[volt-nuts] Resistance standard
phill.r1 at btinternet.com
Wed Dec 16 16:01:03 UTC 2009
It would be very interesting to have the details of his "improvements" to
the Fluke 731's, if this is possible.
From: "WB6BNQ" <wb6bnq at cox.net>
Sent: Wednesday, December 16, 2009 12:03 PM
To: "Discussion of precise voltage measurement" <volt-nuts at febo.com>
Subject: Re: [volt-nuts] Resistance standard
> Hi Rod,
> The modification in the 750A is not terribly involved. My friend, who was
> responsible for the Navy's primary voltage standard made the mod, but I do
> remember the exact details. It involved disconnecting the standard cell R
> and jumping some other point I think. I will pin him down on the
> He also was responsible for a number of improvements to the Fluke 731
> series. He
> modified the 750 after he characterized a large number of 731 units and
> kept the
> best four for his use. One of his ideas was to parallel the four 731's so
> output was a voted value. So the four he kept had equal but opposite
> coefficients such that the error was basically cancelled. I believe that
> Fluke used
> that, among his other ideas, in one of their later units.
> Yes, the Fluke resistors were of the card variety. The oil comment
> regarding the
> Vishays was aimed at the non-hermetically seal units that you were
> considering. I
> would be interested in your findings on the Pomona posts.
> Rob Klein wrote:
>> I want to apologize for making a snap judgement of your background and
>> 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
>> 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
>> 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
>> (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 Pomona 3770's. Their insulation is
>> 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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