Near-infrared moisture meter based on three LED lamps

Abstract

The invention provides a near-infrared moisture meter based on three LED lamps, which is characterized in that a photodiode detector is positioned at the focus of a plano-concave focusing lens, is arranged on one side of an object to be measured and forms an acute included angle with a vertical line, and the three LED lamps are arranged in an equilateral triangle shape and are positioned behind a biconvex focusing lens; one of the three paths of LED lamps is a measuring light source, the other two paths of LED lamps are reference light sources, wavebands of all the light sources are different, and the light sources are integrally positioned on the other side of the object to be measured and are symmetrical about a vertical line with the photodiode detector; the upper computer controls the drive circuit to output three paths of control signals with the same frequency, the same duty ratio, the phase difference of 120 degrees and the real-time adjustable phase amplitude to control the three paths of LEDs to be turned on alternately, and the three paths of LED lamps emit light rays which are incident through the biconvex focusing lens to irradiate an object to be measured. After diffuse reflection of an object to be detected, the light is converged by the plano-concave focusing lens and then irradiates the photodiode detector, the output end of the photodiode detector is connected to the input end of the pre-amplification circuit, and the output end of the pre-amplification circuit is connected to the upper computer. The three LED lamps irradiate after beam expanding and focusing, emergent light rays are approximately combined into parallel light, light source detection surfaces basically coincide, the light spot coverage range is large, the measurement precision is high, the three LED lamps compensate each other through two groups of comparison results of one measuring light beam and two reference light beams, the color difference can be well eliminated, and the measurement accuracy is high. The influence caused by uncontrollable factors such as particle size difference is avoided.

Description

Technical Field

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

[0002] Moisture content is an important indicator of various properties of substances, and has a significant impact on many industries such as chemicals, food, medicine, and metallurgy. For example, in the field of food production, excessive moisture can cause mold during storage; in the field of metallurgy, the amount of moisture content affects the sintering quality of mineral raw materials. In the pharmaceutical field, it has an important impact on the stability, safety, and effectiveness of drugs, and even directly affects the efficacy of drugs. Therefore, how to detect the moisture content of material samples is a very important project.

[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 the sample with the Karl Fischer reagent and then calculates the water content by titration. The Karl Fischer method has been continuously improved in recent years and its scope of application has been continuously expanded.

[0006] Coulometric moisture meters are widely used in measuring moisture in gas. When the measured gas flows through the electrolytic cell at a certain flow rate, the moisture in the gas is electrolyzed and absorbed by the desiccant between the electrodes. The size of the electrolytic current is proportional to the moisture content in the gas. Therefore, as long as the electrolytic current is accurately measured, the moisture content in the gas can be calculated.

[0007] The 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 microwave energy and vibrate. The moisture content is measured by measuring the attenuation of 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 Beer-Lambert law and infrared radiation theory, water molecules have characteristic absorption peaks 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 materials 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] The Chinese patent application with publication number CN118310958 A discloses a near-infrared moisture meter based on dual LED lamps and a measurement method thereof. 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 both sides of the photodetector and a diffusion lens is installed at the front end of the first LED lamp and the second LED lamp. The upper computer controls the driving circuit to output two control signals with the same frequency, the same period and a phase difference of 180° to control the first LED lamp and the second LED lamp to light up alternately. The first LED lamp and the second LED lamp respectively emit light through the diffusion lens to irradiate the object to be measured, and after diffuse reflection by the object to be measured, they are converged by the focusing lens and irradiated on 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 is used as a measuring light source and the other is used as a reference light source. The wavelength band of the measuring 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 measurement 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] The Chinese patent application with publication number CN103760116A discloses a near-infrared moisture meter with online continuous measurement without moving parts, including an optical path mechanism, a detection hardware circuit and a computer. The optical path mechanism is composed of an LED light source, a photodetector, a reflector and a condenser; the photodetector is arranged above the reflector; the condenser is arranged above the photodetector; the LED light source is arranged on the side of the reflector; the LED light source is composed of a measuring light source, a first reference light source and a second reference light source. This patent application changes the time-sharing measurement of the traditional instrument's cut-disk modulation (with moving parts) to the continuous measurement of different wavelengths of LEDs with different frequencies of electrical modulation (without moving parts). The LED light source is continuously irradiated on the measured material to achieve non-contact online continuous measurement, thereby achieving the purpose of reducing the maintenance of the instrument. This patent application adopts the method of continuous irradiation of demodulation signals. Due to the diffuse reflection effect of near-infrared measurement, the reflection is different according to different measured materials. The acquisition signal cannot guarantee its integrity, and coupled with the loss and noise influence after three reflections, the demodulation signal has a large distortion rate. 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 arranged light sources. The actual overlapping positions of the light spots of the parallel arranged LED lamp beads are 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 the 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 with the same texture being tested 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 a to-be-measured object (7) and forms an acute angle with a 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) as a whole and are 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 can be adjusted 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 rays that are incident on the object to be measured (7) through a double convex focusing lens (8). After diffuse reflection from the object to be measured (7), the light rays are 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 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 1450nm, and the wavelength band of the reference light source is 1200nm and 1650nm.

[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 respectively connected to the inverting input terminal of the operational amplifier U1, one end of the resistor R1 and one end of the capacitor C1; 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 respectively connected to positive 5V and one end of the capacitor C2; 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 respectively connected to the other end of the resistor R1, the other end of the capacitor C1 and one end of the resistor R3; the other end of the resistor R3 is respectively connected to the inverting input terminal of the operational amplifier U2 and one end of the resistor R5; 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 respectively connected to positive 5V and one end of the capacitor C4; 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 then 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 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 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 operational amplifier U4, the second output end of operational amplifier U3 is connected to the input end of operational amplifier U4, resistor R10, resistor R11 and resistor R12 are connected in parallel after the output end of operational amplifier 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 operational amplifier 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 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 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 through electrical modulation, so that the three LED lamps are alternately lit, and the modulation is convenient. 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 well eliminate the influence of color differences and particle size differences, especially can effectively eliminate the influence of color differences of materials of the same texture being measured.

[0027] 2. The light source of the present invention adopts LED lamps with specific wavelengths to replace the traditional halogen lamp infrared spectrum light source. Three LED lamps are arranged in an equilateral triangle, and a beam of measurement light and two beams of reference light are generated respectively. After passing through the focusing lens, within a certain distance range, it has a good beam combining effect, and can be approximately regarded as a beam of parallel light emitted, and its irradiation position is approximately at the same position, so that the collected information is effective and has reference value. The LED light source is modulated by a 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 phase can be adjusted in real time by the host computer. By changing the modulation frequency, the output signal amplitude, phase and duty cycle are adjusted in real time, and then the intensity, interval and time of the light source irradiation are 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 the power will not lose data.

[0028] 3. The circuit of the present invention adopts patch design and modular design, which further reduces the requirements for installation size and makes it compact and portable. The modular design reduces the interference between the various circuits, greatly improves the anti-interference ability of the overall circuit, improves the signal-to-noise ratio of the received signal, and is more convenient for maintenance. It adopts a high-precision low-noise weak signal amplifier with 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 It 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 It 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 A diagram of three-way modulation signals output by the single-chip computer system circuit in the present invention;

[0034] Figure 6 This is a test result diagram of the influence of the double-band and triple-band detection results on the 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 clearly understood, 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 lamps, including an optical path structure, a preamplifier circuit 9, a host computer 10, a single-chip 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 lamp 2, a second LED lamp 3, a third LED lamp 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, the first LED lamp 2, the second LED lamp 3, and the third LED lamp 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 the whole 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, and is placed on the other side of the object to be measured 7, and is at an acute angle with the vertical line. In this embodiment, the photodiode detector 1 is at an angle of 15° with the vertical line, and of course, other angles can also be used. The host computer 10 controls the single-chip computer system circuit 11 to output a voltage signal with the same duty cycle, the same frequency, a phase difference of 120°, and an amplitude phase that is adjustable in real time, and controls the first LED lamp 2, the second LED lamp 3, and the third LED lamp 4 to light up alternately 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. The first LED lamp 2, the second LED lamp 3, and the third LED lamp 4 respectively emit light through the double convex focusing lens 8 and then irradiate the object to be measured 7. After diffuse reflection from the object 7, the light passes through the plano-concave focusing lens 5 and converges on the photodiode detector 1. The output end of the photodiode detector 1 is connected to the input end of the preamplifier circuit 9, and the output end of the preamplifier circuit 9 is connected to the input end of the host computer 10. The power supply circuit 15 supplies power to the above circuits and devices.

[0039] In the optical path mechanical structure of the present invention, the LED lamp replaces the halogen lamp, and the mechanical chopper disk, motor and filter are omitted. The optical path structure is simple and compact, and the LED light source has a simple structure, high light efficiency and long life. The single-frequency differential modulation technology is adopted, and the host computer controls the driving circuit to output three-way 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 are alternately lit, and 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. Through the storage system of the single-chip microcomputer, data can be saved in real time and called at any time, and the data will not be lost in the case of power failure, which improves the stability and risk resistance of the system. After the three LED lamps are expanded and focused, they are irradiated, and the emitted light rays are approximately combined into a parallel light, then the light source detection surface basically overlaps, the light spot coverage range is large, and the measurement accuracy is high. The three-way LED lights compensate 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 a 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 is used as a measurement light source, emitting 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 a reference light source. By comparing 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 irradiate 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 and irradiated to the photodiode detector 1 through the plano-concave focusing lens 6. The overall structure of the light source is fixed on the top plate at the same level as the photodiode detector 1, and is 7200mm±50mm away from the object to be measured.

[0041] like Figure 3As shown, the photodiode detector 1 is an InGaAs photodiode detector, which has extremely high sensitivity to light in the near-infrared band and is also one of the mainstream photodiode detectors in the market. 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. The positive input terminal of the amplifier U1 is connected in series with the resistor R1 and then grounded, the positive power input terminal of the amplifier U1 is connected to positive 5V and one end of the capacitor C2, the reverse power input terminal is connected to negative 5V and one end of the capacitor C3, the other end of the capacitor C2 and the capacitor C3 is grounded, the output terminal of the 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, the other end of the resistor R3 is connected to the inverting input terminal of the amplifier U2 and one end of the resistor R5, the positive input terminal of the amplifier U2 is connected in series with the resistor R4 and then grounded, the positive power input terminal of the amplifier U2 is connected to positive 5V and one end of the capacitor C4, the reverse power input terminal is connected to negative 5V and one end of the capacitor C5, the other end of the capacitor C4 and the capacitor C5 is grounded. The other end of the resistor R5 is connected to the output terminal of the amplifier U2 and serves as the output terminal of the preamplifier circuit 9. The photodiode detector 1 is fixed to the top plate as a whole and has the same horizontal height as the overall structure of the light source, 7 200mm±50mm away from the object to be measured.

[0042] See also 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 with adjustable output phase and amplitude in real time is connected to the first voltage-controlled constant current circuit 12, the second output end with adjustable output phase and amplitude in real time is connected to the second voltage-controlled constant current circuit 13, and the third output end with adjustable output phase and amplitude 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 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 capacitors C6 and C7 are grounded. The second reverse input terminal of the operational amplifier U3 is connected to the common terminal of the resistor R8, the resistor R9, and the capacitor C9, the other end of the resistor R9 is grounded, the other ends of the resistor R8 and the capacitor C9 are connected to the output terminal of the operational amplifier U4, the second output terminal of the operational amplifier U3 is connected to the input terminal of the operational amplifier U4, the resistor R10, the resistor R11, and the resistor R12 are connected in parallel after the output terminal of the operational amplifier U4, and the other ends of the parallel resistors R10, R11, and R12 are used as the total output terminal, the positive power input terminal of the operational amplifier U4 is respectively connected to the positive 12V and one end of the capacitor C10, the reverse power input terminal is connected to the negative 12V and one end of the capacitor C8, and the other ends of the capacitor C8 and the capacitor C10 are grounded. The voltage-controlled constant current block adopts a modular design to effectively improve accuracy and stability.

[0044] The single-chip system circuit 11 outputs three modulation signals with the same duty cycle, the same frequency, and adjustable amplitude and phase, such as Figure 5 As shown, one signal is at a high level at a cycle of 1 / 6, one signal is at a high level at a cycle of 1 / 2, and one signal is at a high level at a cycle of 5 / 6. The duty cycles of the three modulation signals are all 1 / 6, and the amplitude can be adjusted in real time. Single-frequency differential modulation technology and DAC+DMA technology are adopted to output three DAC signals, drive three LED lights to light up alternately, that is, only one LED light is lit in a 1 / 3 cycle, which is easy to distinguish, simple in structure, and easy to modulate, solving the problem of inconvenience in 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 processing process of MCU, making the measurement adjustment and feedback faster, and being able to more efficiently measure 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 of 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 of different colors with the same water content are not consistent. Figure 6 As shown in the figure on the right, 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 a 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 the time-sharing modulation technology can ensure the validity and easy-to-distinguish characteristics of the signal.

[0048] In addition, the design of LED lamps can effectively reduce the structure, but at the same time, since the light source is emitted by different LED lamps, its optical path is different. For the measurement requirements, the information obtained when irradiating different positions is different, and the acquisition signal of such measurement light and reference light lacks reference value. Therefore, in the near-infrared moisture measurement, it is extremely important to make different LED light sources irradiate the same position. 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 dual LED lamp irradiation scheme adopted by it, due to the reflection needs, must be reflected into the same detector, and its irradiation position cannot be unified, but will irradiate to two different places. In the online detection, it will have a large difference according to the different conveyor belt speeds in different scenes. Compared with the Chinese patent application with publication number CN103760116A, entitled "Online continuous measurement near-infrared moisture meter without moving parts", it does not make a special design for the arrangement of LED light sources. After it is irradiated to the material to be measured through the reflector, it is not at the same irradiation position, which will also cause the above-mentioned error. 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 the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. 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 embodiments of the present invention.

Claims

1. A near-infrared moisture meter based on three LED lamps, characterized in that: The invention comprises an optical path structure, a preamplifier circuit (9), a host computer (10), a drive circuit and a power supply circuit (15), wherein 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), wherein 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, and 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) as a whole, 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°, 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 rays that are incident on the object to be measured (7) through a double convex focusing lens (8), and then are diffusely reflected by the object to be measured (7) and converged by a plano-concave focusing lens (5) to illuminate the photodiode detector (1). The output end of the photodiode detector (1) is connected to the input end of the preamplifier circuit (9), and 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.

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 1450nm, and the wavelength band of the reference light source is 1200nm and 1650nm.

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 model of the photodiode detector is InGaAs photodetector.

8. The near-infrared moisture meter based on three LED lamps according to claim 1, characterized in that: 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).

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 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 ratios 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 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 positive and negative 5V DC voltage to power the preamplifier circuit (10); 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 operational amplifier U4, the second output end of operational amplifier U3 is connected to the input end of operational amplifier U4, resistor R10, resistor R11 and resistor R12 are connected in parallel after the output end of operational amplifier 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 operational amplifier 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.

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