real-world voltage reference? - Page 1
Forum section: electronics / projects

author: ralphd
author_rank: Frequent Contributor
timestamp: July 25, 2015, 01:58:20 am
content: Is anyone aware of a non-semiconductor voltage reference source with ~1% or better accuracy?For humidity, a saturated NaCl paste is a decent 75% RH reference @25C.For temperature an ice bath is a decent 0C reference.One idea I consider is making a simple lead-acid cell. The output varies not only with temperature but with the sulfuric acid concentration. The temperature I can easily measure, but without a hygrometer I can't measure the sulfuric acid concentration. And even if I could, I doubt I could get 1% accuracy when temperature and acid concentration are factored.Any ideas? I'm going to order some TL431A's (+- 0.8%), but while I wait for them to arrive I'm wondering if there's something I might already have around the house I could use.

author: DanielS
author_rank: Frequent Contributor
timestamp: July 25, 2015, 02:36:22 am
content: If you apply a reasonably constant forward current to some diodes and keep them in a controlled temperature environment, you get a relatively constant forward voltage drop.Of course, forward voltage being so wildly different from one device to the next, you would need to calibrate your circuit on a per-diode basis. Not ideal but still far more accurate and convenient than a lead acid battery.

author: Ian.M
author_rank: Super Contributor
timestamp: July 25, 2015, 02:37:20 am
content: Heathkit used to reckon a fresh zinc carbon cell was 1.55V.Seehttp://www.ohio.edu/people/postr/bapix/vtvms.htmand search the page forcalibration.forIts probably not 1%, but is certainly better than anything else 'domestic'.

author: radioFlash
author_rank: Regular Contributor
timestamp: July 25, 2015, 02:48:03 am
content: Are you familiar with a Weston Cell?Sent from my iPhone using Tapatalk

author: ralphd
author_rank: Frequent Contributor
timestamp: July 25, 2015, 03:20:21 am
content: Quote from: radioFlash on July 25, 2015, 02:48:03 amI wasn't. After reading about it, I won't be trying it since I don't have a local source for the cadmium and mercury.

author: FrankT
author_rank: Regular Contributor
timestamp: July 25, 2015, 03:24:24 am
content: On a slight tangent, I needed to calibrate/verify a sound level meter. Anyone know of a way of doing that without an expensive source?

author: ralphd
author_rank: Frequent Contributor
timestamp: July 25, 2015, 03:32:17 am
content: Quote from: Ian.M on July 25, 2015, 02:37:20 amNo zinc carbons around, but I checked a pack of Wal-mart AA alkalines. My meter read 1.636 for 4 of them, and the fifth read 1.635 at 23C. That would suggest my meter is a touch high...

author: ralphd
author_rank: Frequent Contributor
timestamp: July 25, 2015, 05:22:16 am
content: Quote from: DanielS on July 25, 2015, 02:36:22 amI don't have a known calibration source, so that doesn't really help.When I get the tl431s, I'll test a dozen or so, and the one closest to the mean should give me a .02% accuracy reference. With that I can calibrate my 4-digit multimeter. I'll also have a bunch of tl431's to use on various projects (for only 2c ea on Aliexpress)

author: Ian.M
author_rank: Super Contributor
timestamp: July 25, 2015, 06:07:59 am
content: 1.6V is about right for a fresh alkaline.

author: Gyro
author_rank: Super Contributor
timestamp: July 25, 2015, 10:32:24 am
content: You might be better looking at button cells...A Silver Oxide (watch) battery has a stable 1.55V output for most of its discharge life when very lightly loaded (say, a few uA)The older Mercury button cells had a stable 1.35V (in fact I think they were spec'd to a few more decimal places) but are unobtainable now.To be honest you'd be better going for one of the tighter initial tolerance semiconductor reference. Some of them are not that expensive and are spec'd tighter than your TL431s for initial un-trimmed voltage. By the time you've bought the battery and bought/fabricated some kind of holder, you won't be that far out on cost. Not susceptible to accidental shorts like a battery (which can cause short to long term voltage change).

author: fcb
author_rank: Super Contributor
timestamp: July 25, 2015, 10:40:24 am
content: Quote from: FrankT on July 25, 2015, 03:24:24 amNot really - if you come up with something please let us know.

author: Ian.M
author_rank: Super Contributor
timestamp: July 25, 2015, 11:24:20 am
content: Quote from: ralphd on July 25, 2015, 05:22:16 amTL431A is only good to +/-1% if its from a reputable manufacturer. How confident are you that the parts from Aliexpress will be genuine Texas Instruments TL431A and not reconditioned used parts or Chinese copies? It is likely that all your parts will be from the same batch so they are likely to all have more or less the same deviation from the nominal reference voltage. Averaging doesn't improve the accuracy unless you have a truly randomly selected sample set.

author: Whales
author_rank: Super Contributor
timestamp: July 25, 2015, 12:06:31 pm
content: Quote from: fcb on July 25, 2015, 10:40:24 amIs it possible do something clever using two identical mics at different (exactly known) distances and compare the levels from them? I'm stabbing in the dark at whether or not the inverse cube root of sound amplitude falloff will allow you to find a unique solution to the source's loudness.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 25, 2015, 12:20:35 pm
content: Assuming anechoic conditions, inverse square or cube gets you a hint on the size of an object, but the level is all ratios to the source intensity.Mind that almost all easy "references" (like an electrochemical cell, or hunks of metal alloy in France) are temperature sensitive, so you implicitly have to include an extremely tight temperature control while you are performing this measurement.Tim

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: July 25, 2015, 12:50:46 pm
content: Quote from: ralphd on July 25, 2015, 01:58:20 amhttps://en.wikipedia.org/wiki/Voltage-regulator_tubeNot sure what "Real world" is supposed to mean. Semiconductors are real?

author: ralphd
author_rank: Frequent Contributor
timestamp: July 25, 2015, 03:23:02 pm
content: Quote from: Gyro on July 25, 2015, 10:32:24 amTried a LR44 battery I have lying around and got 1.138V, so I guess it's not silver oxide.I tried a new CR2032 and got 3.331. Varta says 3.2V open circuit (though one of their graphs looks more like 3.25).http://www.varta-microbattery.com/applications/mb_data/documents/sales_literature_varta/HANDBOOK_Primary_Lithium_Cells_en.pdfI'm not getting the TL431s just to make a voltage reference; I want them so I don't have to expand my collection of Zeners. I've also seen circuits for using them as amplifiers and oscillators.

author: ralphd
author_rank: Frequent Contributor
timestamp: July 25, 2015, 03:54:33 pm
content: Quote from: Ian.M on July 25, 2015, 11:24:20 amI'm confident what I'll be getting are new, genuine Wing Shing TL431As.http://www.aliexpress.com/item/Free-shipping-NEW-100PCS-TL431-TL431A-TO-92-Silicon-Transistors-triode-transistor/32328977920.htmlBased on beta testing of transistors (like 3904s), I've found wide variations (200-300 beta) within the same batch. I just measured Vf for a few 1N4006's off the same tape: .508, .510, .524, .513. That's .516V +- 1.5%.So I doubt all the batch of TL431As will have more or less the same deviation. Care to wager?

author: ralphd
author_rank: Frequent Contributor
timestamp: July 25, 2015, 04:00:20 pm
content: Quote from: Ian.M on July 25, 2015, 06:07:59 amAnyone with a 0.1% calibrated meter tried measuring them? I did a couple of google searches and couldn't find anything.Now, I think I did see some thorough voltage testing done on Sanyo Eneloops. I have some AA HR6 Eneloops I could top up, let the charge settle for a day, then compare my voltage readings with published ones...

author: DanielS
author_rank: Frequent Contributor
timestamp: July 25, 2015, 04:22:22 pm
content: Quote from: ralphd on July 25, 2015, 03:23:02 pmThe TL431 is basically a bandgap reference and an opamp in simple three pins packages. It is a really handy little chip with countless potential uses.If you already have a wide assortment of zeners though, you could simply use some of those for the time being. Give constant current and temperature, they won't drift much.

author: Kalvin
author_rank: Super Contributor
timestamp: July 25, 2015, 05:09:00 pm
content: Thermocouple in 0C ice water and some precision amplification?

author: saturation
author_rank: Super Contributor
timestamp: July 25, 2015, 05:12:46 pm
content: To get a reference voltage from natural items requires making some form of a battery. To get a predictable output from a battery requires reagent purity then the calculated reaction is more predictable. Alas, any commercial grade ingredients have undefined concentrations or impurities, so its hard to say if you'll get within 1% or so of any defined voltage.For about 1V, a lemon, penny or orange battery.https://en.wikipedia.org/wiki/Lemon_batteryhttps://en.wikipedia.org/wiki/Penny_battery

author: Gyro
author_rank: Super Contributor
timestamp: July 25, 2015, 05:18:07 pm
content: QuoteNo, the LR44 is a standard Alkaline button cell (and yours is a fairly flat one). You need something starting 'SR'QuoteReally not going to do you any good - the discharge curve is too steep. The variation between batteries from the same pack will be more than 0.1% and strongly temperature dependent too. You need to ditch the idea of an Alkaline as any sort of viable reference.Just go and compare the discharge voltage curves for the SR44 versus LR44 in the datasheets on the web and you'll see what I mean.

author: saturation
author_rank: Super Contributor
timestamp: July 25, 2015, 05:18:38 pm
content: This is a good idea. You can convert the thermocouples output voltage at 100C instead, but I don't know if it will be within 1%.Quote from: Kalvin on July 25, 2015, 05:09:00 pm

author: Gyro
author_rank: Super Contributor
timestamp: July 25, 2015, 05:26:01 pm
content: QuoteA thermocouple needs two junctions - the voltage is proportional to the temperature difference between those two junctions. That's why thermocouple thermometers include cold junction compensation, usually implemented with a semiconductor temperature sensor. Keeping 2 junctions at two precisely known temperatures is only likely to compound your problems in establishing a stable reference. Possible but not very practical.

author: Kalvin
author_rank: Super Contributor
timestamp: July 25, 2015, 05:49:14 pm
content: Measuring the junction voltage of the two different alloys at 0C ice water and amplify that. Cannot be done? If the environmental temperature causes problems, just seal the op amp and drop it into ice water as wellPs. Honestly, I have no idea how accurate this would be.

author: Gyro
author_rank: Super Contributor
timestamp: July 25, 2015, 06:03:06 pm
content: No, sorry - there will always be two junctions, even in unintentional (eg. the connections to the op-amp pins.If you could generate a voltage/current just by immersing a junction in cold water then you would have discovered the secret of free energyFor the Seebeck effect (thermocouple) to work there must always be a temperature difference between two junctions - Google is your friend (I hate saying that).The voltage produced is also very small so the gain of the op amp would need to be large and accuracy difficult. As I say, not impossible (say with pure iced water and pure boiling water) but really not a practical way of producing a voltage reference, compared to using an ACTUAL voltage reference.

author: Kalvin
author_rank: Super Contributor
timestamp: July 25, 2015, 06:08:57 pm
content: Quote from: Gyro on July 25, 2015, 06:03:06 pmYou are correct, I just lost it.

author: Gyro
author_rank: Super Contributor
timestamp: July 25, 2015, 06:18:42 pm
content: Happens to me tooA shame, if it had worked you would have been in the right part of the world to exploit it!

author: NiHaoMike
author_rank: Super Contributor
timestamp: July 25, 2015, 06:36:59 pm
content: What about a thermocouple in ice water and another one in boiling water? Of course, it would have to be distilled water to be accurate.

author: IanB
author_rank: Super Contributor
timestamp: July 25, 2015, 07:00:14 pm
content: Quote from: ralphd on July 25, 2015, 04:00:20 pmA sample of a few unused alkaline cells gave measured voltages between 1.61 and 1.59 depending on age.I seem to recall that a fresh unused Zinc Chloride 9 V battery measures almost spot on 10.0 V, but I don't have one to hand to measure right now.QuoteDon't do this. An NiMH cell is the most unstable, unpredictable voltage source going. There is absolutely no way to know the voltage without measuring it.

author: Macbeth
author_rank: Super Contributor
timestamp: July 25, 2015, 07:05:45 pm
content: Quote from: NiHaoMike on July 25, 2015, 06:36:59 pmSurely an extra thermocouple is redundant and suffers the problem of having to cold junction compensate.Much better to have the one thermocouple with one junction in the ice water and the other in the boiling.

author: Macbeth
author_rank: Super Contributor
timestamp: July 25, 2015, 07:10:31 pm
content: 4.096mV using a K type thermocouple according to NISTCode:ITS-90 Table for type K thermocouple°C 0 -1 -2 -3 -4 -5 -6 -7 -8 -9 -10Thermoelectric Voltage in mV-270 -6.458-260 -6.441 -6.444 -6.446 -6.448 -6.450 -6.452 -6.453 -6.455 -6.456 -6.457 -6.458-250 -6.404 -6.408 -6.413 -6.417 -6.421 -6.425 -6.429 -6.432 -6.435 -6.438 -6.441-240 -6.344 -6.351 -6.358 -6.364 -6.370 -6.377 -6.382 -6.388 -6.393 -6.399 -6.404-230 -6.262 -6.271 -6.280 -6.289 -6.297 -6.306 -6.314 -6.322 -6.329 -6.337 -6.344-220 -6.158 -6.170 -6.181 -6.192 -6.202 -6.213 -6.223 -6.233 -6.243 -6.252 -6.262-210 -6.035 -6.048 -6.061 -6.074 -6.087 -6.099 -6.111 -6.123 -6.135 -6.147 -6.158-200 -5.891 -5.907 -5.922 -5.936 -5.951 -5.965 -5.980 -5.994 -6.007 -6.021 -6.035-190 -5.730 -5.747 -5.763 -5.780 -5.797 -5.813 -5.829 -5.845 -5.861 -5.876 -5.891-180 -5.550 -5.569 -5.588 -5.606 -5.624 -5.642 -5.660 -5.678 -5.695 -5.713 -5.730-170 -5.354 -5.374 -5.395 -5.415 -5.435 -5.454 -5.474 -5.493 -5.512 -5.531 -5.550-160 -5.141 -5.163 -5.185 -5.207 -5.228 -5.250 -5.271 -5.292 -5.313 -5.333 -5.354-150 -4.913 -4.936 -4.960 -4.983 -5.006 -5.029 -5.052 -5.074 -5.097 -5.119 -5.141-140 -4.669 -4.694 -4.719 -4.744 -4.768 -4.793 -4.817 -4.841 -4.865 -4.889 -4.913-130 -4.411 -4.437 -4.463 -4.490 -4.516 -4.542 -4.567 -4.593 -4.618 -4.644 -4.669-120 -4.138 -4.166 -4.194 -4.221 -4.249 -4.276 -4.303 -4.330 -4.357 -4.384 -4.411-110 -3.852 -3.882 -3.911 -3.939 -3.968 -3.997 -4.025 -4.054 -4.082 -4.110 -4.138-100 -3.554 -3.584 -3.614 -3.645 -3.675 -3.705 -3.734 -3.764 -3.794 -3.823 -3.852-90 -3.243 -3.274 -3.306 -3.337 -3.368 -3.400 -3.431 -3.462 -3.492 -3.523 -3.554-80 -2.920 -2.953 -2.986 -3.018 -3.050 -3.083 -3.115 -3.147 -3.179 -3.211 -3.243-70 -2.587 -2.620 -2.654 -2.688 -2.721 -2.755 -2.788 -2.821 -2.854 -2.887 -2.920-60 -2.243 -2.278 -2.312 -2.347 -2.382 -2.416 -2.450 -2.485 -2.519 -2.553 -2.587-50 -1.889 -1.925 -1.961 -1.996 -2.032 -2.067 -2.103 -2.138 -2.173 -2.208 -2.243-40 -1.527 -1.564 -1.600 -1.637 -1.673 -1.709 -1.745 -1.782 -1.818 -1.854 -1.889-30 -1.156 -1.194 -1.231 -1.268 -1.305 -1.343 -1.380 -1.417 -1.453 -1.490 -1.527-20 -0.778 -0.816 -0.854 -0.892 -0.930 -0.968 -1.006 -1.043 -1.081 -1.119 -1.156-10 -0.392 -0.431 -0.470 -0.508 -0.547 -0.586 -0.624 -0.663 -0.701 -0.739 -0.7780 0.000 -0.039 -0.079 -0.118 -0.157 -0.197 -0.236 -0.275 -0.314 -0.353 -0.392°C 0 -1 -2 -3 -4 -5 -6 -7 -8 -9 -10ITS-90 Table for type K thermocouple°C 0 1 2 3 4 5 6 7 8 9 10Thermoelectric Voltage in mV0 0.000 0.039 0.079 0.119 0.158 0.198 0.238 0.277 0.317 0.357 0.39710 0.397 0.437 0.477 0.517 0.557 0.597 0.637 0.677 0.718 0.758 0.79820 0.798 0.838 0.879 0.919 0.960 1.000 1.041 1.081 1.122 1.163 1.20330 1.203 1.244 1.285 1.326 1.366 1.407 1.448 1.489 1.530 1.571 1.61240 1.612 1.653 1.694 1.735 1.776 1.817 1.858 1.899 1.941 1.982 2.02350 2.023 2.064 2.106 2.147 2.188 2.230 2.271 2.312 2.354 2.395 2.43660 2.436 2.478 2.519 2.561 2.602 2.644 2.685 2.727 2.768 2.810 2.85170 2.851 2.893 2.934 2.976 3.017 3.059 3.100 3.142 3.184 3.225 3.26780 3.267 3.308 3.350 3.391 3.433 3.474 3.516 3.557 3.599 3.640 3.68290 3.682 3.723 3.765 3.806 3.848 3.889 3.931 3.972 4.013 4.055 4.096100 4.096 4.138 4.179 4.220 4.262 4.303 4.344 4.385 4.427 4.468 4.509110 4.509 4.550 4.591 4.633 4.674 4.715 4.756 4.797 4.838 4.879 4.920120 4.920 4.961 5.002 5.043 5.084 5.124 5.165 5.206 5.247 5.288 5.328130 5.328 5.369 5.410 5.450 5.491 5.532 5.572 5.613 5.653 5.694 5.735140 5.735 5.775 5.815 5.856 5.896 5.937 5.977 6.017 6.058 6.098 6.138150 6.138 6.179 6.219 6.259 6.299 6.339 6.380 6.420 6.460 6.500 6.540160 6.540 6.580 6.620 6.660 6.701 6.741 6.781 6.821 6.861 6.901 6.941170 6.941 6.981 7.021 7.060 7.100 7.140 7.180 7.220 7.260 7.300 7.340180 7.340 7.380 7.420 7.460 7.500 7.540 7.579 7.619 7.659 7.699 7.739190 7.739 7.779 7.819 7.859 7.899 7.939 7.979 8.019 8.059 8.099 8.138200 8.138 8.178 8.218 8.258 8.298 8.338 8.378 8.418 8.458 8.499 8.539210 8.539 8.579 8.619 8.659 8.699 8.739 8.779 8.819 8.860 8.900 8.940220 8.940 8.980 9.020 9.061 9.101 9.141 9.181 9.222 9.262 9.302 9.343230 9.343 9.383 9.423 9.464 9.504 9.545 9.585 9.626 9.666 9.707 9.747240 9.747 9.788 9.828 9.869 9.909 9.950 9.991 10.031 10.072 10.113 10.153250 10.153 10.194 10.235 10.276 10.316 10.357 10.398 10.439 10.480 10.520 10.561260 10.561 10.602 10.643 10.684 10.725 10.766 10.807 10.848 10.889 10.930 10.971270 10.971 11.012 11.053 11.094 11.135 11.176 11.217 11.259 11.300 11.341 11.382280 11.382 11.423 11.465 11.506 11.547 11.588 11.630 11.671 11.712 11.753 11.795290 11.795 11.836 11.877 11.919 11.960 12.001 12.043 12.084 12.126 12.167 12.209300 12.209 12.250 12.291 12.333 12.374 12.416 12.457 12.499 12.540 12.582 12.624310 12.624 12.665 12.707 12.748 12.790 12.831 12.873 12.915 12.956 12.998 13.040320 13.040 13.081 13.123 13.165 13.206 13.248 13.290 13.331 13.373 13.415 13.457330 13.457 13.498 13.540 13.582 13.624 13.665 13.707 13.749 13.791 13.833 13.874340 13.874 13.916 13.958 14.000 14.042 14.084 14.126 14.167 14.209 14.251 14.293350 14.293 14.335 14.377 14.419 14.461 14.503 14.545 14.587 14.629 14.671 14.713360 14.713 14.755 14.797 14.839 14.881 14.923 14.965 15.007 15.049 15.091 15.133370 15.133 15.175 15.217 15.259 15.301 15.343 15.385 15.427 15.469 15.511 15.554380 15.554 15.596 15.638 15.680 15.722 15.764 15.806 15.849 15.891 15.933 15.975390 15.975 16.017 16.059 16.102 16.144 16.186 16.228 16.270 16.313 16.355 16.397400 16.397 16.439 16.482 16.524 16.566 16.608 16.651 16.693 16.735 16.778 16.820410 16.820 16.862 16.904 16.947 16.989 17.031 17.074 17.116 17.158 17.201 17.243420 17.243 17.285 17.328 17.370 17.413 17.455 17.497 17.540 17.582 17.624 17.667430 17.667 17.709 17.752 17.794 17.837 17.879 17.921 17.964 18.006 18.049 18.091440 18.091 18.134 18.176 18.218 18.261 18.303 18.346 18.388 18.431 18.473 18.516450 18.516 18.558 18.601 18.643 18.686 18.728 18.771 18.813 18.856 18.898 18.941460 18.941 18.983 19.026 19.068 19.111 19.154 19.196 19.239 19.281 19.324 19.366470 19.366 19.409 19.451 19.494 19.537 19.579 19.622 19.664 19.707 19.750 19.792480 19.792 19.835 19.877 19.920 19.962 20.005 20.048 20.090 20.133 20.175 20.218490 20.218 20.261 20.303 20.346 20.389 20.431 20.474 20.516 20.559 20.602 20.644°C 0 1 2 3 4 5 6 7 8 9 10ITS-90 Table for type K thermocouple°C 0 1 2 3 4 5 6 7 8 9 10Thermoelectric Voltage in mV500 20.644 20.687 20.730 20.772 20.815 20.857 20.900 20.943 20.985 21.028 21.071510 21.071 21.113 21.156 21.199 21.241 21.284 21.326 21.369 21.412 21.454 21.497520 21.497 21.540 21.582 21.625 21.668 21.710 21.753 21.796 21.838 21.881 21.924530 21.924 21.966 22.009 22.052 22.094 22.137 22.179 22.222 22.265 22.307 22.350540 22.350 22.393 22.435 22.478 22.521 22.563 22.606 22.649 22.691 22.734 22.776550 22.776 22.819 22.862 22.904 22.947 22.990 23.032 23.075 23.117 23.160 23.203560 23.203 23.245 23.288 23.331 23.373 23.416 23.458 23.501 23.544 23.586 23.629570 23.629 23.671 23.714 23.757 23.799 23.842 23.884 23.927 23.970 24.012 24.055580 24.055 24.097 24.140 24.182 24.225 24.267 24.310 24.353 24.395 24.438 24.480590 24.480 24.523 24.565 24.608 24.650 24.693 24.735 24.778 24.820 24.863 24.905600 24.905 24.948 24.990 25.033 25.075 25.118 25.160 25.203 25.245 25.288 25.330610 25.330 25.373 25.415 25.458 25.500 25.543 25.585 25.627 25.670 25.712 25.755620 25.755 25.797 25.840 25.882 25.924 25.967 26.009 26.052 26.094 26.136 26.179630 26.179 26.221 26.263 26.306 26.348 26.390 26.433 26.475 26.517 26.560 26.602640 26.602 26.644 26.687 26.729 26.771 26.814 26.856 26.898 26.940 26.983 27.025650 27.025 27.067 27.109 27.152 27.194 27.236 27.278 27.320 27.363 27.405 27.447660 27.447 27.489 27.531 27.574 27.616 27.658 27.700 27.742 27.784 27.826 27.869670 27.869 27.911 27.953 27.995 28.037 28.079 28.121 28.163 28.205 28.247 28.289680 28.289 28.332 28.374 28.416 28.458 28.500 28.542 28.584 28.626 28.668 28.710690 28.710 28.752 28.794 28.835 28.877 28.919 28.961 29.003 29.045 29.087 29.129700 29.129 29.171 29.213 29.255 29.297 29.338 29.380 29.422 29.464 29.506 29.548710 29.548 29.589 29.631 29.673 29.715 29.757 29.798 29.840 29.882 29.924 29.965720 29.965 30.007 30.049 30.090 30.132 30.174 30.216 30.257 30.299 30.341 30.382730 30.382 30.424 30.466 30.507 30.549 30.590 30.632 30.674 30.715 30.757 30.798740 30.798 30.840 30.881 30.923 30.964 31.006 31.047 31.089 31.130 31.172 31.213750 31.213 31.255 31.296 31.338 31.379 31.421 31.462 31.504 31.545 31.586 31.628760 31.628 31.669 31.710 31.752 31.793 31.834 31.876 31.917 31.958 32.000 32.041770 32.041 32.082 32.124 32.165 32.206 32.247 32.289 32.330 32.371 32.412 32.453780 32.453 32.495 32.536 32.577 32.618 32.659 32.700 32.742 32.783 32.824 32.865790 32.865 32.906 32.947 32.988 33.029 33.070 33.111 33.152 33.193 33.234 33.275800 33.275 33.316 33.357 33.398 33.439 33.480 33.521 33.562 33.603 33.644 33.685810 33.685 33.726 33.767 33.808 33.848 33.889 33.930 33.971 34.012 34.053 34.093820 34.093 34.134 34.175 34.216 34.257 34.297 34.338 34.379 34.420 34.460 34.501830 34.501 34.542 34.582 34.623 34.664 34.704 34.745 34.786 34.826 34.867 34.908840 34.908 34.948 34.989 35.029 35.070 35.110 35.151 35.192 35.232 35.273 35.313850 35.313 35.354 35.394 35.435 35.475 35.516 35.556 35.596 35.637 35.677 35.718860 35.718 35.758 35.798 35.839 35.879 35.920 35.960 36.000 36.041 36.081 36.121870 36.121 36.162 36.202 36.242 36.282 36.323 36.363 36.403 36.443 36.484 36.524880 36.524 36.564 36.604 36.644 36.685 36.725 36.765 36.805 36.845 36.885 36.925890 36.925 36.965 37.006 37.046 37.086 37.126 37.166 37.206 37.246 37.286 37.326900 37.326 37.366 37.406 37.446 37.486 37.526 37.566 37.606 37.646 37.686 37.725910 37.725 37.765 37.805 37.845 37.885 37.925 37.965 38.005 38.044 38.084 38.124920 38.124 38.164 38.204 38.243 38.283 38.323 38.363 38.402 38.442 38.482 38.522930 38.522 38.561 38.601 38.641 38.680 38.720 38.760 38.799 38.839 38.878 38.918940 38.918 38.958 38.997 39.037 39.076 39.116 39.155 39.195 39.235 39.274 39.314950 39.314 39.353 39.393 39.432 39.471 39.511 39.550 39.590 39.629 39.669 39.708960 39.708 39.747 39.787 39.826 39.866 39.905 39.944 39.984 40.023 40.062 40.101970 40.101 40.141 40.180 40.219 40.259 40.298 40.337 40.376 40.415 40.455 40.494980 40.494 40.533 40.572 40.611 40.651 40.690 40.729 40.768 40.807 40.846 40.885990 40.885 40.924 40.963 41.002 41.042 41.081 41.120 41.159 41.198 41.237 41.276°C 0 1 2 3 4 5 6 7 8 9 10ITS-90 Table for type K thermocouple°C 0 1 2 3 4 5 6 7 8 9 10Thermoelectric Voltage in mV1000 41.276 41.315 41.354 41.393 41.431 41.470 41.509 41.548 41.587 41.626 41.6651010 41.665 41.704 41.743 41.781 41.820 41.859 41.898 41.937 41.976 42.014 42.0531020 42.053 42.092 42.131 42.169 42.208 42.247 42.286 42.324 42.363 42.402 42.4401030 42.440 42.479 42.518 42.556 42.595 42.633 42.672 42.711 42.749 42.788 42.8261040 42.826 42.865 42.903 42.942 42.980 43.019 43.057 43.096 43.134 43.173 43.2111050 43.211 43.250 43.288 43.327 43.365 43.403 43.442 43.480 43.518 43.557 43.5951060 43.595 43.633 43.672 43.710 43.748 43.787 43.825 43.863 43.901 43.940 43.9781070 43.978 44.016 44.054 44.092 44.130 44.169 44.207 44.245 44.283 44.321 44.3591080 44.359 44.397 44.435 44.473 44.512 44.550 44.588 44.626 44.664 44.702 44.7401090 44.740 44.778 44.816 44.853 44.891 44.929 44.967 45.005 45.043 45.081 45.1191100 45.119 45.157 45.194 45.232 45.270 45.308 45.346 45.383 45.421 45.459 45.4971110 45.497 45.534 45.572 45.610 45.647 45.685 45.723 45.760 45.798 45.836 45.8731120 45.873 45.911 45.948 45.986 46.024 46.061 46.099 46.136 46.174 46.211 46.2491130 46.249 46.286 46.324 46.361 46.398 46.436 46.473 46.511 46.548 46.585 46.6231140 46.623 46.660 46.697 46.735 46.772 46.809 46.847 46.884 46.921 46.958 46.9951150 46.995 47.033 47.070 47.107 47.144 47.181 47.218 47.256 47.293 47.330 47.3671160 47.367 47.404 47.441 47.478 47.515 47.552 47.589 47.626 47.663 47.700 47.7371170 47.737 47.774 47.811 47.848 47.884 47.921 47.958 47.995 48.032 48.069 48.1051180 48.105 48.142 48.179 48.216 48.252 48.289 48.326 48.363 48.399 48.436 48.4731190 48.473 48.509 48.546 48.582 48.619 48.656 48.692 48.729 48.765 48.802 48.8381200 48.838 48.875 48.911 48.948 48.984 49.021 49.057 49.093 49.130 49.166 49.2021210 49.202 49.239 49.275 49.311 49.348 49.384 49.420 49.456 49.493 49.529 49.5651220 49.565 49.601 49.637 49.674 49.710 49.746 49.782 49.818 49.854 49.890 49.9261230 49.926 49.962 49.998 50.034 50.070 50.106 50.142 50.178 50.214 50.250 50.2861240 50.286 50.322 50.358 50.393 50.429 50.465 50.501 50.537 50.572 50.608 50.6441250 50.644 50.680 50.715 50.751 50.787 50.822 50.858 50.894 50.929 50.965 51.0001260 51.000 51.036 51.071 51.107 51.142 51.178 51.213 51.249 51.284 51.320 51.3551270 51.355 51.391 51.426 51.461 51.497 51.532 51.567 51.603 51.638 51.673 51.7081280 51.708 51.744 51.779 51.814 51.849 51.885 51.920 51.955 51.990 52.025 52.0601290 52.060 52.095 52.130 52.165 52.200 52.235 52.270 52.305 52.340 52.375 52.4101300 52.410 52.445 52.480 52.515 52.550 52.585 52.620 52.654 52.689 52.724 52.7591310 52.759 52.794 52.828 52.863 52.898 52.932 52.967 53.002 53.037 53.071 53.1061320 53.106 53.140 53.175 53.210 53.244 53.279 53.313 53.348 53.382 53.417 53.4511330 53.451 53.486 53.520 53.555 53.589 53.623 53.658 53.692 53.727 53.761 53.7951340 53.795 53.830 53.864 53.898 53.932 53.967 54.001 54.035 54.069 54.104 54.1381350 54.138 54.172 54.206 54.240 54.274 54.308 54.343 54.377 54.411 54.445 54.4791360 54.479 54.513 54.547 54.581 54.615 54.649 54.683 54.717 54.751 54.785 54.8191370 54.819 54.852 54.886°C 0 1 2 3 4 5 6 7 8 9 10************************************* This section contains coefficients for type K thermocouples for* the two subranges of temperature listed below. The coefficients* are in units of °C and mV and are listed in the order of constant* term up to the highest order. The equation below 0 °C is of the form* E = sum(i=0 to n) c_i t^i.** The equation above 0 °C is of the form* E = sum(i=0 to n) c_i t^i + a0 exp(a1 (t - a2)^2).** Temperature Range (°C)* -270.000 to 0.000* 0.000 to 1372.000************************************name: reference function on ITS-90type: Ktemperature units: °Cemf units: mVrange: -270.000, 0.000, 100.000000000000E+000.394501280250E-010.236223735980E-04-0.328589067840E-06-0.499048287770E-08-0.675090591730E-10-0.574103274280E-12-0.310888728940E-14-0.104516093650E-16-0.198892668780E-19-0.163226974860E-22range: 0.000, 1372.000, 9-0.176004136860E-010.389212049750E-010.185587700320E-04-0.994575928740E-070.318409457190E-09-0.560728448890E-120.560750590590E-15-0.320207200030E-180.971511471520E-22-0.121047212750E-25exponential:a0 = 0.118597600000E+00a1 = -0.118343200000E-03a2 = 0.126968600000E+03************************************* This section contains coefficients of approximate inverse* functions for type K thermocouples for the subranges of* temperature and voltage listed below. The range of errors of* the approximate inverse function for each subrange is also given.* The coefficients are in units of °C and mV and are listed in* the order of constant term up to the highest order.* The equation is of the form t_90 = d_0 + d_1*E + d_2*E^2 + ...* + d_n*E^n,* where E is in mV and t_90 is in °C.** Temperature Voltage Error* range range range* (°C) (mV) (° C)* -200. to 0. -5.891 to 0.000 -0.02 to 0.04* 0. to 500. 0.000 to 20.644 -0.05 to 0.04* 500. to 1372. 20.644 to 54.886 -0.05 to 0.06********************************************************Inverse coefficients for type K:Temperature -200. 0. 500.Range: 0. 500. 1372.Voltage -5.891 0.000 20.644Range: 0.000 20.644 54.8860.0000000E+00 0.000000E+00 -1.318058E+022.5173462E+01 2.508355E+01 4.830222E+01-1.1662878E+00 7.860106E-02 -1.646031E+00-1.0833638E+00 -2.503131E-01 5.464731E-02-8.9773540E-01 8.315270E-02 -9.650715E-04-3.7342377E-01 -1.228034E-02 8.802193E-06-8.6632643E-02 9.804036E-04 -3.110810E-08-1.0450598E-02 -4.413030E-05 0.000000E+00-5.1920577E-04 1.057734E-06 0.000000E+000.0000000E+00 -1.052755E-08 0.000000E+00Error -0.02 -0.05 -0.05Range: 0.04 0.04 0.06

author: ralphd
author_rank: Frequent Contributor
timestamp: July 25, 2015, 07:30:20 pm
content: Quote from: IanB on July 25, 2015, 07:00:14 pmThanks. That supports my conclusion that my meter is reading a bit high (+1%). I also get 5.05V off the USB port of an Acer PC, so if the meter is 1% high, the actual voltage would be bang on 5.0V. Now to figure out how to calibrate my meter (it's got several trimmers on the PCB)...

author: Gyro
author_rank: Super Contributor
timestamp: July 25, 2015, 07:46:41 pm
content: Or your PC might quite reasonably be putting out 4.95 or 5.05 or 5.1 or up to 5.25V and still be in spec. I really wouldn't use that as a basis for adjusting the calibration of a meter, especially if you don't have information on which pot to twiddle.Edit: If it only measured 1.138V on the LR44 then you could just as easily suspect that it's reading low.At the moment it sounds as if the meter is the most accurate reference that you've got!

author: ralphd
author_rank: Frequent Contributor
timestamp: July 25, 2015, 07:53:41 pm
content: I can see 8 trimmer pots on my meter's PCB. Any suggestions on how to tell which one adjusts the voltage reference?

author: Gyro
author_rank: Super Contributor
timestamp: July 25, 2015, 07:55:39 pm
content: PLEASE, non of them

author: ralphd
author_rank: Frequent Contributor
timestamp: July 25, 2015, 07:59:34 pm
content: Quote from: DanielS on July 25, 2015, 04:22:22 pmVishay's datasheet says +-5% for zeners:http://www.taydaelectronics.com/datasheets/A-170.pdf

author: Howardlong
author_rank: Super Contributor
timestamp: July 25, 2015, 08:05:48 pm
content: Quote from: Gyro on July 25, 2015, 07:46:41 pm+1

author: Howardlong
author_rank: Super Contributor
timestamp: July 25, 2015, 08:07:13 pm
content: Quote from: Gyro on July 25, 2015, 07:55:39 pmAnd again, +1.

author: SeanB
author_rank: Super Contributor
timestamp: July 25, 2015, 08:16:21 pm
content: Even the cheap ( or free with coupon) Canada Tyre meter will be accurate on DC voltage to within 0.1%, or basically of the 1999 display the voltage will be correct for the 199 part, the last 9 digit will be up to 5 counts out of the actual voltage. Pretty much any of them out of the box, will agree with the others to this 5 count error.If you need more confidence then get a voltage reference fromwww.voltagestandard.com, or look at 99centhobbies.com ( Frankie Tong, a long standing member here) where he will be able to sell you a BM869s, which will be a lot more resolution than most people require for most uses.

author: ralphd
author_rank: Frequent Contributor
timestamp: July 25, 2015, 08:25:15 pm
content: Quote from: Gyro on July 25, 2015, 07:46:41 pmThen how do you explain the 1.635V reading on the alkaline batteries?

author: IanB
author_rank: Super Contributor
timestamp: July 25, 2015, 08:37:53 pm
content: Quote from: ralphd on July 25, 2015, 08:25:15 pmMaybe the batteries are really 1.635 V? My batteries have been sitting on the shelf for a while. A brand new battery may read higher. You have a sample reading but nowhere near enough data to base any decisions about adjusting your meter.

author: Gyro
author_rank: Super Contributor
timestamp: July 25, 2015, 08:50:35 pm
content: Whathesaid...Just one other thought, check that your meter battery is ok. Some meters can start throwing funny readings before their low battery indicator show up. If you believe that your meter hassuddenlydrifted off then it might be worth changing it. More likely than a significant calibration error.

author: ralphd
author_rank: Frequent Contributor
timestamp: July 25, 2015, 09:42:51 pm
content: Quote from: Gyro on July 25, 2015, 08:50:35 pm8.5V with a ~5mA load (red LED & 1.2K resistor). A newer Duracell alkaline reads 8.7V.I dug up my Ideal clamp-style meter that I mainly use for measuring AC power, but it also has a DC setting (with only 1 decimal place accuracy).I before testing the battery in the CT meter, I did some other tests:36V HP supply: 39.1V(Ideal), 39.0(CT),14.4 NiCd charged: 16.6(Ideal), 16.60(CT)So now that has me thinking the people that say fresh alkaline cells are 1.60V are testing with batteries that are older than mine... (even though alkaline are supposed to have very low self-discharge).For one more data point, I measured the 3.3V supply on a RPi B+ at 3.295V.

author: IanB
author_rank: Super Contributor
timestamp: July 25, 2015, 10:01:27 pm
content: Alkaline batteries are not designed or constructed as reference voltage sources.Different manufacturers may use different chemical formulations. Then the temperature will affect the voltage reading as well as the age.You can say a fresh battery will read about 1.6 V. You can't say it will read about 1.60 V. That's too many digits of precision.

author: ralphd
author_rank: Frequent Contributor
timestamp: July 25, 2015, 10:07:54 pm
content: I thought of using the band gap reference on an AVR MCU, but it looks like they are not very accurate.https://harizanov.com/2013/09/thoughts-on-avr-adc-accuracy/

author: ralphd
author_rank: Frequent Contributor
timestamp: July 25, 2015, 10:19:15 pm
content: I found some old (2013 expiry date) unused Energizer alkaline C cells. 2 read 1.586 and 2 read 1.584V.

author: Alexei.Polkhanov
author_rank: Frequent Contributor
timestamp: July 25, 2015, 10:21:24 pm
content: Quote from: ralphd on July 25, 2015, 03:20:21 am- Ebay, i got my cadmium from US supplierhttp://www.ebay.com/itm/9oz-250g-Pure-Cadmium-Metal-Sticks-99-99-Element-Sample-Rod-1-4-kg-/111333082639?pt=LH_DefaultDomain_0&hash=item19ebf8060fand I got mercury from local chem supplier or I think you can get mercury from 50 or so switches like these:http://www.ebay.com/itm/5pcs-Mercury-Tilt-Switch-24V-0-3A-Alarm-Car-Motion-Position-Angle-/201103317313?pt=LH_DefaultDomain_0&hash=item2ed2b11941Glass work can be of challenge not the materials.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 25, 2015, 11:06:17 pm
content: Much of this thread is going in circles:Thermocouples need temperature (not to mention some very good amplifiers).Temperature of phase transitions depends on pressure.You can use triple points of appropriate materials (water's is a hair over 0C), but then you have to prepare such samples... they also have to be extremely pure, chemically, otherwise the melting point will be slightly depressed, or the vapor phase will be depressed.Electrochemical voltages depend on all these, once again. At least the voltage has a logarithmic dependency on temperature and concentration, but it's still sensitive.And you need an extremely good thermal bath, no small feat of its own, and certainly not compact.Semiconductors implement a voltage reference by using a difference of exponentials, which are ultimately related to the bandgap of the material. Which also varies with temperature, but in a way predictable for a given material; and another bandgap can be adjusted to give a signal proportional to temperature, rather than nominally canceling it out, and that signal used as compensation to Nth order.Which, really, isn't much *better* than taking any half-assed method, measuring the contributing variables (like temperature), and applying a compensation to keep it straight. But it's notable that semiconductors are particularly well suited to this (the reference circuit can be made very independent of applied voltage, so that ambient temperature is basically the extent of it), and have decades of development behind them, perfecting these designs*.*Except for the crap they threw in the ATMegas. Those things are shit. The ADC barely meets useful specs, the reference isn't, and POR/BOD are dV/dt sensitive. The stuff in the XMEGAs looks like they actually got someone who knows their head from their ass, but almost no specs have guaranteed ranges, and the documentation stinks.Tim

author: Ian.M
author_rank: Super Contributor
timestamp: July 26, 2015, 12:17:04 am
content: As I said way earlier, Heathkit used to recommend calibrating against a fresh totally unused Zinc Carbon cell at a nominal 1.55V. I think we can assume room temperature of 25 deg C, but the problem is the cell chemistry may have changed.Way back in the day, it was common to wipe the inside of the Zinc cup anode with Mercury to form an amalgam layer to discourage local action due to impurities that could rapidly pit and eventually hole the Zinc cup. Mercury in disposable batteries is now banned, so current production used ultra-pure Zinc. Also, way way back they were dry Leclanche cells with an Ammonium Chloride electrolyte, however it was found that adding Zinc Chloride to the electrolyte improved performance and reduced corrosion of the Zinc by the Ammonium Chloride in storage, which eventually resulted in so called heavy duty Zinc Carbon cells which have Zinc chloride as the majority of the electrolyte. Currently available cells will be of this type. Its a mature technology and apart from the removal of Mercury and the replacement of asphalt seals with plastic ones , hasn't changed significantly in the last 40 years.Also, we don't know if Heathkit were rounding to the nearest 0 or 5, which would have been approx +/- 1.66% or if it was to the nearest digit which would be approx +/- 0.33%.I also don't have the original Heathkit valve voltmeter manual handy to see if they used a standard (nearer to Leclanche) or heavy duty (Zinc Chloride) cell.With all the above uncertainties, the best way forward would be if those of us with precision bench voltmeters or a 0.1% or better calibration source, were to acquire the freshest Heavy Duty Zinc Carbon AA we can easily get and post the initial unloaded terminal voltage (to 3 decimal places), brand and product name, expiry date and ambient temperature. As they are readily available from pound shops / dollar stores, that shouldn't be too great an imposition.If Heathkit's figure of 1.55V is still reasonably reliable, that will be useful to know when trying to help people in less developed countries, or for a quick sanity check when no precision calibration source is available. If it is not, then the idea needs to be consigned to the dustbin of history.Other types of consumer battery with the exception of the Silver Oxide button cell wouldn't be suitable for calibration use as the manufacturers are still actively developing and tweaking the cell chemistry which results in variations from brand to brand and from one year to the next.

author: IanB
author_rank: Super Contributor
timestamp: July 26, 2015, 12:38:19 am
content: Modern zinc chloride cells are way higher than 1.55 V out of the package. I just bought a couple of Sunbeam 9 V batteries from the dollar store (expiry date 9/2018) and one measures 10.1 V, the other 10.0 V. Assuming six cells, that gives about 1.67 or 1.68 V per cell. That's pretty typical in my experience. Fresh zinc chloride cells usually have a higher voltage than fresh alkaline cells.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: July 26, 2015, 04:05:38 am
content: Maybe keep one of these in a bowl?https://en.wikipedia.org/wiki/Electric_eel

author: ralphd
author_rank: Frequent Contributor
timestamp: July 26, 2015, 05:16:27 am
content: What about primary lithium cells, like CR2032?

author: SeanB
author_rank: Super Contributor
timestamp: July 26, 2015, 08:03:28 am
content: Quote from: ralphd on July 26, 2015, 05:16:27 amFresh CR2032 is around 3V3, but the discharge curve, while it is pretty flat over a large portion, does have some slope along it, and there is a small drop from manufacture till it evens out for a long period.It is a good power source for light loads, but not a very good reference if you want better than 100mV of resolution.Basically look for a 2V5,5V,10V reference online, which are pretty cheap and good enough for most uses. Otherwise buy one of the AD references which have a guaranteed accuracy sped right from the factory. I bought an AD581KH, which is 10.00V out of the box, and it is both cheap, has only 3 terminals and is easy to use. Just supply it with 15V from a simple power supply ( 15VAC wall wart, bridge rectifier and capacitor, then a 7815 regulator to give 15V to drive it) and it gives 10.00V on it's output.

author: Gyro
author_rank: Super Contributor
timestamp: July 26, 2015, 10:15:02 am
content: From your increasing number of spot readings and the anecdotal observations from others about Alkaline battery starting voltages I don't see anything that tells me that your meter is actually reading out of spec - you're seeing some voltages higher than you expected but others lower or the same as you expected.If you are really dead set on using a primary cell as a reference rather than a tightly specified 3 terminal semiconductor one then, in a non-Mercury/Cadmium world, you need to get yourself a Silver Oxide watch battery as I said several pages ago! It has the flattest discharge curve of any of the battery types.All the silver Oxide datasheets say 1.55V with a flat discharge voltage until end of life. The discharge curves all show a small wiggle or drop over the first few hours, but if you load it with the resistance value specified on the relevant datasheet for around 50 hours, then you will be into the flat discharge region.Just go and look up the datasheets for various manufacturers, Energiser, Renata, Maxell etc. Just type in "Silver Oxide battery datasheet" and they are all just a few clicks away. There really is no point in messing around with any battery technology, Alkaline, Lithium (better than alkaline but nowhere near as flat a Silver Oxide) etc that don't have a ruler flat specified discharge curve.You really do need to to some basic research for yourself.Edit: Silver Oxide batteries are used in other things too, calculators, calipers etc. If it starts SR (rather than LR or CR) then it's Silver Oxide. Buy a new one, load it with the resistor compatible with its capacity (datasheet). Leave it 50 - 100 hours, measure it (still under load). Use a holder of some sort - DON'T solder to it (at best you'll damage its characteristics).

author: SeanB
author_rank: Super Contributor
timestamp: July 26, 2015, 11:03:28 am
content: Hard to get a SR cell these days though, you will typically get a LR cell, as the SR cells do contain Mercury inside. I know as I buy a lot of assorted cells for watches, and they typically might be marked as SR"compatible" but are an alkaline cell.Just order the 2 terminal or 3 terminal VR online, the best accuracy grade you can afford. That way you have a simple check as to the accuracy of the meter at at least 1 range and at 2 points ( 0V and the selected point).

author: Gyro
author_rank: Super Contributor
timestamp: July 26, 2015, 11:22:59 am
content: No problems getting them in the UK (ROHS and all), I buy them for my calipers and height gauge. SR44 is the most common one. They don't last 5 minutes with LR44 due to the lower (steeper) discharge voltage.Renata (Swiss) make loads of types for watches - but they use a numeric code rather than SRxx. All the datasheets are there on their website though. Just go to a jewelery shop.I agree with you 100%, an accurate semiconductor reference / VR is by far the most sensible way to go (series types are probably easier for the OP to apply than Shunt types). It's only his insistence on using a battery that is prompting the other advice. Even a TI REF102C (Tightest grade) dip pkg can be had from RS in the UK for GBP10 (probably cheaper in the US), this gives 10V +/- 2.5mV untrimmed. Subtract the cost of a watch battery and the additional hassle involved and it's a no-brainer!

author: ralphd
author_rank: Frequent Contributor
timestamp: July 26, 2015, 03:01:07 pm
content: My point was to see if there is a common household item like a battery that can be used as a voltage reference.It would be useful to hobbyists that aren't going to spend $10 on a precision reference.Anyway, I'll probably end up getting a max6126 just to satisfy my curiosity. And maybe I'll find a common household item that others can use for a 1% reference...

author: IanB
author_rank: Super Contributor
timestamp: July 26, 2015, 03:49:21 pm
content: Quote from: ralphd on July 25, 2015, 08:25:15 pmA sample of new Sunbeam alkaline cells read between 1.626 V and 1.630 V.

author: ralphd
author_rank: Frequent Contributor
timestamp: July 26, 2015, 04:26:15 pm
content: Quote from: IanB on July 26, 2015, 03:49:21 pmThanks.You don't have any fresh CR2032's around do you?I only have 1 unused 2032 left, and it is about 2 yrs since I bought it. I'm reading 3.331V from it.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: July 26, 2015, 05:32:33 pm
content: Quote from: ralphd on July 26, 2015, 03:01:07 pmSteel wool and drain cleaner??More likely to have this lying around than a regulator tube or an eel, I think.

author: Gyro
author_rank: Super Contributor
timestamp: July 26, 2015, 05:50:38 pm
content: QuoteOk, I understand your aim, just question the practicability using torch batteries of various brands and ages (since manufacture, not purchase)As SR44sarea household item in my home (as previously explained)...Fresh SR44: 1.5655V @ 21'C Never loadedI think you need to be including measurement temperature in your investigation due to their fairly large temperature dependence. Putting weak zinc carbon batteries in front of the household fire to revive them was once common practice.

author: ralphd
author_rank: Frequent Contributor
timestamp: July 26, 2015, 06:29:57 pm
content: Quote from: Gyro on July 26, 2015, 05:50:38 pmI mentioned the Wal-mart alkaline AAs were measured at 23C.The CR2032s were in the basement, with a temperature around 21C.Duracel and Energizer have expiry dates, so I still think it is plausible and even probable that a popular brand of batteries with a specific expiry date will have a narrow range of voltage.Thanks for the SR44 reference. As others have pointed out, many batteries are advertized as SR44 compatible, and are actually LR44 or AG13.I found a Aliexpress seller offering a pair of 'genuine TI' REF5050IDGKR for under $4. Under $2 a chip for a .05% reference seems like a pretty good deal...

author: Kalvin
author_rank: Super Contributor
timestamp: July 26, 2015, 06:36:20 pm
content: Buy one of those cheap $5 5-digit voltage meters. Use the meter as isor salvage the reference**. Of build a buffer for the reference using a decent op amp, so you will have a cheap 5-digit volt meter and quite accurate voltage reference** It is possible that the reference is actually software calibrated, so you should buffer the reference with a decent op amp and measure the buffered reference voltage, so you will know actual reference voltage.

author: babysitter
author_rank: Frequent Contributor
timestamp: July 26, 2015, 06:38:47 pm
content: Consider sticking a button cell in your navel, under your armpits, under your tongue or up your A$$, and use it always at rest and at the same time of day. Natural oven controlled cell !

author: Gyro
author_rank: Super Contributor
timestamp: July 26, 2015, 07:00:24 pm
content: QuoteI think any battery that actually has SR44 stamped into it probably is one (ironically you should be able to tell from its voltage, initial voltage for Alkaline appears higher)True, you did state the temperature, but other measurements are coming in without temperature data. Given that this is an international forum ambient conditions from various locations are going to be a factor, as are brands - I've never heard of some of the ones people have posted (probably not sold here).Given the price of a pack of 4 Duracell batteries here you could afford a reasonable reference - as you indicated. BTW on this occasion I might be tempted to buy from a known source as it's not unknown for 'genuine' parts to be fake or re-marked as a more premium grade. However you could still do very well for the price of a pack of batteries - The "Even a REF102C" at £10 is pretty much the practical state of the art (buried zener), without going to ovened references - far tighter than you are needing. I was really just illustrating the degree of precision you can get for RELATIVELY little money these days You can go a LOT cheaper by reducing the initial tolerance a little as you have found

author: Gyro
author_rank: Super Contributor
timestamp: July 26, 2015, 07:03:52 pm
content: @babysitter:You are a true comedian Your talent is clearly wasted on us

author: SeanB
author_rank: Super Contributor
timestamp: July 26, 2015, 07:12:24 pm
content: New still in the wrapper Renata CR2032 Expiry 05 2020 3.288V.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: July 26, 2015, 07:46:43 pm
content: Quote from: babysitter on July 26, 2015, 06:38:47 pmDon't try that with an eel. Or steel wool.

author: Ian.M
author_rank: Super Contributor
timestamp: July 26, 2015, 07:52:15 pm
content: ... or at least, if thats what floats your boat, *please* don't tell us about it!

author: ralphd
author_rank: Frequent Contributor
timestamp: July 26, 2015, 07:56:06 pm
content: Quote from: SeanB on July 26, 2015, 07:12:24 pmThanks. Is that with a calibrated meter?

author: ralphd
author_rank: Frequent Contributor
timestamp: July 26, 2015, 08:09:22 pm
content: Quote from: IanB on July 26, 2015, 03:49:21 pmThat should make a reasonable comparison to the Wal-Mart "Great Value" alkalines I have. Both cheap, made in China batteries.If we take my highest reading of 1.636 and your top reading of 1.630 as being equal, that would mean my meter is +.37%. I suspect my meter uses a cheap TL431B (+-.5%), so +.37% is in the range of what makes sense...

author: SeanB
author_rank: Super Contributor
timestamp: July 26, 2015, 08:14:12 pm
content: Compared to accurate voltage references, and it agrees to within 6 counts, so pretty much good enough for me. If I want a more stable one I would have to get the Tek I have at work at present, as that has been verified with a Fluke calibrator. 2000 count though so I can only measure to 2 decimal places.

author: Ian.M
author_rank: Super Contributor
timestamp: July 26, 2015, 08:33:22 pm
content: Some more data points for you:Cheap far east Lithium 2032, approx 3 years old: 3.29VCheap far east alkaline AG13, approx 3 years old: 1.58V4x Kodak Extra Heavy Duty (Zinc Chloride) D cell, expires 10-2015: 1.63V, 1.61V, 1.63V, 1.58VKodak Xtralife Alkaline 6LR61 (PP3), expires 10-2024: 9.50V4x Kodak Xtralife Alkaline AA, expires 10-2024: all 1.62VAll readings taken with a Maplin Pg22 pocket multimeter (+/-2% + 2 digits) at 20 deg C - I'm down the boat and there's nothing better aboard.

author: ralphd
author_rank: Frequent Contributor
timestamp: July 26, 2015, 08:57:10 pm
content: I forgot to mention the meter I'm using for my measurements is a Mastercraft (CT store brand) auto-ranging model 52-052-2. Nothing obvious that would indicate who the OEM is.

author: Kalvin
author_rank: Super Contributor
timestamp: July 26, 2015, 09:57:08 pm
content: Ikea #502.405.021.5V Alkaline LR6 AA-AM3-MN1500Expiry Date: 2019-01-13Made In China18862Unused, batteries measured in same order as in package, measured twice, rounded to four digits1.594, 1.596, 1.594, 1.596, 1.598, 1.595, 1.585, 1.586, 1.587, 1.586Ikea #802.405.051.5V Alkaline LR03 AAA-AM4-MN2400Expiry Date: 2018-12-11Made In China18862Unused, batteries measured in same order as in package, measured twice, rounded to four digits1.591, 1.592, 1.590, 1.592, 1.590, 1.592, 1.589, 1.592, 1.592, 1.591Room temperature: +24 CelciusMultimeter: UNI-T UT61EComparing the UNI-T UT61E to the UT33C in 2000mV range and Vichy VC99:UT61E: 1.586VUT33C: 1.583VVC99: 1.586V

author: ralphd
author_rank: Frequent Contributor
timestamp: July 26, 2015, 11:49:53 pm
content: Picked up a 3-pack of Sunbeam CR2032s at a local dollar store today. Made in China, best before 03/2018. Measured at 22C:3.357, 3.353 & 3.342VSubtracting 0.4% (my guess for my meter offset until I have a good reference) gives:3.344, 3.340, & 3.329V

author: Macbeth
author_rank: Super Contributor
timestamp: July 26, 2015, 11:50:12 pm
content: Quote from: babysitter on July 26, 2015, 06:38:47 pmYou are a fecking genius! The holy grail - an aged and selected LTZ1000 shoved up the arse for proper tempco. The voltnuts will surely go for it? Of course it will need doctors certificates for traceability instead of the usual NIST paper trail, but I think its a candidate

author: ralphd
author_rank: Frequent Contributor
timestamp: July 26, 2015, 11:58:22 pm
content: Quote from: Kalvin on July 26, 2015, 09:57:08 pmI was at Ikea a couple weeks ago and had considered picking up a pack. I'm guessing they're either a lot older than the Wal-Mart AA's I have, or the chemistry is slightly different since the voltages are about 2% lower even after making a correction for the .35-.45% offset of my meter.

author: IanB
author_rank: Super Contributor
timestamp: July 27, 2015, 12:22:06 am
content: Quote from: ralphd on July 26, 2015, 11:49:53 pmAs did I (two-pack though). Same date. 3.347 V, 3.377 V.The lack of consistency implies poor quality control. Oh well, who can complain at 50¢ each?

author: ralphd
author_rank: Frequent Contributor
timestamp: July 27, 2015, 12:45:46 am
content: Quote from: IanB on July 27, 2015, 12:22:06 amNo typo there? 3.377on the 2nd one?40-50c ea is OK for something you can grab while you're out picking up milk, but I order most of my CR2032s online. I've found the ones that come in the trays are not worth the trouble (many arrive dead), but the ones in the 5-packs on a cardboard strip are good, and can be found for <$2 for 10 (2 packs of 5).I find the cheap Chinese CR2032s don't put out much more than 10mA, which can be a problem for little sensor nodes.

author: deadlylover
author_rank: Frequent Contributor
timestamp: July 27, 2015, 06:04:44 am
content: I checked a few old unused batteries lying around @ 17C, quite chilly in Sydney today...Using an R6581 8.5 digit meter, accurate to about 7ppm, slightly overkill I think. =PVarta 9V alkaline, expiry 12-2020: 9.7649VSony AAA heavy duty, unknown date/expiry : 1.5975VTitanium Innovations CR123A, purchased mid-2011 : 3.2750V, 3.2779VProbably not very useful data for anyone, but I couldn't resist joining in on the fun.

author: Gyro
author_rank: Super Contributor
timestamp: July 27, 2015, 10:50:57 am
content: Hmmm, It looks as if CR2032s from the same pack have surprisingly large variations. Must be either lousy quality control or sensitive to very small variations in the recipe.The Alkalines seem much more consistent in the same pack, but still fairly large variations between kitchens (see what I did there?).Still quite surprised about the Lithiums though, maybe initial voltage stability is inversely proportional to energy density? Older chemistry may be more robust against slight variations in the mix.Come on folks, there must be some electro-mechanical types out there with SR44s - I'm trying to make a point here!

author: ralphd
author_rank: Frequent Contributor
timestamp: July 27, 2015, 08:33:37 pm
content: Quote from: Gyro on July 27, 2015, 10:50:57 amWell, to make you happy, I went out and found a Duracel 301/SR43 silver oxide mercury-free battery. $3 (more than I paid for 100 TL431As) only gets you one of them at the local Wal-Mart!Anyway, my meter fluctuates between 1.597 and 1.598, so call it 1.5975. Temperature: 21C.That puts my reading 2% over yours. I'm pretty confident my meter is not 1% high (more like 0.3-0.5%), so already with a sample of 2 silver-oxide batteries are not good enough for a 1% reference.

author: Gyro
author_rank: Super Contributor
timestamp: July 27, 2015, 09:17:37 pm
content: Doh! That's not what I was expectingMine is probably a year or so old now (waiting for one of the others to run out). Maybe they're only stable when loadedThanks for your dedication to the cause of household metrology anyway

author: lewis
author_rank: Frequent Contributor
timestamp: July 27, 2015, 09:37:59 pm
content: Please, can everyone stop taking about using batteries as voltage references! No standard household battery is going to be accurate enough, stable enough or precise enough to calibrate a DMM.Ralph dude - if you want to calibrate a DMM you're just going to have to bite the bullet and spend the few Canadian Pesos on a decent enough semiconductor reference. Or buy a new meter. You mentioned in a previous post that hobbyists won's spend $10 on a reference. But you've got a several hundred dollar Rigol (on your website). A few bucks on a ref would more than offset the time you've spent trying various different batteries.

author: ralphd
author_rank: Frequent Contributor
timestamp: July 27, 2015, 10:15:14 pm
content: Quote from: lewis on July 27, 2015, 09:37:59 pmI ordered 100 TL431As, and a couple REF5050s, but it will be a few weeks before they arrive from China. In the mean time I was looking for something around the house I could use as a rough reference.Yes, I treated myself to a DS1054Z after >30yrs of tinkering with electronics, and I could only do that after divorcing the first wife. :-)For those with a $10 meter and a couple of $2 Arduino nanos, it would still be useful to have an easy way to tell if their meter is modestly accurate.

author: retrolefty
author_rank: Super Contributor
timestamp: July 28, 2015, 12:05:56 am
content: QuoteOh you mean the 'starter wife'

author: ralphd
author_rank: Frequent Contributor
timestamp: July 28, 2015, 03:09:00 am
content: Quote from: retrolefty on July 28, 2015, 12:05:56 amI don't know, she was pretty hard to get started. :-(

author: ralphd
author_rank: Frequent Contributor
timestamp: August 01, 2015, 01:54:02 am
content: Just watched Dave's latest video, and the Duracell AAA started off at 1.602V.

author: Nerull
author_rank: Frequent Contributor
timestamp: August 01, 2015, 03:47:35 am
content: Quote from: ralphd on July 26, 2015, 03:01:07 pmYour meters out of the box specs are orders of magnitude more accurate than any of the sources you're looking at, it is almost impossible that you will adjust the meter to be more accurate using them, and almost certain that you will make it worse.Pretty extensive experience by a lot of people shows that multimeters really don't drift all that much, at least not at the number of digits you're looking at, and even free meters from hobby freight are spot on for their level of precision out of the box. Meter calibration for hobby use is mostly a waste of time, and if you do want to calibrate something, you need something more accurate to check against, not less.I've taken my never-recaled 87V and checked against freshly calibrated meters at work, no significant difference. When I got my 87V I wanted to see how bad the cheapass no-name walmart meter I had been using before compared - also no difference (though it had fewer digits).

author: Lightages
author_rank: Unknown
timestamp: August 01, 2015, 04:53:14 am
content: If the concern is to get a voltage reference that is cheap:http://www.ebay.com/itm/AD584KH-4-Channel-2-5v-7-5v-5v-10v-High-Precision-Voltage-Reference-Module-/181112567159?hash=item2a2b267577or even cheaper:http://www.ebay.com/itm/AD584-4-Channel-2-5v-7-5v-5v-10v-High-Precision-Voltage-Reference-Module-/261868849256?hash=item3cf8998868

author: lapm
author_rank: Frequent Contributor
timestamp: August 02, 2015, 02:12:23 am
content: Personally i would not use batteries as reference voltage source. They vary way too much by age and temperature... Heck even those 30$ Chinese cheap reference kits are better..

author: ralphd
author_rank: Frequent Contributor
timestamp: August 02, 2015, 06:16:35 pm
content: Quote from: Lightages on August 01, 2015, 04:53:14 amI already mentioned I ordered a bunch of Wing Shing TL431As, and a couple of TI REF5050s.http://www.aliexpress.com/item/REF5050IDGKR-R50F-TI-VSSOP-8-absolutely-new-original-quality-assurance-FREE-Shipping/32327854830.html

author: ralphd
author_rank: Frequent Contributor
timestamp: August 19, 2015, 04:03:29 am
content: The Wing Shing TL431As arrived this week. All labeled:WSTL431A155SDI tested 11 of them at 24C, 9.4mA:2.510, 2.508, 2.511, 2.511, 2.513, 2.517, 2.509, 2.516, 2.514, 2.509, 2.515Vmean = 2.5121, SD: .00308, <0.2% variationThe 2.512 measured vs 2.495 spec voltage suggests my meter is high by 0.68%.p.s. I noticed an Aliexpress seller (but not the one I bought from) that had a photo of a box of (10,000?) Wing Shing TL431As, and it had a 0.3% label on the box. I suspect the TL431As I received are the same.

author: jwm_
author_rank: Frequent Contributor
timestamp: August 19, 2015, 04:24:57 am
content: 2.512v is perfectly within spec for the tl431a. All your measurements are consistent with your meter being spot on spec.You _cannot_ average voltages like that and assume it ends up at the canonical value. There is no expectation that the voltages are normally distributed and it is in fact unlikely for many types of trimming. A hundred 2.520v tl431a's are still legit and in spec. And we're you to repeat the test on a cold day, they all might be 2.470v and you would conclude the opposite about your meter.It is extremely unlikely your meter is out of spec, almost unheard of. And if improving it is a matter of just trimming it, it would be sold with better specs, because your meter has a tempco and aging parts too.But the main issue is assuming averaging gives more accuracy, when in this case, and the battery case, it does not.

author: ralphd
author_rank: Frequent Contributor
timestamp: August 19, 2015, 05:06:53 am
content: For anyone that might be inclined to believe unsupported assertions that the mathematical laws of statistical sampling don't apply to semiconductors, read this:http://www.maximintegrated.com/en/app-notes/index.mvp/id/4489

author: ralphd
author_rank: Frequent Contributor
timestamp: August 19, 2015, 05:18:26 am
content: Quote from: jwm_ on August 19, 2015, 04:24:57 amDid you bother to calculate 2.495 + .3%? It's 2.5025.The .05% REF5050s I ordered should arrive within the next few days, and I'll bet they'll show my meter is at least 0.5% high.In the mean time, I suggest you start searching for a palatable hat.

author: ralphd
author_rank: Frequent Contributor
timestamp: August 19, 2015, 05:27:56 am
content: Quote from: jwm_ on August 19, 2015, 04:24:57 amJust to prove you're full of shit, I stuck my test circuit in the freezer for a few minutes, then measured the reference voltage while it was still in the freezer: 2.511V.After warming back up to 23C I'm reading 2.515.

author: jwm_
author_rank: Frequent Contributor
timestamp: August 19, 2015, 05:38:00 am
content: Quote from: ralphd on August 19, 2015, 05:18:26 amI was going by the datasheet.https://www.fairchildsemi.com/datasheets/TL/TL431.pdftl431amin voltage 2.470max voltage 2.520with a 17mv drift over full temperature range.I was just using the cold day as a way to say that there are systematic reasons they may all appear off spec in the same direction. 17mv difference over temperature range (again, from the data sheet) is enough to make a meter seem high or low, especially if the meter is at a different temperature.I am not sure what you are arguing, your data is consistent with an in spec meter.

author: ralphd
author_rank: Frequent Contributor
timestamp: August 19, 2015, 05:48:46 am
content: Quote from: jwm_ on August 19, 2015, 05:38:00 amMaybe you should re-read this thread after a good night's sleep and a strong coffee tomorrow am. Then you might realize how stupid it is to insist that a Fairchild data sheet is a more reliable source than the actual manufacturer's 0.3% rating."The Wing Shing TL431As arrived this week."

author: jwm_
author_rank: Frequent Contributor
timestamp: August 19, 2015, 05:56:05 am
content: Quote from: ralphd on August 19, 2015, 05:48:46 amYou mean the datasheet that gives even worse bounds on the high end of 2.475V - 2.525V for the grade A version?http://pdf1.alldatasheet.com/datasheet-pdf/view/257613/WINGS/TL431A.htmlJohn

author: ralphd
author_rank: Frequent Contributor
timestamp: August 19, 2015, 06:25:26 am
content: Quote from: jwm_ on August 19, 2015, 05:56:05 amI'll download pdfs from mouser and Digi-key, or a manufacturer site directly, but not some questionable site.I realize you are not going to admit I likely purchased 0.3% rated TL431s. You've posted enough on eevblog to suggest you are not a troll, so you're probably a kook.In either case, I'm sure you'll have an excuse as to how you still right when the 0.05% REF505s confirm my meter is >0.5% high.

author: Muttley Snickers
author_rank: Unknown
timestamp: August 19, 2015, 06:27:16 am
content: I agree and think although somewhat unorthodox batteries parallel is the key, I posted earlier on this but went back later and deleted it thinking it was pointless anyway, but after a few tests it is relevant.I also posted about the Energiser Ultimate Lithium Batteries (non rechargeable) being consistently at 1.80 volts across a number of meters and factoring in the plus and minus count offset of each meter when using a linear power supply at 2.00 volt for reference.Tested two packets of four AA's total of 8 brand new unused batteries and although this was not a lab test by any means I was satisfied with the results, maybe others could post on these batteries with better test gear than I have, Keithley 2000, Fluke 189, Keysight U1272a and a host of others.These batteries are not cheap at $15 AUD for a pack of four and I had a specific application for them in a problematic camera but thought a few comparison tests were in order prior to putting them to use, I am now looking at a proper voltage reference and am still undecided but thats another ongoing thread.And on flat batteries trying to calculate the maths formula for parallel batteries, at the time I just didn't get it, someone else will know or it is simply a variable due to the individual batteries internal resistance.Flat Battery A 1.25Flat Battery B 1.10Parallel Result 1.15

author: ralphd
author_rank: Frequent Contributor
timestamp: August 19, 2015, 06:30:31 am
content: Quote from: 3roomlab on August 19, 2015, 05:59:53 amBut according to John, averaging (a voltage reference) does not give more accuracy. John can't be wrong, can he? :-)

author: ralphd
author_rank: Frequent Contributor
timestamp: August 19, 2015, 06:37:57 am
content: Quote from: Muttley Snickers on August 19, 2015, 06:27:16 amI'd pick up a couple to test the theory, but they are $13 for a pack of 2 AAA at the local wally world...

author: jwm_
author_rank: Frequent Contributor
timestamp: August 19, 2015, 06:44:17 am
content: Quote from: ralphd on August 19, 2015, 06:25:26 amI never said your meter was definitely not high.I said nothing you posted _yet_ supports that conclusion, it is consistent with an in spec meter and a meter that is high by that amount and perhaps (depending on your meters published specs) one that is low by some percent.You said yourself your tl431s were _not_ stated to be 0.3% yet others listed were. if they actually were 0.3%, why would they not advertise that?0.3% is a super high quality tl431, grade double A (also from wing shing) are only 0.5%. wing shing makes at least 4 grades of the chip, they are probably not going to accidentally sell the much more expensive one and not mention it in the listing.Again, I am really unclear why you seem to be upset at this info, voltage references are great, and the ref5050 is a fine one and you may find your meter to be high or low, but you have not done so yet and averaging a bunch of tl431s isn't necesarily going to help.There are many manufacturing methods for these chips, sometimes it is aim for the middle and bin appropriately, other times it is make them high (or low) and laser trim them down to within the spec. They don't go any further than trimming to just within the specified bounds. These will not be normally distributed around the specified voltage so the averaging trick won't work in general.I'm not saying this to be confrontational, your meter may be high, but it would be quite unusual for it to be out of spec new out of the box and your tests so far are not conclusive.

author: jwm_
author_rank: Frequent Contributor
timestamp: August 19, 2015, 06:55:06 am
content: Quote from: ralphd on August 19, 2015, 06:25:26 amSince you don't want to look at the data sheet yourself, Here it is straight from wing shing along with chip marking info for the different grades. Again, I am not being confrontational or even necessarily disagreeing with you, i am curious what the results are myself. I mean, a cheap source of miscataloged 0.3% references would be great, I'd pick up a hundred myself.

author: Gyro
author_rank: Super Contributor
timestamp: August 19, 2015, 09:50:20 am
content: QuoteSo you've purchased Wing Shing parts from an Aliexpress seller and you're comparing them with the datasheet for Fairchild manufactured parts available from Mouser and Digikey? That's actually quite touching, you've restored my faith in the fundamental innocence of humanity.Sorry, couldn't resistbut I think that, on balance, I would probably advise using the Wing Shing published ordering information values as jwm_ posted.

author: jwm_
author_rank: Frequent Contributor
timestamp: August 19, 2015, 10:40:31 am
content: Quote from: ralphd on August 19, 2015, 06:30:31 amWhat? of course I can be wrong. So can you, so can anyone. But it just so happens that there is an objective reality that trumps us both regardless.You can average voltage references of course and get the average of the references, but the average of many inaccurate references is still inaccurate unless you make a further asumption that the values have a gaussian distribution around the nominal value which in general is not true. Now, you can increase precision and stability by combining references in clever ways, but not accuracy unless you use a more accurate reference to characterize yours to begin with.when a datasheet says a value is 1% accurate, it does not mean that the values are centered and scattered about the nominal value, it just means they are within one percent of the value, _nothing else_. In fact, with many manufacturing/trimming techniques, it is actually extremely unlikely the distribution will be centered. This is a common misconception, so much so that dave actually made two videos on the subject. The concluding one is herehttp://www.eevblog.com/2011/11/14/eevblog-216-gaussian-resistor-redux/a few thousand one percent resistors and the average? 0.35% below the stated value, and that is perfectly fine because it is within 1%.I am not saying this to be right, i am saying it because _i have been bitten_ by assuming things that feel intuitive but are not actually guarenteed by the datasheet (and i'm sure others here have too). It is an easy trap to fall into and I don't want others to do so and this particular one is fairly common (hence dave's videos).Your meter may be high or low or spot on, but the tl431a test is not definitive yet. You will know a lot more once your ref5050 comes in.

author: ralphd
author_rank: Frequent Contributor
timestamp: August 19, 2015, 01:12:50 pm
content: Quote from: jwm_ on August 19, 2015, 06:44:17 amSo you're already moving the goalposts from your original statement: "All your measurements are consistent with your meter being spot on spec."If you bothered to read the full thread, it's not just the tl431a's that suggest my meter is high, the alkaline battery measurements and the SR43 battery measurements suggest that as well. Yet you seem to think that my >10yr old "Mastercraft" CAD$20 meter is a more reliable reference than a sample of 11 new (2015 mrf date) TL431As.QuoteThe cheapest 100-lot 431's on Aliexpress that I can find right now are CJ431 Jiangsu Changjiang SOT-23 0.5% for 133c. I've also seen another brand (AMG?) similarly-priced (~1.5c ea). So we seem to have 2 competitors under-cutting Wing Shing's pricing for 0.5% 431's. I've seen old photos of WS 431A parts with date codes of 2008, so they've been making them for at least 7 years, and I'd say probably even more than 10. If 10 years ago they could reliably produce 0.5% parts, it should not be a surprise if they now can reliably produce 0.3% parts. It seems quite sensible to me that they'd update there production testing to bin for 0.3% and 1%, and to save money, stamp them all TL431A. For those that pass 0.3%, simply put a sticker on the box along with the batch numbers. Re-writing and translating the datasheet is an unnecessary cost.QuoteI see another excuse in the making, "You mislead me to think that your meter was new..."

author: ralphd
author_rank: Frequent Contributor
timestamp: August 19, 2015, 01:24:03 pm
content: Quote from: jwm_ on August 19, 2015, 06:55:06 amSee my last post for why it's easier for the mrf to add a sticker on the boxes instead of updating their datasheet and stamping.They're 146c. If you get a batch that are off by >3%, then you can prove I just got lucky. If they're within 0.3%, that doesn't help your argument, but at least you'll have a cheap source of 0.3% references.http://www.aliexpress.com/item/Free-shipping-NEW-100PCS-TL431-TL431A-TO-92-Silicon-Transistors-triode-transistor/32328977920.html

author: jwm_
author_rank: Frequent Contributor
timestamp: August 19, 2015, 08:33:21 pm
content: Quote from: ralphd on August 19, 2015, 01:12:50 pmWhat? this is exactly the same statement.measurements can be consistent with more than one thing that is why I said you cannot conclude anything about your meter yet. They are consistent with the meter being on spec because the measured values are all within the tolerance of the wing shing TL431A part you specified so those measurements can be spot on. They are also consistent with it being off the nominal value by 0.5% because the TL431A is a 1% part so could be that far in either direction.That you cannot in general average a bunch of 1% parts to get a more accurate reading is also well known and empirically tested in daves video.Now, you may have 0.3% parts, or may not. But when you say wing shing TL431A I can only assume wing shings data on their TL431A part is accurate rather than suppositions from an aliexpress listing, in any case, wing shings official specs are all that matters for making engineering decisions rather than a batch that happened to be 0.3%. Also, no matter what the alibaba listing says, I'd say wing shings datasheet trumps it.QuoteLook, this is metrology. specifications mean very precise things and the conclusions you can reach are well definied. As an engineer, you have to assume the worst. 1% means 1% out in the opposite direction. battery chemistry is so variable (the mercury cell being an unusual exception, my keithley electrometer uses one as its voltage standard, still spot on after >20 years) you cannot definitively make decisions based on it. Like you derate capacitor voltages because i may have the worst batch of the lot and my design might encounter some crazy transients.In spec for a meter does not mean at its nominal value, it means within 0.1% 1% or whatever the meter guarentees. When a meter guarentees 1% accuracy, it doesn't mean they were only able to trim it within 1%, of course they could trim it to be spot on, on that day, in that lab. but if they know the parts have a 1% drift over temperature range or expected age, or that their calibration meter is only good for 1% then they rate it as 1% accurate so that is stays within spec during its lifetime. When you calibrate a 1% meter that is at 0.9% off, they don't twist the knob back to 0% because that is in spec.I am not sure why you think these general engineering practices are somehow contrary to what you say. It does not _matter_ whether your meter is on or off for these statements to be true or not. That you cannot conclude _definitively_ (not probably) it is off by 0.5% with a 1% part when the measurements are within the 1% margin (even averaged, if they have not been characterized) is, well, pretty obvious.Again, I have to go by manufacturer data sheets and part numbers as specified. Once you get your ref, you will be able to characterize your tl431s and then say definitively how far out your meter is (up to the accuracy of the ref5050)QuoteAn excuse for what, your measurements _are_ consistent with an in spec meter for TL431As as speced by the manufacturer. They are also consistent with a 0.5% off amount. Our statements are compatible. It would surprise me somewhat less that your meter is out of spec since it is older, but that doesn't mean the original observation that you cannot conclude definitively yet is false.There are many people reading this forum that have to build things that work without relying on probably getting 0.3% parts marked 1% time after time, or that like or need to be _certain_ of the tolerances of their measurements are finitely bounded by a known number.On an engineering board, where we constantly have to take into account _worst case_ (but in spec) scenarios day in and day out, and run into horribly expensive or dangerous failures when someone doesn't take into account the possibility that your 1% parts might actually all be 1% out the wrong way or other allowed things then it is natural for these concerns to come up.I was trying to be helpful by bringing attention to a conclusion that did not yet have enough evidence, the same as I do for design reviews where I am paid to notice these things before they become issues, or become the subject of an audit on who dropped the ball on specing parts properly. Even if you don't seem to get what my statement actually means, and why it is consistent with yours, Consider it good advice for the community and an incidental benefit of this thread.

author: ralphd
author_rank: Frequent Contributor
timestamp: August 20, 2015, 12:40:06 am
content: Quote from: jwm_ on August 19, 2015, 08:33:21 pmAhh, now for the straw man logical fallacy argument. I stated, "The 2.512 measured vs 2.495 spec voltagesuggestsmy meter is high by 0.68%."You promptly pipe in claiming I'm wrong, providing lots of argument and evidence that my observations do not conclusively prove the meter is high by that amount (which is correct), thereby defeating the straw man that you created.Your latest post seems to be an attempt to twist what you said into my observations being consistent with both possibilities of my meter being correct and my meter being accurate. But if that's really what you meant in the first place, then a logical and direct person would have said:"Your meter certainly could be high, but it is still possible that it may be accurate (within 0.1%). You won't know for sure until you test with the REF5050."

author: ralphd
author_rank: Frequent Contributor
timestamp: August 21, 2015, 02:23:44 pm
content: I found the photo of a crate of WS TL431 with the 0.3% rating.

author: Macbeth
author_rank: Super Contributor
timestamp: August 21, 2015, 03:09:21 pm
content: Hey, theres alsothese 0.3% devicesSomebody is going to tell me myAliexpress LTZ1000ACH'sare fakes now, I betcha!

author: technix
author_rank: Super Contributor
timestamp: August 21, 2015, 08:13:42 pm
content: The original primary voltage reference was standard cell, which is a chemical battery that contains mercury. Then with superconductivity and quantum mechanics the new primary voltage reference is a superconducting Josephson junction with an input of a certain frequency.Electrical mains actually can be a decent voltage and frequency standard if you are not living in a place that usually have brownouts. A small transformer will allow you to use it in lower voltage scenarios.If you count semiconductor components not originally intended to be used as a voltage reference, any diode, when in forward bias with relatively stable current, can be used as a makeshift voltage standard. In a discrete linear regulator design I know of the overcurrent protection circuit requires a 1.5V Zener diode, and the designer decided to get away without the Zener and used a red LED with a forward voltage of 1.5V instead, serving as a voltage reference and a overcurrent indicator light at the same time.

author: ralphd
author_rank: Frequent Contributor
timestamp: August 21, 2015, 08:34:08 pm
content: Quote from: technix on August 21, 2015, 08:13:42 pmAlthough most utilities maintain long-term average frequency at 50/60Hz, I'm not aware of utilities that have strict standards for voltage. In North America I've seen from ~117V to ~124V. Even if you have a stable mains voltage, you have to make sure there are no large loads active. A 5500W electric water heater will likely cause the voltage in the whole house to drop at least a few tenths of a volt. A 1200W hair dryer on the same 14/2 circuit can will cause a drop of >1V unless the length is unusually short.

author: ralphd
author_rank: Frequent Contributor
timestamp: August 21, 2015, 08:46:09 pm
content: I tried to crack open the to92 to look at the die like Ken did:http://www.righto.com/2014/05/reverse-engineering-tl431-most-common.htmlI was able to separate the die from the anode plate, but it only exposed the back side of the die. It looked rectangular; ~1x0.6mm vs. the more square looking die for the TI-labeled parts Ken had.Trying to separate the plastic from the front of the die ended up destroying it. And since I don't have a microscope (just a magnifying glass), I doubt I'd be able to identify much on the die anyway.If the WS parts are fuse-trimmed like the TI ones, there should be more than one peak in the distribution of voltages. I may test the whole 100 lot I received and plot the voltages to see what patterns are evident.

author: ralphd
author_rank: Frequent Contributor
timestamp: August 21, 2015, 09:10:06 pm
content: I just tested 14 more of the WS TL431As with my crappy tire meter and 24C ambient:2.512, 2.512, 2.510, 2.514, 2.517, 2.510, 2.512, 2.506, 2.516, 2.515, 2.514, 2.517, 2.515, 2.516mean: 2.5133, SD: .0032

author: kwass
author_rank: Frequent Contributor
timestamp: August 22, 2015, 12:31:11 am
content: Quote from: ralphd on August 19, 2015, 06:37:57 amI happen to have a large number of unused Energizer Lithium AA (they've changed the name several times over the years -- ultimate, advanced, etc. -- but I think that they're all pretty much identical in performance) cells spanning about 10 years of manufacturing dates. I just sampled 20 of them and found voltages in a fairly narrow range from 1.8191 to 1.8275 using a calibrated 34401. So they do seem to make for a good 1.82 voltage reference when unused. Storage of these and testing was all done a pretty constant 21 degrees C, so I have no idea how sensitive these are to temperature changes.

author: Muttley Snickers
author_rank: Unknown
timestamp: August 22, 2015, 01:19:00 am
content: These pictured below are what I referred to and as they were recently at a discounted price I went back and bought another two packets, an expensive round about reference really but that is not what it's about.And with 9X longer life if we add one of those new sleeve thingos with an additional 8X, thats 17X....Thanks for the measurements, I will try and keep tabs on everyone's numbers...Muttley

author: ralphd
author_rank: Frequent Contributor
timestamp: August 22, 2015, 01:36:56 am
content: Quote from: kwass on August 22, 2015, 12:31:11 amThat is a pretty narrow range; 1.8233 +- 0.23%.

author: Flenser
author_rank: Regular Contributor
timestamp: August 22, 2015, 06:52:23 am
content: I have 4 unopened packs of 2xAA Energizer Ultimate Lithium. I measured these using my Brymen BM257.Use-by Date 03-20261.8261.825Use-by Date 03-20281.8061.810Use-by Date 03-20281.8061.806Use-by Date 03-20281.8051.806

author: Muttley Snickers
author_rank: Unknown
timestamp: August 22, 2015, 07:37:29 am
content: Thanks Flenser for the measurements and as the comparisons may or may not go anywhere we probably should have a proper starting point and document such as MS Excel so we may generate graphs and do relative calculations, so possibly a running XLS file with DD:MM:YY - HH:MM which I think is the forums standard. Those that don't have XL could simply post some numbers and others could update the file accordingly.Now to be honest my computer, photography, spelling, grammar and mathematical skills are somewhat really bloody rubbish so although I am more than willing to collate the submitted data out of respect for other members it probably should be done by others more versed and experienced, I will stuff it up.Also should we consider the submission of two exactly the same random batteries measured in parallel which from my tests does make a huge difference on the averaging and this could well be the grail we all are seeking.I am guided by you fellows....Muttley

author: hendorog
author_rank: Super Contributor
timestamp: August 22, 2015, 08:12:27 am
content: QuoteExcel is poor for sharing information as everyone needs to have a copy so you can never tell who has the latest version.Instead I'd recommend sharing a link to an online document - e.g. google docs spreadsheet.

author: Macbeth
author_rank: Super Contributor
timestamp: August 22, 2015, 12:20:07 pm
content: Quote from: hendorog on August 22, 2015, 08:12:27 amI was about to post the same. Google docs is great for this kind of thing

author: ralphd
author_rank: Frequent Contributor
timestamp: August 22, 2015, 05:47:40 pm
content: Quote from: Flenser on August 22, 2015, 06:52:23 amSmaller sample, but wider range: 1.815V +- 0.6%. It's looking like they make for an OK 1% reference.

author: ralphd
author_rank: Frequent Contributor
timestamp: August 22, 2015, 05:53:24 pm
content: Here's a link for the .5% CJ431s going for 136c/100.www.aliexpress.com/item/Free-shipping100PCS-TL431-TL431A-SOT23-SOT-23-CJ431-431-Precision-Voltage-Source/32409866977.htmlThey're a bit different than the other 431's in that their typical voltage is 2.5V instead of 2.495V.http://www.cj-elec.com/txUpfile/20134181414159042.pdfIf they were TO-92 instead of SOT-23 I'd probably order them just so I could compare them to the Wing Shing 431s.

author: ralphd
author_rank: Frequent Contributor
timestamp: August 30, 2015, 05:02:36 pm
content: Quote from: Nerull on August 01, 2015, 03:47:35 amWhere did you pull the specs on my meter from? Out of your arse?It's a Mastercraft branded, Colluck-made meter I paid $20 for.https://www.eevblog.com/forum/testgear/how-bad-can-a-cheap-multimeter-be/According to this post, it's rated 0.8% + 5 counts for DC volts:https://www.eevblog.com/forum/testgear/canadian-tire-mastercraft-dmm-new-and-old-revision-teardown/From the 0.3% TL431s I can tell the meter is at least 0.5% high. And when the 0.05% REF5050s I ordered come in, I'll be able to narrow that down even more.

author: ralphd
author_rank: Frequent Contributor
timestamp: September 01, 2015, 12:15:59 am
content: I tested the first 8 batteries from a pack of HomeDepot "defiant" MIC AAA batteries, Dec 2020 exp:1.610, 1.611, 1.610, 1.611, 1.610, 1.611, 1.610, 1.611This is after adjusting the calibration of my meter to within 0.1%.

author: ralphd
author_rank: Frequent Contributor
timestamp: September 01, 2015, 12:31:53 am
content: Quote from: ralphd on September 01, 2015, 12:15:59 amJust did the math on the (surprising) consistency of the HomeDepot batteries. 1.6105V +- 0.03%.

author: Muttley Snickers
author_rank: Unknown
timestamp: September 01, 2015, 01:06:31 am
content: Quote from: Flenser on August 22, 2015, 06:52:23 amThe four packets of 4 Energizer Ultimate Lithium that I have purchased are all giving a similar result to what Flenser got with the ones that I have marked in blue, the ones in red and also the samples provided by kwass all indicate a higher reading than I was getting possibly indicating a variance related to batch or date codes, so as a reference I think we are back to square one, the date codes on all mine were 12-2034 and purchased from the same retail outlet within a 10 day period.And if we are seeking a real world reference then ideally it should be one that is readily available globally.Muttley