USA Cal Club Round 3 - Page 1
Forum section: electronics / general

author: RandallMcRee
author_rank: Frequent Contributor
timestamp: February 21, 2023, 06:34:18 pm
content: It's time for round 3 of the US Calibration Club!After some informal discussion there are a few ground rules that are proposed:Each member should have the kit for two weeks, or less, exclusive of transit time;If you are away, do not accept the kit (inform Randall by email), you will get the next available slot when you are ready;The kit recipient is responsible for USPS priority mail costs in both directions;It is hub and spoke, so the kit is returned to, at the moment, Randall, and sent by him to you;There are two options: round 2 kit only (kit2) or kit2 plus a resistor set (rkit3), they may ship separately, still trying to figure that outPriority mail costs$17.10$14.75 for kit2 in a medium flat rate box, resistor set, rkit3 is another $17.10now $14.75Both kits in large flat rate box: $22.80now: $19.90Other nice-to-haves:Please post in this thread any questions, comments, etc,Please indicate any pertinent details about your measurement setup, make and model of the DMM, last cal, if any, cables, temperature, etc.Please post data to xdevs.com in the USA Cal Club folder (TBD).PDF instructions from round1/2 from bitseeker:https://drive.google.com/file/d/1AoXDJ-ybEtL40Hh-SGyr5oJMXcGVgf-l/viewInstructions for uploading data to xdevs:https://www.eevblog.com/forum/metrology/usa-cal-club-getting-started-user-guide/msg2527656/#msg2527656EEVblog starting page for kit2:https://www.eevblog.com/forum/metrology/usa-cal-club-getting-started-user-guide/msg2527122/#msg2527122Intro to rkm resistor box:https://www.eevblog.com/forum/metrology/creating-some-high-precision-resistors-for-calibration-purposes/msg4550849/#msg4550849TiN calibrated my Keithley 2002 and recertified the FX reference in kit2:https://xdevs.com/article/usac_2023/TiN also donated a L&N 10K standard for the club that forms the kernel of rkit3:https://xdevs.com/article/usac_2023/#ln4040bLET ME KNOW IF YOU WANT TO PARTICIPATE! send PM or reply here...Thanks,Randallupdated to reflect postal price change, 5/24/2023

author: RandallMcRee
author_rank: Frequent Contributor
timestamp: February 21, 2023, 06:34:57 pm
content: Let's begin. I generated a random permutation of those who signed up... and here it is:CatalinaWowraxedavidrockstedy40SilverSolderrsjsouzajjoonathanbdunham7conrad hoffmancscaccettiuskiAeroETechSmokeymaxwell3e101audioRoadDogrhbycui7rockstedy40mowerzeptochuckbCurtisSeizertI will be contacting you by DM to get your contact details, etc. as the weeks roll by.Thanks,Randall

author: Rax
author_rank: Super Contributor
timestamp: February 21, 2023, 06:53:00 pm
content: I'm in, please.

author: bdunham7
author_rank: Super Contributor
timestamp: February 21, 2023, 07:08:01 pm
content: Me two.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: February 21, 2023, 08:03:29 pm
content: I'll join the fun.I would suggest investigating a large flat rate box or even just a non-standard priority box for the kit3 option. It seems likely the charges would be less than two medium boxes, and cuts the chances for something to go wrong in the post office in half (nah, that never happens.).I am assuming that the precision resistors that went around with the kit in Round 2 will still be there. Comparison data on those relative to the new resistance standard will be useful to those not wanting to do the kit3 option.

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: February 21, 2023, 08:44:44 pm
content: Count me in, but in a few months. Don't want to be at the front of the list so I can be more prepared this time. Translation- so I have time to tune up all my broken, ailing and neglected stuff!

author: rsjsouza
author_rank: Super Contributor
timestamp: February 21, 2023, 08:56:40 pm
content: I might be interested as well, but I would need time to dive into my old/broken/new-to-me Fluke 8505A and see if I can get it up and running... Ah, and get the old PC with the GPIB interface running...

author: jjoonathan
author_rank: Frequent Contributor
timestamp: February 22, 2023, 10:16:24 pm
content: Please put me on the list!

author: cscaccetti
author_rank: Newbie
timestamp: February 24, 2023, 07:40:39 pm
content: Would like to be on the list! Thanks.

author: RandallMcRee
author_rank: Frequent Contributor
timestamp: February 24, 2023, 10:08:12 pm
content: Quote from: CatalinaWOW on February 21, 2023, 08:03:29 pmHi CatalinaWow--one of the reasons that I am going to the resistor setup is because those resistors are somewhat suspect. What I noticed is that their value depends on whether or not you measure them before or after using the PX reference in which they are embedded. So, presumably, a temperature effect. So I thought to eliminate that and add more range as well. I don't have the equipment necessary to characterize their tempco, so I am sort of ignoring them. Forgive me!

author: CatalinaWOW
author_rank: Super Contributor
timestamp: February 25, 2023, 03:54:29 am
content: Quote from: RandallMcRee on February 24, 2023, 10:08:12 pmI think it is appropriate for you to ignore them. By putting yourself in charge of Round 3 you have more than enough to do. But since the data, presumably including the temp sensor data for room ambient is all posted those who might choose this route can do the work themselves. There should be enough data sets to provide at least some good information. I haven't decided which way I will go. But if I decide to go the analysis route I will certainly post the results.

author: Smokey
author_rank: Super Contributor
timestamp: February 25, 2023, 09:52:05 am
content: I don't have anything better at the moment than an old way out of cal 6-1/2 digit Keithley, but I love the idea. Now I'll get updates when you guys do cool stuff.

author: SilverSolder
author_rank: Super Contributor
timestamp: February 25, 2023, 03:31:29 pm
content: I'd like to join in on this round, if I may!

author: rockstedy40
author_rank: Contributor
timestamp: February 26, 2023, 11:37:04 am
content: Hello everyone. I’m new to this group, and am amazed at the incredible engineering going on here. Thanks to all that have made this round 3 possible. I’d like to get in on this round also, as I have an HP 3456A and Fluke 45 I’s like to check.I was thinking about making a Hammon divider to get a decent 1V reference. I noticed in the round 2 thread, post #261, TIN stated that the FX could sink or source up to 20 mA (but at that level there would be no Kelvin compensation). Would a 2mA load affect the output accuracy of the FX? Or should I design the Hammon divider for a lower parallel connection current?ThanksBob

author: RandallMcRee
author_rank: Frequent Contributor
timestamp: February 26, 2023, 10:29:31 pm
content: Quote from: rockstedy40 on February 26, 2023, 11:37:04 amYes, 2 ma does affect the output accuracy. But if you search for Conrad Hoffman’s article on diy metrology you will find techniques that don’t rely on having access to an ultra accurate voltage when making a hamon divider. However, you should be able to calibrate your hp3456 I believe since IIRC you need just a 10v source and a 10k resistor.

author: guenthert
author_rank: Frequent Contributor
timestamp: February 27, 2023, 04:14:11 am
content: Quote from: RandallMcRee on February 26, 2023, 10:29:31 pmWell, any current draw will cause an voltage drop across the leads (iirc the FX has sense wires to the terminals, so there the drop should be small, albeit unknown. For e.g. the Fluke 731b, a 1mA current (10kOhm load) causes a drop of 5ppm at the 10V output). You will need to decide, whether that error is acceptable for your purpose.Quote from: RandallMcRee on February 26, 2023, 10:29:31 pmYou might be thinking of the 3458A. For the (older) 3456A the calibration procedure relies on several reference values (calls for Fluke's 731b as DCV standard, not HP's own 735A, even though it is used with a reference divider as stand-in for a standard cell, ouch) and adjusting up to 14 potentiometers (fortunately accessible from the front).

author: SilverSolder
author_rank: Super Contributor
timestamp: February 27, 2023, 04:30:53 am
content: Quote from: RandallMcRee on February 26, 2023, 10:29:31 pmThat article led me down a very deep rabbit hole.... into the meaning of precision, accuracy, limitations - at the frontier of what can be known.Fascinating stuff.

author: rockstedy40
author_rank: Contributor
timestamp: February 27, 2023, 11:12:23 am
content: Randall, you are correct in that I don’t need to use a precision voltage source to set the Hammon divider, thanks for reminding me about that.The HP3456A does require a separate voltage for each decade :-( But with the FX I can cal the 10V range. With the FX and a 0.1x Hammon divider I can cal the 1V range (accounting for the loading of the divider on the FX by measuring the FX output first with the just calibrated 10V range). Using the 0.1x divider and a 100V source I could also set the 100V range (albeit with less accuracy based on the stability of the 100V source). I was also thinking about making a x0.01 Hammon divider, and using the FX to cal the 0.1V range.I realize that these methods are not up to the typical metrology accuracy, but they should allow me to get close enough for my hobby work.Thanks for all your inputs.

author: AeroETech
author_rank: Contributor
timestamp: February 27, 2023, 12:37:17 pm
content: Please count me in. I have a Keithley 2010 and a Keysight 34420A. They were both calibrated just over a year ago.I also have an Amphenol IRTD-400 (M2801) that is within Cal, so I can confirm the temperature logger. My probe's specified accuracy is +/-0.025 Degrees C, but when it was recently calibrated, it checked out to within 0.003 Degrees C at 0C and 0.008 Degrees C at 420C

author: alm
author_rank: Super Contributor
timestamp: February 27, 2023, 01:00:35 pm
content: Quote from: rockstedy40 on February 27, 2023, 11:12:23 amThese methods have been the standard methods for decades. If you read the freely available book "Calibration - Philosophy in Practice" 1st edition by Fluke (just search for the PDF), then you'll read about using similar techniques, though with a worse voltage divider, when they describe the Fluke 7105A system. They calibrated the Fluke 750A decade to 1.018XV divider using the Fluke 720A Kelvin-Varley divider, and then use the Fluke 750A Kelvin divider to adjust the Fluke 335A calibrator, which is merely used as a stable voltage source, relative to the standard cell. A more modern way would be to use the Fluke 752A Hamon voltage divider to calibrate a calibrator using the exact method your describe.Of course the uncertainty depends on how good your procedure is and how stable your divider and voltage source are over the duration of the calibration. But with excellent execution, this method can get you lower uncertainties than almost any other method (except by using even better dividers).

author: uski
author_rank: Frequent Contributor
timestamp: March 01, 2023, 02:41:23 am
content: I would love to join please, too, but put me towards the end. The reason is that I am getting an LTZ1000A reference going, and would like to compare it at the beginning to get an initial calibration, and then for the next round I can compare again and see how it ages.I also have a few multimeters that would happily compare themselves with a good known source.Thanks

author: RandallMcRee
author_rank: Frequent Contributor
timestamp: March 07, 2023, 11:02:21 pm
content: Updated post #2 with a list of folks who responded.CatalinaWOW is the firstvictimuh participant.It all fits into one large flat rate box, so postage is $22.80 each way.Thanks,Randall

author: CatalinaWOW
author_rank: Super Contributor
timestamp: March 08, 2023, 02:17:42 am
content: I started warming up and checking test gear today. Will be doing test runs tomorrow. Hope to send the stuff back to Randall about three days after it arrives. If I and the rest of us can keep this cadence up those at the end of the list won't have to wait more than a year.

author: Exeter
author_rank: Newbie
timestamp: March 08, 2023, 03:12:32 am
content: Very interesting concept.

author: Rax
author_rank: Super Contributor
timestamp: March 08, 2023, 03:24:52 am
content: Quote from: CatalinaWOW on March 08, 2023, 02:17:42 amI'd (please) not completely blast it from the front door straight to the back - I was under the impression a couple of weeks of using it is fine. The list is not that long, currently (and I assume it's being updated). I am second in line and would hope I'd get a bit of heads up before it's heading my way. Most people have actually asked to be pushed towards the end of the line.I do appreciate the expenditure, I just hope we're keeping things on a similar timeline to what was presented.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: March 08, 2023, 03:49:35 am
content: Quote from: Rax on March 08, 2023, 03:24:52 amMy intent is a gentle nudge more than a push. In Round 2 the dwell times were often very long. How long it takes depends on what you are doing. I am not adding new knowledge to the stability of the standards, merely checking my equipment. I have set up GPIB to automate the data collection, and if 72 hours of data isn't enough it will hardly be improved by adding a few more days or weeks. Experience in the first two rounds suggests that things will happen that make longer than two weeks happen for some folks and some folks have instrumentation good enough that it is worthwhile to have them gather extended data sets, so to achieve a two week average those of us who are able should do it a little faster.By setting up, warming up and doing test runs with my local standards I avoid problems that have occurred to me and others in prior rounds. Things like Windows updates that killed my automation, experiments making sure my instruments temperature was controlled adequately, misplaced equipment and finding unexpected noise and having to locate and squelch it. It is only polite for me to find and correct these on my own time so that others aren't forced to wait.

author: maxwell3e10
author_rank: Frequent Contributor
timestamp: March 08, 2023, 04:16:18 am
content: Please add me to the list as well, I am also happy to be near the end of the round. I was near the end of round 2, so it would be interesting to see how the instruments have drifted over several years.I think it would be good for the community if anyone who receives the kit is almost required to post some results here. Taking long data is fine, but even spot calibration numbers would be useful to get some statistics on stability of various instruments.

author: 1audio
author_rank: Frequent Contributor
timestamp: March 09, 2023, 05:24:59 am
content: I'm interested. I have Fluke 732A with no real history, 2 8506A's, a Prema 6001, Keithley 2015, HP735 and Fluke 731B. Needless to say none agree but they all seem to disagree consistantly. I would hope this helps me get my bearings. Is there a schedule to manage the transitions? Are there others in the Bay Area on the list so the kit could be handed off without shipping?

author: Rax
author_rank: Super Contributor
timestamp: March 09, 2023, 01:44:43 pm
content: Quote from: 1audio on March 09, 2023, 05:24:59 amIs that a consideration? I know at least one person in the list that is my neighbor, and we're not contiguous on the sequencing.

author: RandallMcRee
author_rank: Frequent Contributor
timestamp: March 10, 2023, 06:18:03 pm
content: Quote from: 1audio on March 09, 2023, 05:24:59 amI go to the East Bay (Alameda) a few times a month to visit family, perhaps we could arrange a hand-off? I only suggest this because I am the facilitator of this round, it does not work in general.The logistics of hand-offs is too complicated across an entire group. But if two people like Rax and X (whomever that might be) wanted to share a four-week slot we could have scheduled them together--had we known beforehand. As it stands Rax would have to query everyone who would be inconvenienced by now re-scheduling X up to where Rax is...still not impossible. As well, I doubt that anyone would object to Rax voluntarily moving down the list.Regards,Randall

author: CatalinaWOW
author_rank: Super Contributor
timestamp: March 10, 2023, 09:32:39 pm
content: The lovely box of goodies arrived safely in the mail today, in spite of rain, snow and road closures along its path, and is doing its shakedown run. Everything looks good as far as the voltage references go. One thing that will be interesting to watch in the data will be the FX reference, which was still quite chilly from its travels when I started logging. I will look at the resistances in a couple of days after collection on the voltage references.I won't be blasting it back out again, but will try to avoid the long tail of intervals observed in round 2. By my analysis of the thread documenting round 2 the intervals were (in no particular order) 6, 9, 9, 12, 13, 18, 19, 25,31, 36, 53, 65, 91, 96, 116, 125, 136 and 148 days. There are mitigating circumstances, COVID, trips back to TiN for recheck, and stops that weren't documented in the thread to name a few. Randall suggested a two week goal and I think that is generally achievable. The thing is not to be insanely schedule driven, but mindful of keeping it moving.

author: Rax
author_rank: Super Contributor
timestamp: March 11, 2023, 01:47:13 am
content: Quote from: CatalinaWOW on March 10, 2023, 09:32:39 pmAgreed and thanks for your responsible approach!

author: Rax
author_rank: Super Contributor
timestamp: March 11, 2023, 08:34:07 pm
content: Quote from: RandallMcRee on March 10, 2023, 06:18:03 pmRandall - thank you, I think we'll stick with the current order.Looking forward to the kit!

author: CatalinaWOW
author_rank: Super Contributor
timestamp: March 16, 2023, 04:34:30 am
content: The package is boxed up and will be in the mail tomorrow AM to Randall McCree.It took longer than expected, a combination of equipment failures, family emergencies, power failures at the house and more interesting stuff to measure than there was last time around. I have just begun to reduce the data. It will be posted at XDEV in the next few days (I hope), but due to the demand for sample answers I will post the following pretty raw data. These are readings from my HP3457 or HP3456 and have not been corrected, tracked against prior measurements or anything else. The stdev is only representing the noise in the measurements, no other uncertainties are included. They appear to be relatively accurate, but how accurate will take further looking.1. FX reference with 3457 - 9.9999982 with stdev 6.73E-62. FX reference with 3456 - 10.0001927 with stdev 4.5 e-63. PX reference with 3457 - 7.0456920 with stdev 6.36E-6PX 1k resistor - 1000.00908 with stdev 0.000261PX 10k resistor - 9999.8767 with stdev 0.00215L& N 10000 resistor - two measurements see comment/question following numbersCorrect connection - 10000.055 with stdev 0.011'wrong' connection - 10000.084 with stdev 0.012McCree Resistance BoxResistance St Dev0.0004306 3.95E-510.0038942 4.821E-520.0013949 4.74E-5100.0017945 3.25E-5200.0101323 6.55E-51000.36141 0.00171831999.98289 0.002013810000.36141 0.001718319999.38331 0.001073099999.67856 0.040206190002.132 0.052931000118.609 3.9216It took me a while to find TiNs data sheet on the Leeds and Northrup resistor, so after thinking about it decided that I should put the current drive on the center (top) terminals and the voltage sense on the side (end) terminals. The logic being that the only current flowing from the current terminals to the sense terminals would be that limited by the extremely high impedance of the meter.The data sheet recommends using the side terminals for two wire measurements, but recommends doing the voltage sense on the top terminals when doing four wire measurements. I don't see the logic behind this, but ran a data set connected that way. There is a difference, but it is unclear to me which is correct. Well, actually, the way it was calibrated by L&N and presumably rechecked by TiN is 'correct' so that measurements can be compared, but why is it the better way to do it? I would better understand the Leeds and Northrup recommendation if two wire measurements were also performed using the top terminals. Does anyone know the logic?

author: guenthert
author_rank: Frequent Contributor
timestamp: March 16, 2023, 06:03:46 pm
content: Quote from: CatalinaWOW on March 16, 2023, 04:34:30 amThe error due to the additional current (some 10 to 100pA across a few tens of mOhm) through the meter is insignificant here, regardless how it is connected.For a 10kOhm resistor measured by a 3456A or 3457A it won't matter. But when measuring low impedance shunt resistors or when measuring at the edge of what's possible, then even the point of contact of the sense wires will make a difference (there's a minuscule drop across the nut). There's a pamphlet of one of the resistor manufacturers on the 'net describing such. If the driving current would be applied to the inner connectors, then the point of contact of those would matter. I suppose the point of contact of the sense wires is more easily controllable.Quote from: CatalinaWOW on March 16, 2023, 04:34:30 amI suppose the different recommendation refer to the intended application, not measurement procedure. When the resistor is used as a standard then you'd use 4W measurement (for best results). When the resistor however is meant to be used in an assembly with other resistors (e.g. serial-parallel configuration of a voltage divider), then 4W might not be possible (measured resistance won't be matching the actual used one).

author: CatalinaWOW
author_rank: Super Contributor
timestamp: March 18, 2023, 02:07:12 am
content: Quote from: guenthert on March 16, 2023, 06:03:46 pmAfter more thought I do agree with the first comment. The calculated resistance between the two terminals is about .3 milliohms. That resistance combined with the 10 GOhm input impedance of the HP3457 makes the difference about 3 parts in 10^11, unmeasurable, even with instruments much better than mine.I don't understand the recommendation for two wire resistance connections. The resistance between the two center terminals is "known", that is calibrated and verified. The resistance between the outer two terminals is technically unknown. The theoretical difference is far lower than specified tolerance of the resistance, but still, in principal the center two terminals would be more accurate even in two wire connections. The only reason I have been able to come up with is to reduce wear on the center connections, but this seems a labored justification.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: March 18, 2023, 02:21:21 am
content: Data is posted to the xDevs site. I again was unable to use the directions given for web based access, but using an ftp manager was easily able to transfer the data. I used WinSCP under Windows 10, but I am sure that other programs will work as well or better.I have done little deep analysis of the data, but am pleased that it appears that my HP3457 is tracking the FX reference to about 4 parts per million. The agreement on the 10000 ohm reference resistor is not as good, about 12 ppm.The rest of my analysis will take quite a bit longer, and may or may not be published. The quality of my instruments doesn't really add to the knowledge of the traveling standards so there is little urgency to post them.

author: Rax
author_rank: Super Contributor
timestamp: March 18, 2023, 02:29:52 am
content: Quote from: CatalinaWOW on March 18, 2023, 02:21:21 amGood work, CatalinaWOW. I think all this is about empirical accrual of data, so all contributions with associated certainties baselines (meaning that loosely) are instrumental. I'm no bureaucrat of the US CAL CLUB, but I personally appreciate your diligence in generating this data.

author: RoadDog
author_rank: Regular Contributor
timestamp: March 18, 2023, 05:52:22 pm
content: I'd like to be added to the list. Currently just have an HP34401a but I'll be upgrading at some point this year. I'm building some references as well.

author: RandallMcRee
author_rank: Frequent Contributor
timestamp: March 18, 2023, 05:57:21 pm
content: Quote from: RoadDog on March 18, 2023, 05:52:22 pmAdded in post #2. And we are on Rax, at the moment. He will have the kit mailed to him next week, all goes as planned...GWAGAP

author: guenthert
author_rank: Frequent Contributor
timestamp: March 18, 2023, 11:08:06 pm
content: Quote from: CatalinaWOW on March 18, 2023, 02:07:12 amTrue, but L&N gives this as 0.00004 Ohm  (I suppose the variations due to manufacturing of those "horns" are much smaller than the uncertainty of the resistance element).Quote from: CatalinaWOW on March 18, 2023, 02:07:12 amIf the application calls for two wire connection, you will want to make the connections as well as possible. For that historically mercury cups have been used in which the ends of the horns were sunk. I suppose the outer nuts give a smaller difference to the ends then the top ones, but this is just speculation on my part.https://www.surplussales.com/equipment/testequipment/pdf/eqp-ln-4025b-ln-4045b_PDF.pdf

author: RandallMcRee
author_rank: Frequent Contributor
timestamp: March 19, 2023, 03:26:14 pm
content: Quote from: guenthert on March 18, 2023, 11:08:06 pmThat pdf talks about using mercury for better contact. One of our members asked me about the possibility of mercury contamination on the L&N resistor.Let me just say: neither Randall McRee, nor the USA Cal Club generally, guarantee the safety of this equipment. Everything you do is at your own risk. If you have doubts do not ask for or accept the equipment.As one example, leaded solder has been used in the creation of the items in the equipment. There are well-known dangers associated with lead. Again, if you are concerned do not accept the equipment.Regards,Randall

author: CatalinaWOW
author_rank: Super Contributor
timestamp: March 19, 2023, 04:23:11 pm
content: There is some residual cruft on the ends of the resistor. But as long as you don't touch orr abrade it I suspect the danger is immeasurably close to zero. Far less than including fish in your diet.

author: Rax
author_rank: Super Contributor
timestamp: March 19, 2023, 04:24:05 pm
content: Quote from: RandallMcRee on March 19, 2023, 03:26:14 pmI'm one of those with reluctance to work with L&N resistors. Some of you have posted on other threads on this, as have I, and I personally don't feel my doubts and hesitance have been put to rest. Unless new pertinent information surfaces, I think I'll personally skip the L&N resistor.

author: Rax
author_rank: Super Contributor
timestamp: March 19, 2023, 06:07:24 pm
content: Quote from: CatalinaWOW on March 19, 2023, 04:23:11 pmHow do you know this?

author: CatalinaWOW
author_rank: Super Contributor
timestamp: March 19, 2023, 06:51:37 pm
content: Quote from: Rax on March 19, 2023, 06:07:24 pmI don't know this to a certainty. But any mercury on the resistor is a tiny quantity, physically tightly bound, and if the resistor is treated with the care it deserves not subject to being dissolved and transported from its current location. On the other hand, most fish consumed by humans are apex predators and/or bottom feeders. They concentrate any mercury in the environment. Testing of fish shows widespread mercury contamination.And then the really big reason. You eat the fish, transporting any mercury they contain into your body. Unless you touch the ends of the resistor and then lick your fingers before washing them there is virtually no way for any mercury on the resistor to be transported to your body.For those worried about the resistor, I will point out that it is wrapped in a zip lock bag, which is then placed in a second zip lock bag. You don't have to open either bag if the mercury worries you. If you want to make measurements on the resistor you will have to open the bags, but wearing disposable latex or similar gloves would give you another layer of protection.

author: guenthert
author_rank: Frequent Contributor
timestamp: March 19, 2023, 07:13:17 pm
content: Quote from: CatalinaWOW on March 19, 2023, 04:23:11 pmMine came thankfully with rubber sleeves covering the ends (not sure, whether they are there to protect the ends or me). I haven't taken them off and see no reason to do so.

author: Rax
author_rank: Super Contributor
timestamp: March 19, 2023, 09:09:19 pm
content: Quote from: CatalinaWOW on March 19, 2023, 06:51:37 pmWhich is why I'm very carefully choosing the fish I (and my family) are eating, but that this is comparatively relevant is highly speculative and out of topic.Quote from: CatalinaWOW on March 19, 2023, 06:51:37 pmThis has been documented in other threads, but I personally don't regard the protection by your vanilla latex glove (or even lab grade in the hands of scientists) as sufficient (https://en.wikipedia.org/wiki/Karen_Wetterhahn). Admittedly, the case quoted had to do with organic Hg compounds, but what happens with Hg (salts and whatnot) on terminals which have obviously been handled by (organic) hands for decades is not something that I've been able to find studies on. I'm far from being a specialist or even comprehensive reviewer of literature, but I for one wll be making my own decisions about all this.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: March 20, 2023, 02:58:14 am
content: Rax, the point on which we both agree is that you will make your own decision. Yours is undeniably the safer choice. I doubt if either of us can numerically qualify the danger, and it is likely that you have not formally defined an acceptable risk. These are thoughts that each of us should evaluate in choosing any activity.

author: alm
author_rank: Super Contributor
timestamp: March 20, 2023, 08:40:35 am
content: Quote from: Rax on March 19, 2023, 09:09:19 pmDimethylmercury is a well known neurotoxin (under chemists), but by this logic you could also be afraid of toothpaste because fluorine and hydrogen atoms can also be used to makehttps://en.m.wikipedia.org/wiki/Hydrofluoric_acid, which is an extremely potent acid that readily penetrates the skin and requires labs handling it to have a special first aid kit in case an accident happens.Dimethylmecury isdescribedas:QuoteHow long do you think this liquid would remain on the terminals? Have a look at the synthesis section of Wikipedia to see what it takes to make this. The form of mercury you might find infish, on the other hand...You're obviously free to make your own decisions, but please don't exaggerate by suggesting how the terminals are likely to contain something like dimethylmercury.

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: March 20, 2023, 04:30:09 pm
content: FWIW, I've got about 6-8 of the L&N resistors on my bench, from various eras and sources. Not everybody used them with mercury and it's not hard to tell. I do wonder if the cal labs usually did use mercury on any that came in for certs. Some show corrosion of the ends of the terminal bars due to being used with mercury, but it was decades ago and they've been cleaned so many times I figure any mercury is long combined or removed. In any case, I don't eat off them and it's a location one doesn't routinely touch in use. If you're really worried it might be useful to rub the area with powdered sulphur, which binds with any mercury, making it easier to remove. My guess is there's no metallic mercury present by now. Some of these resistors are quite old and were standardized before the major change in the value of the ohm. I think those will be high by about 0.05 ohms per 100 ohms. I had a lab tell me my resistor was defective because they couldn't grasp that the definition had changed, not the resistor!

author: bdunham7
author_rank: Super Contributor
timestamp: March 20, 2023, 05:07:32 pm
content: Quote from: Conrad Hoffman on March 20, 2023, 04:30:09 pmSo what exactly is the compostion of those horns then? Assuming it is copper on the inside, what are the outer layer(s) that give it a silver metallic appearance?

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: March 20, 2023, 06:36:48 pm
content: The horns are almost certainly copper but I've no idea what they're plated with. Nickel or chrome seem the likely candidates, with nickel being more likely. Actually, chrome is almost always done over nickel. Not sure they took thermocouple effects into account back then. Reading the instruction sheet, it sounds like the mercury was applied to the end surface of the horns, then they were placed in mercury cups for connection. That would make a certain amount of sense and it would let you sand the surface easily to clean it. The wetting process did sound a bit nasty.

author: Rax
author_rank: Super Contributor
timestamp: March 21, 2023, 04:47:55 am
content: Well, I think it's good we've shuffled and discussed a range of thoughts and positions, from the most paranoid (yours truly - I knew I had this!!) to the relaxed end. I only brought it here because Randall asked me, but again, I think it's best to have the information at the surface so everyone has more to work with in order to make their mind about how they want to proceed.In any case, I am currently looking forward to receiving the package (literally in transit). My meters are turned on (well... never shut down), elbow grease applied, etc etc. Excited!

author: rhb
author_rank: Super Contributor
timestamp: March 21, 2023, 06:45:29 pm
content: When I was in grade school, a filling was always accompanied by a pea size drop of mercury if you asked. I've never been concerned. I *always* wash my hands before I handle food or eat. I'll be 70 in May.Mercury poisoning is very serious, but unless you're making hats the old fashioned way it will require considerably more effort tan fooling around with resistance standards.RegBTW Please add me to the tail end of the list. It will take a while to get ready, but I've got a set of standards. Mostly L&N, but also another maker whom I can't recall without digging them out.

author: Rax
author_rank: Super Contributor
timestamp: March 23, 2023, 04:54:58 am
content: The bird has landed!Not much time for much else tonight - XL day at work - and no real guarantees the goods have yet acclimated to my bench, but I thought I'd have a preliminary go at Randall's "standard resistors switcheroo"This is at 67F (the goods have been in the mancave/garage for about 4h before this, so WTW). The instrument doing the measurements is an 8502A, recent Z540-1. I have not tried to mitigate the readings to account for what my deviations from nominal would be per the Z540-1 "as found" readings.10ohms - 10.00334ohms20ohms - 20.00072ohms100ohms - 100.0000ohms200ohms - 200.0066ohms1k - .999983kohms2k - 1.999895kohms10k - 10.00024kohms20k - 19.99908kohms100k - 100.0002kohms190k - 190.0042kohms1M - 1.000131MohmsI have not tried to curate these in any way, they're fresh off the press. I did a quick zero of the 8502A, with the rig's switch on short.

author: Rax
author_rank: Super Contributor
timestamp: March 24, 2023, 01:22:28 pm
content: What have you folks been using for the GPIB adapter? In terms of software on the computer?I would use this with a Fluke 8502A, but plenty other instruments at my bench with GPIB.

author: guenthert
author_rank: Frequent Contributor
timestamp: March 24, 2023, 04:00:17 pm
content: Quote from: Rax on March 24, 2023, 01:22:28 pmLeast trouble for me was a PCI adaptor from CEC (I also have one from NI, but that one optionally offers high speed GPIB which seems to cause some confusion with older gear even though it shouldn't). Alas, I don't have currently a PC with PCI slots close to my measurement gear, so I use an Agilent 82357B (or clone thereof, I can't tell). Occasionally I have to do the rmmod/modprobe USB unplug/plug-in dance, but once working, it continues to work until reboot/power-loss.

author: rhb
author_rank: Super Contributor
timestamp: March 24, 2023, 04:32:18 pm
content: Check out @WaveyDipole's AR488. You can daisy chain up to 10 devices for under $60 and access via USB. @artag designed an Arduino shield which takes care of the wiring so all you need to do is space IDC connectors at the right spacing on the ribbon cable.https://github.com/Twilight-Logic/AR488There's a long thread on EEVbloghttps://www.eevblog.com/forum/projects/ar488-arduino-based-gpib-adapter/@artag's board can be found here.ttps://oshpark.com/profiles/artagI downloaded the files and got 5 for $10 from JLCPCB.BoM for a 2 port unit is under $15. I estimate that ribbon cable and IDC connectors are ~$5 per port. The ribbon cable works best using one AR488 per stack of instrumentsAR488 is pure OSSW/OSHW, so every time I see people buying the counterfeit HPAK devices on ebay I'm always puzzled.Have Fun!Reg

author: Rax
author_rank: Super Contributor
timestamp: March 24, 2023, 05:35:09 pm
content: Thank you both, but I was really hoping for more of a quick guide or pointers on this device specifically. This has been in enough hands that I'm hoping a quick start guide has been figured and possibly exchanged. Please keep in mind I only have this for two weeks tops, so a BOM and boards is not what I'm looking for.I actually have all I need for a whole "GPIB to USB" kit with enclosure, parts, everything, I just never found the time to put it together. And given this kit comes with an assembled interface, it'd be particularly misguided to try doing that now.

author: Rax
author_rank: Super Contributor
timestamp: March 24, 2023, 06:29:55 pm
content: On further reporting, the FX seems to be doing very well. I will put more info on the uploads, but this is fed by an HP 6236B, and is hooked with all copper on copper connections, including Adrian B's shielded low-emf banana cable on the hookup to the meter. On a point of wider interest on this - it seems the banana connector on the FX ref has been replaced with a "spade only" connector, which is not represented in the instructions or anywhere else I can tell. In my case, I have no spade connecting provisions, so I improvised with lo-emf bridges from my meters and a couple of quality female banana connectors I have here. Will enclose pictures later.It started a bit high from dead cold - my meter, per its "as found" Z540-1 data, sees 10.00010V for 10V on the dot. The FX started at about 10.00011V in slight fluctuation with 10.00012V, and within an hour or a maybe bit more, has stabilized to a bit "better" than expected 10.0009V. Per my math, due to the above data, the meter should see 10.00006V for the characterized 9.99996194V (per label on FX). It's currently "rock solid stabilized" at 10.00009V, so a bit closer to 10.00000V than what's stickered on the unit, as far as I can tell.Any flaws with my math?

author: bdunham7
author_rank: Super Contributor
timestamp: March 24, 2023, 10:11:30 pm
content: I don't know if this has been discussed already in great detail (it probably has) but does anyone have a good calculation of the total uncertainty of the FX 10V reference? Is it quasi-traceable in a manner that we all can look at?

author: CatalinaWOW
author_rank: Super Contributor
timestamp: March 24, 2023, 10:47:50 pm
content: There is some discussion on TiNs website of the traceability flow for the PX reference.https://xdevs.com/article/usac_2023/I am not skilled enough to evaluate the degree of traceability this gives. Still trying to wrap my head around it all.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: March 24, 2023, 10:58:33 pm
content: In my first bit of analysis of my data, I notice in my first test run that there was a substantial settling in period for the PX reference. The data is in my folder on the xdev site (USA_Cal_Club_Round3_Test 1.Txt). This was not unexpected since the unit was still quite cold from winter shipping and had just been powered on. I have no meaningful way to estimate the initial temperature of the reference, at best I could have measured the surface temperature. It was cold to the touch, outdoor outdoor temperatures were around freezing and the box was delivered in a mail truck driven with doors and windows open (tough mailmen in our neck of the woods).I went ahead and evaluated the time constant for the stabilization. Though there is not enough data to separate temperature stabilization and power on stabilization at least it gives a figure to use in planning your tests. I came up with a best fit time constant of about 76 minutes. The second digit on that estimate is misleading, the error bars are at least several seconds.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: March 24, 2023, 11:07:51 pm
content: Quote from: Rax on March 24, 2023, 01:22:28 pmI use a NI adapter (possibly a clone) with EZGPIB (under Windows) as the software platform. EZGPIB is free and fairly easy to find. Unfortunately the developer passed some years ago, and there are barriers to anyone else taking it over, so the present (very usable) state is the way it will be forever. If you look through the threads for the first two rounds of the club there are references to other software platforms and at least fragments of Python code to do the job. If you look in the Metrology section there is reference to a program that "Can log data from many kinds of voltmeters." that may be of interest to you.

author: Rax
author_rank: Super Contributor
timestamp: March 25, 2023, 12:39:30 am
content: Further reporting (now on to the PX).But before that, I probably need to clarify that my 8502A has had this Z540-1 I've been talking about done roughly a month and a half ago, so its cal is as fresh as they come.At 22.5C (starting from dead cold) my meter says 7.04574V. About 2.5hrs later, my meter thinks 7.04572V. So the PX is just as solid as a thick brick wall. This is with an HP 3610A dialed in very close to 15V.The Vout value on the unit is listed at 7.0456V.

author: bdunham7
author_rank: Super Contributor
timestamp: March 25, 2023, 12:52:51 am
content: What does the 8502A read if you manually select the 10V range, put a short on the input and let it sit for an hour?

author: Rax
author_rank: Super Contributor
timestamp: March 25, 2023, 01:21:27 am
content: Quote from: bdunham7 on March 25, 2023, 12:52:51 amWithout performing the zeroing procedure, in all scales I'm seeing a perfect zero across the board, except for some occasional 1s in the last digit on the 1V scale, I think.

author: Rax
author_rank: Super Contributor
timestamp: March 30, 2023, 03:08:59 am
content: At Randall's recommendation, I've been keeping track of both the DP8200 and the FX at different temperature points. As expected, the 8200 exhibits more delta, but frankly, less so than I expected. Will plot this out later.I'd welcome some other ideas as to what I could use the time with the standards for. I'm not really able to automate logging data (my GPIB success seems to be somewhere in my future), so all of this is very analog (paper and pen). But overall it seems both my calibrated meter and the standards are extremely stable (well, duh...) and so I feel I'm a bit running out of things to log, measure, submit.I am eager to be a useful contributor so please assist with suggestions. I got about a week allocation left, so I'm hopeful to make the best of it. .

author: SilverSolder
author_rank: Super Contributor
timestamp: March 30, 2023, 04:03:03 pm
content: Re GPIB, I have found the National Instruments GPIB-232CT-A Serial to GPIB box to be a very easy device to get along with for logging data and/or controlling instruments.What I like about it:* Often found on eBay for a good price.* Old school build quality is excellent - steel box with solid connectors that can definitely take a beating.* Compact, easy to hide away.* Easy to connect to a serial port, or you can use a USB to Serial adapter if your PC doesn't have one.* No drivers needed. Just plug it in, and you're good to go.* The high-level commands are simple, you can write VBA commands in Excel for data logging or use a terminal program, the box manages the GPIB .* Compatibility is top-notch. I've used it with a bunch of vintage HP and Fluke gear without any hiccups.* Comes with old school documentation of all functions, features, and commands.The only thing that could be seen as a downside is the speed of the serial connection, but I haven't had any issues with it. The simplicity and the freedom from dealing with bulky drivers or specialized software has made this device a game-changer for me. Well worth a look if you want something that "just works" without having to attain a degree in computer science to get it up and running!

author: RandallMcRee
author_rank: Frequent Contributor
timestamp: May 08, 2023, 11:26:50 pm
content: Although I have not received the kit back from the last user (was out of order) I am expecting to be ready to send on to rockstedy40 in another week or so.Please remember (admonish yourself) to update this thread with any results, etc.Thanks,Randall

author: Rax
author_rank: Super Contributor
timestamp: May 16, 2023, 01:14:01 am
content: Quote from: RandallMcRee on May 08, 2023, 11:26:50 pmAdmonished! There's a good amount of data I am still struggling to cleanup and log, but among the outstanding results I've seen is the agreement between the Prema 6048 and the FX. I've seen them further away from each other than this, but I was at the time still learning how to do a proper zeroing of the Prema (I had it for a minute before I had to send the FX away), so the below is probably as close to the truth as my bench and skill allowed during my custody.What is this... .4ppm off? I know we're getting into gambling territory, but it's still really nice to see such agreement between references.

author: SilverSolder
author_rank: Super Contributor
timestamp: June 23, 2023, 11:13:19 pm
content: I'm delving deep into all the goodies in the USA Cal Club Kit!Currently running a test with the FX reference. The laptop in the foreground does two things:1) Runs and logs the kit temperature/humidity tracking Arduino, using Tera Term for this, which supports logging with timestamps out of the box.2) Runs a little home brewed Delphi program that sets up the four DMMs, then goes in a loop triggering them concurrently and fetching their measurements (via GPIB) and logs the results to a file.Since my DMMs are not really capable of measuring up to the level of quality of the supplied equipment, I am doing it "the other way round", i.e. the objective of the test is to characterize the four DMMs by measuring as close as possible the same input at the same time in the same environment, over an extended time period. For each trigger, all four DMMs take 8,192 samples in 34.1 seconds and averages them, which is the number that is logged. The two units on the right were DIY calibrated three years ago, using a battery powered reference from VoltageStandard.com, while the two on the left have had parts swapped and were not calibrated afterwards.I want to thank all those who have contributed to putting this kit together, it is nothing short of amazing to have access to this level of quality references in a home lab setting!

author: jjoonathan
author_rank: Frequent Contributor
timestamp: July 08, 2023, 04:17:33 pm
content: The kit has arrived in North Carolina and I'm logging away!One of the banana jacks had a strain relief fatality. The connection is redundant so it isn't an immediate problem, but since I am not very far down the volt nut rabbit hole I thought I'd check in before trying to fix it. Can I just strip back the wire, trim its partner to match, and re-seat the terminals? If I need to apply special anti-corrosion schmoo or perform ppm-preserving ritualsI want to make sure to do it right.

author: Rax
author_rank: Super Contributor
timestamp: July 08, 2023, 04:21:21 pm
content: Quote from: jjoonathan on July 08, 2023, 04:17:33 pmNice working space, BTW. Have fun with the kit!

author: RandallMcRee
author_rank: Frequent Contributor
timestamp: July 08, 2023, 06:44:21 pm
content: Quote from: jjoonathan on July 08, 2023, 04:17:33 pmFatigue on the banana jacks? Not surprising!Any voodoo is in the *lack* of voodoo. That is to say, as far as I know, we just rely on the cable being pure copper and the jack being gold-plated along with some good mechanical connection. So, yes, go ahead and fix as you proposed. You do not need to apply any de-oxit/cramolin so long as you do not smear the cable with your hair grease!(That was a joke)Thanks,Randall

author: SilverSolder
author_rank: Super Contributor
timestamp: July 09, 2023, 12:08:29 am
content: I've gotten to the point of looking at the data from the experiment.This being 2023, I asked ChatGPT for some ideas on how to analyze the numbers - here's what GPT-4 suggests:Analyzing your data can be done in several ways. For multi-dimensional data, you can use a pairplot or scatterplot matrix, which will give you a two-dimensional scatterplot for each pair of your four variables (voltmeters). This way, you can visualize any pairwise relationships in your data.Here are some techniques you could use:1. Pairplot or Scatterplot Matrix: This is a great way to visualize multidimensional data. Each scatterplot in the matrix represents the relationship between two of your variables, and the diagonal of the matrix often contains histograms or density plots of each variable. In Python, you can easily create this kind of plot using the seaborn library's pairplot function.2. Correlation Matrix: A correlation matrix would show how correlated each pair of variables is. This would be a way to quantify the relationship that you see in the scatterplot matrix. Correlation values range from -1 (perfect negative correlation) to 1 (perfect positive correlation), with 0 indicating no correlation.3. Time-Series Plots: You can create separate time-series plots for each of the DMMs. Plotting the readings over time would help identify any drift or other time-related patterns in the readings.4. Box Plots: These can provide a summary of the central tendency, dispersion and skewness in your data, and can also help to identify outliers.5. Histograms and Density Plots: These could be useful to visualize the distribution of the readings from each DMM.6. Statistical Tests: Depending on your goals, there are a variety of statistical tests you could use to compare the measurements from the different DMMs. For example, a paired t-test or a one-way ANOVA could be used to test if there is a statistically significant difference in the means of the measurements from the different DMMs.7. Regression Analysis: If you logged the temperature and humidity, you could also perform a multivariate regression analysis to see how these factors relate to the measurements from the DMMs.8. Allan Deviation: As discussed earlier, Allan deviation could be used to assess the stability of the DMMs over time.Remember that visualizations can often help to reveal patterns or relationships in your data that aren't immediately obvious from the raw numbers, so it's a good idea to try several different kinds of plots and analyses. Once you have a sense of what's going on in your data, you can then use more focused statistical tests or models to quantify those patterns or test specific hypotheses.So the question is - how good of an engineer is ChatGPT? Is there a better way to do this?

author: rhb
author_rank: Super Contributor
timestamp: July 09, 2023, 01:42:05 pm
content: QuoteAll of those are sound basic tests. I did this in the context of running an "orphan home for lost problems" at large oil companies including super-majors. Those are all basic, *essential* things to be done *before* you proceed with more detailed and focused methods. In my case, those were design and write the code, apply it to the data and then proceed to the next such step in the process. The suggestions are all part of the "exploratory data analysis phase" that should be applied to *all* data as the first step.ChatGPT makes up data, so it's not reliable as a lawyer recently discovered. He asked for some additional citations which he included in his brief. He got a stern rebuke when the judge discovered the citations were fabricated by chatGPT.Gnuplot is the best tool for doing this. I don't think it does Alan deviation or ANOVA, but the Marquard-Levinburg implementation is the best L2 solver I've used.Have Fun!Reg

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: July 09, 2023, 03:57:58 pm
content: I wouldn't trust ChatGPT as far as I could throw it. OTOH, Gnuplot is great, though it has a significant learning curve to take full advantage of it. I don't use it often enough to be really good, but it will do things that are clumsy or near impossible in Excel. An old program that I loved was Javelin. It was designed for time-based data, which is just what you need for keeping track of standards over time. It would probably still run in one of the emulators, but I don't even have a drive for the disks and I think its time has passed. I think that's what I used for several years worth of data when I did the Mini-Metrology stuff.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: July 09, 2023, 04:12:11 pm
content: I think ChatGPT is much like the internet in general. A great resource for finding new ideas and information. But never trusted and the results never used without auditing and reality checks.

author: mycroft
author_rank: Regular Contributor
timestamp: July 09, 2023, 09:38:22 pm
content: I found NIST's Engineering Statistics Handbook athttp://www.itl.nist.gov/div898/handbook/index.htman interesting resource.

author: SilverSolder
author_rank: Super Contributor
timestamp: July 10, 2023, 10:42:32 pm
content: Perhaps a reasonable approach is to do the first cut in Excel, to get an idea of what's going on, and decide on more advanced methods depending on what turns up?

author: alm
author_rank: Super Contributor
timestamp: July 11, 2023, 06:56:24 am
content: I'd use whatever tool you feel most comfortable with. Excel should be totally sufficient. Excel becomes annoying once things become complicated because formulas are hidden across multiple columns and worksheets, and it's also not very convenient if you want to run the same analysis on multiple sets of data unless you want to go into macros.

author: jjoonathan
author_rank: Frequent Contributor
timestamp: July 11, 2023, 11:29:42 pm
content: Yep, the tool you know has a big advantage over the tool you have to learn!I have some preliminary results. Just the voltage measurements so far; resistances are WIP. If I assume FX is ideal, it looks like the DMM is just outside its 24 hour spec but still within the 90 day spec -- which is just dandy given that it's been 5 years and a disassembly between then and now. I don't see a tolerance band forthaton the datasheetSomething is a bit funky with the PX measurements -- it seems to have 10ppm periodic negative excursions. I'm looking into it, so far I've ruled out autozero and a lack of cable twist but I haven't done a proper job of RF isolation yet. I may be biased, but that's my chief suspect atm, speculation about other possibilities is welcome and appreciatedEDIT: see post below for final results

author: Andreas
author_rank: Super Contributor
timestamp: July 12, 2023, 06:57:27 am
content: Hmm,looks like EMI.check WIFI (in one case it was my printer although I never use it)check mobilescheck USB cables near the setup (in my case it was all 15 seconds from a unused USB RS232 interface plugged in the computer).https://www.eevblog.com/forum/metrology/lowest-drift-lowest-noise-voltage-reference/msg3738565/#msg3738565with best regardsAndreas

author: jjoonathan
author_rank: Frequent Contributor
timestamp: July 13, 2023, 01:24:54 am
content: Yep, sure enough! You can spot the exact moment I closed the shield box, lol.

author: SilverSolder
author_rank: Super Contributor
timestamp: July 18, 2023, 07:55:26 pm
content: I ended up with a zen 'Keep It Simple' approach, doing the analysis using Access and Excel to put the different data series together.The meters need calibration, but their performance in terms of drift doesn't seem too bad.

author: jjoonathan
author_rank: Frequent Contributor
timestamp: July 27, 2023, 12:40:55 am
content: Ok! I've taken all the measurements I plan to take, uploaded the data + plots togithub, and the kit is on its way back to Randall.FXPXRI repaired the FX banana connector and added some strain relief. It turns out that the heat-shrink was just the right diameter for a good press-fit with the plastic housing, so it now has that going for it! See attached.My measurements of the xDevs 10k standard were anomalously low compared to my other resistance measurements (even the other 10ks) and the xdevs measurement. I repeated this on different days and with different 4-wire attachment styles, so I don't think that's the problem. I look forward to seeing what the next person measures

author: SilverSolder
author_rank: Super Contributor
timestamp: August 04, 2023, 01:48:13 pm
content: So, I decided to have a go at using AI to analyze the test data. I used the "GPT-4 Code Interpreter" model from OpenAI (which is able to create and use Python programs on the fly to help analyze and plot data). I uploaded a CSV file with the measurements, and asked the AI to walk me through an analysis of the data.It would be too much to include all the details and plots that were generated, suffice it to say, the results were nothing short of astounding... Jaw dropping.Here's a summary of what was done:SilverSolder (speaking to GPT-4): Can you summarize the analysis we have done on this dataset so far?GPT-4: Below is a summary report of the analysis we performed so far on the dataset containing the measurements from four Digital Multimeters (DMMs).1. Data Preparation and FilteringAction: Removed extraneous rows and outliers, focusing on stable measurements.Interpretation: Ensured clean and consistent data for analysis, allowing for accurate assessments of stability, accuracy, and consistency.2. Allan Deviation AnalysisAction: Calculated overlapping Allan deviation to assess stability across different time scales.Interpretation: Observed U-shaped curves, indicating white noise at short averaging times, optimal stability at the bottom of the U, and potential drift or bias instability at longer times. This information is crucial for understanding the noise characteristics of the DMMs.3. Drift AnalysisAction: Calculated the slope of the drift in voltage measurements for each DMM, expressed in ppm/h.Interpretation: Identified slight downward drift in all DMMs, highlighting potential long-term instability or bias that could affect measurement accuracy over extended periods.4. Frequency Domain AnalysisAction: Performed Fourier Transform to identify frequency components.Interpretation: No dominant frequency components observed, and noise level below 10^{-4}, indicating stable and noise-free measurements. This analysis further affirmed the quality of the DMMs.5. Comparative StatisticsAction: Calculated mean, standard deviation, variance, etc., for each DMM.Interpretation: DMM1 showed the highest consistency; slight differences in mean values across DMMs. These statistics offered a quick overview of the performance characteristics of each DMM.6. Bland-Altman PlotAction: Plotted differences vs. averages to assess agreement between DMM pairs.Interpretation: Provided insights into biases, limits of agreement, and systematic differences between DMMs. This analysis was valuable in understanding how the DMMs compared to one another and identifying any consistent biases.7. Cross-Correlation AnalysisAction: Calculated cross-correlation to study time-lagged relationships between the DMMs.Interpretation: Peak at zero lag indicated synchronization; falling off and rising again reflected complex relationships, possibly due to noise or cyclic variations. This revealed intricate dynamics and relationships between the signals across different time-lags.ConclusionThe comprehensive analysis provided insights into the stability, accuracy, and consistency of the measurements across the four DMMs. Key findings include stable performance with slight downward drift, high consistency in DMM1, and complex time-lagged relationships between DMM pairs.The methodologies applied, including Allan deviation, frequency analysis, Bland-Altman plots, and cross-correlation, allowed for a multifaceted exploration of the data. The findings can inform calibration practices, quality control, instrument selection, and further investigations into underlying factors affecting the measurements.The insights gathered from this analysis can be vital for professionals working with precise measurements, ensuring that the instruments used are reliable and accurate.

author: SilverSolder
author_rank: Super Contributor
timestamp: August 04, 2023, 03:10:10 pm
content: Here is an AI analysis of the DMMs' sensitivity to temperature and humidity. It seems that most of the drift can be explained by these factors, not surprisingly.Graph and regression analysis done by GPT-4 Code Interpreter:Summary of regression analysis:All DMMs exhibit a strong relationship with humidity, with varying degrees of influence.The relationship with temperature is more varied, with some DMMs showing a significant effect and others not.The models explain a substantial portion of the variance in voltage readings, especially for DMM2 and DMM3.

author: mendip_discovery
author_rank: Super Contributor
timestamp: August 04, 2023, 08:01:13 pm
content: That is interesting as spec sheets rarly show much in the way of issues around RH unless it's at the extremes.The lab I work in we monitor and record humidity and I try to keep it at a sensible level though it's never been an issue with the assessors.

author: maxwell3e10
author_rank: Frequent Contributor
timestamp: August 04, 2023, 10:08:00 pm
content: It would be interesting to see raw data that you used for ChatGPT analysis. Correlation analysis is always tricky. The plot you posted above doesn't show humidity variation.

author: SilverSolder
author_rank: Super Contributor
timestamp: August 04, 2023, 11:19:29 pm
content: Quote from: maxwell3e10 on August 04, 2023, 10:08:00 pmSure, attached here!Of course, it could all be coincidence... correlation != causation, as we all know.Here's a couple of example of graphs from the AI:

author: maxwell3e10
author_rank: Frequent Contributor
timestamp: August 05, 2023, 02:26:02 am
content: It seems humidity change is mostly monotonic, so it looks correlated with any drift in DMM signals.

author: Andreas
author_rank: Super Contributor
timestamp: August 05, 2023, 04:34:27 am
content: Hello,humidity (%rH) depends also on temperature.And since humidity changes usually need about 1 week settling time to do component changes (by swelling of the epoxy PCB or component packages) the correlation is clearly temperature instead of humidity.And there is still drift over time and self heating of the instrument.with best regardsAndreas

author: mendip_discovery
author_rank: Super Contributor
timestamp: August 05, 2023, 10:51:06 am
content: Quote from: Andreas on August 05, 2023, 04:34:27 amMy thought is that the kit is getting humidity issues in transport and the powering on for tests is releasing that moisture but with the ambient %RH having an effect on how well the moisture evaporates.

author: SilverSolder
author_rank: Super Contributor
timestamp: August 06, 2023, 12:46:52 am
content: Quote from: Andreas on August 05, 2023, 04:34:27 amWhy would that not show up in the correlation analysis?

author: SilverSolder
author_rank: Super Contributor
timestamp: August 06, 2023, 01:04:26 am
content: Quote from: mendip_discovery on August 05, 2023, 10:51:06 amThe DMMs had also been turned off for several months before this test, it seems reasonable to suppose that they were "letting off steam" as well.Interesting phenomenon, for sure!

author: Andreas
author_rank: Super Contributor
timestamp: August 06, 2023, 05:13:20 am
content: Quote from: SilverSolder on August 06, 2023, 12:46:52 amHello,You would need to PT1-filter the rH% by a time constant of several days to see any correlation.The measurement "over night" is simply too short for that.with best regardsAndreas

author: SilverSolder
author_rank: Super Contributor
timestamp: August 06, 2023, 09:39:24 pm
content: Quote from: Andreas on August 06, 2023, 05:13:20 amMathematically, there clearly is a correlation, though? On four different DMMs measuring at the same time, in parallel? I'm not sure what you mean... are you saying the correlation that is visible is just a mathematical artifact and should be discounted?

author: RandallMcRee
author_rank: Frequent Contributor
timestamp: August 07, 2023, 08:06:27 pm
content: Round 3 members,The person scheduled for the kit is not able to take it, for personal reasons.Does anyone currently waiting want to go next?Please PM me.Thanks,Randall

author: alm
author_rank: Super Contributor
timestamp: August 07, 2023, 08:41:49 pm
content: Quote from: SilverSolder on August 06, 2023, 09:39:24 pmI think temperature is a confounding factor here. The measurement depends on temperature, and relative humidity depends on temperature (even if the amount of moisture in the air remains the same), so the measurement could also be modeled as a function of humidity, using humidity as proxy for temperature. I'd think that if you were doing a regression analysis, then using temperature with multiple lag values would explain the variance just as well as humidity. It is likely to me that there are different time constants at play for temperature: connectors, DUT and different parts of the meters won't all react to temperature changes equally fast.

author: SilverSolder
author_rank: Super Contributor
timestamp: August 08, 2023, 02:04:34 pm
content: Quote from: alm on August 07, 2023, 08:41:49 pmInteresting thought, that could well be true. It doesn't seem intuitively right that things should be this sensitive to RH...For the next cal club round, I will run the same experiment for a much longer time period and hopefully shed some light on the matter!

author: CatalinaWOW
author_rank: Super Contributor
timestamp: August 08, 2023, 06:20:28 pm
content: Quote from: SilverSolder on August 08, 2023, 02:04:34 pmIf you are interested in humidity effects you might want to create your own reference (there are several threads on the subject) and conduct your experiments using that. Even without tracing your reference to a standard it can be used to evaluate variation. And the answer will come much more quickly. The cycle time of the club reference is measured in years.

author: dmmguy
author_rank: Contributor
timestamp: August 26, 2023, 07:01:52 pm
content: Hello everyone,Does this club also include Canada?Can you send the kit to Canada?Thanks

author: RandallMcRee
author_rank: Frequent Contributor
timestamp: August 28, 2023, 05:53:56 pm
content: Quote from: dmmguy on August 26, 2023, 07:01:52 pmUnfortunately, going outside the United States entails extra costs and custom forms. We have decided not to do so, at least on this round.

author: RandallMcRee
author_rank: Frequent Contributor
timestamp: September 01, 2023, 06:13:10 pm
content: Hello all,Unfortunately, the unthinkable has happened!The FX reference sustained some damage.Although minor, the fix requires de-certification. Therefore, it will be a month or so whilst Illya graciously performs surgery and re-certifies.Thanks Illya (bow)RandallYour bearer of bad news!

author: rsjsouza
author_rank: Super Contributor
timestamp: September 02, 2023, 12:55:32 am
content: Well, I am the idiot that broke one of the knobs of the voltage reference. For that, I am very sorry for Randall, Illya and the rest of the cal club for the delay.Randall asked me to provide a summary of "not what to do". I can tell that one should never work with such delicate instruments when one is sleep deprived and with the judgment impaired. I was fixing a bad connection and exerted pressure beyond reasonable on the knob. What was supposed to be a relaxing activity after a long day turned out to be a nightmare.Again, please apologize for the delays and the mess.

author: SilverSolder
author_rank: Super Contributor
timestamp: September 03, 2023, 11:30:07 am
content: Don't feel bad, you have a great future in the QA department!

author: dmmguy
author_rank: Contributor
timestamp: September 11, 2023, 01:18:21 pm
content: Hi, thank you for you answer.

author: RandallMcRee
author_rank: Frequent Contributor
timestamp: October 05, 2023, 11:20:16 pm
content: Quote from: RandallMcRee on September 01, 2023, 06:13:10 pmSome updates on the FX reference. Also Ilya has characterized the 1k/10k and PX reference for our future reference.

author: rhb
author_rank: Super Contributor
timestamp: October 06, 2023, 08:56:21 pm
content: FWIW the transfer of heat from the device to the atmosphere depends upon the specific heat of the air which is a function of water vapor, barometric pressure and temperature. Backing out correlated noise is easy.Reg

author: alm
author_rank: Super Contributor
timestamp: October 06, 2023, 09:04:35 pm
content: Quote from: rhb on October 06, 2023, 08:56:21 pmWhat role do you think heat transfer plays in this data? I'd argue if it plays any role at all, the temperature sweep is too fast, and I trust the sweep to have been done sufficiently slowly so the system is very close to steady state at any point.

author: RandallMcRee
author_rank: Frequent Contributor
timestamp: December 03, 2023, 08:47:44 pm
content: FX reference is back in play...we apologize for the delay.Sending on to bdunham7 soonish.Thanks,Randall

author: bdunham7
author_rank: Super Contributor
timestamp: December 08, 2023, 09:12:05 pm
content: FX received in good shape. First step is to make sure everything sort of works. Here's the first hour of logging on a Fluke 8846A. I guess it's at least nominally functional.

author: RandallMcRee
author_rank: Frequent Contributor
timestamp: December 09, 2023, 12:50:34 am
content: How long was your 8846A on before starting the run? Was the temperature constant?It kinda, sorta, looks like things started to stabilize in the last quarter of that run. The FX itself should not be making "popcorn" jumps.Thanks,Randall

author: bdunham7
author_rank: Super Contributor
timestamp: December 09, 2023, 01:10:46 am
content: Quote from: RandallMcRee on December 09, 2023, 12:50:34 amThe 8846A was warmed up and stable, the FX was fresh out of the box. I didn't have a temperature sensor on it yet, so it may have been quite a few degrees cooler than ambient. Ambient was 23 +/-2C. I probably didn't have the best test lead setup, I'm not obsessing over that yet because I don't have any 8.5-digit meters and 0.2ppm of deviation is just the noise level. I'm running a (hopefully) 24 hour log of two meters plus the temperature of the FX case. So far so good--here's four hours. The FX and 8846A are warmed up and stable, the 34401A had only been on for a half hour beforehand.

author: bdunham7
author_rank: Super Contributor
timestamp: December 09, 2023, 09:22:57 pm
content: OK, the first step is getting some idea of how well I'm going to be able to measure and compare things on my home bench using the FX. I ran the FX against the two meters for 24 hours and you can see the HVAC cycling at night, the house cooling off and warming up, some doors getting opened up. Our housecleaner came this morning and I had to transfer a sick cat to this room as well. So nothing was ideal, but it never is, right? So I'm going to conclude that this is about as good as it is going to get with what I have.

author: bdunham7
author_rank: Super Contributor
timestamp: December 09, 2023, 11:15:04 pm
content: One of the ways to use the FX would be to use the DC Ratio function of the meter with the FX as the reference, then some math as needed to correct for the difference between the FX voltage and the nominal 10V. This can be a first-order approximation of just adding in 3.6ppm since the difference is so small here. However, these meters are both close enough that I'm not entirely sure that this method wil be an improvement.I replotted this using the specified tolerances of the meters as the bounds of the chart. It is29ppm24ppm + 5 counts for the 8846A @ k=2.58, 35ppm + 5 counts for the 34401A @ k=2. The yellow line is the nominal voltage of the FX. It seems clear that both meters are performing much better than expected. The 34401A is about 25 years old and still has a calibration count of 35 (no changes). The 8846A is esssentially new.

author: bdunham7
author_rank: Super Contributor
timestamp: December 10, 2023, 11:20:32 pm
content: Here is an example using the FX reference and the ratio function of the 34401A to track the tempco of a Fluke 731B 10V reference. I knew the tempco wasn't great on this unit, I had roughly estimated it to be 1.5 ppm/F (ambient) from previous usage and testing. The line, which I just drew manually, represents -2.5ppm/C. Note that here I'm measuring the temp of the internal case around the ref amp and precision resistors rather then ambient. I'm using a K-type bead thermocouple with Kapton tape to hold it to the case, reading with a Fluke 289. This leads to some interesting issues that anyone mixing temperature into their logging needs to account for--look at the the graph and see if you can spot the anomaly.Anyway, given the outstanding performance of the two meters in question there isn't too much improvement to be had, but there is a little. You can see the 34401A very closely tracking the 8846A with a delta of between 4 and 5ppm, which would be approximately the sum of the nominal difference (from 10V) of the FX reference plus the previously measured error of the 8846A (about 0.7ppm). If I had a worse meter with a DC ratio function I'd use that for an example, but I haven't characterized my two monsters, the 8505A and 8506A, quite yet. And I'm not even sure they're "worse".

author: bdunham7
author_rank: Super Contributor
timestamp: December 12, 2023, 10:33:36 pm
content: To continue some hopefully helpful experiments on what uses the FX can be put to for those of us of normal means, I've done a plot of a VREF10 reference (from Doug @ voltagestandard.com) using the 34401A with the FX as the ratio reference. I present the chart and the scatter plot without any commentary or conclusions and I invite any readers to comment on what they see. This is the latest version of the VREF10 which is enclosed and is specified to 10ppm for 8 months. The temperature readings were taken by the internal sensor of the F289, not an external thermocouple.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: December 12, 2023, 11:50:12 pm
content: The nice thing about digital filtering is that it is possible to implement zero lag filters as long as you don't need the first group of samples (the group of the same length as your filter). I would suggest a simple boxcar average of the half dozen or dozen samples prior to and after your reference time point to reduce the high frequency noise from the ratio data. That should make the correlation with temperature much clearer. Then you can assume that TINs measurements of the reference dependence on temperature are more accurate than any other contributors in the system and factor that out.You will be left guessing whether it is your instrument or your local reference that is varying with temperature, but there are a couple of ways to tease that out.All of this is made more complicated because there are so many questions in the thermometry. Does the value at the temperature sensor represent the actual temperature at the references or the instrument? What are the thermal time constants of the instrument, references and sensor?

author: bdunham7
author_rank: Super Contributor
timestamp: December 13, 2023, 01:11:16 am
content: One of the more general things I'd like to determine and show is what the practical limits of accuracy are for someone like me in an average home lab. My room is pretty good but not perfect if I take a few precautions. My cables and setup are admittedly mediocre in this example, at least by metrology standards. I think my primary sources of deviation here--in descending order--will be the accuracy of the DC ratio measurement itself, the DUT reference, wiring and lastly the small 0.05ppm/C tempco of the FX. But here are the charts, redone with a 40-sample moving boxcar average, for you to peruse. One interesting issue regarding the 34401A itself disappears when you apply averaging. I'm not sure what else we're looking at. I've added a .zip of the CSV file original data in case someone else would like to torture the data.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: December 13, 2023, 04:54:45 am
content: I am assuming the interesting issue is the quantization of the data and the missing codes apparent in the correlation scatter plot. I have similar issues on my much older 3456 and 3457. Actually only apparent on the 3457 when using the extra digit register. The loop behavior shown in the correlation plot is what I have assumed is caused by thermal lags in "something" that matters, and might still apply even though you have instrumented what should be the critical area, but I don't really know what it is. I'm just not enough of a volt nut to chase it down further. Also problem is smaller in my lab as the temp swings are smaller.

author: Andreas
author_rank: Super Contributor
timestamp: December 13, 2023, 05:44:00 am
content: Quote from: CatalinaWOW on December 13, 2023, 04:54:45 amHello,The 34401A has a problem with rounding (limited resolution on data output). I would try to interchange the inputs to get below 1.0 for the ratio. (so you might gain one digit).with best regardsAndreas

author: bdunham7
author_rank: Super Contributor
timestamp: December 15, 2023, 09:36:47 pm
content: Quote from: CatalinaWOW on December 13, 2023, 04:54:45 amThose were some deliberately induced temperature swings, if I set the HVAC constant and don't open outside doors, it is much better. However your point about the difficulty of knowing how and where to measure the temperature is the real issue--equipment gets a bit warm and I don't have room to separate everything, for example. So analyzing tempco has more variables than are first apparent and temperature gradients are often more important. The Fluke 8846A is the one instrument that I've never been able to figure out any tempco on--I don't even know which way it goes, if any. What the FX helps with here is giving me a good idea how well I can measure stuff (~10V anyway) just setting my HVAC for constant temperature and using normal connections and no special precautions. Here's the FX and 8846A overnight using 4 foot banana-plug-ended plain cables (not twisted) and other stuff running on the bench. I did turn the display off, but I don't think that matters.I got an average reading of 9.9999503 (1.39ppm below FX nominal) and a standard deviation of 1.645µV (0.1645ppm). This is about 0.6ppm lower than previous tests above, but I see no point in trying to improve on that, volt-nut or not. Just quickly retested, I get about the same result if I set the meter up on a different shelf, if I use different cables and even if I use backup (isolated) power.

author: bdunham7
author_rank: Super Contributor
timestamp: December 15, 2023, 10:09:47 pm
content: Quote from: Andreas on December 13, 2023, 05:44:00 amI'm not sure it is exactly a rounding issue, but certainly the extra digit(s) are of dubious value, just like many other meters. Reversing for a reciprocal ratio resulted in an even more bizarre chart.

author: Andreas
author_rank: Super Contributor
timestamp: December 16, 2023, 06:06:37 am
content: Hello,interesting.Internally the 34401A makes obviously several conversions for a ratio measurement (100 NPLC do not last 4 seconds but 12 seconds).I thought the rounding problem exists only at the interface.But obviously each individual value above 10V is rounded differently from a value below 10V.with best regardsAndreas

author: Rax
author_rank: Super Contributor
timestamp: December 28, 2023, 04:33:03 pm
content: Being essentially neighbor with bdunham7 and through the generous flexibility of the "hub/host" I was fortunate to be able to overlap a tiny bit the Keysight 3458A I have on loan from a friend (calibrated by Keysight/Rosemont about two years ago) and the FX.Not sure if anyone will think this is totally black or white magic or what, but upon a fresh ACAL ALL, NPLC = 1000, 25.7C, the 3458A reads the FX at 9.9999647V, which in my book [...counts fingers...] is just at .05ppm of 10V. BaaaAAAaam!Speaks volumes of the calibration work on the FX, and the incredible opportunity it provides to the US CAL Club members to have at their bench.

author: alm
author_rank: Super Contributor
timestamp: December 28, 2023, 07:03:35 pm
content: Quote from: Rax on December 28, 2023, 04:33:03 pmWouldn't it make more sense to compare the reading to the most recent measurement of the FX with low uncertainty that you trust. ProbablyTiN's calibration.I would suggest transferring the value of the FX to your other standards, particularly the Fluke 5440. The 3458A's 24h stability at 10 VDC is specified at > 1 ppm, so be careful to either do sets of measurements of both standards within 10 minutes (for example collecting 16 measurements using built in statistics) and using the 10 minute transfer stability, or better connect the negative terminals of the FX and F5440 together and measure the difference using the 3458A. A lower end DMM would also do because you're probably only measuring a very low voltage, so even a 1% uncertainty wouldn't be a problem. Measure an equal number of samples at both polarities (swap leads between standards) and average the absolute value.

author: Rax
author_rank: Super Contributor
timestamp: December 28, 2023, 07:16:27 pm
content: Quote from: alm on December 28, 2023, 07:03:35 pmThat's exactly what I meant with my note. My bad, probably not everyone is aware that TiN's cal is 9.9999642V.

author: Rax
author_rank: Super Contributor
timestamp: December 29, 2023, 06:33:56 am
content: Quote from: alm on December 28, 2023, 07:03:35 pmThank you for this, alm. I hope I'll have enough time left with both of those to see if I can do something along those lines. We'll see.

author: Rax
author_rank: Super Contributor
timestamp: December 30, 2023, 12:34:33 am
content: Quote from: alm on December 28, 2023, 07:03:35 pmIn case I didn't quite fully clarify my initial point, my comparison was between my own reading of 9.9999647V and the readjusted cal by TiN (this is because the FX recently got broken and it needed recertification) of 9.9999645V. That's the ".05ppm of 10V" I was talking about. My comparison wasn't with 10V (though the difference is technically that many ppms off of 10V), but instead with TiN's reading.Sorry if this is possibly too unpacked, but my initial point was probably a bit cryptic.

author: bdunham7
author_rank: Super Contributor
timestamp: January 10, 2024, 05:21:33 am
content: The kit is on it's way to the next stop and I just wanted to show two less-famous components of the kit. The first is the 4W resistor box that seems to be pretty accurate, probably enough to calibrate a 5.5-digit meter if it has the right values. I measured the values with a recently calibrated Fluke 8846A at:1.000003k1.99997k10.00020k20.0002k99.9990k0.190002M1.000005M0.200008k100.0004R10.00373R0.00063RThen there is a nice little (portable, shippable) GPSDO courtesy ofAndrewBCNandvindoline. I haven't had a GPSDO before and I've relied on cross-checking with various instruments that have come and gone. I made a OCXO board for my HP5316B counter and IIRC I nulled it to the clock in my CMU200 and checked it with an old HP 8644A that came through--or perhaps the other way around--but I've always wondered how close it was. Here it is--and this is perfectly stable, not a 1 in 1000 photo! For those of you not familiar with this counter, it is showing 10.0000000 MHz. 10ppb.

author: Rax
author_rank: Super Contributor
timestamp: January 10, 2024, 02:30:39 pm
content: Quote from: bdunham7 on January 10, 2024, 05:21:33 amIn time-domain, it's just so much "easier" to be on one full level below the "volt world" (ppm -> ppb)... Also, these old HP counters (mine is a 5328A) are as aged as they can be.

author: mendip_discovery
author_rank: Super Contributor
timestamp: January 10, 2024, 04:23:57 pm
content: ppb = nHz/Hz?Nice here you are having fun with the cal club kit. I really need to get my 1281 fixed so I can get my 10V ref and some other bit together so there can be a UK cal club effort.

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: January 17, 2024, 03:45:08 am
content: The kit has landed in Upstate NY and is back up to room temperature. One corner of the box took a hit but everything looks fine inside. I'll be getting hooked up over the next day or so. The plan is to cal and track my three Fluke 731s plus a couple of the old mini-metro references, and compare the GPSDO to my Bodnar unit. I have various L&N resistors, but only one with a calibration, so we'll see how those do as well. I have a heat pump now, compared to the previous time with the wood stove, but it's single digits tonight and the lab is on the cool side. Should be coming up to normal temps soon and be more stable than periodic wood fires!

author: iMo
author_rank: Super Contributor
timestamp: January 17, 2024, 10:14:23 am
content: Quote from: bdunham7 on December 15, 2023, 10:09:47 pmI've tried with the RATIO and I get a nice chart. Getting always 8 digits via serial. No bizarre patterns, no missing codes. Below raw data.PS: For example when having 10V vref and aprox -67mV input I get "-6.7744869E-03" via serial and "-6.774487 m" on the display. With aprox -6mV "-6.3836033E-04" via serial and "-638.3603 u" on the display..Perhaps it needs those 12secs (at 100NPLC) for 2x switching the ranges, 2x AZ, measuring V1 and V2 against the internal 399, calculating V1/V2, sending in SCI format via serial and printing out in ENG format on the display.

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: January 18, 2024, 02:06:41 pm
content: Started with a comparison between the kit GPSDO and my Leo Bodnar unit. It's been running since last night. Quick look at the phase difference before going off to work, the drift is one cycle every 2 minutes 15 seconds. That's already way better than I'll ever need, but I wonder if more running time will see it get better. BTW, that GPSDO is a great piece of kit; having a self contained display is a super feature. Both it and the Bodnar can pick up a good signal in my underground lair, which is surprising in itself.

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: January 19, 2024, 03:58:29 am
content: Running for more than 24 hours, the drift is about 140 seconds per cycle @ 10 MHz. It varies, probably depending on the signal quality. I've never compared two GPSDOs before so it was interesting. I can detect a slight 1 pps feedthru, but it's of no consequence. Naturally I can't tell which unit is closer to "truth." Here's a shot of the screens and such. The scope shot is Bodnar on top supplying the trigger. The kit unit is on the bottom and drifts ever so slowly to the right. Next I'll get on to the voltage stuff, as the lair has stabilized at about 69F.

author: guenthert
author_rank: Frequent Contributor
timestamp: January 19, 2024, 08:59:43 am
content: Quote from: Conrad Hoffman on January 19, 2024, 03:58:29 amDo I understand this correctly, there's an error of about 1 in 1e9?I think it's time the time nuts speak up, but to me this sounds like either GPSDO isn't locked.Quote from: Conrad Hoffman on January 19, 2024, 03:58:29 amIsn't the beauty of a GPS disciplined XO, that you actuallycantell, whether it tells the truth? There might be a jitter of a couple of ns on the PPS signal (on cheap chips, don't know how good high end gear is), but with patience you can reduce the error to almost arbitrary low levels.EDIT: thinking about this a bit, those devices can't be arbitrarily patient of course. If the control loop is, e.g. 1000s and the jitter on the PPS signal some 15ns, then I think they can determine the time with an error of 15ns/sqrt(1000) / s ~= 1/2ns/s, i.e. about 1 in 2*e9. So the observed error isn't all that unexpected after all?

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: January 19, 2024, 01:48:37 pm
content: I'm not a time nut, but from what I've read, 1E-9 is probably typical unless the signal is better. I'm amazed these things can work at all in my basement. I have a piece of RG-174 that goes upstairs, but I don't think it would work for GPS signals. Ultimately I'm setting the oscillators in my frequency counters and the limit is the adjustability. I was playing with an old Optoelectronics UTC8030 counter last night and just getting the phase drift down to a few seconds was nearly impossible. My HP counter has the ovenized oscillator that's trimmed by voltage and that's much easier. I also have an old and ugly Fluke 7260A that I've never adjusted because every time I check it, it's about dead on.

author: vindoline
author_rank: Unknown
timestamp: January 19, 2024, 07:46:18 pm
content: Quote from: Conrad Hoffman on January 18, 2024, 02:06:41 pmConrad, I'm thrilled you like the GPSDO. This is completely AndrewBCN's design - hardware and software. My contribution was designing a PCB to fit my favorite little enclosure (and making a spare to add to the Cal Club kit!). From my point of view, it is not a ‘time nut’ device. I just wanted something to check and calibrate my frequency meters. I am very pleased with how it came out.

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: January 20, 2024, 01:27:19 am
content: Yes, it's quite a wonderful thing. I had wanted a GPSDO for several years before buying the Bodnar. I considered building one but found all the info on what GPS module to buy, plus what the circuits should be, way too confusing, so I never did anything. I can't be alone in that. (I feel the same way about the LTZ1000 references, though I understand it much better. What board? What resistors?)So, my final comparison numbers give a drift of one cycle every 2 minutes and 25 seconds (145 seconds.) That's 0.0069 Hz or 6.9 E-10 of a 10 MHz signal. The Bodnar is the "faster" unit, but I don't own a counter that could resolve the difference. Now, on to the voltage measurements!

author: bdunham7
author_rank: Super Contributor
timestamp: January 20, 2024, 01:37:42 am
content: Quote from: Conrad Hoffman on January 20, 2024, 01:27:19 amThe display of the cal club unit and the Bodnar software should both show an actual frequency, right? Do they both show exactly 10.000000000000000000000000000000000000000000000000000Mhz?The cal club unit was showing me 10.00000002 MHz even after running overnight.

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: January 20, 2024, 02:27:43 am
content: You can see the display in my photos above. The Cal Club unit would read -1 count, or dead on, depending on when you look. The Bodnar unit doesn't have a direct readout, only indication that the signal and PLL are good. As I said above, I think if you want the ultimate performance it would require getting the antenna in a much better location than my underground lair! Regardless, what I'm getting is still much better than I can put to use, even setting my HP ovenized oscillator. A more curious person would mess about with Lady Heather, though AFAIK nobody has gotten it working with the Bodnar units.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: January 20, 2024, 04:59:46 am
content: I am trying to avoid both volt and time nut extremes. Your roughly 10e-9 accuracy is being off about 1 second in 30+ years. More than good enough for most of us.Early in my career our internal cal lab sent our counters back to us with a sticker apologizing that they were only set to 1e-8. I always chuckled because nothing we were doing required better than 1e-4 and most of it was just fine with a percent or two error.It is wonderful knowing my instruments are pretty accurate, but my real need for accuracy beyond four digits is very, very small.

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: January 20, 2024, 01:24:37 pm
content: In 30 years, when I'm 100 years old, maybe I'll miss that second- somebody can dig me up and check! Now, avoiding voltnuttery; them's fightin' words! I'm still waiting for my inexpensive portable Josephson Junction device. I was hoping to get the lab under tighter temperature control, but it's about 9 degrees F outside and I still need to burn some wood, as the heat pump can't keep up at those temperatures. Don't assume "set it and forget it" when it comes to heat pumps and electric cars in the winter!Things will improve over the next few days and today I'll get the reference set up. I don't have an 8.5 digit meter or a scanner, so I'll be doing manual comparisons between 5 voltage standards and the LTZ reference using the Fluke 845. Debating whether to hook everything to a small rotary switch for speed, or just move the wires by hand. I'm afraid the switch (small Grayhill gold plated rotaries) will introduce thermocouple issues. I've never been able to beat clean copper telephone wire in a binding post. Also, the 845 has an output that I could data log to record sub-ppm stuff, but I don't know how stable the 845 itself is. Maybe with a manual periodic zero check?

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: January 25, 2024, 03:29:42 am
content: Figured it was time for an update. After doing the GPS comparison I got everything set up for voltage comparisons. Three Fluke 731s, one "A" and two "B" plus two Mini-Metrology standards. One was from an unknown builder and bought at a hamfest and one was my original unit from the article in 1996, 28 years ago! Null meter was my Fluke 845AB. I got my "as found" numbers and expected to adjust everything and start collecting data the next day. Murphy must have slipped in during the night because the next morning all the numbers were off by several hundred microvolts.It turns out my 845 decided to have a nervous breakdown and develop a leakage path. Not a short, just a subtle guard leak of about 1 megohm that came and went. I put it aside and proceeded using the original Mini-Metrology null meter. That agreed with the initial Fluke numbers and worked well enough for me to start adjusting. It doesn't have the filtering that the Fluke does and I really wanted that Fluke back. Condensing about three days of troubleshooting into two words- tin whiskers. The range switch in the 845 can (apparently) develop tin whiskers from the frame to the connections. All it took was careful brushing to get everything back to normal. I'm fortunate to have an HP 4329A high resistance meter, so can check guards and such at several hundred volts and up to 2E16 ohms. You'd think that would be enough to clear the whiskers just by measuring but the current must be too low.I've got the kit another few days and will collect a run of data on all the references. It's been years since anything was checked or adjusted but I was surprised that almost everything was within a couple ppm. The hamfest mm standard was within 0.3 ppm and my HP3455A bench meter was within 1 count. I guess when things get old enough they stabilize.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: January 27, 2024, 05:58:49 am
content: I really don't think it is tin whiskers. Impedance seems way to high for that. But a bit of dust (or even ash from the wood stove, a problem I have periodically) with a bit of moisture from the air would be consistent with your observations. Glad you got it resolved though.

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: January 27, 2024, 02:49:24 pm
content: I can't prove it was whiskers. Another characteristic was that the problem would come and go. Sometimes it wouldn't show up with my Fluke 73 DVM, but the minute I made a 10 volt (or higher) resistance measurement with the higher voltage meter, the problem would instantly come back and stay back for a good while, easily measured with the 73. Everything is clean and dry inside, plus the case is reasonably well sealed. Tin whiskers seemed as plausible as anything, but once the switch area was brushed out, the meter was as good (or bad) as ever and passes a 500 volt resistance check. "UCO" Unidentified Conductive Object.I've been recording data morning and night on weekdays and will do a noon measurement over the weekend. I'm comparing three 731 references and two Mini-Metrology references. I don't have any kind of scanner so manual measurements are the best I can do. The lab is extremely stable at 68F all the time. The barometer hasn't moved much, nor has the relative humidity. Here's a screen shot from the Excel file. I do dates as Julian dates because they graph better. Every 10 microvolts is 1 ppm and an interesting point is the date 335.861 because the only thing that changed there was a 0.2" drop in barometric pressure, though I find it hard to believe that would be detectable. It's also interesting how everything moved in the first hours after tweaking all the pots and gently rapping things.

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: February 02, 2024, 12:53:53 am
content: The kit has arrived back at Randall's so hopefully will be moving on to the next in line soon! Here's some photos of my primitive setup and a spreadsheet of results.

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: February 02, 2024, 01:02:16 am
content: One more note on the GPS unit. I borrowed a small digital scope from work and put the two units upstairs where the signal is better. Over a day they stayed within about 1E-9 of each other, but either one could be running faster than the other, so they probably average to near nothing. That kind of makes sense for what I've read about GPSDO stability over short durations. At any rate (no pun intended) it's a great addition to the kit.

author: RandallMcRee
author_rank: Frequent Contributor
timestamp: February 07, 2024, 08:34:32 pm
content: Yes, I have the kit. The next two folks in line have failed to respond to PMs sent last week, so...next person to PM me can have it sent to them!(I mean if you are already in the list, of course)Thanks,RandallThanks--we have a winner.

author: chuckb
author_rank: Frequent Contributor
timestamp: February 14, 2024, 01:40:13 am
content: The DC voltage kit arrived today in good condition. I am letting it settle down overnight before I start calibrating things. So far my DC Voltage calibration was only off 4ppm. That was based on the calibration of two Datron 4911s I picked up several years ago. I have over twenty 10V references around the place. It will be good to get a good voltage calibration assigned to each of them. The next week will be busy!

author: RandallMcRee
author_rank: Frequent Contributor
timestamp: February 16, 2024, 07:59:44 pm
content: If you would like the kit after chuckb please PM me.In the meantime, TiN has prepared a report concerning the recent FX incident.https://xdevs.com/article/usac_fix23/Kudos to TiN for his great support.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: February 17, 2024, 12:53:57 am
content: Solid report and analysis, and I will add my thanks for all of the time and material that XDev has put into our club.I have a question which could either be pertinent, a facepalm oversight on my part, or a reveal of more ignorance than I like to admit. In any case I hope to improve my understanding.The snippet above, taken from the first graph in the reports a snapshot of the references performance at two points in time. Error bar is about the same on both, in the 0.3 to 0.4 ppm range. As I think pf ppm a single digit change in the fifth digit to the right of the decimal point on this approximately 10 volt value represents approximately one ppm. The numbers are reported in the SEP.2023 observation for three more decimal places beyond this, which is approximately parts per billion. If the value is only valid to +/- 0.4 ppm those last three digits would seem to have no meaning. The same reasoning would imply that the Jan and Sep measurement are not provably distinguishable from each other, with their separation being within the combined error bars on the two measurements.What am I missing?

author: bdunham7
author_rank: Super Contributor
timestamp: February 17, 2024, 01:42:48 am
content: Quote from: CatalinaWOW on February 17, 2024, 12:53:57 amI can't speak for the details of this particular example, but in general those tolerances are given as expanded uncertainties, usually k=2. It's all a matter of probabilities and you need to look at is as a distribution rather than sharply defined error bars. So if the +/-0.4ppm is an expanded uncertainty with k=2, then that implies that there is a 50% chance that the actual error will be 0.14ppm or less. Maybe the last 1 or 2 digits aren't very useful, but the sixth decimal place one is.

author: bdunham7
author_rank: Super Contributor
timestamp: February 17, 2024, 01:46:51 am
content: Quote from: RandallMcRee on February 16, 2024, 07:59:44 pmI'm still amazed that the FX reference can not only achieve what it does, but that it does so even over many power cycles and despite enduring all of the environmental and physical punishment that the USPS can dole out.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: February 17, 2024, 04:11:07 am
content: Quote from: bdunham7 on February 17, 2024, 01:42:48 amI will quote XDev. No amount of statistical sugar coating beats reality. Yes, there is a likelihood of some meaning to the sixth digit to the right of the decimal point, and it is more likely than not that there was drift over the nine months interval. And the most likely amount of that drift is the apparent difference of the two values.I guess another way to pose my question is this. XDev strikes me as both careful and knowledgeable. My first inclination is that his posting of eight digits beyond the decimal is not accidental, but don't understand how that can be consistent with the uncertainty.

author: SilverSolder
author_rank: Super Contributor
timestamp: February 18, 2024, 08:34:36 pm
content: Quote from: RandallMcRee on February 16, 2024, 07:59:44 pmAmazing work, getting to this level of precision is truly astounding.

author: chuckb
author_rank: Frequent Contributor
timestamp: February 23, 2024, 07:55:38 pm
content: The DC voltage cal kit is headed back to Randall. I was able to calibrate 15 10V sources and three DVM. I also checked my equipment at a cooler temperature to get a rough temperature coefficient for each item. It was a very busy / productive week.More details to follow.

author: RandallMcRee
author_rank: Frequent Contributor
timestamp: February 29, 2024, 04:55:37 pm
content: This is my last post here (as cal club moderator)!I'm turning the reins over to bdunham7!I am sorry that I could not complete round3 but I have suggested to bdunham7 that he continue the round, if interest is shown.Thanks for all the fish! Bring your towel!

author: bdunham7
author_rank: Super Contributor
timestamp: February 29, 2024, 05:07:59 pm
content: Thank you Randall for all the work so far. As soon as I receive the kit I will take an inventory, consult with the remaning Round 3 participants and start a new thread, USA Cal Club Round 3.1. I'm open to suggestions as to how to improve the process, such as streamlining or repackaging the kit contents. Let's consider enrollment in this round to be closed for now. I'll use the remaining Round 3.1 to come up with some ideas for improvements for Round 4 which will hopefully happen soon.

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: February 29, 2024, 05:30:21 pm
content: Randall, thanks for all the work and doing a great job!

author: vindoline
author_rank: Unknown
timestamp: February 29, 2024, 11:58:33 pm
content: Quote from: Conrad Hoffman on February 29, 2024, 05:30:21 pmI agree! Randall thank you for taking over from me and making round 3 a success!

author: ZGoode
author_rank: Frequent Contributor
timestamp: September 12, 2024, 08:22:13 pm
content: Assuming it's not too late for round 3 I'd like to get added to the list to eventually get a turn with the kits. I have a bunch of stuff that has calibration way past due, and it would be nice to confirm everything is still in spec.

author: bdunham7
author_rank: Super Contributor
timestamp: September 12, 2024, 09:23:34 pm
content: Quote from: ZGoode on September 12, 2024, 08:22:13 pmWe're on Round 3.1 and I'm organizing it for now. PM me, the availability is pretty good right now as many people have deferred taking it.

author: maxamp
author_rank: Contributor
timestamp: September 18, 2024, 02:29:23 am
content: Can I join the USA Cal Club Round 3.1?I have a 3458A that has been checked with data in a cal lab and left as is (not recalibrated) a little less than a year ago among other equipment.I also have a GPIB raspberry PI data logging setup with temperature and humidity ready to go.

author: Rax
author_rank: Super Contributor
timestamp: September 18, 2024, 02:35:15 am
content: Quote from: maxamp on September 18, 2024, 02:29:23 amI'll be interested to learn what you see after measuring the FX.

author: Grandchuck
author_rank: Super Contributor
timestamp: March 01, 2025, 04:01:54 pm
content: Is round 3 active?Will there be a round 4?

author: bdunham7
author_rank: Super Contributor
timestamp: March 01, 2025, 05:57:37 pm
content: Quote from: Grandchuck on March 01, 2025, 04:01:54 pmI've taken on the USA Cal Club admin role as of Round 3.1.https://www.eevblog.com/forum/metrology/usa-cal-club-round-3-1/msg5390003/#msg5390003Round 3.1 is mostly over as far as I can tell, but I will send the FX or other parts of the kit out on request as I regroup and put together a Round 4. That might take a bit to get set up as this is all on an "best effort, as time is available" basis. In Round 4 I'm not going to use the method where I make a list and put everyone in order because this just hasn't been working out well--people get busy and can't commit to a particular timeframe that far ahead.

author: Grandchuck
author_rank: Super Contributor
timestamp: March 01, 2025, 07:48:20 pm
content: If possible, I am requesting the FX only, when available.Thanks

author: CalibrationGuy
author_rank: Unknown
timestamp: March 07, 2025, 09:26:36 pm
content: I am willing to donate to the group one traceable ISO17025 calibration (characterization) of your 10 volt reference. If this helps anyone, let the cal club admin know and have them send me a pm.TomG.