Electronics > Metrology

DIY Low EMF cable and connectors

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ermionesrl:
Hello.

I am about to repeat the measurement of thermal EMF of different solder alloys I did in 2016 with different equipment.

Back then I used the Agilent 34401A, now I plan to use Keithley 181 and I fabricated some new all-copper cables (besides the solder joint inside the MIL-DTL-5015 connector - but I ordered a crimp one so it too will be solved), included the lugs.
They are very crude, but preliminary results are very encouraging, instrument reads stable zero +- 3nV at thermal equilibrium.
Here is a photo. You see the crimp and wire-wrap versions. I made also different shapes but the idea is the same... Size are 15mm x 20mm, the hole is 6mm and thickness is 1.1mm.

Best regards,
Andrea Baldoni.

julian1:
I just noticed the possibility of using BNC cables for shielded measurements, versus hand-rolled twisted pair. Any suggestions or preferences for bananna to BNC connectors? These are the two that I found,  but I worry about the combination of alloys and thermocouple offsets.

  Model 1269 Pomona.
    pdf datasheet,
     https://www.pomonaelectronics.com/file/16994/download?token=cRlo0ROC
     ( https://www.digikey.com/en/products/detail/pomona-electronics/1269/603922 )

    MATERIALS: BNC (Female):
    Body: Brass, Nickel Plated, Dielectric: PTFE
    Center Contact: Beryllium Copper, Gold Plate
    Banana Plug - Body: Brass, Nickel Plated
    Spring: Beryllium Copper, Nickel Plated

  Mueller BU-00260   
  pdf datasheet,
      https://au.mouser.com/datasheet/2/279/DS-BU-00260-1622138.pdf

    Material:   Body   Nylon
    BNC  Plated brass body, gold-plated brass center
    Banana Brass body, beryllium copper nine-leaf springs,
    nickel-plated

ermionesrl:
Hello julian1.

Electrometers have triaxial BNC connections, so the idea could work, yet current nanovoltmeters still have special low thermal EMF connectors that avoid dissimilar metals.

Normal BNC, adapters and even most coaxial cables, with dissimilar plating and alloys in the inner conductor and shield, are a nightmare on this respect (triaxial BNC are gold plated in both inner conductors, at least).

By the way, twisted pair work very well, why you don't want to use it? It's even cheaper to roll your own, even with teflon insulation.

OscarM:
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?
[attach=1]
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)

martinr33:
I could see that working. It ise really hard to get good copper bananas!

It would make a good connector for some kind of custom box - resistor testing, for example.

However, most of our instruments use bananas so it isn't useful for the instrument end.

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