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Fixed Type Gas Detection Sensors

Available sensors are catalytic, infrared, methane, toxic and carpark sensors.

Catalytic

 

61-1303LC IR

 

Methane Analyser

 

iQguard

 

iQguard Toxic

Sensor-1    ir non-display-web      MethaneAnalyser-web   IQGUARD   iQguard Toxic
             

Types of Sensors

Catalytic
Infrared
Electrochemical
Semi-Conductor

The catalytic bead sensor consist of two coils of fine platinum wire each embedded in a bead of alumina, connected electrically in a Wheatstone bridge circuit. One of the pellistors is impregnated with a special catalyst which promotes oxidation whilst the other is treated to inhibit oxidation. Current is passed through the coils so that they reach a temperature at which oxidation of a gas readily occurs at the catalysed bead (500-550°C). Passing combustible gas raises the temperature further which increases the resistance of the platinum coil in the catalysed bead, leading to an imbalance of the bridge. This output change is linear, for most gases, up to and beyond 100% LEL, response time is a few seconds to detect alarm levels (around 20% LEL), at least 12% oxygen by volume is needed for the oxidation. [source]

Infrared point sensors are active measurement systems, in that they typically measure the absorption of a gas by passing it through a laser-illuminated chamber and measuring the change in transmitted signal. Infrared imaging sensors include both active and passive systems. For active sensing, IR imaging sensors typically scan a laser across the field of view of a scene and look for backscattered light at the absorption line wavelength of a specific target gas. Passive IR imaging sensors, on the other hand, measure spectral changes at each pixel in an image and look for specific spectral signatures which indicate the presence of target gases. The types of compounds which can be imaged are the same as those which can be detected with infrared point detectors. [source]

Electrochemical gas detectors work by allowing gases to diffuse through a porous membrane to an electrode where it is either oxidized or reduced. The amount of current produced is determined by how much of the gas is oxidized at the electrode. The sensor is then able to determine the concentration of the gas. Manufactures can customize electrochemical gas detectors by changing the porous barrier to allow for the detection of a certain gas concentration range. Also, since the diffusion barrier is a physical/mechanical barrier, the detector tends to be more stable and reliable over the sensor's duration and thus requires less maintenance than other types of detectors.

However, the sensors themselves are subject to corrosive elements or chemical contamination, and may last only 1–2 years before a replacement is required. Electrochemical gas detectors are used in a wide variety of environments such as refineries, gas turbines, chemical plants, underground gas storage facilities, and more. [source]

Semiconductor sensors detect gases by a chemical reaction that takes place when the gas comes in contact with the sensor. Tin dioxide is the most common material used in semiconductor sensors, and the electrical resistance in the sensor is decreased when it comes in contact with the monitored gas. The resistance of the tin dioxide is typically around 50 kΩ in air but can drop to around 3.5 kΩ in the presence of 1% methane. This change in resistance is used to calculate the gas concentration. Semiconductor sensors are commonly used to detect hydrogen, oxygen, alcohol, and harmful gases such as carbon monoxide. One of the most common uses for semiconductor sensors is in carbon monoxide sensors. They are also used in breathalyzers. Because the sensor must come in contact with the gas in order to detect it, semiconductor sensors work over a smaller distance than infrared point or ultrasonic detectors. [source]

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