BAM 1020-9800 Manual Rev W.docx
Page 29
the BAM begins counting beta particles through this clean spot for exactly eight
minutes. (I
0
)
2.
~Minute 08:
The BAM 1020 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 BAM 1020 then lowers the nozzle
onto the filter tape and turns the vacuum pump on, pulling particulate-laden air through
the filter tape on which I
0
was just measured, for 42 minutes at 16.70 liters per minute.
3.
~Minute 50:
The BAM 1020 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 BAM begins counting beta particles through the now dirty spot of tape
for exactly eight minutes (I
3
).
4.
~Minute 58:
The BAM 1020 stops counting beta particles through the dirty spot (I
3
).
The BAM 1020 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
BAM then sits idle until the top of the next hour.
5.
Minute 60:
The beginning of the next hour. The BAM 1020 records the just-
calculated concentration value to memory and sets the analog output voltage to
represent the previous hour’s concentration. The BAM 1020 advances a new fresh
spot of tape to the beta measurement area and the measurement cycle starts again.
4.2 Automatic Span Checks During The Cycle
While the vacuum pump is on and pulling air through the filter tape as described above the
BAM 1020 performs a span check. The user may set up the BAM 1020 to perform the span
check hourly, once per day, or not at all. The BAM 1020 also performs a stability test:
1.
Minute 08:
The BAM 1020 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. The BAM 1020 begins counting the beta particles through this
spot for exactly eight minutes. The measured value is recorded as
𝐼
1
.
2. Minute 16: The BAM 1020 stops counting beta particles 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 is of known mass density (mg/cm
2
).
The BAM starts counting beta particles for eight minutes again, this time through the
membrane and the filter tape spot at the same time. This value is recorded as
𝐼
2
.
3. Minute 24: The BAM 1020 stops counting beta particles through the membrane
withdraws the membrane assembly, and calculates the mass density of the
membrane.
4.
Minute 42:
(Eight minutes before the pump stops) The BAM 1020 counts the beta
particles through the same spot again (without the membrane) for another eight
minutes. This value is recorded as
𝐼
1
′
.
