Electronics > Metrology

Reversing switch

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SeanB:
Wipers will be Beryllium copper, as the addition of a small amount of Be metal does a magic change to pure copper. It becomes hard, non ductile and behaves like spring steel, just with the low resistance of copper.  Amazing in that you oly need a tiny ( less than 0.1%) addition to do this, and the most common use is as a flexible aneroid vessel, used in gauges as the bending element.

Also used as a poison in railway brass centre rail, as the tiny amount is added as a disc in a press fit slug in the main wear area, so that if it is stolen as scrap this small amount of Be will render the whole batch of metal in the furnace to be unusable without further electrolytic refining, and also requiring the replacement of the entire refractory lining in the smelter from the contamination. In use the wear mark limit means the tiny disc will be rubbed away by the pantograph unit just before the limit is reached, removing this from the brass rod and spreading it in a thin coat on the ballast, where dilution renders it safe.

zlymex:
I find that amazing too that Beryllium does to copper. However, the specification of Fluke 5440A-7002 Low Thermal Test Lead Set is not very good at 'Less than 1.3 ?V per degree C when measured while engaged in a five-way binding post of Tellurium Copper Alloy
145, half hard (John Fluke PN 637892 or equivalent)'. That is an indication to me of the influence of Beryllium, Tellurium or Gold to copper.

quarks:
quite a while ago I searched for thermal emf infos
and found copper to beryllium copper is around 5µV/K

https://www.eevblog.com/forum/chat/help-wanted-low-and-high-ohm-measuremet/msg174908/#msg174908

zlymex:

--- Quote from: quarks on April 03, 2016, 08:05:18 am ---quite a while ago I searched for thermal emf infos
and found copper to beryllium copper is around 5µV/K

https://www.eevblog.com/forum/chat/help-wanted-low-and-high-ohm-measuremet/msg174908/#msg174908

--- End quote ---
I have two of those Fluke 5440A-7002 Low Thermal Test Lead Set but seldom use them. Apart from suspicion of thermal EMF, they may come to loose by themselves and pop up from the binding posts.

Also in that post, @robrenz referred 34420A "almost pure copper connections" as well but he "translated Tellurium copper", is that true? I though Agilent say that because pure copper has the best low thermal property but not Tellurium copper.

quarks:
Hello zlymex,

about Tellurium, as discussed with and confirmed by robrenz, CuTe is only used because it is much easier to work with lathe/milling tools. The emf properties should be worse then pure copper. But because there is only very little Te in CuTe, it seems to be there is almost no difference. All you have to avoid/take care of is oxidation. Therefore I prefer gold plating (but without Nickel layer underneath).

About the Fluke 7002 (4mm banana), they are the way to go, if you cannot use/connect the much better spade lug cables. I.e. on Fluke 5450A front connector is unfortunately 4mm banana only, which I do not like at all. Same is true for my R6581 and my 6.5 digit meters. Because of that, I have made several adapters, so I am able to use spade lugs.

Bye
quarks

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