Vishay tempco info

[Steve Varner]

I recieved the following letter from a Vishay rep:

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Steven:

In response to your inquiry regarding temperature-sensitive resistors
(old Tel Labs Q81):

The Ultronix division of Vishay, located here in Malvern, PA,
manufactures a line of precision wirewound resistors, including
temperature-sensitive (i.e. high positive TCR) types.

Tel Labs is now a defunct outfit, of course; they were bought by
Ultronix some years ago.  While the Q81 itself is no longer
available, Ultronix still manufactures a product, called the model U81,
that is very similar to the Q81, however there are some differences as
follows:

The Q81 was a power-type wirewound resistor built on a ceramic core;
the U81 is built on a plastic core, and therefore has a much lower
power and temperature rating.  Specifically, the Q81 was rated 3 Watts
at 25°C, with a max. operating temperature of 275°C.  The U81 is rated
1/8 Watt up to 125°C, with a max. operating temperature of 145°C.

The lead diameter of the Q81 was 0.032" (#20AWG); the lead diameter of
the U81 is 0.026" (#22AWG).

Other than these slight differences, the Q81 and U81 are electrically
identical.  The TCR, ohmic value range, tolerance range, etc. of the
Q81 and U81 are the same.

(You referred to the Tel Labs "model Q81k" in your e-mail.  I don't
recognize what the "k" signifies; I've only ever heard of a plain old
Q81.)

Also, Ultronix can produce a +3500ppm/°C resistor in any of a variety
of package sizes and styles; these might be an option if the physical
size, power rating, lead diameter, etc. of the U81 are not acceptable.
For more info., visit the Ultronix web site at
http://www.vishayultronix.com/006/Product.html.

Yes, this part is available either through distribution, or direct from
the factory, in small quantities.  The part number for a 2kohm ± 1%
resistor would be:

U81 2K0000 1%

A list of distributors is on the web at
http://www.vishay.com/RepList/americas.html

Any further questions, please ask me by e-mail.

Regards,

Jim Vukich
Jim.Vukich at VISHAY.Com
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Steve Varner
varner at k-online.com