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nimal
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Water Measurement

03/09/2012 11:55 PM

how to measure water resistance using ohm meter
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lyn
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#1

Re: water

03/10/2012 12:06 AM

Set your meter to millisiemens and measure it.
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SolarEagle
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#2

Re: water

03/10/2012 12:20 AM

http://www.ehow.com/how_5052989_use-test-water-conductivity-purity.html

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lyn
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#3
In reply to #2

Re: water

03/10/2012 12:36 AM

ehow?
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SolarEagle
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#4
In reply to #3

Re: water

03/10/2012 9:42 AM

"When the ionic concentration is very low (such as in high purity water), the measured conductivity falls below a value of one micro Siemens per centimeter. In order to express these numbers as whole numbers as opposed to fractions, the resistivity scale is often used. The numbers are exactly the inverse of each other. For example: the reciprocal of 0.10 µS/cm [or 1/(0.10 x 10-6 S/cm)] is then 10 x 106 ohms-cm (10 MΩ-cm). This is also commonly referred to as "mega-ohms". Either unit of measurement can be used to state exactly the same value. Commonly the conductivity scale is more versatile as it can be used for a broader range of measurements. "

http://www.mbhes.com/conductivity_measurement.htm

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SimpleMind
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#5

Re: water

03/10/2012 12:02 PM

Well, one way NOT to measure it, is with different material electrodes. S.M.

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StandardsGuy
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#6

Re: water

03/11/2012 1:13 PM

For what purpose?

I have tried to use distilled water as a dielectric. It gets more conductive each day when exposed to air. Don't ask me why.

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Mikerho
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#7
In reply to #6

Re: water

03/12/2012 10:55 AM

Absorption of CO2 → Carbonic acid.

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Mikerho
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#10
In reply to #7

Re: water

03/12/2012 9:43 PM

I should have said more clearly: "Left exposed to the atmosphere, water will continue to absorb CO2 from the surrounding air until it reaches equilibrium (the maximum solubility of CO2 in water at the ambient temperature)".

CO2 + H2O ↔ H2CO3 (acidic)

This will lower the pH and increase the conductivity.

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Carl_E
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#8

Re: Water Measurement

03/12/2012 9:08 PM

Stick the ohm meter probes into the water solution and read the resistance. Take the reciprocal for conductance.

But do not kid yourself that the (reciprocal of the) resistance measurement is the same as a conductivity measurement.

A conductivity analyzer the OP mentioned is a specific instrument designed for analytical conductivity measurements.

The basic unit of conductivity measurement is the siemens (S), formerly called the mho.

However, cell geometry affects conductivity values, so standardized measurements are expressed in specific conductivity units, S/cm for analytical measurements. S/cm compensates for variations in electrode dimensions.

Specific conductivity (C) is simply the product of measured conductivity (G) and the electrode cell constant (L/A), where L is the length of the column of liquid between the electrode and A is the area of the electrodes.

The nature of analytical measurements is that conductivity of solutions varies (dramatically in many cases) with temperature, so analytical conductivity measurements made by conductivity analyzers are corrected to a standard temperature (typically 25°C) by temperature compensation.

So can you read ohmic value of a solution with an ohmmeter? Yes, you can.

Is the ohmic reading from an ohmmeter temperature corrected to the standard solution temperature of 20°C? No.

Does the ohmic reading from an ohmmeter account for the geometry of the measuring probes? It does inherently, but the value is NOT in units of 'specific conductivity' in S/cm.

In summary,

conductivity = S

analytical conductivity = S/cm with temperature compensation

So, take your resistance measurement with an ohmmeter, convert to conductance, but don't fool yourself into thinking that it is temperature corrected specific conductivity in units of S/cm, which is the measurement that a conductivity analyzer produces.
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#9
In reply to #8

Re: Water Measurement

03/12/2012 9:33 PM

And that gets a GA from me. The distinction is somewhat similar to the difference between resistance (units of Ω) and surface resistivity (units of Ω/square).

Every instrument has its sensor(s) with associated errors/deviation/nonlinearity/etc. Good designers know their behavior well and compensate/correct the instrument electronics and/or mechanism(s) to correlate to real/established values. It is not a trivial thing to develop an instrument that gives accurate and reproducible data!

I respect your knowledge in this field.

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