Conductivity: microsiemens converted to megaOhms

A. Sandie,

No, it is not a 1:1 conversion. Microesiemens are measuring conductivity, while megaohms are measuring resistivity. Go to:
www.peunh.com/peu/charts/cond.html ⇩
... there is a handy little conversion chart for you.

Hope this helped.

A. Hello,

It sounds like you are using two different measurements. The mV reading is probably ORP which is not directly related to conductivity. One can prepare solutions of identical conductivity but different ORP, for example.

Hope this helps,

A. Hi Alvaro. Robert is surely right that the units can't be "converted" because they are not the same thing (you can convert inches to centimeters but you can't convert inches to grams).

But I'm not sure that you'd be on the right track assuming that the previous study was investigating ORP (oxidation-reduction potential). I would guess that the previous researchers were also dealing with conductivity, but were measuring it using a voltmeter with a special probe, and that the millivolts on the meter scale did correspond with a specific conductivity ... but that you can only find that relationship within their report or the instructions for the probe they used.

Regards,

A. Sure, that's fine. Just make sure the water you're diluting with is pure enough so that it doesn't itself add any conductivity.

Standard Methods for the Examination of Water and Wastewater
AWWA

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A. Dilution is a standard procedure, also used in calibrating conductivity meters using KCl standard solutions. A correction can be made for the conductivity of the dilution water; see
'Standard Methods ...', (American Public Health Association, Washington, DC) ⇨
Using high purity diluent water (freshly boiled & cooled distilled water or good quality DI water, the error is usually negligible for samples having conductivities > 90 microSiemens/cm and within the pH range 6-9.

See also ASTM D1125, 'Standard Test Methods for Electrical Conductivity and Resistivity of Water.'

A. Osakwe, if you are reporting your results to a government entity you might want to explain to them your method and see if they'll accept it before charging into anything. Especially if it's something you have to sign your name too. Or obtain a meter with a larger range.

A. The likely cause is dissolved carbon dioxide gas. You need to check for this in your RO permeate. Since it is non ionic at the relatively low pH of RO permeate, it doesn't show as conductivity at this point. However, it does become ionic again near the exit point of an EDI stack, and if present in too high a concentration, will result in low resistivity in the treated water.

You my need to install a membrane de-carbonator before the EDI in order to achieve high resistivity water.

A. Virtually all of the popular conductivity or resistivity meters are accurate in this range, provided that they have temperature compensation.

However for water with a resistivity of > 5 Meg-Ohm-cm, you need a meter that is designed and calibrated for high purity water. Above this range of purity, the temperature compensation algorithm is different than it is for lower resistivities.

A. Hi Dirk. We appended your inquiry to a thread which explains that µS is an abbreviation for microSiemens which is a conductance unit and the reciprocal of megaOhms resistance. I.e., 1 µS = 1/megaohms; 2 µS = .5 / megaohms; .1 µS = 10/megaohms.

Regards,