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Proposal makes changes to take into consideration the availability of gases for flame ionization detectors and the linearization of the gas analyzer.
UN R49 defines no linearity requirements for humidity sensors. As the humidity content of the intake air is an essential measure for the calculation of the specific exhaust emission, it is important to add requirement for humidity sensor (Reference: ISO 16183 the accuracy of the absolute humidity shall be +- 5%).
The reasoning for the other amendments to Table 7 is the following.
As the gas divider is a necessary tool to verify the linearization of the gas analyzer it is mandatory that the deviation of the gas divider is lower than that of the instrument under test. In combination with a calibration gas which has an accuracy of 1 % and a gas divider, which has an accuracy of 1 % it is only possible to reach a guaranteed analyzer accuracy of 2 %.
Annex 4B – Amendments to paragraph 9.3.3.1
In the automotive industry Helium is used as so fuel gas for flame ionization detectors (FID) to measure Hydrocarbon emissions. In the FID fuel gas Helium is mixed with Hydrogen in a ratio of 40 % H2 and 60 % He. The annual fluctuations of the helium global market lead to an insufficient supply with FID fuel gas, like happened lately during summer 2018. In order to prevent the industry from the fluctuations of the global helium market, the US legislation reacted already in 2014 and allowed the usage of Nitrogen as batch gas for the FID fuel gas.
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