Product Catalog
Application of Mid-Infrared LED and Photodiodes
Many important gases and liquids have strong absorption lines in mid infrared spectral range. Different materials have different absorption spectra. Radiation from the source passes through the sample cell. The radiation not absorbed by the sample is then detected and the ratio of this to the incident provides a measure of the concentration of target gas in the sample. A second channel tuned to a different wavelength that is not attenuated by any species likely to be present in the sample is normally used to provide this reference measurement.

Range of Applications

Control of technological processes, such as

- Paper industry (water in paper control, paper thickness control)
- Oil and petroleum industry (detection of water concentration in oil and oil products)
- Thickness testing (thickness of plastic, glass bottles)
- Pharmaceutical industry

Medical diagnostics, such as

- Out-breath control (measurement of carbone dioxide, acetone concentration)
- Non-invasive control of glucose in blood
Ecological monitoring, examples:

- Control of carbone dioxide, carbone oxide, exhaust gases in the atmosphere
- Control of methane, propane leakage
- Control of hydrocarbons in water

Food industry and agriculture, such as

- Control of water, fiber, protein concentration in grains, humidity control of coffe beans, corn
- Control of fat and protein in milk

Absorption Bands

Although the spectra are the characteristics of the molecules, in a number of cases they overlap. The frequency of the fundamental vibrations varies with the atomic weight of the constituents. Further spectra exist due to overtones. These are in general much weaker, but there are still possibilities for these to be used for measurement purposes. The absorption strengths also vary with different molecules, so that different path lengths should be provided to obtain adequate absorption in the required sensitivity range. Small measuring cell can be an advantage, notably when rapid response is needed (such as in medical applications).

Wave length Unit: mm

CH4 (methane)
1.65; 2.30;

CO2 (carbon dioxide)
2.00; 2.65;

H2O (water)

N2 (nitrogen)

C2H2 (acetylene)

HOCl (hypochlorous acid)

HCl (hydrogen chloride)

NH3 (ammonia)
2.27; 2.94

C2H4 (ethylene)

HBr (hydrogen bromide)

OH (hydroxyl radical)

NO+ (nitrogen oxide cation)

C2H6 (ethane)

HI (hydrogen iodide)

H2CO (formaldehyde)

HNO3 (nitric acid)

CH3Cl (methyl chloride)

H2S (hydrogen sulfide)

CO (carbon monoxide)

HF (hydrogen fluoride)

OCS (carbonyl sulfide)

HCN (hydrogen cyanide)

HO2 (hydroperoxy radical)

SO2 (sulfur dioxide)

N2O (nitrous oxide)

NO2 (nitrogen dioxide)

C3H8 (propane)

C6H12O6 (glucose)
2.12; 2.27; 2.32

Samples of Application Notes

Carbon dioxide detection

Carbon dioxide has a wide range of commercial uses, from the production of lasers to the carbonation of soft drinks. This gas has become a topic of interest because it is classified among the greenhouse gases, gases which impact the Earth's environment when they reach high concentrations in the atmosphere. Carbon dioxide has the main absorption band at 4200-4300 nm. So, we recommend using light emitting diode LED43 and PD43 series photodiode. See CO2 Detection for more informotion.

Methane detection

Methane is produced by many natural and human-influenced sources. There are several different techniques of methane detection. We offer method of mid-infrared optical absorption based on LED-PD optopair. Methane has the main absorption band at 3200-3400 nm. Weaker absorption bands that can be used for detection are located around 2300 nm and 1650 nm. So, we recommend using:
- for compact measuring cells and/or for detection of low CH4 concentrations: light emitting diode LED34 and PD36 series photodiode;
- for long-path measuring cells and/or for high CH4 concentration detection: light emitting diode LED23 and PD24 series photodiode. See CH4 Detection for more informotion.

Paper moisture measurement

One of the key parameters of paper manufacturing is paper moisture. It is important to know the amount of moisture on every stage of paper manufacturing in order to control the technological process. There are several different techniques of water detection. We offer method of optical absorption based on mid-infrared LED-PD optopair. Water has the main absorption band at 1800-1950 nm. So, we recommend using light emitting diode LED18 or LED19 as a measuring LED, LED22 as reference LED and PD24 series photodiode to detect signals from the both emitters. See H2O Detection for more informotion.

Plastic thickness measurement

Due to constant increase of plastic production and rise of quality requirements it becomes inevitable to use reliable and efficient quality control systems. Thickness measurement is based on the Beer's law which states that intensity of transmitted light exponentially depends on thickness of material. See Plastic thickness measurement for more informotion.

Water in crude oil measurement

Water measurement in crude oil and petroleum products is an actual task for the petrochemicalindustry. The regular control of water concentration in oil well allows field operators to judge about the well performance and regulate the oil extraction process. In time water measurement in petroleum products helps to avoid costly breakdowns with loss of revenue. We offer our mid-infrared LED-Photodiode (PD) optopairs for development of water meters based on the optical absorption principle. See Water-in-oil measurement for more informotion.

For more information, please send email to sales@microsensortech.com

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