Date: Tue, 13 Apr 1999 21:57:44 -0400 From: "mp" <pmalouf@iamdigex.net> To: cp@opus.hpl.hp.com Message-Id: <aabcdefg1332$foo@default> Subject: Re: Question on the conductivity meter
Wilson wrote:
>All right! I have a multimeter which measures voltage, resistance, and
>current. Can I use the multimeter to measure the resistance instead,
>since the unit of conductivity is mho which is 1/ohm? For instance, .5
>mho/unit volume = 20 ohm/unit volume?
The unit of resistivity is (ohm)(length). The unit of resistance
is ohm. Conductivity is indeed the reciprocal of resistivity which
means the unit of conductivity is 1/((ohm)(length)), or in common parlance,
mho/length. The unit of conductance is mho. More scientific circles
use the unit Siemens for conductance, Siemens/length for conductivity.
It is not correct to speak of ohm/(unit volume).
What are you trying to do with your ohm meter, measure the conductivity
of a water sample? You may be hard-pressed to do so accurately with
an ohm meter. A conductivity meter consists essentially of a special
ohm meter in tandem with a special probe. These probes have electrodes
whose surfaces are treated for the purpose of this measurement.
My (commercial )conductivity meter can measure 10 microSiemens/cm
to 19,990 microSiemens/cm, and I have to take care that the surface of
the probe's electrode plates do not become scratched or coated with
impurities.
So even if you did prepare a precisely dimensioned cell 1 cm on a side
that you could fill with a sample of water, you'd have a hard time using
an ordinary ohm meter to measure the conductivity--especially with the
probes that are commonly used to probe a circuit.
Regards,
Perry Malouf
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