Infrared point sensor: Difference between revisions

Revision as of 15:41, 22 January 2008

Latest revision as of 04:48, 7 May 2025

(31 intermediate revisions by 22 users not shown)

Line 1:

{{Short description|Point gas detector}}

A '''infrared point sensor''' is a point [[gas detector]] based on the [[nondispersive infrared sensor]] technology.

{{more citations needed|date=April 2025}}

An '''infrared point sensor''' or point infrared (IR) detector is a type [[gas detector]] that uses infrared absorption at specific wavelengths to detect changes in gas composition in air.<ref>{{Cite web |author=Editorial Staff |date=2017-03-31 |title=Point IR Detectors Vs Open Path IR Detectors |url=https://instrumentationtools.com/point-ir-detectors-vs-open-path-ir-detectors/ |access-date=2025-04-09 |website=Inst Tools |language=en-us}}</ref> Gases that can be detected include hydrocarbons, allowing infrared point detectors to be used in safety applications to detect the presence of flammable gases at low levels and shut down equipment as needed to prevent fire or explosion.

==Principle==

Dual source and [[Passive infrared sensor|dual receivers]] are used for self compensation of changes in alignment, light source intensity and component efficiency. The transmitted beams from two [[infrared]] sources are superimposed onto an internal [[beam splitter]]. 50% of the overlapping sample and reference signal is passed through the gas measuring path and reflected back onto the measuring detector. The presence of combustible [[gas]] will reduce the intensity of the sample beam and not the [[reference beam]], with the difference between these two signals being proportional to the concentration of gas present in the measuring path. The other 50% of the overlapped signal passes through the beam splitter and onto the [[compensation detector]]. The compensation detector monitors the intensity of the two infrared sources and automatically compensates for any long term drift.

The main components are an [[infrared]] source (lamp), a sample chamber or light tube, a [[wavelength]] filter, and the infrared detector. The gas is pumped (or [[diffusion|diffuses]]) into the sample chamber, and gas concentration is measured electro-optically by its [[Absorption (electromagnetic radiation)|absorption]] of a specific wavelength in the infrared (IR). The IR light is directed through the sample chamber towards the detector. The detector has an [[optical filter]] in front of it that eliminates all light except the wavelength that the selected gas molecules can absorb. Ideally other gas molecules do not absorb light at this wavelength, and do not affect the amount of light reaching the detector.

As many gases absorb well in the IR area, it is often necessary to compensate for interfering components. For instance, [[carbon dioxide|CO₂]] and [[water (molecule)|H₂O]] often initiate cross sensitivity in the infrared spectrum. As many measurements in the IR area are cross sensitive to H₂O it is some times not possible to analyse for instance [[sulfur dioxide|SO₂]] and [[nitrogen dioxide|NO₂]] in low concentrations using the infrared light principle.

The IR [[signal processing|signal]] from the source is usually chopped or modulated so that thermal background signals can be offset from the desired signal.

[[Mean time between failures]] may go up to 15 years.

Line 12 ⟶ 10:

==Micro heaters==

Micro [[Heating element|heaters]] can be used to raise the temperature from optical surfaces above ambient to enhance performance and to prevent condensation on the optical surfaces.

==Range==

[[Toxic]] gassesgases are measured in the low parts per million ([[Parts- per notationmillion|ppm]]) range. Flammable gassesgases are measured in the 0 - 100 % [[lower flammable limit]] (LFL) or [[lower explosive limit]] (LEL) range.

==See also==

* [[List of sensors]]

* [[Maintenance-free operating period]]

* [[Service life]]

== External links ==

* [[ATEX directive]] II 1G EEx ia IIC T6

*[http://www.fs-business.com/FAQ/FAQGasDetection.asp#What%20are%20the%20requirements%20for%20all%20point%20detection%20methods? Point detection]

* [[Infrared gas analyzer]] - for gas monitoring and analysis, rather than leak detection.

==References==

{{Reflist}}

[[Category:Gas sensors]]

{{engineering-stub}}

{{chem-stub}}