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Operation and Maintenance Manual 89
Detector Sensitivity
Detector sensitivity is an indicator reflecting the performance characteristics
of a given system, and is a useful tool to determine when Detector
maintenance is warranted. Sensitivity is typically reported as a minimum
detection limit (MDL) as calculated from the following formula:
Where Am't N/S (amount of nitrogen or sulfur) is the mass of nitrogen or
sulfur in picograms that reaches the Detector, PktoPkNoise (peak-to-peak
noise) is the measure of the noise (e.g. in mV), Signal is the height of the peak
in the same units, and Wd1/2ht is the width of the peak at half height in
seconds. The constant 0.66 is used in the calculation assuming the MDL S/N =
3.29.
Before it is released from the factory, each 355 SCD must pass an MDL level of
<0.5 pg Sulfur/second and each 255 NCD must pass an MDL level of <3.0 pg
Nitrogen/second. The response from individual detection systems may vary by
a factor of 2 or 3; however, it is typical for Detectors to perform in the 0.1-0.3
pg S/second range for the 355 SCD and in the 1-2 pg N/second for the 255 NCD
when tested at Agilent.
)()(
)
()/'(66.0
SignalWd
NoisePktoPkSNtAm
MDL
×
××
=
ht1/2