SV: Re: SV: Re: SV: Re: [sdiy] Compensating PTC and NTC resistors

Dave Manley dlmanley at sonic.net
Thu Mar 20 01:41:22 CET 2008


Hi René,

Thanks very much for the detailed explanation.  All is perfect except a 
little typo - an addition instead of a subtraction in the second case. 
This has been an informative thread even with the smog that sometimes 
fills the air ;-)

-Dave


> Lets stick in the figures into the equation again, this time we let TC2 
> come into the picture, and lets see what happens when the R2 has a TC of 
> +100ppm or -100ppm.
> 
> (1000ohm * 3900ppmK^-1 + 163ohm * 100ppmK^-1) / (1000ohm + 163ohm)
> = 3367ppmK^-1
> 
> (1000ohm * 3900ppmK^-1 + 163ohm * 100ppmK^-1) / (1000ohm + 163ohm)

-------------------------^

> = 3339ppmK^-1
> 
> Makes some 15ppm difference. If you happen to have resistors somewhere 
> in your input summing (or other CV processing) stage where their 
> relative TCs are off by more than 15ppm the effects could easily 
> outweigh this.
> 
> Now leaning back and watching the mud-fight on SDIY. :(
> 
> Cheers,
>  René




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