A device and method for detecting online moisture content of grain based on radio frequency impedance method

Abstract

The present invention provides an online grain moisture content detection device and method based on radio frequency impedance method, the device includes a signal generator, the output end of the signal generator is connected to one end of a measuring device through a transmission line, the measuring device includes an aluminum shell, a cylindrical cavity is formed in the aluminum shell, an inner cylinder is arranged in the middle of the cylindrical cavity, the inner cylinder is connected to the inner side of the aluminum shell through a support rod, a grain flow space is formed between the inner cylinder and the cylindrical cavity, a seesaw is arranged on the upper and lower sides of one side of the aluminum shell, the grain flows into the cylindrical cavity through the seesaw, the grain is separated by the inner cylinder, the grain and the aluminum shell form an electrode plate, and the other end of the measuring device is connected to the input end of an oscilloscope through a coaxial cable. On the basis of the principle of capacitance method, with grain moisture content measurement as the core, the online grain moisture content detection technology based on radio frequency impedance method is studied, which provides a scientific basis for the high-precision, large-range, automated, miniaturized and intelligent research and development of grain moisture content measurement sensors.

Description

Technical Field

[0001] The present invention belongs to the technical field of grain moisture detection, and in particular relates to an online grain moisture content detection device and method based on a radio frequency impedance method. Background Art

[0002] In the process of long-term, high-precipitation grain drying using a dryer, how to accurately measure the moisture content of grains under different environmental conditions and at different online conditions is of great significance for timely and accurate adjustment of the working state of the dryer, and for achieving reasonable grain drying and grain storage. Grain moisture is the general term for free water and bound water in grains. Free water is the water that condenses in the capillaries and molecular gaps inside the grain particles through physical adsorption; bound water is the water that is adsorbed in the grain cells or in the grain molecular structure through chemical action. Free water has the general properties of ordinary water and directly affects the physical and chemical properties of grains. As far as the detection of grain moisture content is concerned, the grain moisture content refers to the content of free water. On the one hand, in order to maintain the life of grains and maintain the inherent color, smell, taste, seed quality and edible quality of grains during storage and processing, it is very important to accurately detect the moisture content of grains. On the other hand, in grain drying, the measurement result of moisture content directly affects the control accuracy of the drying system. Therefore, it is very necessary to develop a grain moisture online detection device with high accuracy and fast response. The existing detection devices have high accuracy and good reliability when working offline, but they are not suitable for installation in industrial sites and cannot measure grain moisture in real time. At present, most grain dryers produced in my country do not have high-quality online moisture detection devices, and it is quite common for grains to be too dry or not reach safe moisture after drying. Research on moisture detection started early at home and abroad, mainly in two types: direct detection and indirect detection. For online measurement, indirect detection is generally used, including infrared, microwave, nuclear magnetic resonance, neutron, conductivity, capacitance, etc. The first four types are complex in structure, expensive, and inconvenient to use and maintain. They are mostly used for online detection of large production lines, and have achieved satisfactory results. Capacitive and conductive methods are commonly used methods. The conductive method has the disadvantages of low test accuracy and being greatly affected by the temperature of the electrolyte and the measured grain. Based on the analysis of the principle of the capacitance method, this paper takes grain moisture content measurement as the core and studies the grain online moisture content detection technology based on the radio frequency impedance method, providing a scientific basis for the high-precision, large-range, automated, miniaturized and intelligent research and development of grain moisture content measurement sensors. Summary of the invention

[0003] In view of this, the present invention aims to propose an online grain moisture content detection device based on the radio frequency impedance method. On the basis of the principle of the capacitance method and with the grain moisture content measurement as the core, the online grain moisture content detection technology based on the radio frequency impedance method is studied, which provides a scientific basis for the high-precision, large-range, automated, miniaturized and intelligent research and development of grain moisture content measurement sensors.

[0004] To achieve the above object, the technical solution of the present invention is achieved as follows:

[0005] An online grain moisture content detection device based on a radio frequency impedance method comprises a signal generator, the output end of the signal generator is connected to one end of a measuring device through a transmission line, the measuring device comprises an aluminum shell, a cylindrical cavity is formed in the aluminum shell, an inner cylinder is arranged in the middle of the cylindrical cavity, the inner cylinder is connected to the inner side of the aluminum shell through a support rod, a grain flow space is formed between the inner cylinder and the cylindrical cavity, a seesaw is arranged on the upper and lower sides of one side of the aluminum shell, the grain flows into the cylindrical cavity through the seesaw, the grain is separated by the inner cylinder, the grain and the aluminum shell form an electrode plate, and the other end of the measuring device is connected to the input end of an oscilloscope through a coaxial cable;

[0006] The aluminum shell is in contact with the surface of the grain, and is used to receive the excitation signal generated by the signal generator, and output a corresponding voltage value according to the moisture content of the grain;

[0007] The signal generator is used to generate an excitation signal, and transmit the generated excitation signal to the aluminum shell of the measuring device through a transmission line.

[0008] Furthermore, the diameter of the cylindrical cavity is 65 mm, the diameter of the inner cylinder is 40 mm, and the height of the cylindrical cavity is 100 mm.

[0009] Furthermore, a PVC plastic cylinder is also arranged inside the aluminum shell.

[0010] Furthermore, the signal source emitted by the signal generator is 1 MHZ.

[0011] Furthermore, the signal source of the signal generator is connected to the measuring device via a 1KΩ resistor.

[0012] Compared with the prior art, the on-line grain moisture content detection device based on radio frequency impedance method described in the present invention has the following advantages:

[0013] (1) The cylindrical electrode plate of the present invention has relatively stable electrical parameters. If the capacitance is to be increased, it is only necessary to increase the length of the cylinder, that is, it is relatively convenient to change the capacitance;

[0014] (2) When the grains climb up along the seesaw, the grains’ own weight and wind force exert pressure on the flowing grains between the cylindrical plates, so that the compactness of the grains between the plates remains consistent during measurement, thereby reducing the influence of compactness on the measurement accuracy.

[0015] (3) The entire cylindrical electrode is placed in an iron shell, and the shielding effect of the iron shell reduces the interference of external static electricity;

[0016] (4) A PVC sleeve is added between the cylindrical plate and the aluminum shell to weaken the edge effect of the capacitance field and improve the test accuracy.

[0017] Another object of the present invention is to propose an online grain moisture content detection method based on radio frequency impedance method. On the basis of the principle of capacitance method and with grain moisture content measurement as the core, the online grain moisture content detection technology based on radio frequency impedance method is studied to provide a scientific basis for the high-precision, large-range, automated, miniaturized and intelligent research and development of grain moisture content measurement sensors.

[0018] To achieve the above object, the technical solution of the present invention is achieved as follows:

[0019] A method for detecting grain moisture content online based on radio frequency impedance method comprises the following steps:

[0020] (1) Injecting grain into the detection device and using a signal generator to generate an excitation signal to the measuring device;

[0021] (2) the measuring device outputs a corresponding output voltage to the oscilloscope according to the moisture content of the grain;

[0022] (3) The oscilloscope obtains the moisture content of the grain based on the functional relationship between the moisture content of the grain and the voltage.

[0023] Furthermore, the specific calculation process of the functional relationship between the moisture content of the grain and the voltage in step (3) is as follows:

[0024] (31) The flowing grains are divided into three parts: the gaps between grains, the moisture between grains, and the dry matter of grains. The total capacitance of the grains is C x , the total capacitance of the grain C x It is divided into inter-grain gap capacitance C 0 , Grain moisture capacitance C 1 , Cereal dry matter capacitance C 2 , and satisfy the formula (1):

[0025]

[0026] Among them, H is the height of the cylindrical cavity, D is the diameter of the cylindrical cavity, d is the diameter of the inner cylinder, ε 0——Dielectric constant of the air gap between grains, ε 1 ——Water dielectric constant of grain, ε 2 ——Dielectric constant of grain dry matter, all of which are fixed values;

[0027] (32) Let the weight of the gaps between grains, the moisture between grains, and the dry matter of grains be G respectively. 0 , G 1 , G 2 , the weight of the air in the gap between grains can be regarded as zero, so the total weight G of the three parts is as shown in formula 2:

[0028] G=G 1 +G 2 =πγ d (Dd)H 2 +πγ w (Dd)H 1 (Formula 2)

[0029] Where: γ d ——Specific gravity of dry matter in cereals, γ w ——Specific gravity of grain moisture, which is 1.

[0030] Therefore, the moisture content of the grain to be tested is shown in formula 3:

[0031]

[0032] (33) Let the volume of the inter-grain space, the volume of the inter-grain moisture, and the volume of the grain dry matter be V 0 、V 1 、V 2 , the total volume is V, the void ratio e of the grains between the two plates, that is, the grain packing density, is called compactness, and is defined as follows:

[0033]

[0034] (34) Transform Formula 3 and Formula 4 and substitute them into Formula 1 to obtain the total capacitance C x The relationship with grain moisture content is shown in Formula 5:

[0035]

[0036] K 0 If is set as a constant, then Formula 5 can be transformed into Formula 6:

[0037]

[0038] From the waveform conversion formula (Formula 7) (Formula 8)

[0039] Among them Ua is the actual measured voltage value, K p is the crest factor. Since the input waveform is a sine wave, K is taken. p =1.414,

[0040] Get the moisture content W and the actual measured voltage value U a The relationship is

[0041]

[0042] The online grain moisture content detection method based on radio frequency impedance method described in the present invention has the same beneficial effects as the above-mentioned online grain moisture content detection device based on radio frequency impedance method, which will not be repeated here. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] The accompanying drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the accompanying drawings:

[0044] Figure 1 This is a schematic structural diagram of an online grain moisture content detection device based on a radio frequency impedance method according to an embodiment of the present invention;

[0045] Figure 2 This is a perspective view of an online grain moisture content detection device according to an embodiment of the present invention;

[0046] Figure 3 It is a side view of an online grain moisture content detection device according to an embodiment of the present invention.

[0047] Figure 4 It is a structural schematic diagram of a cylindrical electrode plate model according to an embodiment of the present invention;

[0048] Figure 5 This is the relationship model between the moisture content of grains and the output voltage described in the embodiment of the present invention.

[0049] Description of reference numerals:

[0050] 1-Signal generator; 2-Inner cylinder; 3-Support rod; 4-Seesaw; 5-Oscilloscope. DETAILED DESCRIPTION

[0051] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0052] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", and the like are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, features defined as "first", "second", and the like may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more.

[0053] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood by specific circumstances.

[0054] The present invention will be described in detail below with reference to the accompanying drawings and in conjunction with embodiments.

[0055] like Figure 1 , 2 As shown, an online grain moisture content detection device based on radio frequency impedance method comprises a signal generator 1, the output end of the signal generator 1 is connected to one end of a measuring device through a transmission line, the measuring device comprises an aluminum shell, a cylindrical cavity is formed in the aluminum shell, an inner cylinder 2 is arranged in the middle of the cylindrical cavity, the inner cylinder 2 is connected to the inner side of the aluminum shell through a support rod 3, a grain flow space is formed between the inner cylinder 2 and the cylindrical cavity, a seesaw 4 is arranged on the upper and lower sides of one side of the aluminum shell, the grain flows into the cylindrical cavity through the seesaw 4, the grain is separated by the inner cylinder 2, the grain and the aluminum shell form an electrode plate, and the other end of the measuring device is connected to the input end of an oscilloscope 5 through a coaxial cable; the aluminum shell is in contact with the surface of the grain, and is used to receive the excitation signal generated by the signal generator 1, and output a corresponding voltage value according to the moisture content of the grain; the signal generator 1 is used to generate an excitation signal, and transmit the generated excitation signal to the aluminum shell of the measuring device through the transmission line.

[0056] The measuring device of the present invention is made of a thin aluminum sheet with a thickness of 1 mm, the diameter D of the cylindrical cavity is 65 mm, the diameter d of the inner cylinder 2 is 40 mm, and the height H of the cylindrical cavity is 100 mm. In order to reduce the influence of the dispersion effect on the measurement result, a PVC plastic cylinder with a thickness of 3 mm, an inner diameter of 65 mm, and a height of 140 mm is covered on the cylindrical cavity. The signal source is connected to the measuring device through a 1KΩ resistor, and the oscilloscope 5 is connected to the measuring device through a coaxial cable.

[0057] This experiment uses the F40 digital synthetic function signal generator produced by Nanjing Shengpu Instrument Technology Co., Ltd. It is a precision test instrument with the functions of outputting function signals, frequency modulation, amplitude modulation, frequency scanning and other signals. In addition, this instrument also has the functions of frequency measurement and counting. Main performance indicators: (1) The main waveform is sine wave, square wave, TTL wave, the output frequency is 1000uHz~40MHz, the waveform distortion is 0.1%, and the frequency error is ±5×10 -6 , the frequency stability is ±1×10 -6 (2) The pulse wave duty cycle resolution is as high as one thousandth. (3) The small signal output amplitude can reach 1mV, and the large signal output amplitude can reach tens of volts. (4) The digital frequency modulation resolution is high and accurate. (5) The burst mode has a continuous phase adjustment function. (6) The phase adjustment resolution is 0.1 degrees. (7) The frequency scanning output can set the starting point and end point arbitrarily; the frequency change is only one ten-thousandth. (8) It has frequency measurement and counting functions, and the counting capacity is ≤4.29×10 9 , can be manually or controlled by external gate.

[0058] Oscilloscope 5 is a YB4360 dual-trace and four-trace oscilloscope produced by Jiangsu Lvyang Electronic Instrument Co., Ltd. The main performance indicators are as follows: (1) the maximum input DC voltage is 300 V, and the AC peak-to-peak voltage is 300 V. (2) the input impedance is 1 MΩ±2%, and the input capacitance is 25 pF±3 pF.

[0059] (3) The frequency bandwidth is: AC 10Hz~60MHz, DC 0~60MHz. (4) At room temperature, the accuracy can reach ±5%. (5) The working power supply voltage is AC 220V±10%, and the frequency is 50Hz±5%.

[0060] The method for measuring using the above measuring device specifically comprises the following steps:

[0061] (1) Injecting grain into the detection device and using a signal generator to generate an excitation signal to the measuring device;

[0062] (2) the measuring device outputs a corresponding output voltage to the oscilloscope according to the moisture content of the grain;

[0063] (3) The oscilloscope obtains the moisture content of the grain based on the functional relationship between the moisture content of the grain and the voltage.

[0064] The specific calculation process of the functional relationship between the moisture content of the grain and the voltage in step (3) is as follows:

[0065] (31) The flowing grains are divided into three parts: the gaps between grains, the moisture between grains, and the dry matter of grains. The total capacitance of the grains is C x , the total capacitance of the grain C x It is divided into inter-grain gap capacitance C 0 , Grain moisture capacitance C 1 , Cereal dry matter capacitance C 2 , and satisfy the formula (1):

[0066]

[0067] Among them, H is the height of the cylindrical cavity, D is the diameter of the cylindrical cavity, d is the diameter of the inner cylinder, ε 0 ——Dielectric constant of the air gap between grains, ε 1 ——Water dielectric constant of grain, ε 2 ——Dielectric constant of grain dry matter, all of which are fixed values;

[0068] (32) Let the weight of the gaps between grains, the moisture between grains, and the dry matter of grains be G respectively. 0 , G 1 , G 2 , the weight of the air in the gap between grains can be regarded as zero, so the total weight G of the three parts is as shown in formula 2:

[0069] G=G 1 +G 2 =πγ d (Dd)H 2 +πγ w (Dd)H 1 (Formula 2)

[0070] Where: γ d ——Specific gravity of dry matter in cereals, γ w ——Specific gravity of grain moisture, which is 1.

[0071] Therefore, the moisture content of the grain to be tested is shown in formula 3:

[0072]

[0073] (33) Let the volume of the inter-grain space, the volume of the inter-grain moisture, and the volume of the grain dry matter be V 0 、V 1 、V 2, the total volume is V, the void ratio e of the grains between the two plates, that is, the grain packing density, is called compactness, and is defined as follows:

[0074]

[0075] (34) Transform Formula 3 and Formula 4 and substitute them into Formula 1 to obtain the total capacitance C x The relationship with grain moisture content is shown in Formula 5:

[0076]

[0077] K 0 If is set as a constant, then Formula 5 can be transformed into Formula 6:

[0078]

[0079] From the waveform conversion formula (Formula 7) (Formula 8)

[0080] Among them U a is the actual measured voltage value, K p is the crest factor. Since the input waveform is a sine wave, K is taken. p =1.414,

[0081] Get the moisture content W and the actual measured voltage value U a The relationship is

[0082]

[0083] This application uses the above cylindrical plate as an online grain moisture sensor. Through the above analysis, we can know the relationship between the impedance of the sensor and the grain moisture as a single-valued function. This relationship is affected by the following factors: First, the structural parameters D, d, H of the sensor and the frequency f of the excitation source. For a certain sensor and a certain excitation source, each parameter is a constant. Second, the dielectric constant ε of the three materials 0 , ε 1 , ε 2 , at room temperature, the dielectric constant of grain dry matter ε 2 The dielectric constant of pure water is 2 to 5. 1About 81. During the online measurement process, the change of dielectric constant caused by temperature change cannot be ignored. Experiments have shown that this influence can be corrected by temperature compensation. Third, the change of compactness e is the most important factor affecting the test accuracy of the sensor. In formula 7, each item contains the component of e, so the influence of this factor must be overcome. Most of the previous researchers used batch sampling and constant frequency compaction methods, but they were all batch sampling, not online testing. Some researchers installed an electromagnetic oscillation discharger at the discharge port. When the electromagnetic oscillation discharger oscillates evenly, the density of the grain flowing between the two plates of the sensor remains basically consistent. On the basis of this study, the grain weight and a certain wind force are used to compact the grain to be tested, so that the compactness e of the grain to be tested remains basically unchanged, so the influence of the compactness e on the measurement results is weakened.

[0084] During the measurement process, the grains selected for this experiment are early hybrid rice varieties, and the initial moisture content of the rice is 10.22% to 21.3%. In order to obtain a higher moisture content, the rice is divided into 10 groups, each group is 1 kg, and placed in different glass containers. After labeling, place it in an environment where the temperature and humidity can be relatively controlled. Store at an ambient temperature of 4°C for 7 days to achieve a balance in the moisture content inside and outside the grains. Before the grains are placed in the glass container, different amounts of distilled water should be sprinkled on each grain sample to make the moisture content of the sample different and widely distributed. Before measuring, place each sample at room temperature for 24 hours until the moisture on the surface of the grain evaporates, and then take out a weight of M from each sample. W , use a drying oven to dry (the main parameters of the SC101 constant temperature drying oven used in this experiment are: maximum temperature 300℃, motor power 40w, studio size 50*60*75cm, heating power 6Kw, voltage 220V, frequency 50Hz, speed 2800r / min), dry at a temperature of 135℃ for 24h, take out and measure its dry weight M D , and calculate the absolute water content of each sample.

[0085] Experimental results analysis and verification

[0086] At each different humidity, measurement was performed 10 times, each time using 1MHz, 3MHz, 5MHz, 7MHz, 10MHz, 15MHz, and 20MHz signal sources for excitation. The peak-to-peak voltage of the input signal was 10V. The peak voltage was measured with an oscilloscope, and the measured data was averaged and recorded (see Table 1).

[0087] Table 1 Grain moisture measurement values

[0088]

[0089]

[0090] From the analysis of Table 1, it can be seen that when the frequency of the excitation signal is greater than 5MHz, the measured voltage value cannot accurately reflect the change of the moisture content of the grain; under the signal excitation with a frequency of 1MHz, the humidity difference is the same and the output voltage value difference is the largest. The regression analysis is performed, as shown in Figure 3 As shown, the model is: y = 12.74-23.052x, R 2 =0.8173, used to verify the accuracy of the data.

[0091] Place grains with different humidity levels in the measuring device, measure the output voltage under the excitation of a 1MHz signal, and substitute the measured results into y=21.476-87.288x(R 2 =0.9861), the corresponding grain moisture content is calculated. Then the actual moisture content of the grain obtained by the standard drying method is compared to calculate the measurement accuracy. 10 measurements are made in the range of moisture content of about 13% to 22%. It can be seen from Table 2 that when the grain moisture is measured using this grain online moisture meter, its accuracy is ±1.2%, which can meet the requirements of grain dryer control.

[0092] Table 2 Grain moisture measurement values

[0093]

[0094]

[0095] The present invention has developed a grain moisture measurement device. Under the excitation of different frequency signal sources, the output voltage of the processing device is basically linearly related to the corresponding moisture. Under the excitation of the signal with a frequency of 1MHz, the humidity difference is the same and the output voltage value difference is the largest. Therefore, 1MHz is determined as the characteristic frequency of the processing device, and the prediction model is: y = 12.74-23.052x (R 2 =0.8173).

[0096] The results of the experiment show that under the excitation of a signal source with a frequency of 1 MHz, the prediction model of the online water content detection device is: y = 21.476-87.288x (R 2 =0.9861). The measuring accuracy of the detection device is high, with an error of only ±1.2%, which fully meets the control requirements of the small grain dryer.

[0097] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. An online grain moisture content detection device based on radio frequency impedance method, characterized in that: It comprises a signal generator, the output end of the signal generator is connected to one end of a measuring device through a transmission line, the measuring device comprises an aluminum shell, a cylindrical cavity is formed in the aluminum shell, an inner cylinder is arranged in the middle of the cylindrical cavity, the inner cylinder is connected to the inner side of the aluminum shell through a support rod, a grain flow space is formed between the inner cylinder and the cylindrical cavity, a seesaw is arranged on the upper and lower sides of one side of the aluminum shell, the grain flows into the cylindrical cavity through the seesaw, the grain is separated by the inner cylinder, the grain and the aluminum shell form an electrode plate, and the other end of the measuring device is connected to the input end of an oscilloscope through a coaxial cable; The aluminum shell is in contact with the surface of the grain, and is used to receive the excitation signal generated by the signal generator, and output a corresponding voltage value according to the moisture content of the grain; The signal generator is used to generate an excitation signal, and transmit the generated excitation signal to the aluminum shell of the measuring device through a transmission line; The method for detecting the online moisture content of grains by the online moisture content detection device for grains based on the radio frequency impedance method specifically comprises the following steps: (1) Injecting grain into the detection device and using a signal generator to generate an excitation signal to the measuring device; (2) the measuring device outputs a corresponding output voltage to the oscilloscope according to the moisture content of the grain; (3) The oscilloscope obtains the moisture content of the grain based on the functional relationship between the moisture content of the grain and the voltage; The specific calculation process of the functional relationship between the moisture content of the grain and the voltage in step (3) is as follows: (31) The flowing grains are divided into three parts: the gaps between grains, the moisture between grains, and the dry matter of grains. The total capacitance of the grains is C x , the total capacitance of the grain C x It is divided into the inter-grain gap capacitance C0, the grain moisture capacitance C1, and the grain dry matter capacitance C2, and satisfies the formula 1: Among them, H is the height of the cylindrical cavity, D is the diameter of the cylindrical cavity, d is the diameter of the inner cylinder, ε0 is the dielectric constant of the air gap between grains, ε1 is the dielectric constant of the moisture in the grains, and ε2 is the dielectric constant of the dry matter in the grains, all of which are fixed values; (32) Assume that the weights of the gaps between grains, the moisture between grains, and the dry matter of grains are G0, G1, and G2, respectively. The weight of the air between grains can be considered zero. Therefore, the total weight G of the three parts is as shown in Formula 2: G = G1 + G2 = πγ d ( (D - d)H2 + πγ w (D - d)H1 (Formula 2) Where: γ d ——Specific gravity of dry matter in cereals, γ w ——The specific gravity of grain moisture is taken as 1, so the moisture content of the grain to be tested is shown in Formula 3: (33) Let the volumes of the inter-grain gaps, inter-grain moisture, and grain dry matter be V0, V1, and V2, respectively, and the total volume be V. The inter-grain gap ratio e between the two plates, i.e., the grain packing density, is called compactness and is defined as follows: (34) Transform Formula 3 and Formula 4 and substitute them into Formula 1 to obtain the total capacitance C x The relationship with grain moisture content is shown in Formula 5: If K0 is set as a constant, Formula 5 can be transformed into Formula 6: From the waveform conversion formula Among them U a is the actual measured voltage value, K p is the crest factor. Since the input waveform is a sine wave, K is taken. p =1.414, Get the moisture content W and the actual measured voltage value U a The relationship is 2. According to claim 1, the device for detecting the online moisture content of grains based on the radio frequency impedance method is characterized in that: The diameter of the cylindrical cavity is 65 mm, the diameter of the inner cylinder is 40 mm, and the height of the cylindrical cavity is 100 mm.

3. According to claim 1, the device for detecting the online moisture content of grains based on the radio frequency impedance method is characterized in that: A PVC plastic cylinder is also arranged in the aluminum shell.

4. According to claim 1, the on-line grain moisture content detection device based on radio frequency impedance method is characterized in that: The signal source emitted by the signal generator is 1MHZ.

5. The on-line grain moisture content detection device based on radio frequency impedance method according to claim 1 is characterized in that: The signal source of the signal generator is connected to the measuring device through a 1KΩ resistor.

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