CN101334359A - A portable device and method for non-destructive measurement of plant nutrients - Google Patents

Abstract

The invention discloses a portable device and method for nondestructive measurement of plant nutritional components, comprising a monochromatic light source, a photoelectric detector, a light source driving circuit, a signal conditioning circuit and a micro-control system, the monochromatic light source and the photoelectric detector form an integrated blade The fixture is connected to the light source driving circuit and the signal conditioning circuit respectively through cables, which not only reduces the loss of light energy, improves the signal-to-noise ratio, but also simplifies the measurement device, making the sampling of the fixture flexible and convenient; the light source driving circuit mainly includes a voltage regulator chip , sampling resistor, triode and analog switch, to realize the constant current drive of the monochromatic light source and the program-controlled adjustment of the current value, which not only increases the stability of the light source, but also effectively solves the problem of photodetector saturation, making the photodetector work at In the best detection range, the signal-to-noise ratio is increased and the measurement accuracy is improved. At the same time, the device increases the measurement and subtraction of dark noise in the measurement process, so that the measurement accuracy of plant nutrients is improved.

Description

A portable device and method for non-destructive measurement of plant nutrients

technical field

The invention belongs to the technical field of agriculture and forestry detection, and relates to a portable nondestructive measurement device and method for plant nutrients, in particular to the measurement of nitrogen and water content in plant leaves.

Background technique

Plant nutrient content is an important basis for diagnosing plant growth and nutrient supply. Non-destructive testing of plant nutrient content can be applied to plant growth evaluation, precise water and fertilizer management, variety cultivation and screening, etc., which is of great significance for precision agriculture and forestry. Nitrogen provides important support for plant photosynthesis and ecosystem productivity. It is an important nutrient for plants. Real-time monitoring of nitrogen content can accurately fertilize, promote plant growth, and help reduce environmental pollution. Water is not only an important component of plant cell protoplasm, but also a reaction substance in the metabolic process of plants and a solvent for plants to absorb and transport nutrients. Timely and accurate monitoring of plant water status is of great importance for improving water management levels and water use efficiency of agricultural and forestry crops. Saving water resources is of great significance.

Spectrometry has the advantages of non-destructive, rapid, simultaneous detection of multiple components, and simple operation to measure the nutritional components of plant leaves. At present, devices for non-destructive measurement of various biochemical parameters of plant leaves have also been reported, and due to the many advantages of spectral methods, people have paid more and more attention to them.

Chinese invention patent CN1293379C discloses a system and method for portable non-destructive detection of plant pigments in the field. This patent proposes the measurement of chlorophyll concentration, and uses a neutral reference sample to solve the problem of photodetector saturation when measuring incident light. However, the increase of neutral reference samples complicates the structure and operation of the measurement device, and the way the blade fixture is fixed to the casing makes sampling more difficult.

Chinese invention patent CN1865926A discloses a portable plant leaf pigment detection device, and proposes a measurement method for chlorophyll and carotenoids, but the blade fixture of the device is connected by an optical fiber, which not only increases the complexity of the optical system of the device, but also The optical fiber will lose part of the light energy, and at the same time, the optical fiber is easy to break, which brings inconvenience to the operation of the device.

In addition, due to the presence of dark current, thermal noise and other noise in the photodetector and the electronic device itself after power-on, the dark noise in the measurement signal will bring certain errors to the measurement of the plant component content.

Contents of the invention

The purpose of the present invention is to provide a portable device and method for non-destructive measurement of plant nutrients. In view of the above-mentioned problems, the present invention designs an integrated blade fixture and a programmable light source constant current drive circuit, and at the same time adds dark noise to the measurement method. These measures not only simplify the measurement device, make the operation flexible and simple, but also effectively improve the measurement accuracy.

The present invention is achieved like this:

The portable nondestructive measurement device for plant nutrient components of the present invention includes a monochromatic light source, a photoelectric detector, a light source driving circuit, a signal conditioning circuit and a micro control system.

The monochromatic light source and the photodetector are relatively fixedly installed inside the upper arm and the lower arm of the blade fixture to form an integrated blade fixture. The monochromatic light source and the photodetector are respectively connected with the light source driving circuit and the signal conditioning circuit, and the integrated blade fixture can be operated independently by hand.

The light source driving circuit can realize the constant current driving of the monochromatic light source. The light source driving circuit realizes the stability of the driving current through the principle of voltage feedback, and its circuit structure mainly includes a voltage stabilizing chip, a sampling resistor, a triode and an analog switch. The voltage regulator chip with voltage feedback function feedbacks the voltage at both ends of the sampling resistor in real time to adjust the output voltage of the voltage regulator chip accordingly, and at the same time uses the flat output characteristics of the triode to ensure the stability of the output current. According to different measurement situations, the light source driving circuit can also perform program-controlled selection of the driving current. The digital signal controls the on-off of each channel of the analog switch, and each channel is connected to a sampling resistor. The resistance values of these sampling resistors are different, so the program-controlled adjustment of the driving current value is realized by selecting different channels.

The portable plant nutrient non-destructive measurement device includes three monochromatic light sources, and the monochromatic light sources can be light emitting diodes or laser diodes. The output wavelengths are λ ₁ =510-530nm, λ ₂ =870-910nm and λ ₃ =960-990nm, respectively. Among them, λ ₁ and λ ₃ as the measurement wavelength; λ ₂ as the reference wavelength.

The photodetector can be a photodiode, a photocell or a photomultiplier tube, which can detect light in the range of 400-1000nm.

The signal conditioning circuit converts the current signal of the photodetector into a voltage signal (I/V conversion) to obtain an analog voltage signal meeting the input range requirement of the A/D converter.

The micro-control system is mainly composed of a microcontroller, an A/D converter, a data storage module, a monitoring circuit, a serial communication circuit, a clock circuit, an LCD display, a keyboard and a power supply chip. The micro-controller is the core device of the micro-control system. It not only realizes the control and data processing of other functional modules, but also controls the light source driving circuit to realize that the light source emits light in turn; the A/D converter converts the analog voltage signal into a digital signal; the data storage module is used to store the collected data and processing results; the monitoring circuit is used to monitor the power supply voltage of the microcontroller, and can realize the manual reset function at the same time; the serial port communication circuit realizes the data transmission between the measuring device and the upper computer; The clock circuit provides accurate time for the measurement device; the LCD display is used to display the results and prompt the user to operate; the keyboard is used to select various functions; the power chip provides stable voltage for the device.

The above-mentioned measuring device is used to measure the nutritional components of plant leaves, which is achieved through the following steps:

(1) Turn on the power to keep the integrated blade fixture closed, the microcontroller controls the A/D converter to collect the analog voltage signal output by the signal conditioning circuit, and record the converted digital signal as the dark noise voltage value V _DARK ;

(2) The blade fixture is still in the closed state, and the microcontroller controls three monochromatic light sources to emit light in turn, directly irradiating the photodetector, which is called reference light. The photodetector converts the detected optical signal into an electrical signal, and the analog voltage signal is obtained through the signal conditioning circuit. After A/D conversion, the reference signal voltage values V _R (λ ₁ ) and V _R corresponding to the three wavelengths are respectively obtained. (λ ₂ ) and V _R (λ ₃ );

(3) Open the integrated blade fixture, put the blade under test, close the fixture, the microcontroller controls three monochromatic light sources to emit light in turn, and the light that passes through the blade shines on the photodetector, which is called measurement light. The photodetector converts the detected optical signal into an electrical signal, and the analog voltage signal is obtained by the signal conditioning circuit. After A/D conversion, the measured signal voltage values corresponding to the three wavelengths V _M (λ ₁ ), V _M (λ ₂ ) and V _M (λ ₃ );

(4) Calculate the content of plant leaf moisture and nitrogen according to the following formula:

The nitrogen concentration is C _N :

${\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; N</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; b</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; ln</span>}<span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; DARK</span>}}}{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; DARK</span>}}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; ln</span>}<span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; DARK</span>}}}{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; DARK</span>}}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ]</span>$

The moisture concentration is C _W :

${\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; W</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; b</span>}}_{\mathrm{<span\; class="notranslate">\; w</span>}\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; w</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; ln</span>}<span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; DARK</span>}}}{{\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; DARK</span>}}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; ln</span>}<span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; DARK</span>}}}{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; DARK</span>}}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ]</span>$

Among them b _n0 , a _n1 , b _w0 , a _w1 are coefficients.

The advantages of the present invention are:

(1) The blade fixture adopts an integrated design that integrates the light source and photodetector. The fixture is set separately from the main unit of the device. The fixture is not directly fixed on the main unit of the device, but realizes the light source and photodetector in the fixture through cables. The separate connection with the light source driving circuit and the signal conditioning circuit in the main unit of the device can not only reduce the loss of light energy and improve the signal-to-noise ratio, but also effectively simplify the measurement device and make the fixture sampling more flexible and convenient, especially suitable for narrow spaces or Leaf measurements in special cases such as regular spaces.

(2) The light source constant current drive circuit can choose different currents to drive the light source, which not only increases the stability of the light source, but also effectively solves the problem of photodetector saturation, makes the photodetector work in the best detection range, and increases the signal. The noise ratio improves the measurement accuracy.

(3) The measurement of the dark noise is added in the measurement method of the present invention, and the influence of the dark noise is subtracted from the measurement signal and the reference signal when calculating the nutritional components, which effectively improves the measurement accuracy.

Description of drawings

Fig. 1 is a schematic structural diagram of the measuring device of the present invention;

Fig. 2 is a structural schematic diagram of an integrated blade fixture;

Fig. 3 is a schematic diagram of a light source driving circuit;

Figure 4 is a schematic diagram of the signal conditioning circuit.

Detailed ways

Now, with reference to the accompanying drawings, the implementation of the device for non-destructive measurement of plant leaf nutrient components of the present invention will be described in detail.

The device for non-destructive measurement of nutritional components of plant leaves according to the present invention mainly includes the following parts: a monochromatic light source 1 , a photodetector 2 , a light source driving circuit 3 , a signal conditioning circuit 4 and a micro control system 5 . As shown in FIG. 1 , the micro-control system 5 controls the monochromatic light source 1 connected to the light source driving circuit 3 to emit light in turn and receives the analog voltage signal from the signal conditioning circuit 4 . The micro-control system 5 is mainly composed of a microcontroller 501, an A/D converter 502, a data storage module 503, a monitoring circuit 504, a serial communication circuit 505, a clock circuit 506, an LCD display 507, a keyboard 508 and a power chip 509. It can realize functions such as light source control, data acquisition, data processing, data storage, data transmission between the microcontroller 501 and the upper computer, record collection time, result display, function selection and system reset. The power supply chip 509 is powered by a battery 510 to provide a stable power supply voltage for the entire non-destructive measurement device.

Described microcontroller 501 selection model is the single-chip microcomputer of MSP430F427, and this single-chip microcomputer interior has ADC16 module, can realize the A/D conversion of 16, and A/D converter 502 realizes the analog voltage signal acquisition to characterizing light intensity information, Obtain a digital signal; in order to store a large amount of collected data, the non-destructive measuring device of the present invention expands the data storage module 503 to the micro-control system 5, and the model is 24LC256, which is used to store collected data and data processing results. The monitoring circuit 504 chip selects TPS3823-33, which is used to monitor the power supply voltage of the microcontroller 501, and can realize manual reset and watchdog functions at the same time. The serial port communication circuit 505 chip selects MAX232 to realize the data transmission between the upper computer and the microcontroller 501 in the microcontroller system 5 . The LCD display 507 is LCM12232. The liquid crystal display module of this type of display has low power consumption and is connected with the general I/O interface of the microcontroller 501. The LCD display 507 is used to display the results and prompt the user to operate information. The keyboard 508 is provided with 6 function selection keys, respectively controlling the measurement of the dark noise voltage V _DARK , the reference signal voltage V _R , the measurement of the measurement signal voltage V _M , displaying results and adjusting time. Since the blade clamps are in the closed state when measuring V _DARK and _VR , the device realizes the measurement of V _DARK and _VR by one button. The clock circuit 506 chip selects DS1302 to provide accurate time for the microcontroller system 5, and the backup battery of the clock circuit 506 chip adopts a button battery CR2026.

The light source driving circuit 3, the signal conditioning circuit 4 and the control system 5 in Fig. 1 constitute the main frame of the measuring device, the monochromatic light source 1 and the photodetector 2 constitute the integrated blade fixture 6, and the integrated blade fixture 6 and the main frame are separated from each other, Connected by cable. The integrated leaf fixture 6 is used to measure the nutrient content of the leaf, and the structure of the integrated leaf fixture is shown in FIG. 2 . The monochromatic light source 1 and the photodetector 2 are respectively installed inside the upper arm 601 and the lower arm 602 of the integrated blade fixture 6, wherein the monochromatic light source 1 is connected to the light source driving circuit 3 through a cable 603, and the photodetector 2 is connected with the signal conditioning circuit 4 through the cable 604. During the measurement, the integrated blade fixture 6 is not limited by the position of the main body of the measuring device, and the operator can hold the integrated blade fixture 6 to realize the measurement of the plant blade 7 .

Monochromatic light source 1 chooses light-emitting diode (LED). LED has good stability and monochromaticity. Usually, LED full width at half maximum (FWHM) is 20-40nm, which meets the requirements for light source in the field of plant parameter measurement. LED power consumption is low, and the normal operating current is generally 20 ~ 50mA, which is suitable for the application of portable and battery-powered instruments. The three LED wavelengths selected by the device are λ ₁ =510-530nm, λ ₂ =870-910nm and λ ₃ =960-990nm, wherein λ ₁ and λ ₃ are used as measurement wavelengths; λ ₂ is used as reference wavelength.

The photodetector 2 is a silicon photodiode, the model is S1133-14, the response wavelength range of the photodetector 2 is 320-1000nm, and the dark current is 20pA.

As shown in Figure 3, the described light source driving circuit 3 is designed for the non-destructive measuring device of the present invention, and its circuit structure is mainly composed of a voltage stabilizing chip U3, a triode Q1, an analog switch U1, U2 and sampling resistors R1, R2, R3, R4 composition. The voltage regulator chip U3 in the figure is an ultra-high-precision, ultra-low-noise, series voltage reference MAX6126 with an output voltage of 2.048 volts and an internal accuracy of 0.02%. It forms a constant current circuit with the transistor Q1 to realize constant current driving of the LED. The OUTF pin of the voltage regulator chip U3 is connected to the base of the transistor Q1, and the OUTS pin is connected to the emitter of the transistor Q1. The OUTS pin can monitor the voltage at both ends of the sampling resistor in real time, and then feed back to U3. Adjust the output voltage of the OUTF pin so that the voltage across the sampling resistor remains constant. The analog switch U1 (MAX4066) is controlled by a digital signal to realize that three LEDs emit light in turn. The analog switch U2 (ADG712) realizes the selection of the driving current. The anodes of the three LEDs are connected to +5V, the cathode of the LED with a wavelength of _λ1 is connected to the COM1 pin of U1, and the _λ2 and _λ3 LEDs are connected to the COM2 and COM3 pins of U1 respectively. The NO1 pin, NO2 pin, and NO3 pin of U1 are connected to the collector of the transistor Q1. The IN1 pin, IN2 pin, and IN3 pin of U1 are respectively connected to pins P1.0, P1.1, and P1.2 of the microcontroller 501 to realize the control of the analog switch U1 by the microcontroller 501 . By controlling the analog switch U1, the microcontroller 501 can switch the LED light source on and off, and control the three LEDs to emit light in turn. One end of the sampling resistors R1, R2, R3 and R4 is connected to the emitter of Q1, and the other end is respectively connected to the S1 pin, S2 pin, S3 pin and S4 pin of U2, and the D1 pin, D2 pin, The D3 pin and the D4 pin are connected to ground. The pins S1 and D1 can be turned on and off, the pins S2 and D2 can be turned on and off, the S3 pin and D3 pin can be turned on and off, and the S4 pin and D4 pin can be turned on and off. The IN1 pin, IN2 pin, IN3 pin and IN4 pin of U2 are respectively connected with the pins P1.3, P1.4, P1.5 and P1.6 of the microcontroller 501 to realize the selection of each channel. By selecting each channel, different sampling resistors R1 , R2 , R3 and R4 can be turned on, so as to control the current of the monochromatic light source 1 . The resistance values of the sampling resistors R1, R2, R3 and R4 are different.

Due to the needs of the non-destructive measuring device of the present invention, the measurement of blade nitrogen and water needs to measure the dark noise voltage value V _DARK , the reference signal voltage value V _R when the LED directly irradiates the photodetector 2, and the measurement signal voltage after the blade is placed. Value V _M . It is found through experiments that when the relative positions of the monochromatic light source 1 and the photodetector 2 are determined (taking an example in the experiment process as an example), when the photodetector 2 directly detects the light emitted by the LED, the photodetector 2 measures The V _R can reach 3 ~ 4V, V _DARK is generally between 3 ~ 5mV (negligible), V _M is 500mV maximum, minimum 75mV. The size of V _M has a great relationship with the leaves. When the leaves are yellow, the nitrogen content is relatively small, and the V _M is larger at this time. When the leaves are green, it means that the nitrogen content is relatively large. When the V _M is smaller. It can be seen from the above data that the three measured parameters V _DARK , _VR and V _M have relatively large differences. Since the three LEDs have different penetration abilities to the blades and are driven by the same current, the light intensity of the three LEDs is also different. The photodetector 2 and the signal conditioning circuit 4 of this device are powered by +5V, and the maximum can only be collected For a voltage of about 4V, in order to keep the signal detected by the photodetector 2 within the optimum detection range, it is necessary to use different driving currents for the three LEDs in the system and different measurement situations to meet the measurement requirements. In view of this situation, the light source driving circuit 3 adopts an analog switch U2 (ADG712), and uses different currents to drive different LEDs by adjusting the on-off selection of the resistors R1-R4.

The light source driving circuit 3 not only avoids the saturation phenomenon of the photodetector 2 caused by too strong light emission of the light source, but also keeps the light detected by the photodetector 2 in its optimal detection range by changing the driving current, thereby improving the measurement accuracy get improved. Different currents are used to drive different light sources and different nutritional components, and the light intensity is weak when measuring V _M. At this time, the drive current of the light source is increased by adjusting the on-off of the resistors R1~R4, and the light intensity will increase. The signal-to-noise ratio is improved.

The signal conditioning circuit 4 is mainly composed of digital potentiometer U5 (MAX5420), operational amplifiers U6 (MAX4239), U7 (MAX4239) and U8 (MAX4239), as shown in FIG. 4 . D1 in the figure is a silicon photodiode. The light signal received by the photodetector 2 is converted into a current, and then the voltage signal is obtained through the I/V conversion circuit. The voltage signal is amplified by the operational amplifier U6, and the digital potentiometer U5 and the operational amplifier U7 are built. into a secondary amplifier circuit, and U8 implements a voltage follower, which is used to reduce the mutual interference between the digital circuit and the analog circuit. The size of the resistor R5 determines the detection capability of the signal conditioning circuit 4. When the irradiated light remains unchanged, the larger the value of the resistor R5, the larger the I/V conversion voltage. Similarly, the smaller the value of the resistor R5, the I/V V gets a smaller voltage. Capacitor C3 is used to eliminate noise, and resistor R6 and capacitor C4 implement low-pass filtering. The D0 pin and the D1 pin of the digital potentiometer U5 are respectively connected with the P2.1 and P2.2 pins of the microcontroller 501, and the digital signal output by the microcontroller 501 controls the magnification of U5, and U5 can realize 1, 2, 4, 8 four times of magnification.

The power supply voltage of the signal conditioning circuit 4 is +5V, and the power supply voltage of the microcontroller 501 is 3.3V. The whole non-destructive measuring device of the present invention is powered by a 9V battery 510, and two voltages of +5V and +3.3V are used. The corresponding power supply chip 509, the voltage regulator chip REG1117A outputs a fixed +5V voltage with a 1A drive capability, and the voltage regulator chip TPS79533 outputs a fixed +3.3V voltage with a 500mA drive capability.

In order to minimize the dark noise of the photodetector 2 and each electronic device in the non-destructive measurement device of the present invention, the influence V _DARK of the dark noise on the photodetector 2 is first collected when measuring the nutritional components of plant leaves, and then the reference light is collected respectively For the output voltage value corresponding to the measurement light, V _DARK is subtracted from the output voltage values corresponding to the reference light and the measurement light during the calculation of the nutritional components, thereby eliminating the influence of dark noise on the measurement accuracy.

Apply the non-destructive measuring device of the present invention to non-destructively measure the nutritional components of plant leaves, and the specific measurement steps are:

(1) Turn on the power, keep the integrated blade clamp 6 in the closed state, and the microcontroller 501 controls the analog switch U1 in the light source driving circuit 3 to make the three LED light sources go out. The microcontroller 501 controls the A/D converter 502 to collect the analog voltage signal output by the signal conditioning circuit 4, and the obtained digital signal is recorded as the dark noise voltage value V _DARK ;

(2) Still keeping the integrated blade fixture 6 in the closed state, the microcontroller 501 controls the analog switch U1 in the light source drive circuit 3 to make the three LED light sources emit light in turn, directly irradiating the photodetector 2, which is called reference light. Collect the reference signal voltage values _VR (λ ₁ ), _VR (λ ₂ ) and _VR (λ ₃ ) of the corresponding wavelengths of the three LED light sources.

The specific implementation is as follows: firstly, control the analog switch U1 to make the _λ1 LED glow, and the other two LEDs go out. In the disconnected state, the sampling resistor R1 at this time determines the magnitude of the current of the light source driving circuit 3 .

Then, control the analog switch U1 to make the _λ2 LED light up, and the other two LEDs to go out. At the same time, control the second channel of U2 to conduct, that is, the sampling resistor R2 forms a path with U2 and the transistor Q1, and the other three resistors are in a disconnected state. At this time, the sampling resistor R2 determines the magnitude of the current of the light source driving circuit 3 . Next, control the λ ₃ LED to emit light, the other two go out, and the on-off situation of U2 remains unchanged.

(3) Open the integrated leaf fixture 6, put the plant leaf 7 under test, close the integrated leaf fixture 6, the microcontroller 501 controls the three LED light sources to emit light in turn, and the light through the plant leaf 7 is irradiated to the photodetector 2, called measurement light. Collect measurement signal voltage values V _M (λ ₁ ), V _M (λ ₂ ) and V _M (λ ₃ ) of the corresponding wavelengths of the three LED light sources.

The specific implementation is: control U1 to make the three LED light sources emit light in turn, and the micro-control system 5 collects the measurement signal voltage values V _M (λ ₁ ), V _M (λ ₂ ) and V _M (λ ₃ ). This process is basically the same as the previous step (2), except that the sampling resistors corresponding to each LED are different. The λ ₁ LED corresponds to the sampling resistor R3, that is, when the LED of this wavelength is in the luminous state, the sampling resistor R3 is turned on; the λ ₂ and λ ₃ LEDs correspond to the sampling resistor R4, that is, when the LEDs of these two wavelengths are in the luminous state, the sampling resistor R4 conduction.

After each measurement process is completed, the microcontroller 501 controls the analog switches U1 and U2 to be in an off state.

(4) Calculating the concentration of nutrient components in plant leaves according to the linear regression mathematical model.

Due to the existence of dark noise, there is a deviation between the measurement signal and the reference signal, which will affect the measurement accuracy of plant nutrients. Therefore, in the present invention, the dark noise is subtracted from the measurement signal and the reference signal to obtain the concentration of nutrients in the plant leaves. The formulas for calculating nitrogen and water content in plant leaves are as follows:

The nitrogen concentration is C _N :

${\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; N</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; b</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; ln</span>}<span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; DARK</span>}}}{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; DARK</span>}}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; ln</span>}<span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; DARK</span>}}}{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; DARK</span>}}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ]</span>$

The moisture concentration is C _W :

${\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; W</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; b</span>}}_{\mathrm{<span\; class="notranslate">\; w</span>}\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; w</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; ln</span>}<span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; DARK</span>}}}{{\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; DARK</span>}}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; ln</span>}<span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; DARK</span>}}}{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; DARK</span>}}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ]</span>$

Among them b _n0 , a _n1 , b _w0 , a _w1 are coefficients.

It can be seen from the above two formulas that when calculating the concentration of nitrogen and water, the dark noise is subtracted from each reference signal and measurement signal, that is, the influence of the dark noise on the photodetector and electronic devices in the measurement device is eliminated. Therefore, the application of the measurement method and the measurement device provided by the invention can obtain more accurate plant leaf parameter concentration values.

Claims (5)

1, a kind of portable plant nutrient ingredient damage-free measuring apparatus comprises monochromatic source (1), photodetector (2), light source driving circuit (3), signal conditioning circuit (4) and micro control system (5), it is characterized in that:

Described monochromatic source (1) is formed integrated blade fixture (6) with photodetector (2), wherein monochromatic source (1) and photodetector (2) are installed on the upper arm (601) and underarm (602) inside of integrated blade fixture (6) respectively, and monochromatic source (1) is connected with signal conditioning circuit (4) with light source driving circuit (3) by cable respectively with photodetector (2);

Described light source driving circuit (3) structure mainly comprises voltage stabilizing chip, sampling resistor, triode and analog switch; Voltage stabilizing chip, sampling resistor and triode constitute constant-current circuit, realize the constant-current driving to monochromatic source; Analog switch realizes that by Digital Signals monochromatic source takes turns luminous and by the selectivity break-make of sampling resistor being realized the program control adjusting of driving current value;

Described micro control system (5) is mainly by microcontroller (501), A/D converter (502), data memory module (503), supervisory circuit (504), serial communication circuit (505), clock circuit (506), LCD display (507), keyboard (508) and power supply chip (509) are formed, be used to realize the collection of data, data storage, the supply voltage monitoring, with functions such as the data transmission of host computer and demonstrations as a result, described microcontroller (501) is the core devices of micro control system (5), it has not only realized the control to other functional module, data processing, and control light source driving circuit (3) realizes that monochromatic source (1) is luminous in turn.

2, portable plant nutrient ingredient damage-free measuring apparatus according to claim 1 is characterized in that: described monochromatic source (1) is light emitting diode or laser diode.

3, portable plant nutrient ingredient damage-free measuring apparatus according to claim 1 is characterized in that: described photodetector (2) is photodiode, photoelectric cell or photomultiplier.

4, portable plant nutrient ingredient damage-free measuring apparatus according to claim 1 is characterized in that: described monochromatic source (1) comprises 3 LED monochromatic sources, and output wavelength is respectively λ ₁=510～530nm, λ ₂=870～910nm and λ ₃=960～990nm, wherein, λ ₁And λ ₃As measuring wavelength, λ ₂As reference wavelength.

5, application rights requires a kind of portable plant nutrient ingredient damage-free measuring method of 1 described measurement mechanism, it is characterized in that: may further comprise the steps:

(1) opening power is kept closed integrated blade fixture (6), and microcontroller (501) control A/D converter (502) is gathered the analog voltage signal by signal conditioning circuit (4) output, and the digital signal that obtains after the conversion is designated as dark noise magnitude of voltage V _DARK

(2) still make blade fixture be in closure state, microcontroller (501) 3 monochromatic sources of control (1) are luminous in turn, and direct irradiation photodetector (2) is called reference light; Photodetector (2) changes into electric signal with detected light signal, obtains analog voltage signal through signal conditioning circuit (4), after the A/D conversion, obtains 3 wavelength corresponding reference signal voltage value V respectively _R(λ ₁), V _R(λ ₂) and V _R(λ ₃);

(3) open integrated blade fixture (6), put tested blade (7), the anchor clamps that close, microcontroller (501) 3 monochromatic sources of control (1) are luminous in turn, and the illumination that sees through blade (7) is mapped on the photodetector (2), is called measuring light; Photodetector (2) changes into electric signal with detected light signal, obtains analog voltage signal through signal conditioning circuit (4), after the A/D conversion, obtains the measurement signal voltages value V of 3 wavelength correspondences respectively _M(λ ₁), V _M(λ ₂) and V _M(λ ₃);

(4) calculate the content of plant leaf blade moisture and nitrogen according to following formula:

Different Nitrogen Concentration is C _N:

$C_N=b_{n0}+a_{n1}[\ln \left(\frac{V_M\left({\mathrm{\&lambda;}}_1\right)-V_{\mathrm{DARK}}}{V_R\left({\mathrm{\&lambda;}}_1\right)-V_{\mathrm{DARK}}}\right)-\ln \left(\frac{V_M\left({\mathrm{\&lambda;}}_2\right)-V_{\mathrm{DARK}}}{V_R\left({\mathrm{\&lambda;}}_2\right)-V_{\mathrm{DARK}}}\right)]$

Moisture concentration is C _W:

$C_W=b_{w0}+a_{w1}[\ln \left(\frac{V_M\left({\mathrm{\&lambda;}}_3\right)-V_{\mathrm{DARK}}}{V_R\left({\mathrm{\&lambda;}}_3\right)-V_{\mathrm{DARK}}}\right)-\ln \left(\frac{V_M\left({\mathrm{\&lambda;}}_2\right)-V_{\mathrm{DARK}}}{V_R\left({\mathrm{\&lambda;}}_2\right)-V_{\mathrm{DARK}}}\right)]$

B wherein _N0, a _N1, b _W0, a _W1Be coefficient.

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