Operation Manual HORIBA APDA-371
Particulate Monitor
Date:
April, 2010
______________________________________________________________________________________________________________________
______________________________________________________________________________________________________________________
HORIBA Europe GmbH, Julius-Kronenberg-Str. 9, D-42799 Leichlingen,
: +49(0)2175-8978-0,
: +49(0)2175-8978-50
Page 26
4.2
Automatic Span Check During The Cycle
While the vacuum pump is on and pulling air through the filter tape, (as described above) the APDA-371 doesn’t have
anything else to do, so it performs an automatic check of its calibration (a span check), and checks for instrument drift
caused by varying external parameters such as temperature, barometric pressure, and relative humidity. No span
corrections are made. This check is performed every hour automatically as follows:
1.
Minute 08:
(When the APDA-371 has just finished moving the clean spot to the nozzle and turned the
pump on) there is another clean spot of filter tape upstream four windows, between the beta source and the detector.
This same spot will stay there for the entire time the pump is on (usually 42 minutes), as the tape cannot move with the
nozzle down. The APDA begins counting the beta particles through this spot for exactly eight minutes (I
1
).
2.
Minute 16:
The APDA-371 stops counting beta particles through this spot (I
1
), and extends the Reference
Membrane between the beta source and the detector, directly above the spot of filter tape that was just measured. The
Reference Membrane is an extremely thin film of clear Mylar held in a metal tongue. The membrane usually has a mass
of about .800 mg. The APDA starts counting beta particles for eight minutes again, this time through the membrane and
the filter tape spot at the same time (I
2
).
3.
Minute 24:
The APDA-371 stops counting beta particles through the membrane (I
2
), withdraws the
membrane assembly, and calculates the mass of the membrane “m”, as if it were particulate on the filter tape spot.
4.
Minute 42 (typical):
(Eight minutes before the pump stops) The APDA-371 counts the beta particles through
the same spot again (without membrane) for another eight minutes (called I
1’
or I
1
prime). This checks the ability of the
unit to hold a constant output when measuring blank filter tape, and is not otherwise used.
The mass density “m” (mg/cm
2
) of the reference membrane calculated during this automatic process is compared to
the known mass of the membrane; the “ABS” value. During factory calibration, the actual mass of each individual span
foil is determined and saved as the ABS value of the APDA in which it is installed. Each hourly measurement of m must
match the ABS value within ±5%. If not, the unit records an error for that hour’s data. Typically, the hourly value of m is
within just a few micrograms of the expected value. This span check provides a method of internal diagnostics for the
measurement system, and for the monitoring of external variables such as temperature variations or pressure changes.
The ABS value is unique to each APDA-371, and can be found on the calibration sheet.
4.3
Sample Period Description
The sample period is the time when the vacuum pump is pulling dust-laden air through the APDA-371. As the air enters
the inlet, it first passes through the external PM
10
head which has a screen to keep out bugs and debris, and uses
inertia to separate out and trap particle larger than 10 microns in size. The air then immediately passes through the
Optional PM
2.5
Very Sharp Cut Cyclone (BGI VSCC™) which further separates out and traps particles larger than 2.5
microns in size.
The air then goes down the inlet and through the filter tape, where the remaining particles are deposited. Some
particles smaller than about 0.2 µm may pass through the filter tape and be exhausted. After the sample period is
completed and the particulate spot is measured, there is almost always a clearly visible spot of dirt on the filter tape
where the particulate was deposited. The APDA-371 will put the spots very close together on the tape. At exactly
midnight, the APDA will skip one spot, leaving a blank spot on the tape. This is a visual aid which separates daily
entries on the tape.
