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

author: rhb
author_rank: Super Contributor
timestamp: July 29, 2019, 05:48:04 pm
content: Round 2 has been an interesting and educational process. Many thanks to all who contributed especially cellularmitsosis, TiN and vindoline who did the serious heavy lifting to make it happen.I'd like to raise some issues that seem to me obvious from my experience.1) We need a precision voltage divider able to provide outputs on all the DMM ranges.2) The PX reference needs more robust packaging. TiN did an excellent job on the FX, but the PX is fragile in its present form.3) A GPIB-USB interface combining the Tempduino and an RTC in a case so that people who do not already have a logging system can collect data more easily.4) Test scripts portable to Windows and Linux for all the measurement options which have been thoroughly tested.5) We need more resistors so that all ranges are tested.6) DC current, AC volts and current sources.7) A transit temperature and humidity logger that records to an SD card.Some of this I intend to do, some of it I know how in principle, but probably not to the level of quality needed. And some, all I know is it's needed for a full DMM cal.Have Fun!Reg

author: hwj-d
author_rank: Frequent Contributor
timestamp: July 29, 2019, 11:04:04 pm
content: The original idea behind PX was to have a small, compact, easy to send ltz1000 reference. Not more. With it in mind someone have the ability to compare/verify his 5.5, maybe 6.5 dmm in the 10 voltage range. This was not, at first, as i understand, to test the ref itself in long sessions, to get the reliability and characteristic curve, except as a side effect. One should test its own dmm better as with this chinese ones. So someone take this test, and ship it to the next interested for same simple thing. Same with this resistors, see if your dmm out and how much. The star shipping methode gives the sender, in this case vindoline, the ability, to check the ref for next shipping. In my oppinion, the ref ist robust enough, for input voltages between 12V and 15V for same output voltage, and protected against polarity reversal. The output should be save for >= 10Mohm impendance and not shortcut protected. These are the only conditions.In the course of time, however, further requirements arose from participants that the reference behavior of the measurement should be recorded, and without temperature and humidity sensor with timestamp this would not really make any sense. So Jason kindly sat down again and developed an additional kit.To make long words short, now we are sitting in front of the px, and realize that it is not robust enough for all this, and compare it with tin's reference, which plays in a completely different league. Yes, that's right. But px wasn't meant to be that way in my opinion. Actually, this should also, in its own original compact form, as my suggestion, without all the fuss around, go on its own quick journey.Ok, i'm not at once in the usa club for now, so consider this as a suggestion on my part, hold it simple.

author: Tj138waterboy
author_rank: Regular Contributor
timestamp: July 30, 2019, 11:07:34 am
content: I would like to participate as well as a beginner I agree with both above posts. As a whole I would like the ability to get all voltage ranges as well as resistance ranges which is why im building up a 100v ref. Also from the pics I see the cal club ref looks to be the size you would expect for a basic vref but seems flimsy. Im not sure if this is to keep shipping price down or just what was available to house the unit. The bigger point I would agree on is that probably less than 50% of the eevblog members have better than 6.5 digit meters so the build/quality/accuracy could be more geared towards that kx vs px type. The star pattern shipping seemed to be a good idea to keep track of changes during the voyage but another method could be for the next round, ship to member longest distance first that has known good calibratee 7.5digit or higher gear to get first baseline readings then to nearest member or two that has questionable lesser digit equipment then back to you or another member along the list with good calibrated equipment 7.5digit or better leapfrogging all the while. Also do you have any sort of paypal or such for contributions? Any of you guys putting in this much effort could benefit from posting a link for donations to make this happen. As a side note would there be any issue with using 2-5ppm smd resistors for resistance only measurements more cost effective than getting all ranges of foil type.

author: rhb
author_rank: Super Contributor
timestamp: July 30, 2019, 01:10:18 pm
content: The original intent was to fit the PX in a $3.50 USPS flat rate box. It changed a bit when TiN added the FX. Shipping is now $30/person vs the original $7/person.If we had 3 PX references which were shippable for $3.50, then we could rotate them with the FX to people with 7.5 and 8.5 digit meters and send just a PX to people like me who only have 5.5 and 6.5 digit meters.That would shorten the waiting time substantially and every 4th trip of the FX/PX would give us a comparison on each PX.My ultimate goal is to be able to do a full cal of all my T&M gear with everything traceable to the group cal kit. I've got lots of RF gear whereas other people just have meters and voltage references. I could have bought a new 3458A for what I've spent on RF gear. But then I wouldn't have the RF gear. For my construction and repair projects the 34401A is quite adequate.My hope is that we can fully test DMMs by the end of 2020 and RF gear to 3 GHz by the end of 2021. That's an ambitious goal, but we have come a very long way in the last year. I now have a very well equipped electronics bench in addition to a full machine shop. What I don't yet have is enough of it organized to work efficiently. I'm making progress, but if I just spent time organizing it I wouldn't have any play time.To quote Lao Tsu, "A journey of a thousand miles begins with a single step."

author: SilverSolder
author_rank: Super Contributor
timestamp: July 31, 2019, 12:18:22 pm
content: The simple PX-only suggestion seems a good idea.Of course, it is probably a "gateway drug" to more serious volt-nuttery... but it does potentially open the club to far more people.Before you can become a nanovolt-nut, you have to first be a microvolt-nut... and before that, a millivolt-nut!

author: Tj138waterboy
author_rank: Regular Contributor
timestamp: July 31, 2019, 12:55:30 pm
content: Im looking at this in more of beginner, intermediate and advanced level transfers. Honestly i would probably consider the px an advanced level due to the ltz1000. Kind of comparing a resistor of s102 class tho vhp. Both would be accepted as good enough but the cost would make it less viable to just send a set of vhp class to just anyone that may not be as knowledgable on setup and measurements, "ie running too much current through it or mis-handling". I like the semi instruction manual provided with the current round which does help with user error being less likely and would incorporate it again even for the most basic task. As for your goal of keeping the shipping cost down I think under $15 would be more realistic goal to be able to include a complete kit that would include px ref somewhat in its current configuration, something like a hammond 1590a/b housing some s102 class resistors, a power supply, and a good set of test leads, so theres no variation of power supply used and users without lab supplies will not have to worry. Worst case I could seperating the kits to keep cost lower. Or not putting resistors in an enclosure but using 4 wire shorting blocks with resistor attached instead.

author: rhb
author_rank: Super Contributor
timestamp: July 31, 2019, 09:19:27 pm
content: I was absolutely terrified handling the FX. I've read numerous tales of woe from experienced people who blew a reference they had built, including cellularmitosis who blew the original LTZ1000 for the PX reference.Conrad Hoffman wrote a series of articles on a DIY metrology lab which you can find on line. It's a lot of work to match the resistors TCs, but the experience is valuable and the dollar cost is low.I'd like to know what it would cost to make 3 PX references in sealed Hammond boxes. The references are over $60 each at Digikey, but I gather there are cheaper sources. I rather fear that the current PX reference will need repairs before it makes the rounds to everyone.I'm not interested in super accurate voltage references beyond reading about them. I'm concerned with the practical task of keeping over a dozen pieces of T&M kit in cal. Even if the cals were free, shipping on a lot of my gear would be $300 round trip.And if you think metrology grade DC connectors are expensive, price RF connectors. Mere basic bench RF connectors (e.g. APC-7 to N adapter for an 85046A S parameter set) cost over $130 each. Once you go over 6 GHz the prices get eye watering. A 1 mm 110 GHz RF connector is $1000 for just one!But first things first. Reducing the waiting time and covering more meter ranges and functions are more important.

author: rhb
author_rank: Super Contributor
timestamp: July 31, 2019, 10:47:38 pm
content: I'd like to pose two questions:Best way to extend the references to other ranges including things like the 3478A with its "3" leading digit scales? Simple divider or divider and op amp?Best way to produce a DC current source? Preferably multi-range, but anything is better than nothing.It seems to me that those should be addressed before dealing with AC V & A.Resistors seem fairly simple, more of them in a more robust package separate from the other references.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: July 31, 2019, 10:50:56 pm
content: I am a little confused. RHBs post essentially suggests development of a portable cal lab. One which is essentially plug and play (scripts set, instruments set, interfaces set).While that is a laudable goal I question both the scope of the task and the purpose. Starting with purpose. The need for calibration really comes when delivering product to a specification or when comparing measurements. Both of these requirements are only satisfied by full traceability back to an accepted reference standard. While that kind of traceability could be achieved through this reference, it would require the heart of the star topology to do full evaluation of the kit each trip back, and also to maintain traceability (presumeably through paid calibrations) to reference standards. That is a huge burden on whoever currently owns the middle.I don't know the use cases for each member of the club, but I suspect that a significant majority of us are hobby users at various levels of intensity. We seldom, if ever deliver product based on our measurements. Sharing of data is more common, but often not dependent on high level calibration. So for us this is volt nuttery in its purest form. Something we absolutely don't need, but do for? Fun, curiosity, bragging rights....?So now into the scope side of the issue.Having a canned cal lab sidesteps one of the pleasures of volt nuttery. With prior apologies I will point to Conrad Hoffman. I suspect that much of his pleasure has been derived from the development of his own tools. There is a good deal of that in my own path. Some coming winter will see me measuring many resistors as I assemble my own precision divider.The cost of shipping has already been mentioned, and as more capabilities are added it will only go up. The chance of something horrible happening will remain fairly constant, but the pain of a lost package will grow as more and more is invested. As proud as I am of the USPS, UPS and other services that give us one of the better delivery systems in the world accidents and errors do occur.Rather than extend this rather rambling comment I will put a vote in for the simpler end of the scale. If the club evolves to a portable cal lab, I will probably drop out, as it serves a function I don't need, takes away from the do it yourself element of the project and my membership would add risk to the club and to myself.

author: rhb
author_rank: Super Contributor
timestamp: August 01, 2019, 12:39:00 am
content: I'm interested in building RF gear and specialty lab gear. It matters that if I set the output frequency and level of my 8648C that I know that the frequency is correct, the output level is accurate and there are no major spurs. By the same token if I measure an RF source or amplifier I've built I need to know that what I see on the spectrum analyzer is correct and not an artifact of some fault which has developed in the SA.Even with new gear, it's important to verify performance. With 20+ year old gear greater vigilance is needed.If my T&M gear is not in spec I can waste a huge amount of time chasing down blind alleys.Metrology is a much broader subject than voltage, resistance and time. I'm much more interested in measuring plane surfaces to a fraction of an arc second than I am voltage to 1 ppm. I have practical applications for the level accuracy. I have no application for 1 ppm voltage accuracy. So far as I can tell, people pursuing that are doing it just because they find the problem an interesting challenge.There's no point in sending an RF cal kit to someone with no RF gear, so why would you do that? I won't know until I have time to analyze the data, but I doubt that I have any need of an FX class reference. Getting a PX for an annual check for $7 probably suits my needs a lot better than $30 to get an FX.Volts, resistance and time are arbitrary. You can set the value to anything you want. What matters is that the interrelationships among different quantities are accurately maintained. If your voltage, resistance and amperage measurements don't match ohms law closely enough for the work you are doing you have a problem.

author: Tj138waterboy
author_rank: Regular Contributor
timestamp: August 01, 2019, 01:34:03 am
content: Quote from: CatalinaWOW on July 31, 2019, 10:50:56 pmI don't think this would take away from diy'ers because im sure there are more starters that can't afford or have access to any better than a questionable ebay reference or resistor. Im all for Mr. Hoffmans methods for starters but as for me, all my equipment is more than 5 years out of cal which include 2 HP 3478a one of which came uncalibrated, Hp6111a, Hp54503a, and multiple refs on breadboard and arduinos. Yes any of us can tell arduino to output a specific frequency or measure a alkaline battery but unless there is some form of getting all equipment closely agreeing with a calibrated source then every project I start on I question if its even usable due to my equipment may be off by order of magnitude.

author: tomato
author_rank: Regular Contributor
timestamp: August 01, 2019, 02:09:54 am
content: Quote from: Tj138waterboy on August 01, 2019, 01:34:03 amYou need a calibrated source to tell if your equipment is off by an order of magnitude?

author: RandallMcRee
author_rank: Frequent Contributor
timestamp: August 01, 2019, 02:13:13 am
content: Quote from: rhb on July 30, 2019, 01:10:18 pm(I, Randall, underlined several words for emphasis)Well, CatalinaWow and I do not support your goal. I am not interested in RF gear. Sure, you can calibrate your 5/6.5 digit DC range using the cal kit but I am not sure how SA calibration suddenly became a US cal club concern.I say *NO*. I say hell no.The more complicated this becomes the less likely it is to succeed.Yes, metrology is wide, butNOthe US cal club is only DC volt-nuts. It seems to me that time-nuts are not part of this particular club. (I mean someone could have started such a club--but they did not and have not.) And RF nuts are not part of this either.I find it fascinating to measure DC volts to great precision. I don't need to justify it to rhb or anyone else. If you don't care about it, don't join the club. Simple.So, a long-winded way of saying lets keep things on the simple side.Thanks,Randall

author: ArthurDent
author_rank: Super Contributor
timestamp: August 01, 2019, 04:26:26 am
content: I also am very interested in frequency and actually have had a crystal standard that was running for over 35 years except for down time to replace batteries. However with fairly cheap GPSDOs anyone can have a very precise 10Mhz standard that can always give you traceable standard frequency far more accurate than you'll probably ever need. I have 2 antennas, 2 splitters, and multiple GPSDOs running 27/7 plus Rb and XTAL standards so I have frequency covered quite well.That isn't true for voltage. To have a reliable voltage reference you really need to have your house standard, which will drift, checked against a higher standard on some schedule and the USA CAL Club fills that requirement nicely. I have bench meters like an HP 3457A and others that agree quite well but they haven't been checked in a long time and this club is a good way for me to check this stuff out at very little expense. My LTZ1000A standard has been aging for several months and the 10 VDC output seems to be quite stable. Once I compare my voltage standard against the traveling standard I can a have a little more confidence in my voltage readings and use it to calibrate some of my supplies shown in the photo.Anyone who wants to have a wide range of voltages for their meter (which could be far different than my meter) could build a divider to suit their needs. Having a traveling divider that would fill everyone's needs would be costly and bulky. Keeping this simple is the way to go.

author: TiN
author_rank: Super Contributor
timestamp: August 01, 2019, 08:24:00 am
content: I am in "nay-sayer" club on trying to make DIY calibrator. I tried that idea, (which resulted in KX ref design) but came to (in)sanity after seeing glimpse of the mountain sized iceberg of design and costs to make something capable verifying even just 6.5d meter. Also to make such unit fool-proof will make it big, heavy and expensive to ship.I think inception of CalClubs happen because there are number of people with LM399/LTZ refs and 3458As around who did not want to bear traceable calibration costs/don't have friendly lab nearby. Getting calibrated 10V/10kOhm standards by mail for traceability is all they wanted, thanks to ACAL.Now from purpose point of view. Even if one magically builds a portable highperf calibrator with current, resistances , dividers and whatnot (not unreal, Mickle.T did that more than once, all alone) such calibrator will need traceable calibration by itself. You can take 10V DIY ref and do official calibration by decent lab. But getting accredited lab to do full calibration on wonderbox with DIY UI, protocol and unknown stability - well, tricky to say gently. I have built calibrator from commercial modules and bits, and even with that I am not comfortable shipping it to traceable cal lab. It will still take few more years before I am confident.Price of accredited 6.5d meter calibration even with shipping is small (few hundred $) so those who need/want it just pay that and get their report for all functions/ranges.Now , there is nothing wrong with idea of "portable" calibration lab for transfers between different labs, but it is much more limited and purpose exclusive club. Being part of one it's very expensive and time consuming, and paying $hundreds on shipping alone is not even worth mentioning. Also all members of such club must have similar capability and gear available, so our transfers can be evaluated for validity after each shipment/transfer. No need to say such level is for "lost case" volt/ohm-nuts and amount of participating members is less than amount of fingers on one hand. It is not what USA Cal Club here is about, in my non-member opinionI'd like to note good idea from rhb as well - if one does not need FX reference, such member can ask not to ship FX , and get only PX/ohms ref? It is two cases now, so that can help to reduce shipping expense to half? So there would be two member lists, like "mild volt-nut case" and "severe volt-nut case"?

author: hwj-d
author_rank: Frequent Contributor
timestamp: August 01, 2019, 09:18:59 am
content: Quote from: TiN on August 01, 2019, 08:24:00 amOh, I for myself would have one of this FX too,lovingly.And what would tell me that?Allmy LTZ1000's have the same noise floor of >= 8 µV with >= 1.1x µV StdDev. And I'll bet my ass, that's the same with the FX.And everyone interested knows, why this is as it is.No dmm gets better by the measured reference!

author: rhb
author_rank: Super Contributor
timestamp: August 01, 2019, 11:10:43 am
content: For those who complain I am proposing feature creep, please read the start of the USA Cal Club: Round 2 thread. Jason's intent was a $7 per round trip traveling voltage reference. The current kit is much more capable, but it costs over 4x as much.I am not a volt nut. My concern is practical metrology to support my measurement requirements. Those happen to be more comprehensive than many, possibly even most, of the people active in this section. Metrology is a vast field which is central to *all* engineering and scientific effort. I need dimensional metrology references in addition to electrical references.Building a Fluke 5700A class calibrator is not what I am proposing, nor am I proposing a monolithic kit for calibrating everything anyone might have. What I'm proposing is gradually expanding the range of calibrations that can be performed so that the club is useful to people who are interested in solving practical metrology problems, i.e. if I measure voltage, resistance and current for this voltage source and resistor, will all my measurements agree? And how accurately? The range of subtle issues which must be addressed to simply do that on a single DMM range is large. Doing it on multiple ranges progressively grows in difficulty until even TiN gave up. Not because he could not do it, but because he could not do it to the level of accuracy he sought.I am think there should be 3 PX references and two mailing lists, a PX & FX list and a PX only list. Everyone participating will benefit from that in the form of shorter waiting times and better quality cals. The cost to do that is pretty nominal and I'm quite happy to pick up part of the tab.A voltage reference alone will not calibrate a DMM. All it provides is a comparison against other voltage references. It is a necessary, but not sufficient reference for my purposes. It is all that matters to others.Relative to RF calibrations, voltage calibrations are trivial. Even low frequency AC is vastly harder than DC. Just go look at the specs for AC vs DC on any meter.People who are only interested in voltage references only need access to a voltage reference and s limited range of resistance references.People who want to calibrate a DMM for general work need more references. People who want to calibrate LCR meters need more. People who build radios need even more. There is no point in sending a set of precision capacitance and inductance standards to someone whose sole LCR meter is a $20 ebay unit. Any set of inductors, capacitors and resistors, suitably packaged for which good quality measurements are available is sufficient for them. Someone with a 4284A/4285A set needs something rather better. And if there is a base set of 3 low end references for those with only a $20 LCR meter which rotates around with the precision set to those with higher end meters, then a lot of practical metrology problems are solved.In summary, I'm proposing that if you just need a PX, you get that. If you need an FX, get the FX/PX set and measure the PX as a service for the PX only people. I am proposing that be extended to a best effort full DMM cal kit for those who want that and similar programs for other measurements up into RF. The kits should meet the needs of the recipients who are paying for the shipping costs. And one size does not fit all.Have Fun!Reg

author: TiN
author_rank: Super Contributor
timestamp: August 01, 2019, 11:38:28 am
content: Point was that to calibrate 6.5d meter you do need full fledged MFC. So I don't understand how 3 more PX references can help?Anyone can do full DCV calibration using existing Cal Club equipment. You build youself precision 1:10, 1:100 divider (or buy one from ebay) and null-meter and derive 100mV, 1V, 100V, 1kV from FX(PX)+divider combo, like most of calibration labs are doing. No need reinvent a wheel and trying to invent worse stability 100mV / 1V / 100V / 1kV reference.Maybe get practical and list what items/functions/stability specifications you think are needed.RF, AC, temperature, dimensional, LC and whatnot (we can talk about gases/biomed/ionizing radiation too) seem to be outside of the USA Cal Club scope/desires?QuoteNever! I just build more calibrators...QuoteNot really. Kit is a courtesy of members organized it, and it does not need to meet any needs or recipients, just because they pay $30 for shipping.Participation in community club is not mandatory. If one does not see it useful, no reason to apply for it, just to complain about $30 shipping (which is cheap!).

author: SilverSolder
author_rank: Super Contributor
timestamp: August 01, 2019, 03:59:50 pm
content: Quote from: rhb on August 01, 2019, 11:10:43 amThis sounds eminently sensible.

author: maxwell3e10
author_rank: Frequent Contributor
timestamp: August 01, 2019, 05:41:06 pm
content: For me the interest is not necessarily in absolute calibration but in ability to play with very stable, low noise voltage sources to characterize the performance and quirks of various DMMs. In terms of additional elements to the calibration kit, a calibrated 10:1 and 100:1 divider might be good, its not too bulky or heavy.

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: August 01, 2019, 07:33:42 pm
content: Though I've built many volt-nut gadgets, my main interest is in getting my three Fluke 731B references as close to truth as possible. Even though I only have a couple 6.5 digit meters, I can compare my references to the traveling standard to far better, and also log the results. I break things down into "standards I can self-generate" and "standards I can't". That means I can get frequency from GPS or NIST WWVB stations , and I can create ratios to any degree needed (I also have a 752 to do the meters), but I can't generate my own volt or ohm. For me, the ideal kit would be the good voltage reference and, hopefully, a recently measured stable resistor. Anything else is a bonus I wouldn't refuse, if it doesn't delay things by too much.

author: SilverSolder
author_rank: Super Contributor
timestamp: August 02, 2019, 12:07:48 am
content: Quote from: Conrad Hoffman on August 01, 2019, 07:33:42 pmIt would be very interesting to know how you do that. A stable and sensitive null meter springs to mind, but the two references being compared likely have different enough voltages that it is hard to see how you can null anything without some kind of accurate divider in the middle of it all?

author: vindoline
author_rank: Unknown
timestamp: August 02, 2019, 01:20:25 am
content: Quote from: rhb on July 30, 2019, 01:10:18 pmThat is not true. The current kit fits perfectly in a USPS medium flat rate box. The cost is $14.35 for 2-Day priority mail anywhere in the US.

author: vindoline
author_rank: Unknown
timestamp: August 02, 2019, 01:43:14 am
content: I also think that there has been some confusion about the purpose or intent of the club. Perhaps it's because of our name "USA Cal Club." I don't think that the point has ever been to serve as a rotating calibration service. Frankly, if you need a calibrated meter you should have it calibrated by a professional lab. If you just want to check your 4.5 digit hand held DMM, eBay is full of "DMM check" style references which are fine.What we have offered is the chance to use a stable, low-noise voltage reference that has been verified by multiple experienced members of the "volt-nut" community. In return, those that are able can verify the reference with their equipment and provide feedback and additional confidence in the reference. With TiN's very generous addition of the FX, we now also have a pretty darn good absolute 10V reference!What do I use the PX and FX for? For one thing, I use them to check the stability and drift of my bench meters - an HP3456A, a Fluke 8506A, and a Keithley 196. The stability and tempco of the LTZ1000 refs is much better than the LM399's in my meters. Therefore, if I "log" the LTZ, I actually get an idea of how stable my meters are and what their Tc's are. OK, I also used the FX to "tweak" the 10V scale on my 3456A to exactly 10V. This will let me easily re-check the FX when it returns from each hop.

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: August 02, 2019, 02:45:24 am
content: Quote from: SilverSolder on August 02, 2019, 12:07:48 amPretty easy- 845 null meter between the standards, with the output read by a moderately good meter with GPIB for data logging. Since I'm trimming my standards to match the reference, there's no big mismatch problem.

author: TiN
author_rank: Super Contributor
timestamp: August 02, 2019, 03:22:01 am
content: QuoteFor me, that was the whole point why I decided to donate FX (with help of Jason's resistors, and LTZ) to the club, so I can see how my design survives multiple shippings/abuse from normal users. Eventually next year I'll have it back and compare its performance to original data.

author: bitseeker
author_rank: Super Contributor
timestamp: August 02, 2019, 04:22:55 am
content: I see some possibilities here:1. Since the name, USA Cal Club, is quite broad being limited only by geography, there could be different groups coordinated by potentially different people to satisfy different cal interests: core voltage/resistance, extended voltage/resistance, time, etc.2. Rename this club to something more specific to better reflect its purpose and scope (e.g., USA Volt Cal Club. Hey, that's VCC). Of course, anyone is free to make other purpose-driven clubs.3. Update this club's user guide to explain what this club is for and set appropriate expectations. This would be beneficial in general.

author: GigaJoe
author_rank: Frequent Contributor
timestamp: August 03, 2019, 04:13:31 am
content: true ... my 10Mhz OCXO+battery idea quietly die, due to null response and GPSDO $50+and 4 X ad587 in small +45C enclosure, produced around 2ppm \ year (worst case). but ... we are north and no one close to verify.nulling - pieces of cake, ideally with 10G voltmeter , but if a source has a low impedance, even $20 multi-meter works ... if it had micro volt resolution ...

author: The Soulman
author_rank: Super Contributor
timestamp: August 03, 2019, 07:57:21 am
content: Quote from: GigaJoe on August 03, 2019, 04:13:31 amHigh input impedance isn't absolutely necessary with these low differential voltages current is really limited.Yeah some $20 meter work nicely, but they're typically limited to 100 microvolt resolution (set to millivolt range).But some to 10 microvolt, that already gives 1ppm resolution when comparing two 10 Volt references, good enough for normal people.Beyond that is noise and thermal emf mayhem, fun to look at when designing and building v-refs, but for transferring an absolute value not that necessary.btw, The cheapest data logging bench dmm with microvolt resolution I could find was the Vici vc8145

author: rhb
author_rank: Super Contributor
timestamp: August 03, 2019, 11:38:05 am
content: Quote from: vindoline on August 02, 2019, 01:20:25 amMy $30 figure is based on the recipient paying for shipping both directions. It seems quite unfair to me to ask the person handing the shipping to also pay for it. Just checking and shipping seems quite a lot to ask, even of a volunteer.So I urge everyone who can afford it to reimburse @vindoline when they return the kit. Even if he doesn't ask.At the moment we have a "one size fits all" as a consequence of TiN's generosity. I think there is great merit in, as a first step, arranging for a two track system, PX/FX and PX only, that provides regular measurement of the PX standards by those with the best capability. For that we need to build a couple more PX references. In the process I suggest packaging all the references uniformly using a rubber seal die cast Hammond case of suitable size.The two additional PXs and three 150K:100K:10K:1K voltage dividers made from precision resistors would be a modest expansion of the current kit. The additional 150k accommodates the 3478A ranges using a 7 V reference. It would permit performing calibrations on other ranges on both the 344401A and 3478A class DMMs.One of my goals is an automated full bench cal. That's very bench specific and starts getting rather expensive and heavy when you start switching RF signals. That's not something a Cal Club can provide. Some precision attenuators and RF sources are reasonable, as is sharing switching system designs and programs. But it makes no sense to ship precision attenuators and RF sources to someone who has no RF gear. All that does is delay access for those who do need it.All of this takes a long time to accomplish which is why I raised the subject now. Building two more PXs, repackaging the current one and building 3 precision voltage dividers in the next year seems an achievable goal. The PX kits would essentially be higher grade versions of Doug Malone's excellent DMMCheck with more detailed calibration histories at 2-3 month intervals.While not capable of logging, a 20 uA (50k/V) full scale analog meter will certainly provide uV null detection. Those used to be commonly available, but even the standard 50 uA (20K/V) VOM would work.

author: hwj-d
author_rank: Frequent Contributor
timestamp: August 03, 2019, 12:21:34 pm
content: rhb:What would you suggest about type of resistors, housing and bindingposts it should be for a divider?

author: rhb
author_rank: Super Contributor
timestamp: August 03, 2019, 01:19:46 pm
content: I'm expecting input from TiN and others on how we should do that. At this stage I'm just attempting to articulate requirements. Not how we get there. I only have 3478A and 34401A DMMs, so I can't speak to what Keithley and Fluke owners need.The only comment about how that I have at present is that things should be as robust as possible so that minimal maintenance is needed over a 10-15 year lifespan.The USA Cal Club: Round 2 waiting list is rather long. So I wanted to address how to shorten that for Round 3.I have started a separate thread on the more difficult topic of doing full bench calibrations here:https://www.eevblog.com/forum/testgear/automating-full-bench-calibrations/msg2590392/#msg2590392I was able to sort out the general design for switching DC, low frequency AC and RF over the last couple of days. The spec on the 44421A card relays is a thermal EMF of under 1 uV. While that won't meet TiN's requirements, for a general bench it is entirely adequate. And the 44421/2A cards have provision for reporting the board temperature which would allow improving the accuracy. The sensor is intended for thermocouples and only implemented on the 44422A terminal block. But the jumper provisions on the relay card would easily allow placing a sensor on the relay card itself.Full bench calibrations are a very different subject from the problem of providing access to basic references which is what the Cal Club is all about. Closely related in that you need the latter to implement the former. But still very different.

author: TiN
author_rank: Super Contributor
timestamp: August 03, 2019, 03:20:34 pm
content: No need to wait for my input, as I'm sadly do not see need of additional complications / components to existing Cal Club R2 necessary. What is needed instead - unified data storage, analysis toolkit and error budget analysis, established by members, so everyone onboard know what is the state of things/condition of references at each given time. Otherwise it's just random numbers on pretty displays without meaning, and spending even $1 for shipping hardware is not worth the effort. So instead of getting everything even more complex, somebody with web-programming skills could help a LOT to a club to make a simple site, that consolidate results, plot some pretty graphs, and have bill-board information where references are, who is next, who is on the list, status of reference, last calibration data, etc.Even if set of dividers and additional PX references (still have no clue why need 2 additional PX, triplicating need of their calibration work, instead of using same 1 PX + 1 FX combo?) included - it's not like that magically reduce waiting time for participants. Now participant would need measure not just one or two references but four of them, so how that make things faster? Add dividers, now we measure 4 references 5 times each (as for 100mV,1V,10V,100V,1kV range?). I thought Reg was recently saying he had lot of stress (which we want to avoid!) due to lack of time to get everything logging/working right time even just for 1 measurement and two simple instruments, without trying anything on ppm level? Bit lost here, sorry.We are not inventing anything new, BIPM/Metrology labs doing "Calibration clubs" and rounds with references for decades already, so Cal Club idea is just replicating that on much smaller/cheaper level. And if one think waiting time for few months is long, well.. one round between NMIs usually is 2-3 year feat. Again if there is particular need to calibrate cheap meter like 3478A or 34401A, just shipping those to calibration lab is cheaper and faster, than trying that DIY solution.I admire and love idea being to calibrate stuff in-house, but it's investment of time and money far above what most participants are willing to manage, as a hobby. Ask me how I know that...

author: maxwell3e10
author_rank: Frequent Contributor
timestamp: August 03, 2019, 03:41:37 pm
content: I agree that record keeping is the biggest part that is missing so far. As any metrologist knows (which I am not), careful measurements are useless without accurate records. It should be the expectation that members analyse their own data. Keeping a web log would be the best. There was some discussion back on the other thread about what software to use. If there is no dedicated site, then Google sheets would be fine, anything is better than nothing.

author: TiN
author_rank: Super Contributor
timestamp: August 03, 2019, 03:51:24 pm
content: maxwell3e10I'm afraid most hobbyists not doing it (data analysis) because it's the most difficult part of any measurement. I still wrapping mind around some concepts and calculations.We all love to poke buttons and see some warm fuzzy 10.000000 V readings on fancy DMM, but that all useless withoutcomplete measurement witherror factors accounted for.If you open any BIPM comparison result report, you'll see one paragraph about measurement itself, and dozen PAGES for error calculation and uncertainty math.

author: rhb
author_rank: Super Contributor
timestamp: August 03, 2019, 04:41:39 pm
content: The reason for my stress was the length of the waiting list. If it were shorter I would have been comfortable taking more time .Having 3 PX references and 3 voltage dividers shortens the waiting list by dividing it in half. We also gain more data on the effects of transport on references. From what I have read so far, that is poorly understood. With the addition of transit temperature and humidity logging we might learn something.I expect to spend many hours analyzing the data I collected. I am back at home but still recovering from surgery, so that will not begin for a while yet. A friend who is a professor of economics and statistics at Drexel has all my data. I will upload the PX and ratio data to xdevs.com later today.My first order questions are:Is flicker noise zero mean?Is shot noise zero mean?I do not recall any mention of this in anything I have read so far on either topic. And found nothing in my library during a search earlier this week. So my question to my friend was how does one prove mathematically from the data that a noise process is zero mean in the case of an arbitrary noise process.If someone has references which discuss either, please post them.The only way to get hobbyists to perform PhD level data analysis is to package the requisite mathematics in a piece of software. I spent my career doing that sort of thing. I would not trust anything other than bespoke software for such work. My friend published quite a few papers on gross mathematical errors in Excel. It's unlikely that any spreadsheet program would be any better. Most of my time on such work is spent crafting test cases to verify that the software is correct. The second largest effort is determining what the appropriate calculations are. Actually writing the software takes the least time.

author: SilverSolder
author_rank: Super Contributor
timestamp: August 03, 2019, 06:26:47 pm
content: What math errors are there in Excel (that are not related to its max 15 significant digit maximum)?

author: maxwell3e10
author_rank: Frequent Contributor
timestamp: August 03, 2019, 06:41:29 pm
content: Just like on the equipment thread there are endless arguments about low-end scopes, one can have endless arguments about software.There are many choices of free software for data analysis. I personally use Genplot:www.genplot.com. For something like Allan deviation there are also free analysis tools:www.alamath.com. A lot of other things is just simple record keeping. We are not talking about proper metrology type A and B uncertainty evaluation here. At a basic level, any software can calculate average and standard deviation.

author: Grandchuck
author_rank: Super Contributor
timestamp: August 03, 2019, 08:00:54 pm
content: My thoughts:1/ The person in the center of the star (vindoline currently) should not bear any shipping costs.2/ Round 2 should finish with no changes (unless necessary due to failures, etc.).3/ Round 3 could be diversified according to interests and accuracy needed.

author: rhb
author_rank: Super Contributor
timestamp: August 03, 2019, 08:34:15 pm
content: I've never read Bruce's papers on Excel. We're both pretty intense math wonks who met in Bill Guy's 2 semester Integral Transforms course at UT Austin 30+ years ago. So we only chatted on the phone very briefly about the issues before moving on to more interesting stuff. He was fed up with reading papers with major errors resulting from the author's use of Excel and went on a campaign to embarrass people out of using Excel as the basis for professional papers in economics and statistics.I'll ask him for copies. They were pretty serious issues. These were published in refereed journals. So *not* minor errors.I am interested in getting all the information out of the data possible. I've been very frustrated by plots without data I could analyze independently. I'm fairly certain I can correct aging errors for a period equal to the length of prior data. But have been unable to get access to the multiyear data I need to demonstrate doing that. I'm a retired research scientist, so not a typical hobbyist (except around here where members with PhDs are amazingly common). But I am pursuing metrology lab level analysis even if I don't have access to metrology lab grade references.After all, I could reference my entire lab to any approximately correct standard for the volt, ohm, second, etc and all my repair and design calculations would come out fine as long as the implied definitions for each instrument were the same.As the title states, my proposal is for Round 3, though we might shorten Round 2 if we get the additional PX references ready before then. Those at the end of the Round 2 list won't get the kit until next year.Have Fun!Reg

author: hwj-d
author_rank: Frequent Contributor
timestamp: August 03, 2019, 10:29:19 pm
content: Quote from: rhb on August 03, 2019, 01:19:46 pmI see.

author: dacman
author_rank: Frequent Contributor
timestamp: August 05, 2019, 03:13:32 am
content: In Excel 2003 Microsoft switched to 2-pass statistical functions. 1-pass functions, which some calculators use, are sometimes not as accurate. (HP calculators that store arrays use 2-pass functions.) For standard deviation, for the 1-pass function, each number gets squared. It can take 30 digits to hold the result of a 15 digit number that is squared. If the deviation is beyond about the seventh digit then the deviation will not be seen by the 1-pass function. (A deviation in the 15th digit will be seen by the two-pass function.) If the interim results of the 1-pass function were used to 30 digits, then it would give the same results as the two-pass function. One workaround was to use offsets. For example, if a 10 MHz oscillator was being analyzed for stability, 10 MHz could be subtracted from each measurement. Earlier versions of Excel would then give accurate results if the offsets were analyzed.

author: SilverSolder
author_rank: Super Contributor
timestamp: August 05, 2019, 07:10:31 pm
content: Perhaps it is not completely crazy to use Excel to analyze results, it could even be done with some macros or VB routines that everyone shares, to guarantee consistent / comparable results?

author: CatalinaWOW
author_rank: Super Contributor
timestamp: August 05, 2019, 08:29:19 pm
content: I am often an advocate for Excel as it is almost universally available in corporate environments, and generally works well enough. It does have real limitations on large data sets, so I really recommend listening to and evaluating other options.

author: rhb
author_rank: Super Contributor
timestamp: August 05, 2019, 08:31:54 pm
content: Octave or R are both free and much better suited to the task. R is a professional statistician's tool.Properly analyzing such data is far more work than most would imagine.Each DMM has a temperature and humidity dependence which must be removed from the data as does each reference. There are two of everything in a single measurement series. Two shot noise series, two and possibly as many as four 1/f noise series, thermal EMFs, etc. I don't even have a full list yet.I *think* I have enough data to solve for all the terms, but I might not. I was not prepared for getting the kit and had to make things up on the fly. My data might not be useful for anything other than saying that the 10 V range on both my 34401As still meets spec.I think I might get away with being underdetermined on the 1/f processes, but for most of the stuff you have to be evendetermined to separate the DMM reference from the transfer reference.

author: rhb
author_rank: Super Contributor
timestamp: August 06, 2019, 11:41:16 am
content: Here is a list of Bruce's papers on Excel. I asked if I could post copies and was told that would lead to trouble with the publishers.I don't like spreadsheets because they are very difficult to check and very prone to user error.H.-J. Sun, Kaoru Fukuda and B. D. McCullough"Inaccurate Regression Coefficients in Microsoft Excel 2003: An Investigation of Volpi's Zero Bug"Computational Statistics 32(4), 1411-1421, 2017B. D. McCullough and David A. Heiser"On the Accuracy of Statistical Procedures in Microsoft Excel 2007"Computational Statistics and Data Analysis 52(10), 4570-4578, 2008B. D. McCullough"Microsoft Excel's 'Not the Wichmann-Hill' Random Number Generators"Computational Statistics and Data Analysis 52(10), 4587-4593, 2008B. D. McCullough"The Unreliability of Excel's Statistical Procedures,"Foresight: The International Journal of Applied Forecasting 3 , 44-45, 2006B. D. McCullough and Berry Wilson"On the Accuracy of Statistical Procedures in Microsoft Excel 2003,"Computational Statistics and Data Analysis 49(4), 1244-1252, 2005B. D. McCullough"Fixing Statistical Errors in Spreadsheet Software: The Cases of Gnumeric and Excel"CSDA Statistical Software Newsletter (2004)www.csdassn.org/software_reports.cfmB. D. McCullough and Berry Wilson"On the Accuracy of Statistical Procedures in Microsoft Excel 2000 and Excel XP,"Computational Statistics and Data Analysis 40(4), 713-721, 2002B. D. McCullough"Does Microsoft Fix Errors in Excel?"in Proceedings of the 2001 Joint Statistical Meetings, [CD-ROM]Alexandria, VA: American Statistical AssociationB. D. McCullough and Berry Wilson"On the Accuracy of Statistical Procedures in Microsoft EXCEL 97,"Computational Statistics and Data Analysis 31(1), 27-37, 1999

author: bitseeker
author_rank: Super Contributor
timestamp: August 07, 2019, 05:35:13 am
content: Thanks for the references, Reg.Now, for the hard question: How many of these have already been fixed and in which versions?

author: SilverSolder
author_rank: Super Contributor
timestamp: August 07, 2019, 09:30:19 am
content: Thank you @rhb for opening my eyes to the many shortcomings of Excel for statistical work, which I was not aware of at all.It seems clear that for statistical analyses beyond basic descriptive statistics, Excel is not the best choice.What Excel has going for it, is the fact that it is far more widely used than all the professional level tools put together, so does not have much of a learning curve for most people. It also appears to be true that as long as you don't venture too far away from high school level statistics, you'll probably be fine with respect to the quality of the results.I guess the real question is if calculating the noise of a reference or a DMM requires anything more sophisticated than mean and standard deviation, necessitating the use of more advanced tools?Even the more advanced metrology topics like Allen deviations etc. could be implemented as a formula or even a VBA function, avoiding the use of any built in functions?Signed:Result oriented of Wichita, Kansas

author: rhb
author_rank: Super Contributor
timestamp: August 07, 2019, 12:38:08 pm
content: I'm just getting warmed up on analyzing my data. Give me a month or two to peel away the layers of the onion. So far all I have done is prove that the noise is Gaussian.My goal is to quantify and predict reference aging and hysteresis. I've got a *lot* of work to do to get to that level of error.I did a spreadsheet to model a business turnaround using OpenOffice. I found the spreadsheet UI pretty scary from a correctness perspective. It's extremely difficult to verify that all the fields in a complex spreadsheet are being calculated correctly. However, that was also my first and only attempt to use a spreadsheet. Normally I use C, FORTRAN, awk, etc. So an experienced user might do better.However, I still would not want to board an airplane designed in a spreadsheet.

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: August 07, 2019, 01:14:37 pm
content: Ha! You probably already have. I use Excel almost every day and have never had an issue with non-statistical functions, even out to many significant figures. I will say the graphing is lousy for many of the things I do, and gnuplot usually comes to the rescue there. Without Excel and programming languages I'd be a ditch digger, since I can't remember which variable is what for more than seven seconds. I use a LOT of comments and notes in anything I do. I'm also not above throwing in an extra equation or two, to calculate something using a different method, to see if at agrees with my main program.

author: rhb
author_rank: Super Contributor
timestamp: August 07, 2019, 01:45:11 pm
content: I'm all too acutely aware of the propensity for engineers to use Excel. I've also had to sit on the tarmac while they rebooted an Airbus plane.

author: SilverSolder
author_rank: Super Contributor
timestamp: August 07, 2019, 02:11:38 pm
content: The software revolution is definitely both good and bad... (mostly good, I would add!)

author: tomato
author_rank: Regular Contributor
timestamp: August 07, 2019, 04:45:49 pm
content: Quote from: rhb on August 06, 2019, 11:41:16 amWho publishes a paper about software that's 14 years (and 4 generations) out of date?

author: bitseeker
author_rank: Super Contributor
timestamp: August 07, 2019, 08:17:18 pm
content: Academic papers, journal articles, etc., are about digging into subjects of interest. Time is not necessarily a factor.From a practical standpoint, though, it would be nice to know how many of these issues still exist. Having used Excel since its very first version, I've seen bugs linger for decades, so anything's possible.

author: tomato
author_rank: Regular Contributor
timestamp: August 07, 2019, 09:11:21 pm
content: Quote from: bitseeker on August 07, 2019, 08:17:18 pmTime may not be a factor, but academic papers should betimely.QuoteYes, that really is the point. A paper published in 2017 should have looked at Excel 2013 or 2016, not Excel 2003.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: August 07, 2019, 09:38:33 pm
content: Private individuals and universities with limited budgets may well still be using Excel 2003. Not wanting to pay for the upgrades. Or not wanting to learn a new user interface.You only have to read this forum to find numerous individuals using software dating back to the start of this century for a variety of reasons.

author: rhb
author_rank: Super Contributor
timestamp: August 07, 2019, 09:54:04 pm
content: It might be appropriate to read the paper and find out why it was written before making statements based only upon the title and when it was published.I'm not aware of a statute of limitations that says that an error in a paper published over x years ago is no longer an error. Authors have been known to publish erroneous conclusions. The reason it is wrong might not be found until many years after publication.It's quite common for grad students to find such errors during the work for their dissertation and be obligated to correct the prior author in the process of supporting their work. So they have to write a minor paper to document the issue to satisfy their committee.Everyone who gets a PhD is very familiar with the routine. It is standard practice. If you obtain results which contradict prior work, you have to prove the prior work was wrong and explain why.

author: tomato
author_rank: Regular Contributor
timestamp: August 07, 2019, 09:57:09 pm
content: Quote from: CatalinaWOW on August 07, 2019, 09:38:33 pmDoubtful. Regardless, analyzing software that is 4 generations old has limited utility.

author: SilverSolder
author_rank: Super Contributor
timestamp: August 08, 2019, 05:55:22 am
content: Would be good to have some simple, easily verifiable worked examples that we could try in Excel (using whatever version we have) to check whether there are significant problems.

author: rhb
author_rank: Super Contributor
timestamp: August 08, 2019, 12:28:45 pm
content: Quote from: SilverSolder on August 08, 2019, 05:55:22 amThat's what Bruce did. There are a number of canonical datasets in statistics which have been exhaustively analyzed. He used some to test Excel. I've asked if he has an Excel file I can post.Here's a link to Bruce's homepage:https://www.lebow.drexel.edu/people/brucemcculloughYou can read the abstract of the paper that my personal troll, @tomato, complained about. If you check his posting history you will see that his sole interest on the forum is harassing me. Which must have been very traumatic when I went on vacation for a couple of weeks at the end of June and did not post anything.The problem of irreproducible results is a very serious issue in the research community. There are a lot of people clamoring for archiving all the software and data used in a paper. It is depressingly common that others are unable to replicate published work. Jon Claerbout of Stanford was one of the first when he found that his grad students could not reproduce the work done by a previous student of his.

author: tomato
author_rank: Regular Contributor
timestamp: August 08, 2019, 03:26:39 pm
content: Quote from: rhb on August 08, 2019, 12:28:45 pmMy post had absolutely nothing to do with you. Get over yourself.

author: rhb
author_rank: Super Contributor
timestamp: August 08, 2019, 04:00:47 pm
content: A reply from Bruce.QuoteSure, @tomato. What ever you say. However, anyone can look at your posting history just by clicking on your user name and the "show posts" tag.

author: tomato
author_rank: Regular Contributor
timestamp: August 08, 2019, 04:30:13 pm
content: Quote from: rhb on August 08, 2019, 04:00:47 pmSeriously man, get over yourself. You've made 600 posts in 2019. I've made 50 posts in 2019, and the majority have nothing to do with you.

author: Tj138waterboy
author_rank: Regular Contributor
timestamp: August 10, 2019, 11:56:04 am
content: Quote from: rhb on July 31, 2019, 10:47:38 pmWould there be horrible consequences in adding a ina106 on the output as a switchable 11-1 divider as per datasheet example or would it make more sense just to roll your own?

author: rhb
author_rank: Super Contributor
timestamp: August 10, 2019, 03:52:11 pm
content: After much thought on my part and little comment from TiN and Andreas, to whom the question was largely directed, I concluded that a 150K-100K-10K-1K divider made from good grade metal film or wire wound resistors with banana jacks at the nodes in the divider is the most economical option if using a 7 or 10 V reference. All additional electronics adds noise.Metal foil would be nice, but aren't really needed. What matters is stability, not precision values. By adding small wound copper resistors in series the TC can be nulled.At the moment a reliable RTC-T-H-GPIB interface is at the top of the list. I discovered another Tempduino issue while working on my PX/FX ratio data yesterday.I've got all the parts I need for the logger now, but first I have to fix some bugs in a 15 year old research code I wrote for a major project for big oil.

author: Tj138waterboy
author_rank: Regular Contributor
timestamp: August 10, 2019, 05:33:10 pm
content: You seem to be working on 2 seperate dividers. One for px and one for fx. I was generalizing my question too broadly. From the spec sheet pg5 Referring to Figure 1, the CMR depends upon the match ofthe internal R4/R3 ratio to the R1/R2 ratio. A CMR of 106dBrequires resistor matching of 0.005%. To maintain highCMR over temperature, the resistor TCR tracking must bebetter than 2ppm/°C. These accuracies are difficult andexpensive to reliably achieve with discrete components.Am I correct to assume this is stating that the resistors inside of ina106 are matched to 0.005% and tcr tracking better than 2ppm? If so I would think that the tradeoff of an ots componet like this would at worst be a temporary solution in lieu of trying to find a good match through the hoffman mini lab method.

author: rhb
author_rank: Super Contributor
timestamp: August 10, 2019, 07:15:38 pm
content: OK complete misunderstanding. I was talking about an external divider to drop a 7 reference to under 3 V which is the full scale for the 3478A and to scale voltages to lower scales. This is part of doing a separate PX only track for lower end DMMs so as to reduce the length of time for a cal round. I'm hoping this becomes an annual ritual.I'm unclear what "ina106" is. I'm also unclear which datasheet you are referring to.

author: tomato
author_rank: Regular Contributor
timestamp: August 10, 2019, 07:58:55 pm
content: Quote from: rhb on August 10, 2019, 07:15:38 pmAn INA106 is a differential amplifier made by Burr-Brown/TI. Google will give you a link to the data sheet.

author: hwj-d
author_rank: Frequent Contributor
timestamp: August 10, 2019, 08:13:10 pm
content: Quote from: tomato on August 10, 2019, 07:58:55 pmYes, and what a coincidence, it is (t)herehttps://www.digikey.de/product-detail/de/texas-instruments/INA106KP/INA106KP-ND/251075

author: TiN
author_rank: Super Contributor
timestamp: August 13, 2019, 04:35:17 am
content: I have a few suggestions for Round 3 :* Allocate time-slot for every participating member, so there are somewhat scheduled in-outs. This can help to align calibrations if somebody has specific times when gear calibrated annually, so USAC travel refs can benefit from recent calibrations.* Mandatory listing of equipment that each member have available for measurements. Also, calibration history/traceability attached to each equipment would be great to know. If the member does not have recently calibrated gear, that's ok, can list the latest known calibration instead.Ideally, this information can be useful to estimate the uncertainty of each member over the round, and gain better confidence in travel transfers.Another suggestion is to suspend shipments during the cold/hot season (e.g. ambient <+10°C or over +40°C), to avoid thermal/humidity stress to the references unless shipping out and shipping in members have high-end calibrated standards in-house to verify the shifts accurately.

author: rhb
author_rank: Super Contributor
timestamp: August 13, 2019, 01:21:22 pm
content: I very much agree with TiN's comments. It requires some prior planning, but nothing very difficult to accomplish.Suspending all shipments during hot & cold periods will severely limit the number of cal runs. However, if we have a southern and northern tier hub we could extend the travel period by doing the northern tier in the summer and the southern tier in the winter with due attention to the weather forecast so that things are not shipped when the forecast is unfavorable. I think that there should be tighter restrictions on when the FX & PX reference kit is shipped. If we have the three PX references I proposed that would not impede the schedule excessively. USPS Priority Mail seems to be pretty reliable and NWS forecasts for the next 3-4 days also pretty reliable.I was a bit disturbed to find myself receiving the references in July The inside of a truck can reach ~60 C in the summer in the southern US even when the outdoor ambient is below 40 C. We had an office move when I lived in Dallas and all our Sun workstations spent the weekend in a moving van. Not a single system would boot on Monday morning until I went around and reseated all the internal cabling. The truck temperature is a wild guess, but when Motorola made the first transistor car radios, they were quite surprised at the number of failures. Until someone went out to the parking lot, put a thermometer under the dashboard and discovered it was over 135 F (57 C)I am working on a T&H logger. It's been several years since I last messed around with MCUs so I've got a lot of paging to do. But I have some FRAM based MSP430 dev boards which should be good candidates. However, at the moment I don't even know what I have, much less the capabilities of the boards. To add to the fun, the system disk I was using for MCU work died and I did not have that work backed up. So I'm starting from scratch. But I'm hunting down RTC and T&H sensor documentation for the units I have on hand.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: August 13, 2019, 07:35:20 pm
content: Quote from: rhb on August 13, 2019, 01:21:22 pmAny attempt to split into northern and southern tier clubs would have to carefully account for the shippers movement strategy. As everyone knows all US FedEx packages go to a single point for sorting and distribution. All of the other shippers have their own somewhat similar strategy. The long distances in the US mean that cargo in air freight can to very low temperatures at any time of the year. And finally, truck cargo compartments can reach truly amazing temperatures in the summer in all of the continental US. Dry, clear air leads to really impressive thermal loads.

author: SilverSolder
author_rank: Super Contributor
timestamp: August 13, 2019, 08:04:05 pm
content: Is the temperature in the cargo hold of a plane as tightly controlled as the passenger compartment? I have heard stories of items freezing inside checked luggage so perhaps large temperature swings are a normal "fact of life" of air cargo transportation?Then there are the pressure differences experienced during flight - what is the influence of that? Humidity changes?Mollycoddling a set of references could get complicated...

author: RandallMcRee
author_rank: Frequent Contributor
timestamp: August 13, 2019, 09:28:58 pm
content: I think it was earlier in this thread that the point was made that things should be kept simple.Its pretty much impossible to guarantee any sort of thermal control over packages short of herculean efforts.In my view, we should just use this as an opportunity to investigate the possible effect that thermal changes might make on the PX and FX references. I sort of thought that is exactly why we return them to the gatekeeper each time.One fairly simple thing we could do is a battery-operated temperature logger in the cal club package. Btw, the package itself is already well insulated. So there is that.

author: rhb
author_rank: Super Contributor
timestamp: August 13, 2019, 09:46:41 pm
content: How often do we want to log and for how long? An MSP430FR2433 with an RTC running draws 750 nA typical. So we should be able to log for the cell shelf life using a single CR2032 coin cell.It's got around 15 KB of FRAM so we could comfortably store a 4 byte time, 2 byte temperature and 2 byte humidity once a minute to FRAM and then once a day copy the FRAM contents to an external flash memory device. A 32 MB device would store almost 8 years of data.The TI dev board is ~ 6 x 7.5 cm, however, a custom board could be made the size of a CR2032 holder.This solution would have the advantage of providing a lifetime reference history rather than just transit logging. By using a larger flash device we could store voltage reference data on it also at each measurement location.

author: bitseeker
author_rank: Super Contributor
timestamp: August 14, 2019, 12:06:22 am
content: That sounds like plenty of temperature history, but I'm no expert.

author: zekeymonkey
author_rank: Newbie
timestamp: August 14, 2019, 12:13:11 pm
content: Quote from: rhb on August 13, 2019, 09:46:41 pmLooking at the pictures of the packaging, it's hard to believe the thermal time constant of package would be anywhere near as fast as 1 minute. For logging shipping temperatures, once a minute is probably excessive, but having the extra data can't hurt. If the same measurement is used during reference measurement, faster data may be useful.Of course, when you're talking about tracking the temperature and humidity over such a long period of time and varying conditions, drift of the sensors may become of concern depending on the accuracy desired.

author: rhb
author_rank: Super Contributor
timestamp: August 14, 2019, 02:08:35 pm
content: For reference environmental history, 1 minute is more than needed in most cases. But a package sitting in bright sunlight on a hot day in Texas will get warm very quickly.For data collection I plan a different solution. This is *just* for long term monitoring of references. If someone will do a dedicated board once I have a working prototype, I'd like to mount a dedicated logger on each reference.For the measurements it's very desirable that all the readings are taken at the same time via a GPIB group trigger event. So integrating time, temperature and humidity into a GPIB-USB or GPIB-LAN interface is very desirable.However, as experience has shown in Round 2, lots of things can go awry. So a dedicated Pi or Beagle based data collection system might be worth considering. I think we'll know a lot more by the end of Round 2.

author: MaxFrister
author_rank: Regular Contributor
timestamp: August 14, 2019, 04:31:44 pm
content: These are supposed to be suggestions, right?Most of us have not yet seen the round 2 equipment. It seems vastly premature to be planning (and implementing) round 3 changes.I think a battery operated shipping logger seems okay in theory, but someone would need to research how that effects shipping. My understanding is that anything with a lithium battery (including coin cells) must be in the off position for shipping and can not fly on passenger airplanes.I think integrating environmental monitoring, let alone gpib interfaces, into every reference is a bad idea. I'll be happy to discuss this further later in the current round.

author: rhb
author_rank: Super Contributor
timestamp: August 14, 2019, 05:22:24 pm
content: It takes quite a while for things to actually get done. Which is the entire reason for starting the discussion now.CR2032 cells are rated at 235 mAh. That's not large enough to be an issue. I don't know the exact limitation, but I received 6 RTCs all equipped with CR2032s via USPS a few days ago from CA.I'm *not* suggesting building GPIB-USB or GPIB-LAN interfaces for *each* reference, much less into them. I'm suggesting that a compact logging system that traveled with the references would improve the quality of the data collection. Particularly if it logged all data to an SD card which could be mounted as a mass storage device via USB or WiFi without being removed from the data logger.I fully expect things to change as we gain experience in Round 2.

author: FriedLogic
author_rank: Regular Contributor
timestamp: August 15, 2019, 04:17:29 pm
content: Different carriers have different rules, but even small cells can have restrictions. Might it simplify things to use small alkaline batteries instead?

author: CalMachine
author_rank: Frequent Contributor
timestamp: August 15, 2019, 04:27:58 pm
content: Quote from: MaxFrister on August 14, 2019, 04:31:44 pmQuote from: MaxFrister on August 14, 2019, 04:31:44 pm

author: rhb
author_rank: Super Contributor
timestamp: August 15, 2019, 05:27:30 pm
content: Quote from: FriedLogic on August 15, 2019, 04:17:29 pmWe are in the USA using USPS flat rate shipping. Alkaline cells would certainly work. But the USPS doesn't seem to have an issue with small lithium cells. Big ones are a different story. I used the CR2032 as an example for calculating allowable drains for an MSP430 based logger. I had 6 of them sitting on my bench which had arrived a few days ago via USPS. 235 mAh is a rather small amount of power. The datasheet says ~1% self discharge per year. So I thought that an excellent design metric, nothing more.The point is not the source of power. The point is to actually have a *complete* temperature history for the references. It was officially 104 F in Austin yesterday where @cellularmitosis lives. I'll let you speculate on what the back of a truck carrying mail to Austin is. It's 4 hours from DFW to Austin driving down I-35. That mail does not go by air.Rather than people speculating without even basic information, how about we measure and record actual data?

author: CatalinaWOW
author_rank: Super Contributor
timestamp: August 15, 2019, 06:05:24 pm
content: If you want a very small sample set which is virtually guaranteed not to see extreme possibilities build a recorder. You can at least look back and say something happened and confine your speculation to what effects what happened might have had. If you want to have a pretty good idea of what the possibilities are the attached document is a pretty good resource.

author: rhb
author_rank: Super Contributor
timestamp: August 15, 2019, 10:50:45 pm
content: That's useful information, but it doesn't tell anything about the inside of a truck sitting in the sun. Or an attic. Dad and I once found a thermometer in an attic where we were working which had exploded. It read to 120 F. The end was blown off. The cold extreme is well documented by the publication you linked, which I've saved as it's potentially very useful, but it says *nothing* at all about the limits of high temperature. A flat black box sitting in full sunlight at 120 F ambient will be too hot to pick up with bare hands and probably reach well in excess of 160 F inside.I grew up dealing with having to enter spaces where the heat was potentially lethal. And about once a year in the southern US, some fool leaves a child or animal in a car for a few minutes to run in the store. And comes out to find the child or animal dead. Animals dying don't make the news, so I'd bet that happens a lot more often. But the dead baby is far too common.In any case, what matters is not what *might* happen to a voltage reference, but what *has* happened. And the only way to know the latter is to record the information.My interest is the continuum mechanics of the reference device. In particular the thermoviscoelastoplastic deformation of the metalization layer and the bond wires. FWIW I did *not* make up the alphabet soup adjective. That's what the mechanics of materials crowd uses for such things. So I'm just conforming to the standard nomenclature.On the other hand, TiN, having contributed a very fine piece of gear is justifiably concerned that it not be abused in transit. I think his concerns should be respected.

author: Tj138waterboy
author_rank: Regular Contributor
timestamp: April 19, 2020, 06:20:22 pm
content: Has any more progress or decisions on round 3 kit or kits been made yet? I would like to know which reference boardsWould be used because im about to bulk order some of Tins designed KX boards possibly as well as ar488 gpib adapters also hamon divider module. Would donate some of each to the cause if needed as well as get feedback on my designed hamond divider.

author: KK6IL
author_rank: Regular Contributor
timestamp: April 21, 2020, 02:22:20 am
content: My reference needs are simple. I have two HP3456's, history unknown, a LM399 reference I built, and had a cal lab measure 15 years ago, and an L&N 10K resistor I've had 50 years. Three circulating PX's would only let me calibrate the 3456's and verify the L&N, but not the LM399.The Cal Club Kit Instructions need to specify the output current allowed from the FX. Can it drive a 3.333K Hamon divider to produce 1 Volt?

author: ArthurDent
author_rank: Super Contributor
timestamp: April 30, 2020, 03:06:32 pm
content: Quote from: KK6IL on April 21, 2020, 02:22:20 amI don't know if anyone else has checked to see how the FX behaves under load because measurements are generally done with as close to no load as possible, or poteniametrically with a sensitive null meter like I did with my HP419 null meter set to +/-3uV full scale (diagram below). Using that circuit I checked my LTZ1000ACH reference against the club's FZ with different load resistors and here is what I posted previously."I decided to check the 2 supplies to see how they reacted to light loads and I knew mine could survive a direct short for some time because I designed the added transistor buffer within the opamp feedback loop to handle a direct short and also protect the opamp. With a 100K load both supplies dropped 1uV; at 10K, mine dropped 10uV, the club’s 20uv; and at 5K, mine dropped 20uV, the club’s 40uV so the output resistance of mine is less than the club’s but neither would be loaded like that in any testing situation."Any load will cause the output to drop and it looks like a 3K load could cause the output to drop more than 50uV.

author: TiN
author_rank: Super Contributor
timestamp: April 30, 2020, 11:18:47 pm
content: FX itself able to sustain high (relatively, 20mA any direction) loads, however it need two additional posts to allow 4-wire connection.Once USA Club reference make its way to me, I will modify it and add those posts to allow use of FX as current source.

author: guenthert
author_rank: Frequent Contributor
timestamp: May 02, 2020, 04:17:16 pm
content: Quote from: KK6IL on April 21, 2020, 02:22:20 amAs has been stated before, you'd want to avoid loading the reference. Instead ('potentiometer method') you'd want to drive the Hamon divider with a beefy (low output resistance), stable, noise-less source (say a lead battery or a precision PSU) which has been reduced (resistance divider or something more fancy) to the voltage of the FX reference (verified e.g. using a null meter or a high impedance long scale DMM).

author: rhb
author_rank: Super Contributor
timestamp: May 03, 2020, 01:59:17 am
content: How many people are interested in RF? I've acquired quite a bit of T&M kit of late. Most is uncalibrated, but I'm working on that.Is there interest in reference capacitors and inductors, noise sources, etc? There's no point in sending such to people who are just concerned with volts, ohms and amperes, but there may be people with a wider range of interests. So I have in mind a 2nd set of stuff.I now have both 4284A and 4285A LCR meters and an 8970B noise figure meter and 346B noise source.Have Fun!Reg

author: bitseeker
author_rank: Super Contributor
timestamp: May 03, 2020, 04:05:47 am
content: I'm no RF guru, but have dipped a toe into the waters. Is there a club-friendly way to source a 0, -10, -20, etc. dBm signal to check calibration (and calibration factor) of power meters and thermistor mounts?My interest here is just to verify that my HP 432A meter and 478A and 8478B mounts are in reasonable nick.

author: rhb
author_rank: Super Contributor
timestamp: May 03, 2020, 02:11:14 pm
content: As a first step, circulating a calibrated step attentuator would provide a start. A signal source gets a bit more difficult because of weight and cost.There are plenty of DC to 2.7 GHz JFW step attenuators on ebay. I've got 4x 0-30 dB by 1 dB and a pair of 0-60dB by 1 dB. They're cell tower surplus.I intend to automate a full annual cal via relays and attenuators once I get my lab set up. So this is an essential step in developing that process.I'll look into what it would cost to have a commercial lab calibrate an attenuator for cal club use.Have Fun!Reg

author: bitseeker
author_rank: Super Contributor
timestamp: May 04, 2020, 02:22:59 am
content: Yeah, a typical sig gen would be too much. I was wondering about something that had a fixed frequency (or set of frequencies) at a given output power. Similar to the cal signal on a spec analyzer. Then, attenuators will get you to other power levels.

author: rhb
author_rank: Super Contributor
timestamp: May 04, 2020, 12:53:46 pm
content: I was thinking *exactly* the same thing last night. While it would be very nice to have a lightweight DC to 2.2 GHz RF synthesizer based on a pair of ADF4351s with proper LP filters and ALC, that would be a substantial design effort. Not something I can undertake at this time. But an xtal oscillator with a carefully designed and implemented ALC would be tractable.I did a bunch of work some years ago on an automated version of the xtal tester Chris Trask designed around a Butler oscillator (differential amp) which incorporated ALC. I could readily make up one of those Manhattan style neatly sealed up in a nice aluminum case. All I would really need to do is refine the ALC circuit. I've got a slew of 40 MHz 3rd overtone xtals with a fundamental frequency around 14.3 MHz.That would put it right in the middle of the HF spectrum and avoids the complications at higher frequencies. For this purpose I'd want to put a very good LP filter before the ALC pick off and probably a 2nd ALC on an output buffer. A single frequency source would be much easier to get a good impedance match on the output. It would make an interesting project which is within range of my limited skills. I'm really feeling the limitations imposed by not being proficient with a PCB design tool.I've started looking for 10 dB and 1 dB step electronically controlled lab grade attenuators for my automated cal system. With those calibrated commercially I can then use them in conjunction with my 438A/8482A and 8648C to calibrate a JFW step attenuator over the full frequency range.I've got several JFW attenuators already. They are nice solid builds and are rated at 2 watts. So they should be pretty immune to accidental damage. They are widely used in cell towers so with patience they can be had cheaply on ebay.A 0 dBm xtal source, 1 MHz - 1 GHz diode noise source, attenuator, a bridge for comparing attenuators and a couple of reference capacitors and inductors would be a pretty decent start at RF cal in a small or medium flat rate box.I have a small ocean of WW II era RF gear Dad left me so a bit of digging should turn up some parts I can package up to General Radio reference standards. They probably won't be any specific value, but they will be very stable. Between my 8753B and 11801 I should be able to characterize any residual parasitic reactances very accurately. Add an MSP430 to report temperature and humidity over a USB serial port and we ought to be able to get pretty decent uncertainties.Have fun!Reg

author: bitseeker
author_rank: Super Contributor
timestamp: May 05, 2020, 06:42:06 am
content: Interesting. Yeah, an RF package for those interested in such things.

author: rhb
author_rank: Super Contributor
timestamp: May 07, 2020, 07:35:06 pm
content: Yesterday I got a Fluke 515A portable DMM calibrator while picking up a Tek 577. Not being at all familiar with it, I didn't realize that the switch knob was missing until this morning. I drove 700+ miles yesterday and was rather tired when I bought it and *really* tired when I got back home after 12 hours of driving.Major lesson, do not buy stuff you've never seen without doing more research. All I knew at the time was it was a Fluke DMM calibrator "as is".However, it turns out that it works. It's got 1980 date codes, so it's old, er, "well aged". But at 10 V my best 34401A reads 10.0033 V.After I buy or make a replacement knob, I'm thinking about sending it for a factory cal and then circulating it to anyone who wants to calibrate their DMMs. General notion is that the person using it pays shipping both ways plus a small fraction of the cost of the OEM cal. Unfortunately, it will not fit in a flat rate box and shipping might be too expensive.I also got an HP 343B-K05 RF reference which provides 0 dBm output at 5 and 50 MHz. According to my 8560A the levels are off, but it was made in 1983.Have Fun!Reg

author: bitseeker
author_rank: Super Contributor
timestamp: May 09, 2020, 04:35:59 am
content: Wow, that's a lot of driving. Neat finds, though.I know what you mean about buying something on a whim without prior research. It's really hit or miss, but sometimes hard to resist.

author: Magnificent Bastard
author_rank: Regular Contributor
timestamp: May 09, 2020, 05:13:06 pm
content: My $0.02 on this:All you really need are some "known" fixed points for voltage, resistance, and temperature. So, a 10V reference, a 10K resistor, and a temperature probe. With just these 3 things, everything else can be derived if needed.Each of these should be designed to be: Relatively low cost (compared to commercial standards), rugged enough to be roughly handled without losing calibration, small enough to be shipped in the lowest cost priority mail package, robust enough to be used by inexperienced people without damage, and stable enough to verify up to an 8-1/2 digit meter (or even calibrate a 3458A if you are lucky enough to own one of those).This suggests: An LTZ1000-based 10V voltage reference, a quad-VHP100 based 10K resistor (similar to Lymex's design), and a PT100 based temperature probe.The voltage and resistance standards should have an uncertainty [k=3] of no more than 0.5ppm, and the temperature probe should have an uncertainty [k=3] of no more than 0.01oC.If a person needs to have more voltage or resistance cardinal points, they would be responsible to create them on their own, using the supplied references as standards.Obviously, calibrating these standards would be expensive. Someone with an SR104 could get that calibrated (about $400 plus shipping and insurance, maybe $800 total), and that should be used to calibrate several in-house 10K standards, as well as the 10K traveling standard(s). Someone with a Fluke 732 could get that calibrated (about $500 plus shipping and insurance-- maybe $1000 total), which should immediately be used to calibrate several in-house 10V voltage standards, as well as the 10V traveling standard(s). Someone with a set of fixed-point cells could calibrate the temperature probe(s). Costs for these calibrations would be shared across the calibration club, and shipping of the traveling standards would be paid (in each direction) by each end user for each use. Calibration of the traveling standards against lab standards before shipment and after return would be done on a volunteer basis by the central hub (which could be one hub that handles all standards, or as many as three hubs that only handle one type of standard).There could also be a down-graded kit for people with 5.5-digit (or less) equipment, consisting of an LM399-based 10V reference, a single VHP100-based 10K resistor, and an 100K NTC-based thermistor probe. This kit would also have a slightly downgraded uncertainty for each standard-- say no more than 3ppm for 10V and 10K, and <= 0.1oC for the temperature probe. This would have a lesser participation cost than the higher level standards.This is how I see it as the only alternative for a serious calibration check among club members-- anything else is just "playing", and provides nearly zero real value other than entertainment.

author: rhb
author_rank: Super Contributor
timestamp: May 09, 2020, 05:54:09 pm
content: Perhaps you should read the USA Cal Club Round 2 thread. That kit is pretty close to what you describe, though neither reference is 10 V. It's quite a lot of work to design and build a device to achieve 30 ppm uncertainties from 10 microvolts to 100 volts which is the basic DC spec for the Fluke 515A.What you describe is useless for anything but DC. Using that to calibrate RF gear would take a lifetime of building instruments. And without a time reference, not even possible. The subject of "metrology" covers a lot more than the volt, ohm, ampere and temperature.I'm not even remotely a volt or time nut. I'm concerned with practical calibration of a lab full of LCR meters, VNAs, spectrum analyzers, RF synthesizers, semiconductor testers, etc. That requires accurate volt and time references, but those alone are quite inadequate. It requires quite a lot more and it is vastly more difficult to get 100 ppm RF measurements than 10 ppm DC measurements. And in many instances national laboratories struggle to get 10,000 ppm uncertainties. Try to find a 0.1 dB step RF attenuator good from DC to 18 GHz. After all, at DC that's just a 0.25% accurate resistor ladder. I want one, but I'm still looking. They may not exist above 6 GHz at any price.I started this thread to discuss aspects of speeding up circulation of the references among people and encompassing at least basic AC measurements up to RF. Primarily the latter.Have Fun!Reg

author: Magnificent Bastard
author_rank: Regular Contributor
timestamp: May 09, 2020, 08:01:44 pm
content: Quote from: rhb on May 09, 2020, 05:54:09 pmUnderstood. Your needs are probably different that most of the people in the Cal-Club I think. When I said "everything can be derived from that" I assumed everyone already knew "...with the proper equipment." A super-accurate GPSDO frequency standard can be purchased off of evilBay very cheap (and everyone should probably have one of these)-- so I did not include that. Thermal based AC and RF standards can be MADE, (again, if you have or are willing to build the right equipment, which includes an FRDC calibrator, etc.-- just like NIST does it). At the end of the day, you still need that DC standard to calibrate the AC thermal converter to. AC and DC current require an accurate shunt-- and you need the 10K standard to derive that (..."with the right equipment"). With a stable power supply and a 100:10:1 divider, you can derive all 5 cardinal points-- 1000V, 100V, 10V (from the standard), 1V, and 100mV. With these and a stable AC power supply, a set of thermal converters (that you can make yourself if you also make a FRDC calibrator)-- you can derive the 5 cardinal points for AC voltage-- and then on to AC current. I never said it would be easy, and I never said that you would not need to make or buy some equipment, but with those standards, you CAN derive everything needed. If you are willing to accept higher uncertainties for the standard for temperature, you can use an distilled-water ice bath and boiling distilled water (pressure corrected) to calibrate an NTC thermistor-- so the calibrated temperature probe is not needed in that case, then you only need the 10V and 10K standard.Here's what I am assuming (and please correct me if I'm wrong)--- most of the people in the "Cal Club" are participating because they want to have an accurate volt and ohm in their lab (for DC and LF-AC work), without having to spend the money to have an accredited Cal-Lab provide that. So, it's kind of a "share the love" project-- one person provides the laboratory standards, get's them calibrated, and everyone shares from that. (OR-- No initial calibration nor bona fide lab standards are required, and everyone just compares each other's readings just for fun and entertainment). I don't think anyone in this club wants to buy or own a professional-grade calibration laboratory-- but building "hobby-grade" equipment appears to be (at least for some people) an interesting pastime. The more equipment you make or buy, the more calibration points you can generate (or measure). Different people will need different calibration equipment based on what they have and what they want to do.For RF, building and calibrating the thermal converters is quite a bit more difficult, as a much more technical FRDC calibrator is needed-- but you can MAKE that if you are so inclined-- and you will STILL need the DC standard to calibrate THAT.I have an idea-- why don't you design some home-brew RF calibration equipment, and post your designs in this forum? Obviously, the uncertainties will not be the same as a good calibration from Keysight, but for hobby purposes you CAN design something that is quite good!

author: TiN
author_rank: Super Contributor
timestamp: May 09, 2020, 08:12:22 pm
content: Can only add to Magnificent Bastard words that having standards is only half of the story. Maintaining history and doing uncertainty budget for all results is remaining half, which somehow very lacking on Cal-Club activities.So it's more of spending pastime than any actual calibrations, which are defined as comparisons between STD and DUT with known uncertainty. And rhb is not correct, one of standards in current Cal-Club R2 kit is in fact 10V

author: Magnificent Bastard
author_rank: Regular Contributor
timestamp: May 09, 2020, 08:30:17 pm
content: Quote from: TiN on May 09, 2020, 08:12:22 pmWell, I didn't mention the "paperwork", because most every engineer I know hates doing paperwork. My wife is an accountant-- she would LOVE to do this stuff. But, you are right. As I said, I doubt people on this board are wanting to own and operate a "real" (accredited) Cal-Lab-- but just want to know (within reason) that they have an absolute value of the volt and ohm in their lab that is close to correct. This, and a warm glass of milk will help you sleep at night...One thing I can think of that is really GREAT, is if you have the 10V and 10K standards, AND you have a 3458A having a dubious calibration state, you *could* use those 2 standards to do an artifact calibration of the 3458A. Maybe not as good as sending it in for a "real" calibration at Keysight, but at least you would know that it is closer to correct (and maybe less "dubious"). This alone would be a valuable service to volt-nuts.That said, IF you are building something for sale that may be adversely affected by your in-house values of the volt and/or ohm being incorrect, then for heaven's sake don't be CHEAP-- get your equipment professionally calibrated at an accredited Cal-Lab! {...sheesh!...}

author: TiN
author_rank: Super Contributor
timestamp: May 09, 2020, 08:51:29 pm
content: Cheap and high-end calibrations are not mixing wellI'd add 1 Ohm standard to have a complete kit, so one can use that with 10V and 10kOhm to perform artifact calibration of 5700/5720A.Then calibrator + 3458A data can be verified against each other and can deliver enough points to keep busy with paperwork and uncertainty calculations until milk glass goes bad.Oh wait....somebody at Fluke calibration facility had same idea....Equivalent for RF world would be calibration kits and high-end VNAs.

author: rhb
author_rank: Super Contributor
timestamp: May 09, 2020, 09:49:39 pm
content: I'd forgotten that the FX was 10 V.I do plan to design low cost OSSW/OSHW RF test gear. That is my primary interest. However, to do that you need T&M kit which is reasonably in cal. It can be done without it, but I would not live long enough to finish the task. Been there and tried that 35 years ago.At present I'm trying to quantify what can be done with existing low cost stuff from ebay. The BSIDE ESR02 Pro is slated for extensive evaluation relative to a 4284A LCR meter and a 4145B semiconductor analyzer. I'll do similar testing of the nanoVNA against my 8753B and 11801/SD-24 with an eye to seeing what I can improve. At least if someone else doesn't beat me to it. I ordered a nanoVNA with the intent of implementing TDR on it, but before it arrived someone had already done it. And quite well. However, I've not seen anyone invoke the shift theorem to solve for the travel time of an event to picosecond resolution. So I may still have something to contribute.Recently I've been playing with a new noise source from ebay with a couple of RTL-SDRs V2 and V3. The V3 has more impedance mismatch than the V2. This appears to be a significant issue with both designs.I know that the noise source is flat from 250 kHz to 1 GHz to within +/- 1 dB which is the spec for my 8560A. It looks flat to within +/- 0.5 dB, but no way to be sure yet. That will have to wait on setting up and calibrating my 8970B with the 346B noise source and measuring the new ebay noise source with that.There is *no* resemblance to the 8560A spectrum when using the spektrum program and the RTL-SDRs. At the moment I don't understand why, though I suspect the front end of the RTL-SDR dongles is anything but constant impedance over the full frequency range. The question now is how to measure that. Ideally with cheap kit. Then comes the question of whether I can correct it without redsigning the entire dongle.I haven't posted it, but I did some TDR with a Tek 11801 and SD-24 of two N-F OSL sets, an Anritsu and a Chinese ebay set. The results were rather surprising. The reference planes for the open and short are different and the Chinese load is pretty crappy, but it looks to me as if I can correct cal kit errors mathematically. I spent a couple of hours on the math a few days ago and it looks tractable.The price of a good quality 3.5 mm set for my 8510C is a strong incentive to see if I can pull off determining a correction for an arbitrary OSL set from first principles without reference to a better set. Very likely I could not use it in the 8510C software and would have to export the data to a PC. But it's quite similar to a standard problem in reflection seismic processing. If it works, it could significantly improve the results from a nanoVNA. Even the SDR-Kits Rosenberg cal set is 2x the cost of a nanoVNA. The idea may not work, but it's an interesting problem.Have Fun!Reg

author: guenthert
author_rank: Frequent Contributor
timestamp: May 10, 2020, 03:48:00 pm
content: Quote from: rhb on May 09, 2020, 05:54:09 pmAll good points, but the time reference is thankfully a solved problem, isn't it? For a modest investment one can easily get a GPSDO which yields exact time +/- a few ns and a 10MHz frequency standard better than 0.1ppb. I'd think only the most ambitious time nuts have more stringent requirements.Given, deriving e.g. a 6GHz signal from that 10MHz standard isn't trivial, but isn't that a very specific need and should that really be part of the travelling calibration kit?

author: Kosmic
author_rank: Super Contributor
timestamp: May 10, 2020, 05:29:13 pm
content: Quote from: rhb on May 09, 2020, 09:49:39 pmThe R820T inside the RTL-SDR was originally made to watch TV not being the front end of a spectrum analyzer. I suspect that a lot of the non-linearity you are seeing come from the IC itself. Also the open source driver everybody use was made before the specs of the R820T & RTL2832U was widely available. When you start crosschecking the datasheet to the implementation you realise it's a miracle that it's actually working. The implementation is full of errors. I started reimplementing the driver some times ago, but like a lot of my project it was shelvedPersonally, I think you would probably have more success implementing your own devices (like this guy:https://hforsten.com/improved-homemade-vna.html) than trying to fix those cheap devices.

author: rhb
author_rank: Super Contributor
timestamp: May 10, 2020, 05:31:30 pm
content: The GPSDO solves time for practical lab cals. I'd expect that anyone concerned about lab cals at RF has one. I have two, one of Leo Bodnar's dual output devices and a multi-output 10 MHz unit.Hard stuff at RF:power/amplitudecomplex impedance (i.e. capacitance and inductance in combination with resistance)I'm sure there are other things, but those are the ones I'm most concerned about at present. The new ebay noise source I've been testing and a step attenuator should cover 250 kHz to 1 GHz quite well for power with the addition of a clean 1 or 2 frequency 0 dBm source. I have a pair of HP DC-18 GHz attenuators which I plan to send to Keysight for cal data so I can cal a cheaper unit for the cal kit. That leaves a handful of stable capacitors and inductors. That will all easily fit in a medium flat rate box.At DC I'd like to see two 1-10-100-1K-10k-100k-1m resistor sets and a 2nd PX reference added with some synchronization of distribution so the PX references and the resistor sets get swapped between the high precision and low precision sets each trip. The voltage references and the resistor set would make it possible with modest effort to calibrate other DMM ranges. Adding a 3 V output to the PX would be very helpful for people with 3478Asas their best meter.I was rather alarmed at a post in the Round 2 thread which appeared to indicate that one person has had the Round 2 kit for 3 months. I hope that is erroneous, but unless there is strong justification for that, measures will need to be taken to prevent a recurrence. TiN contributed a rather posh piece of kit. I'd be very upset if it were stolen. We might need to require security deposits via PayPal to protect against theft and to penalize excessively long possession. I felt huge pressure to turn the kit around ASAP as did Conrad and most others. If someone has a 3458A and environmental chamber I'm fine with their keeping the kit for a longer period. But I think there is an obligation to present data to justify it.I have recently realized that when I get set up, I'll actually have most of a state of the art mid-90's cal lab if I simply get a suitable set of references with NIST traceable cals and correctly implement a test program to compare all my instruments. And suffer through the adjustment process for anything out of spec.My primary interest is making 0.1% accuracy affordably available across the full spectrum of electrical measurements. If that happens I'll push for 0.01%. I'll leave 1 ppm to TiN et al. While I find it entertaining, it's not something I care to spend money on.Have Fun!Reg

author: rhb
author_rank: Super Contributor
timestamp: May 10, 2020, 05:45:13 pm
content: Kosmic,I'm very aware of the history of the RTL-SDR. I'm not trying to fix it, I'm trying to give people a reasonably accurate idea of what it is capable of. There are a lot of people for whom a noise source and RTL-SDR are all they can afford. I want to help them. There was a period of many years when that was my situation.If someone wants to fix the RTL-SDR, I'll do what I can to help. As a first step, I plan to measure the input impedance vs frequency of the units I have with my 8753B VNA and post those results. And see if a pair of RTL-SDRs on the reflected and incident ports of a 60dB.com RF bridge will allow better corrections.Have Fun!Reg

author: Kosmic
author_rank: Super Contributor
timestamp: May 10, 2020, 07:11:14 pm
content: Quote from: rhb on May 10, 2020, 05:45:13 pmFYI, the R820T has been discontinued and is not in production anymore. I wonder for how much time they will be able to produce the RTL-SDR and similar products.

author: rhb
author_rank: Super Contributor
timestamp: May 10, 2020, 10:27:21 pm
content: The devices in the 2 versions I got are marked R820T2. I've not bothered to investigate the chip. I remember the Elonics E4000 chip that got it all started. The future status of the RTL-SDR hardly matters. The SDRplay series is much better. though also more expensive. I only bought the 2 RTL-SDR versions to test them. You can be certain someone will find a replacement.Actually relevant to this thread, I opened up an HP 435-K05 which is 5 and 50 MHz 0 dBm reference sources for a look inside. With modest effort I can repackage it to fit in a small or medium flat rate box. So that neatly fits the requirement for a 0 dBm reference. The 50 MHz 2nd harmonic is 50 dB down and the 7th, 8th and 9the are over 60 dB down. The power and frequency are off, so it may do better after a bit of TLC.Reg

author: rhb
author_rank: Super Contributor
timestamp: May 29, 2020, 02:49:50 am
content: FYIhttps://www.eevblog.com/forum/metrology/usa-cal-club-rf-division/new/#new