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74
GAA610-M ADVANCED EMISSION GAS MONITORING SYSTEM | OI/GAA610-M-EN REV. B
... 13 Maintenance
Calibrating the analyzer system
Notice
Impairment of the analyzer function
Impairment of the analyzer function due to improper
calibration.
•
Only persons familiar with the calibration of comparable
analyzer systems are certified as being capable of such
work and should work on the system.
Note
Calibration of the analyzer system has to be performed on board
every 6 to 12 months with test gas, in accordance to agreement
with respective certification class.
Conversion of concentration values
Care has to be taken, that the certified test gas used has to be
specified in % by volume. In case it is specified in volume by mole
there has to be a conversion as following:
Vol
volume fraction of the component
C
X
mole fraction
C
m
molar mass of the component
C
ρ
density of the component in the reference state
C
X
mole fraction of the component in the reference state
T
ρ
density of the carrier gas in the reference state
T
m
molar mass of the carrier gas
T
Basics
The purpose of the calibration (adjustment) is to scale the
analyzer with a reference normal. This reference normal can be a
(certified) test gas or a built-in internal gas filled cell.
When calibrating SO
with infrared analyzers, some
2
characteristics have to be considered. Firstly, SO
soluble gas, which means that parts of the gas may be solved in
water. On the other hand, SO
the infrared range. Therefore, it is important that the water
content in the measured gas is constant. This is achieved by the
gas cooler, which stabilizes the output to a constant dew point
of 3 °C below the entrance dew point. The error caused by the
overlay of the constant water signal is compensated in the
analyzer by shifting the zero point.
In continuous operation you will also get a lossless operation, as
long as the gas concentration and the inlet humidity do not vary
significantly.
is a water-
2
is overlaid by the water signal in
2
Calibration – Principles
Preconditions
•
Ambient air temperature: 5 °C to 40 °C
•
If used, the flow from test gas bottle has to be as similar to
the flow via the membrane pump as possible. The flow of the
test gas bottle can be regulated via the pressure valve on top
of the bottle.
•
Calibration should only be started after the warm-up phase
(Approx. 2.5 h)
Calibration control
The analyzer has two methods to control the calibration:
•
Automatic calibration, see see page 75.
•
Manual calibration, see see page 76.
In the following these are explained step by step.
Plausibility check during the calibration
If during calibration the gas analyzer finds implausible values
(e.g. if the span and zero values are equal), calibration is stopped
and an error message is generated. The values stored for the last
calibration remain in effect.
Output response and waiting period
If the Output Current Response parameter is set to Hold, current
output is halted for a specific time to allow the measurement
value to stabilize after automatic calibration is ended. By default,
this value is not hold.
The complete automatic zero-point calibration with ambient air
takes approx. 15 minutes and zero-point calibration with
ambient air and end-point calibration with calibration cells
approx. 25 minutes (Automatic calibration).
Test gases for zero calibration (without calibration cells)
A zero gas is required for zero calibration in any case. We
recommend using N
for calibration.
2
Test gases for end-point calibration without calibration
cells
A test gas is required for each detector for span calibration
without calibration cells. In the case of automatic and externally
controlled calibration, a test gas mixture is required for all
detectors since all are calibrated simultaneously. The span gas
concentration should be 80 to 100 % of the end value of the
largest measurement range.
No test gas is required for the automatic calibration.
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