Results of Testing
Table 3 shows the particle counts from each instrument for each of the duplicated test runs. This data is normalized to counts per cubic meter (n/m³). The results presented also show the % losses of each test run for the instruments relative to the reference Lasair III 5100. A summary of average losses is given in Table 4.

Conclusions
From the data, all Lasair III particle counters achieved turbulent flow conditions, as all instruments have a Reynolds number > 4000. Therefore the transportation of particles is maximized. However it is a known function of adding tubing to a particle counter that one will experience losses in tubing. The test data showed that these losses are measurable. The following conclusions can be made:

• Particle losses increase as particle size increases. Each of the instruments demonstrates lower losses in 2 m of tubing for the smallest particles (0.5 µm) than is apparent for the large particles (5.0 µm).
• The instruments with the higher Reynolds number transport particles more efficiently. The % loss of 5.0 µm particles for the higher flow rate instrument, the Lasair III 5100, is less than the % loss of particles for the lowest flow rate, Lasair III 310C.
• Average losses for particles in 2 m of transport tubing for large (5.0 µm) particles are between 17% and 27%. This is reflective of previously published data from Particle Measuring Systems3.

Therefore, when choosing a particle counter for different applications, remember that there is a difference between instrument flow rate and potential data, relative to particle losses of the larger particles. For room classification, to either ISO 14644-1 or EU GMP Annex 1, where a single measurement per year is made and that measurement is both of a large sample volume and a critical measurement, the high flow rate Lasair III 5100 is preferred as it both transports particles more effectively and samples the 1 m3 faster.

Particle Measuring Systems recommends minimizing the amount and length of tubing where possible in order to improve true count accuracy.

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