BAM 1020-9800 Manual Rev W.docx
Page 69
to any value between 0.000 and 1.000 volts (0.100V increments). The corresponding voltage
on the VOLT OUT +/- terminals on the back of the BAM 1020 should always match within
±0.001 volts. Use a high-quality voltmeter for these tests. If the actual voltage does not match
the value on the TEST > DAC screen, contact the service department.
Note:
This function is critical for all users of external analog data loggers. Measure the
voltage all of the way to the input of your data logger.
Every millivolt of error is a microgram of
error!
Make sure the logger is scaling the voltage correctly. In most cases 0.000V should
scale as -0.015mg, and 1.000V should scale as 0.985mg. See Section 6.2.
7.13 CALIBRATE Test Menu
– Span Membrane Mass Tests
The TEST > CALIBRATE screen is used to perform tests of the reference membrane span
check which occurs automatically every sample cycle. This test can be run if the BAM 1020
has been logging
D
errors. Each BAM 1020 has an individually weighed membrane, and this
mass
(m)
is measured and displayed during this test. Compare the value from this test with
the ABS value on the calibration sheet for your unit. The values must match within 5%, and
will typically match within just a few micrograms. If not, the most common cause is a dirty
membrane foil, which can be carefully cleaned with canned air or clean water rinse. Alcohol is
not used because it leaves a film. CD cleaner works well for badly soiled membranes.
Caution: The span membrane foil is a thin sheet of polyester and is fragile.
It must be
replaced if damaged. Contact the Service department for replacement instructions.
The CALIBRATE Test Screen
The REF MBRN value indicates if the reference membrane is currently extended
(>)
or
withdrawn
(<)
from the beta particle path.
The COUNT (I
0
) value is the total 4-minute beta count through the filter tape only.
The COUNT (I) value is the total 4-minute beta count through both the filter and the
membrane, and is always less the I
0
count.
The CAL MASS M value is the measured mass of the foil derived from the two count values.
The START soft key starts the test cycle. Counting will immediately begin. After 4-minutes
the I
0
count will stop, the membrane will extend, and the I count will begin. At the completion
of the test, the counting will stop and the mass of the membrane will be calculated. The total
elapsed time is about 8.1 minutes per test.
CALIBRATION MODE
REF MBRN: <
COUNT (Io):
634000
COUNT (I):
556234
CAL MASS M:
0.801 mg/cm2
START
STOP
EXIT