Operation Manual HORIBA APDA-371
Particulate Monitor
Date:
April, 2010
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HORIBA Europe GmbH, Julius-Kronenberg-Str. 9, D-42799 Leichlingen, Telefon: +49(0)2175-8978-0, Fax: +49(0)2175-8978-50
Page 25
4
THE MEASUREMENT CYCLE
This section describes the measurement and timing cycle of the APDA-371 instrument. A clear understanding of the
measurement is helpful for the effective operation and maintenance of the unit. For advanced information on the
underlying theory and mathematics of the measurement see Theory of Operation, Section 11.
APDA-371 Sample and Measurement Stations
4.1
The One-Hour Cycle Timeline
The APDA-371 is almost always configured to operate on 1-hour cycles. The unit has a real-time clock which controls
the cycle timing. You will see from the following timeline that the unit makes two 8-minute beta measurements, and one
42-minute air sample, for a total of 58 minutes. The other two minutes are used for tape and nozzle movements during
the cycle.
This example shows the timeline if the unit is set for a COUNT TIME of 8 minutes (required for PM
2.5
). If the unit is set
for 4 minutes, then the beta counts at the beginning and end of the hour will be only 4 minutes long, with a 50-minute air
sample in between. Again, the total adds up to 58 minutes. Note: This cycle will be slightly altered if the unit is operated
in the special Early Cycle mode with an external datalogger. See Section 8.
1.
Minute 00:
The beginning of an hour. The APDA-371 immediately advances the filter tape forward one
“window” (the next fresh, unused spot on the tape). This takes a few seconds. The new spot is positioned between the
beta source and the detector, and the APDA begins counting beta particles through this clean spot for exactly eight
minutes. (I
0
)
2.
Minute 08:
The APDA-371 stops counting beta particles through the clean spot (I
0
), and moves the tape
exactly four windows forward, positioning that same spot directly under the nozzle. This takes a few seconds. The unit
then lowers the nozzle onto the filter tape and turns the vacuum pump on, pulling particulate-laden air through the filter
tape (the spot in which I
0
was just measured) for 42 minutes at 16.7 liters per minute.
3.
Minute 50:
The APDA-371 turns the vacuum pump off, raises the nozzle, and moves the filter tape
backwards exactly four windows. This takes a few seconds, and puts the spot that was just loaded with particulate back
between the beta source and the detector. The APDA begins counting beta particles through this (now dirty) spot of
tape for exactly eight minutes (I
3
).
4.
Minute 58:
The APDA-371 stops counting beta particles through the dirty spot (I
3
). The unit uses the I
0
and
I
3
counts to calculate the mass of the deposited particulate on the spot, and uses the total volume of air sampled to
calculate the concentration of the particulate in milligrams or micrograms per cubic meter of air. The APDA then sits idle
and waits a few moments for the remaining time in the hour to expire.
5.
Minute 60:
The beginning of the next hour. The APDA-371 instantly records the just-calculated
concentration value to memory and sets the analog output voltage to represent the previous hour’s concentration. The
unit advances a new fresh spot of tape to the beta measurement area and the whole cycle starts over…
Beta Source
Detector
Nozzle
Beta Source
Detector