Document ID: chunk:federal_register_of_legislation:F2021C01210:reg:200:p3
Version: federal_register_of_legislation:F2021C01210
Segment Type: reg
Provision Reference: reg 200 (pt 3/8)
Character Range: 90723–93449

the initial overswing beyond the final steady reading after any momentary variation in input (e.g. the calibration screen) does not exceed 4 per cent of that reading in linear scale units.
        3.7.3 The response time of the opacimeter which is due to physical phenomena in the smoke chamber is the time taken from the start of the gas entering the chamber to complete filling of the smoke chamber; it shall not exceed 0.4 second.
        3.7.4 These provisions shall apply solely to opacimeters used to measure opacity under free acceleration.
        3.8  Pressure of the gas to be measured and of scavenging air
        3.8.1 The pressure of the exhaust gas in the smoke chamber shall not differ by more than 75 mm (water gauge) from the atmospheric pressure.
        3.8.2 The variations in the pressure of the gas to be measured and of the scavenging air shall not cause the absorption coefficient to vary by more than 0.05 m -1 in the case of a gas having an absorption coefficient of 1.7 m -1 .
        3.8.3 The opacimeter shall be equipped with appropriate devices for measuring the pressure in the smoke chamber.
        3.8.4 The limits of pressure variation of gas and scavenging air in the smoke chamber shall be stated by the manufacturer of the apparatus.
        3.9  Temperature of the gas to be measured
        3.9.1 At every point in the smoke chamber the gas temperature at the instant of measurement shall be between 70C and a maximum temperature specified by the opacimeter manufacturer such that the readings over the temperature range do not vary by more than 0.1 m -1 when the chamber is filled with a gas having an absorption coefficient of 1.7m -1 .
        3.9.2 The opacimeter shall be equipped with appropriate devices for measuring the temperature in the smoke chamber.
4.  EFFECTIVE LENGTH "L" OF THE OPACIMETER
        4.1  General
        4.1.1 In some types of opacimeter the gas between the light source and the photoelectric cell, or between transparent parts protecting the source and the photoelectric cell, is not of constant opacity. In such cases the effective length L shall be that of a column of gas of uniform opacity which gives the same absorption of light as that obtained when the gas is normally admitted into the opacimeter.
        4.1.2 The effective length of the light path is obtained by comparing the reading N of the opacimeter operating normally with the reading  obtained with the opacimeter modified so that the test 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