How do i calibrate my multimeters! - Page 1
Forum section: electronics / beginners

author: XMA
author_rank: Contributor
timestamp: August 12, 2018, 07:33:33 am
content: hi there so i got 2 multimeters, I've done some tests and it seems the voltage readings are off, here are comparisons. now my question is how do i calibrate them, i know that the cheap Chinese one has 1 potentiometer that u can calibrate it with and the thing with that is if i calibrate it, after 1 day it goes inaccurate again, and it be acting wierd by not reading voltage but it goes up and up, my guess its toast, now to me another meter, i dont know exactly how many potentiometers it has but i saw 2, so my question is what potentiometer would i need to adjust?Cheap Chinese Multimeter:LI-ION BATTERY VOLTAGE READING: CHARGER - 4.12v MULTIMETER - 4.10vBENCH POWER SUPPLY READING: BENCH - 4.2v MULTIMETER - 4.18vCheap Chinese Multimeter voltage difference 0.02vMICRONTA 22-188:LI-ION BATTERY VOLTAGE READING: CHARGER - 4.12v MULTIMETER - 4.06vBENCH POWER SUPPLY READING: BENCH - 4.2v MULTIMETER - 4.14v-4.15vMICRONTA 22-188 voltage difference 0.06v

author: Kleinstein
author_rank: Super Contributor
timestamp: August 12, 2018, 08:16:06 am
content: For a reasonable calibration is needs an accurate source or meter - normally something at least 10 x better is recommended. So without a much better meter / source, there is not much sense in adjusting the meters. With 20 / 60 mV off at 4 volts this 0.5 and 1.5 off - good enough for a cheap Chinese meter. With the cheap posts, there is a chance the surface is oxidized and it might need a few movements to clean, before doing an adjustment.How the adjustment is done is meter specific. In old ones it can be a pot, but in new ones it might be all software.

author: Old Printer
author_rank: Frequent Contributor
timestamp: August 12, 2018, 01:19:31 pm
content: From what you have posted I would not feel confident that eith of your two "control" voltages are any more accurate that your meter. Neither the charger or the power supply should be expected to be used as a voltage reference. The exception would possibly be a very high quality lab PS that had been recently calibrated. We would need to know more about it, but at this point I would tend to trust the meter before either of those.

author: rhb
author_rank: Super Contributor
timestamp: August 13, 2018, 11:32:27 pm
content: Get a bunch of new AA cells and put some in parallel after removing outliers. I forget what the voltage is, but I don't mind measuring a dozen with my 34401A.Another option is the AD584JH voltage references on eBay for $3 each. Those are good to better than 0.1%.I bought a DMMCheck Plus from Doug Malone, but it's a good bit more expensive. But exactly the tool for the job.

author: rstofer
author_rank: Super Contributor
timestamp: August 13, 2018, 11:44:58 pm
content: The DMMCheck source:http://www.voltagestandard.com/DMMCheck_Plus.html

author: hugo
author_rank: Regular Contributor
timestamp: August 14, 2018, 12:05:47 am
content: Quote from: rstofer on August 13, 2018, 11:44:58 pmThat would cost more than the two meters combined.

author: Brumby
author_rank: Unknown
timestamp: August 14, 2018, 12:54:56 am
content: That's no surprise.Here's a hint as to why...Quote from: Kleinstein on August 12, 2018, 08:16:06 am

author: CatalinaWOW
author_rank: Super Contributor
timestamp: August 14, 2018, 02:03:19 am
content: Before you spend time figuring out how to calibrate your voltmeters, figure out why you would want to. Those requirements will tell you how well you need to calibrate your voltmeters, and also tell you whether those two will ever meet your needs.If you "just want it to be right" that is fine too, but it is the first step to volt nuttery, which can be a long and expensive habit.

author: rhb
author_rank: Super Contributor
timestamp: August 14, 2018, 04:47:14 pm
content: Quote from: CatalinaWOW on August 14, 2018, 02:03:19 amI spent an hour or so yesterday figuring out a calibration sequence for my test gear so as to use the two pieces of gear with a current calibration and a GPSDO and 40 pS rise time pulser to calibrate the rest of the gear.It's been 30+ years, but IIRC the Micronta DMM I have one pot adjusted the voltage and the other adjusted the resistance. The LCD is dead so hard for me to check that. But as long as you mark the location *before* you attempt to adjust it, you can sort it out.You should read Conrad Hoffman's "Mini Metrology Lab" series. He's a regular here, so he should show up at any time. Fresh alkaline cell calibration is free if you buy cells you use. The $3 AD584JH is a very good deal and gives you 2.5, 5, 7.5 and 10 V references. I bought 3 to do a study on aging behavior.There are several forum members who could probably buy a house with the proceeds of selling their test gear. So the risks associated with becoming a voltnut are quite serious.You might also want to look at:https://www.eevblog.com/forum/testgear/habor-freight-giveaway-dmm-test/Cheap meters are quite accurate out of the box, and with a little TLC even better. Sadly the last one I got does not have the trim pot. But the manual tells you to calibrate it annually. :-(Fro background, I have two 6.5 digit HP 34401A DMMs. Both are in spec relative to my DMMCheck Plus which was calibrated before shipment against an in cal HP 3458A. One 34401A had never been calibrated since it left the factory.

author: XMA
author_rank: Contributor
timestamp: August 15, 2018, 08:44:19 am
content: hello, sry for not reply back to all of you but, can I use the voltage out a 5v regulator as a voltage reference and adjust from there? i am not going for a %9999999999999999999.99999 accuracy? and I need to have these meters accurate because I measure li-ion cells with them and such.Quote from: rhb on August 14, 2018, 04:47:14 pm

author: tggzzz
author_rank: Super Contributor
timestamp: August 15, 2018, 09:51:08 am
content: Quote from: XMA on August 15, 2018, 08:44:19 amOf course youcan- but you would be wise to know what voltage that regulator is putting out! And to know that you will either have to know the specified limits (including over temperature and load and time) or measure it.Some regulators are intended to supply an accurate (within limits) voltage with very little current, others are intended to supply current while keeping the voltage within a broad limit.QuoteYou need tounderstand and definewhat is important in your measurements, and then you can specify the accuracy you require. We can't guess that for youSometimes absolute accuracy is less important than stability and repeatability. A company I once worked for made a very expensive test set with an accuracy of 0.1dB and a stability of 0.001dB. The customer didn't care about the 0.1dB, since they were interested inchangesover 1 week. Fromhttps://entertaininghacks.wordpress.com/library-2/good-questions-pique-our-interest-and-dont-waste-our-time-2/Tell us your problem/goal, as well your solution. In most walks of life, technical or non-technical, if we know the reason for the question you will probably get a better answer. Either the answer will be more pertinent to your needs, or perhaps it can suggest a better alternative that you haven’t even considered. Don’t ask “Can you give me a lift into town?” Do ask “Can you give me a lift into town, so I can replace my broken frobnitz?”. The answer might be “There’s a spare frobnitz in the attic”, thus saving time, money, the environment – as well as making some space in the attic.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: August 15, 2018, 12:39:08 pm
content: For measuring Li ion battery's you need 4 1/2 digit precision, and want 4 1/2 digit accuracy. But you can get by without the accuracy. By observing readings on fresh new batteries you can learn the correct behavior as measured by your meters. The other thing you need is stability so the knowledge you gain is useful over time. Having two meters is helpful because they are unlikely to drift the same way. Differences between them that change over time are a warning to re-examine things.

author: Old Printer
author_rank: Frequent Contributor
timestamp: August 15, 2018, 01:14:36 pm
content: For hobby purposes measuring LiPos is not all that critical. 1/10th of a volt plus or minus is close enough to prevent over charging or over depletion. That is a lot for even a $5 Harbor Freight meter to be off. Rather than using a voltage source that is not designed for calibration, you would be better off finding someone with a little better meter than you have to compare readings. Pretty much any $20 multimeter that is new will be far more than accurate enough for monitoring LiPo use. My local Craigslist is loaded with people selling brand new DMM's for cheap that they were given and don't know how to use.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: August 15, 2018, 02:42:28 pm
content: A tenth of a volt is marginally good enough to prevent overcharging/depletion. Not good enough to evaluate balance.

author: Old Printer
author_rank: Frequent Contributor
timestamp: August 15, 2018, 03:31:07 pm
content: Quote from: CatalinaWOW on August 15, 2018, 02:42:28 pmOP has not said anything about balancing, actually he hasn't said much about why he need to do any of this, but yes you are right. Balance can be done with a fairly inexpensive automatic charger/dis-charger. I have a couple for my quads. They are cheap and very accurate and leave you free for the simple things like manning a fire extinguisher

author: Kleinstein
author_rank: Super Contributor
timestamp: August 15, 2018, 07:22:45 pm
content: Quote from: CatalinaWOW on August 15, 2018, 02:42:28 pmFor balancing it is about resolution, not accuracy. Even the cheap meters read 19.99 volt and thus 1/100 of a volt. For balancing there is not need for calibration.For those cheap meters it is usually not worth doing an adjustment: usually they are OK with there moderate accuracy (e.g. 0.5% range). If for some reason they are significant off, chances are that there is a real damage and even after adjustment they would not be reliable (not even to the low levels one can expect from a cheap meter). So unless needed for business reasons there is hardly a need for calibration for the cheap meters. Even than calibration would be a check to see of they are still well within specs - if outside, buy new. Just from the money one might even consider to buy new instead of a calibration.

author: iMo
author_rank: Super Contributor
timestamp: August 15, 2018, 08:16:27 pm
content: It could be the owners of the cheaper multimeters (ie. those $5-$40) are looking for some easy way to check whether their gear actually works. Something like the volnuts do here - they spend years playing with their LTZ1000 stuff, but much faster end cheaper.Maybe for those "normal cheapo dmms" there is a hint like "do stab two nails made of copper and steel into the lemon, wire the nails to your multimeter, and you should see 0.9453 volts at ambient temperature"In fact, I did it few months back - I found a few REF01s in my junkbox (3 legs left, last time used mid 80'), I picked one, wired to 12V and looked at its output with my 3 cheapo multimeters. They showed 9.99, 10.01, 9.99..

author: mcinque
author_rank: Unknown
timestamp: August 15, 2018, 09:26:05 pm
content: Quote from: hugo on August 14, 2018, 12:05:47 amIn reality it is quite cheap.For the calibration of a $100 DMMCheck, a $6.500 value device is used.To calibrate a $300 Rigol DSO, more than $20.000 value devices are used.

author: rhb
author_rank: Super Contributor
timestamp: August 15, 2018, 09:44:58 pm
content: 10 new Rayovac American made alkaline AA cells measured with an HP 34401A. The meter was checked with a DMMCheck Plus and reads about 60 uV high. This 34401A has not been calibrated since it left the factory. The string in the CAL menu reads 21 August 1995.1.624241.624701.625371.624621.623831.625131.625461.625091.62442So there's a zero cost voltage reference accurate to better than 0.1% if you use one cell which is entirely adequate for calibrating a 3.5 digit DMM. Ten cells in parallel will reduce the error to around 0.03%.The 34401A was in 10 Meg input mode. The cheap Harbor Freight 3.5 digit DMMs have a 1 Meg input. In this case it doesn't matter, but I have had to correct for it. This DMM is an older model of the ones they give away. You can read more about those here:https://www.eevblog.com/forum/testgear/habor-freight-giveaway-dmm-test/msg1473132/#msg1473132After setting the trim pot using the 5 V output from the DMMCheck Plus, a 1.62509 cell read 1625 mV on the HF DMM and a cell which read 1.62409 on the 34401A read 1624 on the HF.I had one cell I pulled from the package which read 1.57382 V which likely was a cell which was used very briefly and then found its way back into the package with the new cells. The HF reported it as 1574 mV.Q.E.D.N.B. The list on a 3458A is $9993 and the basic annual cal runs $612/yr with an agreement and $649 without. A primary standards cal with a Josephson junction array is $1789.

author: joseph nicholas
author_rank: Frequent Contributor
timestamp: August 15, 2018, 10:42:11 pm
content: If you're worried about thermal drift over time just buy a new cheap ass DMM every year and compare it to your old cheap ass DMM. No problem. Save all the DMMs and keep comparing them until you feel confidant that you have one that does what you want. This is the perfect way to becoming a volt nut.