Infrared Flame Sensor / Infrared Flame Monitoring

Infrared Flame Sensor - Picture credit: Ingo Bartussek @ Fotolia.com

The pyroelectric detector of a flame sensor detects the typical spectral radiation of burning, organic substances such as wood, natural gas, gasoline and various plastics.

To distinguish a flame from the sun or other intense light source such as light emissions from arc welding, and thus exclude a false alarm, the following independent criteria are considered:

  • A typical flame has a flicker frequency of (1 ... 5) Hz.
  • A hydrocarbon flame produces the combustion gases carbon monoxide (CO) and carbon dioxide (CO2).
  • In addition, burning produces water, which can also be detected in the infrared range.
Infrared Flame Monitoring, welding - Picture credits: arhendrix @ Fotolia.com

For a flame sensor, the absorption bands for the burning byproducts CO & CO2 are set between 4.0 µm and 4.8 µm, and around 12 µm for water. The integrated detector cap in the infrared band-pass filters limits the passage area exclusively to the aforementioned absorption bands. By evaluating the flicker frequencies together with said spectral information of the gases, false alarms can be prevented effectively.

Pyroelectric standard detectors by InfraTec can detect a flame distance up to 100 m reliably even without additional optics. Especially InfraTec’s pyroelectric detectors in current mode with a chip size of (2 x 2) mm² or (3 x 3) mm² have a high signal-to-noise ratio and a very small popcorn noise. This allows for reliable detection.

Signal Amplification as Vital Requirement

For infrared flame monitoring used detectors work with integrated reinforcing elements. A reason for this are the very low charges generated in the pyroelectric crystal, requiring a preamplifier with extremely high input impedances of up to some 10 GΩ. Even at normal humidity of about 60% at an ambient temperature of 22 °C, such preamplifier circuits no longer work without interference. Therefore, it must be inside the sealed detector housing. Detectors without integrated junction field effect transistors (JFET) or operational amplifier (OpAmp) are hardly suitable for gas analysis or flame sensors.

Pyroelectric detectors for infrared flame sensor / Infrared flame monitoring:

  • LME-352/LME-336: single-channel, low power consumption, high sensitivity, large angle of incidence
  • LMM-244: three measuring channels, a reference channel with a high sensitivity for the accurate measurement of combustion gases



Picture credits: © Ingo Bartussek/Fotolia.com, © arhendrix/Fotolia.com

Contact

Headquarters:

InfraTec GmbH
Infrarotsensorik und Messtechnik
Dresden, GERMANY
workPhone:+49 351 871-8625

Branch offices:

InfraTec infrared LLC
Plano, TX 75024
workPhone:+1 877 797 6748

www.InfraTec-infrared.com

InfraTec infrared Ltd
Chesterfield, UK
workPhone:+44 1246 267562

InfraTec Representative for PR of China
c/o German Industry & Commerce
Greater China
Shanghai, PR of China

workPhone:+8621 68758536 ext 1633

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