4–1
CHAPTER 4
DMAs: Using Different
Models with the
Classifier
This chapter describes the Differential Mobility Analyzers (DMA)
that can be used with the Electrostatic Classifier. These DMAs
consist of the Model 3081 Long DMA and Model 3085 Nano DMA.
Custom DMAs can also be used with the 3080 Electrostatic
Classifier but they are not described here.
Model 3081 Long DMA
The Long DMA, as shown in Figure 4-1, is the traditional length
DMA used in the TSI Model 3071 Classifier for many years. The
Long DMA provides the widest size range (10-1000 nm) available of
any of the DMAs.
A cross-sectional view of the Long DMA is shown in Figure 4-2. The
mobility analyzer consists of two cylindrical electrodes made of
polished stainless steel and insulated from each other by a Teflon
®
spacer at the top and an acetyl-plastic (Black Delrin
®
) spacer at the
bottom. The lower spacer allows enough high-voltage leakage to
prevent static charge build up near the exit slit. This gives better
particle transport for small particles than the traditional TSI
Model 3071 Classifier with Long DMA which had Teflon insulators
at both the top and bottom.
The center electrode has an outer radius of 0.369 in. (0.937 cm)
and is coaxial with the outer electrode which has an inner radius of
0.772 in. (1.961 cm). The characteristic length of a DMA is defined
as the length between middle of inlet slit to middle of outlet slit.
However, as the inlet slit is formed by a sharp edge and a radius,
the middle of shortest distance between the edge and the radius,
projected to vertical line is used as the mid point of the inlet slit.
The characteristic length for the long DMA is 17.468 in.
(44.369 cm).
®
Teflon®, Delrin®, and Dacron® are registered trademarks of E. I. du Pont de Nemours and Company.
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