Closed-loop arrangement with critical orifice for DMA sheath excess flow system

Differential mobility analysis (DMA) is well established for size distribution measurements of submicron aerosol particles. A commonly used method for performing a DMA-measurement is to set the sheath flow exactly equal to the excess flow. The flow arrangement for this measurement is usually performed with pressurized air (or gas) supply. With closed-loop arrangement, there's no need for a separate compressed gas supply or additional pumps but operational problems may arise. To achieve a long-term precision and stability with a closed-loop design, a detailed analysis of hardware solutions is reported. Possible adjustment procedures and the required additional monitoring are minimized using critical orifice technique.