What do you use to calibrate your test equipment? - Page 1
Forum section: electronics / testgear

author: Axtman
author_rank: Regular Contributor
timestamp: January 10, 2022, 11:49:28 pm
content: As a hobby I buy, repair, and sometimes sell old test equipment (multimeters, VTVMs, oscilloscopes, function generators, power supplies, etc.) Some of the stuff is vaccum tube some is through-hole distreet components. None is modern digital equipment.I follow the calibration procedures in the manual but many times I don't have the proper equipment. I sure wish there was some inexpensive calibration equipment. BTW, I am not looking to calibrate the equipment to laboratory standards just get it adjusted as best as possible.

author: rob77
author_rank: Super Contributor
timestamp: January 10, 2022, 11:55:45 pm
content: i don't need accuracy, just to make sure my multimeters did not go crazyso here is what i use:for resistance:10K 0.01% wishay resistor, put it in a box with 2 banana plugs, added some desicant and closed it.for voltage:LT1236CN in a box powered with 9V batteries in series. it's trimmed to 10V 0.05% from factory.i don't think you can go cheaper or more simple than this

author: Brumby
author_rank: Unknown
timestamp: January 11, 2022, 12:07:37 am
content: I have a DMMcheck Plus.

author: DaJMasta
author_rank: Super Contributor
timestamp: January 11, 2022, 12:42:16 am
content: Entirely dependent on the equipment being calibrated. If you're working with older gear with looser specs, it's easier to at least check for yourself with a stable reference and a good meter with a tighter spec, but there are dozens of kinds of references and meters depending on what you need.The reason calibrations from a lab cost so much is sort of twofold - one, they require often half a dozen instruments to fully verify the functionality of yours, and two, all those need to be in calibration against a traceable standard... if you don't have both the right gear and that gear in cal, you can't truly do a calibration on your own, even with the full procedure. That said, if you have a couple different instruments you can compare against and which agree, some stable references, and then you run through the procedure, the likelihood that what your 'calibration' produces is in line with a traceable calibration is probably fairly good. These units are designed to be highly stable and more precise than specified to meet those specifications in less than ideal conditions, so if you can corroborate a measurement against a few others and test every part, odds are good the unit you're working with is in fine shape.

author: xrunner
author_rank: Super Contributor
timestamp: January 11, 2022, 12:44:33 am
content: A GPSDO (GPS Disciplined Oscillator) for extremely accurate 10 MHz frequency.

author: J-R
author_rank: Super Contributor
timestamp: January 11, 2022, 01:11:21 am
content: I would get a kick out of having a dedicated calibrator, but so far have gotten pretty far with the following random gear:DCV - PDVS2mini with verification against DMMCheckPlus and some VoltageStandard references for low values, DC-DC step-up converter module + another DMM for high values (1,000V for example)ACV - HP33120A function generator + Gertsch RatioTran (or sometimes flip the primary/secondary on a HV transformer)Resistance - DMMCheckPlus, decade resistor box with a trimmer pot and another DMM to set the value, also have some specific precision resistors hand selectedInductance - DMMCheckPlusCapacitance - DMMCheckPlus, capacitance substitution boxDCA/ACA - variable DC/AC power supplies with another DMM in series to hit the desired set pointFrequency - HP33120A function generator, also have a couple counters to check against, DMMCheckPlus has a dual frequency option

author: tkamiya
author_rank: Super Contributor
timestamp: January 22, 2022, 08:56:01 am
content: I do similar things myself. Buy dead equipment for cheap or sometimes get them for free, fix them, and sell them.I have a set of known good set. (they were calibrated by a local cal-house) If the values are reasonably close, I'll leave them alone. If they are wildly different, then I will try to bring them to what I have. I do repairs and function tests, but I never claim I calibrate.That said.... it would be nice to have standards. Frequency test is easy. Any GPSDO will do fine if you average them over a day or so. (log it on PC and average) I'd like to have a voltage standard, and resistance standard, too. They are future "to buy" items of mine.

author: tautech
author_rank: Super Contributor
timestamp: January 22, 2022, 10:00:53 am
content: Quote from: Axtman on January 10, 2022, 11:49:28 pmI used to do quite a bit of this but now even with the gear I have available just a reasonable scope, a reasonably good AWG, DMM with 3kV capability, a 10 MHz frequency reference and a few standard references is about all you need for most basic repairs and adjustments.

author: NaxFM
author_rank: Regular Contributor
timestamp: January 22, 2022, 10:25:30 am
content: These days I decided to contact some calibration labs just because i wanted to have, at least for just one time, a professional evaluation of the status of my 34401A, the answer I got was basically "fuck you": none of the calibration labs near my home offer calibration for hobbysts...I decided to do it on my own with my own procedureI have one precision 0.03% decade resistor box/voltage divider (paid 60 euro on ebay) and one of those cheap 2.5, 5, 7.5, 10V chinese voltage references. My multimeter reads exactly the voltages reported on the reference box, and this gives me high confidence that the accuracy of at least the 10V range is spot on.I have to start somewhere, and my assumption is that the 10V range, given the perfect readings with the voltage reference, is accurate.I found out that many resistors on the decade are not as accurate as they should be, so i'm going to buy a precision 0.005% resistor for the most important ranges (100, 1k, 10k, 100k ohms), as well as a 4 wire short. With these i can calibrate the multimeter and repair and calibrate the decade box.Ok, now i have a multimeter calibrated for voltage and resistance, and i also have a precise voltage source and a calibrated variable voltage divider. With these i can calibrate the current (at least in the mA range) and the lower voltage ranges. Be careful to account for the shunt resistance when doing the current measurementTotal cost: about 200 bucks, but you end up having extremely stable resistors you can always use as calibration standard, as well as a voltage reference to check if there has been some drift either in the multimeter or in the reference.I don't care much for frequency and small AC voltages, so for that i have a 25MHz siglent function generator i won years ago just because i wrote a review about a cheap oscilloscope i bought online and Siglent decided to do a draft every 10 reviews to win the function generator (theyl little known and trying to advertise their products), basically the only thing i've ever won on my life. Soon i'll modify the function generator with a TCXO to get way better frequency stability.Of course a metrologist would die at just the thought of following my procedure, but we have to work with very limited budget here, and this way, at lest for the most common ranges, you can be pretty sure your multimeter is well calibrated

author: Fungus
author_rank: Super Contributor
timestamp: January 22, 2022, 10:47:42 am
content: I own a couple of high-count multimeters (Fluke 187 and Brymen BM857). I figure that if they agree with each other exactly (they do!) then it's not a coincidence.For sanity checking I also have a few reference parts that I bought on eBay: A couple of 0.01% resistors, a calibrated voltage reference, etc.I also obtained a new 0.05%voltage reference and a 0.1% current reference that I built into a PCB along with the resistors above.I've measured everything on a 6.5 digit meter at a university lab, it agreed with my handhelds.Sure, I'm not using a 6 or 7 digit multimeter but all together it adds up to something.

author: tkamiya
author_rank: Super Contributor
timestamp: January 22, 2022, 06:04:00 pm
content: Quote from: NaxFM on January 22, 2022, 10:25:30 amThat's quite unfortunate.... I take it you are in an EU country. (Placing at least country in your profile helps) Ones around here seems to have open arm policy, and some even have a hobbyist pricing.Did anyone mention oscilloscope and pulse generator? They are handy to have as well. The oscilloscope does not need to be calibrated but pulse generator should be well trimmed.

author: nctnico
author_rank: Super Contributor
timestamp: January 22, 2022, 06:56:30 pm
content: Quote from: Axtman on January 10, 2022, 11:49:28 pmFor such equipment I rather do a functional test. Take a known-good signal (from a function generator or power supply) and feed that into a piece of equipment. Beyond that you are likely into expensive equipment territory quickly. A 6.5 digit DMM to check the level of your function generator for example but that will only get you to several kHz in frequency.

author: NaxFM
author_rank: Regular Contributor
timestamp: January 22, 2022, 07:14:19 pm
content: Quote from: tkamiya on January 22, 2022, 06:04:00 pmYeah, I'm in Italy, didn't know that this was a problem across the whole EU. I wonder why. Maybe they get so little requests by hobbysts that they don't even care? But still, If I had a VAT registration they would have been happy to calibrate my single multimeter, so why don't they just offer their services to everyone, with or without VAT? Now i understand why i wasn't able to find any pricing at all, not even for a single calibration lab in all Italy...Anyway, if fou happen to know it can you tell me the average US cost for calibrating a 6.5 digit multimeter? Just to be sure i won't be scammed if I manage to find a lab willing to calibrate mine.Oh, and thanks for reminding me to update my profile info. I'll definitely do it

author: tkamiya
author_rank: Super Contributor
timestamp: January 22, 2022, 07:24:17 pm
content: My HP34401A was calibrated per "tracible to NIST" method, and the cost was $250. For this, I get a paper stating equipment used for the test and their serial number and the fact that it passed the test. Detailed before and after is, I believe, an extra cost item.I never needed that, so I went this way. The place is in Orlando, Florida.Some will argue "tracible to NIST" is really not a true calibration. That's might be true but for my purpose, this is more than good enough. I heard somewhere EU countries have stricter calibration requirement. I know a fellow here, TIM, who gets his calibrated by a national level lab. There is a lengthy write up somewhere. Quite an interesting process.

author: oz2cpu
author_rank: Frequent Contributor
timestamp: January 22, 2022, 08:12:13 pm
content: i just borrow a DMM from work, with 1 or 2 digits more, than my own private instruments has,with brand new certificate, and then spend the weekend fine trimming my own units to match,24 hr power on before first measurement, and then again double check 48hrs later.it seems like i can actually up-trim my own gear to perform quite a bit better than factory calibration.being a volt-nerd this is quite fun to play with

author: tautech
author_rank: Super Contributor
timestamp: January 22, 2022, 08:21:25 pm
content: Quote from: tkamiya on January 22, 2022, 06:04:00 pmYes, have already.A good modern AWG can do everything a pulse gen can do plus a whole lot more.