'Affordable' Reference Standards to Have On-Hand in a Electronics Lab

[fmashockie]

Hello All! This is my first time posting in the metrology forum.  I apologize if this should belong in the 'Beginners' forum.  But anyway, I guess I have a 2 part question:

1)  I found an old Analogic AN3100 DC calibrator on eBay for cheap.  I figured it could be useful as a precision DC source for calibrating my benchtop meters and power analyzer.  But considering it has not been calibrated in a long time, it will likely require calibration to be of any use.  I attached a screengrab from the manual of needed reference materials.  Haven't been able to find much info on them.  Does anyone know of any alternatives I could look for that might be readily available?

2) In general, I've been looking for precision reference standards for voltage (AC and DC) and resistance.  But everything is very expensive! Is there anything out there that is accurate, but relatively affordable that I could look for to have on-hand in my repair lab?  I'd be interested in DIY kits/solutions as well!

Thanks in advance!!

[Nanitamuscen]

Think about what class of accuracy you need a source. There will be further advice from this.
And what budget do you have for it.

[fmashockie]

Think about what class of accuracy you need a source. There will be further advice from this.
And what budget do you have for it.

Thank you for your reply! So I guess for simplicity, I'll start with the Analogic AN3100.  I've attached the full service manual.  Accuracy is +-50uV.  There is a calibration procedure in the manual.  And it has suggested materials for calibration.  But these do not seem to be available anymore.  Can you provide some alternatives that would work for this calibration procedure?  I'm looking to keep budget <$500.

Thanks!

[Nanitamuscen]

I think you can consider Yokogawa calibrators. Both old versions and more modern ones.
You can also visit the website of the respected Ian Scott Johnston. This person produces small batches of very good calibrators.

[bdunham7]

Thank you for your reply! So I guess for simplicity, I'll start with the Analogic AN3100.  I've attached the full service manual.  Accuracy is +-50uV.  There is a calibration procedure in the manual.  And it has suggested materials for calibration.  But these do not seem to be available anymore.  Can you provide some alternatives that would work for this calibration procedure?  I'm looking to keep budget <$500.

Since you've apparently already acquired it, it would be more useful to consider what you can do with it.  You can verify some of the basic functions of a typical 4.5-digit multimeter, which is a good handheld or low-end bench meter.  You can also use the accurate and stable output for other things, but since we have no idea what you are wanting to do, its hard to know what use the device might be to you.

The device and manual are old enough that the calibration procedures and standards are thorougly obsolete.  The Julie Research items listed in the manual might be found in a museum, but not likely on a metrologists bench.  The way this would be done nowadays would be to simply use a good 6.5-digit DMM (or better) with a recent calibration to verify and adjust if needed.  A cal lab would likely just use their 3458A so as not to have any issues with TUR/TAR or guardbanding.  Professional calibration would probably be pretty cost-ineffective.

Metrology is an expensive  and time consuming hobby!  The best thing I can think of for you to do at or near your budget is to round up a decent condition HP/Agilent 34401A. 

[alm]

I'd say there are three important, somewhat independent, concepts here:

• A stable reference
• The ability to transfer to different ranges / functions
• Traceability to an absolute reference (e.g. NIST)

For DC voltage, the common solution to stability is having a few 10V or ~7V voltage references. On the low end of the spectrum you might have the cheap Chinese AD584 references, then higher you might have AD587/AD588/LT1021-based references (e.g. products by Voltagestandard.com and DMMCheckPlus (previously made by Voltagestandard.com)), and basically the sky is the limit after that. In some cases buying a reference gets you some degree of traceability (Voltagestandard.com and DMMCheckPlus.com will ship you a piece of paper with a presumably traceable measurement), but this doesn't have to be linked. You could build a few references yourself, compare them over time (this will tell you relative drift between the references), and then get one of them compared to a reference with a known value. For example look at the USA Cal Club Round 3 topic.

To transfer to different ranges, I would look into a Kelvin Varley Divider (like Fluke 720A, ESI RV722A or the Julie Research VD106) or a Hamon divider (like Fluke 752A) and a null meter. A DMM could make a null meter if the bias current is low enough (you can measure this), but in general an analog dial is easier to use if you're adjusting trimmers until it reads 0. A good explanation and instructions on how to build some of these is Conrad Hoffman's Mini Metrology lab. The trick here is that the voltage dividers (the Fluke 720A or Hamon divider) can be self-adjusted so they provide an accurate ratio without any external validation. Same with the null meter. This makes your DCV reference the only thing that needs external validation.

AC is much more difficult than DC. There are some solutions that transfer an AC value to a DC value, like Thermal Voltage Convertors or the old Fluke 540B. But they themselves need calibration. And to calibrate many multi meters you need a variety of voltages and frequencies, so you need an ACV calibrators (which are generally expensive boat anchors like the Fluke 5200A or Datron 4200A) in addition to the AC-to-DC transfer. So I'd suggest starting off with DCV and forgetting about ACV for the moment.

[fmashockie]

Wow thank you so much alm.  I really like the idea of trying to build some of these myself.  You gave me a few resources to get started with that! 

Thank you to everyone else as well! I have heard of Ian Scott Johnston's precision voltage reference.  They seem pretty affordable, too.

[dmmguy]

Hi, maybe you can begin with these if you only want to test your DMMs

https://www.ebay.ca/itm/155763974742

https://www.ebay.ca/itm/155751553394

[Alex Nikitin]

The Analogic you have now is a potentially very nice voltage source and to re-calibrate it you only need an access to a freshly calibrated 6.5 digits or better voltmeter or, at the very least, a calibrated 10V reference + a sensitive voltmeter (a "null-meter) which could resolve at least 1uV. . The unit is however very old and most likely needs some TLC, possibly new electrolytic caps. The most precious parts of this unit are the resistors set and the switches. If these are performing well and not damaged, you should be able to restore (or even improve) this reference to be a very useful tool.

Cheers

Alex

[tridac]

Analogic kit is well known for quality and references like that are specifically designed to have long term stability and accuracy, even if not calibrated for years. If that's the only reference you have, and providing it works and the outputs make sense across the range, check against the best dvm you have, then it's already probably the most accurate thing you have in your lab, at least until you have something to compare it to. More than adequate to calibrate analog meters and probably dvm up to 4.5 digits. A good system dvm is essential. Older Hp models like the 3456, 6.5 digit, are an affordable option and are so old now, the aging rate is very low. Have a couple in the lab here, neither formally calibrated in years, but track together within a couple of microvolts once warmed up and are within a handful agaist a Fluke dc standard. The 3457 are 6.5 digits via front panel,  7.5 via hpib commands, but from tests, not convinced they are much better than the 3456. Afaics, Fluke make the best voltage standards, while HP make the best voltmeters. There also low cost options, such as online sellers offering precalibrated fixed output references. Quality might vary, but some of them look pretty good and could be usefull for an initial reference to compare against. A handful of microvolts is more than good enough for many. Any better than that and thermal ambient, lead and connector variations start to affect results. If you think you need better than that, then there should be good reason, as it will be an expensive journey. If the work doesn't care if the measurement is miliivolts out, then it's a waste of money to pay for single digit microvolt accuracy, however much we all strive for the best...

[all_repair]

Check this:
https://www.ianjohnston.com/index.php/onlineshop/handheld-precision-digital-voltage-source-2-mini-detail

No relationship with maker, I wish I have one.

[Kean]

Check this:
https://www.ianjohnston.com/index.php/onlineshop/handheld-precision-digital-voltage-source-2-mini-detail

No relationship with maker, I wish I have one.

I am very happy with my PDVS2mini.  Highly recommended if you can afford it... and if it is in stock...

[Grandchuck]

I also highly recommend the PDVS2mini.

[DH7DN]

ADRmu as a ~10 V DC voltage reference seems to be rock-solid (as far as I can tell, still testing...)
Build your own, download its cooking recipe here: https://github.com/marcoreps/ADRmu

The BOM price is at $350 - $400 per unit and you need at least 3 of them to gain the voltnut-confidence in stability. Monitoring of voltage references demands good, maintained and calibrated equipment under defined environmental conditions so there go few k$. Maintaining traceability to national standards can cost somewhere from $5 to several hundreds/thousands of dollars (every year). Expensive hobby, wouldn't recommend to dive into the 8.5 digit DC Volts metrology. But then again, it's a hobby and hobbies are meant to burn money for the lulz 

Besides that, a German company called "Knick" has manufactured few capable Direct Volts and Direct Current calibrators which are sold relatively cheap.

[CatalinaWOW]

First question is why you want to calibrate?  Any answer is OK, even "just cuz".  But it has to be YOUR answer and will guide what you do and spend in this direction.

[tggzzz]

First question is why you want to calibrate?  Any answer is OK, even "just cuz".  But it has to be YOUR answer and will guide what you do and spend in this direction.

Precisely. I hope the OP reads that and formulates their answer.

[J-R]

I'm no metrology expert, but I've been dabbling a bit over the last couple years and perhaps was in a similar situation back then when needing to calibrate/adjust some DMMs I repaired.

I'd think having a PDVS2mini would negate the need for the Analogic, at least from a practical perspective.  But there is the cost and stock issue.  It could be 6 months or more before they are back in stock, although now that Ian retired, maybe he'll be faster to get the next batch out!  1,000% recommended, though.

The VoltageStandard.com PentaRef seems like the bare minimum to check the Analogic, but it is also out of stock currently.  1V, 2.5V, 5V, 7.5V & 10V for the five outputs could be one option.  You would want to check the Analogic right after receiving the reference for maximum accuracy.  The Analogic has only one official adjustment, 10V.  The zero and 1V are just for verification to ensure the unit doesn't need repair.

The "hack" to make this possible is to connect the Analogic and the Pentaref in series with a DMM and connect the outputs negative to negative OR positive to positive, then measure the difference with the DMM using the mV range.  A decent handheld or bench meter should be able to handle this.  Something with at least 0.01mV of resolution.  Then you don't need a 6.5 digit DMM just yet.

[fmashockie]

Thank you for everyone's recommendations and input!  I just received the Analogic AN3100 yesterday and it looks great! Appears to work well, too! Though I only have my DMM at home right now to test and it's only a 4 sig fig meter.  I do have a HP3478A in the lab (5.5 digit) that I can use to check it, but it is not calibrated. 

The reason I want a precision DC voltage reference (and other standards for resistance and AC voltage) is that I work as a engineer repairing my company's lab equipment (biotech).  We have a very small budget for the test equipment I need to do this.  So I buy a lot of it used for cheap.  I thought it would be helpful to have calibration standards in case I need to get something like a benchtop meter, power analyzer, etc. back up and running.  We are not under any strict regulations here like GMP/GLP for example, but we will be getting ISO 9001 accredited soon.  My electrical testing equipment won't necessarily fall under the scrutiny of that accreditation (some of my other standards will), but I thought it would be a good idea to have an ability to calibrate them if they ever do. 

[J-R]

If you have a slight attraction to older gear, then the Fluke 515A might also be something to keep an eye out for.  I picked one up a while back and it's a fun gadget to have if you can't handle one of the boat anchor Fluke calibrators!

But based on what you are saying you need for work, I think the proper solution is a calibrated bench DMM.  Trying to dig up all this old equipment in order to get enough references is going to be higher risk, more money and more work than just shipping out a bench DMM every year or so.  Which DMM to get is another discussion.

[trobbins]

A cheaper and more social option may be to say hullo to nearby service/manufacturing centres that may have a 6.5 digit DMM they keep in cal.  Invite yourself over for a coffee and chat, and ask if you can take your 5.5 digit, and perhaps your AN3100, to make some spot tests.  Not a calibration, but may give you the confidence to proceed on, and may allow a future opportunity to do another set of spot tests with acclimatized equipment.

[CatalinaWOW]

Not cheap, but certainly not more expensive than the approach you are chasing if you value your time appropriately is to periodically rent a calibrated instrument.  This is probably easier to properly document for your ISO and other certifications.

[Rax]

Excellent input. I am not so far from where you are, and this community has been extremely helpful and the wealth of knowledge and generosity of sharing is unmatched.

You may want to investigate - possibly from this community - if there are any turbo- hobbyists with some good standards at hand. They may help you assess, and possibly adjust yours.
Also, in the educational side of things, Fluke has an excellent calibration manual available for download. It's based on older standards and equipment, but it will teach you a ton on the fundamentals of practicing this.

[EC8010]

I would second the Fluke "Calibration: Philosophy in Practice" recommendation. I downloaded the first edition after I borrowed the hardback 2nd edition from a chap who had been issued with it on a Fluke calibration course. In truth, the principles are unchanged between editions, but I like paper books and it is very good in either edition. I tried to buy a copy of the 2nd edition but it didn't seem to be for sale, so I emailed Fluke from work asking where I could buy a copy. Their very courteous response was to ask for postal address and they sent me a copy FOC. I quite often refer to the Fluke book.

[huababua]

What do you guys think about the Time Electronics 1017 DC V/I/R Multifunction Calibrator?
https://www.timeelectronics.com/portable-voltage-current-instruments/1017-voltage-current-resistance-calibrator/


I know that this is not a "standard" but a "calibrator" (whats the difference anyway? A standard also needs calibration, does it?)
But looking at the specs it seems to me that this could be a "cheap" standard-option?

[PartialDischarge]

Have a look at the Advantest TR6142, schematic is available on ko4bb