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

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From: Hans Mellberg (emcconsultant@yahoo.com)
Date: Mon Oct 25 1999 - 18:16:14 PDT


The temperature effect on a heating resistor is a
function of the RMS current and not the average
current. I mention "function of" rather than
"proportional to" because the temperature of the
resistor, besides (i(rms)^2)*R heating, depends on:
ambient temperature, airflow, surface emissivity
(area, material, surface, etc.), and black body
radiation.

A true rms watt meter is a thermocouple type in a
pseudo calorimeter. The more elaborate power meters
such as those used to measure RF energy at GHz
frequencies are pretty close to true calorimeters.

The highest frequency able calorimeter operates in the
200 GHz range used to measure output power of
transmitters operating in that range.

 

=====
Best Regards
Hans Mellberg
EMC Consultant
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