In the methane mode the sample is directed through a heated catalyst. This catalyst oxidises non-methane species of hydrocarbons in the sample. The THC mode bypasses this catalyst to provide a reading for total hydrocarbon. These two modes allow the derivation of a non-methane hydrocarbon by simply deducting the methane only reading from the total hydrocarbon value.
As a stand alone unit, this cutter is suitable for use with any heated FID to obtain a methane only or non-methane concentration reading.