What is Conductivity? Electrolytic conductivity is a measure of the ability of a solution to carry an electrical current. Current flow in liquids differs from that in metal conductors in that electrons cannot flow freely but must be carried by ions. When solids dissolve in water they separate into ions which have opposite electrical charges. For example, sodium chloride separates to form Na+ and Cl- ions, however since they are invisible, it is difficult to know how much of it has dissolved. A conductivity sensor measures the concentration of ions in a solution by the electrical current able to flow through it.
Electrical conductivity can therefore be used as a measure of the concentration of ionized solids present in the sample. Conductivity units are, by convention, Siemens/cm, or more commonly microSiemens/ cm (µS/cm). Very pure water has around 1µS/cm, nice drinking water about 50 to 500µS/cm, and seawater around 55,000µS/cm.
Most industrial Conductivity applications use conductivity to quantify the level of impurities in a solution and to then adjust these levels via the addition of reagents or by the diversion or dilution of these impurities. The most common application is to monitor waters for suitability for a purpose, such as assessing the purity of condensate before returning it to a boiler, or alternatively, sending it to be purified in demineralizers or reverse osmosis systems. Also, Conductivity is used to monitor dissolved solids levels to control blowdown or dilution with fresh water to avoid scale formation which reduces heat transfer efficiency. Common applications include, cooling tower blowdown, boiler blowdown, purity monitoring for a specific purpose, demineralizer, reverse osmosis, desalination, salinity, TDS (Total Dissolved Solids), and concentration control of NaOH, H2SO4, HCl, or NaCl. As well as monitoring incoming raw water dissolved solids purity, and effluent water dissolved solids compliance.
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