In safety critical applications where oxygen is being measured, oxygen analyzer reliability is vital. The advantages of tunable diode laser (TDL) analyzers are leading to their increased use in the chemical industry; however, the accuracy of some TDL systems is influenced by hydrogen in the gas, while others are not affected. In a new white paper, Mettler Toledo explains which is which.
Tunable diode laser (TDL) oxygen gas analyzers are growing in acceptance across the chemical and petrochemical industries.
Their low maintenance demand, absence of sample extraction and conditioning requirements, tolerance to dust and moisture, and in situ measurement make them highly attractive in many applications.
There are two commonly used signal processing techniques employed in oxygen TDL analyzers: wavelength modulation spectroscopy (WMS) and direct absorption spectroscopy (DAS).
Both, unlike alternative gas measurement technologies, are immune to cross-interference effects caused by other gases in the process - except if large quantities of hydrogen are present.
In these situations, TDL analyzers that use WMS will often report incorrect oxygen levels, whereas analyzers using DAS are unaffected by the presence of hydrogen.
This is because WMS systems have to rely on compensation algorithms, which include assumptions such as a non-varying hydrogen concentration, which is usually not the case.
This distinction is important where the analyzer is being used in safety critical applications, as erroneously low oxygen readings are associated with an increased risk of explosions.
In a new white paper, "The Influence of Hydrogen on the Performance of TDL Analyzers", Mettler Toledo explains why TDL oxygen analyzers with WMS are susceptible to hydrogen and why those with DAS are not.
According to the paper's author, Jean-Nic Adami, Head of Gas Process Analytics at Mettler Toledo, "In oxygen measurement applications where safety is paramount, you must be certain of the oxygen level in the process. DAS-based TDL sensors give you that assurance."
The white paper is available at www.mt.com/o2-gas.