Gas detection refers to the identification and monitoring of potentially dangerous gas levels via the use of gas detection monitoring systems. In this country gas detectors are made use of in a wide array of different practices to ensure the safety of those who work in the space as well as that of the general public.
These specialist devices can be found in a number of different forms so as to meet the differing demands of various gas monitoring applications.
Types of gas detectors
There are four primary types of gas detectors that are used for the purpose of detecting harmful gases – catalytic bead, electrochemical, infrared and photo-ionization sensors.
1 Catalytic Bead Sensors
Catalytic gas detectors are generally used for the measuring of combustible gases for which is the danger of explosion when the concentration is between the LEL (lower explosion limit) and the UEL (upper explosion limit). These gas detectors are based around the principle that the oxidisation of gas results in the production of heat, with the sensor being able to convert the change in temperature with the use of a Wheatstone bridge-type circuit.
One bead in a catalytic sensor is a special catalyst that is there to promote oxidation, while the other has been treated in order to inhibit the process of oxidation. Current goes through the coils to the point of reaching 500 degrees Celsius – the temperature of oxidation – to increase the resistance of the platinum coil, which leads to a bridge imbalance.
The change in resistance is directly correlated to the concentration of gas within the surrounding atmosphere, and the gas reading will be displayed on the meter or other such device.
2 Electrochemical gas sensors
Electrochemical gas sensors measure the concentration of a specific gas either by oxidising or by having the gas reduced to an electrode in order to generate either a negative or positive flow of current. These sensors are generally used for the measuring of the concentration of a specific gas in an external circuit.
Even with such a large number of different gas sensors that are available on the market, electrochemical gas sensors remain the most widely used and commonly understood.
3 Infrared gas sensors
Infrared sensors are often used as a substitute to combustible gas measurements in circumstances without the presence of oxygen or where high carbon dioxide concentrations need to be measured.
These sensors work via the principle of light absorption, whereby absorbed light intensity changes are measured in relation to the light’s intensity at a reference wavelength. The difference in the absorbed light is determined by the infrared sensor, which then reports the gas concentration coming from the absorption.
4 Photo-ionization gas sensors
Photo-ionization gas sensors use an ultraviolet light source into ionising gases into positive and negative ions so that a detector can easily identify them. Ionisation takes place when the light energy of a gas is absorbed by a molecule. Photo-ionization can measure or detect the charge of ionised gases, as the charge is a function of the concentration of VOCs (volatile organic compounds) that are found naturally in the atmosphere.
It is important to know the difference between gas detectors to ensure the right type is used for your work environment.
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