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Some old school instruments showing how it's done (HP 3325A and Fluke 8506a)
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joeqsmith:
Outside of a short note about the there being a fast (Y) and slow (Z) filter and them being a 3-pole Bessel with different cutoffs, they seem to provide very little detail about them.  Maybe the schematic IS the document.   

With Dave's UEI meter, I would feed a chirp into it and record the filters response.   Seems like you could do something like this to test out the hardware filters.
SilverSolder:

--- Quote from: joeqsmith on February 05, 2021, 06:29:41 pm ---Outside of a short note about the there being a fast (Y) and slow (Z) filter and them being a 3-pole Bessel with different cutoffs, they seem to provide very little detail about them.  Maybe the schematic IS the document.   

With Dave's UEI meter, I would feed a chirp into it and record the filters response.   Seems like you could do something like this to test out the hardware filters.

--- End quote ---

I ran the filters from the diagram in LTSpice and came up with the figures in red, in the Active Filter circuit diagram I posted earlier  (i.e. 7.5Hz and 75Hz, 18dB/octave for the slow and fast sections respectively).

I think those numbers are unrelated to the 50ms and 550ms "timeouts" as they are called in the manual.  My theory is that when one of the "timeouts" is activated, the meter simply waits that number of ms after a trigger before performing the reading (to guarantee the filter has settled).  Should be easy to verify on GPIB (still not set up here!)
garrettm:

--- Quote from: bdunham7 on February 05, 2021, 02:57:59 pm ---I didn't see any missing codes using that method either.  Where I saw them was a long-term observation of a 10V source. There was a few PPM of noise and drift, but I would consistently fail to observe certain values.

--- End quote ---

When I get the GPIB figured out I'll try observing my Advantest R6144 at 10V to see if mine does the same thing. I also want to try superimposing a ramp or noise signal on the output of the R6144 with a signal generator and compare the results.
SilverSolder:

--- Quote from: garrettm on February 05, 2021, 07:42:56 pm ---
--- Quote from: bdunham7 on February 05, 2021, 02:57:59 pm ---I didn't see any missing codes using that method either.  Where I saw them was a long-term observation of a 10V source. There was a few PPM of noise and drift, but I would consistently fail to observe certain values.

--- End quote ---

When I get the GPIB figured out I'll try observing my Advantest R6144 at 10V to see if mine does the same thing. I also want to try superimposing a ramp or noise signal on the output of the R6144 with a signal generator and compare the results.

--- End quote ---

Perhaps just turning off the Filter will have the desired (noise) effect?

The filter will suppress any signal over 7.5Hz or 75Hz, respectively, so it is unclear how much effect adding a signal would have unless sample periods get very long?

The noise may need to be added later in the chain, perhaps in the R2 converter itself...
garrettm:

--- Quote from: SilverSolder on February 05, 2021, 05:13:21 pm ---[...]
Nice workaround, I'll see if I can characterize my problem boards this way. 

Perhaps it is just a hardware offset adjustment that is the problem.

--- End quote ---

Hopefully all you'll need is to play with some trimmers, but if not, I have a spare Active Filter module (716316) on hand, though shipping might be more than its worth.

If needed, I could unsolder the j-fets and mail a few off. I recently found out my Current Shunt module has weird offsets that come and go, so I think it needs a few j-fets replaced too. Parting out the spare filter might be able to fix both our problems.

I also have a spare GPIB controller if anyone wants it.
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