§ 89.420 - Background sample.  


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  • § 89.420 Background sample.

    (a) Background samples are produced by continuously drawing a sample of dilution air during the exhaust collection phase of each test cycle mode.

    (1) Individual background samples may be produced and analyzed for each mode. Hence, a unique background value will be used for the emission calculations for each mode.

    (2) Alternatively, a single background sample may be produced by drawing a sample during the collection phase of each of the test cycle modes. Hence, a single cumulative background value will be used for the emission calculations for each mode.

    (b) For analysis of the individual sample described in paragraph (a)(1) of this section, a single value representing the average chart deflection over a 10-second stabilized period is stored. All readings taken during the 10-second interval must be stable at the final value to within ±1 percent of full scale.

    (c) Measure HC, CO, CO2, and NOX exhaust and background concentrations in the sample bag(s) with approximately the same flow rates and pressures used during calibration.

    [59 FR 31335, June 17, 1994. Redesignated and amended at 63 FR 56996, 57018, Oct. 23, 1998]