Device for detecting fruit sugar, preparation method and measuring method thereof

Abstract

The invention discloses a fruit sugar detection device, a preparation method and a measurement method thereof.The fruit sugar detection device comprises an electrode needle head, the electrode needle head comprises a conductive connecting part, a needle head body is fixed to the lower side of the conductive connecting part, and the bottom of the needle head body is provided with a tip which can conveniently penetrate into a fruit; the conductive connecting part is connected with an insulating rear sleeve convenient to operate, and a plurality of conductive layers are arranged on the peripheries of the needle head body and the conductive connecting part; according to the device, transmission of excitation current signals and receiving of response voltage signals are integrally designed, the measurement method can realize sugar detection of fruits of various types and shapes, and the measurement of the sugar content of low-sugar fruits also has high sensitivity.

Description

Technical Field

[0001] The invention belongs to the technical field of fruit quality detection, and specifically relates to a device for detecting sugar content in fruit, a preparation method and a measurement method thereof. Background Art

[0002] In recent years, with the continuous improvement of people's living standards, people's demand for fruits has greatly increased, and the requirements for fruit quality have also become higher and higher. Therefore, the detection of fruit sugar content has become particularly important.

[0003] Sugar content is an important indicator of the freshness, taste and nutritional value of fruits. The following methods are usually used to detect the sugar content in fruits: 1. Refractometer method: Although the refractometer method is simple to operate and has a fast measurement speed, it estimates the sugar content by measuring the refractive index of fruit juice. The change in water content will directly affect the refractive index, resulting in inaccurate measurement results. It cannot be used for solid fruits or fruits that cannot extract juice; 2. Near-infrared spectroscopy: Although near-infrared spectroscopy is non-destructive when measuring fruit sugar content, it has high requirements for the uniformity of the fruit to be tested. It may not provide sufficient accuracy when measuring low-sugar fruits, and the cost of related equipment is high, requiring regular maintenance and calibration; 3. High performance liquid chromatography: High performance liquid chromatography is a commonly used method for determining the sugar content in fruits and has high measurement accuracy, but its measurement operation is complicated and the measurement time is long. The instrument settings, sample pretreatment and analysis processes all need to be precisely controlled. In addition, the use of organic solvents during the measurement process may have an adverse effect on the environment; 4. Enzyme inhibition method: The enzyme inhibition method for measuring fruit sugar content has the advantages of rapid measurement, simple equipment and low cost. However, the enzyme inhibition method can only be used for specific substances. It is less applicable to complex mixtures or other components that do not contain enzyme reaction substrates and cannot be widely measured.

[0004] Combining the above-mentioned commonly used fruit sugar detection methods, it is found that the current detection of fruit sugar mostly has requirements on the type and shape of the fruit to be tested. It can only perform sugar detection on a single type or a specific shape of fruit. It is not universal and has low sugar measurement accuracy for low-sugar fruits, high cost and complicated operation.

[0005] Therefore, how to design a fruit sugar measuring device that is not restricted by fruit type and shape and can ensure high measurement accuracy for low-sugar fruits has become an urgent problem to be solved. Summary of the invention

[0006] The purpose of this section is to summarize some aspects of embodiments of the present invention and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section and the specification abstract and the invention title of this application to avoid blurring the purpose of this section, the specification abstract and the invention title, and such simplifications or omissions cannot be used to limit the scope of the present invention.

[0007] In view of the above and / or existing problems in the prior art when detecting the sugar content of fruits, the present invention is proposed.

[0008] Therefore, the purpose of the present invention is to overcome the shortcomings of the prior art. The present invention provides a device for detecting the sugar content in fruits. The present invention only requires inserting the tip into the fruit to be tested, and the conductive layer and the test module are electrically connected to perform sugar detection. The device is not limited by the shape of the fruit and has a wide range of applications.

[0009] The present invention provides a device for detecting the sugar content of fruits, comprising an electrode needle, wherein the electrode needle comprises a conductive connecting part, a needle body is fixed on the lower side of the conductive connecting part, a tip is provided at the bottom of the needle body for convenient insertion into fruits, an insulating rear sleeve is connected to the conductive connecting part for convenient operation, and a plurality of conductive layers are arranged on the periphery of the needle body and the conductive connecting part.

[0010] As a preferred solution of the device for fruit sugar detection in the present invention, the needle body and the outer periphery of the conductive connecting part are each provided with four conductive layers symmetrically arranged in pairs, and the distance between two conductive layers symmetrically arranged about the central axis of the needle body is d, and d is less than 3 mm and greater than 2 mm.

[0011] As a preferred solution of the device for detecting the sugar content of fruits in the present invention, a guide part is fixed on the outside of the conductive connecting part between the two adjacent conductive layers, a plug hole is opened at the center of the rear sleeve, a guide hole is opened at the center of the rear sleeve below the plug hole, and a plurality of guide grooves corresponding to the guide part are arranged on the guide connecting part at the upper outer edge of the plug hole, and the rear sleeve can be just put on the needle body from bottom to top through the guide hole, and the upper end of the rear sleeve can be just plugged into the corresponding guide part through the guide groove.

[0012] As a preferred solution of the device for fruit sugar detection in the present invention, it also includes an electrode cable nozzle and an electrode locking head, the electrode cable nozzle is provided with a connecting hole, and the lower part of the electrode cable nozzle is arranged with a plurality of clamping openings connected with the connecting hole, and the electrode cable nozzle between two adjacent clamping openings has a clamping part for clamping the needle body, and the outer edge of the clamping part has an outer diameter that gradually increases from bottom to top, and the electrode cable nozzle is just mounted on the needle body from bottom to top through the connecting hole, and the electrode cable nozzle contacts the rear sleeve on the lower side of the guide hole, and the electrode locking head is mounted on the outer periphery of the plurality of clamping parts from bottom to top, and the upper part of the electrode locking head is threadedly connected to the outer periphery of the lower part of the rear sleeve, and when the electrode locking head is screwed upward, the clamping part gradually tightens to clamp the electrode cable nozzle on the needle body.

[0013] As a preferred solution of the device for detecting the sugar content in fruits in the present invention, a plurality of scales are arranged at intervals along the axial direction of the needle body on the periphery of the needle body without a conductive layer.

[0014] Another object of the present invention is to provide a method for preparing a device for detecting sugar content in fruit, comprising the following steps: S1. Soak the electrode needle in degreasing alkali solution to degrease the surface of the electrode needle and lightly polish the surface of the ABS plastic needle with 7000-grit sandpaper; S2, evenly apply the protective coating to the area where the coating deposition is not required for protection, and dry the electrode needle after applying the protective coating to obtain a thickness of protective layer; S3, placing the electrode needle with the protective layer into the coating deposition equipment for coating deposition treatment and forming a coating with a thickness of The coating; S4, removing the protective layer and the coating on the surface of the protective layer, and setting a scale on the needle body from which the protective layer has been removed; S5. Rinse the electrode needle prepared in step S4 with clean water and then dry it to obtain an electrode needle plated with four conductive layers symmetrically arranged in pairs.

[0015] Another object of the present invention is to provide a method for measuring the sugar content of fruit using a measuring electrode, comprising the following steps: Weigh the fruit to be tested with an electronic scale, place the fruit to be tested on the testing platform, hold the rear sleeve and insert the lower end of the needle body into the fruit to be tested, and read the insertion depth according to the scale on the surface of the needle body; A sinusoidal AC excitation signal is applied to any two conductive layers on the conductive connection part that are symmetrically arranged about the central axis of the conductive connection part, and a plurality of sinusoidal AC excitation currents with different frequencies are injected into the fruit to be tested in a frequency sweeping manner; The other two conductive layers collect and process the response voltage signals to obtain the impedance amplitude and phase angle data in the response signals; The impedance amplitude, phase angle, weight and insertion depth data of the five frequency points of the fruit to be tested are substituted into the established sugar content measurement mathematical model to calculate the sugar content.

[0016] As a preferred embodiment of the measurement method of the present invention, the sugar content measurement mathematical model is: ; in, TSC is the sugar content of the fruit; a 0 is a constant term, indicating the baseline sugar content; f i is the frequency of the excitation current; Z (f i ) For the frequency The impedance amplitude under the sinusoidal current excitation; θ(f i ) For the frequency f i The phase angle under the sinusoidal current excitation, W is the weight, d is the insertion depth, a i1 , a i2 , a 6 , a 7 , a 8 and a 9 is the proportionality coefficient.

[0017] As a preferred embodiment of the measurement method of the present invention, the calculation formula of the vector a composed of various proportional coefficients is: ; ; in, n represents the number of samples, W n is the weight of the nth sample, d n is the insertion depth of the nth sample, Y For the first sample to the n The vector of the true sugar content of the samples.

[0018] Compared with the prior art, the present invention has the following beneficial effects: the detection device prepared by the present invention realizes an integrated design for the transmission of the excitation current signal and the reception of the response voltage signal, and the conductive layer is manufactured by a deposition plating method. The coating thickness of the conductive layer is controllable and the coating is uniform, thereby improving the accuracy of the excitation signal transmission, and has the advantages of high adhesion, high stability, reusability, and low contact impedance, thereby greatly improving the measurement accuracy; the most suitable spacing between two relatively set coatings is obtained by accurate calculation, stable excitation signal transmission is provided, and the negative impact of excessive field strength on the measurement is avoided; through the measurement method of the present invention, sugar detection of fruits of various types and shapes can be realized, and the sugar content measurement of low-sugar fruits is also highly sensitive. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. 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 creative labor. Among them: Figure 1 It is a three-dimensional structural diagram of the measuring electrode in the present invention.

[0020] Figure 2 This is an exploded structural diagram of the measuring electrode in the present invention.

[0021] Figure 3 for Figure 2 A partial enlarged view of point A in the middle.

[0022] Figure 4 This is a three-dimensional structural diagram of the electrode needle in the measuring electrode.

[0023] Figure 5 This is the simulation diagram of the excitation electric field under different conductive layer spacing d.

[0024] Figure 6 The insertion depth is , the measurement frequency band is 1 khz ~200 khz , the measurement results of apple electrical impedance characteristic parameters (impedance amplitude, phase angle) with 200 measurement points.

[0025] Figure 7 The insertion depth is , the measurement results of apple characteristic parameters (impedance amplitude, phase angle) with a measurement frequency band of 1khz~200khz and 200 measurement points.

[0026] Figure 8 The insertion depth is , the measurement results of apple characteristic parameters (impedance amplitude, phase angle) with a measurement frequency band of 1khz~200khz and 200 measurement points.

[0027] Fig. 9 This is the measurement result graph of apple characteristic parameters (impedance amplitude, phase angle) with an insertion depth of 30mm, a measurement frequency range of 1khz to 200khz, and 200 measurement points.

[0028] Fig.10 This is a schematic diagram of measuring fruit (Example 3) using the present invention.

[0029] Fig.11 It is a principle block diagram of the detection module in the present invention.

[0030] In the figure, 100 is the electrode needle, 101 is the needle body, 102 is the conductive connecting part, 102a is the guide part, X is the conductive layer, S is the scale, 200 is the rear sleeve, 201 is the guide groove, 300 is the electrode locking head, 400 is the electrode rope nozzle, 401 is the clamping part, 402 is the clamping mouth, and 403 is the connecting hole. DETAILED DESCRIPTION

[0031] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the embodiments of the specification.

[0032] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein, and those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0033] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The term "in one embodiment" that appears in different places in this specification does not necessarily refer to the same embodiment, nor does it refer to a separate or selective embodiment that is mutually exclusive with other embodiments.

[0034] Example 1 Reference Figure 1~Figure 4 , which is the first embodiment of the present invention, provides a device for detecting the sugar content of fruits, which can realize the sugar content detection of various fruits and has a wider range of applications.

[0035] A device for detecting the sugar content of fruit comprises an electrode needle, the electrode needle comprises a conductive connection part, a needle body is fixed on the lower side of the conductive connection part, a tip is provided at the bottom of the needle body for convenient insertion into the fruit, an insulating rear sleeve for convenient operation is connected to the conductive connection part, a plurality of conductive layers are arranged on the periphery of the needle body and the conductive connection part, a guide part is fixed on the outer side of the conductive connection part between two adjacent conductive layers, a plug hole is opened at the center of the rear sleeve, a guide hole is opened at the center of the rear sleeve below the plug hole, a plurality of guide grooves corresponding to the guide parts are arranged on the guide connection part at the upper outer edge of the plug hole, the rear sleeve can be just put on the needle body from bottom to top through the guide hole, and the upper end of the rear sleeve can be just plugged into the corresponding guide part through the guide groove.

[0036] Specifically, four conductive layers are arranged symmetrically in pairs on the periphery of the needle body and the conductive connecting part, and the distance between two conductive layers symmetrically arranged about the central axis of the needle body is d.

[0037] Specifically, it also includes an electrode rope nozzle and an electrode locking head. A connecting hole is opened on the electrode rope nozzle. A plurality of clamping openings connected to the connecting hole are arranged at the lower part of the electrode rope nozzle. A clamping part for clamping the needle body is provided on the electrode rope nozzle between two adjacent clamping openings. The outer edge of the clamping part has an outer diameter that gradually increases from bottom to top. The electrode rope nozzle is just mounted on the needle body from bottom to top through the connecting hole. The electrode rope nozzle contacts the rear tube sleeve on the lower side of the guide hole. The electrode locking head is mounted on the periphery of the plurality of clamping parts from bottom to top. The upper part of the electrode locking head is threadedly connected to the periphery of the lower part of the rear tube sleeve. When the electrode locking head is screwed upward, the clamping part gradually tightens so that the electrode rope nozzle is clamped on the needle body.

[0038] In order to further facilitate observation of the depth of the needle body inserted into the fruit, a plurality of scales are arranged at intervals along the axial direction of the needle body on the periphery of the needle body without a conductive layer.

[0039] Example 2 This is the second embodiment of the present invention. This embodiment is based on the first embodiment. This embodiment provides a method for preparing a device for detecting sugar content in fruit, comprising the following steps: S1. According to the simulation and calculation of the enhancement effect of the excitation electric field, the specific size of the electrode needle is designed: including the distance between the two oppositely arranged conductive layers (i.e., tip diameter), in this embodiment, d is preferably ,length for , end diameter is 10mm, length L2 is And set the depth to The grooves are convenient for applying protective coating and depositing coating; The specific process of determining d is: A set of opposite conductive layers in the electrode needle is selected as the excitation electrode to simulate the excitation electric field. In order to ensure sufficient contact area between the conductive layer and the measured tissue, the arc length is controlled to be 1.2 mm. The excitation electric field is changed by changing the distance d between the electrode plating layers. The distance between the conductive layers at the best tip is selected by observing the intensity of the excitation electric field. A set of opposite conductive layers in the electrode needle is selected as the excitation electrode to calculate the excitation electric field. Assuming that the charge distribution is uniform, the charge per unit area is , a tiny charge element on the surface of the coating dq It can be expressed as: ; Where d is the distance between two conductive layers symmetrically arranged about the central axis of the needle body, dθ is a small increment of angle, dz A small length increment along the coating direction; According to Coulomb's law, the charge of a microelement At a point in the electric field The electric field generated It has radial and vertical components. Due to symmetry, the integrals of the radial components along the axis cancel each other out, leaving only the vertical component (along the axis). direction, The direction is along the axial direction of the needle body), the magnitude of the excitation electric field is obtained by Coulomb's law: ; in, From the charge element To point The distance It can be expressed as: ; The total electric field The direction components are: ; in, ε 0 is the electric constant of vacuum, z is the vertical component from the charge element to point p, and the direction of the electric field needs to be obtained by decomposing the vector. z is the vertical component of the electric field. Due to the symmetry of the electric field, only along the direction The weight will not be offset.

[0040] The simulation process for the enhancement effect of the excitation electric field is as follows: In order to ensure that the conductive layers in the electrode needle do not interfere with each other and the structure has a certain strength, the spacing between the two relatively set conductive layers (there are two groups in total) is controlled. d≥1.5mm.A set of opposite conductive layers in the electrode needle is randomly selected to inject the excitation current and to ensure sufficient contact area between the electrode coating and the measured tissue, the arc length is controlled to be , changing the distance between the conductive layers d to change the excitation electric field.

[0041] The simulation results are as follows Figure 5 As shown in the figure, for the effect of enhancing the excitation electric field, the distance between the two conductive layers set opposite to each other is d The smaller the excitation electric field strength, the higher the excitation electric field strength. However, according to the simulation results of the excitation electric field, it is found that when Although the excitation electric field intensity is very large, the distribution uniformity of the excitation electric field is poor, which may cause the local current in the fruit to be tested to be too large, resulting in deviation and instability in the measurement results of impedance amplitude, phase angle and other information. At the same time, combined with the analysis of the simulation results of the excitation electric field intensity, it is found that when the tip plating spacing When the excitation electric field is evenly distributed, the electric field strength is low, which may weaken the transmission of the excitation signal and result in insufficient measurement accuracy for low-sugar fruits.

[0042] Combining simulation and calculation results, the most suitable spacing between the two conductive layers of the tip symmetrically arranged about the central axis of the needle body is obtained. Between 2mm and 3mm, because it achieves a good balance between the excitation electric field strength and uniformity, it can not only provide stable excitation signal transmission but also avoid the negative impact of excessive field strength on measurement.

[0043] S2, according to the data obtained in step S1, through the precision Print or Finishing manufacturing (which is the prior art, how to prepare is not the innovation of the present invention) an electrode needle (without a conductive layer and without scale), soaking the electrode needle in a degreasing alkali solution, degreasing the surface of the electrode needle, and lightly polishing the surface of the ABS plastic electrode needle with 7000-grit sandpaper; S3, applying a protective coating (the protective coating is composed of 30% by mass of a protective agent, 20% by mass of an adhesive and 50% by mass of an alcohol diluent, the protective agent, the adhesive and the diluent are all prior art, the protective agent can be any one of an organic polymer material polyimide resin, acrylic resin, an inorganic material siloxane, silicon nitride, aluminum oxide or zinc oxide, and the adhesive can be any one of an epoxy resin, polyurethane or cyanoacrylate) uniformly on an area where no coating deposition is required for protection treatment, drying the electrode needle tip coated with the protective coating to obtain a protective layer with a thickness of 50 to 100 μm. In this embodiment, the thickness of the protective layer is 100 ; S4. Place the electrode needle with the protective layer into the coating deposition equipment (which is the prior art. The coating deposition method used is the DC sputtering method. In order to provide an inert environment and ensure that the coating composition is pure copper, the gas introduced into the coating deposition equipment is argon gas. Before starting the deposition, the vacuum chamber is evacuated to a pressure of about 10 -6 Torr vacuum environment, and then argon gas was introduced into the vacuum environment to control the pressure at 10 -2 Torr to The coating deposition process is carried out in the range of 5sccm to 100sccm, and the temperature during the coating deposition process is adjusted between room temperature (20℃~30℃) and 500℃. The target current applied to the pure copper target is , the coating deposition time is , forming a thickness of 1 to 70 In this embodiment, the thickness of the coating is preferably 70 ; S5. removing the protective layer and the coating on the surface of the protective layer (removing the protective layer includes using an organic solvent to remove the protective coating layer whose protective agent is an organic polymer, using hydrofluoric acid or sodium hydroxide to remove the protective coating layer whose protective agent is an inorganic material, and removing the coating on the surface of the protective coating layer by lightly grinding with 10000 mesh ultra-fine sandpaper), and setting a scale on the needle body from which the protective layer has been removed; S6, rinsing the electrode needle prepared in step S5 with clean water and then drying it to obtain an electrode needle plated with four conductive layers symmetrically arranged in pairs; S7. First, put the rear sleeve on the conductive connecting part from bottom to top, rotate the rear sleeve to align the guide groove with the corresponding guide part, insert the rear sleeve on the guide part through the guide groove, and make the rear sleeve abut against the guide part to achieve the circumferential positioning and preliminary axial positioning of the rear sleeve, then put the electrode nozzle on the needle body to make it abut against the rear sleeve, finally put the electrode locking head on the needle body, rotate the electrode locking head, and the electrode locking head is threadedly connected to the lower part of the rear sleeve. When the electrode locking head is continuously screwed upward, the clamping part gradually tightens to clamp the electrode nozzle on the needle body, thereby achieving the fixation of the electrode nozzle, the rear sleeve and the electrode needle, and finally preparing the measuring electrode.

[0044] The preparation process of protective coating is: (1) Weigh the protective agent, adhesive and diluent according to the set mass percentage; (2) Add 60% of a diluent (the diluent preferably includes ethanol and isopropanol, the total amount of the diluent is 30%, of which ethanol accounts for 20% and isopropanol accounts for 10%) into a stirring container, slowly add the organic polymer material protective agent and stir for 40 minutes until it is completely dissolved; (3) In another container, add the remaining diluent (total amount is 20%, of which ethanol accounts for 8% and isopropanol accounts for 12%), add the adhesive and stir for 20 minutes until it is uniform; (4) Slowly pour the adhesive solution into the polymer material protective agent solution, stirring while pouring, for 30 minutes until it is uniform; (5) Filter the protective coating through a 200-mesh filter, place in a sealed container, and store in a dry and cool place.

[0045] Example 3 refer to Figure 10~Figure 11 This embodiment is based on Embodiment 2. This embodiment provides a method for measuring the sugar content of fruits using measuring electrodes, which can achieve the measurement of fruits of various types and shapes, and can ensure high measurement accuracy for low-sugar fruits.

[0046] Specifically, it also includes a detection module, which includes an excitation signal generating unit, an electrode signal acquisition unit, a response signal detection unit, a main control unit and a host computer. The excitation signal generating unit includes a direct digital frequency synthesizer (DDS) and a voltage-controlled current source (VCCS). In this embodiment, the programmable, low-noise, and lowest-power AD9850 in the same series is selected as the signal generating circuit chip. At a working frequency of 125 MHz, the output frequency resolution can reach 0.0291 Hz, and the Arduino UNO as the main control unit can divide the system clock through programming to generate a sinusoidal AC voltage signal with a frequency range of 0.1Hz~40MHz. In this example, the improved Howland current source circuit is preferably used as the voltage-controlled constant current source circuit; the response signal detection unit includes a buffer circuit, a differential amplifier circuit, a logarithmic detection circuit and an A / D conversion module. Preferably, the buffer circuit in this embodiment uses a TL082 dual-channel operational amplifier as a pre-input channel to form two voltage followers to realize impedance conversion. Preferably, the AD8130 differential operational amplifier is used to design the differential amplifier circuit, which can reach a high common mode rejection ratio of 94dB and has a 1MΩ differential input impedance; preferably, the AD8302 chip is used to design the logarithmic detection circuit, which can detect the amplitude ratio and phase difference of two sets of input signals and convert them into DC voltage signals for output. The A / D conversion module uses the built-in 10-bit analog-to-digital converter of Arduino to upload the amplitude and phase information output by the amplitude and phase detection circuit to the host computer through the USB communication line and store them.

[0047] A method for measuring the sugar content of fruit using a measuring electrode, comprising the following steps: Weigh the fruit to be tested with an electronic scale, place the fruit to be tested on the testing platform, hold the rear sleeve and insert the lower end of the needle body into the fruit to be tested, and read the insertion depth according to the scale on the surface of the needle body; A sinusoidal AC excitation signal is applied to any two conductive layers on the conductive connection part that are symmetrically arranged about the central axis of the conductive connection part, and a plurality of sinusoidal AC excitation currents with different frequencies are injected into the fruit to be tested in a frequency sweeping manner; The other two conductive layers collect and process the response voltage signals to obtain the impedance amplitude and phase angle data in the response signals; The impedance amplitude, phase angle, weight and insertion depth data of the five frequency points of the fruit to be tested are substituted into the established sugar content measurement mathematical model to calculate the sugar content.

[0048] Among them, the mathematical model for sugar content measurement is: ; in, TSC is the sugar content of the fruit; a 0 is a constant term, indicating the baseline sugar content; f i is the frequency of the excitation current; Z (f i ) For the frequency The impedance amplitude under the sinusoidal current excitation; θ(f i ) For the frequency f i The phase angle under the sinusoidal current excitation, W is the weight, d is the insertion depth, a i1 , a i2 , a 6 , a 7 , a 8 and a 9 is the proportionality coefficient.

[0049] The least squares method is used to solve the normal equation to obtain the optimal proportional coefficient. The goal is to minimize the sum of squared errors. .

[0050] ; ; ; Among them, a is the vector composed of various proportional coefficients, n represents the number of samples, W n is the weight of the nth sample,d n is the insertion depth of the nth sample, Y For the first sample to the n The vector of the true sugar content of samples, It is The actual sugar content of the samples, The model predicts The sugar content of each sample.

[0051] Example 4 refer to Figure 6 to Figure 10 This embodiment is based on embodiment 3, and this embodiment can further verify that when the depth parameter is added to the mathematical model for sugar calculation, the accuracy of sugar detection can be improved.

[0052] In this embodiment, Fig.10 As shown, the lower end of the needle body is inserted into the apple to be tested, and the insertion position is the intersection of the equator and the meridian of the apple. Two groups of conductive layer groups (each conductive layer group consists of two conductive layers arranged oppositely in two radial directions) are electrically connected to the detection module respectively, and five sinusoidal AC excitation currents with different frequencies are injected into the apple to be tested in a frequency sweeping manner. The five frequency points of the sinusoidal AC excitation current are 1 khz , 10 khz , 50 khz , 100 khz and 200 khz .

[0053] according to Figure 6 to Figure 9 , in the low frequency band ( ), shallow insertion is more sensitive to low frequency signals, and the impedance amplitude The attenuation speed is fast, the initial impedance and phase angle are high, and the electrical characteristics of the surface tissue of the fruit to be tested can be better captured. ), shallow insertion impedance magnitude This indicates that the excitation signal has penetrated deep into the cells of the fruit to be tested and can better reflect the overall sugar concentration of the fruit to be tested.

[0054] according to Figure 6 to Figure 9 , in the low frequency band ( ), deep insertion impedance modulus The attenuation is slow in the low frequency band, and the initial impedance amplitude is Significantly lower impedance magnitude than shallow insertion This is because deep insertion covers more internal tissues and has limited reflection on the electrical characteristics of the surface of the fruit to be tested. , deep insertion impedance magnitude It is significantly lower than that of shallow insertion, and the curve is smoother, which indicates that the excitation signal of deep insertion has been able to penetrate the cell membrane, and the phase angle of deep insertion rises gently with the increase of frequency, and tends to be stable after transitioning to the high frequency band. This shows that compared with shallow insertion, the excitation signal of deep insertion can better penetrate the cell membrane and more comprehensively reflect the overall characteristics of the fruit to be tested, thereby being more sensitive to the overall sugar content.

[0055] Therefore, since different insertion depths will cause different effects on the current at different frequencies, shallow insertion is more sensitive to the impedance response at low frequencies, while deep insertion can better reflect the overall electrical characteristics inside the fruit and has a more significant response to high frequencies. Therefore, the interaction term between the insertion depth and the impedance amplitude at different frequencies is introduced into the mathematical model of sugar measurement: .

[0056] The measurement method in this application can be used to detect the sugar content of fruits of various types and shapes. It also has high sensitivity for measuring the sugar content of low-sugar fruits, and has the advantages of high accuracy, fast measurement speed, convenience and flexibility.

[0057] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A device for detecting sugar content in fruit, characterized in that: The electrode needle comprises an electrode needle, which comprises a conductive connecting part, a needle body is fixed on the lower side of the conductive connecting part, a tip is provided at the bottom of the needle body for convenient insertion into the fruit, an insulating rear sleeve is connected to the conductive connecting part for easy operation, and a plurality of conductive layers are arranged on the periphery of the needle body and the conductive connecting part.

2. The device for detecting sugar content in fruit as claimed in claim 1, characterized in that: The needle body and the conductive connecting part are both provided with four conductive layers symmetrically arranged in pairs, and the distance between two conductive layers symmetrically arranged about the central axis of the needle body is d, which is less than 3 mm and greater than 2 mm.

3. The device for detecting sugar content in fruit as claimed in claim 1, characterized in that: A guide part is fixed on the outside of the conductive connecting part between the two adjacent conductive layers, a plug hole is opened in the center of the rear sleeve, a guide hole is opened in the center of the rear sleeve below the plug hole, and a plurality of guide grooves corresponding to the guide part are arranged on the guide connecting part at the upper outer edge of the plug hole, and the rear sleeve can be just put on the needle body from bottom to top through the guide hole, and the upper end of the rear sleeve can be just plugged into the corresponding guide part through the guide groove.

4. The device for detecting sugar content in fruit as claimed in claim 2, characterized in that: It also includes an electrode rope nozzle and an electrode locking head. The electrode rope nozzle is provided with a connecting hole. The lower part of the electrode rope nozzle is provided with a plurality of clamping openings connected with the connecting hole. The electrode rope nozzle between two adjacent clamping openings has a clamping part for clamping the needle body. The outer edge of the clamping part has an outer diameter that gradually increases from bottom to top. The electrode rope nozzle is just mounted on the needle body from bottom to top through the connecting hole. The electrode rope nozzle contacts the rear tube sleeve on the lower side of the guide hole. The electrode locking head is mounted on the periphery of the plurality of clamping parts from bottom to top. The upper part of the electrode locking head is threadedly connected to the periphery of the lower part of the rear tube sleeve. When the electrode locking head is screwed upward, the clamping part gradually tightens to clamp the electrode rope nozzle on the needle body.

5. The device for detecting sugar content in fruit as claimed in claim 1, characterized in that: A plurality of scales are arranged at intervals along the axial direction of the needle body on the periphery of the needle body without a conductive layer.

6. A method for preparing the device for detecting sugar content in fruit as claimed in claim 5, characterized in that: The following steps are included: S1. Soak the electrode needle in degreasing alkali solution, degrease the surface of the electrode needle and lightly polish the needle surface with 7000 mesh sandpaper; S2, evenly apply the protective coating to the area where the coating deposition is not required for protection, and dry the electrode needle tip coated with the protective coating to obtain a protective layer with a thickness of 1000 Å; S3, placing the electrode needle with the protective layer into the coating deposition equipment for coating deposition treatment and forming a coating with a thickness of The coating; S4, removing the protective layer and the coating on the surface of the protective layer, and setting a scale on the needle body from which the protective layer has been removed; S5. Rinse the electrode needle prepared in step S4 with clean water and then dry it to obtain an electrode needle plated with four conductive layers symmetrically arranged in pairs.

7. A method for detecting the sugar content of fruit using the measuring electrode prepared according to claim 5, characterized in that: The following steps are included: Weigh the fruit to be tested with an electronic scale, place the fruit to be tested on the testing platform, hold the rear sleeve and insert the lower end of the needle body into the fruit to be tested, and read the insertion depth according to the scale on the surface of the needle body; A sinusoidal AC excitation signal is applied to any two conductive layers on the conductive connection part that are symmetrically arranged about the central axis of the conductive connection part, and a plurality of sinusoidal AC excitation currents with different frequencies are injected into the fruit to be tested in a frequency sweeping manner; The other two conductive layers collect and process the response voltage signals to obtain the impedance amplitude and phase angle data in the response signals; The impedance amplitude, phase angle, weight and insertion depth data of the five frequency points of the fruit to be tested are substituted into the established sugar content measurement mathematical model to calculate the sugar content.

8. The measuring method according to claim 7, characterized in that: The sugar content measurement mathematical model is: ； in, TSC is the sugar content of the fruit; a 0 is a constant term, indicating the baseline sugar content; f i is the frequency of the excitation current; Z(f i ) For the frequency The impedance amplitude under the sinusoidal current excitation; θ(f i ) For the frequency f i The phase angle under the sinusoidal current excitation, W is the weight, d is the insertion depth, a i1 , a i2 , a 6 , a 7 , a 8 and a 9 is the proportionality coefficient.

9. The measuring method according to claim 8, characterized in that: The calculation formula of the vector a composed of various proportional coefficients is: ； ； in, n represents the number of samples, W n is the weight of the nth sample, d n is the insertion depth of the nth sample, Y For the first sample to the n The vector of the true sugar content of the samples.

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