Building a dmm calibrator - Page 1
Forum section: electronics / testgear

author: Napalm2002
author_rank: Regular Contributor
timestamp: February 06, 2014, 01:38:54 am
content: So many of us buy used dmm's, and sending all of them out to cal can be expensive. Does anyone have any solutions?

author: jadew
author_rank: Frequent Contributor
timestamp: February 06, 2014, 01:49:15 am
content: Calibrate one and check the others against the calibrated one

author: scientist
author_rank: Frequent Contributor
timestamp: February 06, 2014, 05:03:45 am
content: Read the title as "Building a damn calibrator" O0Couldn't help myself.

author: Dr. Frank
author_rank: Super Contributor
timestamp: February 06, 2014, 09:12:51 am
content: All those above mentioned DIY solutions, e.g. with only one reference (as 5.0000V) are no "dmm calibrators" at all, and therefore are useless, as you need the full range of Cardinal Points for a complete calibration.For DCV calibration, for example, you need at least a stable DCV supply which delivers 1000V, 100V, 10V, 1V, 100mV.Then you need a precise/calibrated reference, i.e. 10V for comparison.And you need a transfer standard to transfer the uncertainty of the 10V reference to the 4 other cardinal voltages.A Hammon type divider like the 752A is needed for that.Same is valid for ACV, DCI, ACI, Ohm, and so forth.I own a Fluke 5442A, 5200A, a HP3458A, a self made precision (1ppm) Hammon divider, several precision 10V and 10kOhm references and constant current sources.So I am able to adjust all of my equipment on my own, but not traceable to the official SI.Anyhow I estimate an SI uncertainty of few ppm for U, I, R....To obtain traceability, that would cost a fortune.Frank

author: Napalm2002
author_rank: Regular Contributor
timestamp: February 06, 2014, 11:09:42 pm
content: I'm Basically looking for something toMake sure that most of what I use is very close to spec. I I found something way of and it wasn't a simple adjustment that I could make then I would send the item out for Cal. Thanks for all the replies!Mike m

author: G0HZU
author_rank: Super Contributor
timestamp: February 06, 2014, 11:53:47 pm
content: Quote from: Napalm2002 on February 06, 2014, 01:38:54 amProbably the best solution is a reality check...Most hobbyists don't 'need' to have their DMMs calibrated. I've got several DMMs here, most of them cost me very little to buy and I've had several of them for >20 years. I've never had any of them formally calibrated. There does seem to be an unhealthy fascination for megadigit £££ DMMs on this forum as well as for buying the official calibrator units. What do hobbyists need this level of accuracy for? Are there really that many people on here that 'need' to know how to measure 5V or 10V or 1V to 6 digits?The other issue with calibrating anything old but decent (eg a HP VNA or spectrum analyser) is that the calibration house can open up your equipment and tweak anything they like in the name of calibration. That is seriously scary and I wouldn't let my RF gear anywhere near a UK calibration house even if they offered me free calibration for life on all my RF test gear.Probably the cheapest solution if you want to check your meters is to buy a few cheap voltage references from Farnell and make sure your meter reads reasonably close.eg maybe spend about £10 total on a few references and a few 0.1% tolerance resistors and also do some cross checking between meters if you have more than one.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: February 06, 2014, 11:55:21 pm
content: Hi,Try and find a Fluke 515A calibrator. This is an entry level calibrator.The Fluke 515A Portable Calibrator is a precision voltage and resistance calibration source for on-site calibration of measuring instruments. AC or battery operation and small size, only 8 1/2W x 3 1/2H x 16D and 13 lbs. Accuracy of ±0.003% or 30 µV. DCV: 0 to 999 µV (0.02 µV resolution), 0 to 1 and 0 to 10 V ranges (0.1 and 1 V steps), 100 V cardinal point ACV: 1, 10, 100 V cardinal points Resistance: 10 ohms to 10 MohmsThe 10V AC is at 400Hz, 4kHz and 50 kHz. The other AC voltages are at 400Hz.If you wanted to design a build one, copying the functionality of the Fluke 515A would be a good place to start.This lets you give a meter a fairly good check, It is not good enough to perform a full calibration.I have a Fluke 5101B which is a full function calibrator. It is a big and very heavy beast. It is suitable for 3 1/2 and possibly 4 1/2 digit meters. Fluke recommended using the Fluke 8506A DMM for accuracy enhancement.Neither of these are 'Volt-nuts', 'Current-nuts' or 'Ohm-nuts' material.Jay_Diddy_B

author: VK5RC
author_rank: Unknown
timestamp: February 07, 2014, 12:16:54 am
content: I would support G0HZUs view with the caveat that building the calibrator, along with the planning design and execution, is a good exercise to understand some electronics, I would generally advise against changing much inside good gear unless clearly broken, regards Rob

author: Napalm2002
author_rank: Regular Contributor
timestamp: February 07, 2014, 02:26:55 am
content: Maybe I should have been more specific. I really would like a way to check various functions and such. And to have a stable source to compare them too. Basically a way to check to see if they have drifted far out of cal. Then I would send them out to cal. I don't know if I would attempt adjustments myself. Thanks to all.Mike m

author: Rick Law
author_rank: Super Contributor
timestamp: February 07, 2014, 03:55:28 am
content: As someone already mentioned, DMM CheckPlus - I echo that. It does a good job as a tool to check your DMM. Check it out. It has a collection of standards on one single board for you to use. I found it very useful.voltagestandard.comIf you want more reference voltage, look also at the Penta Reference (5 voltage to check)Doug runs the place. He gave me excellent service when I purchased mine and I expect all his other customers had similar positive experience. He is spoke of highly here.

author: engineer_in_shorts
author_rank: Regular Contributor
timestamp: February 07, 2014, 05:22:14 pm
content: Quote from: G0HZU on February 06, 2014, 11:53:47 pmCalibration houses will not adjust anything unless you specifically ask for them to do it - and expect the price to go up. One of the common misconception about calibration is that calibration means "adjustment".

author: PA4TIM
author_rank: Super Contributor
timestamp: February 07, 2014, 06:16:03 pm
content: Just forget it, it will be the beginning of the end. It starts with a cheap Vref. But to be usefull it must be calibrated ($$) Then you reach the point that all your meters show an other value and you begin to doubt the reference so you buy as better one, and then a multimeter with more digits, and a second one. Then you need a better calibrator, a kelvin varley devider, and start to worry about current, resistance, crest factors, frequency etc. so you want better test leads, special connectors, start to mumble about burning in references, dance around the house naked at full moon before calibrating a 7.5 digit meter, start to offer Virgins (first from your street but if that source dries up, you buy them deep frozen from Voltnut-R-us.)Then you learn about seebeck, the influence from temperature, relative humidity and start ovenising things, but now the voltnut virus has caught you for real and you buy a 8.5 digit meter and..... And before you know it is to late and the nice men in white coats come for you and if you be a good boy you are allowed to do the tatutatutatu...And this is the result:(standard cells, some transfer standards, two frequency standards, null meter, 2 KV dividers, a Philips and two Fluke calibrators.And then a bunch of self build Vrefs. But you are not satisfied with VDC, VAC, IAC, IDC so you start hunting for resistors,Then you stumble on things like capacitors, coils, and gear to check that so the GR precisiopn lab bridges like the famous GR-1620 fill your lab.But it is never enough. Your scopes, VNA's, spectrum analysers, counters etc also need to be spot on:

author: G0HZU
author_rank: Super Contributor
timestamp: February 07, 2014, 06:30:15 pm
content: QuoteOne of the common misconceptions about calibration houses is that people assume the calibration house is always staffed with competent technicians. At my place of work anyone who sent a decent piece of test gear to a UK calibration house would be in deep trouble (i.e. instead of sending it to the original manufacturer)I can only repeat myself and say I would never, ever send my best RF test gear to a typical calibration house even if they offered me free calibration and free shipping for life.

author: CaptnYellowShirt
author_rank: Frequent Contributor
timestamp: February 07, 2014, 10:14:34 pm
content: Quote from: PA4TIM on February 07, 2014, 06:16:03 pmWhat? Like any of us have anything better to be doing?

author: rjk5378
author_rank: Contributor
timestamp: February 08, 2014, 12:21:09 am
content: For general hobbyist use, it is sufficient to have a few different multimeters (of decent brand, quality, etc., of course) and periodically check them against one another. If 3 to 5 different meters are all reading the same as one another +/- their claimed accuracy and the precision of the thing being measuered then, I have sufficient comfort. Having several precision resistors (+/- 1% or 0.1%) is also handy. I would love to have precision voltage, current, frequency, etc., standards, but I don't need them. Besides, it is much easier to convince my wife that, yes, I really did need to purchase yet another DMM! <g>- Bob, KY3R

author: Co6aka
author_rank: Unknown
timestamp: February 10, 2014, 04:12:55 am
content: Quote from: PA4TIM on February 07, 2014, 06:16:03 pmIndeed; tis wise to just say "No!" to drugs.

author: kawal
author_rank: Frequent Contributor
timestamp: February 12, 2014, 12:45:55 am
content: I made my from some ADR4520 chips - great tool to have :I used a2.048V , 4.096V and a 5.000V chip.Just make sure the chips have room temperature.The references are about $7 each so for less than $30 you can build a nice calibrator.http://www.analog.com/static/imported-files/data_sheets/ADR4520_4525_4530_4533_4540_4550.pdf

author: G0HZU
author_rank: Super Contributor
timestamp: February 12, 2014, 01:11:15 am
content: To the people that spend a fortune on DMM calibration gear at home: Why not simply make a dumb display with maybe 8 digits that showed 10.000000V and occasionally flicked to 10.000001V.Add a few range buttons to change it to show 5.0000000V or 1.0000000V to add to the fun of it allIt would be just as useless in everyday life as having a genuine $$$ mega accurate 10V/5V/1V voltage reference at home but it would save a lot on time and money

author: MadTux
author_rank: Frequent Contributor
timestamp: February 12, 2014, 02:37:25 am
content: QuoteBah, only 7.5 digits, a 3458A has one more, thereby it costs at least 2k$ more

author: pomonabill221
author_rank: Frequent Contributor
timestamp: February 12, 2014, 03:11:24 am
content: Quote from: G0HZU on February 12, 2014, 01:11:15 amNow THAT is FUNNY!!! I got a good one out of that!

author: pomonabill221
author_rank: Frequent Contributor
timestamp: February 12, 2014, 03:20:17 am
content: Quote from: PA4TIM on February 07, 2014, 06:16:03 pmmmmmmmm... delicious!!! WHAT bragging again?!?!?!?Makes my mouth water!!!And all that is of course necessary to calibrate your radio shack/harbor freight dmm! Can't be TOO accuarte!I got a few samples of a AD584 precision reference. Not the caliber of a real calibrator, but very accurate and stable. I just use them to verify my dmm and dvm accuracy.Attached the pdf.If you work it right, you can get samples of things from different manufacturers.

author: CaptnYellowShirt
author_rank: Frequent Contributor
timestamp: February 12, 2014, 04:42:12 am
content: Quote from: G0HZU on February 12, 2014, 01:11:15 amYou'd have make some outrageous claims about it like the audiophiles do about their cables...QuoteAnd then back up the prank by shipping it to various 'in-the-know' members of the EEVBlog community and have them all take pictures of it put against completely staged 'tests' -- like Dave with the 555 timer gag.But why stop at 8? Claim you've made a room temperature JJ array. hash-tag:http://en.wikipedia.org/wiki/P._T._Barnum

author: PA4TIM
author_rank: Super Contributor
timestamp: February 12, 2014, 11:56:31 am
content: Quote from: pomonabill221 link=topic=I g26484.msg385940#msg385940 date=1392175217I have a radio shack, but what has that to do with DDM's. Except that most of my DMM's are in my radio shack.Here you see me testing an ESI standard resistor after I bought it. And as you see on the meter the resistor is spot on, I was afraid I would have to ship it to NIST.

author: pomonabill221
author_rank: Frequent Contributor
timestamp: February 12, 2014, 09:29:41 pm
content: When I said radio shack, I was referring to the company Radio Shack, I guess you don't have these stores where you live?Don't worry, the sell over priced junk as far as I am concerned.They used to be a somewhat good store for hobbyists, but now they seem to concentrate on cell phones and phone plans, and overpriced A/V stuff.

author: lau190
author_rank: Newbie
timestamp: April 10, 2014, 10:50:47 pm
content: Quote from: G0HZU on February 12, 2014, 01:11:15 am:)I like it