How do halogen leak detectors work
In the case of halogen leak detection, the system is charged with halogen gas
Halogen leak detectors work by sensing the presence of halogen gases such as chlorine, fluorine, or bromine. When these gases are detected, the device emits an audible or visual alarm to alert the user.
There are different types of halogen leak detectors:
- Those that use a heated diode sensor
- or an infrared sensor to detect the gases
What is the halogen diode principle?
Gaseous chemical compounds whose molecules contain chlorine and/or fluorine - such as refrigerants R12, R22 and R134a - will influence the emissions of alkali ions from a surface impregnated with a mixture of KOH and Iron (III) hydroxide and maintained at 800 °C to 900 °C by an external Pt heater.
The released ions flow to a cathode where the ion current is measured and then amplified (halogen diode principle). This effect is so significant that partial pressures for halogens can be measured down to 1·10-7 mbar.
Whereas such devices were used in the past for leak testing in accordance with the vacuum method, today – because of the problems associated with the Chlorofluorocarbons (CFCs) – more sniffer units are being built. The attainable detection limit is about 1·10-6 mbar·l/s for all the devices.
Equipment operating in accordance with the halogen diode principle can also detect SF6. Consequently these sniffer units are used to determine whether refrigerants are escaping from a refrigeration unit or from an SF6 type switch box (filled with arc suppression gas).
What is the infrared principle?
An infrared leak detector uses the physical property of molecules being able to absorb infrared radiation. The test gas, which is taken in by the sniffer line, flows through a cuvette which is exposed to infrared radiation. The infrared-active gases (refrigerant) inside the test gas absorb a part of the infrared radiation and thus modify the primary infrared signal. The modified infrared signal is detected by a sensor, processed, and then displayed. The detection limit lies at around 5·10-5 mbar·l/s.
Due to continuous measuring of the ambient air, the background level of the test gas is automatically taken into account during the calculation of the measuring value.
Principes fondamentaux de la détection de fuites
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