What is Conductivity?
Many industries and municipal processes utilize conductivity measurements to monitor the quality of process fluids and equipment. Conductivity values represent the ability of a solution, typically water and other materials, to conduct electric current. Measurement units of siemens per centimeter (S/cm) represent the current. For industrial processes, this unit is typically represented in milli- or microsiemens. The conductivity sensor detects the electrical current generated in the solution by the movement of ions. The magnitude of the current is proportional to the conductivity of the solution. Higher conductivity corresponds to a larger current, while lower conductivity corresponds to a smaller current. Using conductivity sensors provides a quick and reliable method for assessing a solution’s ionic concentration or purity in various industries, such as water treatment, chemical analysis, agriculture, and environmental monitoring.
Conductivity in the Field
Operators can use conductivity measurements for several purposes in a process depending on the particulars of the application. In various industrial applications, operators prevent corrosion through conductivity monitoring and control. Conductivity is also utilized in filtration applications in which monitoring ionic activity is extremely important for water or media quality. In other instances, high conductivity levels can also indicate general impurities and undesirable compounds present in water. Due to this, conductivity measurements are used in numerous applications that demand pure water and media.
Types of Conductivity Sensors
Manufacturers of conductivity sensors may tout different designs based on certain applications. Most conductivity sensors fall under two categories: contacting and inductive. These sensors’ anatomy differs, but their principle functions are the same.
Contacting
Contacting sensors utilize reference electrodes to obtain conductivity values. Operators using contacting conductivity sensors can have a 2-electrode or a 4-electrode sensor. We recommend 2-electrode sensors for processes in which conductivity values are relatively lower and change in value is minimal. In processes experiencing wider ranges of µS/cm, up to several hundred µS/cm, users are more likely to use 4-electrode sensors.
The measuring electrodes are in direct contact with the process media, hence the sensor’s name. Additionally, calibration of the sensors occurs based on the cell factor, which represents the geometric makeup of the two or four electrodes. This is determined by the distance between the electrodes and their surface area. Digital sensors store the cell factor, calibration information, and other valuable data in the sensor head. This means operators can disconnect the sensor and use it elsewhere without re-calibrating or reconfiguring the cell factor.
Inductive/Toroidal
Inductive or toroidal conductivity sensors utilize coils or toroids to obtain conductivity values instead of contacting electrodes. A strong plastic housing often encases the coils of the measuring element. In processes where the media is corrosive or otherwise aggressive, toroidal conductivity sensors are a common choice for operators. The flexibility of the plastic used retains excellent mechanical and chemically resistant properties under high temperatures.
Toroidal sensors have an even wider measuring range than most 4-electrode sensors, up to several thousand mS/cm. Due to their extensive measuring range, we do not recommend toroidal sensors for applications requiring more precise and stable conductivity values. Toroidal sensors are more appropriate for processes where these values fluctuate across wide ranges.
Maintaining Conductivity Sensors
Occasional sensor upkeep and maintenance significantly extend sensor life and keep process measurements accurate. The best practice for maintaining sensor performance with conductivity sensors is through occasional cleaning and constant cell adjustment. Keeping the electrodes and rings of conductivity sensors as clean as possible is the next best option. For processes with heavy suspended solids or aggressive media, ensuring the sensor is free of buildup or other debris is the best practice for keeping the sensor healthy.
