An external charcoal filter may also be used in series with the external water filter and should be installed on the instrument side of the external water trap filter. The charcoal filter is used when known or suspected levels of H2S, hexane, propane, or other non-methane hydrocarbons exceeding one hundred ppm. Presence of these gases can affect the methane channel by indicating artificially high concentrations of methane. The charcoal filter needs to be condition with Calibration gas before use.
Condition the charcoal filter before use in the field by using your cal gas. The best way is to put the filter in line when doing the CH4 calibration although it may take a little longer for the CH4 to reach the correct % your will know that the filter has been conditioned because the % reading of the cal gas has stabilized in the calibration screen.
After conditioning the filter and it is being used in the field do not use the carbon filter in the calibration tubing since it may have containments [hydrocarbons] from the field readings and you do not want them introduced into your calibration (You should have a separate clean hose for your calibration).
When using the carbon filter for the first time the direction it is placed in the tubing does not matter but keep it in the same direction always after the first sampling event.