"negative" resistivity

[Ben]

Hi,

I'm measuring the AC resistivity of a number of parts (capacitors,
actually). Obviously the apparent resistivity decreases with
increasing frequency; however, in certain cases with a certain type of
component I get low resistivity at the high frequency end and
_negative_ resistivity at the low frequency end. I know that this is
bull; however, I don't know why my meters (an agilent 4263B and an
analyser made by somebody else, if that matters)are reading negative.
What does this negative number actually mean ?

thanks for your opinions
Ben

 

[Fred Bartoli]

"Ben" <b_whittle@hotmail.com> a écrit dans le message news:
27053eab.0402250809.5358883@posting.google.com...

Hi,

I'm measuring the AC resistivity of a number of parts (capacitors,
actually). Obviously the apparent resistivity decreases with
increasing frequency; however, in certain cases with a certain type of
component I get low resistivity at the high frequency end and
_negative_ resistivity at the low frequency end. I know that this is
bull; however, I don't know why my meters (an agilent 4263B and an
analyser made by somebody else, if that matters)are reading negative.
What does this negative number actually mean ?

Your cap is becoming inductive. Or better said, the series inductance of
your cap has its impedance becoming greater than the one of your cap :

j L w > 1/(j C w) when w rises.

BTW one don't speak of AC resistivity but impedance (ac generalization for
resistance) and its reciprocal is admittance.


Fred.