The main application of the Aerosol Dilution System DIL 554 is in the verification of test aerosols for testing clean rooms. Guideline EN ISO 14644-3 defines the necessity of appropriate dilution systems when using test aerosols for verification. According to standard VDI 2083 for testing clean rooms and work benches it is compulsory to carry out measurements with increased concentrations in the incoming aerosol.
From the aerosol stream to be diluted a sample is taken through a thin capillary. Particle concentration of the capillary flow rate remains unchanged whereas a HEPA filter removes nearly all particles from the bypassing flow rate. After the capillary and filter both streams are mixed together again and the dilution ratio results from the ratio between the two single flow rates. An extreme advantage of this dilution technique is, that no auxilliary pressurized air is needed for dilution. Therefore no surplus aerosol to be exhausted is generated and chemical composition of carrier gas remains unaffected.
In the applied principle that corresponds to the standard VDI 3491-15, particles are removed from the sample according to the specified dilution ratio – the particle size distribution remains unchanged. Optical particle counters have a physical limit up to which concentration they work accurately. Is this concentration exceeded errors will inevitably occur. By using the dilutor DIL 554 upstream of a particle counter, e.g. LAP 340, a dilution factor of up to 100 can be achieved. Thereby particle concentrations of >106 particles per cf (1cf = 28,3l) can be reduced to 104 per cf. This will put the particle concentration well within the range of standard particle counters.