18 Chinese Metrology Testing
270 Operation Manual
[[FPD+ and ECD Unit Conversion Factors]
[[At the time of publication, China Metrology testing requires noise and drift metrics as shown
below:]
[]
[However, data collection is required to come through the digital output available through the
GC and data system. For the FID, NPD, and TCD, the data system provides data in the desired
reporting units. However, for the ECD and FPD+[], Agilent reports output to its data systems in
“display units,” (DU). This section describes how to accurately convert/scale the FPD+[] and
ECD digital results to make them consistent with Chinese Metrology requirements.]
[The conversion factors for the FPD+[] and ECD take the display unit output from the Agilent
data system digital path to an absolute value for current or voltage. Agilent developed the
conversion factors empirically, based on measurements from a single system that
simultaneously output both the digital and analog data. The conversion factors also
incorporate:]
• [[The scaling applied to analog versus digital signals]
• [An analog signal range setting of 5 (2^5) at the GC]
• [The unique filtering applied by the 35900 ADC]
• [The differences in bandwidth (BW) associated with the GC digital channel (5 Hz) and the
35900 ADC analog path (3 Hz) ]]
[The differences in channel bandwidth between the analog and digital signal paths can be
taken into consideration as follows:]
[BW = 35900 ADC path / GC digital path =
√(3 Hz / 5 Hz) = 0.7]
[]]
[[Conversion factors for the FPD+[]]
[[For the FPD+[], the conversion factor is the same whether the phosphorus or sulfur filter is
used:]
[FPD+[] (phosphorus): 1 DU = 1 x 10[
–12
] A]
[FPD+[] (sulfur): 1 DU = 1 x 10[
–12
] A]
[]]]
[[Conversion factor for the ECD]
[[For the ECD, the China Metrology standard was established based on an earlier model ECD.
Agilent relates display units and Hz (the base unit of measure for the ECD) at a different ratio
for the ECD compared to the ECD used to develop the standard. The ECD correlates a DU to
Detector Reporting units
FID A
TCD mV
NPD A
FPD+[] A
ECD mV
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