Voltage Reference??

Discussion in 'General Electronics Chat' started by Dr.killjoy, Apr 22, 2015.

  1. Dr.killjoy

    Thread Starter Well-Known Member

    Apr 28, 2013
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    I was watching a video on Voltage reference for checking the accuracy of DDM.. How do you guys check the accuracy of your meters??? I was thinking about building a calibration box with voltage,resistance,and current.. But my only problem is that I don't have a meter with a calibration cert or even a meter with that kind of accuracy.. My best meter is a Fluke 87 series II and working on getting a Uni-T 61-E.. What do you guys think ???
     
  2. #12

    Expert

    Nov 30, 2010
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    Basically, I don't. I have a Fluke rated at 1% and a 1% resistor will do a quick check, but it's been soo dependable! If I ever see a reading that looks hinky, I can try a $4 Harbor Freight meter, but I don't need better than 1% accuracy because I don't build, "standards" that need to be calibrated.
     
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  3. Papabravo

    Expert

    Feb 24, 2006
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    I'm with #12 on this. I could never see the purpose having calibrated instruments for what we did. It was digital logic, micro processor stuff, and basic analog controls. No precision instrumentation or stuff like that.
     
  4. WBahn

    Moderator

    Mar 31, 2012
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    If you have confidence that your meter is giving you results that are accurate enough for your needs, then don't waste a lot of time and money verifying it. If you have reason to suspect that your meter is acting up, then worry about it.

    For most purposes, checking the result of two meters against each other is more than sufficient evidence that both meters are close enough to spec to be considered good enough. Put them in parallel across a 9V battery and if they both read the same within the performance specs of the meter (typically 1% or so) then call it good. Similarly, if you use the current meter mode, put them in series as ask the same question. Do NOT put them in parallel across a resistor for the resistance range! Check the same resistor separately with both meters. Do checks like this on all the functions and ranges of interest.
     
  5. #12

    Expert

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    I did 1% precision analog meter calibration, but that was in a factory and I had a 4&1/2 digit DMM. That work calibrated my head so well that everyday chores seem simple. I can mentally account for a loaded-down transformer voltage or a crusty connection or a long cable losing voltage along the way. You will too. The problem is that it's a long journey from, "Where do I put the red probe?" to "Five less volts...must be that 70 feet of thermostat wire".
     
  6. Glenn Holland

    Member

    Dec 26, 2014
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    Unless you are using the meter for an application that requires a "Legal For Trade " certification, attempting to verify calibration is not a critical issue.

    As an example, I used to work in the electronic shop of a rail transit agency which was required to perform testing in accordance with Federal Railroad Administration regs which mandated that instruments be calibrated every 2 years on a "NIST Traceable" calibration station.

    I did an analysis of the normal variations in the "DUT" and they were much more (like several hundred times) than the margin of error of the meter. So other than assuring that the agency was complying with the letter of the law, verifying the calibration was largely a waste of time.
     
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  7. WBahn

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    Yes and no. Without that requirement there would be plenty of places that would never question their measurement tools, so they would be using equipment that had been dumped off the back of a truck and left out in the rain and snow for several weeks before someone spotted it and put it back in the cabinet.
     
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  8. ScottWang

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    Aug 23, 2012
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    TL431.
    LM129AH或LM329AH.
    LTZ1000,LTZ1000A - LTZ1000 ebay.
    LTZ1000 products - from China.
    I bought one Uni-T 61-E from China, quality is good, it can be communicate with computer using RS-232, but the measuring speed has a little slow.
     
  9. crutschow

    Expert

    Mar 14, 2008
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    As WBahn said, comparing two meters is usually sufficient to determine that the accuracy is sufficient for virtually any home project.
    You can use one of the cheap (or free) ones from Harbor Freight for the comparison.
     
  10. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    The calibration schedule at the factory I work is once a year, with a 30 day extension possible on request. We rarely request extensions.

    While frequent recalibration may seem to be wasteful what is does buy you is a shorter period where a defective piece of equipment is being used for product testing.

    Should any piece of equipment fail cal then the entire years worth of product it tested is suspect, and all of it is open for return and retest should the customer request such testing.
     
  11. DickCappels

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    Aug 21, 2008
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    I use a LM4140-1.0 0.1%, 10 PPM/°C. Its greatest use is in initially checking DVMs.

    Only a couple of months ago I found that a cheap DVM I had ordered from Futurlec was several percent off. That could be a problem in power supply efficiency assessments, for example. That DVM was spared the trashcan and is now only used to check continuity.

    1024ref.gif
     
  12. Reloadron

    Active Member

    Jan 15, 2015
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    To calibrate or not calibrate, that is the question. :)

    I have to agree with those who have said the average home hobby enthusiast really does not have much reason to calibrate their home use instrumentation. Additionally for the most part many of today's inexpensive hand held DMMs for example maintain their accuracy fairly well as compared to the instrumentation of years ago. While I would not classify a $19.95 Harbor Freight handheld DMM as a fine piece of test, measurement diagnostic equipment unless you get a lemon their accuracy is generally fine for home hobby use. There is really no need for periodic calibration. All of that changes in a situation like ErnieM mentions where in a commercial manufacturing application where the test, measurement and diagnostic equipment is used to make sure parts and services comply to published specifications but all of that gets into a different world.

    Do I calibrate or test my equipment? No, not really. If I have reason to believe something is suspect I may check it against another piece of measurement equipment or home brew standard but beyond that I see no need to worry about it.

    Ron
     
  13. strantor

    AAC Fanatic!

    Oct 3, 2010
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    A while back I picked up a mystery box of surplus and inside was a box of super accurate 10V reference ICs from Linear Technology. I don't remember the P/N but they were in a TO-5 can and required no external components. I remember checking them with my Fluke 189 and was baffled when I read 10.000V, and thinking "man, these could be handy as a calibration reference." So there you go, check out Linear. They have some rated 0.05% accuracy.
     
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  14. Reloadron

    Active Member

    Jan 15, 2015
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    Those things are great, I use them to power bridges where you want an accurate stable supply to the bridge.

    Ron
     
  15. wayneh

    Expert

    Sep 9, 2010
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    When our manufacturing site went ISO9000 some years ago, we had to establish a calibration protocol and frequency for every single instrument; scales, pH meters, thermometers, on and on. This raised howls of protest, especially from our microbiologists. Their thinking was, "why bother to use precise instruments to run imprecise experiments?".

    But eventually the arguments of the "don't bother calibrating" crowd come down to arguing that they should be allowed to perform their work with uncalibrated instruments. They lost, because that's an indefensible position.

    As others have laid out, the need to calibrate depends on the circumstances. I rarely need any number to better than ~5% precision at home. The second-meter approach probably gets you to ±1% or better. If I really cared that my 12.00V was really 12.12V, I'd have to go find a meter that wasn't free at Harbor Freight.
     
  16. nsaspook

    AAC Fanatic!

    Aug 27, 2009
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    I ran the ISO calibration system at work for many years and had to endure the yearly DNV audits where they check calibration files. Fluke quality meters were the least likely item to be out of calibration so they never asked for those. Load-cells, various types of TC's , sheet resistance/thickness meters, pressure/flow meters and RF energy sensors (1% @>0.3% repeatability Bird 4421 & 4020 sensors) were the things they wanted. So have a golden meter and have it professionally calibrated once as the reference standard for everything else.

    We learned how to game the system with 'reference only' equipment for normal troubleshooting but 'quality' checks must be made with certified instruments at a precision of a least 10x the control points to dial in process parameters. This way you can look at trend data to see changes before they affect what's being made and make corrections before some product is out of spec. It's usually not the absolute value reading that's important, it's the repeatability of measurements to a recipe parameter set point requiring a very low drift factor that makes a Fluke quality meter (and calibrated equipments in general) important. Without calibration (data and uncertainties) you can't know the effect of your measurement of control value changes have on changes to product.
     
    Last edited: Apr 23, 2015
  17. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    At work we have a few benchtop DMMs and some other equipment that is calibrated periodically, but the most of the meters and scopes that are used in the design process are labeled "informative use only" and are not calibrated.
    If you need to do something that requires precision you grab the calibrated 6-1/2 digit DMM, otherwise an uncalibrated 4 digit meter is more than good enough.
    Of course all the instruments used in the manufacuring area are all calibrated.
     
  18. WBahn

    Moderator

    Mar 31, 2012
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    When I was in the service the calibration rules were actually pretty rational. We had some digital multimeters in the shop but they were seldom used (we were a hydraulics shop so we occasionally needed to check servovalve parameters and the like) and they were never used for anything critical, so they never had to be calibrated. We had torque wrenches, on the other hand, that were used for things that were critical and they had to be calibrated by PMEL on a periodic basis and we had to verify the calibration expiration date before using them on every single job they were used on.
     
  19. ian field

    Distinguished Member

    Oct 27, 2012
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    Everyday Practical Electronics have just published a 10.0000...........V reference for checking digital voltmeters.

    They would most likely supply a reprint of the article for a small fee.

    Most of the articles in EPE these days are licensed in from Silicon Chip - so might be worth looking there too.

    AFAIK: EPE supply kits for some of their projects.
     
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  20. Dr.killjoy

    Thread Starter Well-Known Member

    Apr 28, 2013
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    Thanks for all the input ..I was looking to build a simply Voltage ref just to check my meter's accuracy and are within some kind of spec.. My plan was to use a AD584LH with a 4 position rotary switch in a box but the voltage ref below are pretty cheap below and are cal somewhat with exact reading and can't be beat for about $15 for the really nice one....


    Here are the videos I was talking about ..


     
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