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

[m k]

Hi Fabio,
I remembered some problems soldering manganin a while ago, so I googled and this one came up:http://listserv.ipc.org/scripts/wa.exe?A2=technet;a5280f30.1203
So it is possible not all the previous flux was removed. I thought it was fairly stable, hence a good bet for standard resistors, but if overheated like you suspect then all bets would be off as they say.
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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