Looking for instrument to measure 1.0 Ohm to <10ppm - Page 1
Forum section: electronics / general

author: alligatorblues
author_rank: Regular Contributor
timestamp: August 17, 2023, 05:59:04 am
content: I'm searching for an instrument to measure 1.0 Ohm to <10ppm.. Anyone know of one offhand, for less than $2,000.

author: mzzj
author_rank: Super Contributor
timestamp: August 17, 2023, 07:32:12 am
content: Your requirements are off by about a decade. You probably have to choose between 100ppm and 20000 usd.

author: tggzzz
author_rank: Super Contributor
timestamp: August 17, 2023, 08:28:41 am
content: Quote from: alligatorblues on August 17, 2023, 05:59:04 amSo you think purchasing such an instrument will solve your problem.But whatisyour problem?This smells like anXY-problemsituation.

author: Alex Nikitin
author_rank: Super Contributor
timestamp: August 17, 2023, 10:50:24 pm
content: As already noted, not enough information. What kind of resistors, what conditions? If you need to measure only one value - 1 Ohm with, say, +/- 1% distribution with 10ppm accuracy, it should be possible with a reasonably simple bridge setup and one good quality reference 1 Ohm resistor, sayFluke 742-1or an equivalent (only the reference with calibration data will happily eat your budget, I suspect). Whichever way you measure 1 Ohm, there will be some limits, including the maximum allowable power dissipation on the DUT - more current will give you a better sensitivity but the DUT will heat up and unless it has an exceptionally low tempco you can kiss goodbye your 10ppm accuracy. A low current will be better in this respect but the required voltage sensitivity will limit the accuracy again. For example, 1A current will give you 1uV/ppm sensitivity but 1W dissipation which is far too much (Fluke 742-1 spec is 0.5A max current) . 10mA resolves the problem with the power dissipation as it drops to only 0.1mW but the voltage change for 1ppm is almost immeasurable 10nV. 100mA looks like a reasonable compromise with 10mW dissipation which will spoil things a bit but hopefully not too much for a reasonable size resistor, with a low (2-5 ppm/C) tempco (not 0603 size though). 0.1uV/ppm sensitivity also possible to deal with, taking a good care of thermal voltages (reverse polarity switch on the bridge supply etc.). Good quality 4 way connection is required as is a quiet room with a stable temperature.In short - 100ppm accuracy is do-able with a calibrated reference and a good meter, 10ppm from 1 Ohm is not easy at all.CheersAlex

author: thermistor-guy
author_rank: Frequent Contributor
timestamp: August 18, 2023, 03:50:34 am
content: Quote from: Alex Nikitin on August 17, 2023, 10:50:24 pmThis would be a great DIY project - measuring nominal 1 ohm resistors with as low an uncertainty as possible, subject tosome affordable limit on build cost.I have a self-balancing double Kelvin bridge on my DIY project list, but will take more than a year before I can get to it.

author: johansen
author_rank: Super Contributor
timestamp: August 18, 2023, 04:33:57 am
content: I believe i threw away a fluke, vacuum tube volt meter kelvin varley divider. Not much use for them anymore.Its high side 40k ohm resistors were matched pretty well. 4 of them in a bridge configuration, with a 9v battey exciting the bridge and a cheap strain gauge amplifier (aka a 1kg drug scale) across the bridge.. zeroing the scale.. and heating one of the resistors with a soldering iron.. it didnt even move. 0.1ppm or better temperature coefficient, easily.Now regarding measuring 1 ohm to 10ppm.Buy or make yourself some 1ppm resistors on the order of 1 ohm. Test 4 of them in a bridge configuration.Buy yourself a legit strain gauge amplifier. Why? For the 10ppm drift you dont want.Long time ago I described in detail how to take any common digital scale, add two resistors, one of them variable, and you have yourself a milliohm meter. Its as accurate as the linearity of the resistors due to thermal effects of the current flowing during the test.I found that a cheap 1kg scale was able to handle 140 ohm resistors to load the resistor under test and full scale of 1kg was 0.1 ohms. Yielding 0.1 milliohm resolution. I dont recall a single reply.I think people didnt understand that the accuracy is maintained. The strain gauge amplifier is maintaining a constant voltage gain,(probably a chopper stabilized opamp) but its internal adc is using the voltage supplied to the bridge as a reference.Essentially if you can compare any two resistors to each other, it doesn't matter what their value is.There is no need to spend thousands for a miliohm meter certified for 10ppm if you can buy a strain gauge amplifier for a tenth of thatFor 1uV =1 ppm resolution you will need 1 amp through your test resistor. Well within the range of a sensitive strain gauge amplifier.

author: mahyarJbr
author_rank: Newbie
timestamp: August 20, 2023, 07:06:57 am
content: Hiyou can get Fluke 8845A/8846A Multimeters you can buy it from Fluke website or distributer website like amazon,aabtools or mme-ae

author: Alex Nikitin
author_rank: Super Contributor
timestamp: September 01, 2023, 02:23:10 pm
content: Here is a good example of how to measure 1 Ohm to ppm levels... .CheersAlex

author: EC8010
author_rank: Frequent Contributor
timestamp: September 01, 2023, 05:30:13 pm
content: Quote from: johansen on August 18, 2023, 04:33:57 amI tried various key words in a search, but didn't find it. Do you remember where you put it?I have a number of common digital scales that could be savaged, but not a milliohm meter...

author: bastl_r
author_rank: Regular Contributor
timestamp: September 01, 2023, 11:15:30 pm
content: Sorry for hijacking the thread.Based on the measurements of Illya Tsemenko from xdevs on the 1Ohm JRL precision resistors, these should have been well outside the specs. I would have expected the worst measured value to be somewhere around 1.00005 ohms. Strangely, all measured resistors are well above 1.0001 ohms. The worst with 1.000854Ohm even scratches at the 0.1% mark.I can't really imagine that.There should be at least a scatter of 0,99995Ohm to 1,00005Ohm.Or do I have a thinking error here.bastl_r

author: mawyatt
author_rank: Super Contributor
timestamp: September 01, 2023, 11:28:06 pm
content: This might be an area where a SMU can help, some of the older Keithley's might be available for around 2K? The newer ones are above $6K tho!!Best,

author: bdunham7
author_rank: Super Contributor
timestamp: September 02, 2023, 12:27:45 am
content: Quote from: bastl_r on September 01, 2023, 11:15:30 pmI only have a sample of one of those JRL 1 Ohm resistors, but my (admittedly not traceably certified to sufficient accuracy) measurements also indicated that the resistor does not meet its specified tolerances, mine also being a bit high. I don't know why this is, the resistors are Kelvin-connected so it isn't hard to wire them up to the meter and any thermal voltages should result in differences in readings, but mine were pretty stable and repeatable, just off a bit. Perhaps they drift, they're certainly not new. Measuring 1R to 50ppm, let alone 10ppm, is really tough, even with instruments capable of it--which I don't have. I have a meter coming back from calibration tomorrow, it has a 24-hour spec of 30ppm + offset, so I suppose I can zero it and see how close I get.

author: Vgkid
author_rank: Super Contributor
timestamp: September 02, 2023, 03:17:52 am
content: When I checked mine, they were roughly an order of 10x higher in error than the printed tolerance. Then again my 34420a only had its original cal count.

author: Alex Nikitin
author_rank: Super Contributor
timestamp: September 03, 2023, 01:55:00 pm
content: Quote from: Vgkid on September 02, 2023, 03:17:52 amWere these all high in resistance? My understanding is that wirewound precision resistors have a tendency to drift higher in time. My Fluke 742-10K measures around 10.00006K, though at the time of manufacturing the measured value was 9.999996K, so the drift over some dozens of years was +6.4ppm . I have a substantial number of LT450/C precision wirewound resistors, 0.002% stated tolerance, made in 1989, with values from 1K to 1M.Allof these measure high from +10ppm to +50ppm of the stated value (*). These JRL resistors are NOS, so the difference must be due to the ageing.CheersAlex(*) - I suspect that the amount of drift should be roughly the same, probably about +30ppm, and the difference is due to the original tolerance, i.e. a resistor which was -20ppm from the stated value, now measures +10ppm, and the one at +20ppm now is +50ppm. It is also possible that for the low Ohm values the drift can be larger.

author: mendip_discovery
author_rank: Super Contributor
timestamp: September 05, 2023, 07:33:02 pm
content: I assume my Transmille has Vishay resistors in it I thought this might give a general idea of ageing over time.Here is it in graph form,2W4W

author: alligatorblues
author_rank: Regular Contributor
timestamp: September 19, 2023, 01:33:31 am
content: I have an ESI SR104 that has drifted 2.9ppm since 1974.

author: donlisms
author_rank: Frequent Contributor
timestamp: September 21, 2023, 08:24:11 pm
content: Quote from: alligatorblues on September 19, 2023, 01:33:31 amIsn't that amazing, how they did that? So much of the design work was essentially predicting the future - what's going to happen inside this box. Yes, based on past experience and knowledge, but still... mighty impressive, as it all works out in real life, over decades.

author: alligatorblues
author_rank: Regular Contributor
timestamp: October 08, 2023, 06:07:30 am
content: I purchased a 34420A. I'm sending it to Keysight for calibration and repair if necessary. When I get it back, I'll measure some of my manganin standards. I was looking at the Vishay HZ metal foil series. Does anyone know if those will be mass produced. Or all special order. I can't find a single supplier.