The shelf life of all calibration gases as recommended by the manufacturer shall not be exceeded. The expiration date of the calibration gases stated by the manufacturer shall be recorded.
2.1 Pure gases
2.1.1 The required purity of the gases is defined by the contamination limits given below. The following gases shall be available for operation of the test bed measurement procedures:
.1 purified nitrogen (contamination ≦ 1ppm C ≦1ppm CO ≦ 400ppm CO2 ≦ 0.1ppm NO);
2.2.1 Mixtures of gases having the following chemical compositions shall be available:
.1 CO and purified nitrogen;
.2 NOx and purified nitrogen (the amount of NO2 contained in this calibration gas must not exceed 5% of the NO content);
.3 O2 and purified nitrogen; and
.4 CO2 and purified nitrogen
Note: Other gas combinations are allowed provided the gases do not react with one another.
2.2.2 The true concentration of a calibration and span gas shall be within ±2% of the nominal value.
All concentrations of calibration gas shall be given on a volume basis (volume percent or volume ppm).
2.2.3 The gases used for calibration and span may also be obtained by means of a gas divider diluting with purified N2 or with purified synthetic air. The accuracy of the mixing device shall be such that the concentration of the diluted calibration gases may be determined to within ±2%
MEPC39/6/1
ANNEX
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3 Operating procedure for analysers and sampling system
The operating procedure for analysers shall follow the start-up and operating instructions specified by the instrument manufacturer. The minimum requirements given in sections 4 to 9 shall be included.
4 Leakage test
4.1 A system leakage test shall be performed. The probe shall be disconnected from the exhaust system and the end plugged. The analyser pump shall be switched on. After an initial stabilisation period, all flow meters shall read zero; if not, the sampling lines shall be checked and the fault corrected.
4.2 The maximum allowable leakage rate on the vacuum side be 0.5% of the in-use flow rate for the portion of the system being checked. The analyser flows and bypass flows may be used to estimate the in-use flow rates.
4.3 Another method that may be used is the introduction of a concentration step change at the beginning of the sampling line by switching from zero to span gas. After an adequate period of time, the reading should show a lower concentration compared to the introduced concentration; this points to calibration or leakage problems.
5 Calibration procedure
5.1 Instrument assembly
The instrument assembly shall be calibrated and the calibration curves checked against standard gases.
The same gas flow rates shall be used as when sampling exhaust.
5.2 Warming-up time
The warming-up time shall be according to the recommendations of the analyser's manufacturer. If not specified, a minimum of two hours is recommended for warning up the analysers.
5.3 NDIR and HFID analyser
The NDIR analyser shall be tuned, as necessary.
5.4 Calibration
5.4.1 Each normally used operating range shall be calibrated.
5.4.2 Using purified synthetic air (or nitrogen), the CO, CO2, NOx and O2 analysers shall be set at zero.
5.4.3 The appropriate calibration gases shall be introduced to the analysers, the value recorded, and the calibration curve established according to 5.5 below.
5.4.4 The zero setting shall be rechecked and the calibration procedure repeated, if necessary.
5.5 Establishment of the calibration curve
5.5.1 General guidelines
5.5.1.1 The analyser calibration curve shall be established by at least five calibration points (excluding zero) spaced as uniformly as possible. The highest nominal concentration shall be greater thyan or equal to 90% of full scale.
