Reference Filter Weighing. The chamber (or room) environment shall be free of any ambient contaminants (such as dust) that would settle on the particulate filters during their stabilisation. Disturbances to weighing room specifications as outlined in paragraph 1.5.2.1. will be allowed if the duration of the disturbances does not exceed 30 minutes. The weighing room should meet the required specifications prior to personnel entrance into the weighing room. At least two unused reference filters or reference filter pairs shall be weighed within four hours of, but preferably at the same time as the sample filter (pair) weighings. They shall be the same size and material as the sample filters. If the average weight of the reference filters (reference filter pairs) changes between sample filter weighings by more than ± 5 per cent (± 7.5 per cent for the filter pair) of the recommended minimum filter loading (paragraph 1.5.1.5.), then all sample filters shall be discarded and the emissions test repeated. If the weighing room stability criteria outlined in paragraph 1.5.2.1. is not met, but the reference filter (pair) weighings meet the above criteria, the engine manufacturer has the option of accepting the sample filter weights or voiding the tests, fixing the weighing room control system and re-running the test.
Reference Filter Weighing. To determine the specific reference filter weights, at least two unused reference filters shall be weighed within 8 hours of, but preferably at the same time as, the sample filter weighings. Reference filters shall be of the same size and material as the sample filter. If the specific weight of any reference filter changes by more than ± 5µg between sample filter weighings, then the sample filter and reference filters shall be reconditioned in the weighing room and then reweighed. The comparison of reference filter weighings shall be made between the specific weights and the rolling average of that reference filter's specific weights. The rolling average shall be calculated from the specific weights collected in the period since the reference filters were placed in the weighing room. The averaging period shall be at least 1 day but not exceed 30 days. Multiple reconditionings and reweighings of the sample and reference filters are permitted until a period of 80 h has elapsed following the measurement of gases from the emissions test. If, prior to or at the 80 h point, more than half the number of reference filters meet the ± 5 µg criterion, then the sample filter weighing can be considered valid. If, at the 80 h point, two reference filters are employed and one filter fails the ± 5 µg criterion, the sample filter weighing can be considered valid under the condition that the sum of the absolute differences between specific and rolling averages from the two reference filters must be less than or equal to 10 µg. Regulation No 83 page 61 In case less than half of the reference filters meet the ± 5 µg criterion the sample filter shall be discarded, and the emissions test repeated. All reference filters must be discarded and replaced within 48 hours. In all other cases, reference filters must be replaced at least every 30 days and in such a manner that no sample filter is weighed without comparison to a reference filter that has been present in the weighing room for at least 1 day. If the weighing room stability criteria outlined in paragraph 1.3.4. are not met, but the reference filter weighings meet the above criteria, the vehicle manufacturer has the option of accepting the sample filter weights or voiding the tests, fixing the weighing room control system and re-running the test. Figure 13: Particulate sampling probe configuration Regulation No. 83 page 62 Appendix 5 PARTICLE NUMBER EMISSIONS MEASUREMENT EQUIPMENT
