2-16 Electrostatic Classifier Model 3082 and SMPS Spectrometer Model 3938
For SMPS spectrometer measurements—If the aerosol inlet flow allows
multiple selections of impactor nozzles (e.g., all three nozzles can be used
if the aerosol inlet flow rate is 0.7 L/min), use the nozzle with the cut-off
size closest to the upper limit of the SMPS spectrometer measurement
range. This will increase the accuracy of the Multiple Charge Correction
(compare Appendix B). The aerosol inlet flow rate, the corresponding cut-
off size for a selected nozzle and upper limit of the SMPS spectrometer
measurement range are shown in the properties window of both Aerosol
Instrument Manager software and the Classifier; see e.g., Using the Setup
Screen in Chapter 5.
C a u t i o n
The upper limit of the flow range for each impactor corresponds to a
pressure differential of approximately 6 kPa. Operating the impactor at
flow rates that result in a pressure differential of greater than 10 kPa
may result in damage to the differential pressure sensor on the
classifier.
C a u t i o n
Do not use a 0.0457 cm or 0.0508 cm impactor with CPCs in high flow
mode (1.5 L/min) as this creates excessive pressure drop and may
result in low or incorrect CPC inlet flow.
To install an impactor, follow these instructions:
1. Select the correct impactor for your application, based on Table 2-10.
2. If you have not already done so, remove the inlet adapter.
3. Assemble the impactor by pushing the stainless steel impaction plate
into the black impactor body in the orientation shown below.
4. Push the impactor into the classifier inlet. When the impactor is fully
inserted, lock it in place by twisting it in a clockwise direction until the
dot on the impactor aligns with the arrow on the bezel.
5. If an impactor is used as part of an SMPS spectrometer with the CPC
operating at 1 L/min or above, there will be a noticeable difference
between the aerosol flow rate measured by the impactor and the
aerosol flow rate measured by the CPC. This is a result of the CPC
measuring volumetric flow at a low pressure due to the pressure drop
across the impactor. For scanning that requires high precision of
concentration measurements, manually enter the aerosol inlet flow rate
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