That's right. Slightly more intimidating.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Hmm, do you have some model for that, or just an idea? How low a current? I don't know anything about resistors that are greater than 1 G ohm.. One might see a lot more 1/f type noise in big R's?
George H.
There is a paper online somewhere that demonstrates that physically short resistors have shot noise. Electrons take some time to arrange themselves in an orderly queue. I suspect that low electron density will also reduce the self-ordering effect. The limiting case is obvious: only one average free electron within the length of the resistor, no electron interaction.
I needed some high-value resistors, 10s of megs, that had low current noise, so I experimented some. This is NOT an easy thing to measure. My pretty firm conclusion was that I was seeing a lot more current noise in thickilms than in metal film resistors. I didn't do a spectral analysis to separate 1/f from shot noise; that would be an interesting prokect. Problem is, you have to order 20M thinfilms as specials, axials, and buy a reel.
It's impressive how little the resistor manufacturers know about this.
Interesting: imagine a long strip of metallic resistance element on a substrate. e-e interaction along its length makes the electrons correlate and kills the shot noise. Now cut the element midway and bridge the gap (magically somehow)... each half now has half the electron interaction distance. Keep doing that until the segments become very short, below the e-e interaction distance, or until there's less than one free electron per section. Seems like you should have full shot noise. If I understand the mechanism.
I wonder if a curved or spiral or zigzag resistor has less e-e interaction. The bends would have to be smaller than the e-e interaction distance.
If you made a 2-layer resistor, with a really thin metal and really thin insulating gap between the layers, would electrons interact between the layers?
An interesting device is a resistor (or whatever) that allows a flow of strictly periodic, clocked electrons, exactly one electron per clock. I think they exist.
No, because the other segments function like emitter degeneration in a BJT amplifier. Another way of saying it is that the shot noise of each segment is effectively shunted by the segment resistance, in parallel with the resistance of the rest of the segments in series. If you cut the element into N pieces, then from each current source's POV, only 1/N worth of the shot noise current would reach the terminals--the rest just goes round in a tight loop and never gets out of the segment.
That cutting approach predicts the wrong asymptotic falloff of the noise with length, iirc. (It's been awhile since I read up on the Rolf-Landauer-contra-mundum dust-up on that point.)
The mean free path is on the order of 100 angstroms, so the bends would have to be pretty tight. ;)
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
Maybe Soldi state Shot Noise by R. Landauer?
At the very small level I've got only a fuzzy image of what charge transport looks like. My understanding is that it's not the e-e interactions with the other "moving" electrons, but the number of collisions of a single electron as it travels the length of the conductor. (so the magnitude of the current shouldn't matter.) And what comes out the other end (of the resistor) are a series of little mini pulses, one from each scattering event. Each pulse being much smaller than the electron charge... (But as I say this... I find the details fuzzy.)
Yeah well (I think) that's where you need the QM. You really small sections are indeed very small... and that gives you these quantized conductance steps that I showed in my (crappy) bouncing gold wire data. But that is a whole nother ball of wax compared to your typical resistor.
Yeah Phil mentioned it (in this thread?) electron turnstiles.
George H.
I had a closer look on eBay's US site and as John L pointed out, there is more than one available - unfortunately all non-working. One has the meter glass missing, I don't think the movement would survive the shipping. The one I was originally looking at has the protective cap for the input connector missing, I'm assuming this is important for protection from contamination and ESD?
Looking at the completed listings, 610Cs in complete working order don't sell for much more than the $100 being asked for the broken ones, so I'll wait for one of them to turn up.
That probably doesn't matter. The insulator in the connector is easy to clean.
It appears that you do not want to do much in the way of repair work. Replacing a BNC cover, meter glass, or even input FET's are not major repairs.
Broken glass on meters will not destroy the meter movement, but might destroy the needle. Attaching a new needle to the meter movement is tricky, but not impossible. I've done it a few times. The real danger is having scrap metal and dirt enter the meter movement causing erratic operation. Fishing out the scrap metal requires a steady hand, needle point tweezers, and a binocular microscope. I've done it a few times. I've also replaced an analog meter with a digital panel meter.
Don't use eBay "Completed" listings. Use "Sold Listings". Completed listings include those items that did not sell in the last 30 days while sold listings go back 90 days. Looks like $140 to $180 were the selling prices with 0 sold in Sept, 3 sold in Nov, and 1 in Dec. You shouldn't have long to wait.
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
Might the weight of the needle affect the meter linearity?
They come along periodically. Inspired by this thread, I bought one with a 30-day DOA warranty for a $125 (best offer) a week or so ago. Should be here Thursday.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
The counterbalance has to be adjusted or more than linearity will be affected: The counterbalance is the orange blob opposite the needle. Others are made from a piece of solid wire. Some are adjustable, but most are just preset. It's difficult to get this right because the springs affect the adjustment. The replacement needle will probably be heavier than the original. So, some mass needs to be added to the counterbalance. The easiest way is apply tiny blobs of viscous epoxy to the counterbalance while rotating the meter to different positions. If it's off balance, the needle will move when the meter is rotated 90 degrees vertically. If it's properly balanced, the reading will not change. See section on meter balancing in: Rejuvenating Old Meters February 1943 QST Article
Finding a suitable replacement needle is a problem. If I don't care about accuracy or looks, I just use a piece of stiff stainless wire. If I want perfection, I cannibalize another similar meter. Another major problem is finding a clean work area. The meter magnet really attracts difficult to remove junk.
I usually don't need to replace the needle. It's made from brass and will bend back into shape as long as it's not excessively mangled. Flat duck-bill tweezers seem to work well for needle straightening.
In the distant past, I used to do this type of precision work without much difficulty. Today, my eyesight and steady hand have deteriorated to the point where I'm not sure I still can do it. It's been many years since I've replaced a meter needle. I couldn't find any YouTube videos on the process, which suggests that nobody is doing this level of repair.
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
Seems like buying a junker 610 would be easier. Buy two and you could probably make one good one, if you have time to play with it.
Get a Mantis; it's fabulous for close work.I couldn't solder insane things like US8 packages without mine.
That's amazing. Realistically, that instrument is worth kilobucks. Maybe I should get a spare before word gets out.
The "fast" mode (TIA sort of feedback) has never worked on mine. Does it on yours? It's no big deal, just a longer settling time on the lower ranges.
Boat anchors rock, like I done said. ;)
It still isn't as cool as my 410, but it has a much better meter, and is way more practical generally.
Dunno yet. I'll see. Usually there's enough capacitance around that it takes awhile to settle anyway.
It's no big deal, just a longer settling time on the
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
I've never had the fast feedback work on mine. It either pegs the needle, or causes it to vibrate rapidly.
George H.
Guilty as charged. I actually enjoy repairing stuff as a break from design work, but my boss doesn't see it that way. If there were a bigger difference in price between the working and broken instruments, I might give it a try.
Sure, but without access to another instrument at least as capable as the 610C I would have no confidence I hadn't screwed up the repair. The next-best meter I have is a 34410A which (IIRC) can resolve hundreds of nanoamps and up to 10 megohms.
I will go and buy some of the gigaohm and teraohm resistors which were mentioned a while back in any case, to sanity-check the instrument before I use it for Real Work.
What type is the input connector BTW? It doesn't appear to be a BNC from the photos, it's threaded, similar to a N type but smaller and with serrations on the mating face. The manual just describes it as a co-ax connector.
On a normal 4-3/4 digit, 10M DVM, the 400 mV range is also a 0-40 nA range with 1 pA resolution.
Cheers
Phil Hobbs
e with 1 pA resolution.
Yup, and with a giga ohm resistor and a fet opamp you can measure pA, (as long as you don't mind subtracting an offset.) digikey has 1G's for a few bucks. The cheapest 1T I found was at mouser. ~$10.
George H.
e with 1 pA resolution.
Doh! Of course. Good tip, thanks.
I believe the manual has a calibration procedure. I'm too lazy|busy to check right now.
I screwed up. I don't currently own a 610C, although I've used one in the past. I thought it used a BNC connector, but upon closer inspection of some online photos, it appears to be a common SO-239. Sorry about the muddle:
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
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