Document ID: chunk:federal_register_of_legislation:F2024C00356:reg:21:p22
Version: federal_register_of_legislation:F2024C00356
Segment Type: reg
Provision Reference: reg 21 (pt 22/35)
Character Range: 348033–351432

result of the weighings is ±5 µg of the result from the previous weighing session then the weighing session and balance are considered valid.
               The weighing chamber (or room) shall meet the following conditions during all filter conditioning and weighing operations:
               Temperature maintained at 295 ±3 K (22 ±3 °C);
               Relative humidity maintained at 45 ±8 per cent;
               Dewpoint maintained at 9.5 °C ±3 °C.
               It is recommended that temperature and humidity conditions are recorded along with sample and reference filter weights.
              1.3.4.2. Buoyancy Correction
               All filter weights shall be corrected for filter buoyancy in air.
               The buoyancy correction depends on the density of the sample filter medium, the density of air, and the density of the calibration weight used to calibrate the balance. The density of the air is dependent on the pressure, temperature and humidity.
               It is recommended that the temperature and dew point of the weighing environment are controlled to 22 °C ±1 °C and dew point of 9.5 °C ±1 °C respectively. However, the minimum requirements stated in paragraph 1.3.4.1. will also result in an acceptable correction for buoyancy effects. The correction for buoyancy shall be applied as follows:
 Where:
 mcorr                                  =            PM mass corrected for buoyancy
 muncorr                                =            PM mass uncorrected for buoyancy
 ρair                                   =            density of air in balance environment
 ρweight                                =            density of calibration weight used to span balance
 ρmedia                                 =            density of PM sample medium (filter) according to the table below:

 Filter Medium                          ρmedia
 Teflon coated glass fibre (e.g. TX40)  2,300 kg/m3

                ρair can be calculated as follows:

 Where:
 Pabs    =  absolute pressure in balance environment,
 Mmix    =  molar mass of air in balance environment (28.836 gmol-1),
 R       =  molar gas constant (8.314 Jmol-1K-1),
 Tamb    =  absolute ambient temperature of balance environment.

               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.
               Limited deviations from weighing room temperature and humidity specifications will be allowed provided their total duration does not exceed 30 minutes in any one filter conditioning period. The weighing room should meet the required specifications prior to personal entrance into the weighing room. During the weighing operation no deviations from the specified conditions are permitted.
              1.3.4.3. The effects of static electricity shall be nullified. This may be achieved by grounding the balance through placement upon an antistatic mat and neutralisation of the particulate filters prior to weighing using a Polonium neutraliser or a device of similar effect. Alternatively nullification of static effects may be achieved through equalisation of the static charge.
              1.3.4.4. A test filter shall be removed from the chamber no earlier than an hour before the test begins.
              1.4. Recommended System Description
               Figure