Document ID: chunk:federal_register_of_legislation:F2023C00229:reg:9:p28
Version: federal_register_of_legislation:F2023C00229
Segment Type: reg
Provision Reference: reg 9 (pt 28/71)
Character Range: 287790–291146

Calibration procedure

1.5.1.                        Instrument assembly

              The instrument assembly shall be calibrated and calibration curves checked against standard gases.  The same gas flow rates shall be used as when sampling exhaust.

1.5.2.                        Warming-up time

              The warming-up time should be according to the recommendations of the manufacturer. If not specified, a minimum of two hours is recommended for warming up the analysers.

1.5.3.                        NDIR and HFID analyser

              The NDIR analyser shall be tuned, as necessary, and the combustion flame of the HFID analyser shall be optimised (Section 1.8.1).

1.5.4.                        Calibration

              Each normally used operating range shall be calibrated.

              Using purified synthetic air (or nitrogen), the CO, CO2, NOx and HC analysers shall be set at zero.

              The appropriate calibration gases shall be introduced to the analysers, the values recorded, and the calibration curve established according to Section 1.5.5.

              The zero setting shall be rechecked and the calibration procedure repeated, if necessary.

1.5.5.                        Establishment of the calibration curve

1.5.5.1.                    General guidelines

              The analyser calibration curve shall be established by at least five calibration points (excluding zero) spaced as uniformly as possible. The highest nominal concentration must be equal to or higher than 90 % of full scale.

              The calibration curve shall be calculated by the method of least squares. If the resulting polynomial degree is greater than 3, the number of calibration points (zero included) must be at least equal to this polynomial degree plus 2.

              The calibration curve must not differ by more than ± 2 % from the nominal value of each calibration point and by more than ± 1 % of full scale at zero.

              From the calibration curve and the calibration points, it is possible to verify that the calibration has been carried out correctly. The different characteristic parameters of the analyser must be indicated, particularly:

                —    the measuring range,

                —    the sensitivity,

                —    the date of carrying out the calibration.

1.5.5.2.                    Calibration below 15 % of full scale

              The analyser calibration curve shall be established by at least 4 additional calibration points (excluding   zero) spaced nominally equally below 15 % of full scale.

              The calibration curve is calculated by the method of least squares.

              The calibration curve must not differ by more than ± 4 % from the nominal value of each calibration point and by more than ± 1 % of full scale at zero.

1.5.5.3.                    Alternative methods

              If it can be shown that alternative technology (e.g. computer, electronically controlled range switch, etc.) can give equivalent accuracy, then these alternatives may be used.

1.6.                            Verification of the calibration

              Each normally used operating range shall be checked prior to each analysis in accordance with the following procedure.

              The calibration shall be checked by using a zero gas and