Section 86.116-94 - Calibrations, frequency and overview(a) Calibrations shall be performed as specified in § 86.117 through § 86.126 .(b) At least yearly or after any maintenance which could alter background emission levels, evaporative enclosure background emission measurements shall be performed.(c) At least monthly or after any maintenance which could alter calibration, the following calibrations and checks shall be performed:(1) Calibrate the THC analyzers (both evaporative and exhaust instruments), methane analyzer, carbon dioxide analyzer, carbon monoxide analyzer, and oxides of nitrogen analyzer (certain analyzers may require more frequent calibration depending on particular equipment and uses).(2) Calibrate the dynamometer. If the dynamometer receives a weekly performance check (and remains within calibration) the monthly calibration need not be performed.(3) Perform an organic gas retention and calibration on the evaporative emissions enclosure (see § 86.117-90(c) ).(4) Calibrate the gas meters or flow instrumentation used for providing total flow measurement for particulate sampling.(5) Check the oxides of nitrogen converter efficiency.(d) At least weekly or after any maintenance which could alter calibration, the following calibrations and checks shall be performed: (2) Perform a CVS system verification, and(3) Run a performance check on the dynamometer. This check may be omitted if the dynamometer has been calibrated within the preceding month.(e) The CVS positive displacement pump or Critical Flow Venturi shall be calibrated following initial installation, major maintenance, or as necessary when indicated by the CVS system verification (described in § 86.119 ).(f) Sample conditioning columns, if used in the CO analyzer train, should be checked at a frequency consistent with observed column life or when the indicator of the column packing begins to show deterioration.(g) The Administrator, upon request, may waive the requirement to comply with the specified methanol recovery tolerance (e.g., ±2 percent in §§ 86.117-90 and 86.119-90 ), and/or the specified methanol retention tolerance (e.g., ±4 percent in § 86.117-90 ), and instead require compliance with higher tolerances (not to exceed ±6 percent for recoveries and ±8 for retention), provided that: (1) The Administrator determines that compliance with these specified tolerances is not practically feasible; and(2) The manufacturer makes information available to the Administrator which indicates that the calibration tests and their results are consistent with good laboratory practice, and that the results are consistent with the results of calibration testing conducted by the Administrator.56 FR 25774, June 5, 1991, as amended at 58 FR 58422, Nov. 1, 1993; 59 FR 33913, July 1, 1994; 60 FR 34342, June 30, 1995