System and device for measuring water content of grain by using capacitance method

Abstract

The invention provides a system for measuring the water content of grains by using a capacitance method, and solves the problem that a traditional capacitance method grain water content measuring device is easily influenced by the temperature of a volume density meter. According to the technical scheme, the device comprises a container, an impedance measuring circuit and a temperature measuring circuit; the impedance measuring circuit comprises electrode plates, to-be-measured resistors are formed among the electrode plates, the temperature measuring circuit comprises a temperature sensing unit and an impedance measuring circuit, and the temperature measuring circuit transmits collected information to the main control unit of the active circuit. The main control unit calculates the water content of the to-be-measured grain according to a set instruction set and the obtained impedance value, temperature value and loss factor; the main control circuit further comprises a storage unit for storing information including the instruction set, the impedance value, temperature value, loss factor and measured water content; the system further comprises an upper computer unit, and the upper computer unit is in communication connection with the main control unit through the communication unit, so that the upper computer unit can query historical measured grain water content information.

Description

Technical Field

[0001] The present invention relates to the technical field of grain moisture measurement, and particularly relates to a system and device for measuring grain moisture by using the capacitance method. Background Art

[0002] Grain moisture content is an important characteristic for describing grain quality and storage conditions, and has wide applications in the fields of scientific research and engineering technology. Traditional grain moisture meters already have different types of grain moisture testing devices according to the requirements of different usage scenarios, including the needle-type grain moisture tester used under portable conditions, such as the Chinese utility model patent with the patent number CN202120791176.9 and the patent name "Integrated Grain Moisture Tester"; it also includes a method for testing moisture content by means of microwave radiation, such as the Chinese invention patent with the patent number CN201910064268.4 and the patent name "A Method for Measuring Grain Moisture Content Based on Microwave Sweeping Technology".

[0003] Among them, the capacitance method is an indirect way of measuring grain moisture. The moisture content is obtained by measuring the physical quantity related to the moisture change. Specifically, the measurement purpose is achieved through the relationship between the dielectric constant of the grain and the moisture. Generally, the dielectric constant of water is larger than that of the dry part of the grain. The more water the grain contains, the larger the overall dielectric constant. And the dielectric constant is closely related to the capacitance value. Therefore, the grain moisture content can be indirectly obtained by measuring the capacitance.

[0004] Since most grains are granular objects, they need to be placed in a container during measurement. However, the weight of the grain changes at each moisture level, so the volume density of grain samples with different moisture contents will change during the measurement process, and the determination of the dielectric constant and loss factor of the grain will be affected by the volume density. But the general capacitance method measurement does not consider the above factors. Summary of the Invention

[0005] Aiming at the above problems, the purpose of the present invention is to propose a system for measuring grain moisture by using the capacitance method, which solves the problem that the traditional capacitance method grain moisture measurement device is easily affected by the volume density and temperature.

[0006] Its technical solution is as follows: It includes a container for holding the grain to be measured, an impedance measurement circuit for measuring the impedance value of the grain in the container, and an independent temperature measurement circuit for measuring the temperature value of the grain in the container;

[0007] The impedance measurement circuit includes electrode plates on two opposite inner sides of the container, and the grain loaded in the space between the electrode plates forms the measured resistance in the impedance measurement circuit;

[0008] The temperature measurement circuit includes a temperature sensing unit, and the temperature sensing unit is used to measure the temperature information of the grain loaded in the container space;

[0009] It also includes a main control circuit, wherein the impedance measurement circuit and the temperature measurement circuit transmit the collected information to the main control unit of the active circuit, and the main control unit calculates the moisture content of the grain to be measured according to the acquired impedance value, temperature value and loss factor according to the set instruction set, and the main control circuit also includes a storage unit for storing the instruction set, impedance value, temperature value, loss factor and measured moisture content information;

[0010] The system adopts a density-independent algorithm, which reduces the influence of density on detection accuracy by analyzing the relationship between the square root of dielectric constant, square root of loss factor and density.

[0011] It also includes a host computer unit, which is connected to the main control unit through the communication unit, so that the grain moisture content information that has been measured in the past can be queried through the host computer unit.

[0012] In the above or some embodiments, the impedance measurement circuit adopts an impedance measurement chip, and the impedance measurement chip integrates a frequency generator and a 12-bit, 1MSPS analog-to-digital converter. The signal generated by the frequency generator is used to excite the external complex impedance, and the impedance response signal of the resistor to be measured is sampled by the on-chip ADC.

[0013] In the above or some embodiments, the temperature measurement circuit uses a digital temperature sensor, and the digital temperature sensor is bidirectionally communicatively connected with the main control unit via a single-line interface.

[0014] In the above or some embodiments, the communication unit is connected to the main control unit through a serial port.

[0015] In view of the above problems, the purpose of the present invention is to provide a device for measuring the moisture content of grains, so as to solve the problem that the traditional grain moisture measurement device using the capacitance method is easily affected by the temperature of the volume density meter.

[0016] The device for measuring the moisture content of grains comprises a container, an impedance measurement circuit, a temperature measurement circuit, an electrode plate, and a main control circuit. The impedance measurement circuit, the temperature measurement circuit, and the main control circuit form a control circuit, and also comprises a printed circuit board for mounting the control circuit. A temperature measuring rod for loading a temperature sensing unit is arranged in the middle of the container. The container extends downward to form a plurality of columns, and each of the columns forms a space below the container for placing and mounting the printed circuit board.

[0017] In the above or some embodiments, the temperature measuring rod is located at the central position of the container and is a hollow rod-shaped structure. The lower end of the temperature measuring rod is fixedly connected to the bottom of the container, and the temperature sensing unit is installed inside the temperature measuring rod. The temperature measuring rod is connected to the main control circuit through a connecting wire passing through the bottom of the container to form the temperature measuring circuit. An electrode plate is further included and is fixedly connected to the inner wall of the container. The grain loaded in the space between the electrode plates forms the measured resistance in the impedance measuring circuit, and a lead is provided at the bottom of the electrode plate and is connected to the impedance measuring circuit and serves as one end point of the measured resistance.

[0018] In the above or some embodiments, a bottom plate is further included, and connection holes corresponding to the respective columns are provided on the bottom plate. The connection holes cooperate with the columns to form a structure for fixedly installing each of the printed circuit boards.

[0019] In the above or some embodiments, the printed circuit board includes an independently provided main control circuit board and an impedance measuring circuit board. Bases with hollowed-out portions in the middle are provided at both sides below the main control circuit board. The lower end of the base is fixedly connected to the upper end surface of the base, and the upper end surface of the base is fixedly connected to the main control circuit board; the lower end of the impedance measuring circuit board extends to form a hollow isolation column, and the impedance measuring circuit board is fixedly connected to the base through a screw passing through the isolation column.

[0020] In the above or some embodiments, the electrode plate extends to the bottom end of the container, and the bottom plate of the container is fixedly located between the two electrode plates; a fence is further included, and the fence is fixedly connected to the column to form a structure inside the shielding device.

[0021] When the present invention is in use, compared with the traditional pin-type grain moisture tester, its measurement accuracy is more precise, and the structure layout of this solution is relatively simple. It is not limited to a fixed instrument operation table, and users can connect to the device through a mobile phone to observe and process measurement data in real time, replacing the display screen of the conventional grain moisture meter, significantly reducing costs, and having good promotion prospects.

[0022] Explanatory drawings of the specification

[0023] Figure 1 is the principle block diagram of the control circuit in the present invention.

[0024] Figure 2 is the three-dimensional structure schematic diagram of the device in the present invention.

[0025] Figure 3 is a partial cross-sectional view of the device in the present invention.

[0026] Figure 4 is the three-dimensional structure schematic diagram of the device in the present invention from another perspective.

[0027] Figure 5 For Figure 4 An enlarged schematic view of part A in Specific embodiments

[0028] Embodiments of the present invention will be described in detail below. Examples of the embodiments are shown in the drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below by referring to the drawings are exemplary and are intended to explain the present invention and should not be construed as limiting the present invention.

[0029] In the description of the present invention, the meaning of "a plurality" is two or more unless otherwise specifically defined.

[0030] In the above or some embodiments, the system for measuring the moisture content of grains by the capacitance method includes a device, and the device includes a control circuit part and a mechanical structure part. The control circuit includes an impedance measurement circuit 201, a temperature measurement circuit 202, and a main control circuit 203.

[0031] In the above or some embodiments, the impedance measurement circuit 201 includes electrode plates 102 located on two opposite inner sides of the container 101. The grains loaded in the space between the electrode plates 102 form the resistance to be measured in the impedance measurement circuit 201. The impedance measurement circuit 201 uses an impedance measurement chip, including but not limited to the AD5933 chip. The impedance measurement chip integrates a frequency generator and a 12-bit, 1MSPS analog-to-digital converter. The signal generated by the frequency generator is used to excite the external complex impedance, and the impedance response signal of the resistance to be measured is sampled by the on-chip ADC; in the AD5933 excitation circuit, a sine wave signal generated by the frequency generator and a digital-to-analog converter (DAC) is input to a voltage follower composed of an operational amplifier. Its output is connected to the Vout terminal through a current-limiting resistor, and then through a test wire, the resistance to be measured, and connected to the Vin terminal, and finally sent to a current / voltage (I / V) converter composed of an operational amplifier.

[0032] In the above or some embodiments, the temperature measurement circuit 202 includes a temperature sensing unit. The temperature sensing unit is used to measure the temperature information of the grains loaded in the space of the container 101. A digital temperature sensor including but not limited to DS18B20 can be used. The digital temperature sensor is bidirectionally communicatively connected to the main control unit through a single-wire interface. DS18B20 can directly read the temperature of the grains to be measured, and the temperature measurement range is -55°C to +125°C (the measurement accuracy is 0.5°C in the range of -10°C to +85°C).

[0033] It also includes a main control circuit 203. The impedance measurement circuit 201 and the temperature measurement circuit 202 transmit the collected information to the main control unit of the active circuit. The main control circuit 203 also includes a storage unit for storing the instruction set, impedance value, temperature value, loss factor, and measured water content information.

[0034] The system adopts a density-independent algorithm. By analyzing the relationship between the square root of the dielectric constant ε’, the square root of the loss factor ε”, and density, the influence of density on the detection accuracy is reduced. The results show that and There is a strong linear relationship between them, and the linear regression equation is as follows:

[0035]

[0036] where ρ is the grain density, a f and k are the slope and intercept of the linear regression equation respectively. From the above formula, the expression of density can be obtained as:

[0037]

[0038] This equation provides a method to express density ρ in terms of the dielectric constant and loss factor. Considering that density is related to the square roots of the dielectric constant ε’ and the loss factor ε”, and also related to the square root of the loss tangent, by using the ratio of the square root of the loss tangent (tanδ = ε” / ε') to density, a calibration function independent of density can be obtained.

[0039]

[0040] For a given material and operating frequency, the product of af and k in the linear regression equation has been proven to be a constant. Therefore, this product can be omitted from the calibration function to further simplify the calibration function. Thus, the density-independent calibration function can be defined as:

[0041]

[0042] In this simplified form, there is only one external parameter, namely the frequency factor a f , and the value of a f is known to be 1.23, and ξ only depends on the dielectric properties of the material being measured. Through multiple experiments and calculations using the above formula, it can be obtained that ξ increases with the increase of water content and is not affected by density. This result indicates that in the experiment of predicting grain water content, using the density-independent algorithm, the dielectric constant ξ can effectively reduce the influence of density;

[0043] The main control unit uses, including but not limited to, STM32F407ZGT6 as the single-chip microcomputer main control chip. The main control STM32F407ZGT6 is a 32-bit microcontroller based on the Cortex-M4 core, with a working frequency as high as 168 MHZ. The ADC measurement range and the DAC output range are both 0 to 3.3V;

[0044] In the above or some embodiments, in order to facilitate the acquisition and display of information, an upper computer unit 204 is further included. The upper computer unit 204 is communicatively connected to the main control unit through a communication unit, so that the moisture content information of the grain to be measured can be queried through the upper computer unit 204. The communication unit uses an HC-05 Bluetooth module to communicate with the upper computer unit 204. The upper computer includes, but is not limited to, one or several of a smart phone and a PC.

[0045] To implement the above functions, the mechanical structure part is a columnar structure as a whole, including a container 101 and a printed circuit board 103 for installing and carrying the control circuit. The container 101 extends downward to form a plurality of columns 105, and each column 105 forms a space below the container 101 for placing and installing the printed circuit board 103.

[0046] In the above or some embodiments, the container 101 is a regular cube structure. Each column 105 is located at the corner of the lower end face of the cube. Each column 105 is fixedly installed at the bottom end of the container 101 by threads. The container 101 is enclosed by an insulating material including but not limited to a polymethyl methacrylate plate. Electrode plates 102 are respectively arranged on two opposite inner side surfaces of the container 101. The electrode plates 102 are platinum black electrodes, and the cell constant is 0.999 cm -1 , and the platinum black electrode can accurately measure the conductivity with high sensitivity. The grain loaded in the space between the electrode plates 102 forms the measured resistance in the impedance measurement circuit 201. Leads are arranged at the bottom of the electrode plates 102 and connected to the impedance measurement circuit 201 and serve as one end point of the measured resistance. Each electrode plate 102 extends to the bottom end of the container 101. The bottom of the container 101 is fixedly located between the two electrode plates 102. A fixed connection is formed between the bottom of the container 101 and the electrode plates 102, and between each polymethyl methacrylate plate, through a connecting piece or bonding; A fence is also included, and the fence is fixedly connected to the column 105 to form the structure inside the shielding device.

[0047] The temperature measuring rod 104. In the above or some embodiments, the temperature measuring rod 104 is located at the central position of the container 101 and is a hollow rod-shaped structure. The lower end of the temperature measuring rod 104 is fixedly connected to the bottom of the container 101, and the temperature sensing unit is installed inside the temperature measuring rod 104. The connecting wire passing through the bottom of the container 101 by the temperature measuring rod 104 is connected to the main control circuit 203 to form the temperature measuring circuit 202.

[0048] The printed circuit board 103. In the above or some embodiments, the printed circuit board 103 includes an independently provided main control circuit board 103.1 and an impedance measurement circuit board 103.2. The base 106 with a hollowed-out portion in the middle is provided at both sides below the main control circuit board 103.1. The lower end of the base 106 is fixedly connected to the upper end surface of the base 106 by bonding or a connecting member, and the upper end surface of the base 106 is fixedly connected to the main control circuit board 103.1 by bonding or a connecting member; the lower end of the impedance measurement circuit board 103.2 extends to form an isolation column 107 with a hollow structure, and the impedance measurement circuit board 103.2 is fixedly connected to the base 106 by screws passing through the isolation column 107. In the above or some embodiments, a bottom plate 108 is further included. Connection holes corresponding to the respective columns 105 are provided on the bottom plate 108, and the connection holes cooperate with the columns 105 to form a structure for fixedly installing each of the printed circuit boards 103.

[0049] When in use, compared with the traditional pin-type grain moisture tester, the measurement accuracy of the present invention is more precise, and the structure layout of the present solution is relatively simple. It is not limited to a fixed instrument operation table, and users can connect to the device through a mobile phone to observe and process measurement data in real time, replacing the display screen of the conventional grain moisture content measuring instrument, significantly reducing the cost, and having good promotion prospects.

Claims

1. A system for measuring the moisture content of grains using the capacitance method, comprising a container (101) for containing the grains to be measured, and an impedance measurement circuit (201) for measuring the impedance value of the grains in the container (101), characterized in that, It also includes an independent temperature measurement circuit (202) for measuring the temperature value of the grains inside the container (101); The impedance measurement circuit (201) includes electrode plates (102) located on two opposite inner sides of the container (101), and the grains loaded in the space between the electrode plates (102) form the resistance to be measured in the impedance measurement circuit (201); The temperature measurement circuit (202) includes a temperature sensing unit, and the temperature sensing unit is used to measure the temperature information of the grains loaded in the space of the container (101); It also includes a main control circuit (203). The impedance measurement circuit (201) and the temperature measurement circuit (202) transmit the collected information to the main control unit of the active circuit. The main control unit calculates the moisture content of the grains to be measured according to the set instruction set based on the obtained impedance value, temperature value, and loss factor. The main control circuit (203) also includes a storage for storing the instruction set, impedance value, temperature value, loss factor, and the measured moisture content information; It also includes a host computer unit (204). The host computer unit (204) is communicatively connected to the main control unit through a communication unit, so that the historical measured moisture content information of the grains can be queried through the host computer unit (204).

2. The system for measuring the moisture content of grains by the capacitance method according to claim 1, characterized in that, The impedance measurement circuit (201) uses an impedance measurement chip. The impedance measurement chip integrates a frequency generator and a 12-bit, 1MSPS analog-to-digital converter. The signal generated by the frequency generator is used to excite the external complex impedance, and the impedance response signal of the resistance to be measured is sampled by the on-chip ADC.

3. The system for measuring the moisture content of grains by the capacitance method according to claim 3, wherein The temperature measurement circuit (202) uses a digital temperature sensor, and the digital temperature sensor is communicatively connected to the main control unit bidirectionally through a single-wire interface.

4. The system for measuring the moisture content of grains using the capacitance method according to claim 4, characterized in that, The communication unit is communicatively connected to the main control unit through a serial port.

5. A device for measuring the moisture content of grains, comprising the container (101), impedance measurement circuit (201), temperature measurement circuit (202), electrode plate (102), and main control circuit (203) according to any one of claims 1-5, wherein the impedance measurement circuit (201), temperature measurement circuit (202), and main control circuit (203) form a control circuit, and further comprising a printed circuit board (103) for mounting and carrying the control circuit, characterized in that, A temperature measurement rod (104) for loading the temperature sensing unit is arranged in the middle of the container (101). The container (101) extends downward to form a plurality of columns (105), and the space for placing and installing the printed circuit board (103) is formed below the container (101) by each column (105).

6. The device for measuring the moisture content of grains according to claim 6, characterized in that, The temperature measurement rod (104) is located at the central position of the container (101) and is a hollow rod-shaped structure. The lower end of the temperature measurement rod (104) is fixedly connected to the bottom of the container (101), and the temperature sensing unit is installed inside the temperature measurement rod (104). The connecting wire passing through the bottom of the container (101) of the temperature measurement rod (104) is connected to the main control circuit (203) to form the temperature measurement circuit (202). It also includes electrode plates (102) fixed to the inner wall of the container (101). The grains loaded in the space between the electrode plates (102) form the resistance to be measured in the impedance measurement circuit (201). Leads are arranged at the bottom of the electrode plates (102) and are connected to the impedance measurement circuit (201) to serve as one end point of the resistance to be measured.

7. The device for measuring the moisture content of grains according to claim 7, characterized in that, It further includes a bottom plate (108), and connection holes corresponding to the respective columns (105) are provided on the bottom plate (108), and the connection holes cooperate with the columns (105) to form a structure for fixedly installing the respective printed circuit boards (103).

8. The device for measuring the moisture content of grains according to claim 8, characterized in that, The printed circuit board (103) includes an independently provided main control circuit board (103.1) and an impedance measurement circuit board (103.2). At both sides below the main control circuit board (103.1), there are bases (106) with hollowed-out parts in the middle. The lower end of the base (106) is fixedly connected to the upper end surface of the base (106), and the upper end surface of the base (106) is fixedly connected to the main control circuit board (103.1); the lower end of the impedance measurement circuit board (103.2) extends to form an isolation column (107) with a hollow structure, and the impedance measurement circuit board (103.2) is fixedly connected to the base (106) by screws passing through the isolation column (107).

9. The device for measuring the moisture content of grain according to claim 9, wherein, The electrode plate (102) extends to the bottom end of the container (101), and the bottom plate (108) of the container (101) is fixedly located between the two electrode plates (102); it further includes a fence, and the fence is fixedly connected to the column (105) to form a structure inside the shielding device.

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