When accurate measurements are required where entrained liquids, particulates, or varying conditions are present a sample system is often required. Particulates pose an obvious problem - erosion of the sensor leading to inevitable drift and premature failure - hence filtration is generally required.

Liquid entrainment has less obvious effects; most substances are either hydrophilic or hydrophobic (water attracting or repelling). Should these coat the sensor the balance with the measured gas will alter - leading to an apparent offset. To counter this problem coalescing filters are used to remove the liquids, and additional heat will ensure the remainder will not condense out.

With analysers sometimes being located some distance from the tapping point slow reaction times, or the effects of Transpiration can cause problems. To reduce the lag or dilute its effects fast by-pass loops are installed.