Electrode type conductivity sensor

Abstract

The utility model provides an electrode type conductivity sensor, and relates to the technical field of sensors. The sensor comprises a metal shell, an electrode insulation carrier, a temperature sensor, a conductivity electrode and a sensor circuit, wherein the sensor circuit comprises a voltage source for generating excitation; the modulation circuit is used for modulating an excitation signal into a square wave signal and applying the square wave signal to the first conductivity electrode and the fourth conductivity electrode; the signal conditioning circuit is used for acquiring current signals generated by the second conductivity electrode and the third conductivity electrode; the voltage conversion circuit is used for converting an output current signal of the signal conditioning circuit into a voltage signal; the analog-to-digital circuit is used for converting the output of the voltage conversion circuit into a digital signal; and the signal output module is used for outputting signals. According to the sensor, measurement of solutions with different conductivities can be achieved by adjusting the excitation frequency, the conductivity electrode and the temperature sensor are located at the end of the sensor, pollutants can be found more easily, cleaning is easier, the temperature sensor can be closer to the electrode, and therefore the temperature of the measured solution can be obtained more quickly.

Description

Technical Field

[0001] The utility model relates to the technical field of sensors, in particular to an electrode type conductivity sensor. Background Art

[0002] Conductivity is not only a physical quantity, but also an important electrochemical parameter. Conductivity is often used as a basic parameter for the conductivity of liquids to characterize the concentration of conductive ions in a solution. The measurement of conductivity is widely used in water quality monitoring in power plants, chemical industry, metallurgy, medicine, sewage treatment and other departments, as well as in measuring solution concentration through conductivity (such as salt meters, acid-base concentration meters, etc.). With the continuous development of the national economy and science and technology, the requirements for solution conductivity measurement are becoming higher and higher.

[0003] The measurement of conductivity usually adopts electrode conductivity measurement method, electromagnetic conductivity measurement method and ultrasonic conductivity measurement method, especially the first two are more commonly used. Due to the narrow measurement range of electromagnetic measurement method, it is limited to the measurement of high conductivity solution. Electromagnetic measurement method usually has two coils, namely excitation coil and detection coil. A voltage signal of a certain frequency is applied to the excitation coil. According to the principle of electromagnetic induction, an induced voltage is generated in the solution circuit. The output voltage generated by electromagnetic induction of the detection coil by measuring the solution current can obtain the conductivity of the solution. The electromagnetic measurement method has the characteristics of non-contact detection solution, so it will not pollute and damage the detection sample. However, due to the limitation of principle, it can only be used for the measurement of high conductivity solution, and the instrument manufactured by this method is expensive, and it is mainly used to study the conductivity of biological tissue. Electrode conductivity measurement method indirectly measures conductivity by measuring the resistance of solution. Relatively speaking, the electrode conductivity measurement method uses a simple electrode structure, low cost and wide measurement range. The electrode conductivity measurement method uses the resistance measurement method to indirectly measure conductivity based on the principle of electrolytic conductivity. The conductivity measurement electrode behaves as a complex electrochemical system during the measurement process, and there are some measurement peculiarities, so there are generally the following difficulties: electrode polarization phenomenon. Polarization is mainly caused by the electrolysis product causing an electric potential between the electrode and the solution. Its direction is opposite to the external potential, which reduces the current between the electrodes and increases the resistance of the equivalent resistance solution, resulting in errors in resistance measurement; the influence of parasitic capacitance. When the electrode is immersed in the solution, the electrode surface will be charged due to ion adsorption and other reasons, and a double layer will be formed under the influence of the charges; the influence of temperature on the measurement. The temperature directly affects the ionization degree, solubility, ion migration speed, annuality and expansion of the electrolyte in the solution, thereby affecting the accuracy of the solution conductivity measurement; microorganisms and stains on the electrode surface. Currently, the main types on the market are built-in electrodes or electrodes that are not convenient to clean inside the sensor, which directly affects the measurement accuracy of conductivity. Utility Model Content

[0004] The purpose of the utility model is to provide an electrode type conductivity sensor to solve the problem of improving the performance of the conductivity sensor in view of the above-mentioned deficiencies in the prior art.

[0005] In order to achieve the above purpose, the technical solution adopted by the utility model is as follows:

[0006] The utility model provides an electrode type conductivity sensor, which comprises: a metal shell, an electrode insulation carrier, a temperature sensor, a conductivity electrode and a sensor circuit, wherein the temperature sensor and the conductivity electrode are arranged at the end of the electrode insulation carrier, the conductivity electrode comprises a first conductivity electrode, a second conductivity electrode, a third conductivity electrode and a fourth conductivity electrode, and the sensor circuit is arranged in the metal shell.

[0007] The sensor circuit includes: a voltage source for generating excitation; a modulation circuit for modulating the voltage excitation signal generated by the voltage source into a square wave signal and applying it to the first conductivity electrode and the fourth conductivity electrode; a signal conditioning circuit for acquiring the current signal generated by the second conductivity electrode and the third conductivity electrode, the current signal being generated by the conductivity electrode in a conductivity cell containing a solution to be tested in response to the square wave signal; a voltage conversion circuit for converting the output current signal of the signal conditioning circuit into a voltage signal; an analog-to-digital conversion circuit for converting the output of the voltage conversion circuit into a digital signal; and a signal output module for outputting a digital signal.

[0008] Optionally, the first conductivity electrode, the second conductivity electrode, the third conductivity electrode and the fourth conductivity electrode are arranged in a line.

[0009] Optionally, the temperature sensor is in the same plane as the conductivity electrode.

[0010] Optionally, the conductivity electrode is located in the plane of the end of the electrode insulation carrier.

[0011] Optionally, the square wave signal is a PWM square wave signal with a duty cycle of 50%.

[0012] The beneficial effects of the utility model include:

[0013] The electrode type conductivity sensor provided by the utility model comprises: a metal shell, an electrode insulation carrier, a temperature sensor, a conductivity electrode and a sensor circuit, wherein the temperature sensor and the conductivity electrode are arranged on the end surface of the electrode insulation carrier, the conductivity electrode comprises a first conductivity electrode, a second conductivity electrode, a third conductivity electrode and a fourth conductivity electrode, the sensor circuit is arranged in the metal shell, and the sensor circuit comprises: a voltage source for generating excitation; a modulation circuit for modulating a voltage excitation signal generated by the voltage source into a square wave signal and applying the signal to the first conductivity electrode and the fourth conductivity electrode; a signal conditioning circuit for acquiring a current signal generated by the second conductivity electrode and the third conductivity electrode, the current signal being generated by the conductivity electrode in a conductivity cell containing a solution to be tested in response to the square wave signal; a voltage conversion circuit for converting an output current signal of the signal conditioning circuit into a voltage signal; an analog-to-digital conversion circuit for converting an output of the voltage conversion circuit into a digital signal; and a signal output module for outputting a digital signal. The sensor of the present application can measure solutions with different conductivity by adjusting the frequency of excitation. The conductivity electrode and the temperature sensor are located at the end of the sensor, which makes it easier to detect contaminants and clean them. The temperature sensor can be closer to the electrode, thereby obtaining a faster response and obtaining the temperature of the measured solution more quickly. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0015] Figure 1 The schematic diagram of the structure of the electrode type conductivity sensor provided by the embodiment of the utility model is shown;

[0016] Figure 2 The circuit test principle diagram of the electrode type conductivity sensor provided by the embodiment of the utility model is shown;

[0017] Figure 3 A circuit diagram of a voltage source provided by an embodiment of the utility model is shown;

[0018] Figure 4 A circuit diagram of a modulation circuit provided by an embodiment of the utility model is shown;

[0019] Figure 5 A circuit diagram of a signal conditioning circuit provided by an embodiment of the utility model is shown;

[0020] Figure 6 A circuit diagram of a voltage conversion circuit provided by an embodiment of the utility model is shown;

[0021] Figure 7 A circuit diagram for testing a temperature sensor provided by an embodiment of the utility model is shown. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical scheme and advantages of the embodiments of the utility model clearer, the technical scheme in the embodiments of the utility model will be clearly and completely described below in conjunction with the drawings in the embodiments of the utility model. Obviously, the described embodiments are part of the embodiments of the utility model, not all of the embodiments. Generally, the components of the embodiments of the utility model described and shown in the drawings here can be arranged and designed in various different configurations.

[0023] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the present invention to be protected, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0024] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0025] In the description of the present utility model, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inside", "outside", etc. indicate the orientation or position relationship based on the orientation or position relationship shown in the accompanying drawings, or the orientation or position relationship in which the utility model product is usually placed when in use, which is only for the convenience of describing the utility model and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present utility model. In addition, the terms "first", "second", "third", etc. are only used to distinguish the description, and cannot be understood as indicating or implying relative importance.

[0026] In the description of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "set", "install", "connect", and "connect" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0027] The electrode conductivity measurement method uses the resistance measurement method to indirectly measure the conductivity according to the principle of electrolytic conductivity. The conductivity measurement electrode behaves as a complex electrochemical system during the measurement process, and there are some measurement particularities, so there are generally the following difficulties: electrode polarization phenomenon. Polarization is mainly caused by the electrolysis product causing an electric potential between the electrode and the solution. Its direction is opposite to the external potential, which reduces the current between the electrodes and increases the resistance of the equivalent resistance solution, resulting in errors in the resistance measurement; the influence of parasitic capacitance. When the electrode is immersed in the solution, the electrode surface will be charged due to ion adsorption and other reasons, and a double electric layer will be formed under the mutual influence of the charges; the influence of temperature on the measurement. The temperature directly affects the ionization degree, solubility, ion migration speed, annuality and expansion of the electrolyte in the solution, thereby affecting the accuracy of the solution conductivity measurement; microorganisms and stains on the electrode surface. Currently, the main types of electrodes on the market are built-in electrodes or the electrodes are inconvenient to clean inside the sensor, which directly affects the measurement accuracy of the conductivity. In order to solve at least one of the above problems, the present application proposes an electrode conductivity sensor.

[0028] Figure 1 FIG. 1 shows a schematic diagram of the structure of an electrode-type conductivity sensor provided by an embodiment of the utility model. Figure 1 As shown, the utility model provides an electrode type conductivity sensor, which includes: a metal shell 1, an electrode insulation carrier 2, a temperature sensor 3, a conductivity electrode and a sensor circuit, wherein the temperature sensor 3 and the conductivity electrode are arranged at the end of the electrode insulation carrier 2, the conductivity electrode includes a first conductivity electrode 4, a second conductivity electrode 5, a third conductivity electrode 6 and a fourth conductivity electrode 7, and the sensor circuit is arranged in the metal shell 1.

[0029] Figure 2 FIG. 2 shows a circuit test schematic diagram of an electrode-type conductivity sensor provided by an embodiment of the utility model. Figure 2 As shown, the sensor circuit includes: a voltage source 11 for generating excitation; a modulation circuit 12 for modulating the voltage excitation signal generated by the voltage source 11 into a square wave signal and applying it to the first conductivity electrode 4 and the fourth conductivity electrode 7; a signal conditioning circuit 14 for acquiring the current signal generated by the second conductivity electrode 5 and the third conductivity electrode 6, the current signal being generated by the conductivity electrode in a conductivity cell 13 containing a solution to be tested in response to the square wave signal; a voltage conversion circuit 15 for converting the output current signal of the signal conditioning circuit 14 into a voltage signal; an analog-to-digital conversion circuit 16 for converting the output of the voltage conversion circuit 15 into a digital signal; and a signal output module 17 for outputting a digital signal.

[0030] The sensor of the present application can measure solutions with different conductivity by adjusting the frequency of excitation. The conductivity electrode and the temperature sensor are located at the end of the sensor, which makes it easier to detect contaminants and clean them. The temperature sensor can be closer to the electrode, thereby obtaining a faster response and obtaining the temperature of the measured solution more quickly.

[0031] Alternatively, if Figure 1 As shown, the first conductivity electrode 4, the second conductivity electrode 5, the third conductivity electrode 6 and the fourth conductivity electrode 7 are arranged in a straight line. It should be understood that the electrode arrangement can also be sampled in other forms, not limited to Figure 1 In the form of being arranged in a line as shown in . Optionally, the temperature sensor 3 and the conductivity electrode are on the same plane. By arranging the temperature sensor 3 and the four electrodes for testing conductivity on the same plane, it is convenient to handle during cleaning. The temperature sensor 3 and the conductivity electrode are very close, so the temperature of the solution around the electrode can be measured more accurately, and the response time and response speed can be further improved. It should be understood that the temperature sensor 3 can also be extended separately and not on the same plane as the conductivity electrode. Optionally, the temperature measurement can be carried out in the form of 2-wire and 3-wire voltage divider resistors. Optionally, as Figure 1 As shown, the conductivity electrode is located in the plane of the end of the electrode insulation carrier 2. It should be understood that the conductivity electrode may not be in a plane, but may protrude from the surface. Optionally, the square wave signal is a PWM square wave signal with a duty cycle of 50%.

[0032] The specific circuit diagram is as follows Figures 3 to 7 The circuit diagram for generating the voltage source for excitation is shown in Figure 3 As shown. Figure 4 In the modulation circuit, the positive and negative excitation voltage sources are modulated into a square wave output with a duty cycle of 50%, namely the VEXC signal, by using a switching circuit and the PWM generated by the microcontroller. Figure 5 As shown, the modulated excitation signal is transmitted to the electrode J2 through the high impedance amplifier U7-A, and the output signal is SIGNAL_OUT. Figure 6 As shown, the voltage conversion circuit converts the SIGNAL_OUT signal into a voltage signal (VOUT) through a current-to-voltage circuit, and connects VOUT to the ADC (analog-to-digital conversion port) of the microcontroller for signal detection. Figure 7 The circuit diagram for testing the temperature sensor provided by the embodiment of the utility model is shown. Figure 7 The circuit analysis in the figure shows that the temperature signal output Vout is only related to the resistance error value and the reference voltage VREF, which can better improve the accuracy and make the temperature compensation more precise, thus improving the overall accuracy. The high impedance of the operational amplifier is used to obtain the temperature value in real time, reducing the error caused by signal lag.

[0033] In the specific test application, first, the voltage source generates positive and negative excitation. This part is to generate two adjustable voltages with equal positive and negative voltages for excitation, and to generate a PWM square wave with an adjustable frequency and a duty cycle of 50% through the single-chip microcomputer to control the subsequent analog switch to generate positive and negative adjustable excitation voltages; the generated excitation voltage acts on the first conductivity electrode and the fourth conductivity electrode of the conductivity cell through a high-impedance operational amplifier to apply positive and negative signals, so that the first conductivity electrode and the fourth conductivity electrode generate excitation voltages of equal magnitude and opposite phases, and the polarization of the electrodes can be avoided by AC excitation; because there is an alternating excitation on the first conductivity electrode and the fourth conductivity electrode, the second conductivity electrode and the third conductivity electrode also generate corresponding induction signals, which are proportional to the conductivity of the solution. The alternating current signal on the second conductivity electrode and the third conductivity electrode is collected by the circuit, and then the current signal is converted into a stable DC voltage signal, and then the DC voltage signal is collected by the single-chip microcomputer. The DC voltage signal is also proportional to the current solution conductivity. By adjusting different frequencies and switching different sampling resistors Rs, conductivity solutions of different concentrations can be measured.

[0034] In summary, inert conductive metals are used as electrodes in this application, and a PWM square wave with a standard duty cycle of 50% is generated by a single-chip microcomputer. The metal polarization caused by the potential difference is eliminated through positive and negative voltage excitation; the application uses high-frequency AC excitation, and the measurement of solutions with different conductivity is achieved by adjusting the frequency of the excitation; the application can use a high-precision PT1000 temperature sensor, and calculate the signal output by introducing a reference voltage through an operational amplifier, thereby reducing the error caused by measuring resistance through a 2-wire or 3-wire voltage divider, to eliminate and compensate for the influence of temperature on the measured value; the application designs the electrode surface structure to be planar, so that the electrode is on a plane, which is convenient for cleaning and reduces the measurement error caused by contaminants in the liquid.

[0035] The above description is only the preferred embodiment of the utility model, and is not intended to limit the utility model. For those skilled in the art, the utility model can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the utility model shall be included in the protection scope of the utility model.

Claims

1. An electrode type conductivity sensor, characterized in that: The sensor comprises: a metal shell, an electrode insulation carrier, a temperature sensor, a conductivity electrode and a sensor circuit, wherein the temperature sensor and the conductivity electrode are arranged at the end of the electrode insulation carrier, the conductivity electrode comprises a first conductivity electrode, a second conductivity electrode, a third conductivity electrode and a fourth conductivity electrode, and the sensor circuit is arranged in the metal shell. The sensor circuit includes: a voltage source for generating excitation; a modulation circuit for modulating the voltage excitation signal generated by the voltage source into a square wave signal and applying the signal to the first conductivity electrode and the fourth conductivity electrode; a signal conditioning circuit for acquiring the current signal generated by the second conductivity electrode and the third conductivity electrode, wherein the current signal is generated by the conductivity electrode in a conductivity cell containing a solution to be tested in response to the square wave signal; a voltage conversion circuit for converting the output current signal of the signal conditioning circuit into a voltage signal; an analog-to-digital conversion circuit for converting the output of the voltage conversion circuit into a digital signal; and a signal output module for outputting a digital signal.

2. The electrode type conductivity sensor according to claim 1, characterized in that: The first conductive electrode, the second conductive electrode, the third conductive electrode and the fourth conductive electrode are arranged in a straight line.

3. The electrode type conductivity sensor according to claim 1, characterized in that: The temperature sensor and the conductivity electrode are on the same plane.

4. The electrode type conductivity sensor according to claim 1, characterized in that: The conductive electrode is located in the plane of the end surface of the electrode insulation carrier.

5. The electrode type conductivity sensor according to claim 1, characterized in that: The square wave signal is a PWM square wave signal with a duty cycle of 50%.

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