On-peak position offset

[dawncruth]

One of our spectrometer cables broke over the summer and was fixed this past fall. I keep getting the error:
Warning: On-peak position offset for na ka on spectrometer 2 is 0.634750
Warning: On-peak position offset for mg ka on spectrometer 2 is 0.760513

I'm sure this is related to the fix.

How do I adjust PfE to fix the error?

[John Donovan]

This warning is referring to the fact that the "found" peak position for Na Ka is ~0.6 or 0.7 mm away from the theoretical peak position. That is a large offset and usually means that your spectrometer is quite misaligned.

Unless you are peaking on the wrong peak, you can probably ignore this warning until you get the spectrometer properly aligned (that's why it's warning as opposed to an error!).   

Probe for EPMA warns you if the "found" peak position is more than 1/N of the spectrometer range away from the theoretical peak position.  In the SCALERS.DAT file this value for "N" is found on line 34 as seen here:

 400.     400.     400.     400.     400.  "Spec offset warning factors"

In this case the value of N is 400.  You can decrease this value to make the warning "disappear" but I wouldn't do that and would instead get the spectrometer fixed.

You might also want to check these topics:

https://probesoftware.com/smf/index.php?topic=797.0

https://probesoftware.com/smf/index.php?topic=782.0

[dawncruth]

Interesting about the distance from the theoretical value.

The spectrometer was technically fixed and brought back to factory specs during our PM in October. We repeak regularly and have produced high quality data despite the error.

I'll chat with our engineer.

[John Donovan]

Well if you're happy with the spectrometer alignment you could either just ignore the warnings or edit the SCALERS.DAT offset warning value to a somewhat smaller number to prevent PFE from generating them.

[glennpoirier]

Hi Dawn,
I seem to remember you're using a JEOL probe. If that's the case you can initialize the spectrometer and get your positions closer to theoretical. In the PC-EPMA window open Maintenance --> SPC Initialization. This opens a window that will allow you to run the spectrometer up and down to each of the limit switches. It will optionally let you peak an element to set the exact position.
If you do this with PFE connected, it will complain about the spectrometer being out of range, just ignore it.
I run this every time an engineer touches a spectrometer.
Drop me an email if you want more info.

[Anette von der Handt]

Hi Dawn,

I agree with Glenn. Best to initialize the spectrometers in the JEOL software after repairs or realignment of a spectrometer. When you do that, it might slightly change that spectrometer's min/max values and push them beyond what is set in "motors.dat", causing another error message in PFE about exceeding spectrometer limits in wavescans or so.

In that case, just note down the new spectrometer limit values in the JEOL software and change as needed in "motors.dat" under "low limit spect/stage motors" and "high limit spect/stage motors hilim". Let me know if you would like more help with that.

[dawncruth]

Hi all,
Thanks for the pro tips! I will initialize today!