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338
AO2000
CONTINUOUS GAS ANALYZERS | OI/AO2000-EN REV. B
Failure of instrument air supply
Shutting-off gas supply if instrument air supply fails
It must be ensured that the gas supply to the analyzer module is shut off if
the instrument air supply fails.
As a rule, this is ensured by installing a pneumatic shut-off valve in the gas
supply line (recommendation) (see page 48); this valve must be controlled by
the instrument air supply in such a way that if it fails (and as a result con-
tinuous case purging fails) (see page 40), the gas supply is automatically
shut off.
If such a pneumatic shut-off valve is not installed, the following precautions
and measures must be taken:
•
The Overall Status or the "Failure" status of the gas analyzer must be
monitored.
•
If the status appears, the cause must be verified in the gas analyzer on
site:
•
If the gas analyzer is not in operation (e.g. as a result of a supply
voltage failure), the supply gases must be shut off (see section "Gas
analyzer shutdown" (see page 343)).
•
If the gas analyzer is in operation, an adequate instrument air supply
must be verified. If this is the case, the status messages must be
verified. If this is not the case, proceed as follows:
1. Shut off the combustion gas supply.
2. Reestablish instrument air supply.
3. Purge gas analyzer for 20 minutes.
4. Turn on combustion gas supply.
5. Gas analyzer starts automatically.
Note for measuring flammable gases
When measuring flammable gases, it must be made sure that in case of a
failure of the instrument air supply or of the analyzer module itself the sam-
ple gas supply to the analyzer module is shut off and the sample gas path is
purged with nitrogen or synthetic air.