[volt-nuts] Wanted wirewound precision resistors and ESI DB877

[m k]

I accidentally replied just to artechmedia with this reply:
I have seen reports of people having problems reproducing the very low TC's that Vishay has been reporting for their z foil resistors. It seems that the low TC may only be for one particular resistance value in the range?  So although they will be stable and usable, do not take the TC for granted...MK
> Date: Tue, 19 Jun 2012 20:04:40 +0200
> From: FabioEb at quipo.it
> To: volt-nuts at febo.com
> Subject: Re: [volt-nuts] Wanted wirewound precision resistors and ESI DB877
> 
> Here I put some photos of the decade:
> http://www.eevblog.com/forum/product-reviews-photos-and-discussion/db877-teardown/
> 
> Frank Stellmach <frank.stellmach at freenet.de> ha scritto:
> > I think, you should better measure the resistance by a high  
> > resolution DMM, on its normal OHM range.
> > Thats much more stable and less power is dissipated. A comparison  
> > between two of them is also much easier.
> 
> Yes I'm using a pair of multimeters: the keithley 2015 and
> a solartron 7061, the keithley should be not far from real
> values, but has a maximum count of 1200000, the
> solartron is "zeroed" against the keithley,
> has a maximum count of 21000000, permitting to compare
> the 1M and 2M resistors without changing range and resolution.
> 
> I used the fluke to try to test for leackage, I
> tought that if there was some leackage, the current
> would have been higher than V/R ratio and not
> proportional to the voltage.
> 
> > ingresses between the windings. I assume, your resistors are tubular  
> > ones, with plastiv caps around, and they are not hermetically tight,  
> > therefore they cant be filled completely for corrosion protection  
> > and thermal  conductivity, like in the Vishay metal foil VHP type.
> 
> See the link, there is a pic of the resistor, it's open, no protection
> at all.
> 
> >
> > Besides electrical measurement (on OHM range!), I 'd recommen  
> > optical inspection of the case, and if its possible, of the windings  
> > for burnt/overheated areas. Corrosion may be easily identified, also  
> > by slightly stained parts of the wire.
> 
> yes, the low valued resistors (10/20 ohm) seem a little corroded.
> The intermediate valued ones seem ok.
> 
> Is the wire used (manganin?) prone to corrosion?
> 
> Fabio.
> 
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