Campbell Scientific EC155 CO2 and H2O Closed-Path Gas Analyzer and EC100 Electronics with Optional CSAT3A 3D Sonic Anemometer - Manual (Page 22)

EC155 CO
2
and H
2
O Closed-Path Gas Analyzer
The pressure drop in the optional heated intake assembly is approximately 2.5
kPa at 7 LPM flow with no filter. The filter adds approximately 1 kPa pressure
drop when it is clean. This pressure drop will increase as the filter clogs. The
filter should be replaced before the differential pressure reaches -7 kPa (unless
the user has supplied a pressure sensor with a wider range). See Section 9.2,
Intake Filter Replacement for details on replacing the filter.
If the EC155 is configured without the optional heated intake assembly, there
is tubing connecting the sample inlet fitting to the sample cell that will drop the
pressure approximately 4 kPa at 7 LPM.
6.2.3 Filtration
The EC155 will not be damaged by use without an inlet filter, although a
coarse screen (up to 1 mm hole size) is suggested to keep large debris out.
Over time particulates will collect on the optical windows, reducing the signal
levels until the windows must be cleaned (see Section 9.3, Cleaning Analyzer
Windows). Using a filter on the inlet will increase the time before the windows
must be cleaned. A finer pore size will keep the windows clean longer, but
will need to be replaced more frequently. The optional heated intake assembly
includes a 20 micron filter element, which gives a compromise between filter
replacement and window cleaning.
6.2.4 Plumbing Connections
There are three connections to the EC155 sample cell: the sample inlet, zero-
and-span inlet, and pump outlet, as illustrated in FIGURE 6-4. In the normal
mode, a vacuum pump pulls an air sample from the sample inlet through the
sample cell. In zero-and-span mode the pump is turned off and a zero-and-
span gas is pushed backwards through the sample cell, exhausted out through
the sample inlet.
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