Document ID: chunk:federal_register_of_legislation:F2021C01210:reg:200:p2
Version: federal_register_of_legislation:F2021C01210
Segment Type: reg
Provision Reference: reg 200 (pt 2/8)
Character Range: 88155–90970

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 L is the effective length of the light path through the gas to be measured, o the incident flux and  the emergent flux. When the effective length L of a type of opacimeter cannot be assessed directly from its geometry, the effective length L shall be determined
          Either by the method described in paragraph 4. of this annex;
or
          Through correlation with another type of opacimeter for which the effective length is known.
        3.5.2 The relationship between the 0-100 linear scale and the light-absorption coefficient k is given by the formula

        where N is a reading on the linear scale and k the corresponding value of the absorption coefficient.
        3.5.3 The indicating dial of the opacîmeter shall enable an absorption coefficient of 1.7 m  -1 to be read with an accuracy of 0.025 m -1.
        3.6  Adjustment and calibration of the measuring apparatus
        3.6.1 The electrical circuit of the photoelectric cell and of the indicating dial shall be adjustable so that the pointer can be reset at zero when the light flux passes through the smoke chamber filled with clean air or through a chamber having identical characteristics.
        3.6.2 With the lamp switched off and the electrical measuring circuit open or short-circuited, the reading on the absorption-coefficient scale shall be  , and it shall remain at  with the measuring circuit reconnected.
        3.6.3 An intermediate check shall be carried out by placing in the smoke chamber a screen representing a gas whose known light-absorption coefficient k, measured as described in paragraph 3.5.1 is between 1.6 m -1 and 1.8 m -1. The value of k must be known to within 0.025 m -1.
        The check consists in verifying that this value does not differ by more than 0.05 m -1 from that read on the opacimeter indicating dial when the screen is introduced between the source of light and the photoelectric cell.
        3.7  Opacimeter response
        3.7.1 The response time of the electrical measuring circuit, being the time necessary for the indicating dial to reach 90 per cent of full-scale deflection on insertion of a screen fully obscuring the photoelectric cell, shall be 0.9 to 1.1 second.
        3.7.2 The damping of the electrical measuring circuit shall be such that 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