[volt-nuts] Resistance standard

Rob Klein rob.klein at smalldesign.nl
Wed Dec 16 08:40:24 UTC 2009


I want to apologize for making a snap judgement of your background and capabilit
ies.  In all honesty
that was the way it came across to me.

   No worries, cause no offence taken. Perhaps I should have given more
   information about my background in that first post.

In my opinion, I think you may have wasted your money on the lead compensator.

   Nah, I picked it up for $25. Combined shipping with a HP3457A, so it's
   no great loss in any case.

You would be better
served obtaining a Fluke 750A Reference Divider.  It is an extremely good, stabl
e fixed division
divider.  There is a non-destructive modification that was done at the Navy's Pr
imary Standards Lab
to make the comparison section use a 10 volt reference instead of the standard c
ell as was
originally envisioned.

   Interesting! Do you have any more information about this mod? A link to
   a paper or something?

The way the metrology world maintained the Volt [...]

   Well, yes, I know how it was done. It was a rhetorical question in
   reply to your comment about 0.01% not "being considered a standard".

My comment about the oil is depending upon the oil used, it could affect the non
-hermetic resistor's
composition.  Fluke's resistors were sealed with a shellac compound of some sort
, so no, the Fluke
720A resistors are not just some resistive material open to the elements as such
.  The same goes for
the Fluke 750A.  They could be, but then an awful lot would have to be known abo
ut the oil and it's
affects.  The same problem with a potting material of some sort, particularly wi
th regard to leakage

   I highly suspect that the resistors Fluke used are the card wound,
   shellac sealed types we all know and love. Not going to open the
   tank to take a look, though :-)
   The resistors I'm using are not "just some resistive material open to
   the elements" either, they are molded in epoxy. Using a good,
   pure oil, I see little reason why they would be affected.
   I'm thinking about dropping the resin potting idea completely and just
   have one ensemble as is. That way I can compare the behaviour
   of the canned ensemble agains a 'naked' version, which is more

Regarding binding posts and such, many manufacturers specify a temperature that
a component can
withstand before destruction.  Does that really say the stability of the plastic
 (or whatever
material) binding post is going to retain its insulation abilities ?  Many bindi
ng posts, with
regard to leakage, are literally junk even without heating.  Before you select a
 binding post get a
sample, mount it to a panel and apply a kilovolt (you do have a Fluke 335D ?) th
rough a 10 meg Ohm
resistor between the post and the panel monitoring the current flow.  There shou
ldn't be any but
that is obviously unrealistic.  At least you can measure it.

   The ones I got are [1]Pomona 3770's. Their insulation is polycarbonate.
   I'm going to dig out my GenRad megohmmeter this afternoon
   and make some measurements. I'll post the results later.


   1. http://www.pomonaelectronics.com/pdf/d3750-3760-3770_101.pdf

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