USA Cal Club: Round 2

[Conrad Hoffman]

It's been quiet, just curious about the current status?

[vindoline]

Hi Conrad, the kit is with edavid at the moment. You're next after him! I would think in the next week or so. I'll keep you posted as soon as I know anything.

[Conrad Hoffman]

Cool- if I start cleaning up today, I might have some bench space by then! Sometimes my space is more like an archaeological dig than a test bench.

[edavid]

I think I'll have it for about another 2 weeks.

[Conrad Hoffman]

No problem if I'm next, no problem if I'm not. Plenty to do in the meantime.

[vindoline]

I think I'll have it for about another 2 weeks.

edavid, take your time. You had to wait!
Personally, I’m really happy with the turn-around times we've had. It’s a long list, but we’re really making progress!

[RandallMcRee]

I think I'll have it for about another 2 weeks.

Great! Can you tell us something about your equipment and your goals? Are you going to be posting results to xdevs as others have done?

Thanks,
Randall

[CatalinaWOW]

Still a long time before my turn in the barrel.  But it is never too soon to get ready.  As mentioned earlier I found my GPIB controller interface broken by one of the Windows updates and got that sorted out.  For the next arrival I plan to log all of my references and the two club references at the same time, using the multiplexer on my HP 3457.  The attached schematic shows the plan.  Each reference will be measured directly.  In addition the FX reference will be measured differentially with the KMoon reference and the PX reference, allowing use of the lower scale and perhaps achieving better resolution.  I will also do a differential measure with an HP 3456.

The use of the multiplexer brings up the question of what errors are introduced.  A few runs have been done with several channels all connected by nominally identical wiring to the kMoon reference.  The results show that the 3457 is doing as well or better can be expected, but there do seem to be persistent biases between channels.  See the chart showing one data set.  In many data sets collected on this setup a similar, but not identical pattern has been shown.  I still haven't figured out if the differences are noise or something else.  The differences are well down in the noise neighborhood.

Any comments would be appreciated.

[SilverSolder]

Thermal voltages?

[CatalinaWOW]

Thermal voltages?

Could be, though I tried to avoid that.  Photo shows test setup.  Everything had been on for two weeks before the data was collected.  Data showed that meters stabilized in about four hours.  All identical test leads to breakout panel.  Breakout panel has BNCs wired to copper PWB with identical materials and similar lengths to pickoff point for cabling leading to 3457 in.  Those wires are all identical materials and similar lengths, soldered to breakout board and tied to standard 44492 screw terminals on back of 3457.  Room temperature was relatively stable less than 1 deg C variation, and uncorrelated with observed short term drifts seen in all channels.

Another possibility is some sort of noise synchronous with the sampling, since the channels are collected serially, not at the same time.  Haven't been able to come up with anything of this sort either.

The EZGPIP script used is included for reference.  Renamed to text file to allow posting to forum.  If used in EZGPIB just rename back to .488 file.

Still plenty to think about before the reference arrives.  Fortunately there is lots of time on the calendar, who knows how much will be available for this project.

[SilverSolder]

I didn't think mux relays were particularly trustworthy in terms of thermal EMFs?

[CatalinaWOW]

I didn't think mux relays were particularly trustworthy in terms of thermal EMFs?

I agree, and there are other things to worry about in a switching system.  Which is why I am trying to characterize this.  The alternative is to correlate measurements made on several different days with each other.  Neither is without pitfalls. 

Right now my tentative conclusion is that the channel differences are repeatable to within roughly a microvolt and that I can correct the differences gaining about a half microvolt of precision.  And hence an improvement of the accuracy of the comparison to the calibration source.  All of this is trying to use the 3457 way beyond its spec but there seems to be reason to believe the answers.

[SilverSolder]

I didn't think mux relays were particularly trustworthy in terms of thermal EMFs?

I agree, and there are other things to worry about in a switching system.  Which is why I am trying to characterize this.  The alternative is to correlate measurements made on several different days with each other.  Neither is without pitfalls. 

Right now my tentative conclusion is that the channel differences are repeatable to within roughly a microvolt and that I can correct the differences gaining about a half microvolt of precision.  And hence an improvement of the accuracy of the comparison to the calibration source.  All of this is trying to use the 3457 way beyond its spec but there seems to be reason to believe the answers.

Ah, I see, needed another cup of coffee...  -  Is it possible to reverse some of the connections and cancel some errors out with multiple readings?  If only there was a way to measure a reference voltage with AC...

[notfaded1]

Sounds like we need to rename USA Cal Club to USA Gpib Club.
No-one have working datalogging from the first try 

After following this thread this comment almost made me spit my coffee out all over the place!   I agree and decided a real Keysight 82357B was better than messing with some of the other stuff.  Also... the more data the better and putting it all in one place so everyone can compare it is pretty important.

Bill

[FriedLogic]

Right now my tentative conclusion is that the channel differences are repeatable to within roughly a microvolt and that I can correct the differences gaining about a half microvolt of precision.  And hence an improvement of the accuracy of the comparison to the calibration source.  All of this is trying to use the 3457 way beyond its spec but there seems to be reason to believe the answers.

I found a similar (but larger) issue with the HP 34970A and a 34901A relay card. I left the same reference connected to some of the inputs for some time and the differences appeared quite stable, so I left it to investigate later.
Inside a meter is probably not the best place for a relay card to be. I usually leave a cold card at least on hour before starting to use it since there are quite large errors when it's first plugged into a warm meter. I have a card to repair, so I'll try to look at it more when doing that.
There is certainly extra work involved when trying to squeeze the last drop of good data out of equipment.

[KK6IL]

I've given up on getting my UGPlus GPIB adapter working.  So I'll try the AR488 with the cal kit.

What software do I need? EZGPIB?  Are there any scripts available for use with a 3456A? Or better yet, a pair of them.

Is there any value to anyone else of a log file on 3456A's?  One tracks my LM399 within 4 PPM over 10 deg/C, the other 12 PPM.  Not real meaningful without knowing the characteristics of my LM399.  If no value, then I'll then I'll just take an occasional reading over a day, and adjust the 3456A's and LM399.

Just about to add a LM35 temperature sensor IC to my LM399.  Can then easily read by switching to the rear terminals of the 3456A.

[bitseeker]

Yes, you can use EZGPIB. There is a very nice manual available for the AR488: https://github.com/Twilight-Logic/AR488/blob/master/AR488-manual.pdf

To get familiar with the club kit (and links to more AR488 info) also see the guide at https://www.eevblog.com/forum/metrology/usa-cal-club-getting-started-user-guide/

[TiN]

Now since Cal Clubs don't come to me, it's time I come to Cal Club  .

Count me in for 2020 

[niner_007]

I'd love to be in it too

[vindoline]

Now you’re both on the list!

[edavid]

Has anyone made calibrated measurements of the FX or TX references below nominal room temperature?  My lab has been in the 12-15C range lately.

Thanks...

[Grandchuck]

The designer did.  (only down to 20 C) shown.  Maybe Ilya will add some data?

[SirAlucard]

Are we still going with the same round in the cal club? Why is there a new list being generated if the current list hasn't gone through?

[vindoline]

Are we still going with the same round in the cal club? Why is there a new list being generated if the current list hasn't gone through?

It's rather a “rolling admission” type of affair. If you would like, I can add you to the list.

[SirAlucard]

Well yea, I would hope we ended up keeping the order in which we already started.