CIRAS-3 Operation Manual V. 1.09 166 support@ppsystems.com
CO
2
Measurement and Control
CO2r levels are reading higher than expected
• There is a leak somewhere in the gas circuit allowing external ambient air into the system.
Usually this is associated with the absorber columns and the result of a recent desiccant change.
Check that both absorber column assemblies are firmly fitted to the CIRAS-3 console and check
all “O” rings to ensure that they are all firmly seated and not pinched off or cracked.
• Did you store the CIRAS-3 console in the black transport case with a partially pressurized CO
2
cartridge? See Storage on page 14
.
CO2r levels are reading lower than expected
• The soda lime or molecular sieve in the Zero column is exhausted and require replacement.
Check soda lime and molecular sieve and replace accordingly. If any of the columns are
approximately 50% exhausted they should be replaced. Pay special attention to the molecular
sieve as this desiccant is non-indicating and should be replaced when replacing the
Drierite in the same column.
• The CO
2
cartridge is slowly exhausting or missing. The cartridge was put in use at least 1 day
before and most likely is getting low in pressure. See CO2 Cartridge Status on page 68
for more
details. Replace CO
2
cartridge if low in pressure or empty.
• Check to make sure that the cartridge holder is snug to ensure that the cartridge is pierced.
My CO2r is more than 30 µmol mol
-1
from my set point
• You likely forgot to perform a Max C calibration. See Find Max C on page 101 and perform a
Max C calibration.
My CO2r is more than 30 µmol mol
-1
from my set point and in my Settings I’m set to
“Exact reference air” for CO2 Reference
• Are you sure? Go back to Settings to confirm. It is likely set to “Approximate reference air”.
My CO2r or CO2a readings are fluctuating
• First I would check your desiccants and change out if exhausted.
• Your reference or sampling pump might be dirty or dusty and require cleaning or replacement.
See Servicing the Air Sampling Pump (Reference & Analysis). On page 181
. Another quick trick
is to simply swap the pumps to see if the problem follows the pump.
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