A device for detecting sugar content of fruits, a preparation method thereof, and a measuring method thereof

Abstract

The application discloses a device for fruit sugar content detection, a preparation method and a measuring method thereof. The device comprises an electrode needle head, the electrode needle head comprises a conductive connecting part, the lower side of the conductive connecting part is fixed with a needle head body, the bottom of the needle head body is provided with a sharp end convenient for piercing into a fruit, the conductive connecting part is connected with an insulated rear sleeve convenient for operation, and the outer periphery of the needle head body and the conductive connecting part is arranged with a plurality of conductive layers. The device is integrated in the transmission of excitation current signals and the reception of response voltage signals, the measuring method can realize sugar content detection of various types and shapes of fruits, and has high sensitivity for sugar content measurement of low-sugar fruits.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of fruit quality detection, and particularly relates to a device for fruit sugar detection, a preparation method and a measurement method thereof. BACKGROUND

[0002] In recent years, with the continuous improvement of people's living standards, people's demand for fruits has greatly improved, and the requirement for fruit quality is also getting higher and higher, so the detection of fruit sugar becomes particularly important.

[0003] Sugar, as an important indicator of fruit freshness, taste and nutritional value, usually needs to be detected by the following methods: 1. Refractometer method: although the refractometer method for measuring fruit sugar is simple to operate and fast to measure, it estimates the sugar content by measuring the refractive index of fruit juice, and the change of water content directly affects the refractive index, resulting in inaccurate measurement results, and it cannot be used for solid fruits or fruits that cannot extract juice; 2. Near-infrared spectroscopy method: although the near-infrared spectroscopy method is non-destructive when measuring fruit sugar, it has high requirements for the uniformity of the fruit to be measured, and may not provide sufficient accuracy when measuring low-sugar fruits, and the cost of related equipment is high, which needs regular maintenance and calibration; 3. High performance liquid chromatography method: high performance liquid chromatography method is a commonly used method for measuring fruit sugar and has high measurement accuracy, but the measurement operation is complex, the measurement time is long, and the instrument setting, sample pretreatment and analysis process need to be accurately controlled, and organic solvents are used in the measurement process, which may have adverse effects on the environment; 4. Enzyme inhibition method: enzyme inhibition method for measuring fruit sugar has the advantages of rapid measurement, simple equipment and low cost, but enzyme inhibition method can only be used for specific substances, and the applicability of enzyme inhibition method is poor for complex mixtures or other components that do not contain enzyme reaction substrates, and enzyme inhibition method cannot be widely used.

[0004] Comprehensive analysis of the above several commonly used fruit sugar detection methods shows that the current fruit sugar detection methods mostly have requirements for the type and shape of the fruit to be measured, and can only detect the sugar content of single type or specific shape of fruit, which is not universal and has low measurement accuracy for low-sugar fruits, high cost and complex operation.

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

[0006] This section is intended to introduce some aspects of embodiments of the present application, which are further described in the following recitation. This section is not intended to limit the scope or application of the embodiments in any manner.

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

[0008] Therefore, the present application aims at overcoming the deficiencies in the prior art, and provides a device for detecting sugar content of fruits.

[0009] The present application provides a device for detecting sugar content of fruits, comprising an electrode needle head, the electrode needle head comprising a conductive connecting part, the lower side of the conductive connecting part being fixed with a needle body, the bottom of the needle body being provided with a sharp end for conveniently piercing into fruits, the conductive connecting part being connected with an insulated rear sleeve for convenient operation, and the outer periphery of the needle body and the conductive connecting part being arranged with a plurality of conductive layers.

[0010] As a preferred scheme of the device for detecting sugar content of fruits in the present application, the outer periphery of the needle body and the conductive connecting part is provided with four pairs of symmetrically arranged conductive layers, the distance between two conductive layers symmetrically arranged about the center axis of the needle body being d, d being less than 3 mm and greater than 2 mm.

[0011] As a preferred scheme of the device for detecting sugar content of fruits in the present application, the outer side of the conductive connecting part between the adjacent two conductive layers is fixed with a guide part, the center of the rear sleeve is provided with a plug-in hole, the lower side of the plug-in hole of the rear sleeve being provided with a guide hole, the outer edge of the upper part of the plug-in hole being arranged with a plurality of guide grooves corresponding to the guide parts one by one, the rear sleeve being able to be just fitted on the needle body from the lower to the upper through the guide hole, and the upper end of the rear sleeve being able to be just plugged into the corresponding guide part through the guide groove.

[0012] As a preferred scheme of the device for detecting the sugar content of fruits in the application, wherein: an electrode socket and an electrode lock head are further included, the electrode socket is provided with a connecting hole, and the lower part of the electrode socket is arranged with a plurality of clamping openings in communication with the connecting hole, the electrode socket is provided with a clamping part for clamping the needle body between two adjacent clamping openings, the outer diameter of the clamping part gradually increases from bottom to top, the electrode socket is just sleeved on the needle body from bottom to top through the connecting hole, the electrode socket abuts against the rear sleeve on the lower side of the guide hole, and the electrode lock head is sleeved on the outer periphery of the clamping part from bottom to top.

[0013] As a preferred scheme of the device for detecting the sugar content of fruits in the application, wherein: the outer periphery of the needle body without the conductive layer is arranged with a plurality of scales arranged at intervals along the axial direction of the needle body.

[0014] Another object of the application is to provide a preparation method of the device for detecting the sugar content of fruits, comprising the following steps,

[0015] S1, the electrode needle is soaked in a degreasing alkali solution to perform degreasing treatment on the surface of the electrode needle, and the surface of the ABS plastic needle is slightly polished with a sandpaper with a mesh of 7000;

[0016] S2, the protective coating is uniformly applied to the area that does not need to be protected by the deposition of the coating layer to perform protection treatment, and the electrode needle coated with the protective coating is dried to obtain a protective layer with a thickness of ;

[0017] S3, the electrode needle with the protective layer is placed in a coating deposition device to perform coating deposition treatment and form a coating layer with a thickness of on the surface thereof;

[0018] S4, the protective layer and the coating layer on the surface of the protective layer are removed, and the scales are arranged on the needle body from which the protective layer is removed;

[0019] S5, the electrode needle prepared in step S4 is washed with clean water and then dried, so that the electrode needle plated with four pairs of symmetrical conductive layers is obtained.

[0020] Another object of the application is to provide a method for measuring the sugar content of fruits by using a measuring electrode, comprising the following steps,

[0021] The weight of the fruit to be measured is weighed by using an electronic scale, the fruit to be measured is placed on a detection platform, the lower end of the needle body is inserted into the fruit to be measured by holding the rear sleeve, and the insertion depth is read according to the scales on the surface of the needle body;

[0022] The sinusoidal alternating excitation signal is applied on the two conductive layers which are symmetrically arranged on the conductive connecting part with respect to the central axis of the conductive connecting part, so as to inject the sinusoidal alternating excitation current with multiple different frequencies into the fruit to be measured in a frequency sweeping manner;

[0023] The other two conductive layers collect the response voltage signals and process the response signals to obtain the impedance amplitude and phase angle data in the response signals;

[0024] The impedance amplitude, phase angle, weight and insertion depth data of the fruit to be measured at the five frequency points are substituted into the established sugar measurement mathematical model to calculate the sugar content.

[0025] As a preferred scheme of the measurement method in the application, wherein: the sugar measurement mathematical model is,

[0026] ;

[0027] Wherein, TSC is the sugar content of the fruit; a 0 is a constant term, representing the baseline sugar content; f i is the frequency of the excitation current; Z (f i ) is the impedance amplitude under the excitation of the sinusoidal wave current with the frequency of ; θ(f i ) is the phase angle under the excitation of the sinusoidal wave current with the frequency of f i , W is the weight, d is the insertion depth, a i1 , a i2 , a 6 , a 7 , a 8 and a 9 are proportional coefficients.

[0028] As a preferred scheme of the measurement method in the application, wherein: the calculation formula of the vector a composed of each proportional coefficient is,

[0029] ;

[0030] ;

[0031] Wherein, n represents the sample number,W n is the weight of the nth sample, d n is the insertion depth of the nth sample, Y is a vector composed of the true sugar content of the 1st sample to the nth sample. n

[0032] Compared with the prior art, the detection device prepared by using the application has the following beneficial effects: the detection device realizes integrated design of transmission of excitation current signal and reception of response voltage signal, the conductive layer is manufactured by using deposition plating method, the plating thickness of the conductive layer is controllable, the plating is uniform, the accuracy of excitation signal transmission is improved, the conductive layer has the advantages of high adhesion, high stability, reusability and small contact impedance, so that the measurement accuracy can be greatly improved; the most suitable interval between the two relative arranged coatings is obtained by accurate calculation, stable excitation signal transmission is provided, and the negative influence of excessively high field strength on measurement is avoided; by the measurement method in the application, sugar detection of various types and shapes of fruits can be realized, and the sugar content measurement of low-sugar fruits also has high sensitivity. BRIEF DESCRIPTION OF DRAWINGS

[0033] In order to more clearly illustrate the technical solutions of the embodiments of the application, the drawings needed in the embodiment description will be briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the application, and other drawings can be obtained by those skilled in the art without creative labor. Among them:

[0034] Figure 1 is a perspective view of the measurement electrode in the application.

[0035] Figure 2 is an exploded view of the measurement electrode in the application.

[0036] Figure 3 is a partial enlarged view of A in Figure 2

[0037] Figure 4 is a perspective view of the electrode needle in the measurement electrode.

[0038] Figure 5 is an excitation electric field simulation diagram under different conductive layer intervals d.

[0039] Figure 6 is a measurement result diagram of the resistance impedance characteristic parameters (impedance amplitude, phase angle) of the apple with an insertion depth of , a measurement frequency band of 1 khz ~200 khz , and 200 measurement points. ​​

[0040] Figure 7 Fig. 1 is a measurement result chart of the characteristic parameters (impedance amplitude, phase angle) of an apple with an insertion depth of 10 mm, a measurement frequency band of 1 kHz-200 kHz, and 200 measurement points.

[0041] Figure 8 Fig. 2 is a measurement result chart of the characteristic parameters (impedance amplitude, phase angle) of an apple with an insertion depth of 20 mm, a measurement frequency band of 1 kHz-200 kHz, and 200 measurement points.

[0042] Figure 9 Fig. 3 is a measurement result chart of the characteristic parameters (impedance amplitude, phase angle) of an apple with an insertion depth of 30 mm, a measurement frequency band of 1 kHz-200 kHz, and 200 measurement points.

[0043] Figure 10 Fig. 4 is a schematic diagram of the use of the present application in measuring fruits (Example 3).

[0044] Figure 11 Fig. 5 is a schematic diagram of the principle of the detection module in the present application.

[0045] In the figure, 100 is an electrode needle head, 101 is a needle head body, 102 is a conductive connection part, 102a is a guide part, X is a conductive layer, S is a scale, 200 is a rear cylinder sleeve, 201 is a guide groove, 300 is an electrode lock head, 400 is an electrode nozzle, 401 is a clamping part, 402 is a clamping opening, and 403 is a connection hole. DETAILED DESCRIPTION

[0046] In order to make the above-mentioned objects, features and advantages of the present application more obvious and easy to understand, the specific embodiments of the present application will be described in detail below in combination with the description examples.

[0047] In the following description, many specific details are set forth in order to provide a thorough understanding of the present application. However, the present application can be practiced in other manners different from those described herein, and those skilled in the art can make similar generalizations without departing from the scope of the present application. Therefore, the present application is not limited to the specific embodiments disclosed below.

[0048] Secondly, the "one embodiment" or "embodiment" referred to herein means that the specific features, structures or characteristics can be included in at least one implementation of the present application. The "in one embodiment" appearing in different places in the specification does not mean the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments.

[0049] Example 1

[0050] Reference Figures 1-4 ​​For the first embodiment of the present application, a device for fruit sugar detection is provided, which can realize sugar detection of various fruits and has a wider application range.

[0051] The device for fruit sugar detection comprises an electrode needle head, the electrode needle head comprises a conductive connecting part, the lower side of the conductive connecting part is fixed with a needle body, the bottom of the needle body is provided with a sharp end for conveniently penetrating into a fruit, the conductive connecting part is connected with an insulated rear sleeve for convenient operation, the outer periphery of the needle body and the conductive connecting part is arranged with a plurality of conductive layers, the outer side of the conductive connecting part between two adjacent conductive layers is fixed with a guide part, the center of the rear sleeve is provided with a plug-in hole, the center of the rear sleeve at the lower side of the plug-in hole is provided with a guide hole, the guide connecting part at the outer edge of the upper part of the plug-in hole is arranged with a plurality of guide grooves corresponding to the guide parts, the rear sleeve can be just sleeved on the needle body from the lower side to the upper side 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.

[0052] Specifically, the outer periphery of the needle body and the conductive connecting part is provided with four pairs of symmetrically arranged conductive layers, and the distance between two conductive layers symmetrically arranged about the central axis of the needle body is d.

[0053] Specifically, the device further comprises an electrode socket and an electrode lock head, the electrode socket is provided with a connecting hole, the lower part of the electrode socket is arranged with a plurality of clamping openings in communication with the connecting hole, the electrode socket between two adjacent clamping openings is provided with a clamping part for clamping the needle body, the outer edge of the clamping part gradually increases in diameter from the lower side to the upper side, the electrode socket is just sleeved on the needle body from the lower side to the upper side through the connecting hole, the electrode socket abuts against the rear sleeve at the lower side of the guide hole, and the electrode lock head is sleeved on the outer periphery of the plurality of clamping parts from the lower side to the upper side, the upper part of the electrode lock head is threadedly connected to the outer periphery of the lower part of the rear sleeve, and when the electrode lock head is screwed upward, the clamping part is gradually tightened to clamp the electrode socket on the needle body.

[0054] In order to further facilitate the observation of the depth of the needle body inserted into the fruit, the outer periphery of the needle body without the conductive layer is arranged with a plurality of scales arranged at intervals along the axial direction of the needle body.

[0055] Embodiment 2

[0056] The second embodiment of the present application is based on the first embodiment, and the present embodiment provides a preparation method of the device for fruit sugar detection, comprising the following steps,

[0057] S1, the specific size of the electrode needle head is designed according to the simulation and calculation of the enhancement effect of the excitation electric field, including the distance between two oppositely arranged conductive layers (that is, the diameter of the sharp end), in the present embodiment, d is preferably , the length is , and the tail end diameter It is 10mm, and the length L2 is And set the depth at the location where vacuum physical deposition is required. The grooves facilitate the application of protective coatings and the deposition of plating layers;

[0058] The process of determining d is as follows:

[0059] A set of opposing conductive layers in the electrode needle can be selected as excitation electrodes to simulate the excitation electric field. In order to ensure that there is sufficient contact area between the conductive layer and the tissue being tested, the arc length is controlled to be 1.2 mm. The excitation electric field is changed by changing the distance d between the electrode coatings. The optimal distance between the conductive layers at the tip is selected by observing the intensity of the excitation electric field.

[0060] The excitation electric field is calculated by selecting a set of opposing conductive layers in the electrode needle as the excitation electrodes, assuming that the charge distribution is uniform and the charge per unit area is... A tiny charge element on the surface of the coating dq It can be represented as: ;

[0061] Where d is the distance between two conductive layers symmetrically arranged about the central axis of the needle body. dθ It is a tiny increment of angle. dz A small length increment along the coating direction;

[0062] According to Coulomb's law, a infinitesimal charge... At a certain point in the electric field The generated electric field It has radial and vertical components. Due to symmetry, the radial components cancel each other out when integrated along the axis, leaving only the vertical component (along the axis). direction, The direction is along the axial direction of the needle body), and the magnitude of the excitation electric field is derived from Coulomb's law:

[0063] ;

[0064] in, From charge element Time distance, It can be represented as: ;

[0065] Total electric field at The directional components are:

[0066] ;

[0067] in, ε 0is the vacuum permittivity, z is the vertical component of the charge element to point p, 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 the component along the direction is not cancelled.

[0068] 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 head do not interfere with each other and the structure has a certain strength, the distance between the two oppositely arranged conductive layers (a total of two groups) is controlled d≥ 1.5 mm. An excitation current is injected into a group of oppositely arranged conductive layers in the electrode needle head, and in order to ensure that there is sufficient contact area between the electrode plating layer and the measured tissue, the arc length is controlled , the distance between the conductive layers is changed d to change the excitation electric field.

[0069] The simulation results are shown in Figure 5 ; for the enhancement effect of the excitation electric field, the smaller the distance between the two oppositely arranged conductive layers d , the higher the excitation electric field strength, but according to the simulation results of the excitation electric field, it is found that when , although the excitation electric field strength is very large, the uniformity of the excitation electric field distribution is poor, which may cause the local current in the measured fruit to be too large, thereby causing the deviation and instability of the impedance amplitude, phase angle and other information measurement results. Combined with the simulation results of the excitation electric field strength, it is found that when the distance between the two oppositely arranged conductive layers , the uniformity of the excitation electric field distribution is high, but the electric field strength is low, which may weaken the excitation signal transmission, thereby causing the measurement accuracy of low-sugar fruits to be insufficient.

[0070] Combined with the simulation and calculation results, it is found that the most suitable distance between the two oppositely arranged conductive layers with respect to the center axis of the needle head body is between 2mm and 3mm, because it achieves a good balance between the excitation electric field strength and uniformity, it not only can provide stable excitation signal transmission, but also avoids the negative impact of excessive field strength on measurement.

[0071] S2, according to the data obtained in step S1, the electrode needle head (without conductive layer, without scale) is manufactured by precise printing or precision machining (which is prior art, how to prepare is not the innovation point of the present application), the electrode needle head is soaked in a degreasing alkali solution, the surface of the electrode needle head is degreased and the surface of the ABS plastic electrode needle head is lightly polished with 7000 mesh sandpaper;

[0072] S3. A protective coating (composed of 30% protective agent, 20% binder, and 50% alcohol diluent by weight percentage; the protective agent, binder, and diluent are all existing technologies; the protective agent can be any one of the following: organic polymer material polyimide resin, acrylic resin, inorganic material siloxane, silicon nitride, alumina, or zinc oxide; the binder can be any one of epoxy resin, polyurethane, or cyanoacrylate) is uniformly applied to the area where no plating deposition is required for protection. The electrode needle with the protective coating applied is then dried to obtain a protective layer with a thickness of 50–100 μm. In this embodiment, the thickness of the protective layer is 100 μm. ;

[0073] S4. Place the electrode needle with the protective layer into the coating deposition equipment (this is existing technology; the actual coating deposition method used is DC sputtering. To provide an inert environment and ensure that the coating composition is pure copper, argon gas is introduced into the coating deposition equipment. Before starting deposition, the vacuum chamber is evacuated to a pressure of approximately 1000 kJ / L using a vacuum pump). -6 Torr was placed in a 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 was carried out by precisely controlling the argon gas flow rate between 5 sccm and 100 sccm using a mass flow meter. The temperature during the coating deposition process was adjusted between room temperature (20℃~30℃) and 500℃. The target current applied to the pure copper target was... The coating deposition time is A thickness of 1 to 70 is formed on its surface. In this embodiment, the coating thickness is preferably 70 mm. ;

[0074] S5. Remove the protective layer and the coating on the surface of the protective layer (the removal of the protective layer includes using organic solvents to remove the protective coating layer with organic polymer as the protective agent, using hydrofluoric acid or sodium hydroxide to remove the protective coating layer with inorganic material as the protective agent, and lightly polishing the coating on the surface of the protective coating layer with 10,000-grit ultrafine sandpaper to remove it). Set the scale on the needle body after the protective layer has been removed.

[0075] S6. After rinsing the electrode needles prepared in step S5 with clean water, dry them to obtain electrode needles coated with four conductive layers arranged symmetrically in pairs.

[0076] S7, first, the rear sleeve is sleeved on the conductive connecting part from bottom to top, the rear sleeve is inserted on the guide part through the guide groove, and the rear sleeve is abutted on the guide part, so that the circumferential positioning and the axial preliminary positioning of the rear sleeve are realized, then the electrode nozzle is sleeved on the needle body, and the electrode nozzle is abutted on the rear sleeve, finally, the electrode lock head is sleeved on the needle body, the electrode lock head is screwed on the lower part of the rear sleeve, and when the electrode lock head is screwed upwards, the clamping part is gradually tightened to clamp the electrode nozzle on the needle body, so that the electrode nozzle, the rear sleeve and the electrode needle are fixed, and finally the measuring electrode is prepared.

[0077] The preparation process of the protective coating is as follows:

[0078] (1) protective agent, binder and diluent are weighed according to the set mass percentage;

[0079] (2) 60% of the diluent (the diluent preferably includes ethanol and isopropyl alcohol, and the total amount of the diluent is 30%, of which ethanol accounts for 20% and isopropyl alcohol accounts for 10%) is added to the stirring container, and the machine polymer material protective agent is slowly added and stirred for 40 minutes to completely dissolve;

[0080] (3) in another container, the remaining diluent (total amount is 20%, of which ethanol accounts for 8% and isopropyl alcohol accounts for 12%) is added, and the binder is added and stirred for 20 minutes to be uniform;

[0081] (4) the binder solution is slowly poured into the polymer material protective agent solution, and stirred while pouring, for 30 minutes to be uniform;

[0082] (5) the protective coating is filtered through a 200-mesh filter screen, is loaded into a sealed container, and is stored in a dry and cool place.

[0083] Example 3

[0084] Reference Figures 10-11 , this embodiment is based on example 2, and the embodiment provides a method for measuring the sugar content of fruits using a measuring electrode, which can realize the measurement of various kinds and shapes of fruits, and can ensure high measurement accuracy for low-sugar fruits.

[0085] Specifically, the detection module includes an excitation signal generating unit, an electrode signal collecting unit, a response signal detecting unit, a master control unit and an upper computer, the excitation signal generating unit includes a direct digital frequency synthesizer (DDS) and a voltage-controlled current source (VCCS), preferably, in the example, a programmable, low-noise, and lowest-power-consumption AD9850 in the same series is selected as a signal generating circuit chip, and under a working frequency of 125 MHz, the output frequency resolution can reach 0.0291 Hz, and the Arduino UNO is used as the master control unit, and through programming, the system clock can be divided to generate a sinusoidal alternating voltage signal with a frequency range of 0.1 Hz-40 MHz, and in the example, an improved Howland current source circuit is preferably used as the voltage-controlled constant current source circuit; the response signal detecting unit includes a buffer circuit, a differential amplification circuit, a logarithmic detection circuit and an A / D conversion module, preferably, in the example, the buffer circuit is used as a pre-input channel, and a TL082 double-channel operational amplifier is used to form two voltage followers to realize impedance conversion, preferably, the AD8130 differential operational amplifier is used to design the differential amplification circuit, and a high common-mode rejection ratio of 94 dB and a differential input impedance of 1 MΩ can be achieved; preferably, the AD8302 chip is used to design the logarithmic detection circuit, the amplitude ratio and the phase difference of the two input signals can be detected and converted into a direct current voltage signal output, and the A / D conversion module uses the built-in 10-bit analog-to-digital converter of the Arduino to upload the amplitude and phase information output by the amplitude and phase detection circuit to the upper computer through the USB communication line and store the information.

[0086] A method for measuring the sugar content of fruits using a measuring electrode, comprising the following steps:

[0087] The weight of the fruit to be measured is weighed with an electronic scale, the fruit to be measured is placed on the detection platform, the lower end of the needle body is inserted into the fruit to be measured by holding the rear sleeve, and the insertion depth is read according to the scale on the surface of the needle body;

[0088] A sinusoidal alternating excitation signal is applied to any two conductive layers symmetrically arranged about the center axis of the conductive connection part to inject a plurality of sinusoidal alternating excitation currents with different frequencies into the fruit to be measured in a frequency sweeping manner;

[0089] 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;

[0090] The impedance amplitude, phase angle, weight and insertion depth data of the fruit to be measured at the five frequency points are substituted into the established sugar content measurement mathematical model to calculate the sugar content.

[0091] The sugar content measurement mathematical model is

[0092] ​

[0093] in, TSC The sugar content of the fruit; a 0 The constant term represents the baseline sugar content; f i The frequency of the excitation current; Z (f i ) For at a frequency of The impedance amplitude under sinusoidal current excitation; θ(f i ) For at a frequency of f i The phase angle under sinusoidal current excitation, W For weight, d For the insertion depth, a i1 , a i2 , a 6 , a 7 , a 8 and a 9 This is the proportionality coefficient.

[0094] The optimal proportionality coefficient is obtained by solving the normal equation using the least squares method, with the objective of minimizing the sum of squared errors.

[0095] .

[0096] ;

[0097] ;

[0098] ;

[0099] Where 'a' is a vector composed of the various scaling factors. n Indicates the number of samples. W n Let be the weight of the nth sample. d n Let n be the insertion depth of the nth sample. Y For the first sample ~ n A vector composed of the true sugar content of each sample. It is the first The true sugar content of each sample It is the model's prediction of the first Sugar content of each sample.

[0100] Example 4

[0101] Reference Figures 6-10 , this embodiment is based on example 3, this embodiment can further verify that the addition of the depth parameter in the mathematical model can improve the accuracy of sugar detection.

[0102] In this embodiment, as shown in Figure 10 , the lower end of the needle body is inserted into the apple to be measured, and the insertion position is the intersection of the equator and the meridian of the apple. Two groups of conductive layers (each group of conductive layers consists of two conductive layers arranged opposite to each other in the radial direction) are respectively electrically connected to the detection module. In a sweep frequency manner, five different frequencies of sinusoidal alternating excitation current are injected into the apple to be measured. The five frequency points of the sinusoidal alternating excitation current are 1 khz , 10 khz , 50 khz , 100 khz and 200 khz .

[0103] According to Figures 6-9 , in the low frequency band , shallow insertion is more sensitive to low frequency signals, and the impedance amplitude decays rapidly, and the initial impedance and phase angle are high, which can better capture the electrical characteristics of the surface tissue of the fruit to be measured. In the high frequency band , the impedance amplitude of shallow insertion tends to be stable, which indicates that the excitation signal has penetrated into the interior of the fruit to be measured, and can better reflect the overall sugar concentration of the fruit to be measured.

[0104] According to Figures 6-9 , in the low frequency band , the impedance modulus value of deep insertion decays slowly in the low frequency band, and the initial impedance amplitude is significantly lower than the impedance amplitude of shallow insertion, because deep insertion covers more internal tissue, and the electrical characteristics of the surface of the fruit to be measured are limited. In the high frequency band , the impedance amplitude of deep insertion is significantly lower than that of shallow insertion, and the curve is more stable, 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 the phase angle tends to be stable after the transition to the high frequency band, which shows that the excitation signal of deep insertion can better penetrate the cell membrane and more comprehensively reflect the overall characteristics of the fruit to be measured, thereby being more sensitive to the overall sugar.

[0105] Therefore, due to different insertion depths, the current at different frequencies will produce different effects, shallow insertion is more sensitive to low-frequency impedance response, deep insertion can better reflect the overall electrical characteristics of the fruit inside, and the high-frequency response is more significant, so the interaction term between insertion depth and impedance amplitude at different frequencies is introduced into the sugar content measurement mathematical model: .

[0106] The measurement method in the application can realize sugar content detection of various types and shapes of fruits, has high sensitivity for low-sugar fruit sugar content measurement, and also has the advantages of high precision, fast measurement speed, convenience and flexibility, etc.

[0107] It should be noted that the above examples are only used to illustrate the technical solutions of the present application and are not limiting. Although the present application 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 application can be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present application, which should be covered in the scope of the claims of the present application.

Claims

1. A device for detecting the sugar content of fruits, characterized in that: The electrode needle includes a conductive connector, an electrode tip, and an electrode locking head. A needle body is fixed to the lower side of the conductive connector. The bottom of the needle body has a pointed tip for easy insertion into the fruit. An insulating rear sleeve for easy operation is connected to the conductive connector. Several conductive layers are arranged around the outer periphery of both the needle body and the conductive connector. Each outer periphery of the needle body and the conductive connector has four symmetrically arranged conductive layers, manufactured by deposition plating. The distance between two conductive layers symmetrically arranged about the central axis of the needle body is d, where d is less than 3 mm and greater than 2 mm. mm, a guide portion is fixed on the outer side of the conductive connection between two adjacent conductive layers, the center of the rear sleeve has an insertion hole, the center of the rear sleeve below the insertion hole has a guide hole, the upper outer edge of the guide connection portion of the insertion hole has several guide grooves that correspond one-to-one with the guide portion, the rear sleeve can be fitted onto the needle body from bottom to top through the guide hole, and the upper end of the rear sleeve can be inserted into the corresponding guide portion through the guide groove; the electrode tip has a connection hole, the lower part of the electrode tip has several clamping ports that communicate with the connection hole, the electrical connection between two adjacent clamping ports is... The electrode tip has a clamping part for clamping the needle body. The outer diameter of the clamping part gradually increases from bottom to top. The electrode tip is fitted onto the needle body from bottom to top through the connecting hole. The electrode tip abuts against the rear sleeve on the lower side of the guide hole. The electrode locking head is fitted onto the outer periphery of several clamping parts from bottom to top. The upper part of the electrode locking head is threaded to the lower outer periphery of the rear sleeve. When the electrode locking head is screwed upward, the clamping part gradually tightens, clamping the electrode tip onto the needle body. The outer periphery of the needle body without a conductive layer has several graduations spaced along the axial direction of the needle body. A sinusoidal AC excitation signal is applied to two conductive layers symmetrically arranged about the central axis of the conductive connection part, and sinusoidal AC excitation currents of different frequencies are injected into the fruit under test in a frequency sweep manner. The other two conductive layers collect and process the response voltage signal to obtain the impedance amplitude and phase angle data in the response signal.

2. A method for preparing the device for detecting sugar content in fruits as described in claim 1, characterized in that: Includes the following steps, S1. Immerse the electrode needle in degreasing alkaline solution to degrease the surface of the electrode needle and lightly polish the surface of the needle with 7000-grit sandpaper. S2. Apply the protective coating evenly to the areas where no plating deposition is required for protection. Then, dry the electrode needles after applying the protective coating to obtain a thickness of [thickness value missing]. The protective layer; S3. Place the electrode needle with the protective layer into the coating deposition equipment for coating deposition treatment and... Its surface has a thickness of The coating; S4. Remove the protective layer and the coating on the surface of the protective layer, and set the scale on the needle body after the protective layer has been removed. S5. After rinsing the electrode needles prepared in step S4 with clean water, dry them to obtain electrode needles coated with four conductive layers arranged symmetrically in pairs.

3. A method for detecting fruit sugar content using the measuring electrode prepared according to claim 1, characterized in that: Includes the following steps, Weigh the fruit to be tested using an electronic scale, place the fruit on the testing platform, hold the back sleeve and insert the lower end of the needle body into the fruit, and read the insertion depth according to the scale on the surface of the needle body. A sinusoidal AC excitation signal is applied to two conductive layers symmetrically arranged about the central axis of the conductive connection part, and sinusoidal AC excitation currents of different frequencies are injected into the fruit under test in a frequency sweep manner. The other two conductive layers collect and process the response voltage signal to obtain the impedance amplitude and phase angle data in the response signal. The impedance amplitude, phase angle, weight, and insertion depth data of the fruit to be tested at five frequency points are substituted into the established mathematical model for sugar content measurement to calculate the sugar content.

4. The method for detecting fruit sugar content using the measuring electrode according to claim 3, characterized in that: The mathematical model for sugar content measurement is as follows: ； Where TSC is the sugar content of the fruit; a0 is a constant term representing the baseline sugar content; f i Z(f) is the frequency of the excitation current; i ) is at a frequency of Impedance amplitude under sinusoidal current excitation; θ(f i ) is at a frequency of f i The phase angle under sinusoidal current excitation, W is the weight, d is the insertion depth, and a i1 a i2 a6, a7, a8 and a i9 This is the proportionality coefficient.

5. The method for detecting fruit sugar content using the measuring electrode as described in claim 4, characterized in that: The formula for calculating the vector 'a' composed of various scaling factors is: ； ； Where n represents the number of samples, W n Let d be the weight of the nth sample. n Let Y be the insertion depth of the nth sample, and Y be the vector composed of the actual sugar content of the 1st to the nth samples.

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