90.326 Pre- and post-test analyzer calibration.§ 90.326 Pre- and post-test analyzer calibration.
Calibrate only the range of each analyzer used during the engine exhaust emission test prior to and after each test in accordance with the following:
(a) Make the calibration by using a zero gas and a span gas. The span gas value must be between 75 and 100 percent of the highest range used.
(b) Use the same analyzer(s) flow rate and pressure as that used during exhaust emission test sampling.
(c) Warm-up and stabilize the analyzer(s) before the calibration is made.
(d) If necessary clean and/or replace filter elements before calibration is made.
(e) Calibrate analyzer(s) as follows:
(1) Zero the analyzer using the appropriate zero gas. Adjust analyzer zero if necessary. Zero reading should be stable.
(2) Span the analyzer using the appropriate span gas for the range being calibrated. Adjust the analyzer to the calibration set point if necessary.
(3) Re-check zero and span set points.
(4) If the response of the zero gas or span gas differs more than one percent of full scale at the highest range used, then repeat paragraphs (e)(1) through (3) of this section.[60 FR 34598, July 3, 1995, as amended at 70 FR 40449, July 13, 2005]