Document ID: chunk:federal_register_of_legislation:F2021C01210:reg:200:p1
Version: federal_register_of_legislation:F2021C01210
Segment Type: reg
Provision Reference: reg 200 (pt 1/8)
Character Range: 85581–88431

200             1.065

Notes - though the above values are rounded to the nearest 0.01 or 0.005, this does not mean that the measurements need to be made to this degree of accuracy.

Annex 8
CHARACTERISTICS OF OPACIMETERS

  1.  SCOPE
        This annex defines the conditions to be met by opacimeters used in the tests described in annexes 4 and 5 to this Regulation.

  2.  BASIC SPECIFICATION FOR OPACIMETERS
        2.1  The gas to be measured shall be confined in an enclosure having a non-reflecting internal surface.
        2.2  In determining the effective length of the light path through the gas, account shall be taken of the possible influence of devices protecting the light source and the photoelectric cell. This effective length shall be indicated on the instrument.
        2.3  The indicating dial of the opacimeter shall have two measuring scales, one in absolute units of light absorption from 0 to  (m -1 ) and the other linear from 0 to 100; both scales shall range from 0 at total light flux to full scale at complete obscuration.

  3.  CONSTRUCTION SPECIFICATIONS
        3.1  General
        The design shall be such that under steady-speed operating conditions the smoke chamber is filled with smoke of uniform opacity.
        3.2  Smoke chamber and opacimeter casing
        3.2.1 The impingement on the photoelectric cell of stray light due to internal reflections or diffusion effects shall be reduced to a minimum (e.g. by finishing internal surfaces in matt black and by a suitable general layout).
        3.2.2 The optical characteristics shall be such that the combined effect of diffusion and reflection does not exceed one unit on the linear scale when the smoke chamber is filled with smoke having an absorption coefficient near 1.7 m -1.
        3.3  Light source
        The light source shall be an incandescent lamp with a colour temperature in the range of 2800 to 3250 K or a green light-emitting diode (LED) with a spectral peak between 550 and 570 nm.  The light source shall be protected against sooting by means that do not influence the optical path length beyond the manufacturer's specifications.
        3.4  Receiver
        3.4.1 The receiver shall consist of a photoelectric cell with a spectral response curve similar to the photopic curve of the human eye (maximum response in the range 550/570 nm; less than 4 per cent of that maximum response below 430 mm and above 680 nm).
        3.4.2 The construction of the electrical circuit, including the indicating dial, shall be such that the current output from the photoelectric cell is a linear function of the intensity of the light received over the operating-temperature range of the photoelectric cell.
        3.5  Measuring scales
        3.5.1 The light-absorption coefficient k shall be calculated by the formula  = o  e-kL, where