38 AO2000-LS25 LASER ANALYZERS | OI/AO2000-LS25-EN REV. D
… 7 Installation
… Mounting
Housing purging of the transmitter and receiver units
For applications (e.g. small measuring ranges of O
2
, H
2
O and
CO
2
) where purging of the transmitter and receiver units is
required, the connection diagram in Connection diagram flange
- and housing purging on page 38 must be observed.
Purge medium
To avoid contaminating the analyzer’s optical windows, it must
be purged with dry and oil-free instrument air (in accordance
with ISO 8573.1 Class 2–3) or nitrogen depending on the
application, see Air purging of flanges on page 37.
The purge gas flow must not be high to avoid pressure build-up
inside the units.
ABB recommends reducing the purge gas flow to less than
0.5 l/min.
In the event of a purge gas supply failure, the transmitter and
receiver units can maintain a purge gas level of more than 99.5 %
for one hour.
Isolation flanges
Figure 21: Isolation flange (Example)
For toxic gas and highly corrosive applications especially in
combination with high pressure the first flange has to be an
isolation flange which isolates the process from the analyzer.
In these cases a shut-off valve is always necessary in order to do
maintenance on the flange.
The isolation flange has to be “custom tailored” for the
individual process. The isolation flange may be purged if
necessary (refer to Connection diagram flange - and housing
purging on page 38). Due to the additional windows a certain
loss of transmission is to be expected. The analyzer will be
mounted on the isolation flange.
Before dismounting the isolation flange make sure the process
is either turned off and safe or the volume between the nearly
closed shut-off valve and the flange is purged thoroughly to
make sure no harmful gas may leak out.
Connection diagram flange - and housing purging
Figure 22: Purging of the transmitter and receiver units
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