
  • Drying and heating systems for use in industrial settings.
  • Heating systems for residential buildings.
  • Gas turbines for commercial use.

What wavelength is UV flame detector?

UV flame detector operate below 300nm 

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