Electronics > Metrology

DIY Low EMF cable and connectors

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leighcorrigall:

--- Quote from: martinr33 on February 12, 2022, 01:24:24 am ---For that, I use vinegar immersion and a fresh water rinse.

--- End quote ---

Acetic acid (essentially synthesized vinegar) is very effective at removing copper oxides. This is what is commonly used in metallurgy. Wear gloves and use a fume hood well-ventilated area when using the high-molar concentrate because it will burn you and is bad for the lungs. Acetic acid stinks. To prevent tarnishing, rinse with water immediately followed by drying with a clean cloth (or compressed air when the geometry is complex). C101 will remain oxide-free for months after treatment. If the part oxidizes in a few days or weeks, you may have either contaminated it or you are working with a lower purity copper (e.g., C110 and C122).

If all you can access is grocery store vinegar, heat the acid to improve its activity. An ultrasonic cleaner will also help encourage oxide stripping.

 ;)

martinr33:
Here's a picture of the business end of the latest Fluke metrology cables for the 8558 multimeter.

 - the cable is 22GA PTFE shielded twisted pair. It is black, not white.
 - the ends are sleeved in silicone rubber. They are very flexible, so much so that the PTFE insulation may have been stripped back inside the sleeving. They do not behave as if they are still insulated with PTFE, as they will not hold a bend. I wonder if the insulation might have been removed and the wire untwisted to make it more flexible.

TimFox:

--- Quote from: OscarM on February 10, 2022, 07:41:43 pm ---Apologies in advance if this has been covered somewhere but I have looked and failed to find it.
Is there any merit in connectors like this?
(Attachment Link)
Available as FMTC-CU-M for about $5
It is meant for 'copper thermocouples' which strikes me as odd but might be suitable for this application.
Presumably Deoxit is a good idea.
Mates in chassis mounting or inline are available.
PCB mounting is also available.
I have also seen a version with round pins which is larger.

Clearly it isn't shielded/guarded but on the other hand it is small so the coupling loop for EMI is small and the pins are in close proximity and so will be close in temperature (which shouldn't matter because it is all copper)

--- End quote ---

Those thermocouple-style connections are designed to connect copper wires used after a ice-point calibrator (real ice or electronic circuit) that connects the thermocouple materials into the world of copper connections.  Mechanically, they are the same as the connectors for J, K, etc. thermocouples that use the same alloys as the wires.

martinr33:
An update on Pomona low thermal spade connectors.

I started testing with magnets, and found mixed results on individual cables. eg black spades magnetic, red not.

The difference is visible. Low thermal gold plating has a sort of matte look, while gold over nickel is mirror bright.

What I  cannot easily tell is if the nickel is a mistake, or the whole spade is a mistake (i.e. nickel over copper probably OK, nickel over brass is bad).

mzzj:

--- Quote from: ap on August 06, 2018, 01:53:18 pm ---Own measurements have shown that the plating (tin versus gold) does not make a measureable difference (at the levels discussed here), always provided copper is used as the base material. Gold has additional advantages of course.
Brass e.g. used for the spade material is making a difference though, you do see differences.

--- End quote ---
This is my limited experience also. Bog standard tinned spade connectors seem to work very well on 8508A and 3458A compared to bare  copper wire or the 8508A "official" zeroing fixture.
All of the fancy low-emf banana connectors  seem worse than 10 cent tinned spade connector. I'm thinkig this has to do with the thermal mass and conductivity: Adding a "big" hunk of copper to DVM terminals creates slightly different thermal conditions for the binding posts. This is probably even more important if your lab temperature is fluctuating.
Body material, smaller mass and thermal "disturbance" seem far more important than plating.
Probably a different situation with connectors that don't have as firm mechanical connection like binding post+spade as it provides sort of wiping action + ample of contact pressure.

Anyone attempted to chemically strip the ordinary tinned spade connectors to bare copper? Electrolytic stripping with NaOh (drain cleaner) and 6 volt power supply seemed reasonably straightforward.

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