AO2000 CONTINUOUS GAS ANALYZERS | OI/AO2000-EN REV. B 241
Fidas24 NMHC: Notes for calibrating
Sample components and measuring ranges
The Fidas24 NMHC analyzer module measures both the total content of
organic carbons (THC) and the sole methane content (CH
4
) in the sample
gas. The non-methane content of the hydrocarbons (NMHC) is then calcu-
lated from the difference between these alternately measured values.
Two detectors with sample components THC and CH
4
are configured in the
analyzer module. The calculated concentration of non-methane hydrocar-
bons is output as third sample component NMHC.
1 to 4 measuring ranges per sample component are available. The measuring
ranges are factory-set per customer order.
Calibration
The analyzer module is calibrated in ppm C1 in the factory. Therefore, for
example 100 ppm propane are indicated as 300 ppm C1.
Test gases tolerances affect the precision of the NMHC calculation. Hence it
is recommended to calibrate all sample components with methane as test
gas.
For the calibration of the sample component THC, a second (substitute gas)
component CH
4
can be configured in the factory per customer order. Sub-
stitute gas calibration and test gas calibration are then configured as cali-
bration methods. Substitute gas calibration must always be selected as
calibration method in normal measuring operation.
Setting the calibration method
For detailed information on the calibration methods, see the "Calibration
methods" (see page 223) section.
Analyzer module with 1 sample component
1 Select calibration method: Test gas → Single / Common
2 Select measuring range for zero calibration: Zero Meas. Range
3 Select measuring range for span calibration: Span Meas. Range.
Analyzer module with several sample components
1 Select calibration method: Test gas / Substitute gas
2 Select component for zero calibration: Zero Comp.
3 Select measuring range for zero calibration: Zero Meas. Range
4 Select component for span calibration: Span comp.
5 Select measuring range for span calibration: Span Meas. Range
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