Raw Data Conversion To Absorbance - Agilent Technologies 1100 Series Reference Manual

6 Introduction to the Detector

Raw Data Conversion to Absorbance

The raw data flow (from the photodiode array) and conversion to absorbance
spectra for each data point is a multiple step process. This process is outlined
in this section. For exact mathematical equations for the transformation, see
the Understanding Your Agilent ChemStation handbook.
firmware flow diagram.
Subtract Dark Signal
Raw data coming from the photodiode array via the signal conditioning
electronics (which includes a variable gain amplifier) are read from the A/D
converter. For details, see
intensity values of each photodiode of the array.
During a blank measurement a dark signal and electronic offset measurement
is performed for each diode on the photodiode array. This offset spectrum is
stored and subtracted from all subsequent intensity spectra to give dark signal
corrected intensity spectra.
Gain Correction
During a blank measurement every photodiode is assigned a gain value,
depending on the amount of light falling on the diode array. These gain values
are stored in a table. They are used to adjust the amplification factor in the
signal conditioning electronics. This process is used to adjust small signal
levels to the optimum range of the A/D converter.
The DSP firmware uses the gain table to adjust the dark signal corrected
intensity spectra.
248
"A/D Converter" on page 241. These raw data are
1100 Series DAD and MWD Reference Manual
Figure 63 shows the