Thanks to this thread by dchomak, I now use a voltage meter to read current in my high output lights. Most of my DMM's don't agree with each other. I want to know which one is correct and calibrate the others.
Supposedly, you only to hook up 5 volt supply (Thus the USB category) and it will output a highly accurate 4.096 +/-.05% volts. Noise reduction can be had with a 1uF cap between the TRIM/NR Pin and Ground.
Haven't tried to source any, but did see one on ebay (link in picture):
For even more accuracy on all your meter’s readings you can have it professionally calibrated. The meter I bought years ago was calibrated by a third party called AcuCal and I believe it to be dead on.
I had revisited your lab thread earlier today and found myself drooling over stuff I wouldn't have the foggiest idea on how to operate.
This item (link to Post 33 in pic) caught my attention, but is more expensive then I want to spend. I would say the most of my measurements are classified as "it would be nice to know". Given the other monetary demands of my life, that means I want to spend as little as possible to get reasonable accurate readings.
If measurements ever get more critical, I will definitely follow your suggestion above.
EDIT: Regarding "uncalibrated chip": Given the purpose of the chip, wouldn't the manufactures QC check verify proper calibration?
That reference is probably better than a chip, but I would not trust the calibration sticker to be as precise as the above website.
On ebay you can get the above reference without box and calibration sticker to about 1/3 the price of the finished unit (It is not the same circuit, but the reference is the same).
Unsure how accurate this is but what I can say that I have tested half dozen DMMs with it and all were in the +–0.03V range…that’s why I always warn people to trust cheap DMM measurements in the hundredth of a Volt region…
Here is a link to LT:
Edit: I was on the voltage standard.com site but I couldn’t find any prices? The shop seems to be not working…
For $6 i will gladly upgrade my precision on my cheap DMM’s and various volt meters i use around the house
Thanks guys for this thread this is a great idea. I though you had to spend thousands of $ to have any hope of any decent volt precision but now i know better.
Those $6 voltage reference without 15V batteries will work with lower voltage too, as long as you keep the output lower than input. So just use 5V as calibration voltage, and 2x18650 in series as source would work fine. (You know you have a bunch of those, don’t deny it. )
You do NEED batteries as input though, don’t use 15V AC adapter or something, the regular ones are way too noisy for calibration use.
I’ve ordered some LM336 reference chip last month from ebay, the 2.5V version, haven’t arrived. Should be easy enough to build, but the price is too cheap, I don’t know how accurate it will be. They were $0.99 for 10pcs.
Yeah it would work but the question is if input voltage and different power sources make a difference in the output…and with that all the calibration etc. has another’s unknown value in it…that’s why all conditions are measured and written done on the certificates, to rebuild the same conditions like temperature at home or at least to know that there is probably some tempdrift.
Of course everything works but it is hard to tell how good. To compare some different cheap multimeters so that you see each one measures different all these things will be fine, but the question is how precise are these things in total. The only way to make this is to measure it with a known perfectly working meter and write the values down. Also they have to be kind of stable over time so that if you measure next year they show almost the same values.
The lm336 does not be as precise as other references mentioned in this thread before. Can have anything between 2.44V-2.54V judging from the second page of the datasheet.
I’ve re-read the original thread on EEVBlog, and it seems the module uses single 4.2V li-ion, not 15V.
A few of them did a swap with regular Samsung phone battery. There’s even a mod to charge using the cheap usb module.
And even from 4.2V input, the reference have full outputs from 2.5V up to 10V. EEVblog tests still show consistent output voltage regardless of battery charge state. And these guys don’t use cheap DMMs.
This whole concept wades right into the deep end of what I call “The Third-Party Fallacy” — the belief that any 3rd party will make better decisions than you yourself* will.
Given the purpose of the DMM, “wouldn’t the manufacturers QC check verify proper calibration”??
(Full disclosure, I just got one of those Harbor Fright Free DMMs & was, just this moment, working out just this question!)
I found this article to be interesting, if not ultimately “helpful”.
As for me, I tend to eschew “Absolute Precision” since I seldom work with absolutes (not a Rocket Scientist, me!). I’d suggest factoring in a little “trust” (“Initial Plausibility”), and measure a nominal “standard” like the power-supply connections in a “standard” PC. At the end of the day, even NIST or ASTM calibration requires a level of “trust” of an interested 3rd party…
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*
“A man should learn to detect and watch that gleam of light which flashes across his mind from within, more than the lustre of the firmament of bards and sages. Yet he dismisses without notice his thought, because it is his. In every work of genius we recognize our own rejected thoughts: they come back to us with a certain alienated majesty.”
Prober calibration of a reference chip is not maximal precision, these chips do not have a internal calibration that can be adjusted.
When manufacturers wants to make something very precise they do not worry much about the initial value, but much more about how it changes over time and temperature. This is because it is easy to compensate for the initial error in any equipment (Except the cheapest stuff). Today this type of calibration is done with the computer inside the equipment, you just connect it to a known voltage/value and tell the computer inside the equipment to save a calibration factor.
EDIT: Regarding uncalibrated chip Given the purpose of the chip, wouldn’t the manufactures QC check verify proper calibration?
This whole concept wades right into the deep end of what I call “The Third-Party Fallacy” — the belief that any 3rd party will make better decisions than you yourself* will.
Given the purpose of the DMM, “wouldn’t the manufacturers QC check verify proper calibration”?? . . .
Interesting stuff. I may need to try the exercise someday. Thanks.
I should have referenced the chip I was referring to, which is this TexasInstruments REF5040 chip mentioned in the OP. The only purpose of the chip is to output a high precision reference voltage of 4.096 volts. It is supposed to have low temperature drift. So for my simple, non-critical needs, it seems like a great way to check and calibrate my meters.
“Measure with Micrometer, Mark with Chalk, Cut with Axe.”
That PDF claims Accuracy = +/- 0.05. My Fluke 77-IV is only capable of +/- 0.3, so, for me that would be a bit of overkill.
OTOH, “overkill” is still “dead” (as in “dead-on balls accurate” … “It’s an industry term” ~~Mona Lisa Vitto), so that should work very well for you.
But how would you know if the chip was accurate?
(EDIT: for the record, the Harbor Fright “7 Function Digital Multimeter”, a Centech Model 90899, only claims +/- 0.5% accuracy. That means your chip could be off by a whole order of magnitude and the HF meter likely wouldn’t notice, the Fluke (still ~an order of magnitude less accurate than your chip) maybe slightly…
Having said that, when you build your Reference, I’d love to help you “test it” on these…)
When I was a calibration tech years ago (Army 35H) we had to maintain at least a 4:1 ratio of accuracy for the standard and unit under test. A standard at /- 0.05% would have been acceptable for a/- 0.3% uut and definitely not overkill.
Back then this was the dc voltage standard we used: Fluke 332D
Still trying to find the higher current standard but for some lower dc current meters: Fluke 382A
disclaimer: random links found via google and I am not affiliated with either party.
Not to keep harping on it, but that’s still ~an order of magnitude difference — at least “a greater capacity than necessary” — which seems significant…
And you’d be correct to surmise that I didn’t consider that ImA4Wheelr had human lives on the line as you did.
Just trying to point out that there’s still an awful lot of faith involved.
