Hello Rax,
to answer your question in the mail: No I have not experienced a jump like that on my 5442A.
I must have misunderstood your recent point by email where you've identified - but not yet determined the cause of, last we talked - a 5.3ppm, then 3ppm, then 2.5ppm discrepancy with one of your other reference environments. Or maybe you've determined there was no jump and the cause was something else but didn't get a chance to share that with me.
Also, I think alm was making a similar point, I thought:
every time you switch a reference off and on there's a small chance it will jump in value.
Though I think the possibility of even apparently spontaneous changes in the reference voltage are not likely, but possible.
But I am pretty sure what I'm seeing is not tempco. It it were, I assume seeing some correlation between the reading and the ambient temperature would be expected. There's no relationship I can discern. It just switched to a higher reading on the Prema, period. The only temperature-related correlation I can think of is the higher than usual temperature at the time of the event, which, because it's such a distinct event and apparently not reversible, I assume could be caused by a part failure of sorts.
I also doubt that you would find a real damage inside your instrument.
If not that, and not tempco, then what is it?... I'm all ears!!
Your 731B has 1ppm/°C, and very mediocre stability figures on the order of 10ppm/year, 2..5 ppm transfer stability (4h).
I have no doubt you didn't mean to literally state that above, as we both know that's not a correct statement. My 731B doesn't have a 1ppm/C tempco. In fact, probably no 731B "has that." That is a guaranteed minimum specification. My 731B may far exceed that - within some reasonable limitations of design, construction, and just... physics - and we actually well know all Fluke instruments tend to far exceed their spec. My sample is an exceptionally well performing one, particularly with regards to tempco, as confirmed by other voltnuts that have examined it and have far more experience than I do. Between mine and other samples seen in this group I'm talking about, there's been a wide variability in the observed performance of some 731B samples, and mine is a standout.
I'm not saying this 731 is a 732 in disguise - not ovenized, right?... - just that the baseline specification shouldn't be looked at as its
actual performance, which it is not. For a delta T of just about 3C, the output of an unusually stable 731B may not vary as much as one would imagine just based on specs. This particular 731B was recently adjusted by another voltnut friend by transfer with a Keysight-calibrated meter at 23.3C, so not so far from my conditions, and with a respectable pedigree; I'm considering this datapoint when I'm evaluating some of the things I'm seeing. I do strongly trust it within the limitations I just described.
You definitely need a third stable reference to judge over the other two.
Absolutely I do - though my better half may go through with moving me with all my stuff, permanently, in the garage - and I am picking up a, supposedly working, 332D literally this Sunday. Not a 732, but another opinion of my volt at my bench. As it goes for a lot of us here, this is a hobby, so to just grab a 732C because I want my 5440A or 6048 characterized, is absolutely not a feasible scenario. I do the best I can with what I have at hand in a garage (still, just about +-1.5C!...), and I've also just started on this path, so have that in mind when reading on my work and challenges. I can't change a lot of my determinations.
That said, I do have two calibrated meters at my bench right now (one by Fluke), and will have a calibrated (by Keysight) 3458A/002 on loan soon. I'm presenting all this data I can humbly accrue (=0, apparently) based upon a pretty respectable number of instruments, some of which are "prime house" calibrated!
Andreas has a lot of experience with his very hot and unstable lab under the roof .. and he's got a lot of references as well, all have low T.C.
Maybe he can tell, how he deals with this problem. He's as well able to make smooth longterm stability measurements.
Frank
Great point, thank you for sharing this. I'll seek to look over his posts, maybe, and the specific challenges he faced and how he sorted them out.
Maybe there's a chance for this aspiring metrologist!