[sdiy] tempco questions

[Reverend djbluE]

Jim Patchell wrote:
> 
>     You basically got it.  3000ppm means 3000 parts per million, and in
> this case, one should really add "per degree C" to make it a complete
> sentence.  Another way of saying this is 0.3% per degree C (3000/1000000
> * 100), so for every decgree C the temperature rises, the resistance will
> increase by .3%.  The magic number you are looking for 3300ppm/C, as this
> is how much the transconductance of a transistor changes with temperature
> (3000 close enough).

So what we (normally want is) PTC (positive temperature curve?) versus
(NTC (negative) yes?

is the 3000 ppm also known as a "B-Constant"?  what is a normal
tolerance range on a tempco?

-ben