USA Cal Club Round 3.1

[bdunham7]

I have been asked to administer the remainder of USA Cal Club Round 3 and will likely stay on to do a Round 4 if wanted.  I have received most of the kit, but the L&N 10k standard resistor is still enroute.  It has an issue with leaking and I'll be trying to correct that before it goes out with the kit.  I see no reason to delay continuing the round but if someone really wants that 10k standard, they'll need to defer getting the kit until is is available.

Currently the kit consists of the FX reference, the original PX reference, a GPSDO 10MHz source, a multi-value resistor box, a GPIB adapter, a temperature/humidity measuring device and some miscellaneous leads and whatnot.  I'm going to reserve 6 posts below this for each of the major items so that this post isn't so long.  I'll cover things here assuming the reader is new to USA Cal Club, but I may not cover every detail about all the items in the kit.  Please refer to the first post of USA Cal Club Round 3 for links to instructions for the legacy items.

https://www.eevblog.com/forum/metrology/usa-cal-club-round-3/msg4715543/#msg4715543

I will add a transit temperature logger, some low-EMF Z-plug leads for the FX reference and a 4-wire short.  I'm concerned about wear and tear on the FX reference and as much as we like bare copper on binding posts, I think the Z-plugs will spare the FX any further torque-related incidents.  If you have extraordinarily good equipment and a light touch, then go ahead and use the bare wire if you want, but I've not been able to tell any difference. 

I will send a personal message to the remaining participants shortly.  I'm going to loosely try to stick to the order that they were listed by Randall, but my priority is getting through the round in a reasonable time and I may make adjustments to further that goal.  The kit is shipped in a large flat-rate box via USPS and I'd like everyone to continue doing exactly that both ways.  The cost is $19.90 each way.

The current participant list is:

CatalinaWow
rax
edavid
rockstedy40
SilverSolder
rsjsouza
jjoonathan
bdunham7
conrad hoffman
cscaccetti
uski
AeroETech
Smokey
maxwell3e10
1audio
RoadDog
rhb
ycui7
rockstedy40
mower
zepto
chuckb
CurtisSeizert

Update:  Based on the responses so far, I think there needs to be a fundamental shift in the way this is scheduled.  Being prepared and able to receive the kit, use it effectively and return it in 10 days or so requires some planning ahead.  Lots of people need to defer for various reasons and I had the same issue--when my turn originally came I had a medical issue that prevented me from taking it.  I've shipped the kit to the only user who was able to use it immediately so in the next week or so I'll come up with a new plan.  If you are on the list above and are not crossed out, please respond to the PM that I sent you.

[bdunham7]

The FX Reference is the central figure in the USA Cal Club kit, provided by TiN from xDevs.  You can read some of the details on xDevs.com.

https://xdevs.com/article/usac_2023/

What it is and what it does is well documented so I'm just going to concentrate on how to properly set it up and what you can do with it.  It takes a bipolar power supply or 2 12V SLA batteries; the +12V supply will draw about 35mA (due to the LTZ1000 heater) and the -12V about 6mA.  A high quality linear supply is needed and please be very careful about how you connect it as we don't want to see this valuable resource take any damage.  The outputs are binding posts and seem durable, but previous versions have been broken.  I have included some low-thermal-emf leads (silver plated z-plugs) that can be plugged into the banana jack part of these terminals to avoid the issue of putting torque on the posts.  Please gently install the shorting wire when the FX is not powered on or connected to something.

The FX puts out 9.9999642V with a tempco that is negligible for almost all users.  This allows you to adjust or null your homemade 10V references and verify commercial references, DMMs, etc.  What I've found it to be useful for is characterizing the tempco, noise and other errors of my various 6.5-digit class meters.  I'd like to hear from other users exactly how they have found the FX to be useful.  Here is an example of a plot of the FX measured by my Fluke 8846A looking at the difference between having the display on or off.  The temperature indicated is the case temperature of the FX, unfortunately I currently only have the means to log one temperature reading to the PC.  You'll just have to take my word that the ambient temperature was pretty well controlled to 23.7 +/- 0.5C during this test.  The display was turned off for the first half and on for the second and it looks like that made about a 0.2ppm difference.  Note that the entire chart is 1ppm from top to bottom and that with the display on  (as it would have been for calibration) the meter is off (high) by ~0.33ppm. 



The next thing for me to do is to try and characterize the tempco of the meter over a wider range.  I haven't finished this process, but I started by trying to look at the tempco of the FX itself.  I put it in a place where it was not shielded from my HVAC like the rest of my bench was and recorded overnight.  Again, unfortunately, I can't do two temperatures and thus did not log the ambient temp near the meter.  However, it would have started about 23.5C and then cooled off to about 21C overnight, only rising again right at the very end.  What you can learn from this plot is that the FX truly really does have a very low tempco, just as advertised.  And I now know that the 8846A has a slight negative tempco, at least over the small temperature range I've tested here.

[bdunham7]

The PX reference from the original USA Cal Club, provided by cellularmitosis, is a small LTZ1000-based reference without a 10V stage.  It's output was last measured at xDevs at 7.0456489V.  It should be powered by the 12V regulator assembly provided or perhaps by a 12V battery.  There are two resistors, 1K and 10K, built into it and special 4W connectors to interface with it.  I've labeled the cables and there is a clear picture of how to set it up in the orginal instructions.

https://drive.google.com/file/d/1AoXDJ-ybEtL40Hh-SGyr5oJMXcGVgf-l/view

A check of the PX vs 8846A indicates that it seems to be accurate and not very susceptible to temperature changes.  The temp reading is of the PX case.

[bdunham7]

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