[volt-nuts] Test Leads

[Bill Gold]

Randy:

    From my own experiences and what I have done over the years about "low
thermal leads".

    I have made my own leads from the Pomona #4892 double gold plated banana
plugs along with using Pomona #5406 single gold plated banana plugs, where I
needed to spread the leads futher apart than the standard 3/4 inch, such as
plugging into the Fluke 732A.  I have been using Belden #9272 shielded
twinax as my cable material only because it was available at the time to me.
It is a twisted pair of 20 ga. tin plated wires inside of a braided shield.
The purests will say that the tin plating will cause "Thermals" when screwed
down on the Gold plated banana plugs.  I realize that and I now have 100
feet ( 50 red, 50 black ) of Pomona #6733, which is extremely flexable
copper wire with Silicone double insulation.  I will then twist these
together and the put a shield braid over that and finally put a heat shrink
layer over the shield to make my own "copper twisted pair shielded" wire
which I will then attach to the #4892 or #5406 banana plugs to create a
"more perfect" low thermal test lead ( I hope ).  This is all when I get a
"round toit" of course.

    In the meanwhile I have purchased 6 ea Pomona #1756-48 leads.  Frankly I
cannot measure a difference between the #1756 and the homemade leads, once I
wait about 3 minutes for all "Thermals" to settle down.  I also have 2 ea
Fluke P/N 738716 ( 24 inches ) and 1 ea Fluke #738724 twin shielded test
leads.  These are the Fluke 5440A-7002 Low Thermal test lead set that is
recommended by Fluke for use with 732A/B, 5440A/B and other high precision
calibrators.  They are RG-58 with Tellurium Copper conductors/ Beryllium
Copper Tip Springs.  Again I cannot see differences between all of these
cables with the best measuring equipment I have.  HP 3458A DVM and Fluke
845AB Null Detector and measuring between 732A/Bs, 5440B for nulls.

    I am sure that Fluke has done extensive research on this subject.  It
may well be that measurements can be made faster using the "purest" approach
of pure copper and gold plated connectors.  I don't know at the present
time.

    Hope this helps you in making up what you need.

Bill

----- Original Message ----- 
From: "Randy Evans" <randyevans2688 at gmail.com>
To: <volt-nuts at febo.com>
Sent: Tuesday, July 21, 2015 9:33 AM
Subject: [volt-nuts] Test Leads


> I recently acquired a Fluke 752A to go with my Fluke 732A and HP-3458A.
> Now I need to address the need for low thermal test leads.  Does anyone
> have any suggestions for test leads that have low thermal contributions to
> measurements?  I have looked at Pomona 1756 Low Thermal EMF Cables as a
> starting point but haven't found any other candidates.
>
> I have heard that old TV twin lead works well since most are stranded
> copper wire.  I have tried it between my 732A and 3458A and it seems to
> work fine but I would like to use more professional looking test leads,
> particularly with correct copper spade lugs (Pomona 2305 Low thermal EMF
> spade lug, Gold-plated?).  Any other suggestions?
>
> Thanks,
>
> Randy Evans AE6YG
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