I finished cleaning up, calibrating, and testing the Heathkit voltage reference. It is ready to head to ebay. Then I started thinking...
I have a Fluke 8800, Keithley 199, Keithley 197, B+K something or other, and at least one more HP DMM on the shelf. I plan on testing them, doing whatever simple calibration I can, makin' them pretty and selling them (Which will leave me with three 5.5 digit DMMs and three lesser one) to free up space and generate cash. So I look at the EU80-A and think, why don't I keep the that and use it as my voltage reference for calibrating these meters?
Great idea, right? So now the Heathkit is on my test bench, as is the 8800. I will keep the voltage reference long enough to check these meters and then sell it.
And we have another example why nothing ever seems to make it from my "sell" shelf to ebay. ![Laughing :-DD](https://www.eevblog.com/forum/Smileys/default/smiley_laughing.gif)
Are you sure that reference is accurate and stable enough to check 5.5 digit DMM's? Based upon what I saw plus a quick check of it's specs I would think not but that's just me. ![Laughing :-DD](https://www.eevblog.com/forum/Smileys/default/smiley_laughing.gif)
No it is not, though it is reasonably stable if I let it warm up for a couple of hours and set the voltage by measuring it with my known good DMM. I just want to be able to represent that they work on all ranges reasonably well. I won't suggest that I have calibrated them. I will take them to the next hamfest or offer them on a couple of the test equipment lists. About ebay I am not so sure. Certainly not at auction. I am tempted to sell them as-is just so I limit my interactions with PITA buyers.
Stability is more subtle than that.
If you then it off and on again after 1/10/1000seconds, does the value return to the same?
How about popcorn noise? One of my old professional sources has 1.5ppm popcorn noise
And then there's simple drift.
Welcome to the rabbit hole.
![Laughing :-DD](https://www.eevblog.com/forum/Smileys/default/smiley_laughing.gif)
but, my friend, subtlety is not my strong suit...
You are, of course, correct. Using the EU80A results in, at best, slide rule accuracy. But if these DMMs read within a couple of percent of expected value on all scales, I can say, honestly, that they are in good working order and that's all I want to be able to do. For this project, I am matching the precision of the process to the desired goal.
And I shamefacedly admit that this approach is antithetical to everything we stand for in this thread.
![Laughing :-DD](https://www.eevblog.com/forum/Smileys/default/smiley_laughing.gif)