Appendix 1

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.

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:

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.

All gas analyzer signals shall be corrected as follows:

1. (a)

   Each recorded concentration, x_i , shall be corrected for continuous sampling or for batch sampling, $\bar{x}$ ;

2. (b)

   Correction for drift shall be calculated by means of equation (7-149):

   $x_{i\mathrm{driftcor}}=x_{\mathrm{refzero}}+\left(x_{\mathrm{refspan}}-x_{\mathrm{refzero}}\right)\frac{2x_i-\left(x_{\mathrm{prezero}}+x_{\mathrm{postzero}}\right)}{\left(x_{\mathrm{prespan}}+x_{\mathrm{postspan}}\right)-\left(x_{\mathrm{prezero}}+x_{\mathrm{postzero}}\right)}$

   (7-149)

   Where:

   x_{i driftcor}

3. concentration corrected for drift [μmol/mol]

x _refzero

4. reference concentration of the zero gas, which is usually zero unless known to be otherwise [μmol/mol]

x _refspan

5. reference concentration of the span gas [μmol/mol]

x _prespan

6. pre-test interval gas analyzer response to the span gas concentration [μmol/mol]

x _postspan

7. post-test interval gas analyzer response to the span gas concentration [μmol/mol]

x_i or $\bar{x}$

8. concentration recorded, i.e. measured, during test, before drift correction [μmol/mol]

x _prezero

9. pre-test interval gas analyzer response to the zero gas concentration [μmol/mol]

x _postzero

10. post-test interval gas analyzer response to the zero gas concentration [μmol/mol]