Manual adjustment of detector or grating offset is selected via the tabs on the Offset Adjustment Control. The following
describes the procedure for the detector offset adjustment but the grating offset adjustments are performed in the same
manner.
1. If the offset adjustment control is not already displayed press the Display button and select the offset
adjustment control. Click the Detector tab on the offset adjustment control.
2. Set a low-pressure mercury (Hg) pen-ray, or Neon (Ne) lamp (or similar) at the entrance slit of the system.
3. Set the entrance slit width to 10 microns and input the wavelength of a known and recognisable spectral line
into the wavelength control slider. For example the mercury 546.07 or 435.83nm line or the Neon 703.24nm line.
4. Acquire data. The target line should appear close to the centre of the display. Pressing the centre line button
on the offset adjustment control will draw a red line on the centre CCD column of the display and serves as a
useful aid to offset adjustment.
5. If the spectral line is positioned on the centre line then an adjustment to the detector offset value is not
required. If there is a discrepancy between the displayed centre wavelength and the actual wavelength position
of the spectral line the offset should be adjusted.
6. Press the appropriate + or - offset adjustment buttons to bring the centre of the spectral line onto the red centre
line. The adjustment step size may be selected from a drop down list (right-click either of the keys). It will be
found that “zooming” the acquisition display will help the nal ne adjustments.
7. When the target spectral line has been centred the procedure is complete. As a rough rule-of-thumb an offset
adjustment of approx. 3 units will offset the spectral line by 1 pixel (26 micron wide pixel).
Figure 11: Spectra acquired before (left) and after (right) detector offset adjustment.
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