Odp: [sdiy] really basic question .. tolerance

[Roman Sowa]

for parallel:
Tc = Tc1 * R2 / (R1+R2)   +   Tc2 * R1 / (R1+R2)
Tc1 is tempco of R1 and Tc2 of R2

for series connection:
Tc = Tc1 * R1 / (R1+R2)   +   Tc2 * R2 / (R1+R2)

Roman

----- Original Message -----
From: patchell <patchell at silcom.com>
To: <synth-diy at dropmix.xs4all.nl>
Sent: Sunday, January 19, 2003 3:58 AM
Subject: Re: [sdiy] really basic question .. tolerance


>     Heres one for you to think about.  You have a 10K resistor with a
+100ppm./C
> tempco and a 100K resistor with a +1000ppm/C tempco, you connect them together
in
> parrallel to make ~9K, what is the tempco of the resulting ~9K resistance?
>
>     Guess I should work this one out myself to see what the answer is...
>
>     Just a brain teaser I thought up on the spur of the moment...
>
> harrybissell wrote:
>
> > Tell ya what John...
> >
> > I'll buy your arguement that it can't be worse than the original
tolerance...
> >
> > if you buy mine that its likely to be BETTER than the original tolerance...
> >
> > H^) harry
> >
> > John L Marshall wrote:
> >
> > > Tim or Harry or Peter,
> > >
> > > Please show me an example of two 1% resistors in series or parallel where
> > > the tolerance exceeds 1%. I heard this rule many times but I can't see it.
> > >
> > > Complex circuits are another story. I can see how errors accumulate
through
> > > gain stages.
> > >
> > > I need empirical evidence to be convinced.
> > >
> > > Take care,
> > > John
> > > www.sound-photo.com
> >
> ---------------------------------------------------------------------------
> > >
> > > ----- Original Message -----
> > > From: "Tim Ressel" <madhun2001 at yahoo.com>
> > > To: "diysynth" <diy_list at analog-synth.de>; <synth-diy at dropmix.xs4all.nl>
> > > Sent: Saturday, January 18, 2003 1:32 PM
> > > Subject: Re: [sdiy] really basic question .. tolerance
> > >
> > > > Joerg,
> > > >
> > > > That is an optimistic way of looking at it. However
> > > > the worse-case is still the sum. If I'm worrying about
> > > > tolerances, I always look at worse-case.
> > > >
> > > > --tim
> > > >
> > > >
> > > >
> > > > --- diysynth <diy_list at analog-synth.de> wrote:
> > > > > Hi all
> > > > >
> > > > > > tolerance are connected in series that the result
> > > > > will be out of
> > > > > tolerance?
> > > > > >
> > > > > > Add two 100k resistors 101k + 101k = 202k still 1%
> > > > >
> > > > > Sure ? I allways thought, the resulting tolerance
> > > > > gets better with the
> > > > > factor t_res=t_single/sqrt(n), where n is the number
> > > > > of used resistors, and
> > > > > t_single is the tolerance of the single resistor ?
> > > > >
> > > > > Joerg
> > > > >
> > > > >
> > > >
> > > >
> > > > __________________________________________________
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>
> --
>  -Jim
> ------------------------------------------------
> * Visit:http://www.silcom.com/~patchell/
> *-----------------------------------------------
> *I'm sure glad Merry Christmas comes just once a year
> * -Yogi Yorgensen
> ------------------------------------------------
>
>