Method for Measuring the Conductivity of a Solution Excited by Two Frequency Sine Wave Superposition Signals

Abstract

The invention discloses a measurement method of the electrical conductivity of a solution stimulated by sine wave superimposed signals of two frequencies. Two sine wave superimposed signals are used to stimulate an electrode. Electrode response current is filtered through two channels. One channel carries out low pass filtering to precipitate a sine wave signal of a low frequency component. The other channel carries out high pass filtering (or band pass filtering) to precipitate a sine wave signal of a high frequency component. Amplitude and phase detection are respectively carried out on the sine wave signal of the low frequency component and the sine wave signal of the high frequency component, wherein the signals are precipitated by two channels. By combining the parameters of the stimulating signals and detected amplitude and phase of the response current with an electrical conductivity cell equivalent physical model, a joint equation is listed and is solved to acquire Rx, wherein the resistance Rx of the solution to be measured, the electrode distribution capacitance Cp, the electrode polarization impedance, the double electrical layer capacitance Cx of the electrode are unknowns of the joint equation. Electrode constants are combined to calculate the electrical conductivity of the solution. According to the technical scheme, the effects of the electrode distribution capacitance, the electrode polarization impedance and the double electrical layer capacitance of the electrode on measurement can be removed.

Description

technical field [0001] The invention relates to a method for measuring the conductivity or resistivity of a solution, in particular to a method for measuring the conductivity of a solution excited by two frequency sine wave superposition signals. Background technique [0002] The basic measurement method of solution conductivity is to measure the voltage U applied across the electrodes placed in the solution. D and the current I flowing through the electrodes, calculate the resistance R=U between the electrodes D / I, use G=K / R to calculate the conductivity of the solution, where K is the electrode constant. However, the electrode placed in the solution will be polarized after being energized, so that the measured voltage U D In essence, it is not the voltage across the solution itself, but the voltage applied to the two virtual electronic devices in series, the solution resistance and the electric double layer capacitance involving the solution / metal electrode interface pr...

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Problems solved by technology

According to the research results of electrochemical analysis, the element Z described in the above patent method M / F1 It is equivalent to the electric double layer capacitance of the electrode connected in parallel after the electrochemical polarization resistance is connected in series with the concentration polarization impedance (electrochemical polarization resistance, concentration polarization impedance, and the electric double layer capacitance of the electrode are all related to the solution / metal electrode interface process For the equivalent circuit parameters, see the literature: Song Xiaoping. LCR bridge equivalent circuit selection for JONES conductivity cell measurement. [J]. Chemical Analysis and Metrology, 2004,13 (6): 81-82), in the use of AC excitation And the concentration polarization impedance can be ignored when the measurement voltage is not very high, and the electrochemical polarization resistance is much larger than the capacitive reactance of the electric double layer capacitance of the electrode when the frequency of the AC excitation signal is high enough, so when the condition satisfies In the case of , the equivalent circuit parameters of the solution / metal electrode interface process are generally replaced with a capacitor, that is, the electric double layer capacitance of the electrode, so that the electric double layer capacitance of the electrode is also completely equivalent to the element Z described in the above-mentioned patent method. M / F1 , but according to the research results of electrochemical analysis, there is no basis to prove that the electric double layer capacitance of the electrode has nothing to do with the frequency of the excitation signal

Therefore, the equivalent physical model of the conductance cell involved in the above-mentioned patented method has theoretical deficiencies and is not suitable for precise measurement. This method is only suitable for the parameters indicating the degree of polarization caused when the electrodes are excited by more than two frequencies. situation

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