Calibration chart tab

The energy calibration chart allows you to overview the quality of the calibration.

This sheet contains the chart itself at the top, a residual at middle, and a list of candidate fitted peaks at the bottom.

The chart shows the calibration line with red, the standard uncertainty of the calculated energy values in blue; the calibration points' difference from the energy calibration line as filled green rectangles.

The peak list may be used to add new points quickly to the calibration. The peak list is filtered to display the significant peaks only: only the peaks with less than 1% peak area uncertainty will be displayed – however, this value can be edited under the list.

If you find too few peaks in the list, change this value to, say, 5%, and all the peaks below this limit will be listed immediately. To quickly add a peak to the calibration as a new point, click on its row, and click the Add button beside the list.

On the chart, gray triangles depict the positions of the fitted candidate peaks, which are listed in the peak list table. When you click on a gray triangle, its point will be shown with bolder line, and the corresponding data row will be selected.

The fitted peaks are always displayed with zero difference from the calibration curve, as their library energy is not yet known. When Add button clicked, user should select a library peak, then a real difference may be computed.

Notes:

The gray triangles may help you to notify if you are using dangerous extrapolation: if the last fitted peak – that is, the last gray triangle – is too far from the last green calibration point, its computed energy value may be rather uncertain. In this case, it is advisable to add also an other, closer peak as an additional calibration point.
If you see a strong non-random tendency among the linear calibration points, and the difference exceeds, say, 0.1 keV, this may indicate significant nonlinearity of your measurement system. In this case, it is advisable to create a nonlinearity calibration, and use it together with the two-point linear energy calibration as a nonlinearity compensation. See details in section “System nonlinearity analysis”.