Conductivity can be measured either by the 2-AC bipolar method or electromagnetic induction method. The bipolar method measures the current that passes through the solution between a pair of electrodes. The electromagnetic induction method measures the induction current generated by two coils immersed in the solution.
Conductivity meters that use the bipolar method have a simple structure, allowing the creation of a compact measurement system. They are also good for measuring low-conductivity aqueous solutions such as pure water. However, they cannot be used to measure samples that stain or dissolve electrode surfaces, such as highly-concentrated acids and alkaline solutions.
In conductivity meters that work by the electromagnetic induction method, corrosion-resistant materials such as plastics can be used for the parts that become wet, and these meters are good for measuring highly-concentrated acids and alkaline solutions. However, they are not suitable for measuring low-conductivity aqueous solutions such as pure water.
Diagram illustrating the 2-AC bipolar method
Diagram illustrating the electromagnetic induction method
Relation page The Basis of Conductivity