USA Cal Club: Round 2

[bitseeker]

Decent quality linear bench PSU will be fine. For critical measurements (e.g. noise) I use two VRLA 12V batteries.

OK, just checking. Thanks for the confirmation.

[dr.diesel]

We should probably include this, otherwise we add one additional variable, and the possibility of hitch-up damage.

[Svgeesus]

That sounds great!

Thanks!

I threw together this little guy this evening, to include with the ref.  It also spits out CSV data over the USB (serial) connection (for datalogging).

Nice. I have a 4-wire PT100 temperature sensor, so I can also provide temp readings from that (but no humidity sensor alas).

[cellularmitosis]

Nice. I have a 4-wire PT100 temperature sensor, so I can also provide temp readings from that (but no humidity sensor alas).

That would be great -- I still haven't gotten around to performing a boiling-point / ice-bath calibration (on anything!) yet!

[kj7e]

Or the triple point of water method.  Amazing this about the most accurate way to achieve a known temp.

https://us.flukecal.com/literature/articles-and-education/temperature-calibration/video/triple-point-water-realization-techn

[cellularmitosis]

Or the triple point of water method.  Amazing this about the most accurate way to achieve a known temp.

https://us.flukecal.com/literature/articles-and-education/temperature-calibration/video/triple-point-water-realization-techn

so... as it happens, there is a glass blowing shop which is going to open about a month from now, which is literally in the same office park as where I work.

Been planning on learning how to make glass-to-metal feedthrough seals, but now I guess I'll have to add triple point cells to that list... 

[zhtoor]

Or the triple point of water method.  Amazing this about the most accurate way to achieve a known temp.

https://us.flukecal.com/literature/articles-and-education/temperature-calibration/video/triple-point-water-realization-techn

even the ice-bath (double point cell) method (very easily do-able) is very good.

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&cad=rja&uact=8&ved=0ahUKEwih-rO_uejaAhVBcRQKHVoaBPsQFggpMAE&url=http%3A%2F%2Fwww.burnsengineering.com%2Flocal%2Fuploads%2Ffiles%2FApproximating_the_TPW_Presentation.pdf&usg=AOvVaw2iIgLhXVRfoLhXa0c6GoYR

best regards.

-zia

[zhtoor]

Been planning on learning how to make glass-to-metal feedthrough seals, but now I guess I'll have to add triple point cells to that list... 

just break apart a 2N3055 (TO-3) style package, ie; take the cap off, kill the bond wires,
now you have two glass feedthrough's available *including* pretty easy mounting (seal with shellac).
(flea-bay / taobao can be a cheap source of these)

best regards.

-zia

[Conrad Hoffman]

I think the original article had more illustrations, but it didn't seem too difficult to build- https://www.scientificamerican.com/article/tackling-the-triple-point/

[GEOelectronics]

That's George S. from the Fusor group!

George Dowell

[cellularmitosis]

Ok, today's lucky winner is Vgkid!  I've got the ref packaged up and it will ship to him tomorrow.

I threw together a little LM7812 board, so that we can also have a shared supply voltage to use.

To get us started, I hooked the ref up to a Keithley 2015 and logged it overnight, and then the next day, at different temperatures in my apartment.  It looks like the ref + DMM have a significant tempco.  (Relative humidity isn't in the charts, but has been in the low 70% recently).

https://github.com/cellularmitosis/logs/tree/master/20180503-k2015-cal-club-ref

[cellularmitosis]

Looks like the combined tempco of DMM + ref is about 0.6 ppm/C.   

[vindoline]

Looks like the combined tempco of DMM + ref is about 0.6 ppm/C.   

CM, thanks for getting thing going for round 2! I have one question though. How are you able to get sub micro-volt resolution for your data with a 6 1/2 digit meter? Is there some smoothing or averaging? If so, I think we should provide that info with our graphic data so others can try and reproduce with it. Thanks.

[cellularmitosis]

Nope, that’s the secret of the Keithley 2000 / 2015 and HP 34401a: they give you way more resolution over GPIB / RS-232.  Not more accuracy, of course 

[kj7e]

Looks like the combined tempco of DMM + ref is about 0.6 ppm/C.   

90% meter, 10% DUT.

[technogeeky]

I just wanted to chime in to say a few things:

1. Thanks for doing this again! This is an awesome outcome of a great community. There is a lot of individual effort involved too, which I'm sure we all appreciate.

2. Is the TiN-made reference going to be part of USA Cal Club 2? Or 3? Or is he just teasing us?

3. I wanted to remind cellularmitosis to make sure and check that people's addresses are the same before shipping. If they have changed, the device might get blackholed

[cellularmitosis]

Oh, good point about double-checking addresses!

I’m not sure what TiN’s timeline is (I’m not sure if he’s waiting on more resistors), but it is possible round 2 and round 3 might overlap!   My eventual goal is for the cal club to have a “library” of references, which can be checked out at any time.

[TiN]

Teasing? Tempco? What tempco. 

I think my tweaking efforts should end on -0.018 ppm/K, based on Live SVG data from today run. at that reaching 3458A resolution/noise already even with 32C span. Next step is 10V output stange tuning.

I don't need any more parts for USA Cal club FX ("wish to say that for rest of them, eh"), so it's just testing time and then initial 200 hours monitoring to see that reference settled.
Then calibration to my lab DC Volt (that is, measurement only). Then another 800 hours to make sure everybody happy and stable, final TC characterization with everything assembled, noise measurement and then it's ready. So if all goes well, that is 50 days from now. I don't think rushing anything with LTZ1000A-based reference make any sense at 500$ reference. 

Also how about 10KOhm standard for USA Cal Club? There is L&N 4030 measured 10000.215 Ohm (+/-8ppm max abs) that just sits, doing nothing. This is giveaway resistor, I bought it specially for USAC needs, it was just $50.

[cellularmitosis]

That’s great news TiN!

Interesting to hear about the L&N resistor — I saw some of those on eBay.  I think those are manganin?  I have heard they don’t like being handled a lot, but the stability can be very good.  I wonder if it would better as a reference which stays at home, which a traveling transfer standard can be compared to?  Do you have any idea of the tempco or stability yet?

[TiN]

Well, ManateeMafia measured it on his calibrated 3458A (click on the link) over a week, so that much you have for stability. "Oscillations" is due to his aircon setup in warm sunny house .
Since me and MM use higher grade standards to transfer between our labs, and "stay-at-home standards are SR104's", I don't really care if this L&N unit dies from USA Cal club misuse or shipping damage. After all you can use it as testament if 4030 can survive frequent shipping with regular post service  . All you need to do is to send address where to ship. All I want in return is some data plots from participants 

[zhtoor]

phase change media container with 5-10 C and 35-40 C melting points if we can find affordable media

a pretty cheap phase change material can be made by microfine silca (AeroSil type, SiO2) and paraffin wax
with melting / freezing point at 55/45 degC.

ref:
Fabrication and Properties of Microencapsulated Paraffin@SiO 2
Phase Change Composite for Thermal Energy Storage
Benxia Li,* Tongxuan Liu, Luyang Hu, Yanfen Wang, and Lina Gao

can be an *excellent* adjunct for transport of vrefs.

best regards.

-zia

[rhb]

phase change media container with 5-10 C and 35-40 C melting points if we can find affordable media

a pretty cheap phase change material can be made by microfine silca (AeroSil type, SiO2) and paraffin wax
with melting / freezing point at 55/45 degC.

ref:
Fabrication and Properties of Microencapsulated Paraffin@SiO 2
Phase Change Composite for Thermal Energy Storage
Benxia Li,* Tongxuan Liu, Luyang Hu, Yanfen Wang, and Lina Gao

can be an *excellent* adjunct for transport of vrefs.

best regards.

-zia

That's a good suggestion, but 131 F  is too high in my view (but I also have no data).  However, one might be able to create a phase change medium using a mixture of paraffin and mineral spirits.  I use that as a wood finish and it's remarkably temperature sensitive.  In my case it was an annoyance as the paraffin was coming out of solution.  Time for another round of phase behavior of petroleum.  I've got a copy of the NIST STRAP program, but it's probably 15+ years out of date and on 5 1/4" floppies. 

I'd not considered mixture of petroleum products when I posted that.  My focus was on bulk modulus when I dealt with the subject, but now that you bring it up, I suspect it would be relatively easy to come up with phase change media tuned to the problem of shipping precision references.  A blow molded box top and bottom with two different petroleum mixtures.

There is, of course, the Swedish concern which rents temperature controlled containers for shipping medical supplies to places like the African interior.  But rather pricey for a hobby pursuit.  And they are really in the shippable refrigerator business as opposed to maintaining 23-25 C.

[CatalinaWOW]

Not endorsing use of a phase change material, but Glauber's salts in the decahydrate form has a melting point of 32 C  (91 F).  Nice temperature for protecting the reference, but being well below the ambient temperature in much of the US in summer time you are forced to really confront heat flow, exposure time and total heat capacity of the phase change medium.  Which would be true for any phase change material solution.  We could probably get time-temperature profiles from somewhere, maybe just by mailing a logger around.  But we would still end up with a statistical solution.  Do we want to protect against a 3 sigma heat event, or 5 or 8 sigma?

[rhb]

You'd have to have everything in a well insulated box for phase change media to do any good. 32 C is too low to be useful in the summer, but it would work for protecting shipments in the spring and fall.  We do get days when the temperature in the back of a truck would get too high even in the early spring and late fall.  But that would only be during the day, so you'd just need to be able to hold the temperature for 8-10 hours.

It might actually be a good idea to have some small, cheap to ship temperature loggers to send ahead  prior to shipping a high quality reference.

[cellularmitosis]

You'd have to have everything in a well insulated box for phase change media to do any good. 32 C is too low to be useful in the summer, but it would work for protecting shipments in the spring and fall.  We do get days when the temperature in the back of a truck would get too high even in the early spring and late fall.  But that would only be during the day, so you'd just need to be able to hold the temperature for 8-10 hours.

It might actually be a good idea to have some small, cheap to ship temperature loggers to send ahead  prior to shipping a high quality reference.

Yeah, shipping a temperature logger is a great idea.  An attiny with a watch battery should be pretty light weight.