The Lasair III is an airborne particle counter designed for sampling air at standard pressure conditions. The instrument measures the mass flow using a differential pressure sensor that regulates the pressure drop in the sampling region. Pressure drops across the inlet and outlet jets is measured and provides the most precise measurement of flow.
Mass flow is corrected to volumetric flow by using data from an additional atmospheric sensor. The volumetric flow is calculated using the mass flow measured value and the atmospheric pressure.
The instrument flow controller is calibrated for air sampling at standard pressure conditions in accordance with ISO 21501-4; for this reason, it is important to consider several factors while sampling gas other than air.