Dilution system with dilution factor 1:100

Particle-free air with the volume flow V_R circulates through an annular passage around the suction nozzle. Thus, according to Bernoulli, a volume flow V_An is generated at the suction nozzle. The dilution factor V_F is calculated according to the following formula.

Simple, functional test on-site

With this simple test set-up, the Palascascaded dilution systems can be checked by anyone: First, a particle measurement is performed with one dilution step. Here it is essential that the aerosol concentration, e.g., lab air, to be measured does not exceed the coincidence limit (maximum detectable aerosol concentration). In the second step, the dilution step to be tested is connected in series (cascaded). To check the dilution factor of the test step (position 2), the total particle count from the measurement in position 1 is divided by the total particle count from position 2.

Experimental setup

Position 1: Lab air

Position 2: Lab air

The VKL 100 measures coincidence-free with the OPC; the VKL 10 is tested.

Calculation of the dilution factor:

Provided the first measurement is not affected by a coincidence error and the dilution system under test is working (not soiled), a dilution factor of almost 10 is determined. If this should not be the case, there was possibly a coincidence in measurement 1. In this case, the aerosol concentration has to be decreased or a further dilution step used. Another possibility would be that the dilution step to be tested is soiled. In this case, the device has to be cleaned and the test repeated.

Table 1: Technical characteristics of Palas dilution systems

VDI report no. 1973 from 2007 proved metrologically that a reproducible aerosol dilution is possible with the Palas dilution systems down to VF 100,000.