Personal lab cal chain - Page 1
Forum section: electronics / general

author: rhb
author_rank: Super Contributor
timestamp: April 27, 2018, 12:43:15 pm
content: I'm curious what people do to maintain their personal instruments. Rather obviously one cannot afford commercial calibration services for a hobby. Do you have an annual calibration protocol for checking your instruments?Time and frequency are easily handled with a GPSDO and a counter. What is the minimum collection of devices to have calibrated commercially to arrive at NIST traceable calibration for a general lab covering DC to 3 GHz?

author: TiN
author_rank: Super Contributor
timestamp: April 27, 2018, 12:56:24 pm
content: Hobby or not, same process and methods apply. It's only question how far one willing to go on. Probably cheapest way to maintain decent accuracy is to have MFC (like 4808/57xx), reference meter (3458A, better more than three to have rotation cals), resistance bridge system (ESI 242), KVD, reference dividers and supporting standards (10K, 1 ohm, 10V and so on). Economically it's is more viable to do annual calibration for standards, and then use them to maintain all lab gear (thanks to ACAL on 57xx and 3458A, that makes things easier). Similar goes to RF side. So your question is too broad to be answered. Minimum and good enough for somebody might be LM399-ref with few VPG/PWW 10K resistors in DIY box, with meter like HP 3456A or K2000 or so, but for somebody else it is five 3458A's, stack of calibrators and set of 5 ESI SR104's. Pick your poison.

author: e61_phil
author_rank: Frequent Contributor
timestamp: April 27, 2018, 01:46:57 pm
content: I think most people here doesn't have a real traceable calibration against NIST or PTB (or what else is your NMI). One can often see people with high end gear which was only compared to some new 6.5 digit meters in the past or something like that.I would like to see a real traceable chain of uncertainties to anyones 100V here or something like that. To have really traceable values it is more than having some high end stuff. You have to do some math.

author: nanofrog
author_rank: Super Contributor
timestamp: April 27, 2018, 02:08:26 pm
content: Quote from: e61_phil on April 27, 2018, 01:46:57 pmThis is my experience as well, including my personal situation.There are some relatively inexpensive voltage references available, such as theDMM Check Plus. Even less expensive ones on eBay (example).I'm certainly interested in getting better standards, but that'll put me into full volt-nut territory, which is a rather expensive rabbit hole to traverse. Not to mention full-on insanity.

author: e61_phil
author_rank: Frequent Contributor
timestamp: April 27, 2018, 02:17:37 pm
content: Quote from: nanofrog on April 27, 2018, 02:08:26 pmI think in the first place it could be very intersting to do some math and see what real uncertainty against your NMI you have with your current equipment. This should be the starting point to decide on which place in your chain an upgrade is most useful.

author: nanofrog
author_rank: Super Contributor
timestamp: April 27, 2018, 02:26:52 pm
content: Quote from: e61_phil on April 27, 2018, 02:17:37 pmQuite true.But the stuff I'm doing doesn't require a lot of accuracy, so close enough will do in my current situation. That can change of course, which means I can't be lazy* any longer, and properly evaluate my equipment.* For example, I'll use a 4.5 or 5.5digit DMM for a measurement of a whopping 3 significant digits, and ignore the rest.

author: TiN
author_rank: Super Contributor
timestamp: April 27, 2018, 03:20:46 pm
content: Most of folks here who participating for hobby purposes, are going after high accuracy, not so much a traceability. These two matters intersect, but not the same things.Few members who actually into this as business needs, well, they will not be talking on their protocols and chains in public forum, but welcome you as a customer

author: e61_phil
author_rank: Frequent Contributor
timestamp: April 27, 2018, 04:15:36 pm
content: Where is the difference between low uncertainty and high accuracy?Or in other words: How can you trust your accuracy without a traceable chain of uncertainty?

author: TiN
author_rank: Super Contributor
timestamp: April 27, 2018, 04:24:07 pm
content: "Easy".. statistics. I have bank of 8 references (measured to NIST-traceable reference, so that is 2 levels down the chain) and 4 meters, and everything agree's to 2ppm.Based on this there is trust that overall measurement accuracy better than 4ppm, at 4 levels down the chain. But none if this is NMI-traceable, as there is no accredited body, with approved transfer uncertainty, so my 4 ppm are as good as bag of toilet paper for any commercial product. For my needs it's good enough, for actual business needs (let's say I'd take money for customer's meter calibration) - completely different story.

author: cellularmitosis
author_rank: Unknown
timestamp: April 27, 2018, 04:54:21 pm
content: Quote from: TiN on April 27, 2018, 04:24:07 pmIn that fleet, if you had at least one ref which was known to drift down (LTZ1000) and at least one which was known to drift up (SZA263), it seems like you could make a stronger claim about that 2ppm agreement (i.e., with only LTZ's, if there was a common-mode drift downward of 1ppm, the actual drift of any one device is -1ppm +/- 2ppm).

author: TiN
author_rank: Super Contributor
timestamp: April 27, 2018, 04:57:26 pm
content: Yes, but it is still not traceable unless you send the ref itself to NMI accredited lab. But then you get into stability of device itself (we talking DIY refs, not decade-proven 732A for a second), so it's all get messy quick.

author: Dr. Frank
author_rank: Super Contributor
timestamp: April 27, 2018, 05:10:02 pm
content: The phrasing of your question sounds a bit like a contradiction in itself:'Personallab chain', vs. 'NIST traceable'.For personal use, everybody in this metrology-nuts group for sure wants to avoid the expensive traceable calibration, I'm sure.That would also be too easy and boring, just to open your pocket for that.In first instance, the goal is to maintain some SI units to lowest possiblestabilityandratio transferuncertainty .Absolute uncertainty would be the 2nd thing, which would either need that fortune of money, if officially traceable, or some helping hand w/o official traceability.Time / the Second, is maintained to about 1e-9 by 2 OCXO, hp10811, inside 5335A and 5370B, to 1e-11by a Rb, EFRATOM FRS, and a Trimble Thunderbolt GPSDO, which also serves as a calibration device down to about 1e-12 absolute uncertainty. Unfortunately, not easily traceable to NIST /PTB, as the USNO does not officially join the UTC network.The counters serve as ratio transfer devices also.DC Volt is currently maintained by 7 continuously running LTZ1000 references @ 50°C, and two discontinuous references, one LTZ1000A @ 65°C inside the 3458A, and a double, stacked SZA263 @ 55°C inside the 5442A.Relative stability is monitored frequently, demonstrating <1ppm/year stability.Ratio transfer is accomplished by 4 AUTOCAL instruments: A DIY Precision Reference Divider for 100:1 and 10:1 transfers (similar to 752A), a DIY decade divider (similar to first decade of a 720A), the 3458A, and the 5442A.Ohm at 10k level is maintained by a group of five VHP202Z with T.C. correction, plus the Fluke 5450A.Transfer from 1 Ohm to 100MOhm is done via the 3458A and the FLUKE 5450A, at the according uncertainty levels, down to 2ppm.Direct Current from 100nA to 100mA is realized by a DIY precision current source; transfer and relative uncertainty by the 3458A, about 10ppm.Next version of this source will include a 7 digit ratio vernier, from 1pA to 1A.ACV from 1mV to 120V is realized by a 5200A, relative uncertainty and ratio transfer done by the 3458A, at about <30ppm for f <1kHz.AC/DC transfer from 1V .. 5V from 10Hz to 100MHz can be done by a NIST Standard Reference Instrument, an SRI 6002 MJTC, to < 10ppm.Alternating Current will soon be realized by an AC U/I converter from the 5200A, ratio and transfer done by the 3458A, again.Absolute uncertainty (not traceable) is imported into my lab by irregular comparisons of references from/with other friendly volt-nuts, who had their instruments calibrated officially, I have to to mention here:The 8508A and an ESI 104 from quarks, a calibrated Geller SVR-T and a 34470A from HighVoltage, acbern measurements on Travelling Standards (LTZ1000A and VHP202Z) by comparison to his 4910 and SR104, and volt-nuts reunions / exchange with Andreas and branadic, who recently measured another set of Travelling Standards (LTZ1000 and VHP202) with a 3458A.These recent transfers have to be repeated at more convenient environmental conditions, to get better results..In19952015, I also had two freshly calibrated 34465A from KS, which agreed to 10V and 10k to less than 1ppm, which is an additional indicator for the uncertainty of my lab 'baseline'.In the end, I'm much more satisfied by the stability and chain transfer uncertainty in my lab, than simply buying absolute uncertainty by official calibration.The exchange with the volt-nuts friends is most satisfying, and should also be intensified.Frank

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: April 27, 2018, 06:43:00 pm
content: At one point I had decent traceability, with one of my three 731 voltage standards and an L&N resistor certified. Frequency you can get from WWVB or GPS. AC you can get from DC. L&C I didn't bother with, though my cal is pretty good on those by comparison with freshly calibrated meters.The fact is, in 40 years of working for electronics firms, even making very precise scientific instruments, absolute calibration to better than about 3.5 digits hasn't been necessary. Relative measurements to a dozen ppm have sometimes been necessary, but you don't need NIST for ratios. They can be established yourself to any degree necessary with relatively simple equipment. Only in times of economic prosperity have the companies I worked for even done proper periodic calibration. The rest of the time meters and such existed in two states; they were either broken, or they were good enough for the task at hand. It sounds awful, but unless one is doing work where there's a legal liability, or an actual consequence of being off by 1%, modern equipment is so stable it rarely needs attention.

author: Andreas
author_rank: Super Contributor
timestamp: April 27, 2018, 06:43:32 pm
content: Quote from: Dr. Frank on April 27, 2018, 05:10:02 pmBack to the future ?

author: eurofox
author_rank: Unknown
timestamp: April 27, 2018, 07:05:19 pm
content: I have a Weston cell, it is more than 30 years old and still deliver the same voltage

author: G0HZU
author_rank: Super Contributor
timestamp: April 27, 2018, 07:34:19 pm
content: QuoteYes, in my case I've been working in the electronics industry since the mid/late 1980s and I've rubbed shoulders with many hundreds of talented engineers from the world of RF/SW/HW/DSP and in all that time I have never seen any of them get remotely interested in any >=5.5 digit DMM each time one of these meters came back from NAMAS/UKAS calibration. So it isn't just me (or you).If I could shake up one thing in the hobby world it would be to get people to lose their OCD fascination with calibration of DMMs or frequency counters or other test gear. It really isn't that critical and DMMs have been boringly brilliant for decades now. I've not adjusted/calibrated any of my DMMs here at home for probably 20 years now and I think they are all still well inside their spec limits.It's easy to conjure up a hypothetical case where accuracy might be important but one has to be careful not to be self deluding... Here at home in >35 years of using DMMs the only time I needed to make a critical voltage measurement was when I was servicing an old lab grade spectrum analyser. I had to measure/adjust several reference supplies to be something like 5V +/- a few mV and I think a 10V supply had to be within 5mV. But even then I suspect I only needed to get repeatability within a mV or so rather than get absolute accuracy. I therefore didn't lose any sleep over any slight shift in absolute accuracy and the old Fluke 45 I used (cost £35 on ebay) was easily good enough for this despite looking like it still had the original factory cal sticker on it from when it was new. Luckily all the measurements appeared to still in spec on the analyser anyway.I think I've had the Fluke 45 meter for 6 or 7 years now and I doubt it will have aged more than 1mV at 5V. I suspect it will still be within about 1mV of 5V in absolute terms but I'm not that bothered.I'm more concerned with measuring ratios so I think it's worth buying a DMM that has decent design integrity rather than send a new/cheap chinese meter away for regular 'calibration'.

author: G0HZU
author_rank: Super Contributor
timestamp: April 27, 2018, 07:52:40 pm
content: For RF stuff I have a suite of precision RF step attenuators that allow me to check the log range of my spectrum/network analysers to a degree of uncertainty that is acceptable to me. I can also cross check the attenuators with a DMM on DC or AC and a decent attenuator should be about the same at DC up past VHF. An RF mixer and a sound card can also be used to check the step attenuator (1dB) steps (or the 1dB steps of an RF signal generator) across a range of 60dB or more at RF frequencies. The key here is that reliable relative measurements can be made here and cross checked.For measuring the frequency response of signal generators (and RF power heads) up into the GHz region I have a precision HP 26GHz Schottky diode detector. For checking the 50MHz 0dBm reference in one of my thermocouple power meters I use an old HP432A power meter and an even older HP478A power sensor and a decent DMM. I also have other cross checking methods for measuring RF power and I'm happy that I can get agreement within about 0.1dB of 0dBm at 50MHz typically each year. None of this requires any test gear to be formally calibrated on an annual basis.For frequency I use my old 198kHz offair standard I designed >25 years ago and this is generally good enough to output 10MHz +/- 0.03Hz on a typical day. Easily good enough to maintain the various 10MHz OCXO references in my RF test gear. Again, nothing here needs to be sent away for formal calibration and the offair standard can deliver 10MHz +/- 0.03Hz within about 2 minutes from a cold start. Much quicker and much more convenient than a GPSDO and no need to leave anything running 24/7. I typically dig out and turn the offair standard on once or twice a year to check a 10MHz OCXO.I think if you find yourself running test gear 24/7 at home just to try and preserve the accuracy of some ultra precise time or voltage reference you maybe need to sit in a quiet corner for a while and contemplate what real world (tangible) value this actually provides to your hobby.

author: rhb
author_rank: Super Contributor
timestamp: April 27, 2018, 07:54:34 pm
content: If you have voltage, resistance and time, can you derive calibration for the rest through a clever series of measurements?

author: Kosmic
author_rank: Super Contributor
timestamp: April 27, 2018, 08:33:56 pm
content: I was wondering if renting a calibrated dmm once in a while was a good option to try to transfer calibration back to your own equipment ?I was planning to do something like that, but didn' t really check how much they charge to rent a dmm.

author: PA4TIM
author_rank: Super Contributor
timestamp: April 27, 2018, 09:18:04 pm
content: a Guildline cabinet with 4 Weston standard cells and known calibration history from new. besides that a bunch of calibrators for AC an DC, a 10MHz GPS standard, a 5 MHz HP, ESI RS1010's, several other standards for resistance, inductance and capacitance, from GR, HP, Philips, Siemens etc, 2 KV dividers (Fluke 720 and ESI decavider), a industrial calibrator that also does temperature.I compare my gear to each other but I have the luxury that I repair calibration gear (amongst other gear) After repair I use it to check my own gear.I do not have anything for pressure (but I repaired several pressure calibrators)I do not do official calibrations, only repairs but sometimes I have to adjust gear so it can be official calibrated.One thing I not read here is the climatising of your lab. I do not have that, I use tables to correct for that as needed. That works for me.

author: G0HZU
author_rank: Super Contributor
timestamp: April 27, 2018, 09:28:35 pm
content: QuoteIt might be cheaper to simply buy an old but decent DMM at auction. Last year I bought an old Keithley 2000 DMM at a company liquidation auction and the UKAS calibration had only expired by a few months. The meter is a bit dirty and it's 20 years old but it only cost me about £60 and I really bought it for the handle/ears/feet kit it had on it so I could use them on my Keithley 2015THD meter.I bought the 2015 mainly to use as a controlled AC generator and a SINAD meter and I've had it now for about 5 years. I did try checking the meters against each other across maybe 1V to 10V and they were within 2 or 3 LSDs on the full display resolution. So this must have been something like 5.00000V +/- 2LSDs for example.Boringly brilliant and I will never need this level of performance in the real world. I didn't bother checking against the old Fluke 45 but I'd expect the Fluke to be within 1mV at 5V. Even this is way better than I need and I suspect the old Fluke 45 has never been for any formal calibration since it was new. It is going to be decades old. If accuracy is more important to you than most but you don't want to spend money on a formal calibration, my advice would be to simply buy several old but decent DMMs that are nicely aged and stable and not bother with a formal calibration unless one of more of them ages and drifts to disagree with the other meters to a degree that bothers you. If it ever happens to one of my meters I'd probably consider scrapping the meter rather than pay to have it adjusted back into calibration. This is because it will probably keep drifting and would be classed as faulty in my eyes. So calibrating/correcting it would be a waste of money.

author: Dr. Frank
author_rank: Super Contributor
timestamp: April 27, 2018, 09:32:28 pm
content: Quote from: Andreas on April 27, 2018, 06:43:32 pmYep, sort of.I'm breeding over some pictures from my 1990-1995 lab, therefore this Freudian Time Lapse.

author: cellularmitosis
author_rank: Unknown
timestamp: April 27, 2018, 10:46:23 pm
content: Quote from: G0HZU on April 27, 2018, 07:52:40 pmCareful, that's a very judgmental and dismissive attitude towards what others consider "fun".Sometimes it isn't about the end result, but rather about having any arbitrary goal, the path to which forces lots of learning and skill building along the way. Chasing precision has forced me to learn a lot about electronics in general.There is no practical point to my chasingthe voltat home.But of course, I can take that a step further. There's no practical point to my learning anything about electronics, or wood-working, welding, etc. I tend to pursue tool building, but it is all a pyramid scheme of building tools to build more tools, or building measurement devices so that I can build even better tools, and on and on.In my several years at playing with electronics as a hobby, I have produced exactly one practical result: I have replaced the capacitors in a computer monitor to bring it back from the grave. From a strictly practical (time-value of money) viewpoint, I would have been far, far better off having spent zero time and money on electronics, and simply purchased a new monitor on the single occasion in which my hobby became practical.But it isn't about thatEdit: There is also the appeal of being able to make something which is "the best in the world" (or at least in the same class). I'd say a number of forum members here aren't far away from that.

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: April 27, 2018, 11:09:39 pm
content: Ha, making fixtures and tools to make more tools is my life.As for climate control in the lab, if it's too cold I put another log in the wood stove. If it's too hot, I put off whatever task needs to be done until fall or winter. Actually, the secret underground lair is usually 68-70F for most of the year.

author: rhb
author_rank: Super Contributor
timestamp: April 27, 2018, 11:46:20 pm
content: I have acquired a 3478A and a 34401A via eBay. Both are accurate to within the meter resolution when checked against a DMMCheck Plus calibrated to 1 ppm a few weeks ago. The last cal for the 3478A appears to have been 2004 and for the 344401A 1999. Wildly lucky or good design and a drift curve which approaches zero after 8-10 years? I'm strongly inclined towards the latter explanation on physical mechanics of materials grounds. But I'll leave that for another time.Aside from DMMs and analog and digital scopes, I have a spectrum analyzer with tracking generator, 3 GHz synthesizer and frequency counter. Also most of the Peak Technology gadgets. I plan to get a power meter and possibly a noise figure meter if I see a need to do that a lot. Otherwise I'll do the calculations myself using a diode noise source or the synthesizer.I have one of Leo Bodnar's pulsers and his dual frequency GPSDO, though I've not setup the latter yet. Nor have I played with my VNWA 3E. Mostly because I've been too busy making space for the new toys.As a personal discipline, I try to be able to fix anything which I use. So I have a lathe, mill, welders,etc. To calibrate my micrometers and calipers I have a set of gauge blocks. I have a 5000+ volume technical library to remind me of how to use the things I have.In the current situation, none of this makes economic sense. But if the day comes when one cannot go out and buy whatever one needs, it becomes extremely valuable. Predicting the future is a fool's errand.Mostly I do this because it's challenging, interesting and might even prove useful some day.I have learned a great deal from failed or abandoned projects. Much of it has proven very useful in completely unexpected ways.But to go back to the original question.With an accurate voltage source, resistor and clock, how accurately can you measure large a capacitor using a fast comparator? For practical use 100 ppm seems entirely adequate across all measurements. For that one needs 10 ppm or better for the primary references as a ballpark guess.So by way of a concrete example, has anyone put a good quality air variable in a hermetic enclosure with the rotor locked, pulled a vacuum on it and measured it using a precision resistor and a GPSDO? And then used that in a bridge to calibrate an inductor? How well did it work?The result is of only minor interest. The skill to do it is what I find appealing. TiN and Andreas are more narrowly focused, but I find their work quite impressive. I was conditioned by my father's example to be able to do everything. I'm also getting my nose rubbed in the frailty of human memory on a regular basis.

author: zhtoor
author_rank: Frequent Contributor
timestamp: April 28, 2018, 12:56:05 am
content: Quote from: eurofox on April 27, 2018, 07:05:19 pmi have 6 of them - manufactured in february 2004(will build an oven for them when i get around it - courtesy of @blackdog / Bram - an excellent teacher of ovens.)https://www.eevblog.com/forum/metrology/poor-man-gets-his-candies-(6x-weston-cells)/msg1333980/#msg1333980best regards.-zia

author: quarks
author_rank: Frequent Contributor
timestamp: April 28, 2018, 04:53:13 am
content: as mentioned before, if you are a hobbiest like me, who is hunting for as good as possible accuracy and not making money with it, you most likely decide to own your own calibration gear instead of spending money for traceability. Also I by now spend a lot more money than I ever would have thought, when I started, for me it was the right way to go.

author: kj7e
author_rank: Frequent Contributor
timestamp: April 28, 2018, 05:29:42 am
content: I'm stuck asking the same question, do I want all my gear to be as close to NIST as possible or just to all agree with each other knowing they are still close to NIST. Ill still send my newer instruments in for factory cal, but it bugs me how they never seem to quite agree down to the LSD.This drive my OCD off the charts;I just picked up my latest bit of metrology gear, a nice Simpson 260-8, I'm just going to use it as my new standard so everything else will now matchIn all seriousness, I forked over some real cash for a meter, many times better than I will ever really need (DMM7510). This is my house reference standard that I fall back on. I know its not perfect or have absolute accuracy to NIST, its even possible my 34465A my even be closer, but I have no way to know for certain, so I have to trust my best meter as my house standard.

author: PA4TIM
author_rank: Super Contributor
timestamp: April 28, 2018, 06:47:11 am
content: Always forget the last digit.A Simpson 260 as golden reference is the way to go, here I calibrate one of my ESI-1010 resistors with my 260. And as you can see, the 1010 is spoton

author: precaud
author_rank: Frequent Contributor
timestamp: April 28, 2018, 03:27:32 pm
content: Quote from: G0HZU on April 27, 2018, 07:34:19 pmTone it down.... you guys are being far too realistic

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: April 28, 2018, 06:02:41 pm
content: No fear, not needing it at work has driven me to ever lower ppm numbers "needed" at home.

author: GEOelectronics
author_rank: Regular Contributor
timestamp: April 28, 2018, 07:25:06 pm
content: "Ha, making fixtures and tools to make more tools is my life."Ditto here.George Dowell

author: FriedLogic
author_rank: Regular Contributor
timestamp: April 28, 2018, 09:22:30 pm
content: Quote from: kj7e on April 28, 2018, 05:29:42 amHi,This might be where the Calibration Club / Travelling Standard approach could be useful. A reference made specifically to travel well, and which is regularly checked against stable references, could be a very accurate way to check calibration.... assuming that anything can be made to travel unknown paths well!I would have thought that it could be made to travel better than a multimeter anyway.

author: acts238willy
author_rank: Regular Contributor
timestamp: April 28, 2018, 10:09:08 pm
content: I see precious metal (copper-plated) in the background...WillyB

author: kj7e
author_rank: Frequent Contributor
timestamp: April 28, 2018, 10:13:32 pm
content: That's to intimidate my projects, they will work right or else...

author: nanofrog
author_rank: Super Contributor
timestamp: April 29, 2018, 08:37:59 am
content: Quote from: kj7e on April 28, 2018, 10:13:32 pmI guess the rest of us are still cavemen by comparison, relying on big freaking hammers.

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: April 29, 2018, 01:16:52 pm
content: I use walls of test equipment to intimidate the circuits. Not that I ever use 1/100 of it, but the weight of it alone would squash any pcb like a bug.

author: zhtoor
author_rank: Frequent Contributor
timestamp: April 29, 2018, 01:22:24 pm
content: Quote from: Conrad Hoffman on April 29, 2018, 01:16:52 pmwe have these here in pakistan for circuit-intimidation (thats me BOOTSTRAPPING the cow)best regards.-zia

author: nanofrog
author_rank: Super Contributor
timestamp: April 29, 2018, 02:36:25 pm
content: Good aim ^.

author: eurofox
author_rank: Unknown
timestamp: April 29, 2018, 03:40:58 pm
content: Quote from: zhtoor on April 29, 2018, 01:22:24 pmClose loop control