Solution Conductivity Measurement Method

Conductivity is a important chemical quantum.In the method of electrod conductivity measure, the measure electrode behave as a complicated electrochemistry system during measure.The factors that infect the precise measure of conductivity is polarization effect, capacitance effect and temperature.This paper gives a method to measure the conductivity base on choosing frequency.After adding to the electrode with two AC square waves of appropriate frequencies,we can measure the output DC voltage of the circuit. Then the time constant is computed through the equation set,thus the liquor resistance and conductivity is obtained.And the expression of the conductivity's computation is given out.The method is verified by circuit design and establishment of experimental scheme.This method eliminate effectively the effect that the distributed capacitance put on the conductivity measurement. Owing to the use of AC square wave with little amplitude value, the effect of polarization is depressed.The frequency can be adjusted continuously,so.the effect of the double electricity capacitance is depressed too.And the measurement is not affected by the amplitude values of the AC square waves using rule of three in computation,so the precision is promoted.The experiment results suggest that ,when the divider resistance is 100KD and the distributed capicitance is between 500-8000PF,the measurement error of liquor resiatance between 1k-lM is restricted under 1%.After the precise measure liquor conductivity under certain temperature ,the temperature compensation of conductivity is studied in this paper. The method of temperature compensation with single chip machine is studied emphasizedly.The method include polyfiting formula and consulting scheme.