CN108445298B - Electric field coupling type induction type conductivity sensor and characteristic compensator thereof - Google Patents
Electric field coupling type induction type conductivity sensor and characteristic compensator thereof Download PDFInfo
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R27/00—Arrangements for measuring resistance, reactance, impedance, or electric characteristics derived therefrom
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- G01R27/22—Measuring resistance of fluids
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
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Abstract
The invention discloses an electric field coupling type induction type conductivity sensor and a characteristic compensator thereof. The electric field coupling type induction type conductivity sensor probe mainly comprises an exciting coil, an induction coil and a thermal resistor, and the compensator comprises a signal conditioning circuit, an A/D converter, a compensation CPU, a parameter memory and an output unit. In measurement, alternating voltage signals are applied to two ends of an excitation coil, electromagnetic energy is transmitted between the excitation coil and an induction coil through an induced electric field and distributed current in electrolyte solution, so that alternating output voltage is generated in the induction coil, and the output voltage and the liquid conductivity are in a monotonic nonlinear function relationship. The induced voltage and the temperature signal are input to a compensation CPU after signal conditioning and A/D conversion, the CPU processes input data by adopting an intelligent compensation algorithm formed by a binary high-order least square surface fitting model, and then the input data is output by an output unit, so that the temperature characteristic and the nonlinear characteristic of the sensor are compensated.
Description
Technical Field
The invention belongs to the technical field of sensors and detection, and particularly relates to an electric field coupling type induction type conductivity sensor and a characteristic compensator thereof.
Background
In the industrial field, the conductivity detection technology is widely applied to production processes of electric power, petrifaction, papermaking, food, environmental protection and the like, and is used for measuring chemical parameters such as ion concentration of electrolyte solution, electrolyte component content in water, water pollution degree and the like. In the process of power production, conductivity is often used as an important index for measuring the circulating water quality of boilers and turbines; in the field of environmental protection, conductivity is often used as an important index for measuring the pollution degree of industrial wastewater and water bodies; in the tap water production process, the conductivity is also used as an important index for measuring the cleanliness of tap water and ensuring the production quality of drinking water; in the pulp and paper manufacturing process, the measurement of conductivity is used in various aspects, such as indirect measurement of caustic soda dilution concentration, measurement of the clean degree of pulp washing, detection of whether the condensate water of a heater is polluted by black liquor in the chemical pulping process, control of condensate water discharge mode, and the like. Finally, the development and application of the conductivity online detection technology have extremely important significance for various aspects of national production and life.
The conductivity sensor is mainly divided into an electrode type conductivity sensor and an electromagnetic induction type conductivity sensor, wherein the electrode type conductivity sensor can be divided into two electrodes, three electrodes, four electrodes, seven electrodes and the like, and in recent years, along with the application of MEMS technology to electrode processing and manufacturing, the miniaturization and integration of the electrode type conductivity sensor are realized, and the measurement performance is also continuously improved. However, since the electrode of the electrode type conductivity sensor is a metal conductor element, the electrode needs to be placed in a solution for a long time during online measurement, and the electrode immersed for a long time is easy to corrode, so that measurement deviation and even electrode failure occur, and periodic maintenance and maintenance of the electrode are required. In addition, polarization effects, capacitance effects, and contact potential effects all have a large impact on the accuracy of conductivity measurements. The electromagnetic induction type conductivity sensor is a measuring system which is mainly composed of an exciting coil, an induction coil and a magnetic core and is isolated from electrolyte solution, the conductivity is measured based on the electromagnetic field coupling and electromagnetic induction principle, the magnetic core, the coil and the measured liquid can not be directly contacted, so that a sensor probe is not easy to corrode, the problems of polarization effect, electrode capacitance effect, contact potential effect and the like do not exist, the induction type conductivity sensor has incomparable superiority compared with the electrode type conductivity sensor, and the adoption of the induction type conductivity sensor to replace the electrode type conductivity sensor is a necessary trend of detection technology development in industrial application.
However, because of the influence of the nonlinear magnetization characteristic and the temperature coefficient of the magnetic core in the induction type conductivity sensor, the output of the sensor has larger nonlinearity and temperature coefficient, and the measurement characteristic of the sensor needs to be compensated by adopting a related method so as to improve the measurement characteristic and the measurement precision; in addition, the sensor probe is more suitable for the integrated and miniaturized inductive conductivity sensor probe in the process industrial production of petrochemical industry, pulping and papermaking and the like.
Gu Minjie in 2003 discloses an electromagnetic induction type conductivity sensor which realizes the measurement of induction type liquid conductivity and solves the magnetic shielding problem, but does not compensate for temperature, and has low measurement accuracy; in 2010, su Ruidong discloses an electrolyte solution conductivity measurement method based on electric eddy current, which adopts an eddy current induction (namely magnetic field coupling) mode to measure conductivity, and a measurement coil of the method needs to be arranged on the side wall of a container or a pipeline, so that integration and miniaturization of a sensor probe are difficult to realize; in 2012 Liu Guirong et al, a non-contact conductivity sensor is disclosed, and the conductivity detection is performed by adopting inductance and capacitance double parameters, so that the measurement sensitivity is high, but a compensation sensor and a compensation method for the permalloy temperature characteristic are not shown; in 2013, andersoid ebeinhamer et al disclosed "electromagnetic induction conductivity sensor", giving a shielded conductivity sensor integrated in a circuit board, but without probe integration and measurement characteristic compensation; in 2013, liu Chang et al disclose a device and a method for measuring the conductivity of a fluid, wherein a compensation winding connected in parallel with a fluid passage to be measured is additionally arranged between a transmitting coil and a receiving coil, the temperature characteristic of a sensor is compensated by utilizing the output quantity when the compensation winding is connected, the measurement accuracy of a high-temperature environment of the sensor is ensured, but the compensation winding needs to pass through the centers of the transmitting coil and the receiving coil, the integrated design of a sensor probe cannot be realized, and the acquisition process of compensation experimental data is complex; thomas Naguer et al, 2016, disclose "inductive conductivity sensor and method of producing same", with temperature sensor, but no temperature characteristic and non-linear characteristic compensation scheme is seen; in 2016, tollss Tengpei h Shi Tai discloses "inductive conductivity sensor for measuring specific conductivity of a medium", in 2017, e·anderil discloses "method of operating an inductive conductivity sensor and an inductive conductivity sensor", but neither see application of a temperature sensor and compensation of measurement characteristics; 2017, liu Haiyun et al disclose an inductive conductivity sensor based on MEMS technology and a method of manufacturing the same, which applies MEMS technology to the inductive conductivity sensor.
The invention provides an electric field coupling type induction type conductivity sensor and a characteristic compensator thereof, which are used for constructing an integrated and miniaturized induction type conductivity sensor and compensating the temperature characteristic and the nonlinear characteristic of the sensor.
SUMMARY OF THE PATENT FOR INVENTION
In order to adopt an inductive conductivity sensor to replace a common electrode type conductivity sensor, improve the corrosion resistance of the sensor, overcome the problems of polarization effect, capacitance effect and the like, and overcome the defects of larger temperature coefficient and nonlinear characteristic of the inductive conductivity sensor at the same time, the invention designs an integrated and miniaturized inductive electrolyte solution conductivity sensor based on the basic principle of electric field coupling type electromagnetic induction, and designs a measurement characteristic compensator for compensating the temperature characteristic and nonlinear characteristic of the sensor so as to achieve the purpose of carrying out online accurate measurement on electrolyte solution. The invention mainly comprises two aspects of design of an electric field coupling type induction type conductivity sensor and compensation of measurement characteristics of the sensor.
In the aspect of design of an electric field coupling type induction type conductivity sensor, the sensor mainly comprises an exciting coil, an induction coil and thermal resistors, wherein the two coils are tightly wound on a ferrite magnetic ring respectively to form annular magnetic core coils, the two annular magnetic core coils are coaxially installed through an annular insulating support component in the middle to form a cylindrical sensor probe, an electric field coupling system is formed between the two coils by taking electrolyte solution as a medium, and 1 thermal resistor is arranged in the sensor to detect the working temperature of the sensor.
The sensor measuring principle and the signal flow direction relation are as follows: an alternating voltage signal is applied to two ends of an excitation coil, so that an alternating magnetic field is generated in the excitation magnetic ring, a closed alternating coupling electric field is generated in a solution by the alternating magnetic field, the coupling electric field axially passes through the magnetic ring of the induction coil and generates a certain distribution current in the electric field direction, an alternating response magnetic field is generated in the magnetic ring of the induction coil by the alternating inductive coupling electric field and the distribution current along the circumferential direction of the magnetic ring, magnetic flux in the induction coil wound on the magnetic ring is alternated, and an alternating output voltage is generated in the induction coil and is in a monotonic nonlinear function relation with the liquid conductivity, so that the liquid conductivity is measured by outputting the alternating voltage signal.
In the aspect of measurement characteristic compensation, the measurement characteristic compensator consists of a signal conditioning circuit, an A/D converter, a compensation CPU, a parameter memory and an output unit, wherein the signal conditioning circuit comprises a detector for processing alternating current induced voltage signals, a filter amplifier and a direct current bridge for processing thermal resistance signals, and the connection relation among all parts of the compensator is as follows: the induction coil and the thermal resistor are connected to the signal conditioning circuit, two outputs of the signal conditioning circuit are respectively connected to two input channels of the A/D converter, a digital output end of the A/D converter is connected to the I/O interface 1 of the compensation CPU, the parameter memory is connected to the I/O interface 2 of the compensation CPU, and the output unit is connected to the I/O interface 3 of the compensation CPU.
The compensator principle and the signal flow direction relation are as follows: the alternating current induction voltage output by the induction coil is converted into a direct current signal after being detected by a detector, the direct current signal is filtered and amplified by a filter amplifier and then is input into one channel of the A/D converter, meanwhile, the thermal resistance signal is converted into a direct current voltage signal by a direct current bridge and is input into the other channel of the A/D converter, the induction voltage and the temperature signal are input into a compensation CPU after being subjected to signal conditioning and A/D conversion, the compensation CPU processes input data by adopting a binary nonlinear intelligent compensation algorithm and then outputs a final conductivity value by an output unit, so that the temperature characteristic and the nonlinear characteristic of the sensor are compensated, and the measurement accuracy is improved.
The sensor excitation coil and the induction coil are essentially in coupling relation through an intermediate electric field, coupling electric field lines simultaneously pass through magnetic rings of the excitation coil and the induction coil, and electromagnetic energy is transmitted between the excitation coil and the induction coil through the induction electric field and distributed current in electrolyte solution.
The working frequency of alternating voltage signals applied to the two ends of the excitation coil of the sensor is within the range of 1.8 MHz-2.4 MHz, the peak value of the amplitude-frequency characteristic of the sensor in the frequency range is taken, and the excitation signal is generated by a DDS frequency synthesizer.
The exciting coil, the induction coil, the thermal resistor and the insulating support component are arranged in a shell made of polyether-ether-ketone material to form an integrated sensor probe, and two coil and thermal resistor signals are led out from the lead end of the probe to a subsequent compensator through a cable.
The binary nonlinear compensation algorithm adopted by the measurement characteristic compensator takes a temperature value and an induced voltage value as input, takes a conductivity value as output, and the intelligent compensation algorithm model adopts a binary high-order least square curved surface fitting model.
The model parameters of the binary nonlinear intelligent compensation algorithm in the compensator are obtained in an experimental and regression analysis mode, namely, calibration test experiments are carried out on the designed sensor probe, corresponding relation data between induced voltage and standard conductivity under different working temperature conditions are measured, regression analysis is carried out by utilizing an induced voltage value, a thermal resistance output value and a standard conductivity value, and the model parameters of the binary nonlinear intelligent compensation algorithm taking the induced voltage value and the working temperature value as independent variables are obtained.
The parameter memory of the measurement characteristic compensator adopts nonvolatile E 2 The PROM is used for storing compensation model parameters of sensors of different types in advance, and a user can select corresponding compensation model parameters according to the type of the probe.
The compensator output unit scheme comprises an LCD digital display output mode, a 4-20 mA analog signal output mode and an industrial field bus transmission mode, and different output modes are selected according to requirements in specific engineering implementation.
The invention has the following advantages:
(1) The exciting coil, the induction coil, the thermal resistor and other accessories are all arranged in the shell made of corrosion-resistant materials, so that an integrated conductivity sensor probe is conveniently formed, and the corrosion resistance of the sensor is improved.
(2) The sensor establishes an electromagnetic coupling relation between the excitation coil and the induction coil through a coupling electric field, a certain distance is formed between the two coils by the insulating support component, direct magnetic field between the two coils is weak in inductive coupling, and the direct coupling has little adverse effect on output.
(3) The excitation signal frequency of the sensor takes amplitude-frequency characteristic peak points in the range of 1.8 MHz-2.4 MHz, the measurement sensitivity is highest under the condition that the sensor structure and the excitation signal amplitude are certain, and the excitation signal is generated through a DDS frequency synthesizer, so that the frequency adjustment is flexible and convenient.
(4) By adopting the measuring characteristic compensator, the temperature characteristic and the nonlinear characteristic can be compensated at the same time, and the compensation efficiency is high and the cost is low.
(5) The temperature compensation range of the measurement characteristic compensator is wide, the temperature compensation range is not limited by the type of nonlinear characteristics, both convex function type and concave function type can be applied, and the temperature adaptability and linearity of the compensated sensor are good.
(6) The measurement characteristic compensator is suitable for conductivity sensors with different structural parameters, the compensation model parameters are conveniently obtained, and the compensator can store the compensation model parameters of each specification sensor, so that the compensation model parameters can be conveniently selected and adopted according to the specifications of the sensors.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention.
Drawings
Fig. 1 is a schematic diagram of the basic principle of the electric field coupling type inductive conductivity sensor and its characteristic compensator according to the present invention, in which the housing and the insulating support assembly of the sensor probe are not shown.
Fig. 2 is a diagram showing the structure of the probe assembly of the sensor.
Fig. 3 is an amplitude-frequency characteristic of the sensor.
FIG. 4 is a graph of the sensor's induced voltage-temperature-conductivity relationship measurement.
FIG. 5 is a graph of the effect of a voltage-temperature-conductivity binary third-order least squares surface fitting model fit.
Detailed Description
The present invention is described in further detail below with reference to the drawings to enable one skilled in the art to practice the invention by referring to the description.
It will be understood that terms, such as "having," "including," and "comprising," as used herein, do not preclude the presence or addition of one or more other elements or groups thereof.
The invention designs an integrated and miniaturized inductive electrolyte solution conductivity sensor based on the basic principle of electric field coupling type electromagnetic induction, and designs a measurement characteristic compensator for compensating the temperature characteristic and nonlinear characteristic of the sensor so as to achieve the purpose of carrying out online accurate measurement on electrolyte solution. The invention mainly comprises two aspects of design of an electric field coupling type induction type conductivity sensor and compensation of measurement characteristics of the sensor.
In the aspect of design of an electric field coupling type induction type conductivity sensor, the sensor mainly comprises an exciting coil, an induction coil and thermal resistors, wherein the two coils are tightly wound on a ferrite magnetic ring respectively to form annular magnetic core coils, the two annular magnetic core coils are coaxially installed through an annular insulating support component in the middle to form a cylindrical sensor probe, an electric field coupling system is formed between the two coils by taking electrolyte solution as a medium, and 1 thermal resistor is arranged in the sensor to detect the working temperature of the sensor.
The sensor measuring principle and the signal flow direction relation are as follows: an alternating voltage signal is applied to two ends of an excitation coil, so that an alternating magnetic field is generated in the excitation magnetic ring, a closed alternating coupling electric field is generated in a solution by the alternating magnetic field, the coupling electric field axially passes through the magnetic ring of the induction coil and generates a certain distribution current in the electric field direction, an alternating response magnetic field is generated in the magnetic ring of the induction coil by the alternating inductive coupling electric field and the distribution current along the circumferential direction of the magnetic ring, magnetic flux in the induction coil wound on the magnetic ring is alternated, and an alternating output voltage is generated in the induction coil and is in a monotonic nonlinear function relation with the liquid conductivity, so that the liquid conductivity is measured by outputting the alternating voltage signal.
The sensor specific measurement mechanism quantitative relationship can be summarized as follows:
as shown in fig. 1, a voltage signal is applied across the exciting coilAn alternating current is excited in the coil, so that a magnetic field is generated in the magnet ring +.> Creating a closed coupling electric field in solution>From maxwell's equations
Where ω is the angular frequency of the excitation signal. Closed coupling electric fieldAxially through the magnetic ring of the induction coil and generates a certain distributed current in the direction of the electric field, the current density of which is +.>Alternating inductively coupled electric fields and distributed currents generate alternating magnetic fields in the circumferential direction in the magnetic ring of the induction coil>The coupling relation can be expressed as
Wherein mu is the magnetic permeability of the magnetic ring, epsilon is the dielectric constant of the electrolyte solution to be measured, and sigma is the conductivity of the electrolyte solution to be measured. The magnetic flux in the induction coil wound on the magnetic ring alternates, thereby generating an alternating output voltage by electromagnetic inductionIts output relationship can be expressed as
Wherein N is the number of turns of the induction coil, A 0 Is the magnetic conduction radial sectional area of the magnetic ring,for magnetic field->At any radial section A of the magnetic ring 0 Average magnetic flux density at. From the equations (2) and (3), it can be seen that the conductivity sigma changes to causeChanges and->In a monotonic functional relationship with σ. Therefore, it can pass->The conductivity sigma of the solution is measured by the amplitude of (a).
It can be seen that the sensor excitation coil and the induction coil are essentially coupled through an intermediate electric field, and the coupled electric field lines simultaneously pass through the magnetic rings of the excitation coil and the induction coil, so that electromagnetic energy is transmitted between the excitation coil and the induction coil through the induced electric field and the distributed current in the electrolyte solution.
An implementation structure of the sensor probe is shown in fig. 2, an exciting coil, an induction coil, a thermal resistor and an insulating support component of the sensor are arranged inside a shell made of polyether-ether-ketone materials to form an integrated sensor probe, and two coil and thermal resistor signals are led out from a lead end of the probe through a cable to a subsequent compensator.
The exciting coil and the induction coil are respectively and tightly wound on the ferrite magnetic ring to form an annular magnetic core coil, the ferrite magnetic ring is made of zinc-manganese ferrite material with high magnetic conductivity, the initial magnetic conductivity is 2500H/m, the saturation magnetic flux density is 500mT, and the coercive force is 12A/m.
The thermal resistor employs a Pt100 ultra-small platinum thermal resistor temperature sensor, and alternatively a negative temperature coefficient NTC semiconductor thermistor or other integrated semiconductor temperature sensor such as AD590, DS18B20.
The insulating support component is made of polyether-ether-ketone material, has the same inner diameter, outer diameter and height as the magnetic ring, and is coaxially arranged with the two annular magnetic core coils to form the cylindrical sensor probe.
In the implementation example, as shown in fig. 3, in the NaCl solution with three different conductivities (2.13 mS/cm, 5.31mS/cm and 8.89 mS/cm) at the same temperature (30 ℃) is tested through experiments, the amplitude frequency characteristic of the sensor is shown when the exciting signal frequency f=50 kHz-5 MHz, the measuring peak value appears when the exciting frequency is near 2MHz, and the conductivity resolution is high, so the working frequency of the alternating voltage signal applied to the two ends of the exciting coil of the sensor takes a value in the range of 1.8 MHz-2.4 MHz, specifically takes the peak value of the amplitude frequency characteristic of the sensor in the frequency range as shown in fig. 3, so as to improve the measuring sensitivity and resolution of the sensor, and the exciting signal is generated by a DDS frequency synthesizer which is realized by adopting an AD9852 integrated chip.
In an embodiment, the sensor excitation signal takes a peak voltage V PP The effective values of the induced voltages, in which the conductivities vary in the range of 0 to 10mS/cm (measuring ranges) at room temperature (22 ℃), 30 ℃, 40 ℃, 50 ℃, 60 ℃ and 70 ℃, were measured by experiments, respectively, as shown in fig. 4, and it was found that the sensor induced voltage output has a large nonlinearity and is greatly affected by temperature, so that the nonlinear characteristics and the temperature characteristics of the sensor were compensated for using the following embodiments.
In the aspect of measurement characteristic compensation, the measurement characteristic compensator consists of a signal conditioning circuit, an A/D converter, a compensation CPU, a parameter memory and an output unit, wherein the signal conditioning circuit comprises a detector for processing alternating current induced voltage signals, a filter amplifier and a direct current bridge for processing thermal resistance signals, and the connection relation among all parts of the compensator is as follows: the induction coil and the thermal resistor are connected to the signal conditioning circuit, two outputs of the signal conditioning circuit are respectively connected to two input channels of the A/D converter, a digital output end of the A/D converter is connected to the I/O interface 1 of the compensation CPU, the parameter memory is connected to the I/O interface 2 of the compensation CPU, and the output unit is connected to the I/O interface 3 of the compensation CPU.
The compensator principle and the signal flow direction relation are as follows: the alternating current induction voltage output by the induction coil is converted into a direct current signal after being detected by a detector, the direct current signal is filtered and amplified by a filter amplifier and then is input into one channel of the A/D converter, meanwhile, the thermal resistance signal is converted into a direct current voltage signal by a direct current bridge and is input into the other channel of the A/D converter, the induction voltage and the temperature signal are input into a compensation CPU after being subjected to signal conditioning and A/D conversion, the compensation CPU processes input data by adopting a binary nonlinear intelligent compensation algorithm and then outputs a final conductivity value by an output unit, so that the temperature characteristic and the nonlinear characteristic of the sensor are compensated, and the measurement accuracy is improved.
The detector in the signal conditioning circuit adopts an effective value detector formed by an integrated effective value detection chip AD637, and the direct current output voltage value of the detector is equal to the effective value of the alternating current input voltage signal.
The filter amplifier in the signal conditioning circuit has the functions of low-pass filtering and signal amplification, adopts a second-order active low-pass filter formed by an integrated operational amplifier OP07, and has the function of forward proportional amplification.
The direct current bridge in the signal conditioning circuit adopts a Wheatstone direct current single arm bridge, the Pt100 platinum resistor is connected to one of the bridge arms, and the working temperature of the sensor is converted into direct current voltage through the thermal resistor and the direct current bridge to be output.
The A/D converter adopts a double-channel 12-bit ADC chip MAX1383, the output voltage of a direct current bridge for thermal resistance signal conversion is input to a channel 1, the induced voltage is input to a channel 2 after signal conditioning, and the induced voltage can be an ADC integrated chip or an CPU internal integrated ADC channel with the same conversion index instead.
The compensation CPU is realized by adopting an ATmega162 singlechip, and alternatively, the compensation CPU can be an AT89C52 singlechip, an MSP430F149 singlechip, a TMS320F2812 DSP chip and an STM32F103 ARM chip.
The parameter memory adopts nonvolatile E with 8kb capacity 2 The PROM chip AT24C08 is implemented, alternatively, a FLASH chip or a single-chip microcomputer with comparable capacity is integrated with a FLASH data memory.
The I/O interface 1 of the compensation CPU adopts an ATmega162 integrated SPI peripheral interface, the CPU obtains the A/D conversion results of two channels through the SPI interface, the I/O interface 2 adopts PB0 and PB1 GPIO digital interfaces of the ATmega162, and the I/O interface is simulated 2 And the C protocol interface accesses data, the I/O interface 3 adopts two parallel interfaces of PA and PC of ATmega162, and outputs the compensated conductivity data to the LCD output unit for display output through a parallel bus.
The binary nonlinear compensation algorithm adopted by the measurement characteristic compensator takes a temperature value and an induced voltage value as input, takes a conductivity value as output, and the intelligent compensation algorithm model adopts a binary high-order least square curved surface fitting model.
The model parameters of the binary nonlinear intelligent compensation algorithm in the compensator are obtained in an experimental and regression analysis mode, namely, calibration test experiments are carried out on the designed sensor probe, corresponding relation data between induced voltage and standard conductivity under different working temperature conditions are measured, regression analysis is carried out by utilizing an induced voltage value, a thermal resistance output value and a standard conductivity value, and the model parameters of the binary nonlinear intelligent compensation algorithm taking the induced voltage value and the working temperature value as independent variables are obtained.
An example of an implementation of the regression analysis using a binary third-order least squares surface fitting model is given below:
taking a third-order surface fitting polynomial satisfied by the induced voltage U, the temperature measurement value T and the conductivity sigma as
σ＝C 00 +C 10 U+C 01 T+C 20 U 2 +C 11 UT+C 02 T 2 +C 21 U 2 T+C 12 UT 2 +C 03 T 3 (4)
Wherein C is 00 ，C 01 ，C 10 ，C 20 ，C 02 ，C 11 ，C 12 ，C 21 ，C 03 Is a coefficient to be determined.
The sum of squares of errors of the surface fitting model is
In (sigma) t ，U t ，T t ) For the actual data in the implementation presented in fig. 4, t=1, 2, …, n.
Based on the least square method principle, namely the principle of minimum error square sum Q value, the undetermined coefficient in the expression can be obtained by solving, and the extremum of the function Q is obtained according to the principle that the partial derivative is 0, so as to obtain undetermined coefficient C ij A set of equations to be satisfied, i.e
Wherein i=0, 1,2; j=0, 1,2,3. Solving equation set (17) to obtain undetermined coefficient C ij Further, the curved surface fitting expression is obtained
σ＝1.016+4.235U-0.09988T+22.17U 2 -0.2675UT+0.002935T 2 -0.07757U 2 T+0.002424UT 2 -0.0165T 3 (7)
Fig. 5 shows the curve fitting effect corresponding to equation (7). In the implementation of the measurement characteristic compensator, the compensation model parameters given by the formula (7) are stored in a parameter memory of the compensator, and the parameter memory of the measurement characteristic compensator adopts nonvolatile E 2 The PROM is realized, the power failure does not disappear, the compensation model parameters of the sensors of different types are stored in the PROM, and a user can select the corresponding compensation model parameters according to the type of the probe.
The compensator output unit comprises an LCD digital display output mode, a 4-20 mA analog signal output mode and an industrial field bus transmission mode, and different output modes are selected according to requirements in specific engineering implementation.
While embodiments of the present invention have been disclosed above, they are not limited to the use listed in the specification and embodiments. It can be fully applied to various fields suitable for the patent of the present invention. Additional modifications will readily occur to those skilled in the art. Therefore, the present invention patent is not limited to the specific details and illustrations shown and described herein, without departing from the general concepts defined in the claims and their equivalents.
Claims (6)
1. An electric field coupling type induction type conductivity sensor and a characteristic compensator thereof are characterized in that: the sensor mainly comprises an excitation coil, an induction coil and a thermal resistor, wherein the two coils are tightly wound on a ferrite magnetic ring to form annular magnetic core coils, the two annular magnetic core coils are coaxially arranged through an annular insulating support assembly in the middle to form a cylindrical sensor probe, an electric field coupling system is formed between the two coils by taking electrolyte solution as a medium, and 1 thermal resistor is arranged in the sensor to detect the working temperature of the sensor;
the sensor measuring principle and the signal flow direction relation are as follows: applying alternating voltage signals at two ends of an excitation coil so as to generate an alternating magnetic field in the excitation magnetic ring, wherein the alternating magnetic field generates a closed alternating coupling electric field in a solution, the coupling electric field axially passes through the magnetic ring of the induction coil and generates certain distributed current in the electric field direction, the alternating inductive coupling electric field and the distributed current generate alternating response magnetic fields in the magnetic ring of the induction coil along the circumferential direction of the magnetic ring, magnetic flux in the induction coil wound on the magnetic ring alternates, thereby generating alternating output voltage in the induction coil, and the output voltage and the liquid conductivity form a monotonic nonlinear function relationship, so that the liquid conductivity is measured by outputting the alternating voltage signals;
the measuring characteristic compensator consists of a signal conditioning circuit, an A/D converter, a compensation CPU, a parameter memory and an output unit, wherein the signal conditioning circuit comprises a detector for processing alternating current induced voltage signals, a filter amplifier and a direct current bridge for processing thermal resistance signals, and the connection relation among the components of the compensator is as follows: the induction coil and the thermal resistor are connected to the signal conditioning circuit, two outputs of the signal conditioning circuit are respectively connected to two input channels of the A/D converter, a digital output end of the A/D converter is connected to the I/O interface 1 of the compensation CPU, the parameter memory is connected to the I/O interface 2 of the compensation CPU, and the output unit is connected to the I/O interface 3 of the compensation CPU;
the compensator principle and the signal flow direction relation are as follows: the alternating current induction voltage output by the induction coil is converted into a direct current signal after being detected by a detector, the direct current signal is filtered and amplified by a filter amplifier and then is input into one channel of an A/D converter, meanwhile, the thermal resistance signal is converted into a direct current voltage signal by a direct current bridge and is input into the other channel of the A/D converter, the induction voltage and the temperature signal are input into a compensation CPU after being subjected to signal conditioning and A/D conversion, the compensation CPU processes input data by adopting a binary nonlinear intelligent compensation algorithm and then outputs a final conductivity value by an output unit, so that the temperature characteristic and the nonlinear characteristic of the sensor are compensated, and the measurement accuracy is improved;
the binary nonlinear compensation algorithm adopted by the measurement characteristic compensator takes a temperature value and an induced voltage value as input, takes a conductivity value as output, and the intelligent compensation algorithm model adopts a binary high-order least square curved surface fitting model.
2. An electric field coupling type induction type conductivity sensor and its characteristic compensator according to claim 1, wherein: the sensor excitation coil and the induction coil are essentially in coupling relation through an intermediate electric field, coupling electric field lines simultaneously pass through magnetic rings of the excitation coil and the induction coil, and electromagnetic energy is transmitted between the excitation coil and the induction coil through the induction electric field and distributed current in electrolyte solution.
3. An electric field coupling type induction type conductivity sensor and its characteristic compensator according to claim 1, wherein: the working frequency of alternating voltage signals applied to the two ends of the excitation coil of the sensor is within the range of 1.8 MHz-2.4 MHz, the peak value of the amplitude-frequency characteristic of the sensor in the frequency range is taken, and the excitation signal is generated by a DDS frequency synthesizer.
4. An electric field coupling type induction type conductivity sensor and its characteristic compensator according to claim 1, wherein: the exciting coil, the induction coil, the thermal resistor and the insulating support component are arranged in a shell made of polyether-ether-ketone material to form an integrated sensor probe, and two coil and thermal resistor signals are led out from the lead end of the probe to a subsequent compensator through a cable.
5. An electric field coupling type induction type conductivity sensor and its characteristic compensator according to claim 1, wherein: the model parameters of the binary nonlinear intelligent compensation algorithm in the compensator are obtained in an experimental and regression analysis mode, namely, calibration test experiments are carried out on the designed sensor probe, corresponding relation data between induced voltage and standard conductivity under different working temperature conditions are measured, regression analysis is carried out by utilizing an induced voltage value, a thermal resistance output value and a standard conductivity value, and the model parameters of the binary nonlinear intelligent compensation algorithm taking the induced voltage value and the working temperature value as independent variables are obtained.
6. An electric field coupling type induction type conductivity sensor and its characteristic compensator according to claim 1, wherein: the parameter memory of the measurement characteristic compensator adopts nonvolatile E 2 The PROM is used for storing compensation model parameters of sensors of different types in advance, and a user can select corresponding compensation model parameters according to the type of the probe.
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| WO2019202092A1 (en) * | 2018-04-18 | 2019-10-24 | Universiteit Twente | System and method for measuring conductivity |
| CN109342984A (en) * | 2018-11-16 | 2019-02-15 | 南方电网科学研究院有限责任公司 | A kind of magnetoresistive chip temperature and humidity influences rectification building-out system and method |
| CN109870487B (en) * | 2019-02-18 | 2021-06-22 | 中国石油天然气集团有限公司 | Method, device and system for compensating resistance of conductivity sensor verification lead |
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| CN113916943B (en) * | 2021-10-11 | 2024-03-01 | 国家海洋技术中心 | Seawater conductivity measurement method and system |
| CN114018326B (en) * | 2021-11-03 | 2024-04-16 | 国网湖南省电力有限公司 | Low-voltage transformer area environment multi-parameter detection method based on microsystem sensor array |
| CN114034929B (en) * | 2021-11-12 | 2024-04-19 | 国家海洋技术中心 | Non-external field induction type conductivity sensor |
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