The Lasair® III Aerosol Particle Counter is the latest generation of aerosol particle counter from Particle Measuring Systems. The Aerosol Manifold II is designed to work with the Lasair III counter under the control of Particle Measuring Systems facility monitoring software (Facility Net).
The Lasair III particle counter uses a patented pressure measurement system to avoid the undercounting problems traditionally associated with the use of a manifold. At the heart of the system are three separate pressure transducers:
- The first pressure transducer monitors the pressure inside the sample inlet. This sensor allows the Lasair III to measure and correct for the vacuum caused by the manifold pump.
- A differential pressure sensor measures the difference between the pressures before and after the sample cell. The Lasair III uses this information to regulate the flow rate and velocity through the sample chamber.
- A third pressure transducer measures the ambient atmospheric pressure.
Airflow in the Lasair III counter is servo-controlled using the data from the sample inlet and the differential pressure sensors. This information is used to adjust the Lasair III blower/pump to generate a 1.0 CFM flow rate at a constant velocity at the sample inlet pressure. In normal sampling, this sample inlet pressure is approximately the same pressure as in the cleanroom.
When using a manifold, the air at the inlet is at a partial vacuum with respect to cleanroom air. Thus, the 1.0 CF sampled has a lower particle concentration than 1.0 CF of ambient cleanroom air. To correct for this phenomenon, the Lasair III counter calculates the equivalent ambient volume sampled (instead of the nominal 1.0 CF). Once the equivalent ambient sample volume has been calculated, the raw particle counts can be correctly normalized. Both raw counts and equivalent ambient sample volumes are communicated to Facility Net, which then performs the normalization calculations.
The Lasair III particle counter offers the only manifold system that accounts for the error to produce truly accurate counts.
Download the full paper for the details of the Lasair III counter’s correction factor and pressure measurement system, as well as equivalent ambient sample volume data for manifold systems in relation to altitude.