Operating Principle

DGI is a 5-stage cascade low pressure impactor. An impactor has two co-linear plates; the other one acts as a collection surface for the particles, the other one has small nozzle or nozzles in it to control the flow velocity. After the sample passes through the nozzles it is turned sharply before the collection plate; particles larger than stage cut diameter cannot follow the flow stream lines but are impacted on the collection plate. Particles smaller that the stage cut diameter continue to the following impactor stages where they are further size classified or collected. By changing the dimensions in each impactor stage, different sized particles can be collected on different impactor stages. The flow through the DGI impactor is controlled with an external mass flow controller, and can be adjusted between 50 and 100l/min. The nominal flow rate of 70 l/min gives the impactor stages cut points of 2.5, 1.0, 0.5 and 0.2 µm. The cut point values are provided for 50, 60, 70, 80, 90 and 100 l/min flow rates in the calibration data sheet.

The particle size distribution in DGI is determined by analyzing the collected particles gravimetrically or chemically after the sampling period. The substrates used on the collection plates as particle collection surface are 47 mm in diameter. Different material substrates can be used depending on the used particle analysis methods. The collection substrates are held in their place by the jet plates of the above plate so no additional lock rings are needed.