Conductivity Sensor | Conductivity Probe

A conductivity sensor, also known as a conductivity probe or an in-line conductivity electrode, is an analytical instrument that measures the ability of a solution to conduct an electrical current. It is the presence of ions in a solution that allow the solution to be conductive: the greater the concentration of ions, the greater the conductivity. In some applications the purity measurement is made as resistivity (the reciprocal of conductivity). 

There are three technology types of METTLER TOLEDO conductivity sensors and conductivity probes used for process conductivity measurement:

• 2-electrode conductivity sensor
• 4-electrode conductivity sensor
• Inductive conductivity sensor

A METTLER TOLEDO conductivity sensor and conductivity probe can be calibrated against a solution of known conductivity (much like calibrating a pH sensor against a solution of a known pH). Alternatively, an in-line conductivity probe that contains a range of very precise resistors that duplicate known conductivity measurements can be used.

In general, the cell constant of the in-line conductivity electrode will not change; however, if the sensing elements are altered in some way (e.g. solid deposition or other fouling of the electrodes or insulator of the sensor, loss of electrode material through corrosion) the cell constant will change. METTLER TOLEDO conductivity sensors are factory calibrated and the cell constant is precisely determined. Therefore, calibration is typically not required while using the in-line conductivity sensor. However, it is recommended to verify the conductivity sensor or make calibration adjustment if necessary on an annual basis. The frequency of verification or calibration is very much dependent on the applications or on the plant standard operating procedure requirements.

Conductivity is strongly temperature dependent. As the temperature of a sample increases, the viscosity of the sample decreases which leads to increased mobility of the ions. Therefore, the observed conductivity of the sample also increases even though the ion concentrations may remain constant.

In good practices, every conductivity sensor result must be specified with a temperature or be temperature compensated, usually to the industry standard of 25 degrees Celsius.