5–8 Series 3080 Electrostatic Classifiers
Classifier can be set up this way, the complexity of the system can
be reduced dramatically if the sheath and excess flows are
connected into a recirculating flow arrangement.
In this case, the excess air flow is fed back into the DMA as sheath
air. The recirculating flow arrangement requires a pump to move
the air, filters to clean the air entering and leaving the pump, a heat
exchanger to remove heat added by the pump, and a flowmeter to
control the flow. In a sealed system the sheath and excess flows are
equal, therefore, the aerosol flow and monodisperse flows are also
equal. Thus, when the sheath/excess flow is set, the remaining two
flows are set by either the aerosol source or the particle detector.
This greatly simplifies setup and also allows the flows to be set
more precisely.
Setting the sheath flow is simply a matter of dialing a flow from the
front panel. Generally, you should set the sheath flow to a 10:1
ratio with the aerosol flow. So, if you are using a CPC with a
1 L/min sampling flow, you can connect the inlet of the CPC
directly to the Monodisperse Flow fitting of the DMA. This will give a
polydisperse flow of 1 L/min and you can set a sheath flow rate of
10 L/min from the front panel. To set the sheath flow:
1. Turn on the Classifier and rotate the control knob to highlight
the Sheath Flow Rate pane on the display.
2. Click the control knob by pushing in.
3. Scroll by rotating the control knob with your index finger until
the correct flow is indicated and then click the selection.
4. The flow will then update with the actual flow. When it
stabilizes at the set flow, the green Sheath Flow LED will light
up.
Neutralizer
The TSI Model 3077A/3077 Kr-85 Neutralizer is usually required in
a system to provide known charge on the particles going into the
Classifier. This allows calculation of actual particle concentration
based on particle size and number concentration of particles exiting
the DMA. This also allows the correlation of particle mobility with
particle size to correct for multiple-charged particles. In some
cases, however, such as when using an Electrospray Aerosol
Generator (TSI Model 3480) to generate ultrafine particles, the
3077A/3077 Kr-85 neutralizer can be bypassed because the 3480
has a Po-210 neutralizer. If you have not yet installed a neutralizer,
refer to “Installing the Kr-85 Bipolar Charger
” in Chapter 2. The
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