Fluke 732 calibration price list and procedure - Page 1
Forum section: electronics / general

author: MisterDiodes
author_rank: Frequent Contributor
timestamp: October 24, 2017, 04:48:13 am
content: We just received a newly calibrated 732a back from Fluke Everett, WA labs - and I thought I'd share the current price list and customer procedure here. Prices are subject to change and there may be adjustments depending on what you ask for. These are just baseline prices we got from Fluke.Before you send in an older 732a (or 732b), I recommend doing (as required) a complete battery replacement, adjust battery charger, replace power supply capacitors, etc. Let the 732 stabilize for a few months at least and make sure noise and stability is in spec. Also note that when your 732 gets returned all the adjust pots will be sticker-ed over as well as the Battery ON-OFF switch, power module, battery module and top cover. Breaking any sticker invalidates the calibration - so if that's important to your business make sure the 732a/b is up and running well-before-sending it in.The price of calibration listed below is just for the 10V main output. On a 732a if you want the 1V and 1.018V outputs adjusted to ppm accuracy, that's an extra $450. The cost to do the 1.018V output on a 732b is an extra $300. The uncertainty on these secondary outputs is only going to be 0.7ppm.We use a 752a to get an accurate 1V and 100mV derived from the 732's, so we don't use the secondary outs from the 732's anyway.BY DEFAULT the 732 main 10V output is NOT adjusted to 10V +- 0.5ppm during cal. Most of time you want an accurate drift history of your unit and for that you don't really want intervening adjustments; as long as your 732 is within a reasonable distance of 10V, Fluke does NOT recommend adjustment, they will just do a measure only for Z540 data report - that way you know exactly the absolute value of your 732, which is what you're after anyway. They will perform an adjustment if requested. Keep this in mind though: If you do request an adjustment on an older 732a that you're not sure about where the pot adjustment range ends, you might be out of luck. Fluke will not repair 732a's, nor will they change the 732a's coarse adjust jumper board - so it's important to have a rough idea of the absolute value of the 732a before sending it in for cal and requesting adjustment.The cost to EVALUATE the repair cost of a 732b is $300. In other words it'll be $300 minimum to just find out what's wrong with a 732b. The actual repair cost will go up from there.If you can't drive in your 732 to Everett, for an extra $375 + shipping they will rent you a shipping case for your 732a complete with 4 extra battery packs for longer hot run time. This is how they will ship your 732a back to you as an express freight shipping packing weight of 128 lbs. If the "Cal" light goes out (meaning the unit went cold) the calibration is no longer valid. So make sure to coordinate shipping of your unit.Fluke Labs has a measuring uncertainty ratio of 10 to 1...In other words they are measuring and adjusting your 732 to several of their 732's which are on a tight calibration rotation (30, 60 or 90 day) with their JJ-Array, and their measuring resolution is 10X finer than the measured value printed on your report. When your unit leaves the facility your measured absolute voltage value will be to 0.3ppm uncertainty traceable to NIST with 95% confidence. If you had an adjustment done it is typically to 10V +- 0.5ppm or to whatever you've requested and paid for, and then the actual measured value is also on the report.Cost of calibration for 732's:ANSI Z-540 (This is most common) You get the 1 yr cal certificate and measured value of 10V main output: 732a is$789, For 732b:$738A2LA Accredited Calibration - If you need this higher level of legal paperwork you'll know - for 732a:$1126, for 732b:$1075Primary Standard Lab Calibration: If you need to get down to 0.2ppm uncertainty relative to NIST, you can calibrate your unit directly against the JJ-Array. For 732a$1,885. For 732b:$1780The procedure is as follows, and accurate as of October 2017.1. Call in to Fluke Calibration, and get setup with your contact info. If you're a business you send in your business info also, for instance sales tax exemption records, etc. You tell them the serial number of the 732, and which calibration service you want, and setup payment account, Credit Card, or whatever payment method. They will get back to you within a day or so with an RMA number.NOTE: There is an online calibration system on the web, but for whatever reason it does not yet work with 732's. You have to call in to get setup with RMA. At least as of Oct 2017.2. Once you have RMA number, and know how you're going to get your 732 to Fluke (Ship it in or drive it in) you call in to schedule about when your unit can arrive. They want to make sure there is space on the racks available for your unit as soon as it arrives. So you get setup with an appointment for your 732 arrival day.3. Now get your 732 to Fluke - either ship it or drive it in. They will give you the proper address if you're driving it in - and you need to get that from them. They prefer to receive 732's for calibration on Monday / Tuesday / Weds if possible.4. Once they get the 732 it is plugged into mains power. The CAL light should still be on when they get the unit. If the CAL light is off then that will require a longer stay to make sure the unit stabilizes before running any tests.5. The unit is tested for noise, battery pack operation and initial voltage measure is taken.6. A few days later you will get notice that your unit passed initial functional checks and will go in for full calibration cycle, usually about 2 weeks. You will get an estimate of Ship Day. During this time your unit is being scanned and inter-compared with several Fluke 732a/b units, and they look for any signs of TC problems, oven issues, output noise, etc.7. At any time during this period if the 732 fails to meet spec it is marked as aNon Functionalunit. If it is a 732b they will discuss repair options. 732a's are just returned to owner.8. On the morning of Ship Day they will call or email you to let you know the unit is ready. They pull the last measure voltage value at just before 8am (at least for us) and run the math and print the reports. Then your unit gets stickered: All the adjust pots are covered, the cover screws, the rear module access screws and Battery On/ OFF switch. It is ready to travel by about 10am.They will keep the unit plugged in until you arrive to pick it up in person, or they will get the shipping container prepped and ready to go - when the shipping company truck pulls up they will unplug the unit, seal it up in it's box and place it on the courier truck within a few minutes. Either way they will keep those batteries charged up until just before it leaves the facility.After all that, this is what a working - calibrated - 732a looks like, ready to go to work (cert number removed for EEVblog). You hardly ever see this on eBay-Have Fun!

author: TiN
author_rank: Super Contributor
timestamp: October 24, 2017, 04:59:19 am
content: Thank you for detailed walk-thru. I have a question regarding tempco. You mention they will check for TC problems, how is that going to happen?Is there a additional service available to get tempco measured as well?

author: MisterDiodes
author_rank: Frequent Contributor
timestamp: October 24, 2017, 04:24:31 pm
content: RE TC - In a simplified sense the racks with devices under cal is measured / controlled for temperature separately from the rack with the reference units. As the rack with DUT's varies very slightly over temperature (within a degree or so) they are looking for problems during the test period, and to make sure each unit's oven temp sensor / Vref output is staying solid-stable. That's how it is described to me, and that's what I can relay to you here. It's more they aren't measuring actual TC, it is part of a Go / No Go check - and they are making sure that the 732 meets all published specs as tested over the test period.Their absolute value measuring resolution internal to Fluke labs is at .01ppm, so they'd be able to detect an out-of bounds shift on Vref output relativity easily even if the DUT ambient temp shifted less than a degree. The final measure you get on your certificate is 7.5 digits (0.1ppm resolution), and again: Uncertainty to NIST is 0.3ppm for the Z540 cal @ 95% confidence (For the lower-rated cals - the Primary Labs cal is 0.2ppm uncertainty to NIST). At least up to the moment your device leaves the back room and the final measure is taken - that is the recorded absolute voltage value of your unit. You will get the official time stamp of the last measure taken so you can start calculating your extrapolated expected drift compensation down the minute Fluke took it's last reading.Beyond that: You're more than welcome to pay the $1,500 "Observation Fee" where you can go in the magical back room for up to 4 hours and watch your unit get calibrated - just leave your cell phone and any other personal electronics at the security guard desk. For some calibration requirements it's not good enough that you have the paper certificate - if you're in Aerospace especially you'll need to be physically present for the last few hours of calibration and sign off (aka "Witnessed Calibration") and then you'd be free to examine the exact process in detail - and probably still not be allowed to post observed process details online. Fluke has a lot of proprietary processes in that room they wish to keep proprietary, and the Observation Fee setup also includes a pretty strict NDA and background check.As it is when you get to Fluke you're allowed only into the shipping / receiving desk area, and you must show your ID RMA and paperwork for equipment drop off and pickup - and that's as far as you're allowed into the building.That's all I can describe online at least for standard cal procedure. If you need to have a unit specifically measured for TC I think they can do that but you'd have to contact Fluke for a "Custom Lab Service" procedure.

author: dacman
author_rank: Frequent Contributor
timestamp: October 24, 2017, 11:28:09 pm
content: They've given us 0.06 PPM. Go to page 20 in this document and look at the top: "http://download.flukecal.com/pub/literature/NVLAP%20Labcode%20105016_FPLAccreditationScope_Exp%2020180630.pdf"

author: MisterDiodes
author_rank: Frequent Contributor
timestamp: October 24, 2017, 11:55:37 pm
content: ...Check Note 4 - That .06ppm might be misleading and generally more relative to Fluke Labs - and sort of leaves the exact spec up in the air. If that's what you're after, that's OK but all of our cals are spec'd to be relative and traceable to NIST only - which is the real landmark to measure against most of the time here in the US - at least if you have to pass an ISO-type cal audit. 0.3ppm uncertainty to NIST is the best you'll get from Fluke for standard z540 cal, and 0.2ppm relative & traceable to NIST if you cough up the extra $1200 for the Primary Standards cal. on a 732. I just double-checked that with their lab services sales department. If you're after a cal that's relative only to Fluke labs (and done onsite, maybe?) yes then it can be reduced uncertainty. Most certificate audits we need won't accept that though.At that point it's sort of bragging rights anyway, really. How long will it take your 732 to drift .06ppm?EDIT: Also - you got that document for Fluke Park Labs NVLAP (voluntary), not ANSI scope at their Cal lab location. That 10V reference they talk about in that NVLAP scope is their own J-array, not NIST's. NIST traceability is what counts, legally, for a lot of doc requirements.

author: dacman
author_rank: Frequent Contributor
timestamp: October 25, 2017, 12:32:00 am
content: Here is the same document on the NIST website:"https://www-s.nist.gov/niws/index.cfm?event=directory.retrieveDocument&documentId=EFA2EE38EC04463227D2986EC2B09EF1CC011DE7E3B3199D634405632CA6E57FABB392A73B80A93783019527580D5CDAC5E2364510C496ED90E740F1D012CE63&csrfToken=509FCCC06F4FFBBE9FA912B752984623C169A760"Here is the page it's on:"https://www-s.nist.gov/niws/index.cfm?event=directory.detail&labid=248&programId=4&csrfToken=509FCCC06F4FFBBE9FA912B752984623C169A760"If you look at the first page, on the right side near the top, it mentions Z540. We have gotten more than one NVLAP certified 0.06 PPM on-site calibration.

author: CalMachine
author_rank: Frequent Contributor
timestamp: October 25, 2017, 12:35:00 am
content: Quote from: MisterDiodes on October 24, 2017, 11:55:37 pmI think you might have your information a little off, or perhaps I am wrong. But, the measurement uncertainty I've received from Fluke in 2014,15,16 on their 'Service Lab' 17025 accredited cal was 0.3 PPM. The service lab is where a majority of their calibrations occur. This most recent year I spring for the Fluke's 'Standards Lab' 17025 accredited cal. This is where I received a reported measurement uncertainty of 0.06 PPM.Looking at their scope and the ~ J Array CMC of 0.01 PPM, they can very easily report a 0.06 PPM measurement uncertainty (depending on how stable the DUT 732 in question is)Note 4 specifically refers to 'On-site' calibrations. Which would be relevant if you sprung for the calibration package where they send you their characterized 732B. I think it's just a coincidence that their reported measurement uncertainty on these few 732Bs happens to be the same as their onsite CMC.Quote from: MisterDiodes on October 24, 2017, 11:55:37 pmAre you under the assumption that Z540 or 17025 certificates from labs that are not NIST, are not NIST traceable?

author: dacman
author_rank: Frequent Contributor
timestamp: October 25, 2017, 02:31:59 am
content: 0.06 PPM is the uncertainty of the measurement at the time of calibration. It is not the accuracy of the 732. Reports from Fluke on these types of calibrations have a section on adders such as temperature, humidity, pressure, and seasonal effects, which if combined are greater than the 0.06 PPM measurement uncertainty. Accredited laboratories are supposed to trend standards like these and standard resistors and gauge blocks, and most any fixed accredited standard, and they are supposed to determine the uncertainties themselves using the accredited reported values, which can include a trend prediction.

author: MisterDiodes
author_rank: Frequent Contributor
timestamp: October 25, 2017, 02:59:16 am
content: See Page 2, Calibration DC Reference - this is what we're using for Z540 scope - and what Fluke Everett Service Center Cal lab (not Fluke Park) will give you when you send in a 732- and it is indeed 0.3ppm, and printed on my cert I received last week:https://www.a2la.org/scopepdf/2166-01.pdfThat's all I can describe to you, and that matched up to my reality.When I requested Z540, relative and traceable to NIST, this is what I got: 0.3ppm, and that is what I was told was the best uncertainty spec available for that request - outside of going to Primary Lab cal. My cal documentation includes the words "traceable to NIST" which is what I have to have to pass our audit, and it also includes all the equipment and traceable cert numbers from Fluke's equipment.Now they will MEASURE to a finer resolution of course relative to Fluke internal references (10X better than printed on the report) - but the UNCERTAINTYrelative to NISTis no better than 0.3ppm. You have to remember that there are transfers between NIST and FLuke JJ-Array, and then from Fluke JJ-Array to cal lab 732's, and then from cal lab 732's to your 732 under test. There is no such thing as a "perfect" transfer - just low, non-zero uncertainty at every step.NOW: The sales person I double checked with implied that onsite 0.06ppm seemed to believe that is relative to Fluke's own JJ-Array - and not directly traceable to NIST due to Fluke traveling to onsite location and introducing additional unknown uncertainty <maybe>. If you look at Note 4 on the Fluke Park doc that shows that 0.06 ppm uncertainty is -variable-, and that's where the difference lies. Now maybe our wires got crossed somehow - but all I know is I got what I needed. I'll let someone else research the finer points of bragging rights documentation on their time.After all it is mostly all documentation only differences on uncertainty. Unless you have a JJ-Array handy it'll be hard (impossible?) to accurately measure any difference in the end to verify 0.3ppm vs. 0.06ppm uncertainty - especially once the equipment has left the building. Once any drift sets in you're probably outside those limits anyway, and back to the bounds of published operating specs and known drift history extrapolation estimates.Have fun!

author: Moon Winx
author_rank: Regular Contributor
timestamp: October 25, 2017, 04:08:55 am
content: Quote from: MisterDiodes on October 25, 2017, 02:59:16 amI am an engineer over several JVS systems at my work, and I don't know how Fluke does things but it doesn't make any sense to me that there would be traceability to NIST from Fluke's JVS. It's an intrinsic standard with the traceability coming from the frequency source (whatever that may be, for us it's a NIST-corrected GPS signal) and the uncertainties for that are WAY below the uncertainty for the JVS volt (somewhere in the order of parts in 10^11 or 12. Every few years the big US primaries do a JVS intercomparison, usually led by NIST, to see how well each lab compares to one another. The results are anonymous, of course, but you know your lab's measurement so you can see how your system is performing in comparison to other labs. Labs may find they are a significant amount away from the weighted mean and adjust their measurement uncertainty accordingly.We tend to give a measurement uncertainty of 0.05 ppm for the 732Bs we measure with the JVS, and we'll give a printout of the predicted values w/ uncertainty of that value for each day for a little over a year. If we have enough historical data, the uncertainty stays pretty low throughout the interval because the 10V output can be predicted to a great degree. If we have no historical data, the predicted value stays constant while the measurement uncertainty rises throughout the interval, usually surpassing 2 ppm by the end.EDIT: To add, the uncertainty of the JVS volt is REALLY small, I think even sub-ppb, but I'll have to double-check. The 50 nV (k = 2) uncertainty we give comes from the transfer of that volt to the 732B along with all the sources of error that entails.

author: Moon Winx
author_rank: Regular Contributor
timestamp: October 25, 2017, 11:20:36 am
content: I work for a gov't lab, so we can't compete for or accept work that can be done commercially. Sorry, because I personally would love to help out. I just discovered this forum several months ago and I wish our workers had 1/10th of the curiosity/interest in metrology that I see posters here have! Metrology as a hobby?? I never knew such existed!

author: tszaboo
author_rank: Super Contributor
timestamp: October 25, 2017, 11:37:11 am
content: OK, so keeping a calibrated 732 at home is 150 dollar a month. OK.You could also buy an extra bedroom or a car from this money.

author: Gyro
author_rank: Super Contributor
timestamp: October 25, 2017, 11:56:38 am
content: That's why Joe Geller's SVR-Ts were such good value.

author: zhtoor
author_rank: Frequent Contributor
timestamp: October 25, 2017, 01:14:23 pm
content: so what would maintaining a bank of 8 saturated standard cells cost?regards.

author: MisterDiodes
author_rank: Frequent Contributor
timestamp: October 25, 2017, 01:51:50 pm
content: Quote from: NANDBlog on October 25, 2017, 11:37:11 amThis is the cost of doing precision business and chasing PPM's, so if you're doing this you probably want to be seeing a profit somewhere. That's why nobody gives away calibrations.As a business, AND if you do work for any customer who deals with the US Govt. or at least who worries about cal cert documentation - you really have to be able to show traceability to NIST most of the time, (or whatever governing body is in your country). Fluke isn't a government entity, so no matter how good and fancy and stable their reference is - unless they can show traceability to NIST's volt as an unbroken measure chain - their measure is not worth snot for a certificate audit. At least not for what we do or our customers.By the way - you CAN retrieve every cal certificate on every piece of equipment Fluke used between your device and the actual NIST transfer to Fluke. That's an extra documentation fee of $150 per hour, they said it runs around 4 or 6 hours depending - they will give you a closer estimate if you need to order that.

author: tszaboo
author_rank: Super Contributor
timestamp: October 25, 2017, 02:16:37 pm
content: But come on. I am talking about the volt nut, who wants to have the absolute accuracy at home. Just becuase it is a hobby.

author: MisterDiodes
author_rank: Frequent Contributor
timestamp: October 25, 2017, 03:26:48 pm
content: ...I get it. Hence the "nut" in the label, and I respect that. Whatever floats your boat, Have Fun! - all I'm doing is reporting on the current price list and sharing the real experience of how it worked as of last week.

author: CalMachine
author_rank: Frequent Contributor
timestamp: October 25, 2017, 03:30:50 pm
content: Quote from: MisterDiodes on October 25, 2017, 02:59:16 amOfcourse that matched up to your reality. You went for a Z540-1 calibration at their service lab. You won't be getting more than 0.3 PPM uncertainty traceable to NIST, there.But to go and make the claim that Fluke, as an entity, cannot report a measurement (Traceable to NIST) that is below 0.3 PPM, is hogwash. What do you think their NVLAP scope of ISO 17025 accreditation is for? It explicitly states how 'uncertain' their best measurements are traceable to NIST. See notes 1 and specifically note 2.Note 4 for is specifically referring to 'Field' or on-site measurements that do not take place in their laboratory.Quote from: MisterDiodes on October 25, 2017, 03:26:48 pmI very much appreciate the information and content you provide! I hope you don't feel I am being combative. I just want to make sure the right information gets propagated out to the people.

author: MisterDiodes
author_rank: Frequent Contributor
timestamp: October 25, 2017, 03:57:15 pm
content: Sheesh you're a lot of workHang tight - I'm on the phone with Fluke now, as I would like to see the difference as well. They are researching that answer. Right now, the best -NIST traceable- uncertainty cert they offer is 0.2uV/V (.2ppm) for primary standards cal, .3ppm uncertainty traceable to NIST for certificate. That's it. Quote -un Quote.There is no difference between uncertainty between Z540 vs A2LA cert levels, but with primary cal there is one less transfer involved, and so slightly better uncertainty.As I noted before -OF COURSE they can do a lower uncertainty measure- but traceable chain to NIST or not for legal certification is the question.This is what the sales dept. is telling me. So I am asking the difference between that and the Fluke Park labs scope that shows onsite 10V cal to .06ppm uncertainty, but notice that includes Note 4, which leaves that completely open ended. Otherwise Fluke Park will give you 0.4uV/V traceable uncertainty.I am currently waiting on hold... I'll let you know when I know.

author: MisterDiodes
author_rank: Frequent Contributor
timestamp: October 25, 2017, 04:16:14 pm
content: Sorry CalMachine - right now it's only 0.3ppm or 0.2ppm uncertainty traceable to NIST certificate for a 732, that's what they are telling me. They are going to have someone else get back to me on clarification of a custom lab service quote for anything lower uncertainty for a legal -traceable- NIST cert on a 732.So at the moment, no hogwash involved. but I'm moving up the sales dept chain. And presumably moving into even more betterer bragging rights documentation, which should blow even more money on a piece of paper...

author: MisterDiodes
author_rank: Frequent Contributor
timestamp: October 25, 2017, 04:31:39 pm
content: CalMachine - I just got a call back from sales dept. - they wanted to let me know they are referring my question to someone in the metrology group for more advanced scope of accreditation questions on custom lab services.But right now, the official word from their sales dept. on 732 cals for Z540, A2LA is 0.3ppm uncertainty traceable to NIST on the cert, and 0.2ppm for primary labs cal. This is at Everett Service center, and that's all they could sell me right now for NIST traceable uncertainty on a 732 - which is all I'm interested in, because that's what I have to have to pass a cert audit.It could be that custom lab services will offer even more exciting ways to burn through the cal budget, we'll see.

author: CalMachine
author_rank: Frequent Contributor
timestamp: October 25, 2017, 04:35:56 pm
content: Quote from: MisterDiodes on October 25, 2017, 04:31:39 pmI think you should re-read my last comment.I was agreeing with you, that at the service lab you won't be getting better than 0.3 PPM. Their service lab is A2LA accredited.Ispecificallystated their 'Standards Lab' (Park Lab) and their NVLAP scope of 17025 accreditation. You are thinking their service lab scope applies to their standard lab, for some odd reason.I wouldn't seek out, concrete, technical information from sales staff. They have technical support numbers for a reason.

author: Moon Winx
author_rank: Regular Contributor
timestamp: October 25, 2017, 04:46:38 pm
content: I still thinks it's very odd that Fluke would state NIST traceability for their 732B cals. I'm pretty sure they have a Josephson volt so I wonder why they would spend the extra shit-ton of money to have their own 732s calibrated at NIST instead of sending to their primary lab for a JVS measurement.

author: CalMachine
author_rank: Frequent Contributor
timestamp: October 25, 2017, 06:16:43 pm
content: Quote from: Moon Winx on October 25, 2017, 04:46:38 pmThat is what they have to do... All 17025 accredited calibrations are traceable to NIST. All Z540 calibrations are traceable to NIST. Even lower, 'NIST Traceable' cals, which are sometimes colloquially called 'as found cals', are traceable to NIST. Perhaps there is a misunderstanding of what 'traceable to NIST' actually means?The very first sentence on their calibration certificate states 'This calibration is traceable to the SI through recognized national measurement instututes (NIST, PTB, NPL, NIM, NRC, etc.)'.

author: CalMachine
author_rank: Frequent Contributor
timestamp: October 25, 2017, 07:17:30 pm
content: Perhaps I am wrong in my understanding by what it means to be traceable to the SIthroughNIST, and directly traceabletoNIST

author: Bill158
author_rank: Regular Contributor
timestamp: October 25, 2017, 07:57:00 pm
content: Quote from: CalMachine on October 25, 2017, 07:17:30 pmI think an easier way to understand all of this is as follows.1. By an act of the US Congress NIST (NBS) maintains THE LEGAL VOLT for the United States of America! NIST's JVS is right and FLUKE's JVS is somewhat different. Probably not very much and well below 0.1 ppm.2. FLUKE sends NIST a bank of 732Bs with what they think is "THE VOLT", as assigned by FLUKE's JVS.3. NIST sends that bank back, after comparing that bank of cells with the NIST JVS, with the statement "THIS IS THE VOLT" end of discussion!Therefore the 732A that CalMachine gets back from FLUKE is "traceabletoNIST", even though there may be several layers of instruments and measurements between NIST and his 732A. Also FLUKE can state the the biggest error between what NIST says that "THE VOLT" is and the volt that FLUKE assigns to CalMachine's 732A. I don't know, maybe 0.3 ppm?At least that is the way I understand all of this "traceability" stuff.Bill

author: Edwin G. Pettis
author_rank: Frequent Contributor
timestamp: October 25, 2017, 08:17:53 pm
content: What MisterDiodes is saying (and myself) is that customers often require traceability to NIST or they won't do business with you. Our standards must be traceable through whatever cal lab we use to NIST, there are no exceptions that I know of. All of the resistor manufacturers must maintain traceability to NIST of their standards or they can't sell to a wide range of customers including aerospace, industrial and government. Anyone who makes resistor standards must have treaceability to NIST, no exceptions, an SR-104 must have a record of traceabilty to NIST to be accepted (just like mine does), that is the whole point of having a National Calibration Lab so that everybody can trace back to them and the same primary standards, everybody is on the same page. I am sure that Cal Machine, et al are aware of this requirement.I can't say I've heard of JJAs not having some kind of traceability back to NIST as you mentioned, they are compared to each other periodically and tweaked if necessary so that they are all in agreement, whether there is a paper trail for that or not, I don't know, I have no need for a voltage standard with such low uncertainty. The problem with such low sub fractional uncertainties is that they start changing once they are off the primary standard they were compared to, that is the real world, everything affects a standard, whether it is at .01 PPM or PPM levels, everything drifts, there is no getting around it and everything in the environment will affect to some degree or other. Fluke states that once your voltage standard leaves their primary lab, that .06 PPM will start increasing as stated in note 4, it is open ended if you read it. While a nice aged Vref may have very predictable drift, a mathematical prediction does not qualify as a calibration. I know what the drift of my SR-104 is on a yearly average but that doesn't constitute a calibration, it still has to go back to the cal lab to verify it, no freebies unfortunately.

author: Moon Winx
author_rank: Regular Contributor
timestamp: October 25, 2017, 08:20:09 pm
content: Our A2LA/17025 accredited 732B test report has the boiler plate text that includes "...this certification is traceable to the internationally accepted representation of the SI Volt through the Josephson constant (KJ-90 = 483597.9 GHz/V) and the use of a Josephson voltage standard operated by [my lab]". We definitely don't claim NIST traceability for the Volt. If you didn't have a JVS you would need to, but if you can create the volt in your lab that's where the traceability ends (well, actually it ends wherever your frequency source traceability ends, but that's a whole 'nother domain). For intrinsic standards like this and the QHR, the auditors from the accrediting agency look at your inter-lab comparisons and uncertainty calculations to decide whether you can claim a certain uncertainty on your scope of accreditation. NIST or other NMI traceability only applies to non-intrinsic standards.

author: Moon Winx
author_rank: Regular Contributor
timestamp: October 25, 2017, 08:32:11 pm
content: Quote from: Moon Winx on October 25, 2017, 08:20:09 pmTo clarify a little, 732Bs can be traceable to NIST's JVS or any lab's JVS. That's where the volt chain ends. This goes for other intrinsic standards also. A lot of parameters do not have an intrinsic standard and must be traceable to the US standard at NIST. Examples of this are capacitance, inductance, ac voltage (although that is about to change), kilograms, meters, and frequency.

author: CalMachine
author_rank: Frequent Contributor
timestamp: October 25, 2017, 11:07:28 pm
content: I went a little digging into the actual ISO 17025 standard, since I'm still fairly new to this stuff. I found a little excerpt that pertains to this debacle and clears up some of theuncertaintyin my head...ILAC P10 states :QuoteI see I went wrong by thinking that, since NIST is the highest tier on the pyramid in the US on the chain to the SI, you would in-turn have tracebility to them, inherently, by traceability to the SI.I've also gathered some other pertinent information. NIST's current uncertainty is 0.19 PPM on a 10 V measurement. During Fluke and NIST's last comparison, their reported values were insignificantlygreater agreement than that. If NIST ever decided to revisit their budget, everyone could receive more certain measurements 'directly traceable to NIST', if you happen to need them

author: dacman
author_rank: Frequent Contributor
timestamp: October 26, 2017, 02:22:12 am
content: I went through an NVLAP audit with NIST auditors a few years ago and they had us change our traceability statement from traceable to NIST or other national labs to traceable to the international system of measure (SI) through NIST or other national labs (and other things such as ratio or reciprocal type measurements). It doesn't matter what type of report it is. We never state that we are traceable to NIST anymore.NIST was sending out a PJVA (Programmable Josephson Voltage Array) for intercomparison with labs with a JVA unless they couldn't handle another JVA or didn't need the uncertainty, then they would send a bank of four 732Bs. This allows the lab to claim traceability through NIST. Fluke's Primary lab uncertainty statement with their JVA indicates to me that they got the PJVA.Modify message

author: Moon Winx
author_rank: Regular Contributor
timestamp: October 26, 2017, 03:36:02 am
content: The > 0.19 ppm typical measurement uncertainty given at NIST is kind of surprising. That means that they do not measure customer zeners with a JVS but with a bank of other characterized zeners. You would think with current automation that they would just use the JVS but I'm sure they have a good reason for not going that route. We measure all 732s against the JVS, just because the 10 V output uncertainty can easily climb out of our customers' required range during the 1 year calibration interval. Comparing it to our bank would max out the output uncertainty in a matter of weeks or months, depending on the unit.

author: MisterDiodes
author_rank: Frequent Contributor
timestamp: October 26, 2017, 04:37:56 am
content: OK, enough pissing contest. Let's get back to the original topic, and that is calibration of 732a at Fluke Everett Service center, and why they will give you 0.3ppm or 0.2ppm uncertainty of measure traceable to NIST.Part of it has to do with NIST's side of the equation, and NIST being able to verify manufacturer's claims...I had a nice long chat with a PhD metrologust directly at NIST this afternoon to clarify some questions about NIST's involvement of the certification process.1. There is ONE legal volt in US, and that is the NIST version. If you do business internationally then you would specify something along the lines of traceable to SI thru NIST...but none of our needs are met by that. Fluke's volt is Fluke's Volt, and does not count as legal anything, at least for what we need. JJ-Array at point A does not necessarily legally equal JJ-Array at point B, and that is why there still has to be a means to inter-compare the two, either by a fleet of 732b's or transferring compact JVS systems between labs. A JJ-array is close to an intrinsic measure, but not quite...For instance in case of war and the GPS system goes down and we lose a common worldwide time/ freq reference, there will be extra uncertainty if we have to use a different means to keep excitation frequency of the JJ-As matched, but that's a different story.2. NIST uncertainty (95% confidence) is spec'd to 5nV/V on their JVS. Fluke's uncertainty (95% confidence) their JVS is currently is 5nV/V PLUS extra 50nV if you want a traceable measure (That's where Fluke's measure spec uncertainty of 100nV or 0.01ppm on 10V scale comes from). NIST has the luxury of being the golden standard, so they don't have the extra added transfer uncertainty. They ARE the definition of the volt for US. That being said they still intercompare with all the bigger labs - everyone is trying to keep the standards in close agreement.3. For our needs and doing business with our customers, we MUST have have the words "traceable to NIST" on both absolute value and uncertainty. "Traceable to Fluke" is worthless a lot of times. You will see in several places in Fluke documentation that yes you can get a measure at Fluke to better than 0.1uV/V U95 BUT that is relative to Fluke's Volt. The NIST traceability for uncertainty will be larger (that part appears in the fine print).4. YOU CAN cut out Fluke and send your Fluke 732a / b to NIST for Measure and Cal, and they will measure it against the NIST JVS for 30 days, and give you a characterized report. The fee is $2311 and you pay for all shipping.https://www.nist.gov/calibrations/voltage-measurements-calibrationsThe official reports will use 1uV/V uncertainty. For the rest of this post I will assume we are on a 10V scale so that 1uV/V is 1ppm, and 95% confidence.NOW - As explained by NIST, for any known Zener Diode Reference, about the best anyone is going to do is about 0.2ppm uncertainty. They have seen it go as low as 0.1ppm uncertainty but that is rare. So the Calibration is quoted as the best you'll get is 0.19ppm, and the normal range of uncertainty on any Zener Diode Vref they've seen is around 0.1 to 0.5ppmThe limiting factor here is the noise of the Vref. This includes Zener Noise, Temperature, Humidity, Pressure effects on the system. So in the words of NIST: They watch your Vreffor 30 daysat a measuring resolution of down to .005ppm uncertainty and then look at the overall drift and noise - and assign an absolute voltage value and 95% confident uncertainty to the Vref, which will be no better than 0.19ppm.The other problem NIST pointed out: You can measure a 732a/b to some ridiculous fine resolution on a JVS and come up with some value. The problem is making use if that measured value: Unless you're going to use that measured value within a very short time frame, trying to get a transfer measure out of your Vref much below 0.1ppm uncertainty is like trying to measure bowl of jello. And forget transporting the 732 and expecting that measure to still be valid at a very small uncertainty.5. Zener noise of 732a's is spec'd at 1uV RMS or less (typically way less than that when they age, ours are down around 0.35 or 0.50uV). 732b is spec'd at 0.60uV rms (.1 to 10Hz), and usually measure around about that. You are never going to get a Cal certificate better than 0.2ppm uncertainty because anything below that uncertainty is going to be a measure of mostly the noise of the Zener Diode Vref - and not a very stable or usable measure.So the bottom line is YES you could get your 732 measured at NIST - but all that happens is you might get 0.19ppm uncertainty. Send it to Fluke and measure against their JVS and you've dropped all the way down to 0.2ppm uncertainty and saved a few bucks. Plus Fluke will perform an adjustment if you need it.NIST is only going to work with the "Traceable to NIST" uncertainties with values they can verify. And that lower uncertainty limit - for now at least - is about 0.19ppm for a zener diode reference.Have Fun!

author: dr.diesel
author_rank: Super Contributor
timestamp: October 26, 2017, 11:46:34 am
content: Very interesting. Big thanks to all for taking the time to further discuss/elaborate.

author: Moon Winx
author_rank: Regular Contributor
timestamp: October 26, 2017, 03:40:28 pm
content: There may have been some slight miscommunication with the NIST physicist, and I don't expect anyone to take my word over NIST's, but I think some points need to be clarified.Quote from: MisterDiodes on October 26, 2017, 04:37:56 amFluke's uncertainty from their JVS should match NIST's at around 40 - 50 nV. NIST doesn't have the "golden standard" JVS, they have, as you said in (1), the legal standard for the volt. But as I'm trying to convey, the representation of the Volt can be created in any lab with a proper operating JVS. There is no transfer uncertainty involved just due to the JVS being away from NIST. There is no additional uncertainty added and as long as the JVS systems are using the same null voltage measurement equipment/technique and thermal offsets are comparable, the uncertainty of a 732B measurement using the any JVS will roughly be the same (disregarding the short-term stability of the 732). As far as I can tell, this results in a measurement uncertainty of roughly 50 nV.Quote from: MisterDiodes on October 26, 2017, 04:37:56 amDo you have a example of that? A picture of the fine print? This points to Fluke comparing against a bank of volt references rather than Fluke's JVS. There is a relative uncertainty associated with those measurements. The bank itself has an uncertainty associated with its 10 V value, and the reported measurement uncertainty should include this. The difference between the bank's uncertainty and the measurement's uncertainty is the transfer uncertainty. If Fluke is just reporting the transfer uncertainty, that doesn't do the customer much good.Quote from: MisterDiodes on October 26, 2017, 04:37:56 amIf they will measure your 732 against the JVS they need to update the webpage at the link you provided. It just contains verbiage referring to measuring it against a bank of working standards.I think there may be some confusion in what is reported on a JVS 732B measurement. The uncertainty listed on a test report is the uncertainty of the measurementat the time of measurementand has little to do with anything but that. So the owner of the 732 would never use just this value to state the uncertainty of the voltage output... he would need to combine the reported uncertainty with the stability/environmental coefficients of the 732 (from spec) to get the output voltage uncertainty. If you have enough historical data, you can predict the output voltage and pretty much remove the stability part of the equation.I would raise a lot of questions with NIST or Fluke if I received a 732B test report with a 0.19 or 0.2 ppm uncertainty. That's huge.

author: MisterDiodes
author_rank: Frequent Contributor
timestamp: October 26, 2017, 05:29:08 pm
content: Good grief...I'm trying here and this is becoming a bigger time sink than I ever anticipated...Last post from me:RE: In the US, Legal volt is US is the legal volt kept at NIST. Period. NOT Fluke, Boeing, Sandia Labs or anyone else. NIST doesn't have to report a "uncertainty difference to NIST", and that doesn't mean their JVS is better than anyone elses. You can take that argument up on a legal forum. That's what I have to deliver to my customers on a calibration certificate and that's the terminology the auditors look for. I can also use "traceable to the SI " - that would be proper -if- I use JVS documented standards all the way through.There is much more to the conversation - I'm giving you the highlights here, trust me. I think you're missing the point of calibration of a 732TRANSFERSTANDARD. It has to be able to transfer a voltage measured from point A and deliver that measure to another time and location point B. Yes you can can measure the 732 to a lower uncertainty than 0.2ppm. BUT THE NOISE OF THE ZENER itself limits the usability of that measure. Unless you expand the uncertainty limits to a practical value, that measure is only going to be valid on the order of minutes or hours.In the words of the kind NIST Dr. - They could measure it down to 5nv/V uncertainty and be well into the noise of the 732, but then you wouldn't be able to move that 732 down to the other end of the workbench and expect that uncertainty to be valid 5 minutes later. Why on Earth would you want to do that? The measure and calibration limits are there as a practical guideline for how accurate your transfer standard is - and with the assumption that you will transport the Vref to another location and have the measure & uncertainties be valid at least for a practical time frame.That is also why, if you look at NIST lab services - the uncertainties reported for different devices are different. If you want to characterize 1.018V standard cell references, they will give you a minimum .04 ppm uncertainty on that measure. That's because that technology is quieter than a Zener (but more work to maintain over time).RE: Lab IntercomparisonFor instance - NIST traveled very recently to Fluke Everett to do an inter comparison between NIST's compact JVS and Fluke's JVS (as well as many Zener standards) and the difference between labs was much less than expected. I won't give you the results here (hasn't been published yet) but it is way, way less than 40~50nV difference. That result quoted is from an older test.RE: NIST Measurement method: I am told by NIST that NIST has a new scanner system setup and your 732 is readdirectlyagainst their newer JVS to 5nV/V uncertainty, for 30 days. I can only go by what NIST tells me directly. As a taxpayer I want to believe them over you at this point. But that's just me. If that's Fake News or not I don't know...What I know for sure, and is agreed on by Fluke and NIST:Right now, the only practical way to get better uncertainty than a traceable 0.2ppm uncertainty measure cal on on a Zener based reference is to have multiple Zeners Vrefs on a tight calibration schedule measured against a JVS-backed reference group.Otherwise you can purchase a JVS system which I'm sure MoonWinx is familiar with. That is considered a near intrinsic standard, at least if you have an accurate frequency reference available (i.e. GPS is verified working).The push is to develop a more affordable JVS with a programmable Vref output up to 10V, and hopefully requires only ~20GHz excitation frequency, not ~75Ghz. It would be nice if you could have it not require liquid helium also. NIST tells me this is being worked on and improvements made:https://www.nist.gov/news-events/news/2013/04/primary-voltage-standard-whole-worldThe other clarification is: If you reference directly to a JVS, and can show an accurate frequency measure (GPS time lock or your own local atomic clock reference) then that would be a good intrinsic reference, and then the statement on the calibration document would be "Traceable to the SI" which is what the SI volt is.There ya go. Have Fun!

author: Moon Winx
author_rank: Regular Contributor
timestamp: October 26, 2017, 07:16:32 pm
content: Sorry MisterDiodes, I'm not trying to become a time sink for you! I promise I'm here to help clarify some points just so wrong information doesn't spread. I work and help develop these systems everyday and have been doing this for 15 years. I've been through 6 on-site audits for these JVS systems where our methods of performing and reporting zener voltage reference measurements have been scrutinized. We now have 3 of these systems in our lab, including a state-of-the-art pulse-driven AC Josephson system. I know all of the guys who do this work at both campuses of NIST. I talk to them quite often and they are some of the smartest people I've ever met, way smarter than me, so I don't doubt at all what they told you to be true. But I think your interpretation of that *may* be a little off. Remember, NIST is not 17025 accredited (and it makes perfect sense why they wouldn't be) so they don't necessarily have to know about or follow the ISO standard. Some of their metrologists perform audits for NVLAP or A2LA, but NIST is only accountable to their own quality standard.Having said that, I doubt NIST goes against 17025 and reports a measurement uncertainty that takes into account future use of that item. I suspect the reported uncertainty is the measurement uncertainty at the time of measurement and nothing else. And when I use the term "measurement", in the case of a 732, it includes all voltage samples recorded over a span of several days or weeks. Usually the mean of the samples is reported along with the combined measurement uncertainty that takes into account the variation of the readings throughout the measurement (in NIST's case, the readings over the 30 day period). This variation is the largest component of uncertainty in these measurements. Typically we see something like < 100 nV (< 0.01 ppm) scatter over a few weeks of samples, and I suspect NIST sees about the same. So we combine this with other sources of uncertainty and it usually comes out to less than 0.05 ppm (@ k = 2).So you can see why I would raise an eyebrow if NIST or Fluke is reporting something much higher. 0.05 ppm to 0.19 or 0.2 is a huge jump so I am really thinking they are comparing the customer's 732B to a JVS-characterized bank and not measuring it directly with the JVS. That large reported uncertainty makes more sense that way, but I could be wrong. It's also curious that NIST's own webpage with the larger-than-expected uncertainty states it uses the bank comparison method for this. If they measure it with their JVS they could report a much lower uncertainty is all I'm saying.

author: MisterDiodes
author_rank: Frequent Contributor
timestamp: October 26, 2017, 10:56:33 pm
content: MoonWinx - Double Checked at NIST and yes, when you send in a 732 it is checked -directly- against the JVS on their scanner system, and both Fluke and NIST JVS system have 5nV/V uncertainty while measuring against the JVS. Fluke has a small additional uncertainty added to allow for any misalignment to NIST, according to Fluke. For purposes of Calibration report the specified uncertainty can't be better than the noise floor of the device being tested.I am looking at a live data sample from what is considered a very good 732b testing at NIST right now on their JVS and I'm seeing more like +- over 200nV spikes over just a couple days, not weeks. It gets worse than that over 30 days.So you might want to check with your buds and see what the real story is - otherwise you have some extraordinarily good 732's!CalMachine: Fluke did get back to me and -no- traceable Cal Cert will be issued from Everett Fluke (Service or Park) at better than 0.2ppm uncertainty for a 732. Again, their measuring technique will be finer resolution than that while device is under test, but the inherent noise in the Zener Diode is the real limit on the real device uncertainty.In other words taking a certified measure with an uncertainty that's below the usable noise floor of the instrument under test is futile - because it's just noise.Their lab servicesdo include other measures with less uncertainty than that of course- but that's not necessarily for Zener Diode Vrefs and not necessarily traceable. For the purposes of this thread we're talking about a 732 calibration certificate only.If you hear different do let us know, but that's what I found out from this end.Somebody else's turn to research now.

author: Moon Winx
author_rank: Regular Contributor
timestamp: October 27, 2017, 12:23:58 am
content: Quote from: MisterDiodes on October 26, 2017, 10:56:33 pmNow we get into the hairy details! That range you see seems pretty typical for the samples we take too, and our customers don't have especially good 732s and in fact, they are probably the most abused ones out there.As you might imagine there has been a ton of study on how these zener references behave and several years ago a paper was published that gives methods for breaking through the specified day-to-day noise floor specified by the manufacturer.It was an empirical study based on 140 zener references and accurately predicts zener output values during the calibration interval.The voltage samples during the weeks-long measurement are fitted to the known trend curve using a linear least squares fit and the scatter of the samples is computed using the curve fit residuals. This legitimately separates the zener noise from how its known value is changing over those days and so the variation contributor to the measurement uncertainty is lowered a bit. So the +/- 200 nV you see will usually become something (much) smaller after the predicted value curve fit.If you want to get more into the weeds and care to read about this method: PROJECTING ZENER DC REFERENCE PERFORMANCE BETWEEN CALIBRATIONShttp://vmetrix.com/ZenerP.pdf. It's authored by NIST alum Clark Hamilton who pretty much invented the JVS and created the software that still runs most of the world's JVS systems.

author: dacman
author_rank: Frequent Contributor
timestamp: October 27, 2017, 12:37:42 am
content: NIST was certifying JVAs to 0.022 uV/V using a bank of zeners. That is to within 220 nV.Since I get NVLAP certified reports traceable "through" NIST to the SI from Fluke, I'll explain one.I never use the 0.06 uV/V uncertainty as an uncertainty of the Zener. (The uncertainties I use are even well above 0.2 ppm.) 0.06 uV/V is used in an uncertainty analysis.The number does vary. I've seen 0.07 uV/V and years ago used to get 0.1 uV/V (and 0.4 uV/V from the Fluke A2LA lab).The measurement uncertainty (0.06 or 0.07 uV/V) is at k=2 or about 95%. (It is an NVLAP requirement that the approximate percentage be on the report.)Later in the report, it mentions that other factors need to be considered, and if they are not known, Fluke gives some estimates at one standard deviation.I think the estimates in uV/V (at k=1) went something like:Temperature: 0.05Pressure: 0Humidity: 0.05Seasonal Effects: 0.058If the measurement uncertainty of 0.06 uV/V is converted to k=1, then it is 0.06/2 or 0.03.To get the combined uncertainty at k=1, these terms are RSS'd together and the result is: 0.09625 uV/V k=1For k=2, this is multiplied by two: 0.1925 uV/V k=2I would round up to 0.20 uV/V. If I had the 0.05 uV/V reported uncertainty from Moon Winx, the result would be 0.19 uV/V.If this was the only reported value I had, I would need to use the uncertainty in the manual, which is 2 ppm/year.But, I have several calibrations, and these are charted. The value of the Zener is predicted. A standard error of the prediction is calculated (the Excel STEYX function can be used for this). A statistical multiplier for the standard error is used to increase the uncertainty over time.

author: MisterDiodes
author_rank: Frequent Contributor
timestamp: October 27, 2017, 01:02:55 am
content: Yes, those are good math gymnastic stunts, and then on a simpler level: consider the Zener's inherent noise...say .5uV to a 1uV RMS, .1 to 10Hz - at any given time. These devices do have a noise floor at the moment you pull a measure from them. One measure is never enough.Of course as dacman pointed out: the very best predictor is to develop an un-adjusted long term drift history which is what I pointed out a long ways back in the first post. A 732 with a long (many years) recorded calibration report history is much more valuable than a new unit, I say.Back on topic: How does this all relate to purchasing a 732 -Traceable Calibration Certificate- at Fluke with better than 0.2ppm uncertainty in the first place? I'm still kind of wondering how that happens - or if that's something they just don't do anymore? I've talked to 4 people at Fluke, from sales to lab people - all say that just isn't available for the 732.

author: Moon Winx
author_rank: Regular Contributor
timestamp: October 27, 2017, 01:30:22 am
content: Quote from: MisterDiodes on October 27, 2017, 01:02:55 amC'mon man! Nobody takes one sample and calls it a day! I think you are dismissing the mountains of research that have gone into the performance of these devices... that the noise floor you speak of is much, much lower in practice.I don't get this: you dismiss curve fitting as a mathematical stunt but then go on to claim the best predictor is.... a curve fit?Quote from: MisterDiodes on October 27, 2017, 01:02:55 amLooks as though dacman gets them. Maybe he can chime in on that.

author: dacman
author_rank: Frequent Contributor
timestamp: October 27, 2017, 02:18:20 am
content: MisterDiodes, could you contact someone from the Fluke primary lab or possibly Jeff Gust (the head Fluke metrologist who took over from Dave Deaver). I sat through a class he taught on calculating the uncertainty of the predicted value of standards (not just Zeners) and he stated that they were giving 0.07 uV/V on Zeners and I told him they were giving me 0.06 uV/V.I've sat through at least a half-dozen classes on how to calculate uncertainty and two of them were taught by NIST mathematicians. Before combining terms, they should be converted to one standard deviation.If I combine all the terms on the report, I get 0.20 uV/V at k=2, just like you are being told, but the measurement uncertainty is stated to be 0.06 uV/V. (I think pressure uncertainty is estimated to be zero because I'm at the same altitude as Fluke, although pressure is included in seasonal effects.)

author: Edwin G. Pettis
author_rank: Frequent Contributor
timestamp: October 27, 2017, 02:21:37 am
content: MisterDiodes did not say anything about taking one measurement and calling it a day, read it carefully, "One measure is never enough."He is not talking about curve fitting either, he is talking about taking all of the actual readings over a period of years (even more than one reading a year if you're adventurous) and doing a simple average of it, that will give a rather accurate figure for the next drift measurement. These references tend to drift in a general direction at a fairly constant amount every year once they are old enough. No curve fitting or any other mathematical high jinks are needed. It is also a fact that you simply cannot average out very low frequency noise over relatively short periods of time (we're talking days at least for an average), these low frequency components are indeed random and cannot be predicted or averaged by any math for short periods. It is this noise that limits the absolute accuracy and for 732s, that is about 0.2 PPM, sometimes a little lower but that is the best you're going to get and no amount of math fiddling is going to change that. If that was true, NIST and everybody else would be using such techniques to reduce the uncertainties further beyond the noise floor. Ask the experts, they'll give you the same answer, 0.2 PPM for a 732 , maybe 0.1 PPM for an exceptional one. That is all that needs be said, this was the intended subject of this thread in part, nothing to do with JVS as such although the information is indeed interesting.For quite a few 732s, the noise is actually measured between about 0.5uV and 1uV RMS, I do not see where anybody can claim that noise floor is any lower than that, much lower....not for any zener based standards I've seen.

author: Moon Winx
author_rank: Regular Contributor
timestamp: October 27, 2017, 03:12:44 am
content: Quote from: Edwin G. Pettis on October 27, 2017, 02:21:37 amAgain, c'mon man! All of this is known. It's been studied. You don't need to believe me, you can do a search on scholar.google.com and find study after study on zener voltage reference measurements and behavior from all over the world. The output of the zener references can be predicted, and those predictions from years' past have been verified. This isn't woo or "mathematical high jinks".It's not a simple average over a period of years, as that would actually give you a much worse prediction. If you would actually read the paper I linked to in a previous post, you would see there is a sinusoidal pattern on top of a linear drift for ALL zener references, just to different degrees, and you can use this evidence to predict the output (and it's been verified), but it's just a little more complicated than a trendline (as there is a sinusoidal overlay), so it is more appropriately called a curve fit.Quote from: Edwin G. Pettis on October 27, 2017, 02:21:37 amI promise you the output voltage of the 732B can be known to way less than 0.2 ppm. I don't know what else to say other than I scrutinize this every day at work. And NIST knows this too, regardless of what they put on a customer's test report.It has everything to do with the JVS as there really is no other way to measure the 732B output to a degree that can assign a value to it.

author: MisterDiodes
author_rank: Frequent Contributor
timestamp: October 27, 2017, 03:55:52 am
content: I'm asking if there was a way to purchase a 732 traceable fluke cal certificate better than 0.2ppm uncertainty. It sounds like what dacman possibly got was a "measure" lab service product from Fluke, not a traceable cert. maybe? Again: Fluke currently says "No" to any 732 traceable cal cert any better than 0.2ppm (Service center or Park Cal, at least to the four people I've talked to), which is exactly how I reported the process on the first page of this thread.What Fluke tells me is that 0.2ppm is the spec'd usable noise floor of the 732, and remember: They are only measuring for 15 days for the cal cert, even at Fluke's primary cal lab level, measured against their JVS - NIST tells me the same thing about the usable noise floor of the 732 and they measure the DUT over 30 days measured against NIST's JVS, and still the end result in reported measured uncertainty on the calibration cert doc is basically the same ==> 0.2ppm (0.19ppm for NIST). So there is a pattern there, and it doesn't seem to go much below 0.2ppm uncertainty, as Edwin pointed out. We know that 0.1ppm and below is going to be noisy territory for sure, inherent in the Zener itself, and yes I know it can be possible to extract something that might sorta resemble lower uncertainty if you squint hard enough somewhere down in the muddy slime of noise, but that takes time - the longer the better. That's harder to qualify that as a traceable cert though - and that's what I'm after.I know MoonWinx extracts lower uncertainties, (I get it) but does that pass as a legal cal cert?And one thing for sure - my customers are going by the uncertainty listed on the cal cert as my basis for my equipment cal cert audits.I even asked the MoonWinx's smart guys at NIST if there is a "legal" documented way to even have a Vref Volt traceable, cal'd uncertainty Vref system of say 0.1ppm uncertainty available in the lab - and even -they- said that would be very difficult to do without either going to a -very- tight multiple 732 cal schedule (and probably custom characterized & aged 732's), or just purchasing a JVS.I've also looked back at a bunch of 732 docs for older cals, and it's never been anything better than 0.3ppm to 0.5ppm for the "standard" NIST traceable cal certs from Fluke, even from over 20 years ago.So that's what I'm having to go with at this point - this is the information that I'm getting from Fluke -and- NIST - 0.2ppm uncertainty is the practical best uncertainty limit of a documented, traceable, cal'd 732. I know it could possible be lower, but as a cert?I'll have to leave it at that for the moment - because that's what I can verify at this time.

author: CalMachine
author_rank: Frequent Contributor
timestamp: October 27, 2017, 04:52:37 am
content: Quote from: MisterDiodes on October 27, 2017, 03:55:52 amYou've got 2 forum members right here who have recounted on several occasions within this thread the ~'Traceable'~ 17025 accredited certificates from Fluke with a reported measurement uncertainty of 0.06 PPM. Of course these are legal documents.... ISO 17025 accredited calibrations are 100% perfectly legal for the government, lots of the Biomedical industry, some of the consumer audio industry, geothermal industry... I could go on. In fact, many businesses are now seeking out 17025 accredited cals, which has been made clear that we are 'Traceable to SIthroughNIST', and does not directly state 'Traceble to NIST'.Quote from: MisterDiodes on October 27, 2017, 03:55:52 amI am not sure of the level of scrutiny on 'NIST Traceable' calibrations back then; but, these days they are one of the lowest scrutinized levels of 'traceable' calibrations.Your customers' requirements to be 'Traceable to NIST' for the 'LEGAL US VOLT' is barring you from receiving any lower uncertainties. You aren't going to get any better when your 'LEGAL' best is 0.19 PPM. Thankfully, being accredited to an international standard, '~traceable~' to SI... I have the availability to receive more certain measurements on my references. Receiving a 0.3 PPM uncertainty could be the largest contributor in ones' budget. Getting that 0.06 PPM (if everything is done right) could mean the world for a scope.

author: Moon Winx
author_rank: Regular Contributor
timestamp: October 27, 2017, 01:04:46 pm
content: According to an section on JVS traceability on Wikipedia (I know, I know)...Quote..and another section that might be of interest regarding uncertainty and zener referencenoise floor:QuoteThis jives with my experience in measuring the noise in the 732B outputs. 50 - 100 nV or around 0.01 ppm @ 10 V. Again, much less than the specifications state for the 732B.I wonder if the 0.19 or 0.20 uncertainty given to you is because this item has no history with the calibration lab performing the measurement? Did they mention if you sent it in again within a year you could get a better uncertainty?EDIT to add: I just checked on our zener reference measurement system that uses a 734B bank as a standard and our typical measurement uncertainty on the cal reports for this system is around 0.16 ppm, which is good enough for the most common use of these standards (artifact cals of the 5720 & 3458).

author: MisterDiodes
author_rank: Frequent Contributor
timestamp: October 27, 2017, 04:38:34 pm
content: Finally the veil of bullshit is pulled away. Verified info from Fluke (lab manager #5 I've talked to) and NIST (PhD metrologist).First, in response to CalMachine:Yes Fluke will do a raw measure (to ISO17025) of a 732 and get you to .06ppm uncertainty against Fluke's JVS. As I have explained several times. That is a certified "voltage measure", not a calibration certificate. A Calibration Certificate (to ISO 17025 AND Z540-1-1994) from Fluke also includes a Test Uncertainty Ratio of 10:1 and the entire instrument is tested to be in spec. A Calibration Certificate is what I have to supply to my customers, they would never, ever go for just a certified measure. Yes an ISO17025 qualification includes traceable to SI through NIST, but you have to make the distinction between acalibration certificatevs. just avoltage measure.The little tidbit you're leaving out from a Fluke .06ppm uncertainty measure is the warning from Fluke that uncertainty is valid for about 2 hours on a typical 732. That's why they can do this as on on-site measure down to .06ppm with some multiple freshly cal'd 732's, do your measure on-site, and then get back to the JVS and recal those 732's right away.To recap: A Fluke Calibration Certificate on a Fluke 732 is performed to ISO 17025 and ANSI Z540-1, and is traceable to the SI through NIST, and if it is purchased thru Fluke that includes a -complete- instrument verification test and 10:1 Test Uncertainty Ratio (TUR). This is the practical usable limit of a single 732 if it's being shipped anywhere wheretraceability back to SI / NIST volt is maintained.NOTE: You can also have a Calibration Certificate and more Certified Measures done at more frequent intervals to help characterize your 732 to lower uncertainty - but that will vary from unit to unit and has a drift history is developed.Now for use in your own lab you can of course do whatever statistical math you like on your own 732 . For actual commerce beyond your lab it's the Calibration Certificate measurement uncertainty that counts as the basis for any product measure we send to our customers. At least that's only what my customers demand to see - If I tried to claim some measurement uncertainty based on some "certified measure" they'd just laugh at me. I have to be able to show the complete third partytraceable calibration certificate.To MoonWinx:Finally you've got a verifiable number from Fluke Cal. Yes, on a 734a where four 732b's were cal'd at the same time or close to same time, you CAN get a ISO17025 Calibration Certificate for the entire 734a listed as 0.16ppm uncertainty as a group - this number will vary slightly depending on the actual measured noise of each 732, but that is perfectly in the ballpark of a purchased product.Thanks for double-checking that and coming up with a more realistic traceable absolute value uncertainty spec.You have the luxery of having a JVS to play with so that's easy to see those numbers on a 732 even better than spec. Most of us don't have that capability.From NIST:To clarify about a JVS - Yes it is an intrinsic standard ONLY if the operating lab can prove that they have an accurate basis for time and frequency measurement (i.e. GPS or local atomic clock). So the JVS by itself is an intrinsic standard, be in practical terms it requires the minimum known uncertainty of the JJ-Array chip excitation frequency. Also in practical terms for the US - Currently All 20 labs that have JVS's are NVLAP / ISO17025 and participate regularly with NIST to inter-compare JVS's and several 732bs - and NIST also inter-compares with all the other international labs as well.A little more info on the origin the 10:1 Test Uncertainty Ratio (TUR) or Gage Maker's Rule which is typical lab practice:https://blog.alliancecalibration.com/tur-what-is-itWhen you get other measures from Fluke they are typically list as a TUR of 10:1 or in some cases 4:1. A lab measurement of 1:1 would be a bit suspect for lab practice.

author: CalMachine
author_rank: Frequent Contributor
timestamp: October 27, 2017, 05:30:56 pm
content: Quote from: MisterDiodes on October 27, 2017, 04:38:34 pmWhat you say and what I've actually received, and experienced, do not seem to corroborate.If you could be so kind as to interpret this 'CERTIFIED MEASURE' (according to you) document I received back with the 732B? I would greatly appreciate it. I've got years of data from PSNA, FLUKE, and Process Instruments on this unit.

author: Moon Winx
author_rank: Regular Contributor
timestamp: October 27, 2017, 05:53:33 pm
content: MisterDiodes, this is from Fluke's 732/734B manual describing a step in one the calibration options:QuoteThe Fluke Volt, in this case, is a bank of zener references. The "transfers to NIST" are referring to zener references. So Fluke has a calibration against their JVS-calibrated zeners, AND they have a calibration against their NIST-calibrated zeners. The calibration against the NIST-calibrated standards obviously has a higher uncertainty. So, like it says, if you require NIST traceability for DC volts (which I can't think of a good reason for) instead of traceability directly to the SI, you are going to have to settle for a higher uncertainty....and frankly, I don't understand the practical difference between a 17025-accreditted certified voltage measurement and a 17025-accreditted calibration certificate. If they are both accredited, both can be used in an accredited measurement chain. What's special about the certificate?...and no, I don't have a verifiable number from Fluke Cal. The data I was referencing earlier is a customer's 732b calibration using our 734B zener bank as the standard. That measurement for the 732B has an uncertainty of 0.16 ppm because of the standard I'm using.We have 2 conventional DC JVS systems and a zener bank system... One JVS produces a typical 732B measurement uncertainty of 0.05 ppm, the other cryo-cooled system produces 0.05 ppm, and the zener bank system produces 0.16 ppm. All of these are realistic uncertainty specs. They've been verified countless times in a myriad of ways. It's expensive to operate a JVS so most labs just fire it up to calibrate a zener bank, or they may schedule calibrations during a few months out the year when they have helium. We have a closed-loop helium system so it's not a problem for us to use the JVS for every measurement.When USING a 732B as a standard, you have to add other sources of uncertainty (dacman describes this above), as well as a stability specification. Maybe that's where the miscommunication is happening? The difference between measuring the voltage output and using the voltage output?

author: MisterDiodes
author_rank: Frequent Contributor
timestamp: October 27, 2017, 06:21:12 pm
content: Quote from: Moon Winx on October 27, 2017, 05:53:33 pmPlease read my previous post, and the answer lies within.CalMachine:Yep, it does look like to me you have a Certificate of Calibration. How that is 0.06ppm uncertainty eludes all sense from everyone I've talked to at Fluke Park and Service Center, that is down in the mud. As Fluke told me this morning: If they provided an uncertainty of .06ppm, that is certainly doable with their on-site process, but that measurement uncertainty would be only valid for a few hours on a 732 at best - unless perhaps it was a specially characterized unit.I take it that was a Ship-To Cal from Fluke? And that has a lot of history, so maybe that is the difference?I'll check when I get a chance, but frankly it's not on my top priority list anymore - I've got more important fish to fry today.

author: MisterDiodes
author_rank: Frequent Contributor
timestamp: October 27, 2017, 06:34:35 pm
content: CalMachine:Maybe I missed it, but do you have a specified TUR? That -should- be on the last page with the voltage measure displayed. That's where your Cal Cert and mine differ. Otherwise that is more like a 1:1 measure against their JVS (Except they are using 732a's to cal your 732b..gotta love the old stuff!) - and again that uncertainty on a 732 would not last long enough to ship that to you and still be traceable - at least that's what they tell me.That would explain why your listed uncertainty is much lower, but my question is - how does that get on a Calibration Certificate on a unit that is shipped to you?.The puzzler is - nobody at Fluke will admit to providing a shippable 732 CAL Cert with uncertainty that low, and neither will anyone at NIST. You'd think someone would be willing to sell that service outright, if it's valid.I'll ask -again- Fluke Park Labs, but probably not until next week. I do see what you're saying though.

author: CalMachine
author_rank: Frequent Contributor
timestamp: October 27, 2017, 06:59:34 pm
content: Quote from: MisterDiodes on October 27, 2017, 06:21:12 pmYes, this unit has traveled to Fluke many times. Every time, previous, it had been to their standards lab where I would receive your same reported uncertainty of 0.3 PPM. But, just this most recent trip, I sent it to the Standards lab where I always received the 0.06 PPM. With known history and a verified method of predicting drift, this is significant.Quote from: MisterDiodes on October 27, 2017, 06:34:35 pmRead the last paragraph on the front page. It cites the method and procedure for reporting the accredited uncertainty. The lab I work for is accredited through A2LA, while this certificate is from NVLAP. NVLAP is generally known for being more stringent in their accrediting process than A2LA. And you are correct, the TUR isn't explicitly stated anywhere.

author: Moon Winx
author_rank: Regular Contributor
timestamp: October 27, 2017, 07:07:30 pm
content: MisterDiodes: Z540.3requires TUR to be listed on the measurement report. ISO 17025 does not (as of now). What you must have received is a Z540.3-compliant calibration. TUR is a metric of how well you can measure an item relative to that item's specification. Since the 732B is more like an artifact than an instrument, it doesn't really have an obvious specification to compare the measurement uncertainty to. If I had to guess, they probably are using the 2 ppm stability spec, and claiming a measurement uncertainty of 0.2 ppm and a TUR of 10:1.And what you don't seem to believe, but is true, is that a certificate's reported measurement uncertainty has NOTHING TO DO WITH FUTURE USE. It's always AT THE TIME OF MEASUREMENT. So your "not good X minutes after the measurement" argument doesn't hold or make much sense when you realize this. You MUST include the stability specification combined with the measurement uncertainty when you use the item!

author: MisterDiodes
author_rank: Frequent Contributor
timestamp: October 27, 2017, 07:21:56 pm
content: ...Which is why CalMachine's cert clearly states that the uncertainties listed must be added to the stability information listed in the operator manual at the time of use, in lieu of other stability information. Clearly this isn't going to be a good number unless you know what the stability is in the first place - and -all- uses of that voltage measure on the 732 will take place "in the future".CalMachine: You do have a lot of history on this unit, and is this part of a DVMP group?. What do you calculate the uncertainty of measurement at the moment the unit came back to your lab and you took your first transfer from it? As per page 1-7 of the 732b manual?

author: CalMachine
author_rank: Frequent Contributor
timestamp: October 27, 2017, 08:51:16 pm
content: I do not have this unit currently enrolled in Fluke's maintenance program. I do send it out every year for an accredited calibration, though. This unit has been our only reference standard for years, so I am unable to really use this -in the dirt- uncertainty to its fullest potential.Just within this last year I've beefed up our lab and accumulated a decent sized bank of references and some of the other necessary equipment. With our history on this, now deemed transfer reference, and the lab's new bank of references, I hope to reduce our uncertainty to a level where the difference of receiving an uncertainty of 0.3 PPM vs 0.06 PPM could possibly be a significant contributor. All in due timeI will be able to provide accurate data of a transfer between the bank of references and the reported transfer reference value next year.

author: dacman
author_rank: Frequent Contributor
timestamp: October 27, 2017, 10:03:54 pm
content: DVMP is the on-site program. Here is a document that describes it but they are now giving (as low as) 0.06 uV/V vice 0.1 uV/V: "http://download.flukecal.com/pub/literature/2001531_A_w.pdf"If I calculated a standard error of 0.1 uV/V for the stability, the uncertainty at time of use would initially be 0.28 uV/V.

author: MisterDiodes
author_rank: Frequent Contributor
timestamp: October 28, 2017, 05:59:15 pm
content: That's correct. The specified uncertainty at the time of measure -at Fluke- is a good number as an academic measure for calculating yearly drift trends and for prediction calcs... Certainly it is a "snapshot" of measured value at that time of your unit's measured value, and that is a very consistent and good way to build a drift history. But the -real- traceable uncertainty of the -single- unit -at time of use- is very difficult to get down much below 0.3uV/V (at time of use). But do-able if you're careful. Having multiple cal'd references helps keep that low uncertainty verified.This is no news to CalMachine or dacman but for anyone unfamiliar -Remember that .06uV/V uncertinaty measure + known history stability calc is the uncertainty of the Cal'd 732 itself, and you haven't transferred that value or comparison between another local lab reference yet - and that process in itself has some other small non-zero uncertainty during comparison. That all will be documented differently if you use a null meter / DMM or whatever method is used.Time of use here means for instance: Fluke takes last measure at .06uV/V uncertainty Tuesday Morning, ships express overnight, say you get it late on Weds, now as per manual procedure you have to let it be still and plugged in on mains power to stabilize for 24hrs, and then you can start taking measures, maybe late Thurs or early Friday. So you're looking at say the passage of time of around 3 or 4 days since that measure of .06uV/V uncertainty was taken, and you have to take that passage of time into account and add that drifted value + uncertainty to your unit's first measure in your lab. Plus there is the sometimes unknown effect of how much did your unit get bounced around on the trip, so it's good to have local accurate reference comparison measures before and after the unit was shipped to Fluke.Theirs nothing easy or trivial about keeping a sub-ppm reference in your lab, that's for sure.There other factros as well, but these are some of the highlights.CalMachine: I would suggest look at DVMP for your situation if you haven't already - a lot of our customers use that service for 0.1 to 0.2ppm traceable uncertainty docs (I'll check on how that works for .06ppm, since I'm curious about that myself) and from a business standpoint: I'd want to let Fluke risk their own Vref during shipping. Your Vrefs get more and more valuable with each calibration cycle and better and longer drift history - and it doesn't take long for a 732 to have more business profit value in the calibrations than the actual box itself. It is good to have a way to keep your lab aligned to the outside world without risking those very valuable and sometimes irreplaceable references - especially when they age & relax enough to get really, really good.That's like looking at a 200 year-old tree your front yard and trying to put a value on it. Sure the wood is worth some xx monetary amount of worth, but you can't just replace it. In that sense the tree is priceless. We feel that way about working, well aged, well characterized and very stable Vref's

author: chuckb
author_rank: Frequent Contributor
timestamp: October 29, 2017, 03:54:14 pm
content: I was wondering about the labs that need to show "Tracability to NIST". Are they allowed to use an assumed drift rate of the zener references between calibrations?Does the in house calibration lab need to show the calibration history and the linear or log drift equations? Is there any documented guidance for that procedure other than the Fluke application notes?

author: Moon Winx
author_rank: Regular Contributor
timestamp: October 29, 2017, 06:42:25 pm
content: Quote from: chuckb on October 29, 2017, 03:54:14 pmIt depends. 17025 compliant parts of a cal certificate will not contain predicted values. The certificate may have a predicted value formula or charts but that section will not be "accredited". However, as the owner of the item you are free to do the analysis and justification for the values you use and as long as you can show your work, your justification, and it is legitimate and verifiable, then you can certainly use it.I linked to a paper earlier in this thread that provides an industry-accepted method of applying drift rate and removing seasonal variations fo the output voltage. The more data points you have, the more confident you can be in your predictions.

author: dacman
author_rank: Frequent Contributor
timestamp: October 30, 2017, 03:43:32 am
content: The drift rate would not be assumed, it would be calculated. What the study on 140 Zeners shows is that Zeners are more accurate than their specification at one calibration and can be predicted to even better uncertainty with two calibrations. What is significant about that is, with the formulas I use, I need three points to make a calculation of the uncertainty of the prediction. With two points, the calculation for the uncertainty would be infinite.

author: ap
author_rank: Frequent Contributor
timestamp: October 30, 2017, 08:24:55 am
content: Quote from: dacman on October 30, 2017, 03:43:32 amWhat calculations do you refer to?

author: dacman
author_rank: Frequent Contributor
timestamp: October 31, 2017, 12:47:19 am
content: Quote from: ap on October 30, 2017, 08:24:55 amI'm calculating the uncertainty of the predicted value of the Zener. One term is STEYX() in Excel, which requires at least three data points. If the Zener is not calibrated on a periodic basis, then the returned value (which is the standard deviation term) needs to be multiplied by what's after the standard deviation term below in order to calculate the increasing uncertainty with time.

author: ap
author_rank: Frequent Contributor
timestamp: October 31, 2017, 05:45:09 am
content: Thanks, but the standard error function STEYX calculates the standard error of an existing line of best fit accross given historical cal data points. What you would like to get though is a predicted value at a certain time with a given uncertainty (usually K=2; 95%). STEYX always looks at the total and calculates that SE. So maybe I am missing something, but STEYX imo does not support this.(not really on topic, but I guess worth while discussing briefly.)

author: dacman
author_rank: Frequent Contributor
timestamp: November 01, 2017, 12:54:32 am
content: STEYX() is a shortcut way of calculating sigma-hat. (If you look at the graphic I posted with a formula, it has a sigma-hat term.) Sigma-hat is similar to the sample standard deviation except it has n-2 in the denominator vice n-1 (and so does STEYX). If you were to calculate m and b in the linear regression formula, y=mx+b, and calculate each y value at each cal point (x values are dates), and calculate the difference (or residual) between the trend line and calibrated value, and take the standard deviation of the differences with n-2 in the denominator vice n-1, the result will be the same as using STEYX on the raw data. This is then multiplied by a prediction term to the right of sigma-hat to arrive at the standard error of the prediction. In the formula in the graphic, x is the date of the prediction (or the date of the calibration, which could be used for charting). As the date increases from the last calibration point so does the standard error of the prediction.STEYX calculates sigma-hat for a linear prediction. Non-linear predictions can also be used, and the F-Test can be applied to determine the best fit.

author: MisterDiodes
author_rank: Frequent Contributor
timestamp: November 03, 2017, 11:24:04 pm
content: Just a quick update - I did finally get some info out of Fluke that I can share here. Disclaimer: At sub-ppm uncertainty you will have to get your arrangements setup directly with Fluke - this is not an exhaustive description for every lab situation.Mind you I had to pester Fluke a few times to get real information on real uncertainties, and my questions had to get "Escalated" a few times through the tech support system before I could talk to someone in the lab at Fluke Park, so this is the new corporate Fluke policy - it's a little harder to get real information compared to a few years ago. I still don't have all questions answered, but I'll wait for another time.Also my research into this has nothing to do with accreditation, ISO17025 / NVLAP etc. I was on the search for the actual processes involved.All the info provided before is accurate on the uncertainties you'll get on a 732 a/b Cal certificate. As "standard procedure" you'll get 0.3uV/V uncertainty on the lower cals, and 0.2uV/V uncertainty on the primary lab cal. Everett Service Center group does the lower level cals and repairs, Fluke Park Lab down the street does primary lab level cals.IN ADDITION - IF your unit has gone in for several other calibrations before (like for at least three consecutive years prior, might be longer) AND it is deemed stable enough, your cal certificate will show a lower uncertainty of measure, not lower than 0.06uV/V, and will not be lower than the 95% uncertainty of measure while your unit was at Fluke. This is your snapshot absolute value and uncertainty for your long term drift rate calcs as compared to Fluke's reference. The uncertainty listed on the cert will be where you -start- adding all the other documented uncertainty historical rates for this unit over the years while it travels back and forth from one location to another. For true traceable uncertainty on a single 732 unit as shipped to your lab ready for use this uncertainty will probably be around 0.3uV/V (plus or minus, depends on your situation and drift/stability history) and when you are ready to start doing your first transfers / comparisons. This can be lowered over time with more cal cycles and more Vref's to verify.So yes, CalMachine and dacman have very good, predictable 732's. That's the only way you get .06uV/V uncertainty on the cal certificate. They have had successful repeat trips to Fluke calibration and they have developed a good documented history of performance.The 732 is a good predictable reference for sure, but that description applies to around 95% of 732's built. That leaves about 5% or about 1 unit in 20 (about) that might not be as predictable as the rest, and that's why the real way to validate Vref performance is to keep measuring against a JVS over time: you always want see how close the Vref predicted value measured up to the real calibration measure.On the question on why CalMachine's Cert is showing that it was measured against four 732a's and not the JVS - that was an easy answer: Those four 732a's are the "Fluke Four" - these are some older very well documented 732a's that are legendary around the lab as having extraordinary performance and their predictability calcs are spot-on when they are frequently calibrated to their JVS. In other words they are "stellar performers".This way they can use the Fluke Four 732a's working on keeping the production rate high on 732 primary calibrations when the JVS is undergoing its own maintenance and diagnostic procedures.Fluke also offers a service on well known & documented 732's where they will print on your unit's cal cert the expected absolute value + uncertainty on the 1st of each month over the next year, but that is not accredited.By the way - Fluke's JVS uncertainty is currently about 10nV/V - what they list on their online scope description is slightly out of date.This person also talked about a new 732C model in the pipeline - the hope is that they can provide lower than 0.06uV/V uncertainty measures on that design - but none of that will happen until it is proven over time.I also asked about the real usable uncertainty available with their DVMP - and they prefer that to be saved for a conversation directly with Fluke, because every lab will have a different situation (number of references, drift history on those references, etc.). If you're unfamiliar, the DVMP process involves Fluke sending you a 732b to your accredited lab, you pull some measures from Fluke's 732b and then they look at the test results to see how you did. If you pass you can join the DVMP club.From then on Fluke sends you a 732b that you pull your transfer measures to compare each of your references, then you ship the traveling 732b to the next lab in the group, round-robin style. When the 732b gets back to Fluke it is re-measured, and then Fluke tells each lab what the absolute value is of each of the references measured.As I said before achieving true traceable fractional ppm uncertainty at your lab location is not trivial, nor is it cheap. It is do-able but the lower uncertainty you go the required calibrations and documentation labor cost goes up. At some point it becomes more profitable for a lab to just purchase and operate a JVS of their own, and maybe sell JVS measures to other nearby labs to help offset costs.Every situation and requirement is different - use what works best.

author: dr.diesel
author_rank: Super Contributor
timestamp: November 03, 2017, 11:29:42 pm
content: Quote from: MisterDiodes on November 03, 2017, 11:24:04 pmMmmmmm, does this suggest a new/tweaked/modified design?EDIT: I mean, tweaked oven/LTFLU/circuit etc.

author: ManateeMafia
author_rank: Frequent Contributor
timestamp: November 03, 2017, 11:32:01 pm
content: Multiple LTFLU inside?

author: TheSteve
author_rank: Unknown
timestamp: December 03, 2017, 07:33:07 am
content: My new toy, just got new batteries and capacitors. Charge levels were already correct. Trescal was very kind and provided me with the 2015 cal data.

author: ManateeMafia
author_rank: Frequent Contributor
timestamp: December 03, 2017, 07:41:50 am
content: Looks great. Two more to go.

author: MisterDiodes
author_rank: Frequent Contributor
timestamp: December 05, 2017, 06:21:09 pm
content: TheSteve,That unit looks to be the same one from the Harris Semiconductor plant closing auction if I'm not mistaken, and if so it's been cold for over a year (It was cold at that auction at least). The rule of thumb from Fluke is to keep the unit powered up and hot for at least the same amount of time it was powered off -before- sending in for calibration. So if you're planning on having that calibrated at Fluke I would do that no earlier than sometime in 2019, if you don't have other information.Handy tip: Always keep test test leads short, twisted and shielded, and for best results make use of that Guard and Ground....You can always keep an eye on the temp sensor output - that should always be fairly stable no matter what the ambient temperature does, and if that's working well probably the Vref voltage is working too. We've had to repair the oven controller on (very) rare occasion, so just something to keep an eye on.

author: TheSteve
author_rank: Unknown
timestamp: December 06, 2017, 02:31:43 am
content: Quote from: MisterDiodes on December 05, 2017, 06:21:09 pmThanks for the reply MisterDiodes - my unit is indeed the ex Harris unit. This was also confirmed by Trescal when I asked them for the last cal data. The seller claimed it was stored powered on, he also did mention to me that the batteries wouldn't last long enough for shipping(so he knew a little about it). If it really was stored powered on the last year we'll never really know of course. I know when I received it I powered it up and within a few hours it was happily sitting at 10.000122x on my uncal'd 3458A. The last cal value for the unit is 10.0001044. I have had it a little over a week now, powered it off once to change the batteries and caps and it is still at 10.000122x. I am now using shielded twisted pair copper with with the shield going to guard. My only tools to measure how quiet/stable it is are a pair of 3458A's. One is more temp stable then the other but even then I can see the temp changing in the house quite easily(2-3 degree C swing through-out the day). I am hoping I can have a local lab measure the 10 volt value for me at some point. Not sure I want to invest in a Fluke cal in the near future as this stuff is all just for fun. If I do decide to go for the Fluke cal they are only a 2 hour drive away which is nice.Does anyone have a 24 hour plot of a 732A with a 3458A so I know what I might be looking for in terms of deviation etc?

author: MisterDiodes
author_rank: Frequent Contributor
timestamp: December 06, 2017, 05:42:32 pm
content: ...If you're comparing a 3458a to a working 732a...you'll be looking at mostly the drift in the 3458a more than the 732a (probably). You'll need another known working 732a/b or use multiple known Vref's / DMMs to really get an accurate idea. Otherwise just comparing two Vrefs doesn't tell you a whole lot - it just tells you how they drift -relative- to each other. Multiple 3458a's help, but a well aged, working 732a will probably drift a bit less per year than your DMM. A lot of older 3458a are very good performers also, so it could be close.For instance: We've got some 3458a's that drift around 0.8 ppm per yr, and 732a's drifting around 0.5ppm / yr or less. This is not a trivial measure, and you won't do it accurately with unknown, uncal'd equipment. You annual calibration budget will soon add up to more than the purchase price of the tools - so be ready for that. IF you're in it as a business.Don't forget you have to run AutoCal on your 3458a at a minimum every 24 hrs -OR- when temp changes 1 degC - we usually run it every 8 or 12 hrs. if you're chasing PPM - even when temp. is steady.Really you want three ea. 732's and at least one of those should be in current cal from Fluke if you're interested in accurate traceable uncertainty on your voltage measures. Otherwise it's just another unknown but steady voltage source. Hopefully you will be able to check your unit against a cal'd unit soon, and then check it again in 6 or 12 months. That will tell you a lot.Your 732a temp sensor is a very valuable indicator of the health of the box, so add that measure to your scanner switch list.Yes, I saw that at a couple auction sites before it wound up on eBay, and it was cold for those photos also - but you never know. It sounds fairly stable though - just keep an eye on it for the next 6 or 12 months to verify, and then it's probably fine once YOU know it's fine and meets your needs.That's a very good sign that its steady within a ppm for the first week or so after you powered up. That shows you're in the ballpark at least.