4-wire short - 2020

[mawyatt]

but its important to think about the joint because its the parameter that you can change to reduce the effect.

the plating increases drift by a order of magnitude

https://www.edn.com/wp-content/uploads/5.3.01_Minimizing_thermocouples_maintains_20-bit_DAC_precision.pdf

Believe that reference has an error in Figure 6, the op-amp is configured with the 500 ohm and two 500K resistors and has the op-amp inputs reversed. As shown it has positive feedback, which should be negative feedback for a stable result.

Best,

[alm]

I suppose the main point is that the junction is not where the voltage "comes from".  The potential is (pretty much) the same in both sides of the junction - the thermocouple voltage does not appear there.  It's a different way if thinking about things than what some writers present.

I would love too see a detailed description of the Seebeck effect on the molecular level. Plating and oxidation makes a huge difference (see Jim Williams article posted by coppercone2), while it's hard to imagine there being much of a gradient across the plating: in copper-nickel copper, both copper nickel junctions would be at pretty much the same temperature. This suggests to me that there might be more to it than just two junctions with a different temperature across them.

But I've not found a reference supporting this, so maybe I'm wrong and it is just about copper atoms on both sides of the plating being at different temperatures.

[thermistor-guy]

...
It is not the junction that "generates" the voltage, as seems to be commonly thought.  It took me nearly forever to dig up good explanations of this; there are so many explanations, even from otherwise authoritative sources, that say, or imply, that the voltage "comes from" the junction - the point of contact between the two metals...

There is a good introduction, to the Seeback effect in thermocouples, in a National Measurement Laboratory monograph. The third edition (2004) is here:
https://shop.measurement.gov.au/products/monograph-5?variant=1042647327

I have the second edition (2003). There is bold text at the bottom of page 9:

Emf is NOT generated at the junction of two metals.

The monograph also touches on the Peltier and Thomson effects, but states, in the context of metallic thermocouples (2nd ed. page 6):

The only thermoelectric effect of relevance to the thermocouple is the Seeback effect, discussed next.

[alm]

There is a good introduction, to the Seeback effect in thermocouples, in a National Measurement Laboratory monograph. The third edition (2004) is here:
https://shop.measurement.gov.au/products/monograph-5?variant=1042647327

Thanks for the reference! The full text is available from CSIRO (first result with "full text" written under it). I find this indeed a very helpful description that gives intuition for the physics behind the Seebeck effect, how it is really about the gradient across the conductor, and not about the interface. If you had material in between with a very high Seebeck coefficient relative to copper, but the material was entirely isothermal, then it wouldn't contribute towards the Seebeck voltage.

[Miti]

Necro posting but it’s related.
I,ve tried quite few banana plugs with this project, nickel, gold plated, but the best is a 5/32 copper tube from a hobby store. It doesn’t have the flexible contacts but it wedges well enough and after 15 minutes you’ll have a dead zero on a properly calibrated meter.

Cheers,
Miti

[coppercone2]

ehhh you sure that it won't damage your banana jacks? especially if your meter has gold plated ones, I would be really worried jamming copper in there. maybe you should cut a X into it and debur it very well to give it some compliance

Its almost unheard of in precision mechanics to have jammed together pipes in a system that is meant to be assembled more then once. Every connector in exsitance pretty much uses proper spring shapes (tempered too).


My guess is poor cycle life and damage to connectors

and it should also be polished, that looks rather gnarly

amusing if our calibration guy found that jammed inside of the fluke MFC


klingons!!

[donlisms]

I have experimented with copper tubing also.

It may be helpful to saw an end-wise slit into the copper tube and push something springy into the tube, to get some compliance.

It might help to shape the tube leaves carefully to get good contact, but also make sure the cut ens of the tube is shaped so that it isn't scraping the inside of the socket.

It may help to smooth and almost polish the surface, e.g. put the tube in a drill and use some very fine abrasive on it.  At the very least, deburr any cuts.

A quick investigation suggests that beryllium copper has horrible conductivity compared to pure copper, e.g. 15% to 30%.  If that's what the tube is made of, it's something to think about. 

[Miti]

ehhh you sure that it won't damage your banana jacks? especially if your meter has gold plated ones, I would be really worried jamming copper in there. maybe you should cut a X into it and debur it very well to give it some compliance

Its almost unheard of in precision mechanics to have jammed together pipes in a system that is meant to be assembled more then once. Every connector in exsitance pretty much uses proper spring shapes (tempered too).


My guess is poor cycle life and damage to connectors

and it should also be polished, that looks rather gnarly

amusing if our calibration guy found that jammed inside of the fluke MFC


klingons!!

No, no plating in the 34401 jacks, they are bare copper. I don’t jam them hard inside the jack, just a light push. And there’s a little flexibility in them. And you don’t use them every day but once a year to adjust the zero and eventually once in awhile to verify it, if necessary.

[Miti]

I have experimented with copper tubing also.

It may be helpful to saw an end-wise slit into the copper tube and push something springy into the tube, to get some compliance.

It might help to shape the tube leaves carefully to get good contact, but also make sure the cut ens of the tube is shaped so that it isn't scraping the inside of the socket.

It may help to smooth and almost polish the surface, e.g. put the tube in a drill and use some very fine abrasive on it.  At the very least, deburr any cuts.

A quick investigation suggests that beryllium copper has horrible conductivity compared to pure copper, e.g. 15% to 30%.  If that's what the tube is made of, it's something to think about.

Yes, I thought about that but I found it unnecessary. Also, it looks rough in the picture but I polish it once in awhile with Scotchbrite. The material is pure copper.

[donlisms]

Your confidence that it’s pure copper is inspiring… but if I may ask, how do you know?  I might see those words on an auction site, for example, but don’t trust them!  Maybe you have a more reliable and more technical source?

[coppercone2]

you will know BeCu if you handle it compared to any kind of pure copper. its stiff as hell and you will feel it fight you with vibration/spring back. its unpleasant as a material to work with and you will immediately know something is wrong. Threading it by hand feels like fighting a spring lol

also its expenisve and toxic so don't sand that

its like normal bushes vs mean impale yourself on a stick bushes. if you ever made a bow and arrow when your young, its the wood you look for with to make a bow

[Miti]

you will know BeCu if you handle it compared to any kind of pure copper. its stiff as hell and you will feel it fight you with vibration/spring back. its unpleasant as a material to work with and you will immediately know something is wrong. Threading it by hand feels like fighting a spring lol

also its expenisve and toxic so don't sand that

its like normal bushes vs mean impale yourself on a stick bushes. if you ever made a bow and arrow when your young, its the wood you look for with to make a bow

BeCu is expensive. It is used in some high quality connectors an specialty non-sparking tools, not in some hobby tubing.
See here:

https://ksmetals.com/products/cut014-5-32

[Miti]

Your confidence that it’s pure copper is inspiring… but if I may ask, how do you know?  I might see those words on an auction site, for example, but don’t trust them!  Maybe you have a more reliable and more technical source?

Yes, I do. The manufacturer specifications. Now, there's nothing pure in this world as in 100% but it is copper.

https://ksmetals.com/products/cut014-5-32

[Miti]

To be honest I did not expect this kind of replies. Don't damage the jacks, how do I know it is copper, what if it is Be-Cu, like I'm a complete idiot and I don't know what I'm doing, but nothing about the main goal, finding a solution that gives me the lowest thermoelectric voltage for calibrating the zero of a precision multimeter.
34401A has copper plugs, I think 3458 also has copper plugs... I think.
This is one simple solution that I found, it is not intended to be professional nor commercial.