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Infrared Carbon Dioxide Sensors

Infrared carbon dioxide sensors

Systech Illinois’ carbon dioxide analyzers use the well-defined infrared principle for accurate measurement of percent levels of carbon dioxide in most industrial processes.

The infrared sensor is in a self contained unit mounted inside the carbon dioxide gas analyzer with the necessary electronics to process the signal from the sensor and display the carbon dioxide concentration on the digital display.

The theory behind carbon dioxide gas detection

A light source emits light at a very wide range of wavelengths. Only a very narrow band is visible (400-800nm). Wavelengths longer than 800nm are infrared wavelengths. Wavelengths shorter than 400nm are in the ultraviolet region of the spectrum.

Figure 1. Spectrum from a light source

When a light source is exposed to a gas stream containing carbon dioxide, energy from the infrared region of the spectrum is absorbed by the gas. The energy affects the physical nature of the carbon dioxide molecule.

A carbon dioxide molecule consists of one carbon atom and two oxygen atoms. Both oxygen atoms are chemically attached to the carbon atom by double bonds as shown here.

Figure 2. Carbon dioxide molecule

When this molecule absorbs energy, the atoms interact with each other. The absorbed energy makes the atoms vibrate and rotate. The vibrational energy and the rotational energy required from the light source is wavelength specific. Because the carbon to oxygen double bond is so prevalent in carbon dioxide, we can focus on the wavelength that causes the vibrational interaction.

Figure 3. Vibrational interaction between carbon and oxygen molecules.

The graphic above shows the interaction between the carbon and oxygen molecules when infrared light is absorbed. The carbon atom is vibrated between the two oxygen atoms.  The amount of light absorbed by the gas stream is directly proportional to the carbon dioxide content in the gas stream.

Principle of operation

When light passes through a gas stream containing carbon dioxide, the gas absorbs energy from the light at specific wavelengths. The remaining light is filtered to a wavelength specific to carbon dioxide. The amount of light remaining at the specific wavelength is measured. The amount of light absorbed is directly proportional to the amount of carbon dioxide present in the gas stream, thus enabling accurate carbon dioxide measurement.

The infrared sensor offered by Systech Illinois in the carbon dioxide detection equipment is a single beam, dual wavelength temperature compensated sensor. It incorporates an infrared lamp light source and pyroelectric detector. The gas flows through a sample cell with sapphire windows.

Principle of carbon dioxide detection

Two optical filters are mounted on the detector surface. One filter is chosen to pass the infrared light specific to carbon dioxide (measurement filter). The second filter is a reference filter. Light at a wavelength that is not absorbed by carbon dioxide passes through the reference filter. The difference in amount of light between the two filters provides the amount of energy (light) absorbed by carbon dioxide.

The signal generated by the sensor is non-linear. The signal is fed to the electronics where it is linearized and a digital measurement of carbon dioxide concentration is displayed.

Calibration of infrared carbon dioxide sensors

The sensor requires a two-point calibration. First, the carbon dioxide sensor must be zeroed. This is performed by flowing a gas without carbon dioxide through the analyzer and adjusting the zero on the analyzer.

Second, the span needs to be adjusted. A span gas containing an amount of carbon dioxide close to the concentration of carbon dioxide found in the sample gas should be used to span the analyzer. The span gas should be of known concentration and is typically available from a gas supplier.

With span gas flowing though the infrared carbon dioxide analyzer, the span should be adjusted to match the certified value.

Applications of infrared carbon dioxide sensors

The infrared analyzers may be used for measurement of carbon dioxide at any level between 0-100% in gases or gas mixtures.

The Gaspace Advance, Gaspace Advance Micro and Portamap gas analyzer are used by industrial gas producers, industrial gas users and for safety monitoring.

Application Uses

Gas Producers

Ensuring product quality either by measuring for a carbon dioxide impurity or for monitoring for carbon dioxide purity.

Gas Users

Testing of modified atmosphere in food packaging to ensure quality of gases used as production materials in the chemical industry.


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