Visualization of ADC Limits
Overflow could be concealed by smoothing of a filter and thus not visible for the user. In the Agilent ChemStation, the "ADC overflow" event was only shown in the logbook.
This problem did only occur if the Peakwidth (Responsetime) parameter has been set similar or larger than the real width of the chromatographic peak.
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Raw ADC counts The measured light intensity is limited by the max range of the ADC-converter. |
A filter smoothes the peak making it not clearly visible that the max intensity is reached. Also peak area and peak height are distorted which leads to poor linearity performance. Note that "max LU" is not a fix number but depends on the intensity of the reference channel! | |
New implementation (with firmware A.06.11 or above) While any sample value within the filter width is in state "ADC overflow" the max possible LU is displayed in chromatogram. Note that "max LU" is slightly dependent on lamp drift and lamp noise but strongly dependent on the excitation wavelength. |
As a result, the "ADC overflow" is visible as a real flat peak in the chromatogram showing the user, that the setting of the detector parameter (PMT gain or the concentration of the solution) is set to high.
NOTE
The transfer of methods 1:1 from one FLD to another may result into the above "ADC overflow" problem. For details see FLD Scaling Range and Operating Conditions.
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id: 3585958283