Document ID: chunk:federal_register_of_legislation:F2021C01210:reg:200:p4
Version: federal_register_of_legislation:F2021C01210
Segment Type: reg
Provision Reference: reg 200 (pt 4/8)
Character Range: 93207–95936

gas fills a well defined length .
        4.1.3 It will be necessary to take comparative readings in quick succession to determine the correction to be made for shifts of zero.
        4.2  Method of assessment of L
        4.2.1 The test gas shall be exhaust gas of constant opacity or a light-absorptive gas of a gravimetric density similar to that of exhaust gas.
        4.2.2 A column of length Lo of the opacimeter, which can be filled uniformly with the test gas, and the ends of which are substantially at right angles to the light path, shall be accurately determined. This length  Lo  shall be close to the effective length of the opacimeter.
        4.2.3 The mean temperature of the test gas in the smoke chamber shall be measured.
        4.2.4 If necessary, an expansion tank of sufficient capacity to damp the pulsations and of compact design may be incorporated in the sampling line as near to the probe as possible. A cooler may also be fitted. The addition of the expansion tank and of the cooler should not unduly disturb the composition of the exhaust gas.
        4.2.5 The test for determining the effective length shall consist in passing a sample of test gas alternately through the opacimeter operating normally and through the same apparatus modified as indicated in paragraph 4.1.2.
        4.2.5.1 The opacimeter readings shall be recorded continuously during the test with a recorder whose response time is equal to or shorter than that of the opacimeter.
        4.2.5.2 With the opacimeter operating normally, the reading on the linear scale of opacity is N and that of the mean gas temperature expressed in Kelvin degrees is T.
        4.2.5.3  With the known length Lo filled with the same test gas, the reading on the linear scale of opacity is N 0   and that of the mean gas temperature expressed in Kelvin degrees is T o.
        4.2.6 The effective length will be

        4.2.7 The test shall be repeated with at least four test gases giving readings evenly spaced between the readings 20 and 80 on the linear scale.
        4.2.8 The effective length L of the opacimeter will be the arithmetic average of the effective lengths obtained as stated in paragraph 4.2.6. for each of the gases.
  Annex 9
 INSTALLATION AND USE OF THE OPACIMETER

  1.  SCOPE
        This annex specifies the installation and use of opacimeters for the tests described in annexes 4 and 5 to this Regulation.

SAMPLING OPACIMETER
        2.1  Installation for steady-speed tests
        2.1.1 The ratio of the cross-sectional area of the probe to that of the exhaust pipe shall not be less than 0.05. The back pressure measured in the exhaust pipe at the opening of the probe shall not exceed 75 mm (water gauge).