Method and key circuit for measuring solution conductivity through triangular wave excitation and integral processing

Abstract

The invention discloses a method and a key circuit for measuring solution conductivity through triangular wave excitation and integral processing. The method comprises the following steps of: exciting an electrode by using a triangular wave voltage signal with amplitude U and period 2T, integrating excitation voltage and electrode response current at two integral intervals of [t1, tm] and [t1, t2] at any two different moments t1 and t2 and a middle moment tm of the two moments of an upper band or a lower band of the excitation signal, and calculating solution resistance Rx according to one of two formulas shown in the specification; or solving the conductivity by using G=K / Rx, wherein K is electrode constant. According to the technical scheme, a circuit for integrating an excitation voltage signal and a current signal responded by the electrode is also provided. According to the scheme, the influence of distributed capacitance of the electrode is completely eliminated, influence of random interference on a measuring accuracy can be eliminated, and the measuring stability is high.

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 or resistivity of a solution using a triangular wave as an excitation signal. 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, and then 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 two virtual electronic devices in which the solution resistance is connected in series with an electric double layer capacitance involving the solut...

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Problems solved by technology

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 two virtual electronic devices in which the solution resistance is connected in series with an electric double layer capacitance involving the solution / metal electrode interface process, so the formula R=U D There is a theoretical error in / I; in order to reduce the influence of electrode polarization on measurement accuracy, the basic method is to apply an AC excitation signal with positive and negative polarity symmetry on the electrode, but under the action of the AC excitation signal, the measured current I does not It is not the current that simply flows through the solution, but the total current that flows through the branch of the solution resistance branch parallel electrode distributed capacitance (including the electrode inter-electrode capacitance and the electrode lead capacitance). Therefore, the AC excitation method is used to reduce the influence of electrode polarization. At the same time, the influence of electrode distributed capacitance on the measurement is introduced

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