# Re: [SI-LIST] : Heating resistor: RMS or average current (was Re: Effect of low Zo for unterminated lines)

Date: Tue Oct 26 1999 - 11:05:37 PDT

The humble DC pulse width modulator offers a clear conclusion to this
discussion methinks.

How you handle random signal (e.g white noise) modulation of the pulse width
is standard Signal Processing mathematics. Sine wave modulation needs a
slightly different approach. But then, this is a digital discussion, is it
not?

----- Original Message -----
To: <[email protected]>
Sent: 26 October 1999 15:13
Subject: Re: [SI-LIST] : Heating resistor: RMS or average current (was Re:
Effect of low Zo for unterminated lines)

> Larry Miller wrote:
> >
> > RMS IS the heating effect in terms of watts; good RMS meters use
bolometers
> > to measure it with. "Average" is the wrong answer.
> >
> > If you want to know how hot a resistor will get you need a model of its
> > heat flow, conduction, and radiation. You have to come up with an
> > equivalent Theta(case-to-ambient). I think this kind of info is fairly
> > readily available for common resistor types and is easily measured with
DC
> > in any case. Then the temperature rise is simply P(rms) *
> > Theta(case-to-ambient). Dimensional check: Watts * Deg/Watt = Deg.
> >
> > Larry Miller
>
> [...]
>
>
> For more info, HP has a very comprehensive app note on RF power
> measurement at
>
> http://www.tmo.hp.com/tmo/Notes/English/5965-6630E.html
>
> Sorry if this is a duplicate posting - my ISP disconnected on the
> previous attempt, so I don't know if it succeeded.
>
> Best Regards,
>
> Michael R. Monett
> mailto:[email protected]
>
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