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All about Keithley DMM7510. Bugs and features, recipes, advice, notes.
Kleinstein:
Normally the amplifier only add a little noise to the 1 V range. Much of the noise is often still from the ADC (and the references of cause). So the way with only one divider does not add that much noise. The standard high voltage divider are this way, so even 8 digit meters like 3458, Datron 1281 and Keithley 2002 use only 1 divider, though here it may actually help to have 2 divider settings. Switching off the 1:10 divider may however need a relay for switching (or switch at the low side and this a variable impedance), and this can add more trouble than using just 1 divider.
--- Quote from: MegaVolt on July 02, 2020, 10:10:45 am ---Forgot to add. If you disable AZ, then the cunning envelope disappears. And there remains just a certain frequency with a constant amplitude. The signal does not become smaller in amplitude but looks prettier.
--- End quote ---
That is interesting: so the low frequency part is more like an aliasing of the higher frequency part.
The very fast readings well below 1 PLC are often used without auto zero, as this about speed and not so much about accuracy.
MegaVolt:
New firmware released.
https://www.tek.com/digital-multimeter/dmm7510-software/model-dmm7510-firmware-revision-172-and-release-notes
MegaVolt:
First impressions:
Fixed working with memory. For the first time I was able to allocate a buffer for 8.3 million samples.
But unfortunately, as before, it cannot be filled with data during digitization. Somewhere after 4 million there is a pause in filling the buffer :(
Kilo degrees left.
MegaVolt:
I updated the new version and after ACAL I found an additional zero offset of 200 ... 300 nV.
It was in the region of 300-400 became 500-800 ....
Does anyone have a similar effect?
The only thing that I made a mistake and confused ACAL after flashing without turning off the device. That is, he rebooted himself, but I did not remove the power completely. Then I found that the device was not behaving quite correctly (for example, I could not switch the input impedance) and turned off the power. After turning on and re ACAL, I see the same shift :(
Perhaps I ruined something. Or in the new firmware there were some changes about which were not said in the description :(
E-Design:
--- Quote from: MegaVolt on July 15, 2020, 09:08:56 am ---I updated the new version and after ACAL I found an additional zero offset of 200 ... 300 nV.
It was in the region of 300-400 became 500-800 ....
Does anyone have a similar effect?
The only thing that I made a mistake and confused ACAL after flashing without turning off the device. That is, he rebooted himself, but I did not remove the power completely. Then I found that the device was not behaving quite correctly (for example, I could not switch the input impedance) and turned off the power. After turning on and re ACAL, I see the same shift :(
Perhaps I ruined something. Or in the new firmware there were some changes about which were not said in the description :(
--- End quote ---
Hi Megavolt, do you have a low thermal short for when doing zero calibration? Thermal effects from metal of the short and environment can cause voltage gradients of 100+ nV How much thermal settling time? No airflow blowing on the instrument? These are some of the considerations for you. Even a brief power cycle is enough to upset the offset 100nV due to the internal temperature change and re-settling.
Also there will not be any undocumented firmware changes that you didnt see in the description in case you worry about it. If firmware makes a change to calibration or how the measurements are built, it will be described there.
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