Wide-range conductivity sensor with reconfigurable circuit

Abstract

The invention discloses a conductivity sensor with a reconfigurable circuit. The circuit comprises a four-electrode sensitive element, a pulse signal excitation circuit, a single-pole double-throw switch, a double-operational-amplifier differential detection circuit and a bridge type capacitance detection circuit. The pulse signal excitation circuit inputs a square wave signal to the four-electrode sensitive element, the square wave signal passes through a solution to be detected and then is output from the four-electrode sensitive element, and the single-pole double-throw switch gates one path of signal to be amplified and sampled by the double-operational-amplifier differential detection circuit and then is output in the form of an equivalent resistance voltage signal. The single-pole double-throw switch gates the other path of signal, the signal is amplified and sampled through the bridge type capacitance detection circuit and then is output in an equivalent capacitance voltage signal mode, and wide-range conductivity detection is achieved through the relation between the equivalent resistance voltage signal and the conductivity under the low concentration and the relation between the voltage difference of the two groups of voltage signals and the conductivity under the high concentration. The wide-range conductivity sensor with the reconfigurable circuit has the advantages of being large in range, high in resolution, high in precision and the like.

Description

TECHNICAL FIELD

[0001] The application relates to a circuit-reconfigurable wide-range conductivity sensor and belongs to the technical field of sensors. BACKGROUND

[0002] Conductivity sensors are widely used in different fields such as transportation, industrial production and climate detection. There are various types of existing conductivity sensors, and the measurement principles are also various. The existing conductivity detection methods mainly include electromagnetic type, capacitive type and electrode contact type. Among them, the advantages of the electromagnetic type and the capacitive type measurement methods are that they do not need electrodes to directly contact the measured solution, thereby avoiding the problems of electrode corrosion and pollution, but the detection range is usually narrow, and the detection result is easily disturbed by external capacitive coupling and electromagnetic field fluctuation. The electrode contact type detection method has the advantages of high precision, good stability and fast response, can realize rapid and accurate measurement of conductivity, and the electrode structure design is diversified, which is suitable for various application scenarios. SUMMARY

[0003] The application aims at the above prior art, and provides a circuit-reconfigurable wide-range conductivity sensor based on a four-electrode sensitive element and a circuit-reconfigurable structure to realize the expansion of the conductivity detection range and the improvement of the precision and resolution.

[0004] Technical scheme: The application discloses a circuit-reconfigurable wide-range conductivity sensor, which comprises a four-electrode sensitive element, a pulse signal excitation circuit, a single-pole double-throw switch, a double-operational-amplifier differential detection circuit and a bridge-type capacitive detection circuit.

[0005] The circuit-reconfigurable wide-range conductivity sensor inputs a square wave signal to the four-electrode sensitive element through the pulse signal excitation circuit, and outputs the square wave signal from the four-electrode sensitive element after passing through the measured solution. The single-pole double-throw switch selects one path signal, and the signal is amplified and sampled through the double-operational-amplifier differential detection circuit and then output in the form of an equivalent resistance voltage signal. The single-pole double-throw switch selects another path signal, and the signal is amplified and sampled through the bridge-type capacitive detection circuit and then output in the form of an equivalent capacitance voltage signal. The conductivity in a wide range is detected through the relationship between the equivalent resistance voltage signal and the conductivity at low concentration and the relationship between the voltage difference of the two voltage signals and the conductivity at high concentration. According to the mechanism of the solution concentration and the conductivity, at low concentration, the conductivity increases with the increase of the solution concentration, and when the solution concentration gradually rises to C t , due to the association effect between ions, the conductivity decreases with the increase of the solution concentration, resulting in a decrease in the equivalent resistance voltage signal. At high concentration, the conductivity is mainly determined by the ion concentration, and the conductivity increases with the increase of the solution concentration, resulting in an increase in the voltage difference of the two voltage signals. Therefore, the conductivity in a wide range can be detected through the relationship between the equivalent resistance voltage signal and the conductivity at low concentration and the relationship between the voltage difference of the two voltage signals and the conductivity at high concentration. tThe overlap between conductivity and voltage changes on both sides of the axis can lead to misreading, significantly reducing the effective range of conductivity measurement and lowering measurement accuracy. Therefore, this invention proposes a wide-range conductivity sensor with reconfigurable circuitry. This reconfigurable circuit consists of a single-pole double-throw switch, a dual operational amplifier differential detection circuit, and a bridge capacitor detection circuit. The dual operational amplifier differential detection circuit is composed of a dual operational amplifier module, a differential amplifier module, and a filter module. The bridge capacitor detection circuit is composed of a capacitor bridge module, a Wagner grounding module, and a differential amplifier module. The dual operational amplifier module separates the voltage and current signals in the four-electrode sensing element; the Wagner grounding module maintains consistent voltage ratios and phase deviations across the capacitor bridge module; the input port of the single-pole double-throw switch is connected to the four-electrode sensing element; one output port of the single-pole double-throw switch is connected to the dual operational amplifier differential detection circuit; and the other output port of the single-pole double-throw switch is connected to the bridge capacitor detection circuit. The single-pole double-throw switch selects one signal, which is amplified and sampled by a dual operational amplifier differential detection circuit and output as an equivalent resistance voltage signal. When the output equivalent resistance voltage signal falls within the voltage range [0, V] corresponding to low concentration, the signal is selected. t The conductivity at low concentrations is detected by the relationship between voltage signal and conductivity. When the output equivalent resistance voltage signal falls within the voltage range corresponding to high concentrations [V], the conductivity is determined. t [1] Then, the single-pole double-throw switch input signal passes through the bridge capacitor detection circuit and is amplified and sampled before being output in the form of equivalent capacitor voltage. The voltage outputs of the dual operational amplifier differential detection circuit and the bridge capacitor detection circuit will overlap in the high concentration range of the solution. Since the proportions of capacitance and resistance components in the impedance of high concentration solutions are different, the slopes of the equivalent resistance voltage curve and the equivalent capacitance voltage curve change differently, resulting in different voltage differences between the two sets of curves at different conductivities. The conductivity of the solution at high concentrations is detected based on the relationship between voltage difference and conductivity. Since the conductivity and voltage curves at high concentrations C t There is a stagnation point, i.e., a slope of 0, resulting in a small slope of the voltage curve at and near the stagnation point. This leads to lower accuracy and resolution in conductivity detection near the stagnation point. However, the voltage difference curve between the equivalent resistance voltage and the equivalent capacitance voltage generated by the reconfigurable circuit improves the original defects of low resolution and poor accuracy near the stagnation point. In summary, by using a four-electrode sensing element combined with a reconfigurable circuit to detect solution conductivity, the original defects of small range, low resolution, and poor accuracy are improved. Therefore, the reconfigurable conductivity sensor of this invention has the advantages of large range, high accuracy, and high resolution.

[0006] The circuit-reconfigurable wide-range conductivity sensor of this invention differs from traditional conductivity sensors, mainly in the following ways: 1. Traditional conductivity sensors exhibit conductivity saturation in high-concentration regions, while high-concentration C... tThe conductivity and voltage change of both sides of the shaft overlap, and the equivalent capacitance detection of the solution is introduced through the reconfigurable circuit, so that the equivalent resistance voltage and the equivalent capacitance voltage of the solution are fused to determine, thereby widening the detection range of the conductivity sensor; 2, due to the existence of the stationary point of the conductivity and voltage curve at high concentration C t , that is, the slope is 0, so the slope of the voltage curve near the stationary point is small, thereby making the accuracy and resolution of the conductivity detection near the stationary point low, but the voltage difference between the equivalent resistance voltage and the equivalent capacitance voltage generated by the reconfigurable circuit improves the defect that the resolution and accuracy near the stationary point are low, thereby realizing high-precision and high-resolution conductivity detection. 3, the sensor adopts a passive measurement principle, only the four-electrode sensitive element is in contact with the solution, so that it has good waterproofness, excellent wear resistance and long service life. BRIEF DESCRIPTION OF DRAWINGS

[0007] Figure 1 is the circuit principle diagram of the reconfigurable wide-range conductivity sensor of the application;

[0008] Figure 2 is the reconfigurable structure of the application;

[0009] Figure 3 is the schematic diagram of two groups of voltage difference curves generated by the reconfigurable structure of the application. DETAILED DESCRIPTION

[0010] The application will be further explained below in combination with the drawings.

[0011] Embodiment: as Figure 1 shown, the application provides a reconfigurable wide-range conductivity sensor, a pulse signal excitation circuit inputs a square wave signal to a four-electrode sensitive element, and outputs from the four-electrode sensitive element after passing through the solution to be measured, a single-pole double-throw switch selects a signal to pass through a double operational amplifier differential detection circuit for amplification and sampling, and then outputs in the form of an equivalent resistance voltage signal, the single-pole double-throw switch selects another signal to pass through a bridge type capacitance detection circuit for amplification and sampling, and then outputs in the form of an equivalent capacitance voltage signal, and the relationship between the equivalent resistance voltage signal and the conductivity at low concentration and the relationship between the voltage difference of the two voltage signals and the conductivity at high concentration are used to realize the detection of wide-range conductivity.

[0012] According to the mechanism of solution concentration and conductivity, at low concentration, the conductivity increases with the increase of the solution concentration, when the solution concentration gradually rises to C t , due to the association effect between ions, the conductivity decreases with the increase of the solution concentration, resulting in a decrease in the conductivity of the solution, and the conductivity of the solution decreases with the increase of the solution concentration, resulting in a decrease in the conductivity of the solution. tThe overlapping of conductivity and voltage changes on both sides of the shaft causes misreading, thereby greatly reducing the effective range of conductivity measurement and reducing the measurement accuracy. Therefore, the application proposes a circuit reconfigurable wide-range conductivity sensor, the reconfigurable circuit is composed of a single-pole double-throw switch, a double-operational amplifier differential detection circuit and a bridge-type capacitor detection circuit, the double-operational amplifier differential detection circuit is composed of a double-operational amplifier module, a differential amplification module and a filter module, the bridge-type capacitor detection circuit is composed of a capacitor bridge module, a Wagner grounding module and a differential amplification module, the input port of the single-pole double-throw switch is connected with a four-electrode sensitive element, the output port one of the single-pole double-throw switch is connected with the double-operational amplifier differential detection circuit, and the output port two of the single-pole double-throw switch is connected with the bridge-type capacitor detection circuit. The single-pole double-throw switch selects a path signal, which is amplified and sampled by the double-operational amplifier differential detection circuit and then output in the form of equivalent resistance voltage signal, when the output equivalent resistance voltage signal falls in the voltage interval [0, V t ] corresponding to low concentration, the low-concentration conductivity detection is realized through the relationship between voltage signal and conductivity, when the output equivalent resistance voltage signal falls in the voltage interval [V t , 1] corresponding to high concentration, the single-pole double-throw switch inputs another path signal to the bridge-type capacitor detection circuit for amplification and sampling, and then outputs in the form of equivalent capacitor voltage, the voltage outputs of the double-operational amplifier differential detection circuit and the bridge-type capacitor detection circuit will overlap in the high-concentration interval of the solution, because the proportion of the capacitor and the resistance components in the impedance of the high-concentration solution is different, the slope change of the equivalent resistance voltage curve and the equivalent capacitor voltage curve is different, so that the voltage difference of the two curves at different conductivities is also different, and the solution conductivity under high concentration is detected according to the relationship between the voltage difference and the conductivity. Because there is a stationary point on the conductivity and voltage curve at high concentration C t , i.e. the slope is 0, so the slope of the voltage curve near the stationary point is small, thereby the accuracy and resolution of the conductivity detection near the stationary point are low, but the voltage difference curve of the equivalent resistance voltage and the equivalent capacitor voltage generated by the reconfigurable circuit improves the defect of low resolution and poor accuracy near the stationary point. In summary, the solution conductivity is detected by the four-electrode sensitive element combined with the reconfigurable circuit, and the defects of small range, low resolution and poor accuracy are improved, so the circuit reconfigurable conductivity sensor has the advantages of large range, high accuracy and high resolution. In summary, the four-electrode sensitive element and the circuit reconfigurable structure realize the wide-range detection of the solution conductivity, Figure 2 , the circuit reconfigurable structure is shown in the figure, Figure 3 , the equivalent resistance voltage curve and the equivalent capacitor voltage curve generated by the circuit reconfigurable structure are shown in the figure.

[0013] The circuit reconfigurable wide-range conductivity sensor in the application has the following characteristics: 1. The traditional conductivity sensor appears conductivity saturation phenomenon in the high-concentration region,t The conductivity and voltage change of the two sides of the shaft overlap, and the equivalent capacitance detection of the solution is introduced by the reconfigurable circuit, so that the equivalent resistance voltage and the equivalent capacitance voltage of the solution are fused for judgment, thereby widening the detection range of the conductivity sensor. t The conductivity and voltage curve has a stationary point at high concentration C t The conductivity and voltage curve has a stationary point at high concentration C

[0014] The criteria for distinguishing whether it is this structure are as follows:

[0015] (a) The change in conductivity in the solution to be measured is equivalent to the change in capacitance, and a bridge-type capacitance detection circuit is used to generate an equivalent capacitance voltage curve, which solves the problem of overlapping voltage changes at high concentrations and expands the detection range of the sensor.

[0016] (b) A reconfigurable circuit structure is used to generate equivalent resistance voltage curves and equivalent capacitance voltage curves with different slopes, and the voltage difference between the equivalent resistance voltage and the equivalent capacitance voltage solves the problem of small slope at high concentrations, thereby improving the accuracy and resolution of the sensor.

[0017] A structure that meets the above two conditions should be considered as a wide-range conductivity sensor with reconfigurable circuit.

[0018] The above only describes the preferred embodiments of the present application, and the protection scope of the present application is not limited to the above embodiments. Any equivalent modifications or changes made by those skilled in the art based on the disclosed content of the present application shall be included in the protection scope recited in the claims.

Claims

1. A circuit reconfigurable wide range conductivity sensor characterized in that, The sensor comprises a four-electrode sensitive element, a pulse signal excitation circuit, a single-pole double-throw switch, a double-operational amplifier differential detection circuit and a bridge-type capacitance detection circuit, the pulse signal excitation circuit inputs a square wave signal to the four-electrode sensitive element, and outputs the square wave signal from the four-electrode sensitive element after passing through a solution to be measured, the single-pole double-throw switch selects a signal to pass through the double-operational amplifier differential detection circuit to be amplified and sampled, and then outputs the signal in the form of an equivalent resistance voltage signal, the single-pole double-throw switch selects another signal to pass through the bridge-type capacitance detection circuit to be amplified and sampled, and then outputs the signal in the form of an equivalent capacitance voltage signal, and the equivalent resistance voltage signal and the conductivity at a low concentration and the voltage difference between the two voltage signals and the conductivity at a high concentration are used to realize the detection of a wide-range conductivity.

2. The circuit reconfigurable wide range conductivity sensor of claim 1, wherein, The equivalent resistance and the equivalent capacitance of the solution are equivalent to the conductivity change of different concentrations. The single-pole double-throw switch selects a signal path. After the signal is amplified and sampled by the double operational amplifier differential detection circuit, it is output in the form of equivalent resistance voltage signal. The separation voltage of the low concentration interval and the high concentration interval is V t . When the output equivalent resistance voltage signal falls in the voltage interval [0, V t ] corresponding to the low concentration, the detection of the low concentration conductivity is realized through the relationship between the equivalent resistance voltage signal and the conductivity. t When the output equivalent resistance voltage signal falls in the voltage interval [V ,1] corresponding to the high concentration, the single-pole double-throw switch selects another signal path. After the signal is amplified and sampled by the bridge capacitance detection circuit, it is output in the form of equivalent capacitance voltage. The detection of the high concentration conductivity is realized through the voltage difference between the two voltage signals and the conductivity.

3. The circuit reconfigurable wide range conductivity sensor of claim 2, wherein, The reconfigurable circuit is composed of the single-pole double-throw switch, the double-operational amplifier differential detection circuit and the bridge-type capacitance detection circuit, the input port of the single-pole double-throw switch is connected to the four-electrode sensitive element, the output port one of the single-pole double-throw switch is connected to the double-operational amplifier differential detection circuit, and the output port two of the single-pole double-throw switch is connected to the bridge-type capacitance detection circuit.

4. The circuit reconfigurable wide range conductivity sensor of claim 3, wherein, The double-operational amplifier differential detection circuit is composed of a double-operational amplifier module, a differential amplification module and a filter module, and the bridge-type capacitance detection circuit is composed of a capacitance bridge module, a Wagner grounding module and a differential amplification module.

5. The circuit reconfigurable wide range conductivity sensor of claim 4, wherein, The double-operational amplifier module separates the voltage and current signals in the four-electrode sensitive element, and the Wagner grounding module can keep the voltage ratios of the capacitance bridge module consistent and the phases of the capacitance bridge module without deviation.

Images