Accurate monitoring of water quality and solution composition is crucial in various fields of human production and life. From drinking water safety to industrial production process control, from ocean resource development to battery performance optimization, conductivity sensors are playing the role of "invisible guardians" and providing indispensable technical support for these key links.

Working principle of conductivity sensor

The working principle of conductivity sensors is based on the ion conductivity characteristics of solutions. There are freely moving ions in the solution, which will undergo directional movement under the action of an electric field, forming an electric current. The conductivity of a solution is related to the type, concentration, and temperature of the ions it contains.

Conductivity sensors are typically composed of two or more electrodes made of metal or graphite. These electrodes are inserted into the test solution to form a closed circuit. The sensor also contains electronic components such as signal processing circuits and amplifiers, which are used to convert the measured weak signals into readable conductivity values.

When a certain DC or AC voltage is applied to a pair of electrodes of the sensor, an electric field is generated in the solution. Under the action of an electric field, positive and negative ions in the solution move in opposite directions, forming an electric current. By measuring the current intensity flowing through the circuit, the conductivity of the solution can be indirectly reflected. According to Ohm's law (I=V/R), combined with known electrode spacing and cross-sectional area, the conductivity of a solution can be calculated.

In practical applications, sensors usually have built-in calibration coefficients and temperature compensation functions to ensure the accuracy of measurement results. Because the conductivity of a solution increases with temperature, it is necessary to consider the influence of temperature and make corresponding corrections when measuring conductivity.

Classification of Conductivity Sensors

According to different measurement principles and methods, conductivity sensors can be divided into electrode type conductivity sensors, inductive conductivity sensors, and ultrasonic conductivity sensors.

Electrode type conductivity sensor: Based on the principle of electrolytic conductivity, resistance measurement method is used to measure conductivity. The conductivity measuring electrode exhibits a complex electrochemical system during the measurement process. The two electrode conductivity sensor consists of a pair of electrodes, and a constant voltage is applied to the electrodes. The change in the resistance of the liquid in the conductivity cell causes a change in the current of the measuring electrode, which conforms to Ohm's law. Conductivity is used instead of resistivity, and conductivity is used instead of resistance in the metal to achieve the measurement of liquid conductivity. However, when measuring conductivity with two electrodes, under the action of excitation voltage, the electrodes will electrolyze the solution, forming a potential opposite to the direction of the applied voltage, increasing the equivalent resistance of the measured solution and causing polarization phenomenon. The four electrode conductivity sensor uses two pairs of coaxial current electrodes and voltage electrodes. During the measurement process, the two pairs of electrodes are placed in the measured solution, and an AC signal is applied to the current electrodes. A current is transmitted from the current electrodes to the measured solution, and the measured solution will generate an electric field. At this time, the two voltage electrodes generate voltage, keeping the voltage at both ends of the voltage electrodes constant. The conductivity of the measured solution is calculated by the linear relationship between the current between the current electrodes and the liquid conductivity. Due to the separation of the excitation electrode and the measurement electrode, the polarization effect of the two electrodes is effectively avoided.

Inductive conductivity sensor: based on the principle of electromagnetic induction, it measures the conductivity of liquids. The detector does not directly come into contact with the measured liquid, so there is no problem of electrode polarization or electrode contamination. Its measurement range is 1000-2000000 μ S/cm, with strong anti pollution ability and corrosion resistance. There is no electrode polarization or capacitance effect, and it can be used for high conductivity liquid measurement. The structure is simple, easy to use, and the manufacturing process is simple.

Ultrasonic conductivity sensor: measures conductivity based on changes in ultrasonic waves in liquid.

Among them, electrode type and inductor type conductivity sensors are the most widely used.

Application fields of conductivity sensors

· Laboratory and research fields: widely used in water quality analysis, solution concentration monitoring, and control of chemical reaction processes. Researchers use conductivity sensors to accurately measure the conductivity of various solutions, in order to understand the ion concentration and chemical reaction process in the solution. This is of great significance for experimental research in fields such as chemistry, biology, and environmental science.

· Power industry: used to monitor the conductivity of cooling water and boiler water to ensure that the water quality meets the requirements for equipment operation. High conductivity water may cause equipment corrosion and scaling, affecting the performance and lifespan of the equipment.

· Chemical production: used to monitor the conductivity of various chemical reaction solutions to control the reaction process and product quality. For example, in electrolytic oxygen and hydrogen production facilities, conductivity sensors are used to monitor water quality and ensure the smooth progress of the electrolysis process.

· Food processing: used to monitor the conductivity of cleaning water and solutions during processing to ensure the hygiene and safety of food. High conductivity water may contain excessive impurities and microorganisms, which can affect the quality and safety of food.

Environmental protection field

· River water quality monitoring: widely used for water quality monitoring of natural water bodies such as rivers and lakes. By measuring the conductivity of water bodies, the ion concentration and pollution level in the water can be understood, providing important data for environmental protection and water resource management.

· Industrial wastewater treatment: used to monitor the conductivity of wastewater to evaluate the effectiveness of wastewater treatment. By reducing the conductivity of wastewater, the discharge of harmful substances in the wastewater can be reduced, protecting the environment.

· Drinking water treatment: used to monitor changes in water quality before and after treatment during the drinking water treatment process. By measuring the conductivity of drinking water, the ion concentration and impurity content in the water can be understood, ensuring the safety and hygiene of drinking water.

· In the field of ocean research and development, it is used to measure the conductivity of seawater to understand parameters such as salinity, temperature, and density. These parameters are of great significance for the exploration of marine resources, monitoring of marine environment, and research on marine ecosystems. For example, in the deep-sea temperature and salinity profiling recorder, conductivity sensors are used to measure the conductivity and temperature of seawater to understand the vertical structure and circulation patterns of the ocean.

· Other fields: In addition to the above-mentioned fields, conductivity sensors are also widely used in the battery industry, semiconductor industry, agricultural irrigation, and groundwater monitoring. In the battery industry, conductivity sensors are used to monitor the conductivity of the electrolyte in the battery to ensure its performance and lifespan. In groundwater monitoring, conductivity sensors are used to measure the conductivity of groundwater to understand its quality and pollution level.

Source: Sensor Expert Network