Ode
At 10:11 AM 4/28/2005 -0500, you wrote:
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The conductivity of a solution depends on the numner of positive and negative ions (cations and anoins) that the solution contains and their relative electricl strenght. It is also temperture dependent. The PPM referes to the parts per million of any ONE soluble molecule. [any number of atoms or molecules as compared to the weight of a volume of the water it's in, be it in solution OR in suspension, whether it contributes to conductivity or not.<<<<
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It is a measure of concentration, while the conductivity is an electrical measurement. They are not related in any way, except that if you have a solution of a single known ion, the conductivity can be calculated.<<<<
Or any known ions and cations in solution, but the calculation changes. PPM/TDS meters generally use a fudge factor for 'saline' to calculate conductivity into a PPM figure in salt water. Usually a factor of 2 is used but can also range from x 1.2 up to x 2 depending on what substance is suspected to be in the water and who made the meter for what purpose. Particles in suspension ..not dissolved..don't register at all.
That said, in weak purely ionic CS, a meter that reads right in saline might read a slightly higher PPM than it actually is.
If the CS is strong with a lot of suspended particles, the meter will read slightly lower than what the PPM actually is.
I find [approximately] a 1 uS rise in conductivity per 10 degree F rise in temperature.[ within a 0 to 25 uS range of a "PWT"]
A meters temperature compensation doesn't adjust for the temperature of the solution. It adjusts for the temperature of the meter. [Just try and get Hanna Tech to admit that]
To get a more accurate reading and to prevent the meter readout from "hunting", store the meter and the solution in the same place for a while so they'll both be the same temperature and don't hold the sample [or meter] tightly in your warm hand.
..especially when using a Hanna sachet of calibration solution..The sachet is highly thermally conductive and will mess up calibration attempts badly if it's held in your hand while adjusting the meter.
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regards<<<<
FCR
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