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

[karl dalen]

--- harrybissell at wowway.com skrev:

> I think the idea is that the change of the carbon resistor is so small
> compared to the 3900TCR that it could be considered ~linear~
> 
> So what you do is to make up a resistor where one portion of the total
> resistance is the TCR, and the other fixed... so the overall tempco is
> reduced. Its a ~mixture~ problem... maths left to the interested :^)

Yes, but still, where do one get the -600ppm resistor?
The user cant compensate a +3900ppm with a +/-600ppm resistor! Nor are the ppm
part fixed with temp, nor linear even manufacturers want to claim that. Most
papers on the subject suggest xxxppm but they let the sign out! Elby papers for
example does not suggest any sign nor do Rene's! So do the user use a carbon
mass (hehe), carbon film, metal film, metal oxide, plastic, ceramic compound,
or any of the myrriad of new resistor techs thats available today.

Another small suprice are that so few are using resistor nets, SIL's as input
buses to expos and signal inputs. In the old days these was strictly for
digital
pull dow/upp's and had pretty lousy specs but today +/- 100ppm TC are bog
standard. Alltought thick film tech and 1% but they are dead
cheap.Interestingly
to note are that above 50ohm individual TC tracking are 50ppm. And one can get
without much effort a R-net with 5ppm tracking and 15ppm over all and 0.5%.

KD


> 
> H^) harry
> 
> 
> On Mon, 17 Mar 2008 03:28:11 +0100 (CET), karl dalen wrote
> > For example if one finds carbon film resistors having +/-350ppm TCR 
> > and metal film +/-100ppm TCR so which one do you use to compensate 
> > down the 3900ppm TCR PTC resistor? Obviously you serialize it with a 
> > -600ppm resistor. But where do one get a -600ppm metal film 
> > resistor? :-)
> > 
> > KD


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