Advice/Experience for Keysight DMM Calibration? - Page 1
Forum section: electronics / general

author: fiddleback
author_rank: Contributor
timestamp: September 07, 2019, 11:46:59 pm
content: I’m thinking of having my 34465A DMM “calibrated” by Keysight. But I’m wary of what they’re actually going to do once they get the instrument.The website description of the calibration service says “Includes all adjustments and as-received datafor any out-of-tolerance instrument”. But they don’t ever indicate what constitutes an “out-of-tolerance” instrument. Sounds like if my unit isn’t “out-of-tolerance”, they won’t actually do any adjustments!! I’m a bit concerned that they’ll send the unit back to me saying “Nice unit you got there – we didn’t actually do anything to it. But we charged you $240.” Obviously I'm hoping that they'll adjust the instrument to the best of their ability - i.e. as well as they would "adjust" a new unit. Since the adjustment is all software-driven and automated, I can't see why they wouldn't "adjust" it.Someone please allay (or confirm!) my concerns. I’m assuming that Keysight is the best place to get a Keysight instrument calibrated. Is that a bad assumption?Thanks.

author: BravoV
author_rank: Super Contributor
timestamp: September 07, 2019, 11:59:19 pm
content: Quote from: fiddleback on September 07, 2019, 11:46:59 pmHuh, whats wrong with that ?Also, the labour cost of checking, verifying and adjustment IF needed is the whole package, dont see any cheating on that.

author: fiddleback
author_rank: Contributor
timestamp: September 08, 2019, 12:06:41 am
content: If I knew (if they stated anywhere) what "out-of-tolerance" means, then I'd at least know what I'm signing up for. If "out-of-tolerance" means 1 year specs, then I'm probably going to look elsewhere. The word "tolerance" appears nowhere in the calibration procedure, and nowhere in the user manual. So I'm really just interested in understanding what "out-of-tolerance" means.

author: xrunner
author_rank: Super Contributor
timestamp: September 08, 2019, 12:50:05 am
content: Quote from: fiddleback on September 07, 2019, 11:46:59 pmOh but they will have done something for $240. They will have verified that the unit is within it's stated tolerances. That isn't doing "nothing". You get back a unit that's been verified to be in tolerance - calibrated.

author: AG7CK
author_rank: Regular Contributor
timestamp: September 08, 2019, 01:41:40 am
content: Quote from: BravoV on September 07, 2019, 11:59:19 pmAll (I guess) cal labs offer a package that also includes Data / Adjustment or similar (measurements as received, adjustments, measurements after adjustments). You must of course pay more.The other day someone here told me that a calibration in Thailand for a HP34401A, priced at some 400USD or so, wasn't too bad. What they didn't know is that the calibration in question was a performance test with adjustments only if necessary. Yep, 400+ bucks.I can throw away my money on women, wine and song - OK. But not for an "in-spec" Y/N test of a DMM.I do however have a brand new Keithley DMM6500, so I have compared and noted down the readings for the two instruments. Given that I can trust the DMM6500, and given that the 34401A is not too far away from the DMM6500, I say this is good enough for a crude check.And then I wait until I find a cheaper calibration with Data.

author: fiddleback
author_rank: Contributor
timestamp: September 08, 2019, 02:18:51 am
content: I should clarify here, that my real concern is not with the cost. My concern is that the criteria that Keysight uses to determine whether or not to perform adjustments is simply not stated. I've tried submitting the question via their website, but so far have not gotten a reply.

author: niner_007
author_rank: Frequent Contributor
timestamp: September 08, 2019, 02:44:13 am
content: Calibration is not adjustment. How will they know it's in tolerance depends on the calibration procedure, look in the Operating and Service guide, which is available for download from Keysight. On page 508 there is a performance verification sheet which documents the tolerances, they'll most certainly use that to determine whether to adjust or not. You can always ask for adjustment, including Keysight when you calibrate, even if the instrument is in spec. That's likely a bad idea as you can easily lose the trend over time if you do constant adjustment and even disturb its aging process, making it worse and ending up with a less accurate and stable instrument. I'd never adjust if it's in spec.

author: fiddleback
author_rank: Contributor
timestamp: September 08, 2019, 03:33:12 am
content: Quote from: niner_007 on September 08, 2019, 02:44:13 amThanks, niner. Now we're getting to the crux of the matter! The manual does indeed list acceptable "Error from Nominal" figures. In fact, they list FOUR DIFFERENT SETS of these - 24 hour/90 day/1 year/2 year. So which of these would they use? One would hope 24 hour, but this is speculation. I'll try to get in contact with them via phone or via email to see if I can get a definitive answer.

author: maat
author_rank: Regular Contributor
timestamp: September 08, 2019, 04:14:08 am
content: "Out-of-tolerance" is not just depending on the numbers. Keysight will also check your DMM pyhsically and if for example there are any broken/missing buttons or so (not counting the usual wear and tear), they unit will be considered 'out-of-tolerance'. They will then contact you and ask you how to proceed. Whether they should repair it (at additional cost) or if it is minor, they can still perform just the calibration. They will then compare the device to its 1-year spec to see if the numbers are ok. The same will be done after adjustment.I hope this helps.

author: niner_007
author_rank: Frequent Contributor
timestamp: September 08, 2019, 04:38:28 am
content: Quote from: fiddleback on September 08, 2019, 03:33:12 amthey'll use time since last calibration, the meter won't be in 24hr spec after 1 year, or when you last calibrated, if that's more than 24hrs

author: 2N3055
author_rank: Super Contributor
timestamp: September 08, 2019, 02:02:15 pm
content: When you send instrument for calibration, if instrument is checked against 90 days test limit and fails, then calibration adjustment is performed. After calibration adjustment is performed, instrument has to be within 24 specs. If it's not, another calibration adjustment is needed, and if it fails that then it needs to be repaired.****The acceptance test results should be compared against the 90 day test limits.You should use the 24 hour test limits only for verification within 24 hours after performing the calibration adjustment procedure. If the instrument fails performance verification, calibration adjustment or repair is required.***That means that if you send it in they will measure it (performance verification) and if your instrument is within 90 days spec , no adjustment will be done, unless specifically asked for.If they do adjustment, they guarantee it will leave their facility with 24 h specs...

author: tszaboo
author_rank: Super Contributor
timestamp: September 08, 2019, 02:07:08 pm
content: Actually, you should familiarize yourself with the proper terminology."In measurement technology and metrology, calibration is the comparison of measurement values delivered by a device under test with those of a calibration standard of known accuracy. Such a standard could be another measurement device of known accuracy, a device generating the quantity to be measured such as a voltage, a sound tone, or a physical artefact, such as a metre ruler....Strictly speaking, the term "calibration" means just the act of comparison, and does not include any subsequent adjustment." -Wiki

author: 2N3055
author_rank: Super Contributor
timestamp: September 08, 2019, 02:14:20 pm
content: Quote from: NANDBlog on September 08, 2019, 02:07:08 pmThat is terminology, and in pure metrology circles things are cleanly and clearly defined that way.Keysight itself calls things:calibration = "performance verification"instruments adjustments = "calibration adjustment"So most people think that when you say "calibration", that that means shorter version of second term....Not everybody is Voltnut. Most people in small companies don't need things calibrated at all, and in larger companies, calibration is sticker that magically appears on meters every now and then when people in charge of calibration do their job..

author: fiddleback
author_rank: Contributor
timestamp: September 08, 2019, 04:46:46 pm
content: Quote from: 2N3055 on September 08, 2019, 02:02:15 pmThanks, 2N.What you have described sounds most rational to me, so I'm thinking that it is correct. I still intend to attempt to follow up with Keysight to verify. If I get an answer from them, I'll post it.I'm also curious about the option to simply request an adjustment, especially since this was not an option listed for the 34465A. I'll ask about that too...P.S. I think that your statement is, for the most part, very true:Quote

author: 2N3055
author_rank: Super Contributor
timestamp: September 08, 2019, 08:34:38 pm
content: Quote from: fiddleback on September 08, 2019, 04:46:46 pmAbsolutely ask for clarification and explanation of work to be performed. Just in case..

author: tszaboo
author_rank: Super Contributor
timestamp: September 08, 2019, 09:55:47 pm
content: Quote from: fiddleback on September 08, 2019, 04:46:46 pmBut why would they. Unless you abused it, it is very unlikely to be out of spec.I would be more upset if they silently just brought the unit in spec, saying nothing.Quote from: AG7CK on September 08, 2019, 01:41:40 amYou should clearly only calibrate it, if you make money with the thing. For example production testing, production calibration, adjustment, making test reports etc. If you have it just for the kick of it, then dont calibrate it. I can relate to that, it would be nice to have a 6-7-8 digit meter at home, but I would be too cheap to calibrate it as well. I mean it costs more in a year then Netflix.

author: dl1640
author_rank: Regular Contributor
timestamp: September 08, 2019, 11:35:33 pm
content: Local Keysight would charge you the standard calibration price even the unit is completely non-functioning as expected and their reason is the work is done so you must pay, after fight with them they just send back the unit free of charge. Be aware of that!

author: niner_007
author_rank: Frequent Contributor
timestamp: September 09, 2019, 07:45:30 am
content: Quote from: fiddleback on September 07, 2019, 11:46:59 pmThey looked at it and calibrated it, that's everything, the cost includes a lot more than the labor, they have to maintain a lab, with very expensive instruments, they need to keep the instruments always in spec, and regularly calibrate all of them, that's very, very expensive!

author: tszaboo
author_rank: Super Contributor
timestamp: September 09, 2019, 08:20:45 am
content: Quote from: niner_007 on September 09, 2019, 07:45:30 amExacltly, you have to pay them having a Fluke 5720A other equipment there. That is an 80000 USD gear. And that one is probably only can be calibrated by a selected few specific labs, or national standards. And the calibration procedure takes time, so you actually have to pay someone standing there, making the connections, etc. It is really not that expensive if you think about it.

author: maat
author_rank: Regular Contributor
timestamp: September 09, 2019, 09:40:23 pm
content: Quote from: NANDBlog on September 09, 2019, 08:20:45 amFor 344XXX cal33250A Function/Arbitrary Waveform Generator5720A Calibrator5725A Amplifierto be preciseTheir calibration prices are rather modest I would say (In comparison to Fluke et al.). Especially if you wait until the end of the year, when they do special deals.

author: Qmavam
author_rank: Regular Contributor
timestamp: September 10, 2019, 01:49:35 am
content: My one and only experience with a calibration service was, after sending two emails discussing my particular unit, I sent it in only to get a call says, "your unit is out of calibration.If it wasn't I could have certified it. But since it needs calibration, my equipment is not able to calibrate your two lowest ranges."I countered with aren't most units sent in because the need calibration, "no, usually we just verify there are up to specs and return them."So, you you get certification for your $240, but often, no alignment/adjustment is done.I sent my unit to another calibration service, I hope it comes back within the 1% factory tolerance on all ranges over the rated bandwidth.Mikek

author: TiN
author_rank: Super Contributor
timestamp: September 10, 2019, 04:19:18 am
content: Was this Keysight calibration lab? Inability to calibrate some ranges sounds bit strange because equipment requirements needed for verification and calibration adjustment is usually same.Adjustment in modern DMMs is done digitally, so you don't need to trim pots or adjust any parts inside, only need to know true input reference value and uncertainty of the measurement and DUT.

author: fiddleback
author_rank: Contributor
timestamp: September 15, 2019, 10:00:18 pm
content: A quick update: The following information is what I have received DIRECTLY FROM KEYSIGHT:1) The following is from a telephone conversation with a technician who works on 34465A's at Keysight's Roseville, CA facility. He was unequivocal about this:For the 34465A (and some other newer instruments), Keysight ALWAYS PERFORMS AN ADJUSTMENT. In fact, what they do is:a) Take a set of "as received" readings,b)Perform the adjustment,andc) Take a set of "as adjusted" readings.Following completion of this process, the unit should be "adjusted" as well as it was when it left the factory new.2) As part of the service agreement, Keysight provides the following statement IN WRITING:"If the unit is sent in for calibration only, and fails, a new quote will be issued adding repair to your calibration request. If you reject the quote, 50% of the calibration cost will be charged."Answer #1 is precisely what I had hoped for in the first place.(It was fear that this would not happen that led to my snarky remark in the original posting. I'm swearing off snarky remarks!!) Not surprisingly the software assessment/adjustment process is sufficiently automated so there is no point in not doing an adjustment. Having gotten this information, I immediately paid my money, boxed up the unit, and shipped it back to Roseville.Answer #2 makes sense and seems reasonable to me. (I don't anticipate that my unit will need repair.)So, at the moment, I am completely on-board with Keysight's processes and policies for the 34465A. I do, however, wish that their website (which indicates that the "adjustment" is conditional) was correct. I'll post an update when I get the unit back, to confirm what actually happened...(BTW, it took several attempts, and the starting of a service agreement, to get through to someone who could actually answer my question, but it eventually did work...)

author: TiN
author_rank: Super Contributor
timestamp: September 16, 2019, 01:23:23 am
content: Regarding 1) hopefully this does not apply to 3458A and alike, or many customers would be upset.

author: dl1640
author_rank: Regular Contributor
timestamp: September 16, 2019, 10:59:43 am
content: Quote from: TiN on September 16, 2019, 01:23:23 amAs a standard option, they do.

author: fiddleback
author_rank: Contributor
timestamp: October 06, 2019, 11:54:27 pm
content: Just to finish up here, regarding 34465A calibration/adjustment by Keysight:The meter was returned within about a week, and Keysight kept me very well posted regarding its progress. In fact I was able to retrieve the complete Measurement Report from their website several days before I actually received the unit back.The unit was indeed "adjusted" as promised verbally (but contrary to the wording of the service agreement)As promised, very comprehensive 'as received' and 'as adjusted' reports were providedSomewhat surprisingly to me, 1 year upper and lower limits were used in the reports - even for the 'as adjusted' comparison. All of the 'as adjusted' readings on my unit appeared to be within the 24 hour spec. But this does indicate that I could have received a unit back that just barely met 1 year limits and it would have "passed" calibration.Somewhat surprisingly to me, the unit was adjusted at a temperature of 25.6C, and ACAL'd at 25.3C. (Working mostly with boat anchors, I was expecting 23.0C.) I'm guessing that since this unit has an ACAL capability (that I'm wary of using), Keysight judges that any adjustment temperature is OK. Personally, I don't exactly buy into this, because ACAL only corrects for DC voltage and resistance measurements. Others (current, AC voltage) are spec'd based on the "CAL" temperature.As to performance, +10VDC was found to be 5PPM low (it was 1PPM low at time of manufacture). After adjustment it was <1PMM low.10K Ohms was found to be 3PPM high (it was <1PPM low at time of manufacture). After adjustment, it was dead on.As an aside, I've found the DCV tempco of this unit to be approximately 0.20 PPM/C, which I find to quite respectable.All-in-all, I'm fairly pleased with the Keysight calibration and would do it again, although I have to say that if a different model were being calibrated, I'd go through the entire up-front communications effort again - to find out what they ACTUALLY do, not what the website SAYS they do.

author: Andreas
author_rank: Super Contributor
timestamp: October 07, 2019, 06:08:40 am
content: Hello,the 25.6 deg C are they stated as room temperature or is this internal device temperature?On the "as received" data is there any reading outside of 70% of the 1 year spec?This is the limit that I found on a formerly Keithley web site (no longer available) for doing adjustments.with best regardsAndreas

author: e61_phil
author_rank: Frequent Contributor
timestamp: October 07, 2019, 06:43:56 am
content: Quote from: fiddleback on October 06, 2019, 11:54:27 pmSuch numbers only make sense together with uncertainties. Could you also say how big the uncertainties of the calibration are?I also read in the 34401A manual that HP suggested to always adjust these "lower precision" meters every time to ensure it stays in spec over one year.Calibration against the values of the used calibration intervall (normally one year) is normal. Otherwise you would need lower uncertainties which is more expensive and not needed. The 24h are over before the unit has been returned.

author: fiddleback
author_rank: Contributor
timestamp: October 07, 2019, 03:53:12 pm
content: Quote from: Andreas on October 07, 2019, 06:08:40 amInternal temperature.The calibration page on the display shows the current internal temperature in real time. It also shows the difference between the current temperature and the calibration temperature to a tenth of degree Celsius, and it updates a couple of times per second. So adding the difference to the current temperature give you what was presumably the internal temperature at time of last calibration.Note that this device has a fan that runs all the time, and doesn't produce much heat, so I find that internal temperature is generally not all that much hotter than room temperature.Quote from: Andreas on October 07, 2019, 06:08:40 amNo, everything was very close to nominal - way inside even the 24 hour spec. If I get a chance, I'll calculate PPMs for each measurement - there are very many! - and report on my findings.Quote from: e61_phil on October 07, 2019, 06:43:56 amKeysight DOES offer a calibration with an uncertainty report, but, of course, this is more costly. They do, however, indicate the calibrator used (5730A), and the certificate number of its current calibration. The "cal due date" on the calibrator was 30Aug2020, so I'mguessingthat the calibrator may have been calibrated only a few weeks prior to calibrating my unit.Quote from: e61_phil on October 07, 2019, 06:43:56 amTrue, of course. But I suspect that 24 Hour specs are intended more for use in transfer measurements. The HP 33401A Service Guide says:"The 24-hour accuracy specification indicates the multimeter's relative accuracy over its full measurement range for short time intervals and within a stable environment Short-term accuracy is usually specified for a 24-hour period and for a +1 C temperature range."I suspect that the key word here is "relative". Even if the absolute accuracy of the unit is way off, the relative accuracy is typically more meaningful in transfer measurements.Thanks for the great questions and observations!

author: Grandchuck
author_rank: Super Contributor
timestamp: October 07, 2019, 06:00:34 pm
content: As to performance, +10VDC was found to be 5PPM low (it was 1PPM low at time of manufacture). After adjustment it was <1PMM low.My 34465A has drifted low on the +10VDC by an amount similar to yours. It has not been sent back for calibration. I also have a 3458A and some trusted references and that is how the drift has been determined.Has any one else seen this type of drift? Not complaining BTW ... just curious

author: e61_phil
author_rank: Frequent Contributor
timestamp: October 08, 2019, 10:47:08 pm
content: Quote from: fiddleback on October 07, 2019, 03:53:12 pmof course?!?!?! Without uncertainties I wouldn't call it a calibration certificate. Guessing isn't the right approach in metrologyEven the most 3458A certificates from Keysight I saw stated uncertainties of a couple of ppm even in the 10V range.It is nice that it shows readings close to the nominal values, but as already said it means nothing. I often saw DMMs which agreed perfect to each other and after comparing them to a well known standard one could show both are wrong in the same direction and value. And even with a freshly calibrated calibrator it doesn't mean that the calibrator was adjusted, if it was still within spec (3.75ppm/a for 10V, everything else is worse). It depends how they use the 5730A (and if they do it like Fluke suggests). Normally you run an artifact calibration from time to time. That expands the calibration cycle of the 5730A to two years. Otherwise Fluke recommends to calibrate the 5730A yearly. In the end it is the decision of their department.

author: Gandalf_Sr
author_rank: Super Contributor
timestamp: October 20, 2019, 09:52:03 am
content: I just had my 34461A calibrated by Keysight in Roseville and, like fiddleback, I found their web site to be as clear as mud. I too called a couple of times and got passed around until I eventually spoke to someone in their calibration department called Neil who confirmed what fiddleback said above; their $240 calibration service does a pre adjustment test, then the meter is adjusted, and then tested again; the results of both the pre and post adjustment tests are included in the calibration report and they send you a paper calibration certificate.On the subject of logistics/cost, it's cheaper to take the $228 'Keysight Calibration Agreement' option ($228) because, apart from the$12 saving, you only have to pay for the shipping TO Keysight and they ship it back at their cost; the 'Keysight Calibration - Per Incident' option ($240) performs the same calibration but you have to pay the shipping both ways.When you take the Keysight Calibration Agreement option, you have to fill in a load of information and then you get a receipt that says you've paid for a service agreement which was very confusing and, at first, I thought they'd conned me into paying twice but, in reality, the agreement you purchase includes the ability to send the meter back for calibration at any time during the year of coverage (you pay to ship it to them with an RMA number they issue after you request the calibration service) and then they ship it back to you at their cost.

author: mzzj
author_rank: Super Contributor
timestamp: October 20, 2019, 03:13:14 pm
content: Quote from: e61_phil on October 08, 2019, 10:47:08 pmThat's how it goes with big names like Keysight and Fluke. Factory calibration certificates are often good as toilet paper even from the big names.For example National Instruments sells you traceable calibration without uncertaintieshttps://www.ni.com/services/calibration-compare/Consensus among metrology folks is pretty strong that you can't have traceability without uncertainties...

author: e61_phil
author_rank: Frequent Contributor
timestamp: October 20, 2019, 03:48:50 pm
content: Quote from: mzzj on October 20, 2019, 03:13:14 pmThe certificates that came with the Keysight 34470A were such factory calibration certificates without any use (we need them for accreditation). But the Fluke 8508A and also the Fluke 5730A came with proper calibration certificates. But that is calibration gear and therefore probably not comparable.I don't know how the test rig for the adjustment and end test of such meters look, but if there is a rig with a calibrator which is used to adjust the meter the first time after producation and after that test ("calibrate") the meter it is no surprise, that all these meters are "spot on". That would be even the case if the used calibrator is way off.

author: dl1640
author_rank: Regular Contributor
timestamp: October 21, 2019, 11:18:48 am
content: iirc, the 5730A is calibrated on 2-year basis, in between maybe to execute a cal check to get a bird view of drift, if they calibrate 8.5 digit meter, the reference is a reference meter, the 57xx is used as a stable source.

author: tszaboo
author_rank: Super Contributor
timestamp: October 21, 2019, 12:29:34 pm
content: Quote from: e61_phil on October 08, 2019, 10:47:08 pmThe uncertainty is written in the datasheet of the multimeter. There are like 3 pages of it.

author: dl1640
author_rank: Regular Contributor
timestamp: October 21, 2019, 01:28:27 pm
content: no, uncertainty on calibration certificate is not your meter’s data sheet. the uncertainty is evaluation of how uncertain the reported measurement data is, usually it includes short term repeatability of your meter, finite display resolution of your meter, measurement standards uncertainty, measurement procedure uncertainty, tempco if relevant etc., in general it is limited by the class of your meter because finite resolution, intrinsic noise etc., you can’t get better reported uncertainty of 34401 than 3458, different class, even the cal source is the same 5730.

author: tszaboo
author_rank: Super Contributor
timestamp: October 21, 2019, 02:48:27 pm
content: Quote from: dl1640 on October 21, 2019, 01:28:27 pmQuote

author: dl1640
author_rank: Regular Contributor
timestamp: October 22, 2019, 12:34:57 am
content: well, your meter’s spec normally includes calibration uncertainty of manufacturer, this is true in many of Fluke calibrators, they call this absolute uncertainty and is reported as 3 sigma to give you more confidence but sometimes conservative, however if you have better measurement standards than Fluke have, you are able to have better meter spec...but i don’t think that is needed for daily applications unless you are a true nuts.