Largest Value of Resistance Ever Measured? - Page 1
Forum section: electronics / general

author: xrunner
author_rank: Super Contributor
timestamp: June 24, 2013, 11:31:17 pm
content: Reading this thread here on the forum where the Transmille's 8081 Precision DMM is shown in a video, I thought of a question -I hope Dave gets one of this for next teardown :-)It can apparently measure resistance into the Terraohm range.What is the largest value of resistance ever accuratley measured and how was it done?

author: c4757p
author_rank: Super Contributor
timestamp: June 24, 2013, 11:45:02 pm
content: These resistance standardsgo to 10 petaohm, so I'm sure the largest ever measured is insanely high...

author: xrunner
author_rank: Super Contributor
timestamp: June 24, 2013, 11:49:52 pm
content: Quote from: c4757p on June 24, 2013, 11:45:02 pmDay-um.At least you don't have to worry about the res. of the contacts when making those. I'd love to see what's inside that box. What substance does the actual resistance consist of that allows you to make petaohn values.

author: c4757p
author_rank: Super Contributor
timestamp: June 24, 2013, 11:53:12 pm
content: I'll take contact resistance any day over what youdoneed to worry about to measure those!

author: dr.diesel
author_rank: Super Contributor
timestamp: June 24, 2013, 11:53:42 pm
content: Quote from: c4757p on June 24, 2013, 11:45:02 pmMmmmm, what industry would purchase a 10petaohm standard?

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: June 24, 2013, 11:54:20 pm
content: So at the maximum specced voltage of 1Kv, current is 0.1pA , which I make about 60,000 electrons per second.I suspect noise might be an issue - I expect you'd need to measure over a pretty long period.

author: c4757p
author_rank: Super Contributor
timestamp: June 24, 2013, 11:55:17 pm
content: My suspicion? They're purchased to calibrate resistance meters, which are used to make the resistors, which are used to calibrate resistance meters, which are used to make the resistors...

author: xrunner
author_rank: Super Contributor
timestamp: June 24, 2013, 11:57:29 pm
content: Quote from: c4757p on June 24, 2013, 11:55:17 pmSlow down ...

author: dr.diesel
author_rank: Super Contributor
timestamp: June 24, 2013, 11:57:40 pm
content: Ha, apparently to cal 10petaohm standards and 8081 DMMs!

author: Mechatrommer
author_rank: Super Contributor
timestamp: June 25, 2013, 12:15:51 am
content: i measured infinity, so whats the big deal?

author: xrunner
author_rank: Super Contributor
timestamp: June 25, 2013, 12:17:34 am
content: Quote from: Mechatrommer on June 25, 2013, 12:15:51 amInfinite resistance or are you going off-topic ...

author: c4757p
author_rank: Super Contributor
timestamp: June 25, 2013, 12:18:18 am
content: Sure, but for all we know you only measured it +/- 10000%...

author: c4757p
author_rank: Super Contributor
timestamp: June 25, 2013, 12:19:44 am
content: Quote from: xrunner on June 25, 2013, 12:17:34 amHis sense of humor is almost as bad as mine.

author: ftransform
author_rank: Frequent Contributor
timestamp: June 25, 2013, 01:42:40 am
content: I would assume the petaohm resistors are pieces of plastic thats not teflon.

author: phatcenter77
author_rank: Newbie
timestamp: June 25, 2013, 03:48:32 am
content: OL?I see it every time my meter switches to ohms...

author: Unknown
author_rank: Unknown
timestamp: June 25, 2013, 10:37:28 am
content: Quote from: mikeselectricstuff on June 24, 2013, 11:54:20 pm0.1 pA isn't that extreme, 'standard' Keithley electrometers will go down to the fA with aA resolution. Of course guarding and leakage are going to be an issue, you will need custom test fixtures to measure this. Some of them will go up to 10 POhm. This is high, but still achievable with commercial equipment. You're not up to the experimental physicist level yet, which I'm sure goes even higher.

author: amyk
author_rank: Super Contributor
timestamp: June 25, 2013, 11:20:57 am
content: Quote from: alm on June 25, 2013, 10:37:28 amI haven't found any equipment that claims to go to exaohms yet...

author: Unknown
author_rank: Unknown
timestamp: June 25, 2013, 11:35:31 am
content: You won't find it in commercial equipment. Only the popular and 'easy' stuff gets commercialized, but the same and more has usually be done in the lab (either R&D or academic) first. For example,this publication from 1931(behind a paywall) already describes a method to measure resistors up to 0.1 EOhm. I'm sure there have been further developments since then.

author: olsenn
author_rank: Frequent Contributor
timestamp: June 25, 2013, 11:52:04 am
content: Petaohms? Why?? That's just an open circuit!

author: xrunner
author_rank: Super Contributor
timestamp: June 25, 2013, 12:06:31 pm
content: Still ... I'm interested in the question I posed. What's the highest value of resistance ever actually, accurately,measuredby any sort of set-up? Is it a Guinness world record? Has it been done in a lab somewhere?

author: Stonent
author_rank: Super Contributor
timestamp: June 25, 2013, 02:34:09 pm
content: The largest resistance ever to be measured by mankind will be the day my wife tells me I'm about the age to need a colonoscopy

author: ftransform
author_rank: Frequent Contributor
timestamp: June 25, 2013, 02:39:40 pm
content: How many ohms is a vacuum gap?

author: bitwelder
author_rank: Super Contributor
timestamp: June 25, 2013, 04:31:40 pm
content: Well, Dave recently got a petaohmmeterin 'EEVblog #455 - Auction Bonanza' (check from 11:00)I'd be really curious to watch how to measure with such an instrument, i.e. avoid all the disturbances that may affect the reading of such extreme resistance values.

author: xrunner
author_rank: Super Contributor
timestamp: June 25, 2013, 04:38:02 pm
content: Quote from: ftransform on June 25, 2013, 02:39:40 pmWell, R = E/I, so you'd have to tell me what current you measured across the gap before I can tell you how many ohms it is. Remember. if even asingleelectron (-1.602 x 10-19 C) gets across the gap it's a valid current, albeit very tiny. Can you assure us that not even the charge of asingleelectron gets across the gap? How are you sure this doesn't happen ftransform?

author: c4757p
author_rank: Super Contributor
timestamp: June 25, 2013, 04:47:17 pm
content: I spent almost an hour digging around for an article, but my Google-fu left much to be desired. I saw a paper a few months ago (granted, I think it was much older than that) measuring the resistance of anair(not vacuum) gap. Spoiler alert: it was very high.Considering that conductance through a vacuum is likely to be due mostly to thermionic emission, there's going to be a very strong dependence on temperature for that one. I wonder if you could get a back-of-the-envelope calculation of the resistance of vacuum at room temperature by extrapolating a filament current vs. plate current curve for a vacuum diode.

author: dr.diesel
author_rank: Super Contributor
timestamp: June 25, 2013, 04:56:01 pm
content: Renegade electrons are a problem though. That's why I installed those little plastic wall socket plug covers, keeps those anxious ones from making the jump and raising my electric bill. I tried jamming them back in with a butter knife, wasn't the best idea I've ever had....

author: xrunner
author_rank: Super Contributor
timestamp: June 25, 2013, 05:20:16 pm
content: 1 A = 1 C/s1 C = 6.241 × 1018electrons1 A = 6.241 × 1018electrons / s1 / 6.241 × 1018= 160-21So I think the current of a single electron (one electron passing a point every second) is 160-21A or 160 sextillionths of an A or 160 zepto amps.If the voltage across a resistance was, say, 10V, and you got a current of 160 sextillionth amp you'd have a resistance of10V / 160-21= 62 x 1018ohms or 62 exa ohms.Somebody correct me if I'm wrong.Reference for scales -http://en.wikipedia.org/wiki/Order_of_magnitude

author: SeanB
author_rank: Super Contributor
timestamp: June 25, 2013, 05:46:00 pm
content: Highest values I ever saw measured was around the gigaohm range, which was a 2m long quartz glass tube filled with triple distilled deionised water used as a current limiting resistor in a high voltage lab. 1 million volts applied to it and one was glowing, as it was contaminated ( probably salt in the ppB range from being touched) while the others were fine, they just gave an arc at the bottom when the ground rod was brought close. Without it you lost a lot of electrode rather fast as plasma. The demo was to show the effect of lightning on a grass roofed hut, it had an impressive collection of burns on it already. Fun was getting a student with long hair to stand on the 2m high glass chair and touch the HV electrode, instant Gorgon hair and glowing ends. Talk about a bad hair day......

author: JuKu
author_rank: Frequent Contributor
timestamp: June 25, 2013, 07:10:44 pm
content: I've seen a current meter that counted electrons.

author: xrunner
author_rank: Super Contributor
timestamp: June 25, 2013, 07:30:51 pm
content: Quote from: JuKu on June 25, 2013, 07:10:44 pmWell then, if such a thing exists, and it can count electrons, then only time is the limiting factor.In other words if 1A = 6.241 × 10^18 electrons / s then instead of reducing the charge to get a lower current, you can increase the time.If I wanted 0.5 A I can just as well pass 1/2 the electrons (3.12 x 10^18) per second, or all of them (6.241 × 10^18) every 2 seconds, and get the same answer.So if we can measure the current by counting electrons, then what's the longest time somebody has sat around after witnessing one electron passing, to count the next one for a current measurement, and thus calculate a resistance?

author: dr.diesel
author_rank: Super Contributor
timestamp: June 25, 2013, 07:38:06 pm
content: It probably counted by converting the current reading into equivalent electrons, not the other way around.

author: Neilm
author_rank: Super Contributor
timestamp: June 25, 2013, 07:48:49 pm
content: I've measured to about 5 T ohm. The biggest issue I had doing that was it didn't take much to upset it - even breathing reasonably close to it (within 0.5m) seemed to cause the reading to fluctuate. We ended up putting on cotton gloves, cleaning everything, putting a good guard around the resistor and putting it into a special box with the terminals guarded.Neil

author: JuKu
author_rank: Frequent Contributor
timestamp: June 25, 2013, 08:13:47 pm
content: Quote from: xrunner on June 25, 2013, 07:30:51 pmAnd the warming speed of the gryogenic chamber (that thing only works in 4K or so and below); besides, prof. Heisenberg throws in a fake electron every now and then.

author: lemmegraphdat
author_rank: Frequent Contributor
timestamp: June 26, 2013, 12:46:16 am
content: Quote from: xrunner on June 25, 2013, 04:38:02 pmHappens in an electron microscope. Wonder what's the highest resistance that thing ever measured. They do use it for that.