USA Cal Club: Round 2

[hwj-d]

No battle plan survives first contact with the enemy, but that sounds pretty good!

[SilverSolder]

No battle plan survives first contact with the enemy, but that sounds pretty good!

"Everybody has a plan...  until they get punched in the face."  -- Mike Tyson

[TiN]

• 4 wire measurements of each resistor using the 3 meters sequentially (i.e., resistor hooked to only 1 meter at a time) for 2 hours
• Log Px for 24 hours with standard wired to 3 meters in parallel
• Log Fx for 7 days with standard wired to 3 meters in parallel

Resistance measurements for 2 hours barely enough to see any correlation. I'd suggest interleaving resistance tests with voltage tests. I always try to run resistance tests for days, to battle hysteresis effecte. Using PTFE wiring and robust connections is also important for last bit of accuracy. TBH connections for DUT resistors in kit are inadequate for even 5.5-digit DMM, but it's what it is.

Logging PX or FX in absolute direct measurement also hinders your measurements a lot, as both references are much more stable than any 6.5 digit DMM.
Measuring difference between PX and FX on 100mV DMM range will give you much better data for stability test. Then you can use calibrated value of FX to estimate drift of your DMMs alone over time period. After you know both errors from reference (e.g. settling after transport/power on/your ambient temperature variations), and from DMM (own tempco, noise, short-term stability) you can use obtained data to get rough calibration accuracy of each DMM.[/list]

[Edwin G. Pettis]

Just for notation, the Fluke 732C had been made with Vishay resistor networks, for good reasons, they have been replaced with precision wire wound resistors again.....

[MaxFrister]

TiN: thank you very much for the suggestions. 

I can interleave resistance measurements with voltage for the week by employing just the 34970a without degrading precision.  I could arrange for all the meters to measure it but it would require an additional matrix switch.

I'll go ahead and order some PTFE wire.  I was planning on using cat5 wire.

My understanding is that the PX is nominally 7V and the FX is 10V.  On the FX schematic the 7V is available but unbuffered  and I certainly don't want to open the case.  I'm not certain how to wire them up to provide a difference of less the 100mV.

[TiN]

Ah, my bad, I forgot that PX is direct unbuffered output. 100mV range is useless then. Cat5 cable is usually fine for 10V measurement, if your environment around references is quiet (no PWM LEDs, no soldering irons, no other RF/EMI generating stuff nearby). For 10k resistance at 6.5 digits PTFE is not really important, but always good to have.

I can interleave resistance measurements with voltage for the week by employing just the 34970a without degrading precision.  I could arrange for all the meters to measure it but it would require an additional matrix switch.

It's just few resistors and DC refs, I'd just do swaps manually, no need to worry about matrices.

[Conrad Hoffman]

I haven't found that PTFE makes much difference as most wires are supported in air anyway. PTFE requires that the wire be silver plated. I get my best results with plain untinned solid copper wire- stripped out of phone pairs or what they sell as "bell wire". Wire directly screwed in the jacks if possible. I've gotten my worst possible results with shielded cable as the center conductor and shield are often different materials- thermal emf city!

[MaxFrister]

Here is the current setup using stunt doubles for the FX, PX and resistors. 



I’m glad that I started the setup and practice logging in advance of receiving the reference standards.  Despite having GPIB logging running on another computer it still took some fussing to get it running on a different laptop.

I also learned some lessons that were not obvious (at least to me) in advance:

• Turn off energy saving on the computer so that it doesn’t stop logging.
• Don’t close the lid on a laptop
• Don’t turn off the master lab power (this is a safety habit; I taped over the switch so I would stop turning it off).
  

My current plan is to log 3 different setups.  All 3 setups will log:

• Time
• Ambient Temperature
• Humidity
• Barometric pressure
• HPAK 34970A measuring
  
  • Temperature near the references
  • Voltage of PX
  • Voltage of FX

Setup 1:

• HPAK 34401A measuring 1k resistor (all resistance measurements will be 4-wire)
• Datron 1081 measuring 10k resistor

Setup 2:

• HPAK 34401A measuring 10k resistor
• Datron 1081 measuring 1k resistor

Setup 3:

• HPAK 34401A measuring FX
• Datron 1081 measuring FX
• HPAK 34970A measuring (in addition to the above):
  
  • Ohms of 1k
  • Ohms of 10k

   
I plan to run setup 1 for 24 hours, setup 2 for 24 hours, and setup 3 for 7 days.   There are, of course, much more that could be measured but I want to keep the standards for about 10 days and get it moving to the next member.

[KK6IL]

Haven't seen any new msgs here for awhile.The standard still
floating around or did COVID halt progress?

[vindoline]

Haven't seen any new msgs here for awhile.The standard still
floating around or did COVID halt progress?

I can't imagine that the virus crisis is doing us any good...however the club is still going strong! Currently the kit is with technogeeky.

Here is the current lineup:

technogeeky
TWMIV
Muxr
SirAlucard
MaxFrister
CatalinaWOW
JBeale
Grandchuck
t1d
orin
VNUTDENYER
KK6IL
Mark03
maxwell3e10
TiN
niner_007

If anyone isn't on the list and you think you should be, please contact me! Thanks!

[hwj-d]

Hi Vindoline,

what is the status of measurements. Why no postings about here in this group. Some calclub members posts comprehensive announcements, and then, nothing. Wasn't it the real point to at least post summaries here?

Thanks for your work. 

[VNUTDENYER]

Maybe post when getting or sending kit would allow planning by upcoming members (borrowing gear, Covid sheltering, lab upgrades, etc.). 

[Grandchuck]

Has anybody been able to download all of the data from the folders on the Cal Club FTP site established by TiN?  I can download some of the folders but not all.

[SirAlucard]

I think life keeps getting in the way of everyone, for sure COVID has something to do with it. However I do like people that get the kit to post either their findings or how they are testing.

[rhb]

It takes a lot more to do than you expect until it's sitting in front of you.  Then it's pretty intimidating with a long list of people waiting on you to finish.

I think there is huge value in how different people approach the project and the results they get.

Reg

[SirAlucard]

I know a lot of you guys are in the camp of "I want to measure this over a long period of time and verify my findings with everyone else". I'm more in the camp of "I want to verify if my equipment is measuring close enough to everyone else and just send it along".

[Conrad Hoffman]

Everybody has different needs. Those of us with elderly 6.5 digit meters mostly want to get everything close to calibrated and probably can't contribute much to the stability studies. I could have done that long ago when I had ovenized standard cells, but got rid of them in an effort to reduce the amount of mercury in the lab. The cells themselves were trouble-free, but I spent a lot of time and money on the battery backup system. Never met a gel-cell that lasted more than a few years.

[hwj-d]

I'm more in the camp of "In between a short statement about the state of things, doesn't hurt."

[KK6IL]

During the brief period Wavetek was trying to produce a 0.005% differential multimeter (DC/AC V, Ohms Hz, Ratio), we had a bank of 10 standard cells in a lead bathtub inside a polystyrene insulated container. Depended on that to slow down and reduce temperature shifts. Meter references were a pair of ~6.2V zeners with a +TC one matched with equal -TC. What a PITA those were to make.

My needs are modest - 10V to calibrate my pair of 3456's and LM399 standard, and a 10K to verify my 10K L&N standard is still close. 

[bitseeker]

Indeed, it would be good to post status updates at least, what, once a week, while you possess the kit. Performing a long study is OK. At least let everyone know you're still OK (and what you've experienced thus far would be interesting).

[rhb]

Indeed, it would be good to post status updates at least, what, once a week, while you possess the kit. Performing a long study is OK. At least let everyone know you're still OK (and what you've experienced thus far would be interesting).

Seconded.

[VNUTDENYER]

As for comparing the PX and FX outputs, I had planned on adding selected 3 of 8 standard cells in series to get difference below 60mv (unless consensus is that would be harmful to PX OR standard cells).  Hope to add more gear before time at plate.     

[VNUTDENYER]

Maybe should have been a question.  Is it ok to series up by best 3 standard cells with PX and monitor difference to FX?  This would only be after logging noise/stability of cells, E1412A zero, etc.  Thanks for any tips.

[dr.diesel]

So @technogeeky has had the hardware for 3 months now?

[alm]

I don't see any issue with putting standard cells in series with an LTZ1k reference, since the standard cells are floating. Of course the usual caveat of limiting current draw from standard cells applies, so you may want to check the bias current and impedance of your DMM.