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A Helium analyzer is an instrument used to identify the presence and concentration of helium in a mixture of gases. In
/ref> A typical thermal helium analyser comprises two chambers, each with an identical thermal conductivity sensor. One chamber is sealed and is filled with pure helium as the reference gas, and the other receives the sample gas. The difference in thermal conductivity of the reference and sample gases is measured and converted into a concentration value by the electronic circuitry in the instrument. The system is inherently stable and when precise temperature compensation is made, the system is more than adequately accurate for
A Helium analyzer is an instrument used to identify the presence and concentration of helium in a mixture of gases. In Technical diving
Technical diving (also referred to as tec diving or tech diving) is scuba diving that exceeds the agency-specified limits of recreational diving for non-professional purposes. Technical diving may expose the diver to hazards beyond those normally ...
where breathing gas mixtures known as Trimix comprising oxygen
Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as ...
, helium
Helium (from el, ἥλιος, helios, lit=sun) is a chemical element with the symbol He and atomic number 2. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas and the first in the noble gas group in the periodic table. ...
and nitrogen
Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...
are used, it is necessary to know the fraction of helium in the mixture to reliably calculate decompression schedules for dives using that mixture.
Thermal conductivity principle
Portable instruments for the analysis of helium content of breathing gas mixtures may be based on a thermal conductivity sensor ( katharometer). These sensors can be very stable and maintenance free and also highly reliable and accurate.Thermal Conductivity Sensors/ref> A typical thermal helium analyser comprises two chambers, each with an identical thermal conductivity sensor. One chamber is sealed and is filled with pure helium as the reference gas, and the other receives the sample gas. The difference in thermal conductivity of the reference and sample gases is measured and converted into a concentration value by the electronic circuitry in the instrument. The system is inherently stable and when precise temperature compensation is made, the system is more than adequately accurate for
breathing gas
A breathing gas is a mixture of gaseous chemical elements and compounds used for respiration. Air is the most common and only natural breathing gas, but other mixtures of gases, or pure oxygen, are also used in breathing equipment and enclosed ...
analysis. Accuracy and display precision is typically within 0.1%, and accuracy within 1% is considered sufficient for most decompression algorithms.
The thermal conductivity of nitrogen and oxygen are very similar, and that of helium very different so that the ratio of oxygen and nitrogen in the mix is relatively unimportant, and need not be compensated. This allows a direct reading of helium fraction from these instruments. However, for greater accuracy and compensation to oxygen cross-sensitivity, some instruments include an oxygen cell
An electro-galvanic fuel cell is an electrochemical device which consumes a fuel to produce an electrical output by a chemical reaction. One form of electro-galvanic fuel cell based on the oxidation of lead is commonly used to measure the concen ...
, and in these cases can generally give a full helium and oxygen analysis of the mixture simultaneously.
Speed of sound principle
Helium content may also be determined on the basis of measuring the speed of sound in the analyzed gas mixture. The speed of sound depends on the mixture of gases and the temperature of the mix; in the analysis of trimix the speed of sound can be described by a non-linear function of temperature, oxygen content and helium content, and thus the content of helium can be determined by measuring the speed of sound through the mix, the temperature of the mix and its oxygen content.See also
* Gas blending#Gas analysisReferences
External links
* {{Underwater diving, divsup Breathing gases Underwater diving safety Measurement