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

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joeqsmith:

--- Quote from: SilverSolder on January 27, 2021, 09:32:32 pm ---
--- Quote from: joeqsmith on January 27, 2021, 07:23:11 pm ---Shown is about 4.5 hours.   Increasing the histogram's bin size to look at the missing codes,  the meter has not put out any 1s, 2s, 6s and 7's in the extended code.   We see something similar with the HP not showing 3s & 8's.

To test it out, I changed the voltage standard to delta E (uV resolution) and slowly adjusted the output voltage.  No missing codes.

--- End quote ---

That is a little bizarre...   Some kind of rounding or precision issue with the calculation of the running average?

Floating point operations are not perfect, of course. 
https://docs.oracle.com/cd/E19957-01/806-3568/ncg_goldberg.html

--- End quote ---

Again it does show the least significant digit hitting all the buckets.  But I guess the question is does it do it at 10V and there are specific codes that are in question.  Of course just eyeballing things isn't going to get you too far. 

Voltage source set at 10V.   The easiest thing to do would be to add some error by adjusting the trimmers but I would rather not touch it again as the unit is close now and buttoned up.   Instead, because my meter reads the standard a little hot, I just used a decade box to shunt it small amounts.  The histogram is plotting the least significant digit.  Note that the 2,3 and 7 buckets are lower but they certainly do occur  with my meter.   


--- Quote ---... I have yet to see a 9.99999 7, 10.00000 2 or 10.00000 3. 
--- End quote ---

Shown is with the LSD set to 2. 

bdunham7:

--- Quote from: SilverSolder on January 28, 2021, 03:16:02 am ---The rear connector is an ELCO 8016- 20 Pin socket - you can find both sockets and connectors on eBay.....

--- End quote ---

You made my day!  I was absolutely convinced it was Amphenol for some reason.  That cross-pin or tuning fork design is pretty interesting--the male and female ends using the same pins. Now I'll be able to make a 4W Ohms harness and test the X-REF circuits to make sure they're not blown up by whatever burned the 39K resistors on the input board.

bdunham7:

--- Quote from: joeqsmith on January 28, 2021, 04:40:57 pm ---Again it does show the least significant digit hitting all the buckets.  But I guess the question is does it do it at 10V and there are specific codes that are in question.  Of course just eyeballing things isn't going to get you too far. 

Voltage source set at 10V.   The easiest thing to do would be to add some error by adjusting the trimmers but I would rather not touch it again as the unit is close now and buttoned up.   Instead, because my meter reads the standard a little hot, I just used a decade box to shunt it small amounts.  The histogram is plotting the least significant digit.  Note that the 2,3 and 7 buckets are lower but they certainly do occur  with my meter.   

Shown is with the LSD set to 2.

--- End quote ---

Assuming the 8506A and 8505A use the same software, it looks like mine is just sloppy A/D converter linearity adjustment.  Interesting that your counts are lower, but not zero (I've eyeballed more than 250 samples by now...).  I suppose that the distribution of LSDs could be used as a test of linearity, or at least the accuracy of the alignment of the ladders which should correlate to linearity.

SilverSolder:

--- Quote from: bdunham7 on January 28, 2021, 05:43:53 pm ---
--- Quote from: SilverSolder on January 28, 2021, 03:16:02 am ---The rear connector is an ELCO 8016- 20 Pin socket - you can find both sockets and connectors on eBay.....

--- End quote ---

You made my day!  I was absolutely convinced it was Amphenol for some reason.  That cross-pin or tuning fork design is pretty interesting--the male and female ends using the same pins. Now I'll be able to make a 4W Ohms harness and test the X-REF circuits to make sure they're not blown up by whatever burned the 39K resistors on the input board.

--- End quote ---

It took me something like 2 years to figure out what that connector is...   it is one of the best kept secrets on the Web!  :D

SilverSolder:

--- Quote from: bdunham7 on January 28, 2021, 05:52:23 pm ---[...] I suppose that the distribution of LSDs could be used as a test of linearity, or at least the accuracy of the alignment of the ladders which should correlate to linearity.

--- End quote ---

That's the kind of approach I was thinking of, perhaps tuning the A/D converter by feeding it a triangle wave sweep with added white noise, and looking for patterns in the output that shouldn't be there?

That is something for a dark winter's night for sure...

Absolutely have to have GPIB (or serial) working for anything like that!






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