Electronics > Metrology

poor man's calibration? (calibrate 5.5 digit with 6.5digit dmm)

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mzzj:

--- Quote from: bdunham7 on November 27, 2021, 05:36:00 pm ---
--- Quote from: Kleinstein on November 27, 2021, 04:56:38 pm ---Using a 6 digit meter to check a 5 digit meter is not so bad. One will see of the source is stable enough to get usefull readings - in most ranges I would expect the SMU to get stable enough to get a good reading fast and with reading from the display, with no need to use extra measures like recoring of both readings and than check afterwards.

--- End quote ---

It will depend a bit on which 6.5 and 5.5 digit meters are involved, but yes--with some care, you can do a decent job on a 100ppm meter using a 35ppm meter as a reference, at least on the lower DC ranges.  As for the stimulus, a good quality SMU will typically be excellent for this, even a very good PSU may do.  My old Power Designs 5020 is more stable and less noisy than typical mid-to-lower end calibrators.

--- End quote ---
HP6632 outputting 10 volts is also stable to 5ppm over a time perioid of few minutes.

mzzj:

--- Quote from: mendip_discovery on November 27, 2021, 08:22:02 pm ---

I will see if I can find any reference to how unc are to be expressed on the scheduls. I get a feeling it's been a rule for a while but UKAS have just made a decisions on it. Some of them prefer ppm, and I got a larf when I suggested that the dimensional should then all meters and none of this microns and stuff like 10 + (8 × L in m).

--- End quote ---
Latest trend was that accredited ranges can't overlap on accreditation scope.
1 to 10 volts @ 6ppm and 10 to 100 volts @12ppm is no good as the customer wouldn't know what uncertainty they get at exactly 10.00000000000 volts
Had to redefine the scope with mess of smaller or equal or larger <>= markings so that some poor bastard would't get confused.

I'm also eagerly waiting when they ask us to break down the thermocouple uncertainty for every thermocouple and every temperature range, resulting in something like 12x12 matrix of possibilities.  :scared:

trobbins:
cnt, you may find that the biggest uncertainty with the 197 is how well it has aged - mine still has a jitter significant enough to influence the last 2 digits that I couldn't exorcise after identifying a worse jitter source.

cnt:
interesting.  I didn't know that was an issue.  with my testing I only see the last digit move 1-2 counts over a few seconds in ohms or volts, with a really stable source. 

What timescale is the jitter you experience on?

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