Fluke 5200A AC Calibrator vs. Keithley DMM6500 - Page 1
Forum section: electronics / general

author: wn1fju
author_rank: Frequent Contributor
timestamp: August 25, 2019, 08:20:57 pm
content: I let both the 5200A and DMM6500 warm up for several hours, then set the 5200A for 1V @ 1kHz. Ran it to the Keithley DMM on the 1V scale with default 3Hz detector bandwidth. Let the DMM graph and run statistics for one hour. I saw virtually no voltage drift and the standard deviation was ~1uV.That's 1 ppm which seems too good to be true and seemingly beats the Fluke spec by at least an order of magnitude, if not more.What is the explanation:1) The Keithley DMM6500 AC conversion process really can't resolve down low enough to make the 1uV standard deviation a meaningful result2) My particular Fluke 5200A is so good that it belongs in the Test Equipment Hall of Fame3) Other.....

author: Mr. Scram
author_rank: Super Contributor
timestamp: August 25, 2019, 08:23:36 pm
content: A rare case of both drifting the same way?

author: Kleinstein
author_rank: Super Contributor
timestamp: August 26, 2019, 07:23:58 am
content: The specs on calibrators are usually quite conservative and an upper limit that all units should meet. Especially the case of an old instrument at constant temperature is expected to be quite stable. A stability in the 1 ppm range over 1 hour is not unexpected.Similar for the DMM6500, at a rather constant temperature 1 ppm stability is possible, though not guaranteed.Also with a low cost meter the specs a an upper limit and a typical meter is quite a bit better than the specs, when it comes to numbers like the temperature coefficient, that can be positive or negative. If it is property where they don't do adjustments or though out quite some bad units, I would expect about half the meters to have a TC that is less than 1/4 the spec limit.There is a 50% chance for both instruments to drift in the same direction.

author: wn1fju
author_rank: Frequent Contributor
timestamp: August 26, 2019, 02:26:26 pm
content: OK, I'll attribute it to "luck."It just seemed surprising since the 5200A performance (over the one hour) is on par with my Fluke 5440B DC calibrator. The former has a single SZA263 reference in a (well shielded) non-ovenized compartment, whereas the latter has dual ovenized SZA263's along with two other ovens for the preamp and range resistors. One would think the 5200A performance couldn't come close to the 5440B, but I guess anything is possible over the short term if the temperature within the units are stable.I probably should try the same experiment with a different DMM though.

author: RandallMcRee
author_rank: Frequent Contributor
timestamp: August 26, 2019, 03:22:00 pm
content: I must have missed something...what was the temperature variance during the measurement?So far, I would say that you cannot say either luck *or* stability w/out at least temperature data.

author: wn1fju
author_rank: Frequent Contributor
timestamp: August 26, 2019, 05:43:59 pm
content: Well, I don't really know the exact temperature variance during the one hour. The equipment is in my home basement. The basement is 90% below grade and experience (and a thermometer) shows that the temperature varies extremely slowly. I can pretty much guarantee that the ambient temperature didn't move more than 1 degF during the one hour. And I wasn't present in the basement during the run. Inside the actual equipment - well, that might be a different story.Anyway, regardless of any potential temperature coefficients, I am pleasantly surprised by the 5200A stability. One can only surmise that Fluke really did know what they were doing when it came to building calibrators. And I'm sure they still do - although I certainly can't afford to buy one of their new units!!!