Author Topic: USA Cal Club: Round 2  (Read 140403 times)

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Offline cellularmitosisTopic starter

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Re: USA Cal Club: Round 2
« Reply #125 on: June 22, 2018, 05:29:49 am »
Excited!!!  ;D
« Last Edit: June 22, 2018, 05:32:24 am by cellularmitosis »
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Offline RandallMcRee

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Re: USA Cal Club: Round 2
« Reply #126 on: June 24, 2018, 02:48:06 pm »

Newark is having a sale on some precision resistors that may be of interest to club members (or anyone, really)...

on their site search for "bargains" and filter (very bad user experience, slow site) or try
"bargains hpz" or "bargains alpha electronics hc series" to bring up just the good ones. I also bought some cheapish ltc5400 networks although those are not so much of a bargain.

Have fun,
Randall

 

Offline Svgeesus

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Re: USA Cal Club: Round 2
« Reply #127 on: June 24, 2018, 07:41:10 pm »
They only seem to have the 9k + 1k LT5400 when I looked just now.

With the Linear site and direct-order shop shut down, basing my big DAC-centric project around 10k LT5400 is looking like a less good decision ...
 

Offline kj7e

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Re: USA Cal Club: Round 2
« Reply #128 on: June 27, 2018, 06:26:10 pm »
Sorry for the delay,

Measured on a recently calibrated DMM7510: https://drive.google.com/file/d/13cKhjYruHux91m3_qTZ2RLhpINJhBPT-/view

It appears either my DMM7510 has drifted up or my 10v reference down by about 0.4ppm since last month.

Before and after temp sweeps, settled within 1uV, final measurement at 23.0C = 7.045,641,29

The Cal Club LTZ1000A TC is -0.08ppm/Deg C

Measured noise is very low, ~820nV P-P and 141nV RMS (divide the scope displayed value by 1000, so 1mV = 1uV)



« Last Edit: June 28, 2018, 12:37:00 am by kj7e »
 
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Offline cellularmitosisTopic starter

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Re: USA Cal Club: Round 2
« Reply #129 on: June 27, 2018, 10:13:36 pm »
 :-+

Looks like the RMS 1/f noise measurement lines up with my own (though my p-p values seem to differ): https://github.com/cellularmitosis/logs/blob/master/20180324-ltz1000-1f-noise/README.md#setup-8-ltz1000-11
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Offline cellularmitosisTopic starter

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Re: USA Cal Club: Round 2
« Reply #130 on: June 28, 2018, 05:30:49 pm »
Quick logistics note: martinr33 reached out to me when the ref was about to embark to kj7e.  He's got some pretty high-spec gear and believes he is sub-ppm at the moment.  It turns out he's a stone's throw away from kj7e over in Cali, so he asked if the ref could make a stop at his lab on its way back to me.  I think this makes sense -- minimize the travel/time between what are possibly our two best data points so far.

So the ref should be in martinr33's hands in a day or two!   :-DMM
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Offline bitseeker

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Re: USA Cal Club: Round 2
« Reply #131 on: June 28, 2018, 10:00:03 pm »
Sounds good to me. Looking forward to seeing how the data compares.
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Offline martinr33

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Re: USA Cal Club: Round 2
« Reply #132 on: July 02, 2018, 01:43:09 am »
My measurements are done. My goal was to compare with a known 732a.

My conclusion is       7.04564563V as of July 1, 2018
Compare to KJ7E      7.04564129

Difference of about 0.6 ppm - (corrected from 6ppm) thanks to CalMachine's obervation. The traveling standard does settle out very quickly. Almost surprisingly so.

Here are the details
3458a reading of 732A 10V standard   10.0000565   V
Actual standard voltage verified 1/7/18   10.000050           V
Scale factor                                    0.99999935   
Measured voltage                            7.04565021   V
Scaled Voltage                                    7.04564563   V
Standard Deviation                          150   nV
Temperature                                       23C

My 732a was confirmed today July 1 2018 against two other 732as and a 732b. My 732a is not moving from last time we checked it. The 732b is checked regularly against a bank of very stable 732as maintained by a friend of mine. (actually, none of the 732as had moved, but the B had shifted a little). I did not do any lead reversal to manage offsets, but I don't expect that to make much difference. I ran autocal before the readings.

I'll have the box in the mail back to home base tomorrow. Thanks to KJ7E and cellularmitosis!




(I just took one last look at the setup. The temp is now 27C, so 4 degrees up. The unit is reading 7.0456506, so up 0.6ppm - but with no autocal. Point is, not much movement compared to the difference in readings).


« Last Edit: July 02, 2018, 03:03:42 am by martinr33 »
 
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Offline CalMachine

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Re: USA Cal Club: Round 2
« Reply #133 on: July 02, 2018, 01:53:15 am »
My measurements are done. My goal was to compare with a known 732a.

My conclusion is       7.04564563V as of July 1, 2018
Compare to KJ7E      7.04564129

Difference of about 6 ppm - much more than I was expecting. The traveling standard does settle out very quickly, thouugh.

That is 0.6 ppm.
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Offline kj7e

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Re: USA Cal Club: Round 2
« Reply #134 on: July 02, 2018, 02:25:11 am »
^ What he says.  4.32uV at 7.0v is ~0.6ppm.  Not too shabby at all.
 

Offline martinr33

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Re: USA Cal Club: Round 2
« Reply #135 on: July 02, 2018, 03:01:53 am »
Well, that was a quick fix...

And if you figure your meter drifted by 0.4ppm, that leaves the gap at 0.2ppm. Now, that's with a brass connection in there, and I did not null out my 3458a - but I think that the gap would drop another uV if I did that.

I'll correct the original post to reflect this conversation.

« Last Edit: July 02, 2018, 03:44:56 am by martinr33 »
 
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Offline cellularmitosisTopic starter

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Re: USA Cal Club: Round 2
« Reply #136 on: July 02, 2018, 04:11:24 am »
Hi Martin,

There should be a set of lead included which terminate as bare copper wire.  Couuld you also take a measurement with the copper wires clamped under the binding posts of the 3458A?  I'd e curious to see the difference.
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Offline TiN

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Re: USA Cal Club: Round 2
« Reply #137 on: July 02, 2018, 04:20:25 am »
Also differential measurement vs known 732A will be much better Sdev/resolution than direct DCV measurement.

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Offline martinr33

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Re: USA Cal Club: Round 2
« Reply #138 on: July 02, 2018, 05:00:55 am »
OK, so it's warm out there. I am taking these readings by eye, but the setup is very stable - +/- a couple of counts once it settles. No surprise given the 150nV standard deviation.

With the bare copper - the last three digits switch from 480 to 490 if I reverse the connections at the meter (that's 48.0 to 49.0 microvolts)

With the nickel-over-brass banana jack - same result, once it settles. Doesn't take but a minute or two, it is warm out there (27 degrees). Off the bat, maybe 475 - 495 rather than 470 - 480.

I also did a quick zero test on the meter with a short, no surprise 1uV  (10 counts) of  offset (which matches the difference from reversing the cables, which is why you should always take two readings, one forwards and one reverse voltage.

Conclusion: the non-thermal connectors aren't making a significant difference if you keep air currents away, and you let them stabilze.

My garage is thermally variable, electrically noisy - but it is not drafty!
(I live in sight of some big TV towers - even my garage door opener will only work from about 25 feet from the opener, which means 10 feet from the door... so everything I do tends to be twisted pair).

Now, if you really want to see voltages move, try a nanovoltmeter.

 
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Offline martinr33

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Re: USA Cal Club: Round 2
« Reply #139 on: July 02, 2018, 05:27:45 am »
"Also differential measurement vs known 732A will be much better Sdev/resolution than direct DCV measurement."

Yes,I should have done it that way!

However, the SD is only 150nV, and I would still be on the 10V range because of the 3V difference. The whole setup seems surprisingly quiet.

The K2002 could do this on the 3V range. But I have not figured out how to do an easy recal on that unit.
(and as a complete aside, the K2002 is a lot noisier than the 3458a, but seems more temperature stable - and the noise is random so it can be averaged out)
 
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Offline cellularmitosisTopic starter

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Re: USA Cal Club: Round 2
« Reply #140 on: July 02, 2018, 05:47:24 am »
Thanks for the follow-up!

With the nickel-over-brass banana jack - same result, once it settles. Doesn't take but a minute or two, it is warm out there (27 degrees). Off the bat, maybe 475 - 495 rather than 470 - 480.

The dual banana jack is the Pomona 4892.  The body which the wires screw into is brass, but the banana plug spring is copper.  From the datasheet, the 4898 is nickel plated, while the 4892 is gold plated, but it is a bit ambiguous whether that means the 4892 is both nickel plated and then gold plated, or if the gold is directly plated onto the brass and copper.

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Offline bitseeker

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Re: USA Cal Club: Round 2
« Reply #141 on: July 02, 2018, 06:00:57 am »
Nice results, Martin, especially with the warm temps recently.
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Offline martinr33

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Re: USA Cal Club: Round 2
« Reply #142 on: July 02, 2018, 06:27:52 am »
Gold needs a diffusion barrier to be plated over copper. Nickel is common, silver also works.

The Viborg bananas are gold over silver over copper, an give good results.

For these banana jacks, the issue is the big chunk of brass that makes up the body. You can get a good thermal differential across the two terminals that takes a while to settle.
 
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Offline cellularmitosisTopic starter

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Re: USA Cal Club: Round 2
« Reply #143 on: July 10, 2018, 05:31:50 am »
The ref arrived this weekend, but I just hooked it up (got distracted over in the ovens thread  ::) ).

Initial reading is 7,045,697uV to 7,045,700uV at 21.3C.  Looks like it is trending slightly downward as it warms up.

Can't wait to throw this thing into a 25C oven tomorrow!

I had wanted to coincide this post with an announcement of a new PX-ref board, but unfortunately there may be a bug in it  :(  I found a stock of old OHMTEK CERDIP chips which have enough resistors in them to serve as R2 through R5 of an LTZ circuit, they are hermetically sealed, low tempco, just under $10 from taobao.  I designed a board around these and I was hoping to give them out with lowimpedance's LTZ1000 chips (the user would just need to supply a 120R resistor), but the first one I soldered up latched the LTZ heater control fully on  :palm:  so this board may not be ready for prime time yet.  I'll keep you all posted!
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Offline TiN

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Re: USA Cal Club: Round 2
« Reply #144 on: July 10, 2018, 06:46:39 am »
I see noone cared enough to upload data to single spot, so my regrets about current 'CalClub' format and lack of transparency stays :)
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Offline kj7e

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Re: USA Cal Club: Round 2
« Reply #145 on: July 10, 2018, 03:12:11 pm »
I see noone cared enough to upload data to single spot, so my regrets about current 'CalClub' format and lack of transparency stays :)

I created a directory on ftp.xdevs.com;
/CalClub/USA/Round_2/PX_Vref/kj7e

And will upload my data later today. Data uploaded.
« Last Edit: July 10, 2018, 05:27:58 pm by kj7e »
 
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Offline cellularmitosisTopic starter

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Re: USA Cal Club: Round 2
« Reply #146 on: July 18, 2018, 05:44:15 am »
OK, time to stop fooling around with ovens get this ref on its way again!

Here's a random ordering of the rest of the participants in round 2:

nikonoid
Svgeesus
dr.diesel
hwj-d
Vacuuminded
flittle
bitseeker
orin
GEOelectronics
rhb
RandallMcRee
ArthurDent
edavid
CalMachine
Conrad Hoffman
VintageNut
vindoline
technogeeky
TWMIV
Muxr
SirAlucard
MaxFrister
CatalinaWOW

If you don't see your name in the list, I'm sorry I forgot you!  Just send me a PM.

Probably the biggest issue right now is how long it will take to get through this list with only one active ref.  There are some things in the works to address that (TiN's ref is in progress, I'm working on a number of additional refs, and soon ~6 others will get lowimpedance's LTZ chips and may be able to participate), but all of those will take time to stabilize as well, so things may be slow for a bit longer.

As they say, the best time to plant a tree was 20 years ago, the second best time is right now!
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Offline bitseeker

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Re: USA Cal Club: Round 2
« Reply #147 on: July 18, 2018, 06:28:43 am »
Wow, I didn't realize that we had grown so much. Yay, cal club.

Even if it does take some time, better that than no club ref. :-+
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Offline RandallMcRee

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Re: USA Cal Club: Round 2
« Reply #148 on: July 25, 2018, 11:22:48 pm »
Recently acquired a new instrument in order to feel the love from the cal club--an Advantest R6581T (8.5 digits!).

This was mislabeled on ebay as an advantest r6518t...but obviously from the pics was the 6581. Dim display...I think it was still a steal.

Just trying to learn how to drive it. It has easy calibration steps, although I'm pretty sure I goofed somewhere. If anyone wants one there is still one out there on ebay.

Randy
« Last Edit: July 25, 2018, 11:57:03 pm by RandallMcRee »
 
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Offline martinr33

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Re: USA Cal Club: Round 2
« Reply #149 on: July 26, 2018, 02:47:04 am »
Nice catch - these are good units. I did replace the battery on mine. But it was still at 3.7V after 20 years. Japanese low power SRAMs from that era are remarkable.

Next step is to clean it up, and bed it in. And then see if you can measure its drift.

and then after that comes a 732a 10V standard. Then you need a 10k standard. I built a 10k box after kj7e's pattern, it is quite good.
 


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