[volt-nuts] Fluke 731A Transfer Standard and Fluke Wire WoundResistors

[Bob Smither]

On 09/16/2012 04:54 PM, J. L. Trantham wrote:
> Pete,
> 
> Thanks for the reply.
> 
> I was just looking at the properties of the wire.  I guess I don't
> understand the 'resistivity' of 43-48 uOhmcm for the wire that is about the
> same size as what the resistor is made of.

Example:

  45 uOhmCm * L / A = Ohms

L = length of wire in Cm
A = Area of wire in Cm^2

> It lists a tempco of .00001 per K.

Hmmm - 10 ppm / C?  Not great.  I assume that the resistors are empirically
matched in pairs during manufacturing.

> As best I can tell, the 5903 ohm resistor is about 15.5 mm long, on a 1 inch
> flat form about 1 mm thick (about 2 inches per turn) and about 14 turns per
> mm as best I can tell.  I measured the wire at .05 mm thickness.  That would
> put it at about 217 turns, 434 inches, and about 13.6 ohms per inch.  My
> original calculation appears to be wrong.

Using 45 uOhmCm:

  45E-6 * 434 in * (2.54 Cm / in) / (pi * (.005 cm / 2)^2) = 2.52 KOhm

At the risk of stating the obvious, have you considered Vishay resistors for the
rebuild?

Best regards,

-- 
Bob Smither, Ph.D.                                       Smither at c-c-i.com
==========================================================================
  "I'm sorry I ever invented the Electoral College." -  Al Gore 11/08/00
==========================================================================
-------------- next part --------------
A non-text attachment was scrubbed...
Name: smither.vcf
Type: text/x-vcard
Size: 140 bytes
Desc: not available
URL: <http://www.febo.com/pipermail/volt-nuts/attachments/20120917/839b494a/attachment.vcf>