USA Cal Club: Round 2

[JBeale]

If someone happening across this thread was to consider adding their name to the list, it might be useful to know an "estimated wait time" based on (current list count x average cycle time).  I don't know either of those numbers myself.

[TiN]

+1, Would be great to see current queue and list of members 

[CatalinaWOW]

Vindoline is the authority on this, but going back through the thread it appears that the average dwell for the reference has been about 50 days, with longest at 148 and shortest at 9.  There seem to be sixteen people still to be serviced in the current cue.  Some of the longer delays came when Cellularmitosis, the club starter encountered a series of health, work and other issues, but there have been long recent delays also.

I think the goal was for the dwell to be about 14 days. 

[Grandchuck]

Vindoline is the authority, but as a guess this is who is left based on an older list:
edavid
CalMachine
Conrad Hoffman
VintageNut
vindoline (CEO of the club)
technogeeky
TWMIV
Muxr
SirAlucard
MaxFrister
CatalinaWOW
JBeale
Grandchuck
t1d

[VNUTDENYER]

Please correct me if I'm wrong but old list did not stop after t1d.

[Grandchuck]

TiN has been added and one other person ... NOT OFFICIALLY.  I am not the keeper of the list.

[maxwell3e10]

Do we have an up to date list of participants?

Here is the current membership list:

Vgkid
kj7e
martinr33
nikonoid
Svgeesus
bitseeker
Vacuuminded
hwj-d
rhb
RandallMcRee
orin
ArthurDent
edavid
CalMachine
Conrad Hoffman
VintageNut
vindoline
technogeeky
TWMIV
Muxr
SirAlucard
MaxFrister
CatalinaWOW
JBeale
Grandchuck
t1d
VNUTDENYER
KK6IL
Mark03
maxwell3e10

dr.diesel
GEOelectronics
flittle
dr.diesel, flittle and Geoelectronics asked to be skipped this go-around. rhb is up next.

I am not sure how far down the list we are at the moment

[rhb]

Vindoline is the authority on this, but going back through the thread it appears that the average dwell for the reference has been about 50 days, with longest at 148 and shortest at 9.  There seem to be sixteen people still to be serviced in the current cue.  Some of the longer delays came when Cellularmitosis, the club starter encountered a series of health, work and other issues, but there have been long recent delays also.

I think the goal was for the dwell to be about 14 days. 

In which case I did not do as badly as I thought.   A few days over target IIRC.   Sad thing is now I have a 3457A/44492A.  With it I could have hooked up all my references and compared them to the PX & FX at the same time.    That will have to wait for round 3, but by then I'll be moved into a fully shielded 12' x 16' lab with DIY RF absorbent on the walls.

The walls will be soldered 26 gauge galvanized steel, covered with sheetrock and sprayed with mixtures of sheetrock mud, charcoal and powdered iron if I can find it cheap.  I plan to start with a minimum mud mix and gradually thin it to very little charcoal and iron for the top layer, then paint bright flat white.  Power through a 2.5 kVA isolation transformer.  I'm hoping it will be very quiet when I am done.

Reg

[rhb]

A rack would not work.  I could not use the gear if the door was closed.   And I'd need at least four 6 ft racks.  The 16' room dimension is dictated by the need to have the displays at a comfortable height.  The 4284/5As could be above comfortable eye level, but my  Tek 7104 and 11801 would not be much fun at an awkward height.

I'm an old man, but I'm not a car nut.  I've bought a staggeringly expensive and lavish mid 90's lab for less than a neighbor paid for a 70's Roadrunner in so-so condition.  I've never spent a fraction of that on a car.  Which is why I can afford the lab gear.

Reg

[vindoline]

Sorry I've been out of touch for a while people! Currently, the kit is on its way to Conrad Hoffman. After him the list is:

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!

[Conrad Hoffman]

The kit arrived safely today; what a nice case! I'll be cleaning the test bench tonight.

[rhb]

Conrad,

I do hope you will report in some detail on your adventures.  I've been looking forward to hearing from you about your experience with the kit.

Some testing with your DIY metrology lab kit would be very useful information.

Have Fun!
Reg

[Theboel]

charcoal and powdered iron if I can find it cheap.

the cheapest i have seen from browsing around is $1/ 25kg graphite, $10-ish /1kg FeO4. there are also ferrite powders about $16-ish / kg iirc. as usual, the source i browse from is china.
have you started? if not i thought i would persuade you not to do it. instead make a active-climatized equipment rack, far smaller and could be moved to other locations. 

I agree with 3roomlab, I have done shielding not one layer but two layer (steel and copper) the improvement with noise etc under 500Khz is not worthy compare to cost.

[Conrad Hoffman]

Hopefully I can get some data this weekend. Not sure how to apply my DIY stuff as the null detector was intended as the front end of a battery powered DVM for maximum isolation, so not practical for data recording. I think I have several of the old voltage references and can compare those to their original calibrations. The few I've looked at have remained remarkably stable. Unfortunately TI/LT hasn't made that reference (LT1027BCH) in a metal can for a long time and that was the secret to how good it was. The plastic version was subject to stress and environmental issues. I notice there's now what looks like a ceramic SMT package available that might warrant testing.

My main interest is in how well my three Fluke 731s are doing. I've also got an Analogic 6 digit calibrator that's LM399-based that could use a check-up. Not sure if my equipment is good enough but I'm also interested in measuring the noise level of the reference. I've never considered the 731s as quiet as one might desire and expect the traveling standard to do much better.

[Andreas]

Unfortunately TI/LT hasn't made that reference (LT1027BCH) in a metal can for a long time and that was the secret to how good it was. I notice there's now what looks like a ceramic SMT package available that might warrant testing.

Hello,

I fear the SMT ceramic package is not better than the plastic package.
Unfortunately I never had a LT1027 in metal can package.

I would rather put my money on some AD586LQ:

https://www.eevblog.com/forum/metrology/t-c-hysteresis-measurements-on-brand-new-lt1027dcls8-5-voltage-reference/msg1332775/#msg1332775

with best regards

Andreas

[rhb]

charcoal and powdered iron if I can find it cheap.

the cheapest i have seen from browsing around is $1/ 25kg graphite, $10-ish /1kg FeO4. there are also ferrite powders about $16-ish / kg iirc. as usual, the source i browse from is china.
have you started? if not i thought i would persuade you not to do it. instead make a active-climatized equipment rack, far smaller and could be moved to other locations. 

I agree with 3roomlab, I have done shielding not one layer but two layer (steel and copper) the improvement with noise etc under 500Khz is not worthy compare to cost.

My primary concern for the room is blocking AM and FM broadcast signals.  The stuff below 500 kHz is primarily local devices and hopefully any I have not squelched will be too far away to matter.

For a variety of reasons, I'm going to do the initial  build out of the room with just the steel studs, 26 gauge steel covered with 1/4" dry wall and paint and ESD vinyl flooring.  I'm also going to cover the bench top with the ESD vinyl flooring. The bench will be a pair of 7' x7' x 4' sections on casters, each with 3 toggle supports that will lift the bench off the casters and level it. 

Magnetic fields below 500 kHz really require mu metal or thick, low carbon iron.  That's only practical for a small enclosure because of cost.  I have one which is still a WIP.  At present it's a pair of steel chassis with piano hinge, EMI gaskets and a pull down hasp.  Still to be added is the Peltier heating and cooling, the PCB mount, thermal insulation, feed thrus and such.  The steel box is 4" x 7" x 11".  Once my new lab is set up I'll be able to test various shielding options fairly easily.  For example, I can get 1/2"- 3/4"  low carbon steel plate to cover the surfaces and measure the performance.  Then toss the plate in the steel stock pile and substitute the equivalent amount of mu metal if it proves beneficial.

With respect to internal room  reflections, I plan to do TDFD modeling to evaluate room noise with various levels of attenuation on the walls and also to test the effect of building the room out of square.

I found powdered iron for $7/lb which is 1/3 of what I found before.  But it's still expensive enough to merit testing the actual performance before spending the money.  While I can't get accurate measurements of dielectric and permeability constants with a DIY fixture, I can make relative measurements which will suffice.

Henry Ott's EMC book has lots of data from experiments he made on the effectiveness of various shielding materials.  His writing is atrocious, but there is a lot of good information.

Reg

[Conrad Hoffman]

Well, nothing happens as quickly on the bench as it does in my mind. Ten minute jobs turn into hours! I finished the last thing that was on the bench and shoved everything aside to make some space. Yes, it's still a mess. I had forgotten the LTZ reference needs bipolar supplies. My normal supplies are the big fan cooled Kepcos in the center of the photo, brought out to the Fahnestock clips. I don't like leaving those on unattended, though no doubt they can handle 24/7 operation. Instead, I modified an L-frame supply from 15 down to 12 volts; quiet and unobtrusive. That's the rack mount thing on the left.

You can see my three Fluke 731s at the upper right. The best one is actually a 731A that I tweaked for minimum TC. The other two are the B version. My 845 is a bit noisy so I'm using an HP3478A for a null meter as the lowest scale is extremely sensitive. With quick lousy wires and immediately after power-up, the Fluke was about 24 uV below the LTZ. IMO, pretty amazing. To the right of the LTZ is the original reference from the Mini-metrology article, and another one found at a hamfest on top of the far 731. I'll check those after they've warmed up a bit. Now that I know things are working, I'll improve the wiring and try to set up some data-logging. I'll also try the other reference.

I heat with wood in the next room and control the lab temperature by how far the door is open. Things are much better in warmer weather, but with some attention I can keep it around 23C. The room is dehumidified but this time of year it will sit at about 40-45% on its own.

Hopefully more to follow over the next week. (edit- replaced the wires with clean copper and matched bananas at the meter. Difference dropped to 7 uV!)

[Conrad Hoffman]

Mid-week progress report. Everything has stabilized and I've collected some data, but I need to add code to my data logger software to get the temp and humidity info from the very nice sensor unit. My Fluke reference, though I did my best to lower the TC some years ago, is no match for an ovenized unit. I also did a comparison with the original Mini-Metrology unit from about 15 years ago. Remember, that used common 1% metal films with some selection. At the time I had it checked by the local cal lab, since defunct, and it was near dead on to 10V. It's drifted about 75 uV since then, which isn't too bad for such an inexpensive circuit. Hopefully I can get my data logging software fixed up this week and do some runs over a wider temperature range when the weekend comes. I was hoping to get the unit back on the road within a week, but a few more days would be useful. How anxious is the next user? 

[CatalinaWOW]

I can't speak for the next guy in line, but I am downstream and say that if you are actively working to get data go for it. 

[rhb]

I well understand how Conrad feels.  I had my turn already, but I think that Conrad's prior work in the field merits his taking as much  time as needed for anything he chooses to do.

And I'd love to see an eval of the DIY kit from the papers.

Go For It!
Reg

I've been thinking more about it.  And I can not think of a more valuable effort than to take the time to characterize the mini metrology lab to the extent that the PX and FX references provide additional accuracy.

[guenthert]

[..]
My 845 is a bit noisy so I'm using an HP3478A for a null meter as the lowest scale is extremely sensitive.
[..]

  Hmmh, my 3478A is pretty noisy in the 30mV range, the least two digits are fairly random.  I thought that was to be expected, as its specifications state that it'll be accurate to within 250ppm + 40 digits 24h after calibration.  I realize now, that the manufacturer's specification tell very little about the noise of an individual unit (some 30 to 40 years after production).  Never bothered to actually measure the distribution, e.g. using a short as in https://www.eevblog.com/forum/metrology/dmm-adc-noise-comparison-testing-project/.   

  Perhaps you can add test results from yours to that list?  I don't have access to mine at this time (and I'm afraid I need to replace some aging caps).

[Conrad Hoffman]

I can and should do that! The question that always comes to mind is, do you get the same noise numbers for a short, as for a "perfect" noiseless voltage? I can think of many reasons why they might be different. It might be possible to watch the slow discharge of a big film cap to find out. Other ideas?

I'm still working on my data-logging software but should have that done soon, then I can try a long run over a large temperature range.

[guenthert]

I can and should do that! The question that always comes to mind is, do you get the same noise numbers for a short, as for a "perfect" noiseless voltage? I can think of many reasons why they might be different. It might be possible to watch the slow discharge of a big film cap to find out. Other ideas?
[..]

  Yes, auto-zero might have an influence for one, but at least everyone has access to a short.  I once had my Datron 1271 connected to a alkaline battery -- there was little noise, but also little stability: with a long scale DMM, the self-discharge rate gets in the way; that might not be such a problem on a 5.5digit multimeter.  Wished I had a saturated standard cell, but that might not do any good for the low ranges either.  I'm afraid 0V from a short is the best I can come up with.

  Well, how about two unlike metal junctions, one in ice water, the other at room temperature (protected from draft)?  While not all that well defined, at least over short time (seconds) the resulting thermal EMF should be fairly noise-less.

[Conrad Hoffman]

Just finished the mods to my primitive data logging software so it gets temperature from the Cal Club unit, plus fixed some bugs. Hopefully it will still work when I put it on the lab PC in the basement, then I'll start collecting data. My HP3478A seems pretty good. I don't see any downside to leaving auto zero on, and since the goal is to measure long term stability, that seems reasonable. I'll also plug in the Mini-M article null front end and see if that improves things or makes them worse. 

[Conrad Hoffman]

Getting near the end here. Hopefully will ship the standard kit later this week, but will still need some time to ponder the data. Most of my data logging just reflects my aging equipment, not anything to do with the standards, so may be of limited interest. I'll start with the ancient Mini-Metrology project voltage reference. It's hard to believe I did that 24 years ago, but I have the original reference that appeared in the photos, plus one found at a hamfest from the same time period. Both are now owned by a local friend.

The first was originally measured in 1996 by a local cal lab and tagged at 9.999948 VDC. 24 years later it measures 10.000125 VDC. Maybe the chip drifted. Maybe the inexpensive metal film resistors drifted, but IMO, that's not bad. The second one was measured by me, so it would have been against an ovenized standard cell bank; it was tagged at 10 VDC even. It now measures 10.000334 so also not too terrible at 2+ decades. I didn't build the second one so no idea if the resistors were thermally matched or how good the parts were. Interesting that both went up; maybe chance or maybe that's how the LT1027 ages?

My three Fluke 731 references proved to be interesting. My "golden" 731A turned out to have a hum issue. I don't know if it's normal or not, but the other two 731B units are much better. It would be interesting to know why Fluke decided to do design changes and come out with the B version. All have a significant amount of high frequency noise and I'll post some scope photos soon. The MML references are similar. The FX reference is much quieter than anything I own without filtering, though a 10 kHz filter puts everything on a more even footing.

The FX reference is 9.9999585 at my lab temp, so I set my three Flukes at 41 uV higher. I'm thrilled if things are within about 2 ppm and noise prevents me from doing much better. Even my HP3455A was still within about 5 ppm from its last cal, which was over a year ago using the old SV traveling standard.

More soon!