Why measure Conductivity?
It can be used as a fairly inexpensive and low maintenance indicator of water quality. Good quality water with little contaminants will have a low conductivity. There is far less maintenance than pH and minimal calibration. Conductivity is used in Boiler feedwater, RO, and Demineralizer applications.
Since conductivity, up to a point, increases with an increase in the concentration of the ions in the process, we can use it to correlate to a % concentration value of solutions such as acids or bases. Again, since conductivity is non-specific, % concentration can only be measured on ONE chemical at a time and not a mixture of contributing chemicals.
There are two basic sensor styles used for measuring Conductivity: Contacting and Inductive (Toroidal, Electrodeless).
When Contacting Sensors are used, the conductivity is measured by applying an alternating electrical current to the sensor electrodes (that together make up the cell constant) immersed in a solution and measuring the resulting voltage. The solution acts as the electrical conductor between the sensor electrodes.
The accuracy of conductivity measurements can be influenced by the following factors:
- Contamination: Deposits or coating on the electrode surface of a 2-pole cell have a similar effect to polarization errors, i.e. the conductivity reading is lower than usual. These effects can also be prevented with a 4-pole conductivity cell.
- Cable resistance: The cable resistance can induce error in the measurement and must be taken into account.
- Temperature: Conductivity measurements are temperature dependent, if the temperature increases, conductivity increases.