how do you calibrate a dvm with 6.5 digits? - Page 1
Forum section: electronics / testgear

author: Joop01
author_rank: Contributor
timestamp: May 01, 2023, 02:40:41 pm
content: I'm planning the layout of my own lab, I planned for a R&S dvm HMC8012, but unfortunately it is no longer manufactured, that is that all shops no longer deliver the meter. So refocus. The HMC was 5 3/4 digit, it must be the same or better. If you make a list you end up with 5.5 or 6.5 digits meters. If you look at the specs you can read that its valid for a year. After that it won't be off that much, but after some time you need to re-calibrate, but how do you calibrate those meters? Send it back for calibration?, which has the risk that the box is dropped on the floor or so when its send to the manufacturer (or what's available) or returned to you. This is the reason I want to do it myself, but with what? I have designed calibration stuff, but that's 0,1% at best. Those 5.5 or 6.5digit meters have a lot more 0 figures behind the decimal point. Buy two meters (from different manufacturers)?

author: BeBuLamar
author_rank: Super Contributor
timestamp: May 01, 2023, 02:53:26 pm
content: If I were you I either send it to the manufacturer for calibration or not having it calibrated as I don't think they change much over the years. I think you can buy the equipment to calibrate it but then they are very expensive and they need to be calibrated too.

author: Fungus
author_rank: Super Contributor
timestamp: May 01, 2023, 03:08:37 pm
content: Quote from: Joop01 on May 01, 2023, 02:40:41 pmYou don't need zeros after the decimal point to see if it's changing. Measure the most stable reference you own using the meter when it arrives. Measure it again every six months using the same reference under the same conditions, see how much it changes (if at all). You might need an oven to get a stable temperature for this.These meters are designed to not change with time, and they usually don't. The best bet is just to monitor it and take no action unless you think it needs it.Youcouldspend the first few days of ownership messing around with a trimmable voltage reference in your oven. See how many zeros you can get after the decimal point using the circuit in the datasheet.

author: nctnico
author_rank: Super Contributor
timestamp: May 01, 2023, 03:13:05 pm
content: Quote from: Joop01 on May 01, 2023, 02:40:41 pmYou are overreacting here. Test equipment is shipped around all the time for calibration. Just make sure to ship it in the box + packaging it came in; that has been designed to survive any kind of transport. IOW: just send it to the manufacturer for calibration and be done with it.

author: coromonadalix
author_rank: Super Contributor
timestamp: May 01, 2023, 03:26:48 pm
content: Exactly same toughts, to build you own cal lab you need control over humidity / temperatures etc .... you can not play godi always heard for a 6.5 digit you need at least 7.5 or even 8.5 digit calibrators, and check all their used prices lolllbetter send it, you receive the cal sheet etc ... and way less costly in time or ressources

author: Joop01
author_rank: Contributor
timestamp: May 01, 2023, 03:45:30 pm
content: Quote from: nctnico on May 01, 2023, 03:13:05 pmMay be, last shipment on my door had a harmonica shape. Double boxes, so box in a box! Power supply casing split in two. Got a new one. Last time on tv, some footage of tntpost, three packages on the edge of the van floor and they dropped on the street. So I have some mixed feelings about that.

author: Joop01
author_rank: Contributor
timestamp: May 01, 2023, 03:50:10 pm
content: Quote from: coromonadalix on May 01, 2023, 03:26:48 pmLast is true, but controlling humidity and temperature is way easier then most think. One of the tricks is too wait for the right conditions. You need of course two meters for that, one for humidity and one for temperature.

author: nctnico
author_rank: Super Contributor
timestamp: May 01, 2023, 03:51:35 pm
content: Quote from: Joop01 on May 01, 2023, 03:45:30 pmOfcourse you'd ship equipment with UPS or Fedex. Not regular postal serviceNevertheless, equipment should be packed well enough to survive a drop from 1 meter high (which IIRC is part of a standard for packaging requirements).

author: Fungus
author_rank: Super Contributor
timestamp: May 01, 2023, 03:56:39 pm
content: Quote from: nctnico on May 01, 2023, 03:51:35 pmThere's a difference in how they treat things?

author: NoisyBoy
author_rank: Frequent Contributor
timestamp: May 01, 2023, 05:14:08 pm
content: If you are truly serious about calibration to bring it within spec, it simply isn’t feasible for most labs, let alone home labs. There are numerous calibration point within each function, each requiring an extreme stable source. My 6.5 digit meters requires Fluke 5720A and 5725A or later for proper calibration, these equipment would far exceeds the cost of most home labs.It depends on where you live, in the US, I am fortunate to have Keysight. They have a service depot locally, they come out in their padded equipment van to pick up the equipment from my lab for calibration. It is always fun to peek inside their van to see what other exotic test equipment is on the way back for calibration or repair. I read they may not serve home labs, if that is the case, look for other local cal labs. My local third party cal labs also do pick up and delivery, which minimize the risk due to shipping damage.

author: Joop01
author_rank: Contributor
timestamp: May 01, 2023, 06:17:37 pm
content: Quote from: NoisyBoy on May 01, 2023, 05:14:08 pmWhat amazes me is how difficult they do about what a product cost. With some trouble I found the 5720A, way above my head or what I want to spend on it. Didn't found 5725A. Did found that the 6.5 digit is no longer in catalog. They have now only a 5.5 digit Bench meter. Back to my question, if it is not possible to calibrate your own equipment, then what is the point in having, say, a 6.5 digit bench multi meter?. What I looking at?

author: alm
author_rank: Super Contributor
timestamp: May 01, 2023, 07:11:08 pm
content: Quote from: Joop01 on May 01, 2023, 06:17:37 pmCalibration is about having readings that are traceable to national standards. For many applications you need resolution (to determine how much a value changes with temperature, for example), but not necessarily accuracy. Also, good quality 6.5 digits like the classic HP/Agilent/Keysight 34401A are known to stay within their stated 1 year accuracy or most ranges for years, though if you want to certify this, you will need to have it calibrated every year. But for many hobbyists, knowing that a voltage is 5V +/- 1% but it's varying at most 0.5 mV over load or temperature is good enough.If you need traceability, for example because your customers demand it, then you'd send it to a cal lab at the interval the manufacturer recommends (often 1 year, sometimes if you want higher accuracy). I haven't kept track of prices, but I'd think that calibration of a 6.5 digit meter would be in the ball park of $200.The problem with calibrating it yourself is a) that you need another reference with traceable calibration with lower uncertainty than the desired uncertainty of the calibration and b) that you need stable sources for all signals that the meter needs, unless you want to do a limited calibration of only DCV and Ohms, let's say. For a full calibration might need DC voltages from 100 mV to 1000 V, resistance from 100 Ohm to 100 MOhm, DC currents from 10 mA to 2 A, AC voltages from 100 mV to 750 V from 10 Hz to 50 kHz and AC currents at 1 A and 2 A at 1 kHz (this is for the 34401A, check the service/calibration procedure for your DMM). Especially high frequency, high voltage AC is often difficult in your average lab. This all needs to have a stability much better than the desired uncertainty. So a basic 1/4W resistor will definitely not be stable enough for this comparison.So either you would need a more accurate DMM that was calibrated before and stable sources for all these signals, or a calibrated multi-function calibrator that can source all these signs with a low enough uncertainty. This is how the cal labs do it, but they might be investing $100k in equipment and another $10k or so for yearly calibration. They make this back in the volume of equipment they calibrate.

author: bdunham7
author_rank: Super Contributor
timestamp: May 01, 2023, 07:49:55 pm
content: Quote from: Joop01 on May 01, 2023, 06:17:37 pmIf you actuallyneeda current traceable calibration certificate then you have to ship it to a certified (to whatever standard you require) calibration lab. To actually set that up yourself for a typical 6.5-digit bench meter like Keithley DMM6500 or Keysight 34465A would take an enormous investment in equipment and then you'd still have to get whatever accreditation you require--and then you'd still have to have that equipment calibrated periodically at an exponentially higher cost. Nobody does that unless they have hundreds or thousands of instruments to calibrate. The point of having a calibrated 6.5-digit meter is that you can take measurements with the meter and be fairly sure that the are accurate within the specifications of the meter.Now if you wanted to check the calibration unofficially, you could get a few standards or DMM-check type units that would at least verify that your meter is not broken and hasn't drifted grossly out of spec. However, to get the precise high-voltage and high-frequency calibration stimuli that is required for a full calibration would still be a very daunting task. Some of us do this sort of thing as hobby, but I would never guarantee results although I'm pretty sure I can get pretty close.I have no idea why you think that nothing can ever be shipped--how do you get your new meters? If getting a new meter is the only way you can get something without it being smashed, just buy a new meter every year or two, depending on your calibration cycle. It will be way cheaper, especially if you sell your old one.

author: Fungus
author_rank: Super Contributor
timestamp: May 01, 2023, 08:01:14 pm
content: Yeah, is this calibration needed for legal reasons or are you just doing it as a hobby?As noted, these things are designed not to go out of calibration. Maybe all you need is a way to convince yourself of that fact.Adjusting it if it ever goes out of spec usually needs a lot of fancy equipment. You usually need severalveryprecise references, one for each range.

author: David Hess
author_rank: Super Contributor
timestamp: May 01, 2023, 09:02:45 pm
content: I usually settle for periodically checking the calibration as best I can against my best references and my best other multimeter.

author: Joop01
author_rank: Contributor
timestamp: May 01, 2023, 10:09:03 pm
content: Quote from: bdunham7 on May 01, 2023, 07:49:55 pmFirst question, jump in my car and drive to the reseller. I have a special floor in the car for transporting equipment. Second remark, thanks, figured out the same thing. I have downloaded a service manual for a dvm and what you need to do the job. As said before, that's way above what I want to spend. Second hand somewhere between 60.000 and 75000 dollars, so new will be much more. Also with so much figures behind the decimal point I think you can safely ommit the last two. Also I agree with you that you can buy a new every two years, prices are dropping due to some genius in China who put all in one chip.

author: Joop01
author_rank: Contributor
timestamp: May 01, 2023, 10:14:40 pm
content: Quote from: Fungus on May 01, 2023, 08:01:14 pmNo, I'm just a hobbyist who happens to have a hobby with equipment which is not available on the market. Your second remark, I could not find specs for a period longer than 1 year. I think your right.

author: Martin72
author_rank: Super Contributor
timestamp: May 01, 2023, 10:26:43 pm
content: QuoteIt never occurred to me to calibrate my measuring instruments myself, because I simply do not have the means to do so and do not want to buy them.It is much easier and cheaper to have them calibrated externally.If it were necessary in the hobby area.I had once exemplary done and my Brymen 869S calibrated externally (cost 79 €).In the "Pro" area it looks different, we have to calibrate all our measuring equipment annually.If we had them calibrated to the DakkS standard, we could extend the time between calibrations.But it is enough to have them calibrated according to ISO with equipment calibrated according to DakkS.Why do you need the accuracy of a 6.5 digit meter in the private sector, that is another question.If I have to measure something to three decimal places, then it doesn't matter whether my 6.5 digit meter is calibrated or not.

author: bdunham7
author_rank: Super Contributor
timestamp: May 01, 2023, 10:34:12 pm
content: Quote from: Joop01 on May 01, 2023, 10:09:03 pmWell, depending on where you are, Tektronix Eindhoven seems driveable, at least to me, and they likely can recalibrate your meter. If that isn't driveable, buy a Pelican case for it. I have these for my better handheld and my best bench meter so that they can travel with an almost indestructable shield. I doubt any reasonable courier service would destroy a fairly light and well protected package like that on such a short trip--it's usually the heavy ones that get slammed.https://www.tek.com/en/calibration-services/netherlands/eindhovenIf you buy a new Keithley DMM6500, it has a 2-year calibration cycle (at slightly worse specs than 1 year) and is actually pretty unlikely to go out of spec even over a decade. One ISO-17025 calibration after two years should convince you of that.https://download.tek.com/datasheet/1KW-61315-1_DMM6500_Datasheet_072121.pdf

author: Someone
author_rank: Super Contributor
timestamp: May 01, 2023, 10:58:36 pm
content: Quote from: Martin72 on May 01, 2023, 10:26:43 pmall? at places I have worked the safety and compliance bits were kept calibrated but the rest didn't matter. Where "the rest" could be 99% of the equipment and never less than half.

author: Martin72
author_rank: Super Contributor
timestamp: May 01, 2023, 11:05:49 pm
content: OK, not all...Multimeter, current clamps, current probes for scopes, oscilloscopes, poweranalyzer, high voltage tester, isolation tester, current shunts, temperature sensors, frequency counters, spectrumanalyzer, data logger/recorder, frequency generators, pressure gauge, test pumps for testfield.Crimp tools, torque wrench and soldering stations in the production area.

author: BeBuLamar
author_rank: Super Contributor
timestamp: May 01, 2023, 11:30:42 pm
content: Quote from: Joop01 on May 01, 2023, 10:14:40 pmI have sent some Fluke meters in for repair. Some of them are like 10 years old and after the repair they did the calibration and sent me the reports. All of them said in specs no adjustment needed and thus I don't worry about having my meter calibrated every year.

author: BeBuLamar
author_rank: Super Contributor
timestamp: May 01, 2023, 11:32:28 pm
content: Quote from: Joop01 on May 01, 2023, 10:09:03 pmLet assume that you have the money for the calibration equipment but those eqeipment need calibration too right?

author: Martin72
author_rank: Super Contributor
timestamp: May 01, 2023, 11:39:21 pm
content: QuoteMeh....Fluke I agree immediately, we have a fluke 87 from 1992, until now every year calibrating without any re-adjustments needing.My brymen 869s was external calibrated a few weeks after buying it new and needed some re-adjustments while calibrating.My hint in general:Buy a "cheap" reference and when something suspicous occurs while measuring, give the meter away for calibrating.https://www.welectron.com/DMMCheck-Plus-Multimeter-Calibration-Reference

author: Tony_G
author_rank: Super Contributor
timestamp: May 02, 2023, 12:40:58 am
content: Just wanted to add that if you're in the US then you can get the unit that Martin referenced fromhttps://dmmcheckplus.com/- They used to be made byhttps://voltagestandard.com/here in WA state but I seem to remember that the volume rate was too low or something like that and they sold off that part of the business.I have one and have been pretty happy with it over the years.TonyG

author: J-R
author_rank: Super Contributor
timestamp: May 02, 2023, 03:16:51 am
content: Be sure to cruise the Metrology forum. There are a lot of conversations about this topic over there.My top comment is: don't forget to observe accuracy specifications. For example, with the HMC8012 a 10V DC input could display between 9.9972-10.0028 and still be within the 1 year spec. It also requires a 90 minute warm-up period. So you probably could get away with sanity checking it against a $175USD 50,000 count DMM in this case.This next thought was mentioned in passing, but start building a small collection of references/standards that you can use to check your equipment regularly. It's better to ship those out than the equipment itself. Only if your test equipment shows evidence of being out of spec would you then have it calibrated/adjusted.Unfortunately, all three of the top references/standards that I would suggest for a typical hobbyist to consider are currently out of stock:https://dmmcheckplus.com/shop/ols/products/dmmcheck-plus-without-enclosurehttps://voltagestandard.com/shop/ols/products/pentarefhttps://www.ianjohnston.com/index.php/onlineshop/handheld-precision-digital-voltage-source-2-mini-detailAlso, it's good to have some precision resistors for checking resistance functions, but also for various Ohm's law calculations. This can help you generate additional inputs for your equipment in order to check things from different directions.Used/vintage gear can be popular due to stability from aging. You could mix vintage for stability along with new for modern features like ethernet and big, color screens.

author: TheDefpom
author_rank: Frequent Contributor
timestamp: May 02, 2023, 09:43:27 am
content: Quote from: J-R on May 02, 2023, 03:16:51 amI believe Ian is currently building some more PDVS2 Mini's so he may have stock soon, he did a video on it the other day.

author: tautech
author_rank: Super Contributor
timestamp: May 02, 2023, 09:48:07 am
content: Quote from: TheDefpom on May 02, 2023, 09:43:27 amI hear he might be short of caps after he sent a booby prize package to you.

author: TheDefpom
author_rank: Frequent Contributor
timestamp: May 02, 2023, 09:53:31 am
content: Quote from: tautech on May 02, 2023, 09:48:07 amI still need to sit down and start sorting those out...

author: Tony_G
author_rank: Super Contributor
timestamp: May 02, 2023, 11:26:43 pm
content: I need to revisit my TEA cred, I haven't tried to acquire one of Ian's standards because I had the DMMCheck (along with an uncalibrated 5200A & a working 5440B).Quote from: TheDefpom on May 02, 2023, 09:53:31 amShould probably get onto that, assuming you haven't run him out of the "Cap Game" DefPom.TonyG

author: NoisyBoy
author_rank: Frequent Contributor
timestamp: May 03, 2023, 12:19:30 am
content: Of the three standards, I like DMMCheck the best because it checks more than voltage, but other functions such as AC/DC voltage/current, resistance, frequency, and duty cycle as well. I noticed they now have an add-on LC reference module.This would be my pick for a sanity check reference if I suspect the DMM is acting up. The key is understanding what its name implies - Check, it is a validation reference, not a calibration reference, and definitely not for 6.5 digit meters. But it may be good enough to be used to calibration cheap handheld DMMs with calibration pots.I like all three suggestions, good picks.Quote from: J-R on May 02, 2023, 03:16:51 am

author: David Hess
author_rank: Super Contributor
timestamp: May 03, 2023, 07:32:22 pm
content: I have been thinking ofQuote from: J-R on May 02, 2023, 03:16:51 amI have been thinking of getting the Pentaref with a set of voltages that I can accurately multiply up to higher voltages like 19 (9.5x2), 190 (9.5x20), and 950 volts (9.5x100) for calibrating higher ranges.

author: NoisyBoy
author_rank: Frequent Contributor
timestamp: May 03, 2023, 08:16:29 pm
content: It only goes up to 10V, not sure how you plan to scale it up to 100x. I doubt a 9V battery driven reference will provide you anything stable at higher voltages to reliably check 6.5 digit meters.

author: Fungus
author_rank: Super Contributor
timestamp: May 03, 2023, 08:33:58 pm
content: Quote from: NoisyBoy on May 03, 2023, 08:16:29 pmEasy! You buy 100 of them and connect them in series.

author: David Hess
author_rank: Super Contributor
timestamp: May 03, 2023, 09:40:32 pm
content: Quote from: NoisyBoy on May 03, 2023, 08:16:29 pmI plan to scale it up with a precision high voltage gain stage. A gain of 2 is easy, but there are other higher gain values which are not too difficult. The tricky parts are self heating and the voltage coefficient of resistance of the resistive divider which take place at higher voltages, but for specific values of gain these can be handled.

author: GigaJoe
author_rank: Frequent Contributor
timestamp: May 03, 2023, 10:30:36 pm
content: yeah been there ... any instability multiplied by x100 , self- heating divider sucks even with 10ppm resistors, noise multiply by x100 ... need rare capacitors at least 600V in serial ...im end up to build 2 fixed sources on 250V and 2 variable 90-200 , 250-350, so you can connect in ser and adjustin overall cheapest solution - get a trusted one , ask performance paper, no adjustment, then do value transfer adjusting against performance report. so target is - to acquired \ build all necessary sources for value transfer.

author: J-R
author_rank: Super Contributor
timestamp: May 04, 2023, 01:01:22 am
content: Fully calibrating/adjusting any DMM is no trivial task as you'll typically need access to high voltage AC and DC signals. The path I've taken frequently is to use another DMM along side the DMM that needs calibration/adjustment and then carefully dial in the source. For example, I recently needed 1kV DC, which required about an hour of tinkering and waiting for the Spellman DC-DC converter to stabilize, then within about a 5 second window I quickly stored the calibration point while observing the value on another DMM that I had calibration data for. The results are acceptable for a hobbyist, not so much for a volt-nut perhaps.For AC, I use a function generator with a transformer. When that limit is reached, I've been known to insert an amp in between to push the voltage higher. I recently acquired some additional custom transformers to see if I can get better results especially for higher frequencies.I have also acquired some vintage gear that has helped with providing stable sources. The Fluke 515A is pretty handy, although one issue is that it has reduced specs when using a DMM with a 10M input. Another nifty bit of gear is the Advantest R6144. Both took many months of searching to find at a reasonable price point.

author: coromonadalix
author_rank: Super Contributor
timestamp: May 04, 2023, 07:10:50 am
content: when you have many meters, you make one calibrated and serve as a reference ...but if you do serious stuff .... other than hobbyistyou know what to do even if its costly ...

author: David Hess
author_rank: Super Contributor
timestamp: May 04, 2023, 11:16:55 am
content: Quote from: GigaJoe on May 03, 2023, 10:30:36 pmIf the resistor temperature coefficients match, then a string of resistors can be used in an isothermal environment to improve tracking. Using a string makes sure that the voltage and current of each resistor is the same. If the voltage and current is the same, then the power is the same and the temperature of each resistor should be the same.If the voltage coefficients of resistance match, then the resistor string can be tested and verified at low voltage.Noise and instability would be multiplied in any design using a low voltage reference. In a good design the noise and drift from the reference dominates, so that means using a better reference, like a buried zener, or multiple references in series/parallel. While that would be nice, I could change the reference later if it is a problem.

author: GigaJoe
author_rank: Frequent Contributor
timestamp: May 05, 2023, 10:26:52 pm
content: I'm really had no idea how it goes, so such high voltage source was my first attempt to learn things. at first shot it more less acceptable. would be great if would be some discussion about.