CN109507391B - Soil heavy metal content detection device based on DDS - Google Patents
Soil heavy metal content detection device based on DDS Download PDFInfo
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
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Abstract
The invention provides a DDS-based detection device for detecting the heavy metal content in soil, which is completely different from the prior art, and comprises: the device comprises a sensor, a Direct Digital Synthesizer (DDS), a current sampler, a voltage sampler, an instrument amplifier, an A/D converter, an interface circuit, an MCU, input equipment, a temperature control module and a power supply module, wherein the DDS is connected with the current sampler; the sensor is also internally provided with an electric heater and a thermocouple; during detection, the collected soil sample is filled in the sensor. The heavy metal content of the soil can be inverted according to the shapes of the Cp-f curve and the Tan (Delta) -f curve of the soil sample obtained by measurement.
Description
Technical Field
The invention relates to a soil heavy metal content detection device based on a DDS.
Background
The heavy metal pollution of the soil refers to the phenomenon that the content of heavy metal in the soil is obviously higher than a background value and causes the existing or potential soil quality degradation and ecological and environmental deterioration because the heavy metal is brought into the soil due to natural reasons or human activities. The heavy metal sources of soil are wide, and mainly comprise atmospheric dust fall, sewage irrigation, improper stacking of industrial solid wastes, mining activities, pesticides, chemical fertilizers and the like. In the industry using heavy metals and materials containing heavy metals as raw materials for production, the heavy metals can be discharged in the production process, and if the heavy metals are not properly disposed, environmental pollution can be caused.
In the process of preventing, monitoring and treating heavy metal pollution of soil, the detection of the content of heavy metal in the soil is a very important link. The quantitative detection and analysis technology of heavy metals generally comprises the following steps: ultraviolet spectrophotometry (UV), Atomic Absorption Spectroscopy (AAS), Atomic Fluorescence (AFS), Inductively Coupled Plasma (ICP), X-ray fluorescence spectroscopy (XRF), and inductively coupled plasma mass spectrometry (ICP-MS). In addition to the above methods, there is also spectroscopic detection. Also, X-ray fluorescence spectroscopy (XRF) was used for analysis.
In the detection methods, the adopted instruments and equipment are precise, expensive and large in size, and need to be fixed and used after being installed and debugged in a laboratory, and cannot be carried about for use.
When the heavy metal pollution condition of soil needs to be detected and analyzed quickly, a detection instrument and a detection method which can be used for field detection, are convenient to carry and are low in cost are urgently needed.
In another invention patent application on the same day of the invention patent application, a detection device for detecting the heavy metal content in soil based on a programmable signal generator is provided, and the detection device comprises a sensor, the programmable signal generator, a current sampler, a voltage sampler, an instrument amplifier I, an instrument amplifier V, an A/D converter I (namely ADC-I), an A/D converter V (namely ADC-V), an interface circuit, an MCU, an input device, a temperature control module and a power supply module.
Disclosure of Invention
The invention aims to solve the problems in the prior art, and provides a brand-new detection instrument and a measurement method for the heavy metal content in soil, which are completely different from the prior art.
The specific technical scheme for realizing the purpose of the invention is as follows:
the utility model provides a detection device of detection soil heavy metal content based on DDS, includes:
the system comprises a sensor, a Direct Digital Synthesizer (DDS), a current sampler, an instrument amplifier, an A/D converter, an interface circuit, an MCU (micro control Unit), an input device, a temperature controller and a power supply module; the sensor is also internally provided with an electric heater and a thermocouple; the power supply module provides electric energy for the MCU, the sensor, the direct digital frequency synthesizer, the current sampler, the instrument amplifier, the A/D converter, the interface circuit, the input equipment and the temperature controller; during detection, the collected soil sample is filled in the sensor; the current sampler is generally constituted by a small resistor in series with the sensor, wherein the resistance of the small resistor is significantly smaller than the resistance of the soil sample, the resistance of the small resistor being determined by the accuracy of the measurement;
the input equipment is electrically connected to the MCU, the signal input end of the direct digital frequency synthesizer is electrically connected to the MCU, the signal output end of the direct digital frequency synthesizer is electrically connected to the sensor, the current sampler is electrically connected with the signal input end of the instrument amplifier, the signal output end of the instrument amplifier is electrically connected to the analog signal input end of the A/D converter, and the digital signal output end of the A/D converter is electrically connected to the MCU through the interface circuit; in some direct digital frequency synthesizers adopting a table look-up device architecture, the voltage value of the electric signal generated by the direct digital frequency synthesizer can also be reversely transmitted to the MCU;
the sensor comprises a pair of parallel round sheet-shaped metal plates, and each metal plate is connected with an alternating current signal input end and a signal output end of the direct digital frequency synthesizer; an electric heater and a thermocouple are also arranged in each metal plate, namely two electric heaters and two thermocouples are arranged in the sensor; the electric heater and the thermocouple extend out of the metal plate through the lead wires, and the electric heater and the lead wires are electrically insulated from the metal plate, namely the electric heater and the lead wires are provided with insulating sleeves; the electric heater and the thermocouple are connected to the temperature control module through leads, so that the temperature of the soil sample is kept at a temperature value preset by the MCU during detection;
the input device is used for inputting preset measurement parameters and detection instructions to the MCU;
the direct digital frequency synthesizer can receive an instruction sent by the MCU and synthesize an alternating current signal with frequency and amplitude preset by the MCU according to the instruction sent by the MCU; during detection, presetting the generated alternating current signal as an alternating current signal with frequency f changing along with time t and amplitude keeping unchanged;
at any moment, the output alternating voltage signal of the direct digital frequency synthesizer, namely the alternating voltage signal at the two ends of the sensor, is generated by an instruction sent by the MCU;
in a direct digital frequency synthesizer which is not based on a table look-up device framework, the voltage value of an electric signal generated by the direct digital frequency synthesizer is directly sent out by an MCU instruction; in a direct digital frequency synthesizer which is not based on a table look-up device framework, a D/A converter, a filter and the like are arranged inside the direct digital frequency synthesizer, the D/A converter receives a digital value of an alternating voltage signal sent by an MCU, converts the digital value into an analog alternating voltage signal, and outputs the analog alternating voltage signal after high-frequency digital noise is filtered by the filter;
therefore, in the subsequent measurement work, the voltage of the alternating current signal at the two ends of the sensor does not need to be measured, and the voltage value of the alternating current signal is stored while the MCU sends a command to the direct digital frequency synthesizer; in the subsequent measurement work, only the current value of the alternating current signal passing through the sensor and the soil sample needs to be measured;
the direct digital frequency synthesizer outputs the alternating current signal to the sensor to detect the soil sample;
during detection, the MCU also sends an instruction to the temperature controller to enable an electric heater arranged in the sensor to work and control the temperature value of the sensor to be maintained at a preset value;
the AC current signal passing through the sensor passes through the current sampler and then is output to an instrument amplifier for amplification, and then an A/D converter converts the amplified analog signal into a digital signal to obtain the digital value of the AC current signal passing through the sensor; the digital value of the alternating current signal passing through the sensor is transmitted to the MCU in real time through the interface circuit and is stored by the MCU in real time, the MCU calculates the apparent capacitance real part Cp, the apparent capacitance imaginary part Cp' and the loss tangent value Tan (Delta) of the soil sample according to the amplitude and the phase of the alternating current signal passing through the sensor and the alternating voltage signals at two ends of the sensor, and simultaneously stores the calculation result in real time;
when the heavy metal content of the soil sample is detected, the MCU normalizes an apparent capacitance real part-frequency curve, namely a Cp-f curve and a loss tangent value-frequency curve, namely a Tan (Delta) -f curve of the soil sample, identifies the characteristic degree of the normalized curve, automatically matches the normalized curve with a curve in a standard curve library prestored in a memory arranged in the MCU, and obtains the heavy metal content of the collected soil sample by referring to a numerical value in the standard curve library, wherein the standard curve library records the normalized apparent capacitance real part-frequency curve, namely the Cp-f curve and the loss tangent value-frequency curve, namely the Tan (Delta) -f curve of a plurality of standard soil samples which are measured in advance and have different heavy metal contents.
Preferably, the sensor comprises a pair of parallel metal plates, each of the pair of parallel metal plates being in the form of a thin circular sheet;
preferably, the thin sheet metal plate has a dimension in the order of centimeters and a thickness in the order of millimeters;
preferably, the input device can be any one of a keyboard, a button and a touch screen;
the two electric heaters may be electrically connected to the temperature control module in series or in parallel;
a Micro Control Unit (MCU), also called a single Chip Microcomputer (smg Chip Microcomputer) or a single Chip Microcomputer (MCU), is to properly reduce the frequency and specification of a Central Processing Unit (CPU), and integrate peripheral interfaces such as memory, counter (Timer), USB, a/D conversion, UART, PLC, DMA, etc., and even an LCD driving circuit on a single Chip to form a Chip-level computer, which is used for different combined control in different application occasions.
Each curve in the standard curve library, from daily work: when the heavy metal content in the soil is detected by adopting any one of an ultraviolet spectrophotometry (UV), an atomic absorption method (AAS), an atomic fluorescence method (AFS), an inductively coupled plasma method (ICP), an X fluorescence spectrum (XRF) and an inductively coupled plasma mass spectrometry (ICP-MS), the technical scheme of the invention is adopted to measure the real part-frequency curve of the apparent capacitance of the soil sample, namely a Cp-f curve, and the loss tangent value-frequency curve, namely a Tan (Delta) -f curve, and the measured Cp-f curve, the Tan (Delta) -f curve, the corresponding heavy metal species and the content of the heavy metal of the soil sample are recorded into a standard curve library.
The measurement principle of the present invention is described as follows:
when the solid medium is subjected to the action of an external electric field, an electric polarization effect can occur, and the electric action and influence are shown in an electric polarization mode with the misaligned positive and negative charge centers; the main role played in this is the bound charge (positive and negative ions in the solid matter, extra-nuclear electrons bound by the nucleus). The electric polarization rule of bound charges in the solid medium under the action of an electric field is closely related to the microstructure of the medium.
The basic process of electrical polarization is three: firstly, the distortion polarization of electron cloud outside the nucleus; (relative) displacement polarization of positive and negative ions in molecules; and the steering polarization of the inherent electric moment of the molecule. Under the action of an external electric field, the dielectric constant epsilon of the medium comprehensively reflects the macroscopic physical quantities of the three microscopic processes; it is a function epsilon (f) of the frequency f.
Under the action of an external electric field, charged defects in the solid medium jump from one equilibrium position to another equilibrium position, or ions vibrate back and forth in a certain local area, and the effect is equivalent to the turning of electric torque. Some solids with strong ionicity (bond) have electrostatic dielectric constant s much larger than n2, and the difference is caused by the jump of charged defects under the action of external electric field except the contribution of ion displacement polarization. For a solid medium with defects (particularly impurity ions), under the action of an external electric field, not only an electric polarization process but also a conductance process exist, and a macroscopic conduction current effect and an increase of a loss tangent Tan (Delta) are shown.
For a soil sample polluted by heavy metal, because the mass of heavy metal ions is obviously greater than that of ions/atoms of other elements, the frequency response process of ions with different masses in an alternating electric field is obviously different, and in the process that the frequency of the alternating electric field is gradually increased, the heavy metal ions are more and more difficult to follow the direction change of the additional alternating electric field, and the ions with larger masses are more and more; and because the heavy metal ions exist in the soil sample in the form of impurity ions, when the soil sample is subjected to an external electric field, loss caused by conduction current also exists, the resistance effect is shown, the more impurity ions contained in the soil sample, the larger the leakage current is, and the apparent capacitance imaginary part Cp' and the loss tangent value Tan (Delta) are shown to be increased during the test.
In a soil sample polluted by heavy metals, the types and the contents of the heavy metals obviously influence the shapes of a real part of apparent capacitance-frequency curve, namely a Cp-f curve, a loss tangent value-frequency curve, namely a Tan (Delta) -f curve, the distortion degree of the curve shape and the distortion position, and reflect the weight of substances with different components in the soil.
The shapes of a real apparent capacitance part-frequency curve, namely a Cp-f curve and a loss tangent value-frequency curve, namely a Tan (Delta) -f curve of the soil sample obtained by experimental measurement can be inverted to show the heavy metal content of the soil. During inversion, the accuracy of the heavy metal content of the soil depends on the sample abundance degree of the established standard curve library.
Details not described in this specification are within the skill of the art that are well known to those skilled in the art.
The invention has the beneficial effects that:
compared with the prior art, the technical scheme of the invention has the following remarkable advantages:
the detection instrument can be made to be small in size and portable, and the testing device does not have precise and delicate components such as ultraviolet spectrophotometry (UV), Atomic Absorption Spectroscopy (AAS), Atomic Fluorescence (AFS), Inductively Coupled Plasma (ICP), X fluorescence spectroscopy (XRF) and inductively coupled plasma mass spectrometry (ICP-MS), so that the detection instrument is very suitable for field rapid detection.
Because the processing of normalizing the test data is adopted, the area and the distance of the parallel metal plates are not required to be substituted to convert the dielectric constant in the previous step, and even if the soil sample is compacted between the parallel metal plates, the soil sample is not really and completely filled in the space between the parallel metal plates, and even if partial holes and defects exist, the measurement deviation of the apparent capacitance real part Cp and the apparent capacitance imaginary part Cp' can be brought, but after the normalization processing, the influences disappear, and in the subsequent data processing, the absolute size of the measured values is not required to be considered, but only the shape of the measured curve is required to be considered. This brings convenience to the measurement.
In the ultraviolet spectrophotometry (UV), Atomic Absorption Spectroscopy (AAS), Atomic Fluorescence (AFS), Inductively Coupled Plasma (ICP), X fluorescence spectroscopy (XRF), and inductively coupled plasma mass spectrometry (ICP-MS), no precise and careful pretreatment of the sample is required, and care must be taken in the measurement.
In addition, the technical scheme of the invention is suitable for field rapid detection, and the operation is very simple and convenient, so that the monitoring efficiency in environmental protection work is greatly improved.
Compared with the technical scheme of the invention patent application on the same day, the voltage sampler, the voltage amplifier and the voltage signal A/D converter are omitted, the circuit structure is further simplified, and the cost is reduced.
Drawings
FIG. 1: the invention relates to a structure diagram of a detection device for rapidly detecting the heavy metal content in soil on site.
FIG. 2: in the sensor of the detection device of the present invention, two electric heaters are incorporated in the sensor as shown by broken lines. The insulating sleeves provided for both the electric heater and the lead wires are not shown, nor are the temperature sensors shown.
FIG. 3: the invention relates to a structure diagram of a power module in a detection device.
Detailed Description
For the convenience of understanding, the technical scheme of the invention is specifically described by combining the examples.
As shown in fig. 1, a DDS-based detection apparatus for detecting heavy metal content in soil includes:
the system comprises a sensor, a Direct Digital Synthesizer (DDS), a current sampler, an instrument amplifier, an A/D converter, an interface circuit, an MCU (micro control Unit), an input device, a temperature controller and a power supply module; the sensor is also internally provided with an electric heater and a thermocouple; the power supply module provides electric energy for the MCU, the sensor, the direct digital frequency synthesizer, the current sampler, the instrument amplifier, the A/D converter, the interface circuit, the input equipment and the temperature controller; during detection, the collected soil sample is filled in the sensor;
the current sampler is generally constituted by a small resistor in series with the sensor, wherein the resistance value of the small resistor is significantly smaller than the resistance value of the soil sample (typically in the order of kilohms), for example a few ohms;
the input device is electrically connected to the MCU, the signal input end of the direct digital frequency synthesizer is electrically connected to the MCU, the signal output end of the direct digital frequency synthesizer is electrically connected to the sensor, the current sampler is electrically connected to the signal input end of the instrument amplifier, the signal output end of the instrument amplifier is electrically connected to the analog signal input end of the A/D converter (namely ADC-I), and the digital signal output end of the A/D converter is electrically connected to the MCU through the interface circuit;
the sensor comprises a pair of parallel circular sheet-shaped metal plates, wherein each metal plate is connected with an alternating current signal input end and a signal output end of a Direct Digital Synthesizer (DDS); an electric heater and a thermocouple are also arranged in each metal plate, namely two electric heaters and two thermocouples are arranged in the sensor; the electric heater and the thermocouple extend out of the metal plate through the lead wires, and the electric heater and the lead wires are electrically insulated from the metal plate, namely the electric heater and the lead wires are provided with insulating sleeves; the electric heater and the thermocouple are connected to the temperature control module through leads, so that the temperature of the soil sample is kept at a temperature value preset by the MCU during detection;
the input device is used for inputting preset measurement parameters and detection instructions to the MCU;
a Direct Digital Synthesizer (DDS) can receive an instruction sent by the MCU and synthesize an alternating current signal with frequency and amplitude preset by the MCU according to the instruction sent by the MCU; during detection, presetting the generated alternating current signal as an alternating current signal with frequency f changing along with time t and amplitude keeping unchanged;
at any moment, the output alternating voltage signal of the direct digital frequency synthesizer, namely the alternating voltage signal at the two ends of the sensor, is generated by an instruction sent by the MCU;
a Direct Digital Synthesizer (DDS) is a Direct Digital frequency Synthesizer that is not based on a table look-up device architecture, and a voltage value of an electrical signal generated by the Direct Digital frequency Synthesizer is directly sent by an MCU command; therefore, in the subsequent measurement work, the voltage of the alternating current signal at the two ends of the sensor does not need to be measured, and the voltage value of the alternating current signal is stored while the MCU sends a command to the direct digital frequency synthesizer; in the subsequent measurement work, only the current value of the alternating current signal passing through the sensor and the soil sample needs to be measured;
the direct digital frequency synthesizer outputs the alternating current signal to the sensor to detect the soil sample;
during detection, the MCU also sends an instruction to the temperature controller to enable an electric heater arranged in the sensor to work and control the temperature value of the sensor to be maintained at a preset value;
the AC current signal passing through the sensor passes through the current sampler and then is output to an instrument amplifier for amplification, and then an A/D converter converts the amplified analog signal into a digital signal to obtain the digital value of the AC current signal passing through the sensor; the digital value of the alternating current signal passing through the sensor is transmitted to the MCU in real time through the interface circuit and is stored by the MCU in real time, the MCU calculates the apparent capacitance real part Cp, the apparent capacitance imaginary part Cp' and the loss tangent value Tan (Delta) of the soil sample according to the amplitude and the phase of the alternating current signal passing through the sensor and the alternating voltage signals at two ends of the sensor, and simultaneously stores the calculation result in real time;
when the heavy metal content of the soil sample is detected, the MCU normalizes an apparent capacitance real part-frequency curve, namely a Cp-f curve and a loss tangent value-frequency curve, namely a Tan (Delta) -f curve of the soil sample, identifies the characteristic degree of the normalized curve, automatically matches the normalized curve with a curve in a standard curve library prestored in a memory arranged in the MCU, and obtains the heavy metal content of the collected soil sample by referring to a numerical value in the standard curve library, wherein the standard curve library records the normalized apparent capacitance real part-frequency curve, namely the Cp-f curve and the loss tangent value-frequency curve, namely the Tan (Delta) -f curve of a plurality of standard soil samples which are measured in advance and have different heavy metal contents.
As shown in fig. 2, the sensor includes a pair of parallel circular sheet-shaped metal plates, each of which is connected with an AC signal input terminal, AC1 and AC2, respectively, for connecting to a signal output terminal of a Direct Digital Synthesizer (DDS); an electric heater is also arranged in each metal plate, namely two electric heaters are arranged in the sensor; the electric heater extends out of the metal plate through the lead, the electric heater and the lead are electrically insulated from the metal plate, namely, the electric heater and the lead are provided with insulating sleeves; the electric heater is connected to the temperature control module through a lead wire, so that the temperature of the soil sample is kept at a temperature value preset by the MCU during detection; the two electric heaters are respectively provided with a lead end Heater1 and a Heater1-1, a Heater2 and a Heater2-2, when in use, the lead end Heater1 can be electrically connected with the Heater2-2, the Heater1-1 and the Heater2 are electrically connected together, and the two electric heaters are connected to the temperature controller in a parallel mode.
As shown in fig. 3, the power module is composed of a MAX610 chip as a core, which is supplemented with a peripheral resistor-capacitor element.
When the detection device is used for detecting the heavy metal content in the soil, the steps are as follows:
collecting a soil sample on site; removing patrinia scabiosaefolia and macroscopic broken stone particles during collection; the sampling amount of the soil sample is several grams to ten grams, so that the measurement error is not large because the sample amount is too small, and the excessive time and the excessive electric energy consumed for heating and drying because the sample amount is too large are avoided. Generally, for soil samples of several to ten grams, heating and drying are carried out in a compacted state to a constant weight, generally 3 to 5 minutes are required;
crushing the collected soil sample, directly placing the crushed soil sample between a pair of parallel metal plates of a sensor to apply pressure and compress, scraping redundant parts leaking out of the parallel metal plates by a scraping blade, and preparing into a sheet-shaped sample with the same shape and size as the parallel metal plates;
the MCU sends a heating instruction to the temperature controller, and the compacted soil sample is heated and dried to constant weight in a compacted state; the soil sample is dried to constant weight, so that the moisture contained in the sample is prevented from bringing large errors to subsequent electrical measurement. The temperature for heating and drying the compacted soil sample in a compacted state is between 110 and 120 ℃.
Frequency sweep test: under constant temperature, applying an alternating electrical signal vt with constantly changing frequency on a pair of parallel metal plates of a sensor by utilizing a Direct Digital Synthesizer (DDS) to act on a dried soil sample, wherein the frequency f of the alternating electrical signal vt output by an alternating signal source changes along with the time t, and the signal amplitude is kept unchanged; a Direct Digital Synthesizer (DDS) is controlled by an instruction sent by the MCU; in one example, the output alternating electrical signal v of a Direct Digital Synthesizer (DDS)tThe frequency f of (2) is changed once every 200ms, the frequency is increased from 100Hz, the difference between every two frequencies is 1.1 times, until the frequency is increased to about 1MHz, and the specific frequency list is as follows:
100Hz, 110Hz, 121Hz, 133.1Hz … …, 777.88KHz, 855.67KHz, 941.23KHz, 1.035MHz, 98 frequency points in total, and 49s of time is needed for the test to be completed.
Detecting and recording the electric parameters of the alternating electric signal passing through the pair of parallel metal plates and the soil sample in real time, wherein the electric parameters comprise an apparent capacitance real part Cp, an apparent capacitance imaginary part Cp', a loss tangent value Tan (Delta) and a frequency f of the alternating electric signal; wherein the loss tangent Tan (Delta) is equal to the ratio of the imaginary apparent capacitance Cp' to the real apparent capacitance Cp;
the MCU respectively derives the data obtained by detection and recording to obtain an apparent capacitance real part-frequency curve, namely a Cp-f curve, and a loss tangent value-frequency curve, namely a Tan (Delta) -f curve; in all the apparent capacitance real part-frequency curves, namely Cp-f curves and loss tangent value-frequency curves, namely Tan (Delta) -f curves, the frequency is logarithmic, namely, logf or lgf; an output alternating electrical signal v of the Direct Digital Synthesizer (DDS)tThe frequency f is as low as Hz magnitude and as high as MHz magnitude; output alternating electric signal v of alternating signal sourcetThe frequency f of (d) varies as a function of time t as a logarithmic rule;
the MCU normalizes the obtained apparent capacitance real part-frequency curve; the loss tangent Tan (Delta) -frequency f curve is a dimensionless and normalized curve without normalization;
when the heavy metal content of the soil sample is detected, the MCU normalizes an apparent capacitance real part-frequency curve, namely a Cp-f curve and a loss tangent value-frequency curve, namely a Tan (Delta) -f curve of the soil sample, identifies the characteristic degree of the normalized curve, automatically matches the normalized curve with a curve in a standard curve library prestored in a memory arranged in the MCU, and obtains the heavy metal content of the collected soil sample by referring to a numerical value in the standard curve library, wherein the standard curve library records the normalized apparent capacitance real part-frequency curve, namely the Cp-f curve and the loss tangent value-frequency curve, namely the Tan (Delta) -f curve of a plurality of standard soil samples which are measured in advance and have different heavy metal contents. In all the curves of the real part of the apparent capacitance versus frequency, the tangent loss versus frequency, the frequency is logarithmic, i.e., logf or lgf. In the standard curve library, each curve further has additional information, and the additional information includes: all extreme points of the normalized apparent capacitance real part-frequency curve and loss tangent value-frequency curve, zero point of the first derivative curve and zero point of the second derivative curve;
the actual test temperature value is the same as the measured temperature in the standard curve library.
According to practical experience, in a low frequency band, the curves of the apparent real capacitance part Cp-frequency f and the loss tangent Tan (Delta) -frequency f of a sample usually change slowly, if the frequency f changes linearly along with time t, the time consumption is too long and reaches several hours from the hundred Hz magnitude to the megaHz magnitude, and the obtained data volume is too much, so that no obvious change can be seen in the low frequency band; the selection frequency f changes according to the logarithmic rule with the time t, so that only about 1 minute is needed, and the change rule can be shown in each frequency band.
When the detection result reports that the heavy metal content in the soil is remarkably over-standard, the soil marking the sampling area is polluted by the heavy metal, and any one of an ultraviolet spectrophotometry (UV), an Atomic Absorption Spectroscopy (AAS), an atomic fluorescence method (AFS), an inductively coupled plasma method (ICP), an X fluorescence spectrum (XRF) and an inductively coupled plasma mass spectrometry (ICP-MS) is adopted for further identifying the heavy metal type and accurately measuring the content.
It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.
Details not described in this specification are within the skill of the art that are well known to those skilled in the art.
Sounding: the patent project of the invention is funded by project fund of 'research on ultra-wideband and wearable antenna in wireless body area network (KFKT2016A 05)' and 'research on self-assembly technology for flexible antenna and microwave integrated circuit (17KJA 470007)', and here shows thank you.
Claims (9)
1. The utility model provides a soil heavy metal content's detection device based on DDS which characterized in that, detection device includes: a sensor, an amplifier, an A/D converter, a direct digital frequency synthesizer (DDS for short), and an MCU (micro control unit, MCU for short); during detection, the collected soil sample is filled in the sensor;
the direct digital frequency synthesizer receives an instruction sent by the MCU to synthesize an alternating current signal with the frequency and the amplitude preset by the MCU; during detection, presetting the generated alternating current signal as an alternating current signal with frequency f changing along with time t and amplitude keeping unchanged; at any moment, the output alternating voltage signal of the direct digital frequency synthesizer, namely the alternating voltage signal at the two ends of the sensor, is generated by an instruction sent by the MCU;
the sensor comprises a pair of metal plates which are connected to the signal output end of the direct digital frequency synthesizer;
the direct digital frequency synthesizer outputs an alternating current signal to the sensor; when the heavy metal content of the soil sample is detected, calculating by using the MCU to obtain an apparent capacitance real part Cp, an apparent capacitance imaginary part Cp' and a loss tangent Tan (Delta) of the soil sample; the method comprises the steps that the MCU normalizes the Cp-f curve and the Tan (Delta) -f curve of a soil sample obtained through detection, identifies the characteristic degree of each normalized curve, automatically matches the curves with the curves in a standard curve library prestored in a memory arranged in the MCU, obtains the heavy metal content of the collected soil sample according to the numerical values in the standard curve library, and records the Cp-f curve and the Tan (Delta) -f curve of the standard soil sample with different heavy metal contents, which are obtained through measurement in advance, through normalization.
2. The sensing device of claim 1, wherein the sensing device further comprises:
the device comprises a current sampler, an instrument amplifier, an interface circuit, input equipment, a temperature controller and a power supply module; the sensor is also internally provided with an electric heater and a thermocouple; the power supply module provides electric energy for the MCU, the sensor, the direct digital frequency synthesizer, the current sampler, the instrument amplifier, the A/D converter, the interface circuit, the input equipment and the temperature controller;
the input equipment is electrically connected to the MCU, the signal input end of the direct digital frequency synthesizer is electrically connected to the MCU, the signal output end of the direct digital frequency synthesizer is electrically connected to the sensor, the current sampler is electrically connected with the signal input end of the instrument amplifier, the signal output end of the instrument amplifier is electrically connected to the analog signal input end of the A/D converter, and the digital signal output end of the A/D converter is electrically connected to the MCU through the interface circuit;
the input device is used for inputting preset measurement parameters and detection instructions to the MCU;
during detection, the MCU also sends an instruction to the temperature controller to enable an electric heater arranged in the sensor to work and control the temperature value of the sensor to be maintained at a preset value;
the AC current signal passing through the sensor passes through the current sampler and then is output to an instrument amplifier for amplification, and then an A/D converter converts the amplified analog signal into a digital signal to obtain the digital value of the AC current signal passing through the sensor; the MCU calculates the apparent capacitance real part Cp, the apparent capacitance imaginary part Cp' and the loss tangent value Tan (Delta) of the soil sample according to the amplitude and the phase of the alternating current signal passing through the sensor and the alternating voltage signal at the two ends of the sensor, and simultaneously stores the calculation result in real time.
3. A test device according to claim 1, wherein:
in the direct digital frequency synthesizer which is not based on the table look-up device framework, the direct digital frequency synthesizer internally comprises a D/A converter and a filter, wherein the D/A converter receives a digital value of an alternating voltage signal sent by an MCU, converts the digital value into an analog alternating voltage signal, and outputs the analog alternating voltage signal after high-frequency digital noise is filtered by the filter.
4. A test device according to claim 1, wherein: the input device is any one of a keyboard, a button, and a touch screen.
5. A test device according to any one of claims 1 to 4, wherein: in a soil sample polluted by heavy metals, the types and the contents of the heavy metals influence the shapes of a Cp-f curve which is a real part of the apparent capacitance and a frequency curve, a Tan (Delta) -f curve which is a loss tangent value and a frequency curve, the distortion degree of the curve shape and the distortion position, and reflect the weight of substances with different components in the soil.
6. A test device according to any one of claims 1 to 4, wherein: an electric heater and a thermocouple are also arranged in each metal plate of the sensor, namely two electric heaters and two thermocouples are arranged in the sensor; the electric heater and the thermocouple extend out of the metal plate through the lead wires, and the electric heater and the lead wires are electrically insulated from the metal plate, namely the electric heater and the lead wires are provided with insulating sleeves; the electric heater and the thermocouple are connected to the temperature control module through leads, so that the temperature of the soil sample is kept at a temperature value preset by the MCU during detection.
7. A test device according to any one of claims 1 to 4, wherein: two electric heaters built in the sensor are electrically connected to the temperature control module in parallel.
8. A test device according to any one of claims 1 to 4, wherein: the power module is composed of a MAX610 chip as a core and a peripheral resistance-capacitance element.
9. The utility model provides a soil heavy metal content's detection device based on DDS which characterized in that: the detection device comprises: a sensor, an amplifier, an A/D converter, and an MCU; during detection, the collected soil sample is filled in the sensor; the sensor comprises a pair of parallel sheet metal plates, and each sheet metal plate is connected with an input end of an alternating current signal; the MCU is used for measuring and obtaining a Cp-f curve and a Tan (Delta) -f curve of the soil sample, and inverting the heavy metal content of the soil according to the measured Cp-f curve and the Tan (Delta) -f curve of the soil sample; where Cp is the real part of the apparent capacitance of the soil sample, Tan (Delta) is the loss tangent of the soil sample, and f is the frequency.
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Application publication date: 20190322 Assignee: Nantong Hongjingtian Mechanical Equipment Technology Co.,Ltd. Assignor: Nantong University Technology Transfer Center Co.,Ltd. Contract record no.: X2023980049389 Denomination of invention: A DDS based detection device for soil heavy metal content Granted publication date: 20210406 License type: Common License Record date: 20231203 |