Hi Phillip,
I don't know if you've read your way through the whole thread, but based on the testing that Gareth and I have done on our instruments there might be as few as two different settings for these limits which depend on the instrument generation. But it would be good to confirm this on more instruments.
Range of 0-5V for newer SX100 and SXFive, which appear to have this "dynamic baseline" behaviour, where the minimum baseline value you can set in PeakSight depends on the gain setting, i.e. a linear correlation from baseline 0.369V at gain zero to 0.994V at gain 4096.
Range of 0.56 - 5.54V for older SX100s, where the minimum baseline you can set in PeakSight is always 0.56V. This is basically a 5V range as well - I think the missing 0.02V to 5.56V might just be the width of the final channel (5V / 256 channels = 0.0195V, rounded to 0.02V).
One way to find out your PHA range might be by saving a PHA scan to ASCII in PeakSight (click the Save button in the top right corner of the SX Control | Display | WDS | PHA window, only available in newer PeakSight versions). PeakSight seems to display the last PHA ROM/MCA scan even if it was acquired with PFE, so you can export the data for the same PHA scan in both softwares (in PFE doing both the verbose log window and normal export) and compare directly in Excel, which is how I created the graph I attached to the last post.
One thing we're also seeing on our "old" SX100 is a slight shift in the PHA distribution depending on if it is acquired directly after the Faraday cup is switched out or if the beam has already been on the sample/standard for some time. The counting system seems to have to settle for some time once hit by x-rays. I don't know exactly for how long, might be less than a second. But this is why I when doing these tests always switch the cup out, wait a couple of seconds and then do the PHA scan. After that initial "settling" period the PHA peak doesn't appear to shift anymore.
Cheers,
Karsten