Odp: [sdiy] really basic question .. tolerance

[Tim Stinchcombe]

Hi Roman, Tim et al,

> Well, I checked again, and it seems correct. I also did
> ran a couple (67 actually) of numbers to be absolutely
> sure and it works.
> 
> Anybody to confirm this?

I can. I had to grab a book from the shelf to find out what the 'tempco'
actually is (er, well, at least I know now!), but then some simple algebra
yields the result as Roman stated:

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

However, the expression for the parallel case:

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

appears to be a 'first order' approximation (I had to ditch the second order
tempco terms, and say that R + R*Tc*temp is approx R itself, for both R1 and
R2. For those still reading and who would like to check my maths, here it
is;

Tc = (Tc1*R2 + Tc2*R1 + (R1+R2)*Tc1*Tc2*temp)/(R1 + R1*Tc1*temp + R2 +
R2*Tc2*temp)

where temp is of course the temperature...)

Fine family fun!

Tim

__________________________________________________________
Tim Stinchcombe 

Cheltenham, Glos, UK
email: tim101 at tstinchcombe.freeserve.co.uk