Operation
29
N o t e
Greater accuracy will be obtained with longer samples. The time
you permit for sampling often depends on the reference
instrument and characteristics of the measured aerosol. It may
take some time to collect sufficient aerosol onto a filter cassette
for accurate gravimetric analysis. Refer to instructions of your
reference instrument for sampling times.
6. Stop sampling with both instruments at the same time.
7. Record the DustTrak monitor average concentration by viewing the
sample average in the Data screen. (Data Screen is reviewed later in this
chapter.)
8. Determine the mass concentration in mg/m
3
from your reference
instrument. For gravimetric sampling this means weighing the gravimetric
sample.
N o t e
If you used the internal gravimetric filter in the DustTrak Model
8530, the flow rate used to compute the concentration should be
2 L/min, not 3 L/min since only 2 L/min of aerosol flow reaches
the filter.
9. Compute the new calibration constant, NewCal, using the following
formula:
CurrentCal
ion
Concentrat
DustTrak
ion
Concentrat
Reference
NewCal
10. Select
Photometric
from the User Cal drop down selection and enter the
NewCal factor using the onscreen controls.
