Definition
An online TDS detector is an analytical instrument used to monitor the total dissolved solids content in liquids in real time. Total dissolved solids refers to the total amount of inorganic salts and small amounts of organic matter dissolved in water, usually expressed in mass concentrations in milligrams per liter or ppm. The instrument continuously measures process liquids and feeds the data back to the control system, making it suitable for industrial and experimental scenarios where continuous monitoring of water quality or solution concentration is required.
Principle
The online TDS detector is mainly based on the conductivity measurement principle. Since ions dissolved in water enhance the conductivity of the solution, and the conductivity is correlated with the ion concentration under certain conditions, the TDS value can be indirectly derived by measuring the conductivity of the solution. The instrument usually uses an electrode sensor, and its measurement process conforms to the conversion relationship between conductivity and TDS: TDS = k × EC, where EC is the conductivity value and k is the conversion coefficient, which varies according to the composition of the solution, generally between 0.5 and 0.8. The instrument is internally corrected by a temperature compensation circuit to correct the effect of temperature on conductivity to improve measurement accuracy.
Measurement method
In-line TDS detectors typically use direct immersion or flow-through installations for continuous measurement. The sensor is in direct contact with the liquid being measured, and the instrument applies an AC voltage through the excitation electrode, measures the resistance of the solution and converts it into a conductivity value, and then calculates the TDS concentration according to the preset conversion factor. The measurement signal is processed by analog or digital and output as a standard current signal or digital communication. Some instruments support multi-point calibration, using standard solutions to calibrate the measurement range to meet the measurement needs under different application conditions.
Influencing factors
The measurement results of the online TDS detector are affected by a variety of factors. Changes in the temperature of the solution will cause changes in conductivity, so the instrument needs to have a temperature compensation function. There are differences in the conductive properties of different ionic components, and changes in the composition of the solution may lead to deviations in the conversion coefficient. Contamination or fouling of the sensor can interfere with the distribution of the electric field, affecting measurement accuracy and requiring regular maintenance and cleaning. Fluctuations in fluid flow rate and pressure can affect the stable contact of the sensor. In addition, environmental conditions such as installation location and mode, electromagnetic interference and other environmental conditions may also have a certain effect on signal acquisition.
Applications
Online TDS detectors are widely used in process monitoring and control in many fields. In drinking water treatment and water supply systems, it is used to monitor the quality of water after purification. In the water monitoring of industrial boilers, water quality changes can be reflected in real time. Ultrapure water preparation processes in the electronics industry are used to monitor ion removal effects. In the food and beverage production process, it is used to monitor the concentration of raw material water and finished products. In agricultural irrigation and hydroponic systems, it is used to monitor nutrient solution concentrations. The field of environmental monitoring can be used for continuous observation of surface water and discharged water. These applications rely on real-time data from the instrument to support process decisions.
Selection considerations
When selecting an online TDS detector, multiple technical parameters need to be comprehensively considered. The measurement range should cover the concentration variation interval in practical applications. Choose the appropriate sensor material and protection level according to the installation environment, such as corrosion resistance or explosion protection requirements. The output signal type needs to match the existing control system. The temperature compensation range and accuracy should meet the requirements of working conditions. Long-term instrument stability and maintenance cycles are also important considerations. In addition, ease of calibration, response time, sensitivity to changes in flow rate, and adaptability to installation methods should be evaluated. During the selection process, relevant industry standards and specifications should be referred to to ensure that the instrument meets the technical conditions of specific application scenarios.