Chapter 3
22
Size Corr
Changes the factory calibration of the
particle distribution, based on Arizona
Road Dust, to actual aerosol being
measured. See below for sets to set this
calibration.
User Cal [on,off]
Selecting
On
will activate current user
calibration and deactivate the previously
selected user calibration.
Photometric Calibration Factor
In most situations, the D
UST
T
RAK
™
monitor with its built-in data logging
capability can provide very good information on how the concentration of an
aerosol changes for different processes over time. Factory calibration to the
respirable fraction of standard ISO 12103-1, A1 test dust is fairly
representative of a wide variety of ambient aerosols. Because optical mass
measurements are dependent upon particle size and material properties, there
may be times in which a custom calibration would improve your accuracy
for a specific aerosol.
Determining a aerosol specific photometric calibration requires that you
determine a true mass concentration (e.g., gravimetric analysis) for the
aerosol you want to measure. The true mass concentration is used to
calculate the custom calibration factor for that aerosol. Once you have a
custom calibration factor, you can reuse it each time you make
measurements in the same aerosol environment.
Determining the Calibration Factor for a Specific Aerosol
The D
UST
T
RAK
™
II monitor is factory calibrated to the respirable fraction of
standard ISO 12103-1, A1 test dust. The D
UST
T
RAK
™
monitor can be easily
calibrated to any arbitrary aerosol by adjusting the custom calibration factor.
The D
UST
T
RAK
™
monitor’s custom calibration factor is assigned the value
of 1.00 for the factory calibration to standard ISO test dust. This procedure
describes how to determine the calibration factor for a specific aerosol.
Using the value of 1.00 will always revert back to the factory calibration.
To determine a new calibration factor you need some way of accurately
measuring the concentration of aerosol, hereafter referred to as the reference
instrument. A gravimetric analysis is often the best choice, though it is
limited to nonvolatile aerosols. The internal 37 mm filter cartridge, in the
desktop units, can be used to collect the reference gravimetric
reference sample.
