Getting this DMM out of US customs is incredibly frustrating, is this paranoid crap a new thing?
Occasionally customs gets freaked out by test equipment.
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Nothing new as far as I'm aware.
thank you very much for the script, however there seem to be an issue with the readingbuffer, that every time the script is ran it seems to change the reading buffer to fill mode "once", even when i manually change the fill mode back to continuous on the dmm, so the script eventually stops itself. Is there anyway to change the fill mode to continuous in the script?. I noticed this aswell on the power measurement script aswell
Thanks!!
Yeah, by default buffers are fill-once. Add these commands after the buffers have been created (so around line 15):
readingBuffer.fillmode = buffer.FILL_CONTINUOUS
powerBuffer.fillmode = buffer.FILL_CONTINUOUS
Manually changing them should work too, but you have to change both buffers. The fillmode command in on page 742/15-41 of the reference manual.
EDIT: oh, you also need to change a couple other things: the for loop needs to become a "while true do" and you need to add "i = 1" before the loop and "i = i + 1" at the bottom of the loop since we're removing the iterable for loop.
The lowest resistance range is very noisy as expected, getting usable values that low requires slow integration and filtering. Averaging reaches the point of diminishing returns around 5 NPLC with 100x repeat filter. A hundred readings took a little over an hour. Doing 15 NLPC with 100x filter took 3 hours and provided very similar numbers. It's either the limit of the instrument or the limit of my crude methodology.
There are diminishing returns for higher NPLC for most signals, and in fact higher NPLC may be less accurate. Page 203/5-58 in the reference manual discusses this a little bit. At higher NPLC, the measurement interval starts to cover a time frame where the DMM's internal drift starts to matter. Unless you expect a lot of power line noise, I would recommend 1-5 NPLC and averaging.
The interface is a lot of fun to use, there are still a few things that I hope will be adressed in a firmware update. Not a big deal, the yellow cursor have no reason to exist on the 6500 since there's no knob to control it (it seems to have been written more for the smus and the 7510) unless I didn't figure out how to move it around. It makes the behaviour of the enter key a bit random, it's whatever default was selected on the page.
The swipe to change pages can be risky to operate, I sometimes press one of the functions by mistake, which wipe out the currently running acquisition. I would love to cycle the pages with the home key or something, maybe an option to remove the function page completely since there's already a dedicated function button to popup that menu. Maybe a toggle to prevent interrupting the measurement? A dialog yes/no for anything which would clear the buffer? Something like that. When running a trigger and count other than plain continuous, the content of the buffer is probably important.
Interesting idea for the enter key to move between swipes... To remove the Functions swipe screen, you can use same command I gave to PTR_1275 earlier:
display.delete(display.SCREEN_FUNCTIONS_SWIPE)
to bring it back:
display.create(display.SCREEN_HOME, display.OBJ_SWIPE, display.SCREEN_FUNCTIONS_SWIPE)
You could add these to
autoexec.tsp to have the swipe removed on start up.
In fact, here's the list of the swipe screens if anyone else wants to remove one of them. You could even remove all of them! If for some reason you wanted that...
display.SCREEN_FUNCTIONS_SWIPE
display.SCREEN_SETTINGS_SWIPE
display.SCREEN_SECONDARY_SWIPE
display.SCREEN_GRAPH_SWIPE
display.SCREEN_STATS_SWIPE
The very low resistance means measuring very low voltage and there thermal EMF effects at the "resistor" can also limit the accuracy. It might help to cover the resistor to protect it from air drafts. Thermal EMF combined with temperature fluctuations is one of the limiting factors for long time averaging. This is inside the meter and also at the DUT. For the copper resistor this could also be just a fluctuation of the resistance due to temperature changes.
Also make sure the covering is a Faraday cage, stray electrical signals become a problem at the 1 ohm range. Really the 4-wire 1 ohm range is approaching the volt-nut territory so you'd have to start looking a the physical limitations of your measurement setup like you say.
I wish they enabled a 1000x repeat filter for a 1 NLPC reading, which would probably yield one least significant digit in the 1 ohm range. All other ranges are ultra stable and don't really need this. That 1 ohm range is already crazy impressive but it can still be improved in software even more.
Improving the physical measurement setup would have a much larger impact than more averaging if you're talking about going from 100 to 1000 readings. Software can only do so much if you have too much noise. Even our electrometer has a 100 reading limit on averaging.