I was measuring a DUT I’m very familiar with on my QA401, and started getting some unusual errors using the PwrThdVersusPower.dll testplugin. On the main screen the THD and THD+N values vs. different power levels were all as expected based on familiarity (dropping to about -95 THDN). But the plot and trace export after running the testplugin kept outputting a plot that was far too low - below 110 db THDN for example. Exporting the trace to a csv also showed incorrect values that did not match the measurements on the main screen while the test was executing.
The dll also appears to be ignoring settings / has stuck settings. For example, no matter how I change early abort settings the test ignores the early abort (I’ve used it successfully hundreds of times). The settings UI for this testplugin also seems to not remember changes I make - for example, if I set -60 for the early abort it reverts to -40 (my usual setting) next time I select that plugin. It also ignores whether I toggle to measure THD only vs THD+N - the same wrong values are plotted on the graph tool graph.
I’ve tried resetting the application to defaults from the file menu, unplugging and repowering the QA401, same issue. I’ve tried un-installing the software and re-installing (version 1.920) and no change. After rolling back to 1.907 things started behaving again. Un-installed 1.907, re-installed 1.920, and the issues returned. Another testplugin I use (AmpThdVersusFrequency) runs and graphs properly.
Can you help me figure out why using PowerThdVersusPower isn’t working correctly for me? I’m using windows 10 and grabbed 1.920 from the QA401 section of Github (unless I should be using QA40x?)
EDIT: The graphtool won’t plot THD with 1.920. I’ve attached two screenshots of the familiar (expected) DUT performance with what I’m getting with 1.920.