# Commission Delegated Regulation (EU) 2017/654 of 19 December 2016 supplementing Regulation (EU) 2016/1628 of the European Parliament and of the Council with regard to technical and general requirements relating to emission limits and type-approval for internal combustion engines for non-road mobile machinery, Appendix 1

Extent: E+W+S+N.I.

Drift Correction
1.
Scope and frequency
The calculations in this Appendix shall be performed to determine if gas analyzer drift invalidates the results of a test interval. If drift does not invalidate the results of a test interval, the test interval's gas analyzer responses shall be corrected for drift according to this Appendix. The drift-corrected gas analyzer responses shall be used in all subsequent emission calculations. The acceptable threshold for gas analyzer drift over a test interval is specified in point 8.2.2.2 of Annex VI.
2.
Correction principles
The calculations in this Appendix utilize a gas analyzer's responses to reference zero and span concentrations of analytical gases, as determined sometime before and after a test interval. The calculations correct the gas analyzer's responses that were recorded during a test interval. The correction is based on an analyzer's mean responses to reference zero and span gases, and it is based on the reference concentrations of the zero and span gases themselves. Validation and correction for drift shall be performed as follows:
3.
Drift validation
After applying all the other corrections–except drift correction–to all the gas analyzer signals, brake-specific emissions shall be calculated in accordance with point 3.8. Then all gas analyzer signals shall be corrected for drift according to this Appendix. Brake-specific emissions shall be recalculated using all of the drift-corrected gas analyzer signals. The brake-specific emission results shall be validated and reported before and after drift correction according to point 8.2.2.2 of Annex VI.
4.
Drift correction
All gas analyzer signals shall be corrected as follows:
(a) Each recorded concentration, xi , shall be corrected for continuous sampling or for batch sampling, x – ;
(b) Correction for drift shall be calculated by means of equation (7-149):
x i driftcor = x refzero + x refspan − x refzero 2 x i − x prezero + x postzero x prespan + x postspan − x prezero + x postzero
(7-149)
Where:
xi driftcor concentration corrected for drift [μmol/mol]
x refzero reference concentration of the zero gas, which is usually zero unless known to be otherwise [μmol/mol]
x refspan reference concentration of the span gas [μmol/mol]
x prespan pre-test interval gas analyzer response to the span gas concentration [μmol/mol]
x postspan post-test interval gas analyzer response to the span gas concentration [μmol/mol]
xi or x – concentration recorded, i.e. measured, during test, before drift correction [μmol/mol]
x prezero pre-test interval gas analyzer response to the zero gas concentration [μmol/mol]
x postzero post-test interval gas analyzer response to the zero gas concentration [μmol/mol]
(c) For any pre-test interval concentrations, concentrations determined most recently before the test interval shall be used. For some test intervals, the most recent pre-zero or pre-span might have occurred before one or more previous test intervals;
(d) For any post-test interval concentrations, concentrations determined most recently after the test interval shall be used. For some test intervals, the most recent post-zero or post-span might have occurred after one or more subsequent test intervals;
(e) If any pre-test interval analyzer response to the span gas concentration, x prespan, is not recorded, x prespan shall be set equal to the reference concentration of the span gas: x prespan = x refspan;
(f) If any pre-test interval analyzer response to the zero gas concentration, x prezero, is not recorded, x prezero shall be set equal to the reference concentration of the zero gas: x prezero = x refzero;
(g) Usually the reference concentration of the zero gas, x refzero, is zero: x refzero = 0 μmol/mol. However, in some cases it might be known that x refzero has a non-zero concentration. For example, if a CO2 analyzer is zeroed using ambient air, the default ambient air concentration of CO2, which is 375 μmol/mol, may be used. In this case, x refzero = 375 μmol/mol. When an analyzer is zeroed using a non-zero x refzero, the analyzer shall be set to output the actual xrefzero concentration. For example, if x refzero = 375 μmol/mol, the analyzer shall be set to output a value of 375 μmol/mol when the zero gas is flowing to the analyzer.

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Source: https://www.legislation.gov.uk/eur/2017/654/annex/VII/appendix/1 (the official version)
Page: https://openlegislation.uk/eu-regulation-2017-654/annex-VII/appendix-1
Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives.