Largest Value of Resistance Ever Measured?

[xrunner]

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?

[c4757p]

These resistance standards go to 10 petaohm, so I'm sure the largest ever measured is insanely high...

[xrunner]

These resistance standards go to 10 petaohm, so I'm sure the largest ever measured is insanely high...

Day-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.

[c4757p]

I'll take contact resistance any day over what you do need to worry about to measure those!

[dr.diesel]

These resistance standards go to 10 petaohm, so I'm sure the largest ever measured is insanely high...

Mmmmm, what industry would purchase a 10petaohm standard?

[mikeselectricstuff]

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.

[c4757p]

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... 

 

[xrunner]

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... 

 

Slow down ...

[dr.diesel]

Ha, apparently to cal 10petaohm standards and 8081 DMMs!

[Mechatrommer]

i measured infinity, so whats the big deal?

[xrunner]

i measured infinity, so whats the big deal?

Infinite resistance or are you going off-topic ... 

[c4757p]

Sure, but for all we know you only measured it +/- 10000%...

[c4757p]

Infinite resistance or are you going off-topic ... 

His sense of humor is almost as bad as mine.

[ftransform]

I would assume the petaohm resistors are pieces of plastic thats not teflon.

[phatcenter77]

OL?

I see it every time my meter switches to ohms... 

[alm]

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.

0.1 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.

[amyk]

You're not up to the experimental physicist level yet, which I'm sure goes even higher.

I haven't found any equipment that claims to go to exaohms yet...

[alm]

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.

[olsenn]

Petaohms? Why?? That's just an open circuit!

[xrunner]

Still ... I'm interested in the question I posed. What's the highest value of resistance ever actually, accurately, measured by any sort of set-up? Is it a Guinness world record? Has it been done in a lab somewhere?

[Stonent]

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 

[ftransform]

How many ohms is a vacuum gap?

[bitwelder]

Well, Dave recently got a petaohmmeter in '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.

[xrunner]

How many ohms is a vacuum gap?

Well, 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 a single electron (-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 a single electron gets across the gap? How are you sure this doesn't happen ftransform?

[c4757p]

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 an air (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.