[SI-LIST] How they measure true RMS

  • From: Doug Brooks <doug@xxxxxxxxxx>
  • To: si-list@xxxxxxxxxxxxx
  • Date: Mon, 15 Dec 2003 15:42:06 -0800

I was in Sears today and saw a very nice digital multimeter with * TRUE RMS 
* AC capability for $69.00  That got me thinking about HOW they measure 
true RMS value. In the old days they passed the waveform through a resistor 
and measured the heat. Can a $69 multimeter have enough processing power to 
be truly sampling and integrating the waveform to get the true RMS value? 
Or do they use some other technique?

Just wondering if anybody knew (the salesperson in the store, of course, 
didn't even understand the question!!)


Doug Brooks' new book, "Signal Integrity Issues and Printed Circuit Board 
Design" has just been released by Prentice Hall. See details and ordering 
info at www.ultracad.com
Also look for UltraCAD's new differential impedance calculator on the same 

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