Trouble with aggregate intensity count times

[Mike Jercinovic]

  OK, I wonder if anyone else has encountered this.  We see it fairly frequently and I have been trying to figure out a way to absolutely make it happen.  It is still inconsistent.  If I set up multiple spectrometer integration, say for Pb on two spectrometers, each counting on peak for 600 seconds using multi-point backgrounds, then store that unknown as a setup, I can digitize my unknowns and use it and it runs fine.  Now if I create a new unknown and base it on the just stored setup, or on any of the digitized unknowns that I might have stored as setup files, something interesting SOMETIMES happens...the first Pb spectrometer is just as it was stored with full 600 sec. count time, but my second spectrometer Pb measurement has now defaulted the count time back to the standard count time of 20 seconds on peak.
  This happened yesterday when I acquired an unknown, then adjusted the multipoint backgrounds to change the number of points to use in the regression, then stored that unknown as a setup, hoping that if I use that as a setup for my next unknown, it would use the multipoint regression parameters I had just completed.  I didn't check my count times before running, and, indeed, it had reset my second spectrometer Pb count time back to 20 seconds, so many hours of worthless results...bummer.  Seems like I just have to remember to carefully check these count times before using the new setups.
   This is tricky because it does not always happen.  It happens pretty often when using Pb Mb (which we use for xenotime and zircon), but I have seen it happen once with Pb Ma.

[John Donovan]

Mike,
If you can find out how to reproduce this issue, I'm sure I can fix it.  I'll just need the steps outlined...
john

[Probeman]

Could this be related at all to the "On Peak Time Fraction" feature?
john

[Mike Jercinovic]

OK, here are the steps...
1) In Acquire, set up a new sample (unknown), call it "Zircon setup 1", which has Pb Mb on SP3 and Pb Mb on SP4, on peak 900 sec, off peak 260 sec, multipoint acquisition, TDI, on peak time factor 0 0.01, Nth pt 10.
2) In Analyze, add this unknown to setups.
3) Digitize an unknown zircon sample, call it "zircon unknown 1" and run it after assigning "Zircon setup 1" to this digitized sample.
4) When this unknown sample run is complete, display multipoint backgrounds.
5) Edit the multipoint results for "zircon unknown 1" SP3 Pb by changing iterate low from 2 to 3, then assign fit to selected channel for all lines
6) Edit the multipoint results for "zircon unknown 1" SP4 Pb by changing iterate low from 2 to 3, then assign fit to selected channel for all lines
7) Close (multipt. window)
Click analyze in Analyze window
9) In the Analyze window, highlight "zircon unknown 1" and add to setup
10) In Acquire, start New Sample, call it "Zircon setup 2" and Load Sample Setup - choose "zircon unknown 1"
11) Click OK
12) In Acquire, click elements/cations to make sure everything is there OK,
13) In Acquire, click count times.  SP3 PbMb is now 900sec on peak, 260 sec off peak as it should be, but SP4 Pb Mb is now 20 sec. on peak, 10 sec off peak.

I tried this without any editing of the multipoint backgrounds and the count times are not affected, that is, both SP3 and SP4 Pb Mb stay at the prescribed 900 sec on peak and 260 sec off peak.

[John Donovan]

What if you have the On Peak Count Time Fraction set to 1.0?

Do the steps above still produce the issue?
johhn

[Mike Jercinovic]

I set up a run last night with the on peak time fraction set to 1, and unchecked so as not to try to use this at all.  Then this morning I just followed the steps 4-13 above, and get the same result, that is, sp4 Pb Mb goes to 20 seconds on peak, 10 second off peak.  So, the on peak time fraction appears unrelated as I get the same problem whether I use OPTF or not.

[John Donovan]

Hi Mike,
Ok, I could not reproduce the problem you are seeing. However, I do see a place in the code related to the update iterate parameters that could cause a problem, so that is fixed.

Update PFE as usual from the Help | Update Probe for EPMA menu and see if that fixed it.

Please let me know.
john

[Mike Jercinovic]

Looks good John!  I updated and tried it with the sequence above and it now seems to retain the counting times on aggregate counting of multiple spectrometers.  Excellent, thanks a million!

Edit by John: it was a subtle timing related issue which was probably why I couldn't reproduce it on my computer, but glad I found the problematic code anyway!  You owe me exactly one beer!