[Elecraft] Your Farm's Soil Electrical Conductivity

[Stephen Prior]

I hope nobody minds....because...

I'm jumping in here without having really followed this thread, but I can
comment on this.

Bill is right that 17 mmho/cm is not equal to 17 mS/m, as you say it should
be /cm, not /m.

The unit is confusing however, and bears no relation to a per cm or per m at
all in the usual way that we think of these units.

It starts with the definition of resistivity which has the units of ohm
metres.  Many people interpret that as ohms/m, but it's not- that would be a
resistance per unit length and is entirely different.

Since conductivity is the reciprocal of resistivity, the units of
conductivity become /ohm/m or mho/m or S/m, to use the SI unit.  As I said
above, it's just a unit and does not imply a 'per unit length' at all.

One formula for conductivity would be:

Conductivity = (conductance x length)/area

And it is simply the fact that we have a length divided by an area that
gives us the /m bit of the unit.  The advantage of using the concept of
conductivity is that it yields a number which does not refer to a particular
sample of material of a certain size, but refers only to a property of the
material itself.  Rearranging the formula above then allows you to find the
conductance of a particular sized sample of that material/soil whatever..

Anyway, the aforementioned conversion is wrong- a slip of the keys no doubt!

Hope that helps

73 Stephen G4SJP  


On 22/04/2008 14:59, "Bill W5WVO" <w5wvo at cybermesa.net> wrote:

> Steve wrote:
> 
>> 15) Use the millimhos/centimeter number as mS/m.
>> Thus, 17 millimhos becomes 17 mS/m. This is the
>> electrical conductivity of your Fresnel Zone.
> 
> Given that 1 mho = 1 Siemens, then how does 17 mmho/cm (given by the tool)
> equate to 17 mS/meter? The denominator unit is different. And is the distance
> linear or area? Obviously this is just my ignorance about this, but I don't
> get it. Somebody explain please?
> 
> Bill W5WVO


On 22/04/2008 14:59, "Bill W5WVO" <w5wvo at cybermesa.net> wrote:

> Steve wrote:
> 
>> 15) Use the millimhos/centimeter number as mS/m.
>> Thus, 17 millimhos becomes 17 mS/m. This is the
>> electrical conductivity of your Fresnel Zone.
> 
> Given that 1 mho = 1 Siemens, then how does 17 mmho/cm (given by the tool)
> equate to 17 mS/meter? The denominator unit is different. And is the distance
> linear or area? Obviously this is just my ignorance about this, but I don't
> get it. Somebody explain please?
> 
> Bill W5WVO
> 
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