Both the 3456A and 8505A have been on for approx 18 hours and I have some interesting results.
Test set-up. One of the AD584-M's powered by USB and powered continuously during the test. It was set to the indicated 9.99691V. That voltage is achieved at 25 C. I noticed during the Winter months that both my AD584-M's read lower due to ambient 21 C and take a while to warm up.
Results: Within approx 2 hours the 3456A stabilized and didn't vary all night. The 8505A did not fair well. It started out agreeing with the 3456A within one or two digits but as the test progressed it's measurement kept continuing to drift lower and lower and it wasn't until maybe 12 hours into the test that it stopped. The 3465A stabilized at 9.99693V to 95. The 8505A finally stopped drifting at 9.99676V to 78. In real world applications that doesn't mean a hill of beans. But to a volt-nut that's tragic. And if you compare it to the other three AD584-M voltages it begins to tell a story....
AD584-M 3456A 8505A
2.50066V 2.50061V 2.50062V
4.99794V 4.99792V 4.99790V
7.50011V 7.50012V 7.50000V
You can clearly see a pattern here. As the voltage increases the 8505A becomes more and more inaccurate.
And as further proof that something is amiss with the 8505A. Here is the other AD584-M
AD584-M 3456A 8505A
2.49937V 2.49938V 2.49938V
5.00030V 5.00034V 5.00030V
7.50042V 7.50050V 7.50038V
10.00096V 10.00108V 10.00094V
I don't have the ability to perform a full calibration on the 8505A and I don't think it's worth the effort and expense to send it to a cal lab. And unfortunately there are no cal labs within reasonable driving distance. But I suspect there's more going on here than just a calibration. The non-linear delta as the voltage increases is very suspicious. And in order to troubleshoot this DMM you need an extender board which is almost impossible to find. So my choices are sell this 8505A as a parts only unit or just quietly retire it and hope that one day an extender board shows up. I haven't decided what to do yet.
And as a side note. Speaking of the Siglent SDM 3055. I've decided that when the budget allows I'm going to sent it in for a full calibration rather than attempt to “tweak” it myself. And here it is measuring the same 9.99691V after it's been powered up for over 12 hours. I would expect at least a reading of 9.9968V or 69. And it's off at least that much on all the other references.
Very interesting, and it's plain to see that you are not just teetering on the edge of that rabbit hole but rapidly sliding head first down it and for what other reason than OCD, I mean we are just talking of micro volts, when was the last time you had to measure or adjust something to that level Bugs Bunny is waiting at the bottom of rabbit hole and when you get there, he'll ask you only the way he can "Err whats up Doc?"
It has nothing to do with volt-nuttery... He paid "New From the Distributor" price for that Siglent to have "one meter to rule them all". And now he has 3 high-end used meters that all agree (to certain definitions of the term) with each other... but NOT with that "brammy-spankin' new meter", and haven't since he got it.
I can see where that's a reasonable gripe. I'd have sent it back and requested they double-check it under warranty myself. Given that it's long past warranty period now, I agree with the argument that it should be re-cal'd by a Cal Lab & given a cal cert, so he has that "one cal'd meter to rule them all", which is what he paid the big bux for in the first place.
mnem
*huggles his 189 close*
Totes agree 100% about the Siglent, I was referring to the Fluke and HP. The Siglent ought to have agreed with the AD584's in the first instance, but even then its only a very tiny amount (uV) off the mark and given the type of thing its used for, old scopes just don't demand that level calibration. The other 3,4 and 5 digit meters are IIRC "dead nuts"
The only 6.5 digit meter that I'll end up with is my 1905A, my 2 Solartrons are going, I don't need that number of digits as I never look past the mV anyway, so they might as well be funding other TEA item acquisitions. I have plenty of 3, 4 and 5.5 digit meters, including 4.5 and 5.5 digit handhelds.