Local calibration labs

[Conrad Hoffman]

We have a few local labs and I was looking at their "certificate & scope" documents. They're all about the same, using the same equipment. Unless I'm missing something, they're  not very good in terms of voltnut requirements. Heck, I think I can do better with the antiques in my basement! This is typical- am I missing something here?

[try]

Hi Conrad,

First of all, I'd like to thank you for your making your metrology mini lab article series available!

It could be that you are missing something there.

When checking calibration certifications on file the Elmtec company nearby (Germany) states two different figures.
 Their certification distinguishes between dc measurement devices >0,33V <=33V with 22ppm and dc sources between 0,2V and 20V with 6ppm.

Does your lab show similar differences or is there just one entry on file for the range in question?

Elmtec is not an extraordinary lab.

Fluke Germany, p.e. has a certificate entry for voltage references showing 0.2ppm for a 10V reference. This is probably the best you can get here. The only disadvantage with that annoying company is that they even refused to quote me a price for a self-built reference.

I doubt that you can do better just with the 731 models you own...

Regards
try

[ManateeMafia]

For 10V DC transfers, there is usually another entry in the Scope of Accreditation. I usually look for a Fluke 732A/B entry as the standard used. If they don't have that entry, chances are they can't support it.

For the resistance, I use a lab in Pittsburg that has good pricing for standard resistors. This was recommended to me by Edwin Pettis.

[MisterDiodes]

Correct: A lot of labs aren't setup to calibrate other "high accuracy" equipment.  You really need to talk to the lab manager at your local facility:  Trying to calibrate a 3458a blindly another 3458a + opt 002 is not doing much good especially if that 002 option unit is more than a few years old and not maintained at Loveland, CO.  At that point its golden LTZ Vref has morphed into any other 3458a Vref and the "002 option" is just more expensive voodoo fluff.  If possible, to maintain a 3458a it's just better to buy a 5 yr contract at Loveland, and then they take care of everything when you send in your 3458a for cal (batteries, adj. etc.) And all under warranty.  When you look at final cost, that's really the best value.  Even with shipping (or take a vacation in Colorado if you drive your stuff in yourself).  IF you make a living with your equipment, you don't complain about the maintenance charges.  There is no such thing as "zero drift" in the PPM world.

A real lab will have access to much more than just a 3458a - there will be at least one loaded 734 rack involved with routinely cal'd 732's on board to maintain a good volt.  Or the facility will have a JJA available that's ref'd to NIST, like at Fluke or Boeing in Washington state, two facilities that are local to the Pacific Northwest in USA.

Some well equipped labs are now able to use a "shippable" JJA that goes back and forth to NIST, but you have to check.  That's another option.

If you have your equipment calibrated at one of the cheaper "chain" labs, you're basically just buying paperwork and stickers.  Which is fine for a lot of companies who don't really care about absolute accuracy, they just want that sticker on the front of their equipment to pass an ISO 900x audit (usually).  That's sort of why the cheaper chain labs exist (TransCal, etc.).  A few of those labs are better equipped, but you have to call and talk to them directly.

A lot of times all someone really wants is that magical sticker and cal certificate, and they have no idea to what uncertainty and confidence the equipment was "calibrated" against. 

Do it right and have your equipment cal'd at a real lab. It probably won't be the cheapest, but you get what you pay for.

[try]

Hi MisterDiodes,

I had sent you a personal question months ago regarding your LTZ1000 experience.
Would you mind looking at it?

January 16, 2017, 11:26:07 AM    "jumpy" LTZ1000    MisterDiodes

Regards
try

[CalMachine]

Here is ENI Labs scope.  Bear in mind these uncertainties are old and haven't been improved recently.  They will be reduced significantly here in the next year or two, as I've been overhauling our DC/low frequency program.

https://www.a2la.org/scopepdf/2147-01.pdf

If you have your equipment calibrated at one of the cheaper "chain" labs, you're basically just buying paperwork and stickers.  Which is fine for a lot of companies who don't really care about absolute accuracy, they just want that sticker on the front of their equipment to pass an ISO 900x audit (usually).  That's sort of why the cheaper chain labs exist (TransCal, etc.).  A few of those labs are better equipped, but you have to call and talk to them directly.

A lot of times all someone really wants is that magical sticker and cal certificate, and they have no idea to what uncertainty and confidence the equipment was "calibrated" against. 

Soooooo much this!  Being in the cal industry, many labs are sticker machines, and some even purposefully fail items because they can charge more for them.  I could go on and on about the cal industry, but it's probably not smart for me to do so    Most end customers have no clue what they really need or why they need it.  They just know that they need an accredited cal because their quality policy says so.  It's a little frightening how little some people know quality, in the quality field.  And these are people employed and some big name corporations.

Do it right and have your equipment cal'd at a real lab. It probably won't be the cheapest, but you get what you pay for.

Unfortunately, sometimes even the 'Big Names' will give a suspect cal on an item.

[Conrad Hoffman]

Nowhere in the equipment lists for the local labs did I see any reference to a trio of voltage standards, IMO the minimum requirement if you want to maintain the volt. Their calibrators aren't even close to the latest and greatest. My guess is the above is correct- everybody wants to pass their audits but they don't really need great absolute accuracy. It's all about stickers and paperwork.

Way back (1996!) when I did the MML articles, the local lab had me wait until right after their equipment came back from Fluke so everything was "fresh". They also had in-house standards. Alas, that guy retired and the lab is long gone.

CalMachine- good stuff, you cover a lot more area then the local labs.

[Vgkid]

Here is IET Labs
https://www.a2la.org/scopepdf/2073-01.pdf
The best local lab, I wish these places would hire people. I would like to give it a try 
https://www.a2la.org/scopepdf/2171-01.pdf

[Cerebus]

For 10V DC transfers, there is usually another entry in the Scope of Accreditation. I usually look for a Fluke 732A/B entry as the standard used. If they don't have that entry, chances are they can't support it.

For the resistance, I use a lab in Pittsburg that has good pricing for standard resistors. This was recommended to me by Edwin Pettis.

In UKAS accreditations, they show different sections for sourcing and measuring voltage/resistance/whatever. My local-ish lab has an accreditation that shows an expanded (k=2) uncertainty for sourcing 10V DC at 0.80 ppm, sourcing 1.1 to 11V DC at 2.4 ppm + 20 uV and measuring 100mV to 100V DC as 20 ppm expanded uncertainty.

[Edwin G. Pettis]

I do not know of any high level calibration labs that will calibrate a 'private' voltage standard, they just will not do any 'privately' made equipment.  Even if you 'know' somebody at the lab it is unlikely they will do it.  You may be able to get a secondary lab to calibrate your 'private' standard, you'll have to contact the lab and talk to them about it.  If you are just looking to get an accurate reading of your 'standard', you might be able to find somebody with a recently cal'd 3458A and get them to give you a reading but of course that will still limit the accuracy and uncertainty of your unit.  The options available to get your LTZ checked to capability is very limited for a private individual.

At any rate, the 3458A, as good as it is, is not a voltage standard by definition, it is a DVM, it can be used as a short term transfer standard as long as it is in calibration and certified.  The only voltage standard, short of a JJA is 732s/734 A/B which can be used to calibrate and certify 'working' voltage standards and DVMs of high accuracy.  At around $1,400 per 732B for certification per year, you're looking at a pretty high cost to maintain a voltage standard (absolute minimum of three 732Bs which are rotated for calibration, usually four is the prescribed minimum).  You absolutely cannot use a 3458A to 'certify' a LTZ Vref, you can use it to get an accuracy to a few PPM and an uncertainty of maybe 1 or 2 PPM but you're not going to get 1 PPM in any way, shape or form.  You can't even get a guaranteed accuracy drift reading over a year's time, you're only comparing one LTZ's drift against another.

[try]

For 10V DC transfers, there is usually another entry in the Scope of Accreditation. I usually look for a Fluke 732A/B entry as the standard used. If they don't have that entry, chances are they can't support it.

For the resistance, I use a lab in Pittsburg that has good pricing for standard resistors. This was recommended to me by Edwin Pettis.

I have never seen any reference to equipment used in the certification documents.
Could you show me a link for a certification document with an Fluke 732A/B entry?

[CalMachine]

For 10V DC transfers, there is usually another entry in the Scope of Accreditation. I usually look for a Fluke 732A/B entry as the standard used. If they don't have that entry, chances are they can't support it.

For the resistance, I use a lab in Pittsburg that has good pricing for standard resistors. This was recommended to me by Edwin Pettis.

I have never seen any reference to equipment used in the certification documents.
Could you show me a link for a certification document with an Fluke 732A/B entry?

For every 17025 accredited cal there will be standards used and the date on which they were cal'd last.  And I can tell you for a fact, there have been many accredited certifications handed out in the industry with a Fluke 732B listed as a standard.  I have performed many cals, myself, using our Fluke 732B.   

If you happen to get a crappy NIST-traceable cal?  Sure... there might not be standards listed.

[MisterDiodes]

The only real lab I know of that would do an accurate measure of a DIY box is Boeing  - IF they inspect your device and determine it is well-built zener reference they will measure for you at around $800 a pop.  No adjustments, just a measure against several 732's that are ref'd to the JJA down the hall.  They will have openings a few times a year on their measurement scanner rack, on a first-come, first served basis.  They will not measure DMM's or anything other than a good zener reference to make sure they aren't wasting anyone's time.  You get a small amount of shelf space, a small amount of power is supplied on a mains supply; they will plug it in and let it stabilize for a day or two and then take some measures over 18 or 24 hrs or so.  You get your device back with a printout.  That's it.  The will certify the measurement to NIST standard, but not the device itself.  If you want accurate drift data you keep sending your device in after a few months (or whatever time frame) and pay each time.  Knock yourself out.

If you have a Fluke box, send it to Fluke for Cal.  They will at least do an adjust for you (if you pay for that).

There might be a few others but usually labs aren't going to bother with hobbyist boards - that's not going to be a good profit center for the lab.  You can always call the lab direct though and find out.  I know there are a few labs on the west coast that would measure a hobby board, but you wouldn't trust the result too much if you're after true absolute voltage values.

If you're in it as a business, you probably won't be trying to characterize a self-built-in-the-garage reference anyway.

If you're going to be in PPM world, it's far better to acquire your own 732's, null meters, KVD's and maybe some 3458's or similar, and keep those in a working, cozy warm, cal'd condition.  And then measure your own self-built references to your own freshly cal'd equipment, in your own lab.  As pointed out countless times:  You need multiple voltage references to measure against even to get to accurate low PPM absolute measures - at least 3 references to get down in the 2 or 3ppm range usually, if not more.  More sources and measurement techniques lowers uncertainty and raises confidence.

If a lab says they just have a 3458a as their only Vref, look elsewhere if you really want true absolute accuracy.  That instrument is -not- a long-term voltage standard.

[ManateeMafia]

Here is Keithley's PSL.   https://www.a2la.org/scopepdf/2462-01.pdf

[0.01C]

Here is ENI Labs scope.  Bear in mind these uncertainties are old and haven't been improved recently.  They will be reduced significantly here in the next year or two, as I've been overhauling our DC/low frequency program.

https://www.a2la.org/scopepdf/2147-01.pdf



The ENI Lab can cal.  1k-10k standard at +-1.7mOhm..... use calibrator and dmm only?

[CalMachine]

The ENI Lab can cal.  1k-10k standard at +-1.7mOhm..... use calibrator and dmm only?

Up to 10K, yes.  The DMM is used as a transfer from the calibrator.  At 10k, you would drop down to the 0.017 Ohm uncertainty.  Our scope is fairly weird and it will be more intuitive in the future, once I am the one in charge of our uncertainty budget.  Most of these were written/set up and done before I started working @ ENI.

[doktor pyta]

Maybe slightly off-topic, but I need help from colleagues located in the U.S.

Could You please reccomend a calibration lab in Minnesota capable of calibrating standard capacitors (with proper certificate)?
Lowest value is 1 fF (one femtofarad) with uncertainty of +/-(0.01%+0.03fF) or better.
I could use google off course - but it's better to have someone's recommendation.

Thanks !

[thermistor-guy]

I do not know of any high level calibration labs that will calibrate a 'private' voltage standard, they just will not do any 'privately' made equipment.  Even if you 'know' somebody at the lab it is unlikely they will do it.  You may be able to get a secondary lab to calibrate your 'private' standard, you'll have to contact the lab and talk to them about it..."

Several years ago I was looking at forming a test equipment startup, with a focus on temperature measurement to near primary-level uncertainties. I asked the Australian primary calibration lab, NMI (formerly CSIRO) at Lindfield NSW, to give me a tour and discuss if/how they could help me. NMI showed me their primary PRTs, temperature baths, black body references and so on. Very educational.

NMI was willing to test my company's prototypes. Most of the expense of the testing was in the report writing and checking. If I wanted just the measurement data, without an official NMI report, it would cost me much less.

I didn't go ahead with the start-up, but as it turns out, I have returned to that area of technology. If I talk to NMI again re prototype testing against its standards, I'll post an update on a suitable thread here.

[Moon Winx]

As far as accredited measurements go, keep in mind that the values listed in these documents that are linked in this thread are for the lab's best measurement uncertainty, not the measurement uncertainty you would be receiving on your device. As an example, we are accredited for a 42 nV uncertainty in the 10 V DC voltage measurement parameter, but it would be rare if we turned out a device with a reported measurement uncertainty of 42 nV. Probably somewhere close to that, but uncertainties listed in these accreditation documents usually are based on an exceptionally good test unit and most customer items, even of the same model, don't match the performance of the device used for the analysis.

[Theboel]

I deal with 2 NMI lab in south east asia region and they are very helpful even when I asked them for a special task for my DIY voltage reference.   

[martinr33]

In thinking about the thread, it seems that we have three levels of calibration out there, something like this (and please do edit my numbers!). I'm sort of thinking publicly accessible when I do these numbers. Using Government numbers could double them? Triple them?

Type               Access      Uncertainty             Metrology Use
Josephson           10         0.2 microvolt          Calibrate reference devices eg 732. Not very accessible. I assume that all the tech governments have one of these including China, Japan, Taiwan and a few others in the G7.
Many 732           30         1 microvolt             Microvolt calibration of other 732; metrology grade 8.5 digit calibration. Top cal labs, government labs, some research universities.
Single 732         200        2 microvolt             Short term metrology grade calibration of 8.5 digit DMM (i.e. like a many 732 cal 6 months later...)
Fluke calibrator   800        20 microvolt           Calibration for 6.5 and 7.5 meters. If not under contract, the 7.5 is very doubtful.

For most activity, the lowest grade of calibration is fine. And, although your 6.5 digit meter can be calibrated to a couple of digits in the last place, it is actually allowed something like +/-20 counts - which is +/- 200uV. I have a couple of current cal 6.5s   that look to me to be 120uV off. That's within spec, of course.

I'd figure our 8.5 digit voltnuts  to be headed to the 10uV  zone, with some doing better. 6.5 digit owners might get to 30uV.

[Cerebus]

As far as accredited measurements go, keep in mind that the values listed in these documents that are linked in this thread are for the lab's best measurement uncertainty, not the measurement uncertainty you would be receiving on your device.

For UKAS certifications, the certification is for the deliverable. So if a lab runs multiple streams of deliverable then, as I understand it, each of those gets its own accreditation. That's why UKAS accreditation certificates sometimes list the same basic capability twice with different uncertainties. You just have to make sure that you order the right service to get that level of uncertainty.

[Moon Winx]

As far as accredited measurements go, keep in mind that the values listed in these documents that are linked in this thread are for the lab's best measurement uncertainty, not the measurement uncertainty you would be receiving on your device.

For UKAS certifications, the certification is for the deliverable. So if a lab runs multiple streams of deliverable then, as I understand it, each of those gets its own accreditation. That's why UKAS accreditation certificates sometimes list the same basic capability twice with different uncertainties. You just have to make sure that you order the right service to get that level of uncertainty.

I wonder what the reasoning is behind that? It would be impossible to know the uncertainty of a measurement before the measurement is made, so stating that one would receive a specific uncertainty doesn't seem very forthright. I know that in practice the uncertainty contributors that can only be determined at the time of measurement are usually swamped by other sources of uncertainty, but I also know of many cases where that is definitely not true.

[Cerebus]

It would be impossible to know the uncertainty of a measurement before the measurement is made, so stating that one would receive a specific uncertainty doesn't seem very forthright.

Eh? If you don't know the uncertainties inherent in a making a particular type of measurement with a particular method and particular instruments before making the measurement how will you suddenly know them after making the measurement. I think you're conflating absolute error and uncertainty.

[Moon Winx]

It would be impossible to know the uncertainty of a measurement before the measurement is made, so stating that one would receive a specific uncertainty doesn't seem very forthright.

Eh? If you don't know the uncertainties inherent in a making a particular type of measurement with a particular method and particular instruments before making the measurement how will you suddenly know them after making the measurement. I think you're conflating absolute error and uncertainty.

You can have an incomplete picture of the uncertainty before a measurement, but there are components of the total uncertainty that are unknown until the measurement occurs. Repeatability is probably the most common. Sometimes this component completely swamps the other, referenced uncertainty contributors.