A Simplified Look At Gas Sensors

Gas Sensors are used in residential and commercial buildings that require continuous monitoring for various gas leaks

. Most modern commercial and industrial buildings use one or other form of gas detection for example: Refrigerant gas detectors in fresh produce storage units, toxic gas detectors in sewerage plants, combustible gas detectors in a manufacturing plant or volatile organic compound detectors in a science laboratory.

Depending on the type of gas and the range of detection required, one sensor technology is more suitable than others. Gas sensors are grouped by their sensitivity range and modern gas sensors fall under four main categories: Electrochemical, Semiconductor, Infrared point sensors and Ultrasonic.

What types of Gas Sensors do you get?

Electrochemical gas sensors consist of a porous membrane and a type of electrode. Gases pass through the porous membrane (which can be customised to different concentration ranges) and a current is generated by the electrode in proportion to the amount of gas optimised at the electrode. Typical gases detected include: Ammonia, Carbon Monoxide, Chlorine, Ethylene, Fluorine, Silane, Hydrogen, Nitrogen Dioxide, Oxygen, Ozone & Sulphur Dioxide.

Semiconductor sensors rely on chemical reactions which only occur when the sensor comes into direct contact with the gas. Typical gases detected include: HCFC's, CFC's, Hydrocarbons, Natural Gases and Volatile Organic Compounds.

Infrared (IR) Point Sensors exploits the fact that radiation energy is absorbed by different gases at different wavelengths. These IR sensors detect radiation passing through a volume of gas to monitor for leaks. Typical gases detected include: Products emissions such as Carbon Dioxide and flammable gases.

Ultrasonic gas sensors use ultrasonic sound level sensors to detect variations in the background noise of the monitored area. Measuring these acoustic changes allows the sensor to not only detect leaks but assess the rate of leakage. Such detection is usually used in areas which are subject to external conditions (For example outdoors where the weather dissipates gas before it can be detected or underground where a gas can be unevenly absorbed into soil air pocket.).

Because Electrochemical and Semiconductor sensors generally have to come into direct contact with the gas they generally tend to have a smaller sensitivity range than Ultrasonic and Infrared point sensors.

Locating Gas Sensors

There are two approaches to sensor location: perimeter protection or point detection. Perimeter detection works on the approach of placing sensors along the perimeter of the area that requires monitoring. Typically this would be at the centre of each wall in a room.

Point Detection refers to placing sensors at specific locations such as compressors, expansion valves, mechanical joints or cable duct trenches. It is a good rule of thumb to locate sensors no further than 1.5 meters from the point to be monitored.

Quite often a distinction is made between the physical gas sensor and the entire gas detection unit. This is because the sensor is considered to be one unit of a whole. You can setup multiple gas sensor units with different functions to one control panel and all of this would fall under the title of "the gas detection system" or the IAM (Integrated Area Monitor).

by: Carla Jack

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