Dust Samplers

The control of flow is an essential part of high volume air samplers as any sampler without this is likely to have erronous readings. The main benefits of having automatic volumetric flow control is:

1. During a 24 hour period of sampling the temperature, pressure and humidity of air is almost certain to change. Changes in air pressure result in a change of the volume of air being sampled by a dust sampler, and therefore a change in the dust collected. When temperatures increase, the volume of air increases and the amount or air (and particulates) sampled is lower. When temperatures drop the volume of air decreases and more air (and particulates) are sampled.
   
   
   
2. The flow of a high volume air sampler can also be influenced by particulate/dust loading on a filter. As the filter increases its particulate/dust load the resistance to air moving through the filter increases and the pressure differentiation on either side of the filter increases. To ensure a steady volumetric flow the HiVol must increase its suction as particulate load increases.
   
   
   
3. When using a size selective inlet (PM₁₀ or PM_2.5) with a high volume air sampler a constant flow rate must be obtained to ensure the SSI size cut point stays constant and accurate and PM₁₀ or PM_2.5.

It should be noted that many samplers only measure and control mass flow, however with a change in air density, due to pressure or temperature fluctuations, the actual velocity through the size selective inlet and filter will change. Automatically correcting mass flow for these changes in ambient temperature and pressure enables volumetric flow rate to be determined and controlled in real-time. This constant adjustment maintains a constant volumetric flow rate ensures that air velocity remains constant even when air density changes.