Multimeter calibration ? - Page 1
Forum section: electronics / testgear

author: JanJansen
author_rank: Frequent Contributor
timestamp: November 13, 2016, 04:25:52 pm
content: Hi, some other brands then Fluke calibrate theyr multimeters to a Fluke,what does Fluke use to calibrate theyr own multimeters ?Is fluke the only brand that is perfect calibrated ?Suppose i buy a Hameg/R&S multimeter, how do i know if it is good calibrated ?I also read the manual that you need to calibrate every year, that will cost you 100 euros every year.How does it work ?, thanks

author: Assafl
author_rank: Frequent Contributor
timestamp: November 13, 2016, 09:46:59 pm
content: Fluke calibrate voltage (as does HP) with a primary standard. Voltage with a Josephson array and resistance standards traced to a quantum Hall effect resistance standard.DMM should be calibrated if you need traceability - for example if your insurance depends on it.Modern DMMs don't drift much. My HP34401a is still within 1 year drift numbers - it was manufactured 20 years ago. So is the Gossen and Agilent DMMs.

author: Fungus
author_rank: Super Contributor
timestamp: November 14, 2016, 09:08:11 am
content: Quote from: JanJansen on November 13, 2016, 04:25:52 pmNo. Multimeters are calibrated against voltage references. Many companies make them, they're small chips that output a very precise voltage. You can build your own for under $10 (depending on how much precision you need).eg.http://www.linear.com/products/voltage_referenceshttps://www.ti.com/lsds/ti/power-management/voltage-reference-products.pageQuote from: JanJansen on November 13, 2016, 04:25:52 pmNo.Quote from: JanJansen on November 13, 2016, 04:25:52 pmIt's a good idea to own two or three meters. With two meters you can compare readings and see if they agree. This lets you know if something is wrong. If you combine this with a voltage reference you can be confident that your meters are working.Quote from: JanJansen on November 13, 2016, 04:25:52 pmThat's only if you need to provide somebody else with guaranteed, legal proof that your meter is in calibration. Otherwise use the method above.In normal use, no reasonable meter is going to go out of calibration if you treat it well. Not even cheap, non-Fluke ones. A bigger worry is that they might be damaged by static electricity, overloads, etc. In this case it's enough to compare readings with two meters simultaneously, use your voltage reference, etc.

author: MosherIV
author_rank: Super Contributor
timestamp: November 14, 2016, 10:14:59 am
content: QuoteYes and NO !Yes, as Assafl says meters are calibrated against 'Primary' voltage standards.There are NOT just the simple Vref Chips that you can buy.For most common 3 to 4 digit meters, the calibration is done with a dedicated calibration machine like thishttp://eu.flukecal.com/products/electrical-calibration/electrical-calibrators/5080a-high-compliance-multi-product-calibra-0These will in turn be calibrated against a known local primary or 'sub-standard' reference which is traceable back to the primary standard for that country, which is in turn traceable back to the international standard.The simple Vref chips that you can buy as a good, quick test BUT they are not the standard by which DMMs are calibrated against.

author: Fungus
author_rank: Super Contributor
timestamp: November 14, 2016, 10:39:53 am
content: Quote from: MosherIV on November 14, 2016, 10:14:59 amSorry I didn't mean to imply that those chips are used at the factory. I meant:a) Meters are calibrated against voltage references,notagainst other metersandb) Those chips are examples of voltage references.Thebestof those chips only have about 0.025% accuracy - good for a confidence check but obviously not enough to calibrate a high-end DMM.

author: JanJansen
author_rank: Frequent Contributor
timestamp: November 14, 2016, 03:31:54 pm
content: Quote from: MosherIV on November 14, 2016, 10:14:59 amHow would they calibrate that one ?Quote from: Assafl on November 13, 2016, 09:46:59 pmThat is nice to know, you have all these primary standards in house ?

author: Fungus
author_rank: Super Contributor
timestamp: November 14, 2016, 03:45:53 pm
content: Quote from: JanJansen on November 14, 2016, 03:31:54 pmWith a bigger one!

author: MosherIV
author_rank: Super Contributor
timestamp: November 14, 2016, 03:53:49 pm
content: QuoteQuoteFluke would have to have some (or all) of their Primary and Sub-Standard references calibrated by the National Standards lab.Once this is done, they can calibrate any meter against their Primary and Sub-Standard references.They can also calibrate any other equipment against the Primary and Sub-Standard references using calibrated meters.

author: JanJansen
author_rank: Frequent Contributor
timestamp: November 14, 2016, 03:59:17 pm
content: Does the shops calibrate other brands themself ?,i often see in some shops they have various packs from the same meter with different calibration.Aint that weird that it is not calibrated in factory ?, or maybe they are tuning the old stock every year against aging ?How many multimeters do they sell?, not so much i quess, if i buy maybe its 3 years old ?

author: MosherIV
author_rank: Super Contributor
timestamp: November 14, 2016, 04:07:02 pm
content: QuoteWhat shops are we talking about?I doubt it. The only vendor that I know that does calibration on meters for customers is RS components.I suspect that they do not do the calibration themselves but send if off to a known trusted Calibration Lab/company.There are many companies/labs with each country that will perform calibrations. They in turn should have their equipment calibrated either by the National Standards lab or by another company that has their equipment calibrated by the National Standards lab.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: November 14, 2016, 04:16:31 pm
content: You and the audience here would need to know more about how you are using your multimeter to answer your questions the needs for calibration. In its totality calibration is a huge subject, worthy of days of discussion.Just a couple of examples.If you are doing servicing of almost anything but measurement gear you are unlikely to need calibration for technical reasons (legal reasons can creep in anywhere). It would be useful to have multiple meters to detect an outright failure, but the 2-3% accuracy of even the cheapest meters will allow you to adequately verify voltage points in circuits and measure component resistances.If you are using a high precision meter to trace shorts on a PWB you don't need a calibration. You are looking at relative voltages and you will find the short even if the absolute answer is off be many percent.If you are servicing measurement equipment you need calibration. How good a calibration you need depends on what you are servicing. You need to have high assurance that your measurements are significantly more accurate than the accuracy requirements of the instrument you are servicing. A voltage reference purchased over the internet my be sufficient for low accuracy instruments, while you will have to go to much greater lengths for better instruments. Those lengths will include analysis and measurements indicating not only the accuracy of the calibration train, but the durability of that train (how long the accuracy lasts) in your specific situation. People spend entire careers doing this.

author: Assafl
author_rank: Frequent Contributor
timestamp: November 14, 2016, 11:37:59 pm
content: Quote from: JanJansen on November 14, 2016, 03:31:54 pmFluke have a primary source (a Josephson Junction Array) in house. They do, however have to verify that it had not gone wondering so I assume they use a transfer standard (small portable standard that is good for short periods of time) - and they send that around to be compared to other primary standards and make note of any drift. I know NIST also has a Josephson Array based transfer standard (portable) but I assume that is used mostly between countries (but perhaps Fluke and Keysight as well).QuoteThe are not primary standards - nor standards. They are DMMs.I purchased a 20 year old HP DMM (made before the Agilent/Keysight name changes). Since the DMM has an internal counter for whenever a calibration adjustment was changed (it is stored in non-volatile memory) - and since it was a low number - it was clear that it was never sent to HP/Agilent/Keysight for their calibration/adjustment service (so the constants in the memory were the same as when it was manufactured).So I sent it to a local calibration lab to verifying the readings on the DMM (it helped that the service costing about 40$ here so pretty reasonable) .It was well within the 1 yr maximum drift figures. It is well aged so it is probably going nowhere (unless abused). And once you get the high resolution and high accuracy meter back - you can use it to compare to the other meters (and verify their accuracy) as well.I do have a few reference voltage sources, a few solid states as well as a Weston Cell. The latter would have been part of a primary standard before the 70's brought the Josephson's Junction Array. But only as part of a group of at least three cells and usually 5-6 cells (so if one drifts off - you'd know which one is broken - if you have one and it drifts - you are in trouble. That is why fungus recommended owning 2 DMMs instead of one. Even if they are of somewhat lesser quality.)