Campbell Scientific CPEC200 Closed-Path Eddy-Covariance System - Manual (Page 50)

CPEC200 Closed-Path Eddy-Covariance System
7.1 Enclosure Desiccant
Check the humidity indicator card in the mesh pocket in the CPEC200 system
enclosure door and the EC100 enclosure door. The humidity indicator card has
three colored circles that indicate the percentage of humidity (see FIGURE
4-14). Desiccant packets inside the enclosure should be replaced with fresh
packets when the upper dot on the indicator begins to turn pink. The indicator
card does not need to be replaced unless the colored circles overrun.
Campbell Scientific strongly suggests replacing desiccant
instead of reactivating old desiccant. Improper reactivation
can cause the desiccant packets to explode.
The replacement desiccant pack is the 4905 Single 4-Unit Silica Desiccant Bag
which can be purchased in quantities of 20 as pn 6714. The replacement
humidity indicator card is pn 28878. See Section 4.1.5, Replacement Parts, for
more detail.
If the desiccant packs in the CPEC200 system enclosure are requiring frequent
replacement, check that the feedthrough cap is properly installed. In very
humid conditions it may be helpful to seal the cable feedthrough with
plumber’s putty as described in Section 5.3.4, Apply Power.
7.2 EC155 Intake Filter
Over time, the EC155’s intake filter will become plugged with particulates
from the air causing an increased pressure drop. The EC155 has a differential
pressure sensor with a ±7 kPa range to measure the sample cell pressure with
respect to ambient pressure. As the intake filter plugs over time, the
differential pressure will decrease from approximately –3 kPa (typical for a
clean filter at 7 LPM). If the differential pressure reaches –7 kPa, the data will
no longer be valid. It is important to monitor the differential pressure and
replace the filter before this limit is reached.
The default replacement filter is pn 26072. It is a 2.5-cm (1.0-in) diameter,
sintered stainless steel disk filter of 20 µm pore size, with a molded
Santoprene™ shell. An alternative 40 µm filter (pn 28698) is also available.
Choose the 40 µm filter if the default 20 µm filter clogs long
before the EC155 optical windows become dirty.
See the EC155 CO
2
and H
2
O Closed-Path Gas Analyzer Manual for details on
replacing the intake filter.
7.3 EC155 Windows
Over time, the optical windows of the EC155 will become dirty and will need
to be cleaned. To evaluate the cleanliness of the windows, monitor the CO
2
signal and the H
2
O signal. These will have a value of approximately 1.0 for
clean windows, but will decrease as the windows become dirty. The EC155 is
calibrated for a range of signal levels down to 0.80. Clean the windows as
instructed in the EC155 CO
2
and H
2
O Closed-Path Gas Analyzer Manual
before the CO
2
and H
2
O signals reach 0.80.
CAUTION
NOTE
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