Who cares where Sanjay was trained?  I've  met some real morons in my day
that hold college degrees from reputable colleges.
Aren't we talking about the sensitivity of the circuit used to make the
measurement and the power dissipation/efficiency of any impedance
transformation device used.  A traditional analog meter uses 10kohms/1volt.
This why the older SAMS circuits gave voltage reading points with the "load"
of the meter taken into account.  A modern digital multimeter (DMM) has a
sensitivity of 10megaohms/1volt, I've even seen one with 20mohms/volt once.
Another classic example is RF current meters in transmitters.  Certainly an
RF current meter inserted in a transmission line path will not require 5% of
the radiated power.  If this was so, a 1.5kw transmitter would lose 25watts
to the meter and it would require a small heatsink. If the analog meter
movement was replaced with a digital readout that had an active power
supply, would it suddenly require 5% of the radiated power?  I've never seen
a heat dissipating RF current meter in my life.     The earlier idea of
winding a transformer seems to have much more merit to  me than to give up
5% of the power.
 > Hi Sanjay, sorry I don't know where you were trained,
> but I was taught that to get good reliable measurements
> of "active" signals you need to allow 2% to 5% of the
> total for the measurement equipment. You mention a
> sense resistor of 1 milliohm, this is ridiculous. I have
> a good milliohm meter, and any electrical connnection will
> give you a few milliohms resistance. Your sense resistor
> will have two of these connections.
>
> My suggestion for good accuracy is to sacrifice 5% of
> your total power to the subwoofer load and use that
> to measure the current waveform, then of course allow
> for that 5% in your calcs. Don't ever expect accurate
> results from a 1 milliohm resistor!!
> :o)
> -Roman
>
>
>
> > ----- Original Message -----
> > From: "Sanjay Punjab" <piclistguy@YAHOO.COM>
> > To: <PICLIST@MITVMA.MIT.EDU>
> > Sent: Sunday, July 29, 2001 7:07 AM
> > Subject: [EE]: Having difficulty interfacing a current sense resistor to
> > create a proportional voltage
> >
> > > I have an application where I need to monitor and
> > > digitize the current waveform output of an audio power
> > > amplifier into a subwoofer (speaker).
> > > Previously, I used a hall-effect based sensor, but for
> > > cost purposes (consumer product), it is impractical.
> > > So instead, I have decided to use a 1 milli-ohm
> > > current sense resistor. The problem now is creating an
> > > electrical interface...
>
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