[sdiy] Tempco 2k +3350ppm Group buy

[HA.Synth at t-online.de]

Thanks Ryan,

looks like I should go for +3500. But I have one questons. If i look at the 
tracking chart of PT146-35 it says 3440ppm at 25 and 3500ppm at 100degC.
In your paper you wrote +3369 at 25C and +3430 at 100C.
If I look at RES/TEMP CURVE at their site I can read +3369 at 25C and +3420 at 
100C.
What am I missing here? Is the tracking chart wrong?

Harald

> hi,
>
> for precisionresistor.com tempcos, I believe that +3500 is the correct
> part to buy. They specify that these are actually more like +3369 at
> room temperature. thats pretty close to to the +3355 that is needed. The
> problem is how they measure tcr and they comment on using the +3500ppm
> instead of the lower +3350ppm at the website. the tcr isn't linear and
> there is some tolerance on the parts anyway. It would be better to have
> a tcr that is to high than too low since correcting the error is easier
> that way. I wrote some document about using the precisionresistor PT146
> here:
> http://www.sdiy.org/destrukto/notes/tempco_calculations_pt1.pdf
>
> note: most credit goes to Ian for this since it was his analysis and
> answers to my questions that helped me write it.
>
> btw. if anyone sees a problem, let me know so I can correct it.
>
> Ryan Williamsf