Device for Measuring NaCl Concentration in Water Based on a Conductometric Sensor
DOI:
https://doi.org/10.31649/1997-9266-2025-181-4-17-21Keywords:
conductometric sensor, NaCl, Wheatstone bridge, circuit, ion concentration, calibration, electrodes, temperature compensationAbstract
The article presents modern approach to determining NaCl concentration in water, using a conductometric sensor that combines classical electrochemical methods with advanced circuit design and mathematical modeling solutions.
Key component of the measuring device is a coaxial conductometric sensor with flat electrodes capable of forming a stable electric field for accurate measurement of solution conductivity. The sensor operation is based on the direct relationship between conductivity and the concentration of dissolved ions, particularly Na⁺ and Cl⁻. The device is also equipped with a temperature sensor (a hermetically sealed thermistor), which enables automatic temperature compensation by accounting for changes in ion mobility at different temperatures.
Detailed mathematical model has been developed to describe the dependence of conductivity on ion concentration, temperature, sensor geometry, and ionic molar conductivity. In particular, it has been shown that the temperature increase by one degree Celsius leads to 2…3 % rise in conductivity, justifying the need for temperature correction.
Wheatstone bridge circuit is employed to sensitively detect changes in resistance associated with variations in salt concentration. The resulting analog signal is processed by an operational amplifier and then converted into a digital form using an ADC. The relationship between the sensor's output voltage and NaCl concentration is analytically modeled and supported by numerical simulations.
Sensor calibration is performed using Milwaukee standard solutions certified according to NIST standards. Metrological evaluation confirmed high accuracy, with a relative error of only 1.46 % at a concentration of 342 ppm.
The developed device is characterized by a simple design, accessible component base, and suitability for both laboratory and field applications. The proposed solution holds promise for integration into automated water quality monitoring systems, particularly in agriculture, industry, and healthcare.
Future research directions include enhancing the sensitivity element through microstructuring of the electrodes, expanding the measurement range via automatic scaling, implementing wireless interfaces for remote monitoring, introducing self-calibration algorithms, and extending functionality to multi-ion analysis in real water systems.
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