[sdiy] Tempco 2k +3350ppm Group buy

[Ryan Williams]

HA.Synth at t-online.de wrote:
> Well,
> 
> i have an answer from the German distributer if precisionresisters.com. They 
> want to sell me 2k +3500ppm Resistors. delivery Time 11 weeks, 4,40 EUR per 
> piece. Not wat I want. If they don't make custommade +3350ppm resistors I can 
> go with 1k +3500ppm out of their stock at a much lower price. I asked them 
> for that one. So looking forward to the answer from www.weltronic.de .
> 
> 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