An infrared gas detector uses infrared (IR) radiation to detect the presence of gases in the atmosphere. Every gas has its own IR footprint. That means that it absorbs light of a specific IR frequency or wavelength, a property that makes it identifiable when using the appropriate detector.
Gas detectors, in general, indicate the existence of specific gases in the surrounding area and measure their concentrations. They are used mainly in detecting dangerous gas leaks and concentrations that exceed safe limits, and when this is the case, they trigger some kind of alarm. A certain type, the infrared gas detector, uses infrared radiation to identify the presence of potential hazards in the nearby environment.
The main components of the infrared gas detector are the following a source of IR radiation, which can be a regular incandescent light, also known as the transmitter; IR sensors or receivers; selective spectral filters that are placed in front of the sensors; and a measurement chamber where the gas sample is being diffused. The space between the transmitter and the receiver is the optical path. The beam of light must travel through this space in order for the system to make a measurement.
In simple terms, the light source will emit light that covers a small region of the infrared spectrum, and the gas inside the measurement chamber will absorb a specific frequency or wavelength characteristic to its molecular structure. The absorbed wavelength is unique to each compound, and this property is used to identify it. The amount of the absorbed radiation is a direct measure of the gas concentration inside the chamber.
There are two main variations of the conventional infrared gas detector. In the first one, the system uses two beams of the same wavelength in the IR region of the electromagnetic spectrum that derive from the same source. One is used as a reference beam, and the other passes through the gas volume. Both beams will travel along different optical paths and — after the beams have been received by the sensors — the system will make the necessary analysis.
In the second variation, the system uses two beams of different wavelengths. These beams travel alternately along the same optical path. Both variations of infrared gas detectors have their advantages and disadvantages, depending on the user's needs.
The infrared gas detector in its simplest form is designed to detect a single gas. More complicated multi-gas detectors are also available. The detected gases might be toxic, such as carbon monoxide, or even flammable, such as methane or propane.