Nondispersive infrared sensor

Last updated

A nondispersive infrared sensor (or NDIR sensor) is a simple spectroscopic sensor often used as a gas detector. It is non-dispersive in the fact that no dispersive element (e.g a prism or diffraction grating as is often present in other spectrometers) is used to separate out (like a monochromator) the broadband light into a narrow spectrum suitable for gas sensing. The majority of NDIR sensors use a broadband lamp source and an optical filter to select a narrow band spectral region that overlaps with the absorption region of the gas of interest. In this context narrow may be 50-300nm bandwidth. Modern NDIR sensors may use Microelectromechanical systems (MEMs) or mid IR LED sources, with or without an optical filter.

Contents

NDIR-analyzer with one double tube for CO and another double tube for hydrocarbons NDIR.JPG
NDIR-analyzer with one double tube for CO and another double tube for hydrocarbons

Principle

The main components of an NDIR sensor are an infrared (IR) source (lamp), a sample chamber or light tube, a light filter and an infrared detector. The IR light is directed through the sample chamber towards the detector. In parallel there is another chamber with an enclosed reference gas, typically nitrogen. The gas in the sample chamber causes absorption of specific wavelengths according to the Beer–Lambert law, and the attenuation of these wavelengths is measured by the detector to determine the gas concentration. 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 however some cross-sensitivity is inevitable. [1] For instance, many measurements in the IR area are cross sensitive to H2O so gases like CO2, SO2 and NO2 often initiate cross sensitivity in low concentrations.[ citation needed ] [2]

The IR signal from the source is usually chopped or modulated so that thermal background signals can be offset from the desired signal. [3]

NDIR sensors for carbon dioxide are often encountered in heating, ventilation, and air conditioning (HVAC) units.

Configurations with multiple filters, either on individual sensors or on a rotating wheel, allow simultaneous measurement at several chosen wavelengths.

Fourier transform infrared spectroscopy (FTIR), a more complex technology, scans a wide part of the spectrum, measuring many absorbing species simultaneously.

Research

Miniature IR sources based on microelectromechanical systems (MEMS) have been experimentally applied to NDIR systems since 2006 and is useful since 2016. The low energy of MEMS emission means a sensitive detector circuit based on lock-in amplification is needed. [4] Other useful detectors include the photoacoustic gas sensor which use a MEMS microphone to detect IR-gas interactions. [5]

Gases and their sensing wavelengths

Mid-infrared absorption spectra of some gases Mid-infrared absorption spectra of Gases.png
Mid-infrared absorption spectra of some gases

Gases do not have a specific sensing wavelength, rather there are regions of the IR spectrum where there are typically many thousands of closely spaced absorption lines. See the Hitran database for more information.

Applications

Related Research Articles

<span class="mw-page-title-main">Infrared</span> Form of electromagnetic radiation

Infrared is electromagnetic radiation (EMR) in the spectral band between microwaves and visible light. It is invisible to the human eye. IR is generally understood to encompass wavelengths from around 750 nm to 1000 μm.

<span class="mw-page-title-main">Thermographic camera</span> Imaging device using infrared radiation

A thermographic camera is a device that creates an image using infrared (IR) radiation, similar to a normal camera that forms an image using visible light. Instead of the 400–700 nanometre (nm) range of the visible light camera, infrared cameras are sensitive to wavelengths from about 1,000 nm to about 14,000 nm (14 μm). The practice of capturing and analyzing the data they provide is called thermography.

<span class="mw-page-title-main">Fused quartz</span> Glass consisting of pure silica

Fused quartz,fused silica or quartz glass is a glass consisting of almost pure silica (silicon dioxide, SiO2) in amorphous (non-crystalline) form. This differs from all other commercial glasses in which other ingredients are added which change the glasses' optical and physical properties, such as lowering the melt temperature. Fused quartz, therefore, has high working and melting temperatures, making it less desirable for most common applications.

<span class="mw-page-title-main">Spectrophotometry</span> Branch of spectroscopy

Spectrophotometry is a branch of electromagnetic spectroscopy concerned with the quantitative measurement of the reflection or transmission properties of a material as a function of wavelength. Spectrophotometry uses photometers, known as spectrophotometers, that can measure the intensity of a light beam at different wavelengths. Although spectrophotometry is most commonly applied to ultraviolet, visible, and infrared radiation, modern spectrophotometers can interrogate wide swaths of the electromagnetic spectrum, including x-ray, ultraviolet, visible, infrared, and/or microwave wavelengths.

<span class="mw-page-title-main">Near-infrared spectroscopy</span> Analytical method

Near-infrared spectroscopy (NIRS) is a spectroscopic method that uses the near-infrared region of the electromagnetic spectrum. Typical applications include medical and physiological diagnostics and research including blood sugar, pulse oximetry, functional neuroimaging, sports medicine, elite sports training, ergonomics, rehabilitation, neonatal research, brain computer interface, urology, and neurology. There are also applications in other areas as well such as pharmaceutical, food and agrochemical quality control, atmospheric chemistry, combustion research and knowledge.

<span class="mw-page-title-main">Carbon-dioxide laser</span> Form of gas laser

The carbon-dioxide laser (CO2 laser) was one of the earliest gas lasers to be developed. It was invented by Kumar Patel of Bell Labs in 1964 and is still one of the most useful types of laser. Carbon-dioxide lasers are the highest-power continuous-wave lasers that are currently available. They are also quite efficient: the ratio of output power to pump power can be as large as 20%. The CO2 laser produces a beam of infrared light with the principal wavelength bands centering on 9.6 and 10.6 micrometers (μm).

<span class="mw-page-title-main">Total organic carbon</span> Concentration of organic carbon in a sample

Total organic carbon (TOC) is an analytical parameter representing the concentration of organic carbon in a sample. TOC determinations are made in a variety of application areas. For example, TOC may be used as a non-specific indicator of water quality, or TOC of source rock may be used as one factor in evaluating a petroleum play. For marine surface sediments average TOC content is 0.5% in the deep ocean, and 2% along the eastern margins.

<span class="mw-page-title-main">Zinc selenide</span> Chemical compound

Zinc selenide is the inorganic compound with the formula ZnSe. It is a lemon-yellow solid although most samples have a duller color due to the effects of oxidation. It is an intrinsic semiconductor with a band gap of about 2.70 eV at 25 °C (77 °F). ZnSe occurs as the rare mineral stilleite, named after Hans Stille.

A carbon dioxide sensor or CO2 sensor is an instrument for the measurement of carbon dioxide gas. The most common principles for CO2 sensors are infrared gas sensors (NDIR) and chemical gas sensors. Measuring carbon dioxide is important in monitoring indoor air quality, the function of the lungs in the form of a capnograph device, and many industrial processes.

Endress+Hauser Optical Analysis, Inc. is a manufacturer of optical-based gas sensors for the industrial process, environmental monitoring and clean technology markets. The company's sensors measure the absorption of laser light at specific wavelengths to detect carbon dioxide and water vapor in industrial process control and environmental monitoring applications. Such applications include non-contact measurement of moisture, carbon dioxide, and other corrosives in the energy industry, petrochemical industry, arsenic and other impurities in drinking water (Water Quality), and airborne water vapor and other atmospheric measurements from commercial aircraft for the U.S. and International Weather Services (Atmospheric). Clean tech applications include identifying and harvesting methane (CH4) as a clean energy source, as well as mounting sensors on commercial airliners to enable real-time monitoring of weather conditions to avoid commercial flight delays totaling $1 billion per year in wasted time and fuel.

A gas detector is a device that detects the presence of gases in an area, often as part of a safety system. A gas detector can sound an alarm to operators in the area where the leak is occurring, giving them the opportunity to leave. This type of device is important because there are many gases that can be harmful to organic life, such as humans or animals.

A flame detector is a sensor designed to detect and respond to the presence of a flame or fire, allowing flame detection. Responses to a detected flame depend on the installation, but can include sounding an alarm, deactivating a fuel line, and activating a fire suppression system. When used in applications such as industrial furnaces, their role is to provide confirmation that the furnace is working properly; it can be used to turn off the ignition system though in many cases they take no direct action beyond notifying the operator or control system. A flame detector can often respond faster and more accurately than a smoke or heat detector due to the mechanisms it uses to detect the flame.

NOAA-13, also known as NOAA-I before launch, was an American weather satellite operated by the National Oceanic and Atmospheric Administration (NOAA). NOAA-I continued the operational, polar orbiting, meteorological satellite series operated by the National Environmental Satellite System (NESS) of the National Oceanic and Atmospheric Administration (NOAA). NOAA-I continued the series (fifth) of Advanced TIROS-N (ATN) spacecraft begun with the launch of NOAA-8 (NOAA-E) in 1983. NOAA-I was in an afternoon equator-crossing orbit and was intended to replace the NOAA-11 (NOAA-H) as the prime afternoon (14:00) spacecraft.

<span class="mw-page-title-main">Fourier-transform infrared spectroscopy</span> Technique to analyze the infrared spectrum of matter

Fourier-transform infrared spectroscopy (FTIR) is a technique used to obtain an infrared spectrum of absorption or emission of a solid, liquid, or gas. An FTIR spectrometer simultaneously collects high-resolution spectral data over a wide spectral range. This confers a significant advantage over a dispersive spectrometer, which measures intensity over a narrow range of wavelengths at a time.

<span class="mw-page-title-main">Infrared gas analyzer</span> Scientific equipment to analyse gas composition using absorption of infrared radiation

An infrared gas analyzer measures trace gases by determining the absorption of an emitted infrared light source through a certain air sample. Trace gases found in the Earth's atmosphere become excited under specific wavelengths found in the infrared range. The concept behind the technology can be understood as testing how much of the light is absorbed by the air. Different molecules in the air absorb different frequencies of light. Air with much of a certain gas will absorb more of a certain frequency, allowing the sensor to report a high concentration of the corresponding molecule.

NOAA-6, known as NOAA-A before launch, was an American operational weather satellite for use in the National Operational Environmental Satellite System (NOESS) and for the support of the Global Atmospheric Research Program (GARP) during 1978-1984. The satellite design provided an economical and stable Sun-synchronous platform for advanced operational instruments to measure the atmosphere of Earth, its surface and cloud cover, and the near-space environment.

Infrared open-path gas detectors send out a beam of infrared light, detecting gas anywhere along the path of the beam. This linear 'sensor' is typically a few metres up to a few hundred metres in length. Open-path detectors can be contrasted with infrared point sensors.

<span class="mw-page-title-main">NIRCam</span> Imaging instrument aboard the James Webb Space Telescope

NIRCam is an instrument aboard the James Webb Space Telescope. It has two major tasks, as an imager from 0.6 to 5 micron wavelength, and as a wavefront sensor to keep the 18-section mirrors functioning as one. In other words, it is a camera and is also used to provide information to align the 18 segments of the primary mirror. It is an infrared camera with ten mercury-cadmium-telluride (HgCdTe) detector arrays, and each array has an array of 2048×2048 pixels. The camera has a field of view of 2.2×2.2 arc minutes with an angular resolution of 0.07 arcsec at 2 microns. NIRCam is also equipped with coronagraphs, which helps to collect data on exoplanets near stars. It helps with imaging anything next to a much brighter object, because the coronagraph blocks that light.

NOAA-10, known as NOAA-G before launch, was an American weather satellite operated by the National Oceanic and Atmospheric Administration (NOAA) for use in the National Environmental Satellite Data and Information Service (NESDIS). It was the third of the Advanced TIROS-N series of satellites. The satellite design provided an economical and stable Sun-synchronous platform for advanced operational instruments to measure the atmosphere of Earth, its surface and cloud cover, and the near-space environment.

NOAA-11, known as NOAA-H before launch, was an American weather satellite operated by the National Oceanic and Atmospheric Administration (NOAA) for use in the National Operational Environmental Satellite System (NOESS) and for support of the Global Atmospheric Research Program (GARP) during 1978–1984. It was the fourth of the Advanced TIROS-N series of satellites. The satellite design provided an economical and stable Sun-synchronous platform for advanced operational instruments to measure the atmosphere of Earth, its surface and cloud cover, and the near-space environment.

References

  1. "NDIR Gas Sensor Light Sources". International Light Technologies. Archived from the original on 5 December 2012. Retrieved 9 May 2016.
  2. Title 40: Protection of Environment, Part 1065—Engine-Testing Procedures, Subpart D—Calibrations and Verifications, §1065.350 H2O interference verification for CO2 NDIR analyzers
  3. Seitz, Jason; Tong, Chenan (May 2013). SNAA207 – LMP91051 NDIR CO2 Gas Detection System (PDF). Texas Instruments.
  4. Vincent, T.A.; Gardner, J.W. (November 2016). "A low cost MEMS based NDIR system for the monitoring of carbon dioxide in breath analysis at ppm levels". Sensors and Actuators B: Chemical. 236: 954–964. doi:10.1016/j.snb.2016.04.016.
  5. 1 2 Popa, Daniel; Udrea, Florin (4 May 2019). "Towards Integrated Mid-Infrared Gas Sensors". Sensors. 19 (9): 2076. Bibcode:2019Senso..19.2076P. doi: 10.3390/s19092076 . PMC   6539445 . PMID   31060244.
  6. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 Korotcenkov, Ghenadii (18 September 2013). Handbook of Gas Sensor Materials: Properties, Advantages and Shortcomings for Applications Volume 1: Conventional Approaches. Springer Science & Business Media. ISBN   9781461471653 . Retrieved 16 April 2018 via Google Books.
  7. 1 2 3 4 5 6 Technologies, Jason Palidwar, Iridian Spectral. "Optical Filters Open Up New Uses for MWIR, LWIR Systems". photonics.com. Retrieved 16 April 2018.{{cite web}}: CS1 maint: multiple names: authors list (link)
  8. "Archived copy". Archived from the original on 2017-09-16. Retrieved 2020-01-16.{{cite web}}: CS1 maint: archived copy as title (link)
  9. Montgomery, Tami A.; Samuelsen, Gary S.; Muzio, Lawrence J. (1989). "Continuous Infrared Analysis of N2O in Combustion Products". Journal of the Air & Waste Management Association. 39 (5): 721–726. doi:10.1080/08940630.1989.10466559. S2CID   56277453.
  10. 1 2 3 "Archived copy" (PDF). Archived from the original (PDF) on 2018-02-24. Retrieved 2020-01-16.{{cite web}}: CS1 maint: archived copy as title (link)