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

Abstract

The invention discloses a method and a key circuit for measuring solution conductivity through triangular wave excitation. The method comprises the following steps of: exciting an electrode by using a triangular wave voltage signal with amplitude U and period 2T, sampling electrode response current i t2 and i t2 at two different moments t1 and t2 of an upper band (or lower band) of an excitation signal and calculating solution resistance Rx by using an equation that Rx is equal to an absolute value of 2U(t2-t1) / (T(i t2-i t1)); or sampling excitation voltage u t1 and u t2 at the same moment and calculating Rx by using an equation of Rx=(ut2-ut1) / (i t2-i t1); or detecting a change rate of the excitation voltage and a change rate of the electrode response current, dividing the two to obtain Rx, and solving the conductivity by using G=K / Rx, wherein K is electrode constant. According to the scheme, the influence of distributed capacitance is completely eliminated.

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, 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 of the electric double layer capacitance that is connected in series with the solution resistance and involves the solutio...

Examples

Embodiment 1

[0061] When testing, place the electrode in the solution to be tested, and use an AC symmetrical triangular wave voltage signal with a voltage amplitude of U and a period of 2T to excite the electrode, and remove peaks and troughs in the upper or lower band of the excitation voltage signal. The current signal of the electrode response is sampled at any two different moments t1 and t2, and the sampling values ​​of the two current signals are respectively i t1 and i t2 , using the expression R x =|2U(t2-t1) / (T(i t2 -i t1 ))|Obtain the resistance value Rx of the solution to be measured.

Embodiment 2

[0063] When testing, place the electrode in the solution to be tested, and use an AC symmetrical triangular wave voltage signal with a voltage amplitude of U and a period of 2T to excite the electrode, and remove peaks and troughs in the upper or lower band of the excitation voltage signal. The current signal of the electrode response is sampled at any two different moments t1 and t2, and the sampling values ​​of the two current signals are respectively i t1 and i t2 ; Also sample the excitation voltage signals at time t1 and t2, and the sampling values ​​of the two voltage signals are respectively u t1 and u t2 , using the expression R x =(u t2 -u t1 ) / (i t2 -i t1 ) to obtain the resistance value R of the solution to be measured x .

Embodiment 3

[0065] During detection, put the electrode into the solution to be tested, and use an AC symmetrical triangular wave voltage signal with a voltage amplitude of U and a period of 2T to excite the electrode. figure 2 The circuit shown detects the change rate of the excitation voltage signal and the change rate of the electrode-responsive current signal, and divides the change rate of the excitation voltage signal by the change rate of the electrode-responsive current signal by the follow-up circuit to obtain the solution to be measured. Resistance R x ;

[0066] In the above embodiments, the AC symmetrical triangular wave used refers to a triangular wave in which the peaks and troughs of the triangular wave have opposite polarities, equal amplitudes, and the absolute values ​​of the slopes of the upper and lower bands are equal.

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, 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 of the electric double layer capacitance that is connected in series with the solution resistance and involves the solutio...

Examples

Embodiment 1

[0061] When testing, place the electrode in the solution to be tested, and use an AC symmetrical triangular wave voltage signal with a voltage amplitude of U and a period of 2T to excite the electrode, and remove peaks and troughs in the upper or lower band of the excitation voltage signal. The current signal of the electrode response is sampled at any two different moments t1 and t2, and the sampling values ​​of the two current signals are respectively i t1 and i t2 , using the expression R x =|2U(t2-t1) / (T(i t2 -i t1 ))|Obtain the resistance value Rx of the solution to be measured.

Embodiment 2

[0063] When testing, place the electrode in the solution to be tested, and use an AC symmetrical triangular wave voltage signal with a voltage amplitude of U and a period of 2T to excite the electrode, and remove peaks and troughs in the upper or lower band of the excitation voltage signal. The current signal of the electrode response is sampled at any two different moments t1 and t2, and the sampling values ​​of the two current signals are respectively i t1 and i t2 ; Also sample the excitation voltage signals at time t1 and t2, and the sampling values ​​of the two voltage signals are respectively u t1 and u t2 , using the expression R x =(u t2 -u t1 ) / (i t2 -i t1 ) to obtain the resistance value R of the solution to be measured x .

Embodiment 3

[0065] During detection, put the electrode into the solution to be tested, and use an AC symmetrical triangular wave voltage signal with a voltage amplitude of U and a period of 2T to excite the electrode. figure 2 The circuit shown detects the change rate of the excitation voltage signal and the change rate of the electrode-responsive current signal, and divides the change rate of the excitation voltage signal by the change rate of the electrode-responsive current signal by the follow-up circuit to obtain the solution to be measured. Resistance R x ;

[0066] In the above embodiments, the AC symmetrical triangular wave used refers to a triangular wave in which the peaks and troughs of the triangular wave have opposite polarities, equal amplitudes, and the absolute values ​​of the slopes of the upper and lower bands are equal.

Images