40 CFR 91.304 - Test equipment overview.
(a) All engines subject to this subpart are tested for exhaust emissions. Engines are operated on dynamometers meeting the specification given in § 91.305.
(b) The exhaust is tested for gaseous emissions using either a constant volume sampling (CVS) system as described in § 91.414, or using the raw gas sampling system as described in § 91.421. Both systems require analyzers (see paragraph (c) of this section) specific to the pollutant being measured.
(c) Analyzers used are a non-dispersive infrared detector (NDIR) absorption type for carbon monoxide and carbon dioxide analysis; paramagnetic detector (PMD), zirconia (ZRDO), or electrochemical type (ECS) for oxygen analysis; a flame ionization detector (FID) or heated flame ionization detector (HFID) type for hydrocarbon analysis; and a chemiluminescent detector (CLD) or heated chemiluminescent detector (HCLD) for oxides of nitrogen analysis.