Operating SMPS™ Hardware 4-3
use of the flow equalizer assembly (filter and valve) to provide
filtered makeup air to the CPCs.
Figure 4-3
Schematic Flow Diagram of the Classifier with Nano DMA
The Nano DMA has the option of using a bypass flow to draw
additional flow up to the inlet slit of the DMA to reduce transport
time and, therefore, diffusion losses for small particles. This flow
can be controlled separately by the Classifier in much the same
way as the Sheath flow. However, the normal operation mode of the
Long DMA is to connect the sheath flow and bypass flow loops in
the Classifier in series. This boosts the flow (by having two pumps
instead of one) and allows the DMA to reach 20 L/min maximum
flow easily. The nano DMA can also be used with the sheath flow
and bypass flow loops connected in series to reach 20 L/min
maximum flow. Consult the Classifier manual for how to connect
the plumbing for each DMA.
Selected flow rates influence the particle sizes that can be sampled.
Lower flow rates are needed to measure larger particles; higher flow
rates are needed to measure smaller particles. Generally, when
setting up the SMPS
™ spectrometer, particle size range is the
governing parameter. Table 4-1 shows recommended flow rates for
each DMA and CPC combination and the corresponding flow
settings.
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