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Keithley DMM7510, SMU 2450 & 2460 problems

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maxwell3e10:
I have slight hope that the autozero problem is fixed in DMM6500, but wouldn't hold by breath. If it has as low noise as DMM7500 and the only difference is in the voltage reference, it would be a great meter.

In general, I think they are putting more effort into a nice user interface than into the intricacies of analog design. And it makes market sense, it's both easier to hire engineers who can design apps and easier to sell meters based on shiny interface than on obscure specs. Even on eevblog  there are more posts about "noise" as in fan noise instead of actual electrical noise. So, as someone else had said here, its not obvious that a meter rivaling HP3458 will ever be build.

niner_007:

--- Quote from: Kleinstein on May 19, 2018, 09:28:05 am ---We don't know for sure, but the likely cause of the extra noise for the 10 s time scale is likely due to the AZ implementation. The script for the workaround also supports this.
--- End quote ---
silly question, what if you turn AZ off and don't use it at all?

maxwell3e10:

--- Quote from: niner_007 on May 19, 2018, 11:11:18 pm ---silly question, what if you turn AZ off and don't use it at all?

--- End quote ---
Look at reply #3 in this thread. Basically, the autozero algorithm behaves as if it's not even used until about 30 sec, while the 1/f noise of the meter is such that it would benefit from autozero after 1 sec.

niner_007:

--- Quote from: maxwell3e10 on May 19, 2018, 11:34:38 pm ---
--- Quote from: niner_007 on May 19, 2018, 11:11:18 pm ---silly question, what if you turn AZ off and don't use it at all?

--- End quote ---
Look at reply #3 in this thread. Basically, the autozero algorithm behaves as if it's not even used until about 30 sec, while the 1/f noise of the meter is such that it would benefit from autozero after 1 sec.

--- End quote ---
is the noise because of the drift? if you have a super stable environment, would it still happen? so after AZ is ran, it starts to drift until you run it again? basically constantly drifting?

kj7e:
AutoZero corrects offset voltage drift from the input gain and A/D stage.  These drifts happen to all DMM's including the 7510, 34470, or the 3458.  The AZ function switches from the input signal to an internal short or known zero to calibrate the zero offset.  The issue with the 7510 seems to be how and when the AZ happens.  Its not a major issue (IMHO), just appears not to work as well as it should and it shows up as some extra front end noise.  It is a concern, especially if it could be better optimized in software.  So far Keithley has not made any public comments on this, so its possible it's not an easy task.

It would not matter how stable your environment is, you cant stop the internal voltage offset drifts from happening.  See this video which helps explain some of this behavior;

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