Study On TDS Measurement System Of Aqueous Solution

The total dissolved solids(TDS)refer to the total amount of solid that can be dissolved in one liter of water.The determination of TDS in aqueous solution is of great significance to water quality monitoring.When the TDS value in domestic water is large,it indicates that the mineral content in the water is too high.This is not only detrimental to human health,but also shortens the life of the water pipe.Therefore,there is strict requirement on the value of TDS in the "drinking water health standards",its value cannot exceed 1000 mg/L.Methods for measuring TDS in aqueous solutions are weighing method and electrode method.Weighing method is obtained by drying the solid residue and then weighing the quality.Electrode method is to measure the conductivity of the solution and calculate the TDS value by the use of the conductive properties of soluble solids in water.Electrode method is more convenient and more accurate weighing method,so the method of measuring TDS is mainly based on the electrode method;this article will also obtain TDS value by the use of electrode method.In this paper,TDS of aqueous solution measurement system is designed according to the measurement requirements.The measuring range is 0-1200 mg/L.The excitation source amplitude can be adjusted in the range of 0-10.2375 V.The frequency adjustable range is 5-2000 Hz.The factors that affect the accuracy of the electrode method in the measurement process are mainly polarization effect and temperature.This paper takes full account of these two points in the design system.Hardware is designed based on ATmegal28 chip.The excitation source selects the bipolar square wave signal to reduce the polarization effect.In the data acquisition design we propose a synchronous sampling circuit scheme in order to simplify the A/D and conversion process and improve the measurement accuracy.And we add the temperature compensation circuit.Software design is closely to the hardware system of the synchronous sampling circuit,the use of PWM(pulse width modulation)function can accurate control of timing,and we use LabVIEW to build data display and storage platform.On the basis of the realization of the TDS measurement system,we have carried out the system error measurement experiment.The experiment shows that the system error can be controlled within 2%and the stability is good,and the error source is analyzed according to the experimental data.In addition,we changed the amplitude and frequency to measure TDS respectively,and amplitude and frequency have an impact on the measurement accuracy according to the experimental data.Then we propose the suggestion for the excitation source signal parameter setting,which provides some reference for TDS measurement system design in the future.