[sdiy] Tempco 2k +3350ppm Group buy

[Ian Fritz]

At 03:11 PM 5/22/06, René Schmitz wrote:

>Still, I don't see how (linearity provided) the tangent would be any 
>different from the slope. :-)

The problem comes if an inappropriate -- or misunderstood --  reference 
temperature is used.  For example, if they use
[R(50) - R(0)] / R(0)  or
[R(100) - R(25)] / R(62.5)
then the ideal tempcos would be 1/273 or 1/336.  In other words, the slopes 
would be correct (as you point out), but tempco depends on the slope 
divided by the reference resistance.


>I would expect a linear ideal 3354ppm 1k resistor to show
>1K + (t-25°C)*3.354Ohms/K. Or R(T) = 3.354Ohms/K * T.
>I think this way of writing it is a lot more clear than this whole 
>buissiness with ppm/K.

Yes, I agree.  It would be best if a clear notation was always 
used.  Including the nonlinear correction.  I have a feeling that some 
devices are more linear than others, but this is confusing to figure out.

   Ian