At 05:36 AM 9/8/2011, you wrote:
>  I've been looking at the specifications for a domestic water heater and =
in
>the sales bumph they specify the minimum water resistivity required (2K795
>x inches or 1K1 x cm's). I've never seen such a specification before for
>this kind of water heater nor the unit resistivity per area/length.
>
>I can find no documents on the interrent apart from those referring to
>measurement devices for analytical purposes.

IME, water conductivity (the reciprocal of resistivity) is often used as a
measure of water purity (like TDS). The units are siemens/unit length (for
example uS/cm =3D 1/Mohm-cm).

Resistivity is rho, where R =3D rho * L/A in the measuring cell.
So rho =3D R * A/L, and you can see the units are ohms per unit length.

Impure water can corrode the system and will cause scaling to quickly build
up on the heaters, leading to poor heat transfer. They spec it so they can
void your warranty if your water quality sucks and kills their product
prematurely.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the rewar=
d"
speff@interlog.com             Info for manufacturers: http://www.trexon.co=
m
Embedded software/hardware/analog  Info for designers:  http://www.speff.co=
m



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