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Products => Test Equipment => Topic started by: TERRA Operative on May 07, 2019, 05:46:58 pm

Title: Triaxial test cables for HP 4140B pA meter?
Post by: TERRA Operative on May 07, 2019, 05:46:58 pm
I recently got my hands on a HP 4140B pA (pico amp) meter and DC voltage source for a good price. I figured it'd be something fun to play with. :)

It looks like the pA input uses a triaxial connector, of which I have nothing in my stock of parts.
I found this on Digikey, but it's not the cheapest test lead out there (I know triax is expensive...)
https://www.digikey.com/product-detail/en/pomona-electronics/5342/501-1407-ND/737265 (https://www.digikey.com/product-detail/en/pomona-electronics/5342/501-1407-ND/737265)

Does anyone have any suggestions on what sort of test lead I should even be looking at? Also, does 50ohm/75ohm matter here?
Title: Re: Triaxial test cables for HP 4140B pA meter?
Post by: HighVoltage on May 08, 2019, 05:34:56 pm
The keyword to search on the used market is "trompeter" and "triax".
Sometimes you can get lucky to find good cables and connectors for a good price.

The price on Digikey is not too bad.
I have seen much higher prices for name branded cables.
Title: Re: Triaxial test cables for HP 4140B pA meter?
Post by: VK5RC on May 08, 2019, 07:39:11 pm
+ search for the term TRB connector, the cable is relatively cheap but the connectors crazy, watch out for 2 (older) and 3 lug versions. If you make your own - remember the impedance needs to be in terraohms - no touch!
Title: Re: Triaxial test cables for HP 4140B pA meter?
Post by: TERRA Operative on May 08, 2019, 08:23:50 pm
Cool, thanks for the info, I'll keep having a look around here and there.

I have the 3 lug type on my machine, they seem common enough.
I'll also be sure to not touch stuff, maybe I'll wear gloves if I assemble my own cable. Would a wipe down in 99.9% Isopropyl alcohol be alright if needed?
Title: Re: Triaxial test cables for HP 4140B pA meter?
Post by: VK5RC on May 13, 2019, 10:05:42 pm
I made two  2 to 3 lug adapter cables - to join my Keithley Electrometers  (617 619)  to a HP Test Fixture Set  (16058A).
I used the no touch technique - but had washed my hands in IPA first - and the resistance between the layers of triax was not measurable - so I was happy.
Those are expensive connectors!
Hope it goes well.
Rob