Maintenance, Service, and Troubleshooting 6-23
7. Run a scan with the HEPA filter installed. Do not end scan before it
has finished—let it scan the across the entire high voltage range of the
classifier. There should be zero (or very few) particles detected across
the particle size distribution.
To perform the SMPS spectrometer Zero test, follow these instructions:
1. Install a DMA and leave the classifier inlet open to the air.
2. From the classifier display, set the sheath flow rate to 30 L/min, or if
preferred, to the flow rate that will be used in your application.
3. From the CPC display, set the aerosol flow rate to 1.5 L/min, or if
preferred, to the flow rate that will be used in your application.
4. From the classifier display, turn off the DMA voltage by clicking on the
power button icon ( ) next to the high voltage reading.
5. The detector concentration should drop to zero. If the detector counts
particles, either the sheath-to-aerosol flow ratio is too low or there is a
leak in the system. A sheath-to-aerosol flow ratio of at least 5:1 is
preferred for this test.
(continued on next page)
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