USA Cal Club: Round 2

[bitseeker]

That's tight and tidy all right. Nicely done!

[SirAlucard]

Thanks! I really enjoy tight and tidy wiring and soldering jobs. After going through this all I ended up purchasing some parts to make a relatively accurate 1/4w decade resistance box.

After looking back I probably should have gotten the Omron switches instead of the Adafruit ones because the Adafruit ones add 1Ω once it's all together. Each switch was measuring about .17Ω between common and 0. I also would have been ok with 1/10w resistors or 1/8th.

I purchased extras on the resistors so I could match my resistors going up the decade so there wasn't a significant drop between each. So for instance if one was 9.9972k the next would be 10.0013k to round it out as near to 10k as I can. For my 1Ω I used 1% 50ppm, 10Ω .1%15ppm, 100Ω .1% 25ppm, 1kΩ .1% 15ppm, 10k .1%25ppm 100k .1% 50ppm, 1M .1% 50ppm. On another look I should have gone with lower PPM on the 100k and 1M, and definitely a lower wattage cause they were huge, but I made them fit.

Anyways here are some pictures of that build.


Each module ready to be connected together.


After wiring each one to each other I had realized what a tight job it was.


Quick check on the meter. Showing .007% accuracy.


Fit into it's little box.


And done.

So after doing this project it made me wonder, we have the kit going around, what are the chances of getting more ranges sent around? Would be great to be able to calibrate the entire range of my meter to match that of other's. There should be a full calibration kit, in decades 1, 10, 100, 1k etc with a verified reading on someone's fancy highly expensive already fully calibrated machine. At least for resistances. Just a thought.

[Grandchuck]

Superb piece of work!

[bitseeker]

That's quite tight and tidy, SirAlucard. Nicely done!

[Grandchuck]

Posting to let everyone know the Cal Kit is on it's way back. I've uploaded all my logs of what my 3478a was giving. Definitely needs to be calibrated to be a bit more accurate. Was able to calibrate at least the 30v range using the FX as a reference, as well as the 1k and 10k Ohm ranges. Which is perfectly fine for me. As those are my most used ranges anyways. Eventually I'll get the whole thing calibrated. For now close enough is good enough for my use case.

It has been a while ... any recent information about the Cal Kit?

[SirAlucard]

That's quite tight and tidy, SirAlucard. Nicely done!

Yea unfortunately I'm not happy with the 0Ω setting resistance. Each thumbwheels 0 is about ~0.2 ohms over the corse of all 7 thumbwheel switches it adds up to about 1.3ohms giving the whole unit an offset and never having a true 0 ohm end digit. I ended up bypassing the 1 ohm so at least 2 would = 2 instead of 3. I'm thinking about taking it apart and either A) getting some boards made with thicker traces and gold plating to keep the resistance lower and more precise, or B) reflowing a somewhat decent layer of solder over the traces which seems to have improved the low end resistance a bit. I mean I kind of expected to have lower quality switches considering I paid $8 for a pack of 5 adafruit switches, vs $18-$19 for 1 when buying an omron thumbwheel switch which would have taken the price and almost multipled it by 4. Tho I didn't think the low end resistance would have been so bad.

[Conrad Hoffman]

I know it would add to the complexity but the "good" boxes I know of, like ESI, were set up as 4-terminal resistances. I have an ESI box that's 2-terminal, but it's not for very low values. I also have an ancient L&N terminal and plunger box for low values that uses very heavy wiring and assumes you'll make a 4-terminal connection to the giant brass binding posts.

[SirAlucard]

I know it would add to the complexity but the "good" boxes I know of, like ESI, were set up as 4-terminal resistances. I have an ESI box that's 2-terminal, but it's not for very low values. I also have an ancient L&N terminal and plunger box for low values that uses very heavy wiring and assumes you'll make a 4-terminal connection to the giant brass binding posts.

I am checking resistances with a kelvin clip up until the binding posts, and I have a few extra switches that I've tried modifying and playing with. I was able to take the one and bring it's resistance from .22Ω to .126Ω just by adding a layer of solder to the board, but I still don't think that's the way to go as it's not a super great connection.

[Conrad Hoffman]

It's hard to believe any switch could have a resistance that high, if it's clean and if it uses metal on metal contacts. Have you ever disassembled one to see how it's made?

[Grandchuck]

Does anybody know anything about the Cal Kit?  I have sent a couple of PMs but have not been able to learn anything

[bitseeker]

I haven't heard anything. I assume vindoline received the kit back, but haven't seen confirmation of that.

[CatalinaWOW]

Vindoline has contacted me and the kit is headed my way.  His schedule has apparently been very full lately.

[bitseeker]

Very good. Thanks for the update!

[CatalinaWOW]

The reference arrived today.  I had my meters on and stabilizing for two weeks prior to a five hour power outage yesterday.  They will have had at least a day to stabilize before I start for real.  This evening will be initial hookup and test runs, with the real data gathering starting tomorrow.  I hope to finish and have it on its way within a week.

[CatalinaWOW]

No plan survives contact with reality.  I had planned to use the HP 6626 power supply to power everything, but when I quickly realized that a lot of harnessing work would be required.  Switched to a Power Designs supply.  Allowed using existing harnesses for the club references and simplified the others.  Not totally happy with the noise, there are several millivolt spikes at around 1500 Hz running on the millivolt or so of white noise.  Will probably make a battery powered run later if all else goes well.  Also ran into problems using the Hp3456 in differential mode between the FX and my KMoon reference.  So I just paralleled the HP 3456 with the Hp 3457.

Rather than figuring out the software interface for the club temp sensor I compared the on screen measurements of the club sensor with my own.  About 0.1 deg C difference on temperature and 1% RH difference so carried on with my own.  I will continue to compare them from time to time, though my lab area is fairly stable in temp this time of year so will probably not get enough information to make a slope correction, just more confirmation on offset.

System is up and gathering data.  I'll run 24 hours in this configuration and look at the data before deciding what to do next.  Looking at the resistors and initial voltage data it appears my old and lame instruments have held calibration fairly well, but will reserve judgement for a closer look at the data.

I will post some brief data samples here, but most data will be posted in TiN's data site.

Document shows final test configuration and photo shows data logging plugging along.

[CatalinaWOW]

I'm done and the reference will be on its way today.  I did do a battery powered run, but haven't analyzed the data to see if it made a difference.  All data posted on TiN's server, but ended up marked private.  I don't know how to change that, or if that will affect visibility to others.

[TiN]

All data is available here as usual. If it's uploaded, then there is no such thing as private data.

[Grandchuck]

The CalKit arrived with a not working FX voltage reference.  It is on its way back to the manufacturer (TiN).  As can be seen in the photo, the FX is showing only 10 mA and presents a very low output voltage.  The PX is good and its output is as expected.  More to follow.

[CatalinaWOW]

It will be interesting to find what TiN discovers.  I went back and reviewed data and the FX was operating properly until I stopped logging.  The final run was made with the reference operating on two 12V lead acid batteries. 

1.  Logging program was stopped.  Shutdown was normal.  This means that the HP3457 input mux was connected to the PX reference.  The FX mux input on the HP3457 was open.  The HP 3456 was continually connected to the FX reference.

2.  Power was removed from the references.  This occurred within a couple of minutes of the last logging event.  There is no information on power sequencing, and I don't remember whether I removed +V or -V first, but both were removed within an interval of a couple of seconds (probably less than a second, but as it involved pulling banana plugs the timing is not documented.)  The ground connections were then removed.

3.  The FX power cable was removed and packed.

4.  The FX output connections were removed and the shorting bar installed. 

5.  The FX reference was placed in the shipping container.

While none of this was performed at an anti-static workstation, I observed my normal static precautions which involved grounding myself to equipment ground before touching any hardware.  Static conditions were not extreme as seen by the RH measurements.

While I don't see anything I did which should have killed the reference, I am looking forward to the diagnosis and will take responsibility for anything which I did wrong.

Hopefully this will lead to another note in the Start-Up guide which will help prevent any future problems.

[TiN]

Probably just mechanical issues, as internally there are wires from power BNC inputs and reference output to posts.
Will see, also I'll get an answer on my whole reason donating FX to calclub - what happens to non-rugged LTZ1000A ref when its shipped around and used by random people in random ways for 1 year. Could not ask for more real-life test that this. 

[SilverSolder]

Probably just mechanical issues, as internally there are wires from power BNC inputs and reference output to posts.
Will see, also I'll get an answer on my whole reason donating FX to calclub - what happens to non-rugged LTZ1000A ref when its shipped around and used by random people in random ways for 1 year. Could not ask for more real-life test that this. 

Probably nothing a dose of hot snot can't cure! 

[CatalinaWOW]

Have finished a first run of analysis on my data and came up with a few happy for me conclusions.

1.  My HP 3457 still meets its 24 Hr specs for DCV and 4 Wire resistance on ranges checked.  Since it is many years since its last calibration this bodes very well for continued long term stability and for accuracy on the unchecked functionality.

2. My HP 3456 wasn't quite as good, but still meets 90 day spec.

3. Both instruments showed small temperature drift over the range seen in my tests.  This data must be taken with a grain of salt because the temperature monitor placement was selected to get best approximation of the reference temperature and wasn't well coupled to the instruments.  But the overall temperature environment was very slowly varying and relatively stable so there is some good here.

4.  The best estimate for my KMoon reference value turned out to be 10.00279 volts, compared to the 10.00276 volts inked on the reference in 2015.  Apparently mine was one of the ones that was actually measured, not just written down, and also it appears to be relatively stable over time.

Analysis spreadsheet will be loaded on TiNs site, though I was unsuccessful this AM.  Probably a problem with my internet connection - I am in the boonies and I get lots of "special" experiences.

[TiN]

Got the box. Autopsy revealed that patient died due to autopsy.

Jokes aside, FX reference still works just fine. I've connected it to powersupply for +12/-12V , hooked meter to it and on power on its drawing expected 42mA and 5mA on rails. Output is about +1.5ppm so far wrt assigned value in May 17, 2019. Live data: https://xdevs.com/usac_fx_as_received_k2002x_nov2020/

Why it didn't work before? It was an operator error, now that I looked closer on the posted photo. I think CatalinaWOW will feel relief that it's not borked on his watch I see connected +12V to PSU ch2 output HI and -12V to ch2 LO. Common return wires from either power rail are not connected to anything. So there is no ground provided to reference and no workie as result.

Perhaps instructions on connecting were not clear enough to stress that FX require bipolar power, it cannot work with single +12 supply and was not designed for single supply.

Since I have it here anyway, i will replace bad cracked pomona 3770 posts (very common issue with these low cost posts, sadly) with something better and fully recalibrate the unit. It may take few weeks. Will also donate hard-case for it and make users manual with proper connections shown with photos.

[CatalinaWOW]

Excellent news.  I don't know what your expectations for stability were, but 1.5 ppm sounds pretty good to me, so excellent news on that side too.

[Grandchuck]

Oh, what a bonehead!

Thanks a bunch TiN!  Very impressive long-term stability!