MAGEE Scientific Aethalometer AE33 User Manual page 136

Aethalometer
Model AE33
Automatic Zero and Span
The Aethalometer Model AE33 offers the capability for automatically checking the 'zero-air'
response of the instrument under dynamical operating conditions. This test is implemented by
back-flushing the inlet connection with an excess flow of internally-filtered air and circulating
the filtered air in the instrument. The data reported during this period are analyzed for the mean
value and the point-to-point variation. The mean value should be close to zero under ideal
conditions; any positive value greater than zero represents the leakage of BC-containing room
air into the instrument's analytical zone.
instrument's measurement noise level under actual operating conditions of actual flow – i.e., a
'dynamic' test. The point-to-point variation for the wavelength 880 nm at the time-base set to
one second is about 350 ng/m3, which translates to a few ng/m3 at 1-minute time resolution
(Figure 9).
3000
2500
2000
1500
1000
500
268 ng/m3
0
-500
-1000
1000
Figure 9. 'Zero-air' check – the Aethalometer Model AE33 switches form sampling ambient air to filtered
air – 1 second time resolution point-to-point variation is very stable.
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User's manual – Ver. 1.55
The point-to-point variation represents the
Point-to-point variation @ 1 second:
355 ng/m3
1500 2000
t (s)
July 2017
1 second timebase
30 point adjecent averaging
301 ng/m3
2500 3000
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