A fruit moisture content measuring circuit, measuring method and measuring instrument

Abstract

The application discloses a fruit moisture content measuring circuit, a measuring method and a measuring instrument, wherein a central processing unit controls positive and negative voltage switching of a moisture sensor through a decap effect circuit; a fruit moisture content signal to be measured is sent to the central processing unit after being amplified by a logarithmic amplifier measuring unit; an environmental temperature signal of the fruit is sent to the central processing unit after being processed by a temperature measuring unit; the central processing unit corrects the resistivity of the fruit to be measured according to environmental temperature data of the fruit, calculates the moisture content of the fruit according to the corrected resistivity and outputs the moisture content. The application can intuitively view the moisture reduction process, timely correct drying process parameters according to the moisture content and target value, and on the other hand, based on the adjustment and control of the accurate process parameters of the moisture content target and process, the drying cycle can be shortened to the maximum, the energy consumption of the drying process is reduced, the sensory, physical and chemical indexes of the product are improved, and thus the product quality is improved.

Description

Technical Field

[0001] This invention relates to the field of measurement and control technology for food drying processes, specifically to a fruit moisture content measurement circuit, measurement method, and measuring instrument. Background Technology

[0002] Fruit drying is a crucial part of industrial and agricultural production, but it is also a highly energy-intensive process. Energy consumption varies significantly depending on the drying equipment and processes used. Domestically and internationally, energy consumption for drying accounts for 7% to 15% of the total national energy consumption, while the thermal efficiency is only 25% to 50%. The drying of fruits such as longan and lychee is no exception; different drying processes affect the product's color, flavor, nutrition, and texture.

[0003] Currently, in the drying technology of fruits such as longan and lychee, drying methods can be divided into natural drying and artificial drying according to the source of heat energy required for drying and the method of moisture removal. Natural drying utilizes natural environmental conditions such as sunlight, shade, and wind to dehydrate and dry materials. However, due to the influence of sunlight and the high oxygen content in the air, it is greatly limited by natural conditions and is susceptible to microbial contamination. Therefore, artificial drying is more commonly used in the fruit industry. Commonly used artificial drying methods include hot air drying, heat pump drying, freeze drying, and microwave drying. Regardless of the drying technology, equipment, and process used, an automatic control system is indispensable, and the prerequisite for the automatic control system to implement the drying process is the measurement of basic parameters. Moisture content measurement is a crucial parameter in the drying process. However, current large-scale commercial drying equipment lacks online moisture measurement methods and devices in its control systems. Instead, it relies primarily on empirically derived time as the basis for adjusting parameters such as temperature, humidity, and airflow, resulting in crude control and unclear moisture reduction processes. Alternatively, it uses sampling (oven-drying method) to determine the moisture content of samples, which lacks timeliness and hinders precise real-time adjustment of drying process parameters based on moisture content. Since drying is a complex nonlinear process, its temperature, humidity, and airflow need adjustment as the material's moisture content changes. These physical quantities are interconnected and influence each other, exhibiting nonlinear characteristics. Therefore, improvements to existing technologies are needed to enhance the accuracy of moisture content measurement during fruit drying and reduce energy consumption. Summary of the Invention

[0004] The purpose of this invention is to provide a fruit moisture content measurement circuit, measurement method, and measuring instrument, which can solve the problems of low measurement accuracy and high energy consumption in the artificial drying process in the prior art.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] In a first aspect, the present invention provides a fruit moisture content measurement circuit, including a central processing unit, a capacitance-reducing circuit unit, a logarithmic amplifier measurement unit, a temperature measurement unit, a moisture sensor, and a temperature sensor. The central processing unit controls the moisture sensor to switch between positive and negative voltages at time intervals t through the capacitance-reducing circuit unit. The moisture sensor collects the moisture content signal in the fruit in real time and sends it to the logarithmic amplifier measurement unit. The temperature sensor collects the ambient temperature signal of the fruit in real time and sends it to the temperature measurement unit. The logarithmic amplifier measurement unit processes the moisture content signal through a logarithmic amplifier and sends it to one A / D port of the central processing unit. The temperature measurement unit processes the ambient temperature signal of the fruit and sends it to another A / D port of the central processing unit. The central processing unit corrects the resistivity of the fruit based on the ambient temperature data, calculates the moisture content of the fruit based on the corrected resistivity, and outputs the result.

[0007] Furthermore, the capacitance reduction circuit unit includes a resistor R87, a transistor T1, a switch K1, a diode D13, an LED D9, and an LED D10. One end of the resistor R87 is connected to the control terminal P22 of the central processing unit, and the other end of the resistor R87 is connected to the base of the transistor T1. The emitter of the transistor T1 is grounded. The collector of the transistor T1 and the anode of the diode D13 are connected to one end of the switch K1. The other end of the switch K1 is connected to the voltage VCC and the cathode of the diode D13. The moving contact of the switch K1 switches between positive and negative voltages at time intervals t. The moving contact of the switch K1 is also connected to a moisture sensor. The cathode of the LED D9 and the anode of the LED D10 are connected to the moving contact of the switch K1. The anode of the LED D9 and the cathode of the LED D10 are connected in series with a resistor R84 and then grounded.

[0008] Furthermore, the logarithmic amplifier measurement unit includes resistors R70, R80, R79, R72, and R73; operational amplifier IC6A and IC6B; capacitors C43 and C44; transistors IC5A and IC5B; potentiometers P6 and P5; and a Schottky diode D7. One end of resistor R73 is connected to the moisture sensor, and the other end of resistor R73 is connected to the inverting input of power amplifier IC6B and the collector of transistor IC5A. The non-inverting input of power amplifier IC6B is connected to analog ground. The output of power amplifier IC6B is connected to one end of resistor R72, and capacitor C43 is connected between the inverting input and output of power amplifier IC6B. The other end of resistor R72 is connected to the emitter of transistor IC5A and the emitter of transistor IC5B. The base of transistor IC5A... Connect the sliding terminal of potentiometer P5; connect the two ends of potentiometer P5 to voltages VR+ and VR- respectively; connect the base and collector of transistor IC5B to the non-inverting input of power amplifier IC6A; connect the inverting input of power amplifier IC6A to the sliding terminal of potentiometer P6; connect the output of power amplifier IC6A to the A / D port AD12 of the central processing unit; connect resistor R70 between the positive and non-inverting inputs of op-amp IC6A; connect the positive terminal of capacitor C44 to the output of op-amp IC6A and the negative terminal to analog ground; connect the anode of Schottky diode D7 to analog ground, the cathode to voltage VCC, and the common terminal to the output of op-amp IC6A; connect one end of resistor R80 to analog ground and the other end to one end of potentiometer P6; connect the other end of potentiometer P6 in series with resistor R79 to the output of op-amp IC6A.

[0009] Furthermore, the temperature measurement unit includes resistors R1, R2, R3, R4, R5, R6, R7, R8, and R10, a potentiometer P9, capacitors C1, C2, and C3, a power amplifier IC9, and a Schottky diode D1. One end of resistor R8 and one end of resistor R7 are connected to a temperature sensor Pt100B, and one end of resistor R3 and one end of resistor R6 are connected to a temperature sensor Pt100A. The other ends of resistors R8, R7, R4, and R10 are interconnected. The other ends of resistors R3 and R4 are connected to a reference voltage. The other end of resistor R10... One end of resistor R2 is connected to the inverting input of power amplifier IC9; the other end of resistor R6 and one end of resistor R1 are connected to the non-inverting input of power amplifier IC9; the other end of resistor R1 is connected to analog ground; capacitors C2 and C3 are connected in parallel to the negative input voltage terminal of power amplifier IC9; the other end of resistor R2 is connected to the output terminal of power amplifier IC9 and one end of potentiometer P9; the other end of potentiometer P9 is connected to the A / D port AD00 of the central processing unit; capacitor C1 and resistor R5 are connected in parallel, one end of which is connected to the other end of potentiometer P9 and the sliding end, and the other end is connected to analog ground; the anode of Schottky diode D1 is connected to analog ground, the cathode is connected to voltage VCC, and the common terminal is connected to the other end of potentiometer P9.

[0010] Secondly, the present invention provides a method for measuring the moisture content of fruit, comprising the following steps:

[0011] Set the time interval t;

[0012] The central processing unit controls the moisture sensor to switch between positive and negative voltages at time intervals t through a decapacitation circuit.

[0013] The water content signal of the fruit to be tested is amplified and processed by the logarithmic amplifier measurement unit and then sent to the central processing unit.

[0014] The ambient temperature signal of the fruit is collected is processed by the temperature measurement unit and then sent to the central processing unit.

[0015] The central processing unit corrects the resistivity of the fruit based on the ambient temperature data, calculates the water content of the fruit based on the corrected resistivity, and outputs the result.

[0016] Thirdly, the present invention provides a measuring instrument, including a power supply unit and a display unit, characterized in that it further includes the aforementioned fruit moisture content measuring circuit, wherein the power supply unit supplies power to the fruit moisture content measuring circuit, and the display unit is used to display the data output by the fruit moisture content measuring circuit.

[0017] This invention employs online measurement of the moisture content of fruits, particularly longan or lychee, based on a logarithmic amplifier circuit. On one hand, it allows for a direct view of the moisture reduction process, enabling timely adjustments to drying process parameters based on the moisture content and target value. On the other hand, by precisely adjusting and controlling the process parameters based on the moisture content target and process, the drying cycle can be shortened to the maximum extent, energy consumption during the drying process can be reduced, and the sensory and physicochemical properties of the product can be improved, thereby enhancing product quality. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a block diagram of the fruit moisture content measuring circuit of the present invention;

[0020] Figure 2 This is a circuit schematic diagram of the logarithmic amplifier measurement unit and the capacitance removal circuit unit of the present invention;

[0021] Figure 3 This is a circuit diagram of the temperature measurement unit of the present invention;

[0022] Figure 4 This is one embodiment of the central processing unit and power supply of the present invention;

[0023] Figure 5 This is one embodiment of the display unit of the present invention;

[0024] Figure 6 This is a flowchart of the fruit moisture content measurement method of the present invention. Detailed Implementation

[0025] The embodiments of this disclosure will now be described in detail with reference to the accompanying drawings.

[0026] The following specific examples illustrate the implementation of this disclosure. Those skilled in the art can easily understand other advantages and effects of this disclosure from the content disclosed in this specification. Obviously, the described embodiments are only a part of the embodiments of this disclosure, and not all of them. This disclosure can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of this disclosure. It should be noted that, in the absence of conflict, the following embodiments and features in the embodiments can be combined with each other. Based on the embodiments in this disclosure, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this disclosure.

[0027] The present invention provides a fruit moisture content measuring circuit, such as... Figure 1 As shown, the system includes a central processing unit (CPU), a capacitance-reducing circuit unit, a logarithmic amplifier measurement unit, and a temperature measurement unit, all connected to the CPU. It also includes a moisture sensor and a temperature sensor. The moisture sensor is a needle-type moisture sensor, installed on the fruit to be measured, used to collect the water content signal in the fruit in real time and send the signal to the logarithmic amplifier measurement unit. The temperature sensor is a resistance temperature detector (RTD) sensor, but other temperature sensors can also be used. This embodiment uses an RTD sensor as an example, but this should not be used to limit the scope of protection of the invention. The RTD sensor is used to collect the ambient temperature of the fruit in real time and send the ambient temperature signal to the temperature measurement unit. The CPU controls the moisture sensor to switch between positive and negative voltages at time intervals t via the capacitance-reducing circuit unit. The logarithmic amplifier measurement unit amplifies the water content signal and sends it to one A / D port of the CPU. The temperature measurement unit processes the ambient temperature signal and sends it to another A / D port of the CPU. The CPU corrects the resistivity of the fruit based on the ambient temperature data, calculates the water content of the fruit based on the corrected resistivity, and outputs the result.

[0028] The moisture content measurement circuit of this invention can be applied to the moisture content measurement of most fruits, and is particularly effective for fruits with high water content. Taking longan or lychee as examples, this invention, based on the drying experiment process of longan or lychee and the electrical characteristics of moisture measurement, shows that the moisture content of longan or lychee is related to its resistivity, and the resistivity of longan and lychee (fruits) is mainly determined by the moisture content and the ambient temperature. Since the resistivity changes by approximately 10°C when the moisture content changes from saturated to completely dry, this invention demonstrates the significant difference between the resistivity and the moisture content of longan and lychee. 1 Up to 10 5Between 10 and 20, conventional operational amplifiers connected as linear amplifier circuits cannot effectively compress the electrical signal, resulting in very limited resolution and accuracy of moisture content measurement. Therefore, logarithmic amplification measurement units are needed to process the significantly compressed electrical signal, which can effectively solve the signal compression problem and greatly improve the resolution and accuracy of moisture content measurement.

[0029] Furthermore, the capacitor-eliminating circuit unit of the present invention, as shown in the example... Figure 2 As shown, the circuit includes resistor R87, transistor T1, switch K1, diode D13, LED D9, and LED D10. One end of resistor R87 is connected to the control terminal P22 of the central processing unit, and the other end of resistor R87 is connected to the base of transistor T1. The emitter of transistor T1 is grounded. The collector of transistor T1 and the anode of diode D13 are connected to one end of switch K1. The other end of switch K1 is connected to voltage VCC and the cathode of diode D13. The moving contact of switch K1 switches between +8V and -8V. The moving contact of switch K1 is also connected to a moisture sensor. The cathode of LED D9 and the anode of LED D10 are connected to the moving contact of switch K1. The anode of LED D9 and the cathode of LED D10 are connected in series with resistor R84 and then grounded to GND.

[0030] The working principle of the capacitance reduction circuit unit of this invention is as follows: the capacitance effect circuit is driven by the control terminal P22 of the central processing unit (STC8A4K32SA12). The capacitance effect circuit includes a switching PNP transistor T1 (8050), an electronic switching switch K1 (5VDC relay), a clamping diode D13 (IN4001), positive and negative power supplies, light-emitting diodes D9 and D10, and a resistor R. 84 The circuit is composed of (3K) capacitors. Its working process is as follows: the central processing unit sets the time interval t to control the switching of positive and negative voltages applied to the input terminal of the moisture sensor, so as to eliminate the capacitor effect caused by a single positive or negative voltage. The output terminal of the power supply is connected to one end of the moisture sensor, and the other end is connected to the 0V terminal of the power supply.

[0031] The time interval t is the switching time interval between the positive and negative voltages at the input terminal of the moisture sensor, which is taken as 6 seconds in this embodiment. The time interval t can be adjusted according to actual needs and is not limited to a single value of 6 seconds.

[0032] Furthermore, the logarithmic amplifier measurement unit of the present invention, as shown in the figure... Figure 2As shown, the system includes resistors R70, R80, R79, R72, and R73; operational amplifier IC6A and IC6B; capacitors C43 and C44; transistors IC5A and IC5B; potentiometers P6 and P5; and a Schottky diode D7. The Schottky diode D7 is a series-connected transistor pair with three pins: positive, negative, and common. Transistors IC5A and IC5B form an NPN transistor pair, and operational amplifiers IC6A and IC6B form an operational amplifier chip. One end of resistor R73 is connected to the moisture sensor, and the other end is connected to the inverting input of power amplifier IC6B and the collector of transistor IC5A. The non-inverting input of power amplifier IC6B is connected to analog ground AGND. The output of power amplifier IC6B is connected to one end of resistor R72, and capacitor C43 is connected between the inverting input and output of power amplifier IC6B. The other end of resistor R72 is connected to the emitters of transistors IC5A and IC5B. The base of transistor IC5A is connected to the slider of potentiometer P5. Potentiometer P5 is connected to voltages VR+ and VR-, respectively. The base and collector of transistor IC5B are connected to the non-inverting input of power amplifier IC6A. The inverting input of power amplifier IC6A is connected to the slider of potentiometer P6, and the output of power amplifier IC6A is connected to the A / D port AD12 of the central processing unit. Resistor R70 is connected between the positive and non-inverting inputs of op-amp IC6A. The positive terminal of capacitor C44 is connected to the output of op-amp IC6A, and the negative terminal is connected to analog ground AGND. The anode of Schottky diode D7 is connected to analog ground AGND, the cathode is connected to voltage VCC, and the common terminal is connected to the output of op-amp IC6A. One end of resistor R80 is connected to analog ground AGND, and the other end is connected to one end of potentiometer P6. The other end of potentiometer P6 is connected in series with resistor R79 and then connected to the output of op-amp IC6A.

[0033] The logarithmic amplifier measurement unit of this invention utilizes a high-precision, high-bandwidth operational amplifier and a pair of transistors with identical characteristics (transistor IC5A and transistor IC5B) to form a logarithmic amplifier circuit. When the two poles of the needle moisture sensor are connected to longan or lychee, the voltage at the input terminal (one end of resistor R73) of the logarithmic amplifier measurement unit changes nonlinearly with the resistance value of the two poles of the needle moisture sensor as the moisture content changes.

[0034] The power amplifier IC6B, resistor R73, transistor IC5A, resistor R72, and potentiometer P5 constitute an inverting relative digital amplifier circuit. The function of potentiometer P5 is to adjust the zero point, and the output voltage U o1 That is, the voltage U across resistor R72 R72 and input voltage U i1 The relationship can be expressed as:

[0035] U o1 =-Ui1 ×lg U i1 / R 73 (1)

[0036] (1) In the formula, U o1 U is the emitter voltage of IC5A, in volts (V). i1 R is the input voltage of the moisture sensor, in volts (V). 73 This is the resistance value of resistor R73, in Ω.

[0037] Transistor IC5B, resistor R70, power amplifier IC6A, resistor R79, resistor R80, and potentiometer P6 constitute a non-inverting operational amplifier. Potentiometer P6 is used to adjust the amplification factor. Since the current I flowing through resistor R72 and resistor R70 is the same, U... i2 and U o1 The relationship between them is:

[0038] U i2 =R 70 ×(U o1 / R 73 (2)

[0039] (2) In the formula, U i2 R is the output voltage, in volts (V). 70 This is the resistance value of resistor R70, in Ω; U o1 R is the emitter voltage of transistor IC5A, in volts (V). 73 This is the resistance value of resistor R73, in Ω.

[0040] Therefore, we can conclude that:

[0041] U o2 =U i2 ×R 79 / (R 79 +R 80 +P6) (3)

[0042] (3) In the formula, U i2 R is the output voltage, in volts (V). 79 R is the resistance value of resistor R79, in Ω; 80 R80 is the resistance value in Ω; P6 is the resistance value after adjustment of the adjustable resistor P6, in Ω.

[0043] The capacitor C44 serves as a buffer and filter, while the Schottky diode D7 limits the output voltage between +VCC and -0.7V.

[0044] Furthermore, the circuit diagram of the temperature measuring unit of the present invention is as follows: Figure 3As shown, the circuit includes resistors R1, R2, R3, R4, R5, R6, R7, R8, and R10, potentiometer P9, capacitors C1, C2, and C3, power amplifier IC9, and Schottky diode D1. One end of resistor R8 and one end of resistor R7 are connected to temperature sensor Pt100B, and one end of resistor R3 and one end of resistor R6 are connected to temperature sensor Pt100A. The other ends of resistors R8, R7, R4, and R10 are interconnected. The other ends of resistors R3 and R4 are connected to the reference voltage Vref. The other end of resistor R10 and one end of resistor R2 are connected to the inverting input of power amplifier IC9. The other end of resistor R6 and one end of resistor R1 are connected to the non-inverting input of power amplifier IC9. The other end of resistor R1 is connected to analog ground AGND. Capacitors C2 and C3 are connected in parallel to the negative input voltage terminal of power amplifier IC9. The other end of resistor R2 is connected to the output of power amplifier IC9 and one end of potentiometer P9. The other end of potentiometer P9 is connected to the A / D port AD00 of the central processing unit. Capacitor C1 and resistor R5 are connected in parallel, with one end connected to the other end of potentiometer P9 and its sliding contact, and the other end connected to analog ground AGND. Schottky diode D1 is a series-connected pair package with three leads: anode, cathode, and common terminal. The anode of Schottky diode D1 is connected to analog ground AGND, the cathode is connected to voltage VCC, and the common terminal is connected to the other end of potentiometer P9.

[0045] The ambient temperature of longan and lychee is measured by a temperature measurement circuit, and the error correction of the effect of temperature on resistivity is performed in the central processing unit.

[0046] This invention also provides a method for measuring the moisture content of fruit, the flowchart of which is shown below. Figure 6 As shown, the specific steps include:

[0047] Set the time interval t;

[0048] The central processing unit controls the moisture sensor to switch between positive and negative voltages at time intervals t through a decapacitation circuit.

[0049] The water content signal of the fruit to be tested is amplified and processed by the logarithmic amplifier measurement unit and then sent to the central processing unit.

[0050] The ambient temperature signal of the fruit is collected is processed by the temperature measurement unit and then sent to the central processing unit.

[0051] Using the measurement circuit of this invention, experimental data testing is conducted on the fruit under test: Fruits with different moisture contents (from oven-dried to saturated, sampled at different points) are placed in environments with different temperatures (from room temperature to the highest processing temperature, sampled at different points). The output value of the measurement circuit is recorded and compared with the output value at room temperature to obtain temperature error correction data, which is then stored in the central processing unit (CPU). During the data acquisition process, the more sampling points with different moisture contents (calculated using the oven-dried method) and temperatures, the higher the accuracy of the temperature correction value for moisture content. The CPU corrects the resistivity of the fruit under test based on the ambient temperature data, calculates the moisture content of the fruit based on the corrected resistivity, and outputs the result.

[0052] This invention makes the fruit drying process more intuitive, allowing for real-time monitoring of moisture content changes during drying, and enabling multi-channel measurement units to analyze moisture content distribution at different locations. It avoids the non-real-time nature of methods that rely on oven-drying followed by weighing for moisture content detection.

[0053] The present invention also provides a measuring instrument, including the above-mentioned fruit moisture content measuring circuit, and further including a power supply unit and a display unit. The power supply unit supplies power to the fruit moisture content measuring circuit, and the display unit is used to display the data output by the fruit moisture content measuring circuit.

[0054] The power supply unit and display unit can be implemented using existing technologies. As a specific embodiment of the present invention, the circuit schematic is as follows: Figure 4 As shown on the left, the input voltages of the power supply circuit are V+ and V-. After rectification and filtering, different voltages are output to power different unit circuits in the moisture content measurement circuit. As a specific embodiment of the present invention, the display unit is as follows... Figure 5 As shown. It should be noted that the power supply unit and display unit shown in this embodiment are merely one specific implementation of the present invention. Besides this, the power supply unit and display unit of the present invention can also be implemented using other methods in the prior art, and should not be construed as limiting the scope of protection of the present invention. Any simple substitutions using existing technology should fall within the scope of protection of the present invention.

[0055] In this invention, unless otherwise expressly specified and limited, the first feature "on" the second feature may be in direct contact with the first and second features, or indirect contact with the first and second features through an intermediate medium. "A plurality of" means at least two, such as two, three, etc., unless otherwise expressly and specifically limited.

[0056] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between them; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0057] The above description is merely illustrative of the embodiments of the present invention and is not intended to limit the present invention. For those skilled in the art, any modifications, equivalent substitutions, improvements, etc., made without creative effort within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A fruit moisture content measuring circuit, characterized by comprising: The moisture sensor is a needle type moisture sensor, is installed on the fruit to be measured, and is used for collecting a water content signal in the fruit in real time and sending the water content signal to the logarithmic amplifier measurement unit; the temperature sensor collects an environmental temperature signal of the fruit to be measured in real time and sends the environmental temperature signal to the temperature measurement unit; the logarithmic amplifier measurement unit sends a water content signal amplified and processed to an A / D port of the central processor; the temperature measurement unit sends an environmental temperature signal of the fruit processed to another A / D port of the central processor; the central processor corrects an error of the resistivity of the fruit to be measured according to the environmental temperature data of the fruit, calculates the water content rate of the fruit according to the corrected resistivity, and outputs the water content rate; The de-capacitance effect circuit unit comprises a resistor R87, a triode T1, a switch K1, a diode D13, a light emitting diode D9 and a light emitting diode D10, one end of the resistor R87 is connected to a control end P22 of the central processor, the other end of the resistor R87 is connected to a base of the triode T1, an emitter of the triode T1 is grounded, a collector of the triode T1 and an anode of the diode D13 are connected to one end of the switch K1, the other end of the switch K1 is connected to a voltage VCC and a cathode of the diode D13; a moving contact of the switch K1 is switched between a positive voltage and a negative voltage at a time interval t; the moving contact of the switch K1 is also connected to the moisture sensor; a cathode of the light emitting diode D9 and an anode of the light emitting diode D10 are connected to the moving contact of the switch K1, an anode of the light emitting diode D9 and a cathode of the light emitting diode D10 are connected to the ground through a resistor R84 in series.

2. The fruit moisture measurement circuit according to claim 1, characterized by, The logarithmic amplifier measurement unit includes resistance R70, resistance R80, resistance R79, resistance R72, resistance R73, operational amplifier IC6A, operational amplifier IC6B, capacitor C43, capacitor C44, triode IC5A, triode IC5B, potentiometer P6, potentiometer P5 and Schottky diode D7; one end of resistance R73 is connected with the moisture sensor, the other end of resistance R73 is connected with the inverting input end of operational amplifier IC6B and the collector of triode IC5A respectively; the non-inverting input end of operational amplifier IC6B is connected with analog ground; one end of resistance R72 is connected with the output end of operational amplifier IC6B, capacitor C43 is connected between the inverting input end and the output end of operational amplifier IC6B; the other end of resistance R72 is connected with the emitter of triode IC5A and the emitter of triode IC5B; the base of triode IC5A is connected with the sliding end of potentiometer P5; the two ends of potentiometer P5 are connected with voltage VR+ and voltage VR- respectively; the base and the collector of triode IC5B are connected with the non-inverting input end of operational amplifier IC6A; the sliding end of potentiometer P6 is connected with the inverting input end of operational amplifier IC6A, the output end of operational amplifier IC6A is connected with the A / D port AD12 of the central processing unit; resistance R70 is connected between the voltage positive and the non-inverting input end of operational amplifier IC6A; the positive pole of capacitor C44 is connected with the output end of operational amplifier IC6A, the negative pole is connected with analog ground; the anode of Schottky diode D7 is connected with analog ground, the cathode is connected with voltage VCC, the common end is connected with the output end of operational amplifier IC6A; one end of resistance R80 is connected with analog ground, the other end is connected with one end of potentiometer P6; the other end of potentiometer P6 is connected with the output end of operational amplifier IC6A after being connected with resistance R79 in series.

3. The fruit moisture measurement circuit according to claim 1, wherein The temperature measurement unit includes resistance R1, resistance R2, resistance R3, resistance R4, resistance R5, resistance R6, resistance R7, resistance R8, resistance R10, potentiometer P9, capacitor C1, capacitor C2, capacitor C3, operational amplifier IC9 and Schottky diode D1; one end of resistance R8 and one end of resistance R7 are connected with temperature sensor Pt100B, one end of resistance R3 and one end of resistance R6 are connected with temperature sensor Pt100A; the other end of resistance R8, the other end of resistance R7, one end of resistance R4 and one end of resistance R10 are connected with each other; the other end of resistance R3 and the other end of resistance R4 are connected with reference voltage; the other end of resistance R10 and one end of resistance R2 are connected with the inverting input end of operational amplifier IC9; the other end of resistance R6 and one end of resistance R1 are connected with the non-inverting input end of operational amplifier IC9; the other end of resistance R1 is connected with analog ground; capacitor C2 and capacitor C3 are connected in parallel between the input voltage negative end of operational amplifier IC9; the other end of resistance R2 is connected with the output end of operational amplifier IC9 and one end of potentiometer P9; the other end of potentiometer P9 is connected with the A / D port AD00 of the central processing unit; capacitor C1 and resistance R5 are connected in parallel, one end of which is connected with the other end and the sliding end of potentiometer P9, the other end of which is connected with analog ground; the anode of Schottky diode D1 is connected with analog ground, the cathode is connected with voltage VCC, the common end is connected with the other end of potentiometer P9.

4. A method of measuring the water content of fruit, characterised in that, The method comprises the following steps: Set time interval t; The central processor controls the moisture sensor to switch positive and negative voltage at time interval t through the decap effect circuit unit; The moisture content signal of the fruit to be measured is sent to the central processor after being amplified by the logarithmic amplifier measurement unit; The temperature signal of the environment where the fruit is located is sent to the central processor after being processed by the temperature measurement unit; The central processor corrects the resistivity of the fruit to be measured according to the temperature data of the environment where the fruit is located, calculates the moisture content of the fruit according to the corrected resistivity, and outputs the result; The decap effect circuit unit includes a resistor R87, a triode T1, a switch K1, a diode D13, a light-emitting diode D9, and a light-emitting diode D10. One end of the resistor R87 is connected to the control end P22 of the central processor, and the other end of the resistor R87 is connected to the base of the triode T1. The emitter of the triode T1 is grounded. The collector of the triode T1 and the anode of the diode D13 are connected to one end of the switch K1. The other end of the switch K1 is connected to the voltage VCC and the cathode of the diode D13. The moving contact of the switch K1 switches between positive voltage and negative voltage at time interval t. The moving contact of the switch K1 is also connected to the moisture sensor. The cathode of the light-emitting diode D9 and the anode of the light-emitting diode D10 are connected to the moving contact of the switch K1. The anode of the light-emitting diode D9 and the cathode of the light-emitting diode D10 are connected in series with the resistor R84 and then grounded.

5. A measuring instrument comprising a power supply unit and a display unit, characterized in that It also includes the fruit moisture content measurement circuit according to any one of claims 1 to 3. The power supply unit supplies power to the fruit moisture content measurement circuit. The display unit is used to display the data output by the fruit moisture content measurement circuit.

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