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Some old school instruments showing how it's done (HP 3325A and Fluke 8506a)

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bdunham7:

--- Quote from: SilverSolder on January 31, 2021, 01:26:11 am ---
--- Quote from: joeqsmith on January 31, 2021, 12:55:13 am ---For DCV (where the bias spec I copied came from),  it routes to the DC signal conditioner, then to the filter and finally to the ADC.   Not sure what peaks you are expecting to see.

--- End quote ---

We can't rule out that the CPU switches the signal conditioner in and out of the high quality bus for each measurement, which could affect things at the margins?

Time to take a look...

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1) there's no reason it would
2) I would hear it since these units use relays
3) My 8846A would notice, especially on high-impedance sources like the 1V range of the 731B.  It picks right up on other meters that have charge pulses due to autozero and I can plot a nice graph of it happening.  In this case, there's no such noise.

SilverSolder:

A crude scope shot of the inputs doesn't show any immediate signs of any switching at the reading speed.

I agree there is no reason to do any switching, but maybe some digital noise makes it back out in a periodic way as a side effect of the readings?

joeqsmith:

--- Quote from: garrettm on January 31, 2021, 01:32:29 am ---...
 My unit has the laser trimmed glass/ceramic resistor packages in the DC Signal Conditioner module. So I'm curious how well mine performs now that everyone is sharing data from their units. If anyone is curious, I can take photos of the DC Signal Conditioner or other boards.
...

What software are people using to collect and process the data? I have MATLAB and could write my own code to collect and plot the data, but if there is a turn-key solution I wouldn't mind using that to start with.

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I would like to see the signal conditioner inside of yours.   Guessing it's a fair bit different than the one shown on the XDEV site.  I only opened the ADC and ohms clam shells.   

Which interface is your meter using?   I use LabView.

garrettm:

--- Quote from: SilverSolder on January 31, 2021, 01:55:48 am ---
That looks very interesting!

What manual are you finding that diagram in, I don't seem to be able to find that diagram in any of the ones I have?  (One found online, another purchased from Artek).

I guess it's time to open up the DC conditioners and see what revision level they are...   do you happen to know the rev letter on yours?

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The diagrams are errata notes tacked on at the end of the manual. Apparently Fluke was too lazy to actually update the manual (though HP was often just as lazy). The pdf on xDevs for the 8505A (with 1991 revision date) has them at the end of the document. It looks like the same pdf I got from Fluke's website. So sadly there isn't a better quality scan of the circuit diagrams unless your Artek manual has them in it.

I don't remember the rev. code for my module, but I'll post some photos of it here in the next day or so.

garrettm:

--- Quote from: joeqsmith on January 31, 2021, 02:52:03 am ---I would like to see the signal conditioner inside of yours.   Guessing it's a fair bit different than the one shown on the XDEV site.  I only opened the ADC and ohms clam shells.   

Which interface is your meter using?   I use LabView.

--- End quote ---

Looking back at the photos of your unit, someone has replaced your DC Signal Conditioner with a newer module. The older modules used two metal stickers while later units switched to a single plastic sticker and molding the warning text into the lid. What number does your module show on the label (I can't see it in the photo)?

I have the standard IEEE488 interface on mine and a GPIB to USB adapter floating around somewhere that I need to find...

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