A near-infrared moisture meter based on three LED lamps

Abstract

The present invention provides a near-infrared moisture meter based on three LED lamps, wherein a photodiode detector is located at the focus of a plano-concave focusing lens and is placed on one side of an object to be measured and forms an acute angle with a vertical line. The three LED lamps are arranged in an equilateral triangle and are located behind a biconvex focusing lens, the center of the equilateral triangle is located on the central optical axis of the biconvex focusing lens, one of the three LED lamps is a measuring light source, and the other two are reference light sources. The wavelengths of all the light sources are different, and the light sources as a whole are located on the other side of the object to be measured and are symmetrical with the photodiode detector about the vertical line. A host computer controls a driving circuit to output three control signals with the same frequency, the same duty cycle, a phase difference of 120 degrees, and real-time adjustable phase amplitude to respectively control the three LEDs to light up alternately. The three LED lamps respectively emit light that passes through the biconvex focusing lens and is incident on the object to be measured. After diffuse reflection by the object to be measured, the light is converged by the plano-concave focusing lens and is then irradiated on the photodiode detector. The output end of the photodiode detector is connected to the input end of a preamplifier circuit, and the output end of the preamplifier circuit is connected to the host computer. The three LED lamps of the present invention are irradiated after being expanded and focused, and the emitted light rays are approximately combined into a parallel beam, so that the light source detection surfaces basically overlap, the light spot coverage range is large, and the measurement accuracy is high. The three-way LED lamps compensate each other through two sets of comparison results of one beam of measurement light and two beams of reference light, which can effectively eliminate the influence of uncontrollable factors such as color difference and particle size difference.

Description

Technical Field

[0001] The invention belongs to the technical field of moisture content detection of substances, and in particular is a high-precision substance moisture measurement device using near-infrared spectroscopy. Background Art

[0002] Moisture content is a crucial indicator of various material properties and has a significant impact in numerous industries, including chemicals, grain, pharmaceuticals, and metallurgy. For example, in grain production, excessive moisture can lead to mold during storage. In metallurgy, moisture content affects the sintering quality of mineral raw materials. In the pharmaceutical industry, moisture content has a significant impact on drug stability, safety, and efficacy, and can even directly influence drug efficacy. Therefore, determining the moisture content of material samples is a crucial task.

[0003] The main methods for determining moisture include drying method, Karl Fischer method, distillation method, coulometric method, conductivity method, capacitance method, neutron method, microwave method, near-infrared spectroscopy, etc.

[0004] Among the manufacturers of moisture meters currently produced at home and abroad, the most common methods are Karl Fischer method, Coulometric method, microwave method and infrared method.

[0005] The Karl Fischer method is a chemical method that quantitatively reacts the water in a sample with the Karl Fischer reagent, and then calculates the water content by titration. The Karl Fischer method has been continuously improved over the years, and its application has continued to expand.

[0006] Coulometric moisture meters are widely used to measure moisture in gases. When the gas being measured flows through an electrolytic cell at a constant flow rate, the moisture in the gas is electrolyzed and simultaneously absorbed by the desiccant between the electrodes. The magnitude of the electrolysis current is proportional to the moisture content in the gas. Therefore, by accurately measuring the electrolysis current, the moisture content in the gas can be calculated.

[0007] Microwave moisture meter is similar to the principle of near-infrared spectroscopy. The microwave wavelength it uses is very long and has strong penetrating power. After passing through materials containing water molecules, the water molecules will absorb the energy of the microwave and vibrate. The moisture content is measured by measuring the attenuation of the microwave energy. It is mostly used to measure liquid samples.

[0008] Near-infrared spectroscopy is a method of measuring the moisture content of materials by measuring near-infrared light. Specifically, according to the Lambert-Beer law and infrared radiation theory, water molecules have a characteristic absorption peak in the near-infrared band. Therefore, the energy attenuation caused by the absorption of infrared radiation by water molecules is proportional to the water content. The moisture content of the material can be indirectly measured by measuring the transmitted or reflected near-infrared light.

[0009] Existing near-infrared moisture meters have problems such as complex structure, large space occupation, high light source energy consumption, inconvenient modulation, and long response time.

[0010] Chinese patent application publication number CN118310958 A discloses a near-infrared moisture meter based on dual LED lamps and its measurement method. The optical path structure includes a first LED lamp, a second LED lamp, a diffusion lens, a focusing lens, and a photodetector. The photodetector is located at the focus of the focusing lens and directly above the object to be measured. The first LED lamp and the second LED lamp are located on either side of the photodetector, and a diffusion lens is installed at the front end of each of the first and second LED lamps. The host computer controls the driving circuit to output two control signals with the same frequency, the same period, and a phase difference of 180 degrees to control the first and second LED lamps to light up alternately. The first LED lamp and the second LED lamp respectively emit light through the diffusion lens to illuminate the object to be measured. After diffuse reflection by the object to be measured, the light is converged by the focusing lens and illuminates the photodetector. The output end of the photodetector is connected to the input end of the preamplifier circuit. One of the first LED lamp and the second LED lamp serves as a measurement light source, and the other serves as a reference light source. The wavelength band of the measurement light source is 1450nm, and the wavelength band of the reference light source is 1200nm. The patent application has a simple optical path structure, fast detection speed, low energy consumption, convenient modulation and high precision. However, its dual-band modulation uses a measuring light source and a reference light source. Comparing the two reference signals cannot effectively eliminate the impact caused by color differences of materials of the same texture being measured.

[0011] Chinese patent application publication number CN103760116A discloses a near-infrared moisture meter with online continuous measurement and no moving parts. The instrument comprises an optical path, detection hardware circuitry, and a computer. The optical path consists of an LED light source, a photodetector, a reflector, and a condenser. The photodetector is positioned above the reflector; the condenser is positioned above the photodetector; and the LED light source is positioned to the side of the reflector. The LED light source comprises a measuring light source, a first reference light source, and a second reference light source. This patent application shifts from the time-sharing measurement of traditional instruments using a chopped optical disk (with moving parts) to a continuous measurement method using LEDs of different wavelengths and frequencies electrically modulated (with no moving parts). The LED light source continuously illuminates the material being measured, achieving contactless online continuous measurement and reducing instrument maintenance. This patent application utilizes a continuous illumination method to demodulate the signal. However, due to the diffuse reflection effect of near-infrared measurement, the reflection varies depending on the material being measured. The integrity of the acquired signal cannot be guaranteed. Furthermore, due to the loss and noise from three reflections, the demodulated signal suffers from significant distortion. Moreover, in this patent application, the optical path is not reduced much compared to the traditional solution. It only replaces the single halogen lamp light source with three parallel light sources. The actual overlapping position of the parallel arranged LED lamp beads light spots is small, resulting in a small overlap of the light spot detection surface during measurement, which cannot guarantee the accuracy of the measurement results. There is much room for improvement in measurement accuracy. Summary of the Invention

[0012] The technical problem to be solved by the present invention is how to effectively eliminate the influence caused by the color difference of the materials to be tested of the same texture and ensure the validity of the signal.

[0013] The present invention adopts the following technical means to solve the above technical problems:

[0014] A near-infrared moisture meter based on three LED lamps comprises an optical path structure, a preamplifier circuit (9), a host computer (10), a drive circuit and a power supply circuit (15). The optical path structure comprises a first LED lamp (2), a second LED lamp (3), a third LED lamp (4), a plano-concave focusing lens (5), a biconvex focusing lens (8) and a photodiode detector (1). The photodiode detector (1) is located at the focus of the plano-concave focusing lens (5) and is placed on one side of the object to be measured (7) and forms an acute angle with the vertical line. The first LED lamp (2), the second LED lamp (3) and the third LED lamp (4) are arranged in an equilateral triangle and are located behind the biconvex focusing lens (8). The center of the equilateral triangle is located on the central optical axis of the biconvex focusing lens (8). One of the first LED lamp (2), the second LED lamp (3) and the third LED lamp (4) is a measuring light source, and the other two are reference light sources. The wavelength bands of the light sources are different. The light sources are located on the other side of the object to be measured (7) and are symmetrical with the photodiode detector (1) about a vertical line. The host computer (10) controls the driving circuit to output three control signals with the same frequency, the same duty cycle, a phase difference of 120 degrees, and a phase amplitude that is adjustable in real time to control the first LED lamp (2), the second LED lamp (3), and the third LED lamp (4) to light up alternately. The three LED lamps respectively emit light that passes through a double convex focusing lens (8) and is incident on the object to be measured (7). After diffuse reflection from the object to be measured (7), the light is converged by a plano-concave focusing lens (5) and is then irradiated on the photodiode detector (1). The output end of the photodiode detector (1) is connected to the input end of a preamplifier circuit (9). The output end of the preamplifier circuit (9) is connected to the host computer (10). The power supply circuit (15) is used to supply power to the preamplifier circuit (9) and the driving circuit.

[0015] As a further optimized technical solution, the wavelength band of the measuring light source is 1450 nm, and the wavelength bands of the reference light source are 1200 nm and 1650 nm.

[0016] As a further optimized technical solution, the photodiode detector (1) forms an angle of 15° with the vertical line.

[0017] As a further optimized technical solution, the first LED lamp (2), the second LED lamp (3) and the third LED lamp (4) are located at the rear 1 / 4 focus of the double convex focusing lens (8).

[0018] As a further optimized technical solution, the overall height of the light source is the same as the horizontal height of the photodiode detector (1), and is 200 mm ± 50 mm away from the object to be measured (7).

[0019] As a further optimized technical solution, the anode of the photodiode detector (1) is grounded, and the cathode is connected to the inverting input terminal of the operational amplifier U1, one end of the resistor R1 and one end of the capacitor C1 respectively. The non-inverting input terminal of the operational amplifier U1 is connected in series with the resistor R1 and then grounded. The positive power input terminal of the operational amplifier U1 is connected to positive 5V and one end of the capacitor C2 respectively. The reverse power input terminal is connected to negative 5V and one end of the capacitor C3. The other ends of the capacitors C2 and C3 are grounded. The output terminal of the operational amplifier U1 is connected to the other end of the resistor R1, the other end of the capacitor C1 and one end of the resistor R3 respectively. The other end of the resistor R3 is connected to the inverting input terminal of the operational amplifier U2 and one end of the resistor R5 respectively. The non-inverting input terminal of the operational amplifier U2 is connected in series with the resistor R4 and then grounded. The positive power input terminal of the operational amplifier U2 is connected to positive 5V and one end of the capacitor C4 respectively. The reverse power input terminal is connected to negative 5V and one end of the capacitor C5. The other ends of the capacitors C4 and C5 are grounded. The other end of the resistor R5 is connected to the output terminal of the operational amplifier U2 and serves as the output terminal of the preamplifier circuit (9).

[0020] As a further optimized technical solution, the model of the photodiode detector is InGaAs photodetector.

[0021] As a further optimized technical solution, the driving circuit comprises a single-chip computer system circuit (11), a first voltage-controlled constant current circuit (12), a second voltage-controlled constant current circuit (13) and a third voltage-controlled constant current circuit (14); a first output end of the single-chip computer system circuit (11) whose output phase and amplitude are adjustable in real time is connected to the first voltage-controlled constant current circuit (12); a second output end of the single-chip computer system circuit (11) whose output phase and amplitude are adjustable in real time is connected to the second voltage-controlled constant current circuit (13); a third output end of the single-chip computer system circuit (11) whose output phase and amplitude are adjustable in real time is connected to the third voltage-controlled constant current circuit (14); an output end of the first voltage-controlled constant current circuit (12) is connected to an input end of a first LED lamp (2); an output end of the second voltage-controlled constant current circuit (13) is connected to an input end of a second LED lamp (3); and an output end of the third voltage-controlled constant current circuit (14) is connected to an input end of a third LED lamp (4).

[0022] As a further optimized technical solution, among the three modulation signals output by the single chip computer system circuit (11), one signal is at a high level at a 1 / 6 cycle, one signal is at a high level at a 1 / 2 cycle, and one signal is at a high level at a 5 / 6 cycle, and the duty cycles of the three modulation signals are all 1 / 6.

[0023] As a further optimized technical solution, the power supply circuit (15) outputs a 3V3 DC voltage to power the single-chip computer system circuit (11), outputs a positive and negative 12V DC voltage to power the first voltage-controlled constant current circuit (12), the second voltage-controlled constant current circuit (13) and the third voltage-controlled constant current circuit (14), and outputs a positive and negative 5V DC voltage to power the preamplifier circuit (10);

[0024] The output signal of the single chip computer system circuit (11) in the voltage controlled constant current circuit is connected to one end of the resistor R6, the other end of the resistor R6 is respectively connected to the second positive input end of the operational amplifier U3 and one end of the resistor R7, the other end of the resistor R7 is connected to the first negative input end of the operational amplifier U3 and the first output end of the operational amplifier U3, the first positive input end of the operational amplifier U3 is connected to the output end of the operational amplifier U4, the positive power input end of the operational amplifier U3 is respectively connected to the positive 12V and one end of the capacitor C7, the reverse power input end is connected to the negative 12V and one end of the capacitor C6, the other ends of the capacitor C6 and the capacitor C7 are grounded, and the second reverse input end of the operational amplifier U3 is connected to The common end of resistor R8, resistor R9, and capacitor C9, the other end of resistor R9 is grounded, the other ends of resistor R8 and capacitor C9 are connected to the output end of op amp U4, the second output end of op amp U3 is connected to the input end of op amp U4, resistor R10, resistor R11, and resistor R12 are connected in parallel after the output end of op amp U4, and the other ends of the parallel resistors R10, R11, and R12 serve as the total output end, the positive power supply input end of op amp U4 is respectively connected to positive 12V and one end of capacitor C10, the reverse power supply input end is connected to negative 12V and one end of capacitor C8, and the other ends of capacitor C8 and capacitor C10 are grounded.

[0025] The advantages provided by the present invention are:

[0026] 1. In the optical path mechanical structure of the present invention, LED lamps replace halogen lamps, eliminating the need for mechanical chopper disks, motors, and filters. The optical path structure is simple and compact, and the LED light source has a simple structure, high light efficiency, and long service life. Using single-frequency differential modulation technology, the host computer controls the drive circuit through electrical modulation to output three control signals with the same frequency, the same duty cycle, a phase difference of 120°, and an amplitude that can be adjusted in real time, so that the three LED lamps light up alternately, which is convenient for modulation. At the same time, compared with traditional mechanical modulation, the modulation frequency of electrical modulation can reach the KHZ level, and the detection speed is faster. The three LED lamps are irradiated after beam expansion and focusing, and the light source detection surfaces basically overlap. The light spot coverage range is large, and the measurement accuracy is high. The comparison of the three LED lamps can effectively eliminate the influence of color differences and particle size differences, especially can effectively eliminate the influence of color differences of materials with the same texture.

[0027] 2. The light source of the present invention adopts LED lamps of specific wavelength to replace the traditional halogen lamp infrared spectrum light source. Three LED lamps are arranged in an equilateral triangle, which respectively generate a beam of measurement light and two beams of reference light. After passing through the focusing lens, they have a good beam-combining effect within a certain distance range. They can be approximately regarded as a beam of parallel light emitted, and their irradiation positions are approximately at the same position, so that the collected information is effective and has reference value. The LED light source is modulated by the single-chip microcomputer driving circuit with single-frequency differential modulation. The measurement light and the reference light have the same frequency, the same duty cycle, a phase difference of 120°, and the output amplitude and phase can be adjusted in real time by the host computer. By changing the modulation frequency, the output signal amplitude, phase and duty cycle can be adjusted in real time, and then the intensity, interval and time of the light source irradiation can be adjusted to adapt to different measurement environments and different objects to be measured. At the same time, the output signal can achieve real-time data storage function through the single-chip microcomputer, and data will not be lost when the power is off.

[0028] 3. The circuit of this invention adopts a patch design and modular design, further reducing the installation size requirements and achieving compactness and portability. The modular design reduces interference between individual circuits, greatly improving the anti-interference ability of the overall circuit, improving the signal-to-noise ratio of the received signal, and facilitating maintenance. The use of a high-precision, low-noise weak signal amplifier achieves high measurement accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 A schematic diagram of a near-infrared moisture meter based on three LED lamps provided by the present invention;

[0030] Figure 2 A schematic diagram of the actual overlapping positions of the LED light spots of the near-infrared moisture meter based on three LED lamps provided by the present invention;

[0031] Figure 3 This is a topological diagram of the preamplifier circuit in the near-infrared moisture meter based on three LED lamps of the present invention;

[0032] Figure 4 This is a topological diagram of the voltage-controlled constant current circuit in the near-infrared moisture meter based on three LED lamps of the present invention;

[0033] Figure 5 This is a diagram of three-way modulation signals output by the single-chip microcomputer system circuit in the present invention;

[0034] Figure 6 This is a test result diagram showing the effects of using dual-band and triple-band wavelengths on the detection of yellow and white sand of the same texture in the present invention;

[0035] Figure 7 This is the beam combining effect diagram simulated by TRACEPRO software.

[0036] In the figure: 1 photodiode detector, 2 first LED lamp, 3 second LED lamp, 4 third LED lamp, 5 plano-concave focusing lens, 6 platform, 7 object to be measured, 8 biconvex focusing lens, 9 preamplifier circuit, 10 host computer, 11 single-chip microcomputer system circuit, 12 first voltage-controlled constant current circuit, 13 second voltage-controlled constant current circuit, 14 third voltage-controlled constant current circuit, 15 power supply circuit. DETAILED DESCRIPTION

[0037] In order to make the objectives, technical solutions and advantages of the present invention more clear, the technical solutions of the present invention are clearly and completely described below in combination with specific embodiments and with reference to the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments.

[0038] like Figure 1 The figure shows a high-precision infrared moisture meter based on differential modulation of three LED lights, including an optical path structure, a preamplifier circuit 9, a host computer 10, a single-chip computer system circuit 11, a first constant current circuit 12, a second constant current circuit 13, a third constant current circuit 14, and a power supply circuit 15. The optical path structure includes a photodiode detector 1, a first LED light 2, a second LED light 3, a third LED light 4, a plano-concave focusing lens 5, a platform 6, an object to be measured 7, and a biconvex focusing lens 8. The object to be measured 7 is placed on the platform 6, and the first LED light 2, the second LED light 3, and the third LED light 4 are arranged in an equilateral triangle and placed behind the biconvex focusing lens 8. The center of the equilateral triangle coincides with the optical axis of the biconvex focusing lens 8 and is placed on one side of the object to be measured 7. The photodiode detector 1 is placed behind the plano-concave focusing lens 5, on the other side of the object to be measured 7, and forms an acute angle with the vertical line. In this embodiment, the photodiode detector 1 forms an angle of 15° with the vertical line, but other angles are also possible. The host computer 10 controls the single-chip computer system circuit 11 to output voltage signals with the same duty cycle, frequency, 120° phase difference, and real-time adjustable amplitude and phase. These signals are passed through the first voltage-controlled constant current circuit 12, the second voltage-controlled constant current circuit 13, and the third voltage-controlled constant current circuit 14 to control the alternating lighting of the first LED lamp 2, the second LED lamp 3, and the third LED lamp 4. The first LED lamp 2, the second LED lamp 3, and the third LED lamp 4 each emit light through a biconvex focusing lens 8 and then illuminate the object to be measured 7. The light is diffusely reflected by the object 7 and then passes through a plano-concave focusing lens 5 before converging on a photodiode detector 1. The output of the photodiode detector 1 is connected to the input of a preamplifier circuit 9, which in turn is connected to the input of the host computer 10. The power supply circuit 15 provides power to the aforementioned circuits and devices.

[0039] In the optical path mechanical structure of the present invention, LED lamps replace halogen lamps, eliminating the need for mechanical chopper disks, motors, and filters. The optical path structure is simple and compact, and the LED light source has a simple structure, high light efficiency, and long life. Using single-frequency differential modulation technology, the host computer controls the drive circuit to output three control signals with the same frequency, the same duty cycle, and a phase difference of 120° through electrical modulation, so that the three LED lamps light up alternately. The modulation is convenient. The amplitude, phase, and duty cycle of the output signal can be adjusted in real time by the host computer, and the measured signal intensity and change curve can be observed in real time, which can meet the measurement requirements of different scenes and different objects to be measured. At the same time, compared with traditional mechanical modulation, the modulation frequency of electrical modulation can reach the KHZ level, and the detection speed is faster. The storage system of the single-chip microcomputer can save data in real time and call it at any time. The data will not be lost in the event of power outage, which improves the stability of the system and its risk resistance. The three LED lamps are irradiated after being expanded and focused, and the emitted light beams are approximately combined into a parallel beam, so that the light source detection surfaces basically overlap, the light spot coverage range is large, and the measurement accuracy is high. The three-way LED light compensates each other through two sets of comparison results of one measuring light and two reference lights, which can effectively eliminate the influence of uncontrollable factors such as color difference and particle size difference.

[0040] The first LED lamp 2, the second LED lamp 3 and the third LED lamp 3 emit measurement light and reference light, and the measurement light and the reference light bands are different. Specifically, the first LED lamp 2 is an LED lamp with a specific wavelength of 1450nm, which is used as the measurement light source, and the second LED lamp 3 and the third LED lamp 4 are LED lamps with specific wavelengths of 1200nm and 1650nm, respectively, which are used as reference light sources. According to the principle of spectral technology, water molecules have a strong absorption effect on near-infrared light of a specific wavelength. The first LED lamp 2 serves as the measurement light source and emits 1450nm light that can be greatly absorbed by water. The second LED lamp 3 and the third LED lamp 4 select a near-infrared band that is insensitive to water absorption as the reference light source. By contrasting and compensating the measurement light source and the reference light source, the influence of environmental error factors can be well eliminated. The light emitted by the measurement light source (the first LED lamp 2) will be irradiated onto the object to be measured 7 through the double convex focusing lens 8, and reflection and diffuse reflection will occur on the object to be measured 7. Most of the light will be converged by the plano-concave focusing lens 6 and irradiated onto the photodiode detector 1. The entire structure of the light source is fixed on the top plate at the same level as the photodiode detector 1 and is 7200 mm ± 50 mm away from the object to be measured.

[0041] like Figure 3As shown, photodiode detector 1 is an InGaAs photodetector with extremely high sensitivity to light in the near-infrared band. It is also one of the mainstream photodiode detectors on the market. The anode of photodiode detector 1 is grounded, and the cathode is connected to the inverting input of op amp U1, one end of resistor R1, and one end of capacitor C1. The non-inverting input of op amp U1 is connected in series with resistor R1 and then to ground. The positive power input of op amp U1 is connected to positive 5V and one end of capacitor C2, respectively. The negative power input is connected to negative 5V and one end of capacitor C3. The other ends of capacitors C2 and C3 are grounded. The output of op amp U1 is connected to the other end of resistor R1, the other end of capacitor C1, and one end of resistor R3, respectively. The other end of resistor R3 is connected to the negative input of op amp U2 and one end of resistor R5, respectively. The non-inverting input of op amp U2 is connected in series with resistor R4 and then to ground. The positive power input of op amp U2 is connected to positive 5V and one end of capacitor C4, respectively. The negative power input is connected to negative 5V and one end of capacitor C5, and the other ends of capacitor C4 and C5 are grounded. The other end of resistor R5 is connected to the output of op amp U2 and serves as the output of preamplifier circuit 9. The photodiode detector 1 is fixed to the top plate as a whole and at the same level as the overall light source structure, 200 mm ± 50 mm from the object to be measured.

[0042] See Figure 1 The driving circuit includes a single-chip computer system circuit 11, a first voltage-controlled constant current circuit 12, a second voltage-controlled constant current circuit 13, and a third voltage-controlled constant current circuit 14. The first output end of the single-chip computer system circuit 11, whose output phase and amplitude can be adjusted in real time, is connected to the first voltage-controlled constant current circuit 12, the second output end of the output phase and amplitude can be adjusted in real time, is connected to the second voltage-controlled constant current circuit 13, and the third output end of the output phase and amplitude can be adjusted in real time is connected to the third voltage-controlled constant current circuit 14. The output end of the first voltage-controlled constant current circuit 12 is connected to the input end of the first LED lamp 2, the output end of the second voltage-controlled constant current circuit 13 is connected to the input end of the second LED lamp 3, and the output end of the third voltage-controlled constant current circuit 14 is connected to the input end of the third LED lamp 4.

[0043] like Figure 4As shown, the output signal of the single-chip computer system circuit 11 in the voltage-controlled constant current circuit is connected to one end of the resistor R6, and the other end of the resistor R6 is respectively connected to the second positive input terminal of the operational amplifier U3 and one end of the resistor R7, the other end of the resistor R7 is connected to the first negative input terminal of the operational amplifier U3 and the first output terminal of the operational amplifier U3, the first positive input terminal of the operational amplifier U3 is connected to the output terminal of the operational amplifier U4, the positive power supply input terminal of the operational amplifier U3 is respectively connected to the positive 12V and one end of the capacitor C7, the reverse power supply input terminal is connected to the negative 12V and one end of the capacitor C6, and the other ends of the capacitor C6 and the capacitor C7 are grounded. The second inverting input of op amp U3 is connected to the common terminal of resistors R8, R9, and C9. The other end of resistor R9 is grounded. The other ends of resistors R8 and C9 are connected to the output of op amp U4. The second output of op amp U3 is connected to the input of op amp U4. Resistors R10, R11, and R12 are connected in parallel after the output of op amp U4, and the other ends of the parallel resistors R10, R11, and R12 serve as the total output. The positive power input of op amp U4 is connected to positive 12V and one end of capacitor C10, respectively. The reverse power input is connected to negative 12V and one end of capacitor C8. The other ends of capacitors C8 and C10 are grounded. The voltage-controlled constant current block adopts a modular design to effectively improve accuracy and stability.

[0044] The three modulation signals with the same duty cycle, frequency and adjustable amplitude and phase output by the single chip microcomputer system circuit 11 are as follows: Figure 5 As shown, one signal is high at a cycle of 1 / 6, one signal is high at a cycle of 1 / 2, and one signal is high at a cycle of 5 / 6. The duty cycle of the three modulated signals is 1 / 6, and the amplitude can be adjusted in real time. Using single-frequency differential modulation technology and DAC+DMA technology, three DAC signals are output to drive the three LED lights to light up alternately, that is, only one LED light is lit in 1 / 3 of the cycle. This is easy to distinguish, has a simple structure, and is easy to modulate, solving the problem of inconvenient modulation of traditional modulated light sources. Through DAC+DMA technology, the intensity and phase of each output signal can be adjusted in real time by the host computer 10 during the measurement process, skipping the MCU processing process, making measurement adjustment and feedback faster, and more efficient measurement of the moisture content of different environments and different objects to be measured.

[0045] The power supply circuit 15 outputs a 3V3 DC voltage to power the single-chip computer system circuit 11, outputs a positive and negative 12V DC voltage to power the first voltage-controlled constant current circuit 12, the second voltage-controlled constant current circuit 13 and the third voltage-controlled constant current circuit 14, and outputs a positive and negative 5V DC voltage to power the preamplifier circuit.

[0046] Compared with the Chinese patent application with publication number CN118310958 A, entitled "A near-infrared moisture meter based on dual LED lamps and its measurement method", the instrument of the present invention uses three bands as a measuring instrument, which can effectively eliminate the color difference of the materials with the same texture. The experiment was conducted using 0.5-1mm yellow and white sand of the same texture, and the results are as follows: Figure 6 As shown, it can be obtained from Figure 6 As can be seen from the left figure, the test results of single ratio for gravels with the same water content but different colors are not consistent. Figure 6 As shown in the right figure, the use of double ratios can effectively eliminate the impact of color differences, has a good linear relationship, and both yellow sand and white sand show good correlation with the overall trend.

[0047] like Figure 5 As shown, compared with the Chinese patent application with publication number CN103760116A and titled "Online Continuous Measurement Near-Infrared Moisture Meter without Moving Parts", the present invention detects reflection once and uses time-sharing modulation technology to ensure the validity and easy-to-distinguish characteristics of the signal.

[0048] Additionally, the use of LED lighting can effectively reduce the size of the structure. However, since the light sources are emitted by different LEDs, their optical paths differ. For measurement purposes, the information obtained when irradiating different locations is different, making the collected signals of the measurement and reference light less valuable. Therefore, in near-infrared moisture measurement, it is extremely important to have different LED light sources illuminate the same location. Compared to Chinese patent application publication number CN118310958A, entitled "A Near-Infrared Moisture Meter Based on Dual LED Lamps and Its Measurement Method," the dual-LED illumination scheme employed in this patent requires reflection, requiring the light to be reflected onto the same detector. This illumination position is not uniform, but rather illuminates two different locations. This can lead to significant variability in online detection depending on the conveyor speed in different scenarios. Furthermore, compared to Chinese patent application publication number CN103760116A, entitled "Online Continuous Measurement Near-Infrared Moisture Meter with No Moving Parts," this patent does not specifically design the LED light source arrangement. The fact that the light is not uniformly illuminated after passing through the reflector onto the material under test can also cause the aforementioned errors. The present invention adopts the distribution of LED lights arranged in an equilateral triangle behind the focusing lens. After refraction by the lens, within a certain distance range, Figure 7 The simulation results of TRACEPRO software show that it has a good beam combining effect and the irradiation positions are approximately at the same position.

[0049] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A near-infrared moisture meter based on three LED lamps, characterized by: The optical path structure includes an optical path structure, a preamplifier circuit (9), a host computer (10), a drive circuit and a power supply circuit (15). The optical path structure includes a first LED lamp (2), a second LED lamp (3), a third LED lamp (4), a plano-concave focusing lens (5), a biconvex focusing lens (8) and a photodiode detector (1). The photodiode detector (1) is located at the focus of the plano-concave focusing lens (5) and is placed on one side of the object to be measured (7) and forms an acute angle with the vertical line. The first LED lamp (2), the second LED lamp (3) and the third LED lamp (4) are arranged in an equilateral triangle and are located behind the biconvex focusing lens (8). The center of the equilateral triangle is located on the central optical axis of the biconvex focusing lens (8). One of the first LED lamp (2), the second LED lamp (3) and the third LED lamp (4) is a measuring light source, and the other two are reference light sources. The wavelength bands of all the light sources are different. The light source is located on the other side of the object to be measured (7) and is symmetrical with the photodiode detector (1) about the vertical line. The host computer (10) controls the driving circuit to output three control signals with the same frequency, the same duty cycle, a phase difference of 120 degrees, and a phase amplitude that is adjustable in real time to control the first LED lamp (2), the second LED lamp (3), and the third LED lamp (4) to light up alternately. The three LED lamps respectively emit light through a double convex focusing lens (8) to irradiate the object to be measured (7). After diffuse reflection from the object to be measured (7), the light is converged by a plano-concave focusing lens (5) and then irradiated onto the photodiode detector (1). The output end of the photodiode detector (1) is connected to the input end of the preamplifier circuit (9). The output end of the preamplifier circuit (9) is connected to the host computer (10). The power supply circuit (15) is used to supply power to the preamplifier circuit (9) and the driving circuit. The driving circuit comprises a single-chip computer system circuit (11) and a first voltage-controlled constant current circuit (12), a second voltage-controlled constant current circuit (13), and a third voltage-controlled constant current circuit (14) respectively connected to the single-chip computer system circuit (11); the output ends of the first voltage-controlled constant current circuit (12), the second voltage-controlled constant current circuit (13), and the third voltage-controlled constant current circuit (14) are respectively connected to the input ends of the first LED lamp (2), the second LED lamp (3), and the third LED lamp (4); The output signal of the single chip computer system circuit (11) in the voltage controlled constant current circuit is connected to one end of the resistor R6, the other end of the resistor R6 is respectively connected to the second positive input end of the operational amplifier U3 and one end of the resistor R7, the other end of the resistor R7 is connected to the first negative input end of the operational amplifier U3 and the first output end of the operational amplifier U3, the first positive input end of the operational amplifier U3 is connected to the output end of the operational amplifier U4, the positive power input end of the operational amplifier U3 is respectively connected to the positive 12V and one end of the capacitor C7, the reverse power input end is connected to the negative 12V and one end of the capacitor C6, the other ends of the capacitor C6 and the capacitor C7 are grounded, and the second reverse input end of the operational amplifier U3 is connected to The common end of resistor R8, resistor R9, and capacitor C9, the other end of resistor R9 is grounded, the other ends of resistor R8 and capacitor C9 are connected to the output end of op amp U4, the second output end of op amp U3 is connected to the input end of op amp U4, resistor R10, resistor R11, and resistor R12 are connected in parallel after the output end of op amp U4, and the other ends of the parallel resistors R10, R11, and R12 serve as the total output end, the positive power supply input end of op amp U4 is respectively connected to positive 12V and one end of capacitor C10, the reverse power supply input end is connected to negative 12V and one end of capacitor C8, and the other ends of capacitor C8 and capacitor C10 are grounded.

2. The near-infrared moisture meter based on three LED lamps according to claim 1, characterized in that: The wavelength band of the measuring light source is 1450 nm, and the wavelength bands of the reference light source are 1200 nm and 1650 nm.

3. The near-infrared moisture meter based on three LED lamps according to claim 2, characterized in that: The photodiode detector (1) forms an angle of 15° with the vertical line.

4. The near-infrared moisture meter based on three LED lamps according to claim 3, characterized in that: The first LED lamp (2), the second LED lamp (3) and the third LED lamp (4) are located at the rear 1 / 4 focus of the double convex focusing lens (8).

5. The near-infrared moisture meter based on three LED lamps according to claim 4, characterized in that: The overall height of the light source is the same as the horizontal height of the photodiode detector (1), and is 200 mm ± 50 mm away from the object to be measured (7).

6. The near-infrared moisture meter based on three LED lamps according to claim 1, characterized in that: The anode of the photodiode detector (1) is grounded, and the cathode is connected to the inverting input terminal of the operational amplifier U1, one end of the resistor R1 and one end of the capacitor C1 respectively. The non-inverting input terminal of the operational amplifier U1 is connected in series with the resistor R1 and then grounded. The positive power input terminal of the operational amplifier U1 is connected to positive 5V and one end of the capacitor C2 respectively, and the reverse power input terminal is connected to negative 5V and one end of the capacitor C3. The other ends of the capacitors C2 and C3 are grounded. The output terminal of the operational amplifier U1 is connected to the other end of the resistor R1, the other end of the capacitor C1 and one end of the resistor R3 respectively. The other end of the resistor R3 is connected to the inverting input terminal of the operational amplifier U2 and one end of the resistor R5 respectively. The non-inverting input terminal of the operational amplifier U2 is connected in series with the resistor R4 and then grounded. The positive power input terminal of the operational amplifier U2 is connected to positive 5V and one end of the capacitor C4 respectively, and the reverse power input terminal is connected to negative 5V and one end of the capacitor C5. The other ends of the capacitors C4 and C5 are grounded. The other end of the resistor R5 is connected to the output terminal of the operational amplifier U2 and serves as the output terminal of the preamplifier circuit (9).

7. The near-infrared moisture meter based on three LED lamps according to claim 6, characterized in that: The photodiode detector is an InGaAs photodetector.

8. The near-infrared moisture meter based on three LED lamps according to claim 1, characterized in that: The first output end of the single-chip computer system circuit (11) whose output phase and amplitude are adjustable in real time is connected to a first voltage-controlled constant current circuit (12), the second output end whose output phase and amplitude are adjustable in real time is connected to a second voltage-controlled constant current circuit (13), and the third output end whose output phase and amplitude are adjustable in real time is connected to a third voltage-controlled constant current circuit (14).

9. The near-infrared moisture meter based on three LED lamps according to claim 8, characterized in that: Among the three modulation signals output by the single chip computer system circuit (11), one signal is at a high level at a 1 / 6 cycle, one signal is at a high level at a 1 / 2 cycle, and one signal is at a high level at a 5 / 6 cycle. The duty cycles of the three modulation signals are all 1 / 6.

10. The near-infrared moisture meter based on three LED lamps according to claim 8, characterized in that: The power supply circuit (15) outputs a 3V3 DC voltage to power the single-chip computer system circuit (11), outputs a positive and negative 12V DC voltage to power the first voltage-controlled constant current circuit (12), the second voltage-controlled constant current circuit (13) and the third voltage-controlled constant current circuit (14), and outputs a positive and negative 5V DC voltage to power the preamplifier circuit (10).

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