Document ID: chunk:federal_register_of_legislation:F2023L01529:body:0:p45
Version: federal_register_of_legislation:F2023L01529
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Character Range: 124704–127856

to determine the chamber's hydrocarbon background and leak rate. Initial and final readings of hydrogen concentration, temperature and barometric pressure are used in the following formula to calculate the mass change.

       Where :

                     MH2 = hydrogen mass, in grams

                     CH2 = measured hydrogen concentration into the enclosure, in ppm volume

                     V = enclosure volume in cubic metres (m3) as measured in paragraph 2.1.1. above.

                     Vout = compensation volume in m³, at the test temperature and pressure

                     T = ambient chamber temperature, in K

                     P = absolute enclosure pressure, in kPa

                     k = 2.42

       Where: i is the initial reading

                     f is the final reading

       3. Calibration of the hydrogen analyser

        The analyser should be calibrated using hydrogen in air and purified synthetic air.  See paragraph 4.8.2. of Annex 7.

       Each of the normally used operating ranges are calibrated by the following procedure:

       3.1. Establish the calibration curve by at least five calibration points spaced as evenly as possible over the operating range.  The nominal concentration of the calibration gas with the highest concentrations to be at least 80 per cent of the full scale.

       3.2. Calculate the calibration curve by the method of least squares.  If the resulting polynomial degree is greater than three, then the number of calibration points shall be at least the number of the polynomial degree plus two.

       3.3. The calibration curve shall not differ by more than two per cent from the nominal value of each calibration gas.

       3.4. Using the coefficients of the polynomial derived from paragraph 3.2. above, a table of analyser readings against true concentrations shall be drawn by steps no greater than 1 per cent of full scale.  This is to be carried out for each analyser range calibrated.

        This table shall also contain other relevant data such as:

           (a) date of calibration;

           (b) span and zero potentiometer readings (where applicable);

           (c) nominal scale;

           (d) reference data of each calibration gas used;

           (e) real and indicated value of each calibration gas used together with the percentage differences;

           (f) calibration pressure of analyser.

       3.5. Alternative methods (e.g. computer, electronically controlled range switch) can be used if it is proven to the technical service that these methods give equivalent accuracy.

Annex 7 – Appendix 2

Essential characteristics of the vehicle family

       1. Parameters The family may be defined by basic design parameters which shall be common to vehicles within the family.  In some cases there may be interaction of parameters.  These effects shall also be taken into consideration to ensure that only vehicles with similar hydrogen emission characteristics are included within the family.

       2. To this end, those vehicle types whose parameters described below are identical are considered to belong to the same