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

[Robert Atkinson]

Hi Fabio,
the DB877 is a nice box and is still available from IET Labs. See http://www.ietlabs.com/sitesearch?q=db877 The manual is here http://www.ietlabs.com/sitesearch?q=db877 

They will sell you parts but they are not cheap. You won't find a compact 8 decade box with it's accuracy very easily. Even with standard 0.1% resistors subsituted it's a nice unit.

Robert G8RPI



________________________________
 From: Fabio Eboli <FabioEb at quipo.it>
To: Discussion of precise voltage measurement <volt-nuts at febo.com> 
Sent: Tuesday, 19 June 2012, 19:04
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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