CN112924402A - Absorbance sensor for underwater dragging system and working method thereof - Google Patents
Absorbance sensor for underwater dragging system and working method thereof Download PDFInfo
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Abstract
The invention relates to an absorbance sensor for an underwater towing system and a working method thereof, wherein the absorbance sensor comprises a light source module, an absorption pool, a signal collection module and a system control module, a compact optical path structure design is used for realizing multi-channel measurement, and the absorption pool is matched with the towing system to realize measurement of seawater absorbance free three-dimensional space in a towing area; the system control module removes the interference of background light by using a digital phase locking technology, synchronously acquires the light source and the transmission signal, is used for correcting the signal change caused by the light source, and improves the detection accuracy and sensitivity of the sensor. The invention realizes multi-channel measurement of absorbance through the integrated design of the compact absorption tank and the absorption tank, reduces the volume and the weight of the sensor, simultaneously uses the digital phase locking technology based on the FPGA, improves the signal-to-noise ratio, realizes high-quality absorbance signal detection, and has strong practicability.
Description
Technical Field
The invention relates to an absorbance sensor for an underwater dragging system and a working method thereof, belonging to the technical field of ocean optical detection.
Background
The seawater absorbance is an important parameter for describing the optical characteristics of seawater, can directly reflect the light transmittance of the seawater and the attenuation degree of the seawater to light, and can be used for monitoring the quality of the seawater and analyzing the material components and the content of the seawater; the seawater absorbance information has great guiding significance for the safe navigation of the submarine and the mine laying, so that the detection of the seawater absorbance has important significance for the aspects of ecological monitoring, military application and the like.
In recent years, in-situ detection systems based on the absorbance principle are rapidly developed and can be used for measuring physical parameters such as light absorption and light attenuation and detecting some chemical parameters, high-end instruments in the market are almost provided by several foreign companies such as SeaBird, TriOSGmbh and Wet Labs, wherein the typical representative is a C-Star transmissometer, and the C-Star transmissometer has the advantages of simple instrument structure, low cost and stable mechanical structure, but the C-Star transmissometer is used for single-channel measurement and has few measurable wave bands. Many systems developed in China are still in the laboratory or prototype stage, are not completely developed into products which can be directly used, and have large volume, heavy weight and high cost.
In summary, the problems of the prior art are as follows: the measurement performance of the existing instrument greatly improves the three-dimensional space, information is difficult to obtain, and urgent requirements of high precision and stability of seawater in-situ measurement cannot be met. In addition, in the aspect of a photoelectric detection device, a spectrometer is adopted as the photoelectric detection device in the measuring instrument based on the absorbance principle, the measurement range of a wider waveband and the high resolution of the instrument can be ensured to a certain extent, but the appearance of the spectrometer is fixed, the overall hardware design of the instrument is not facilitated, the spectrometer is expensive and limited to factors such as cost, volume and weight, and the conventional instrument is difficult to realize seawater in-situ measurement. The difference between the absorbance sensors at home and abroad is mainly reflected in the aspects of structural design and selection of hardware, and the miniaturization, multi-channel, high precision and the like of sensor equipment are the future development directions.
Therefore, a set of seawater absorbance sensor with low cost and high precision and capable of being practically applied is researched, and the sensor has important significance for marine ecological environment and military application.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides an absorbance sensor for an underwater dragging system, which realizes multi-channel measurement by using a compact optical path design, namely, a multi-channel light source shares 1 absorption cell to realize the miniaturization and the light weight of an instrument; the absorbance sensor is positioned on the drag chain, and can detect the absorbance three-dimensional section of the sea water in the test sea area along with the movement of the ship; in the signal collection module, a photodiode detector is used for receiving signals, data processing is matched with a digital phase locking technology of an FPGA to realize absorbance signal detection with high signal-to-noise ratio, and miniaturization, multi-channel and high precision of sensor equipment are realized.
The invention also provides a working method of the absorbance sensor for the underwater dragging system.
The technical scheme of the invention is as follows:
an absorbance sensor for an underwater dragging system comprises a light source module, an absorption cell, a signal collection module, a system control module and an upper computer,
a light source module is arranged at one end of the absorption tank, a signal collection module is arranged at the other end of the absorption tank, the light source module and the signal collection module are both connected with a system control module, and the system control module is connected with an upper computer;
the light source module is used for transmitting a multichannel signal and comprises a first collimation light source and a plurality of second collimation light sources, a plurality of first dichroic mirrors are arranged on an emergent light path of the first collimation light source, one side of each first dichroic mirror is provided with one second collimation light source, and the first dichroic mirrors are also positioned on an emergent light path of the second collimation light sources, so that emergent light of the second collimation light sources shares emergent light of the same emergent light path with the first collimation light sources after passing through the first dichroic mirrors;
the signal collection module is used for receiving multi-channel signals and comprises a first photoelectric receiver and a plurality of second photoelectric receivers, wherein the first photoelectric receiver is arranged on a transmission light path of the absorption cell and used for receiving transmission light signals of a first collimation light source penetrating through the absorption cell; a plurality of second dichroic mirrors are arranged between the first photoelectric receiver and the absorption cell, and a second photoelectric receiver is arranged on a reflection light path of each second dichroic mirror, so that the second photoelectric receiver receives a transmission light signal of a second collimation light source penetrating through the absorption cell; enabling the absorbance sensor to realize multi-channel measurement;
the system control module is used for driving the light source module to emit light signals, collecting the signals of the signal collection module and transmitting the collected signals to the upper computer;
and the upper computer processes the signals acquired by the system control module based on the FPGA digital phase locking technology and then calculates to obtain the absorbance of the solution to be detected.
The absorbance sensor provided by the invention adopts the first dichroic mirror matched with the light source at the light source transmitting end, the multichannel collimated light is transmitted by using a compact design, the LED collimated light of a plurality of wave bands shares one absorption cell, and the multichannel and multiband measurement is greatly optimized in the aspects of the volume and the weight of the instrument compared with the C-Star measurement. The light source module provides high-quality collimated light for signal detection by the LED. The first dichroic mirror reflects light source signals in corresponding wave bands, transmits light source signals in other wave bands, and can realize that a multi-channel light source enters an absorption cell simultaneously through reasonable arrangement without mutual interference; the second dichroic mirror reflects corresponding band signals, transmits other band signals, and correspondingly arranges the multi-channel signals to enter the corresponding photoelectric receivers simultaneously without mutual interference. The absorption tank is not designed in structure generally, so that the seawater absorbance measurement in any space can be carried out conveniently during towing, the absorption tank is filled with a solution for carrying out the absorbance measurement, and the absorption tank realizes the measurement of the underwater free three-dimensional space through a towing system.
According to the invention, preferably, the first collimation light source and the second collimation light source both comprise an LED, an aperture diaphragm and a collimation lens which are sequentially arranged, an integration cavity is arranged outside the LED, a reference detector is arranged on the outer surface of the integration cavity, and the reference detector is connected with the system control module;
further preferably, the reference detector is a surface-mounted Si photodiode detector.
The emitted light of the LED passes through the aperture diaphragm and the collimating lens to generate parallel light. The LED is selected as the light source, and has the advantages of long service life, small volume and low cost. The aperture diaphragm structure provides a high-quality LED point light source, collimated light is obtained through the collimating lens, and the collimated light enters the absorption cell as an emitting end light source.
In the actual detection process, the LED light source has the fluctuation problem, the LED light source fluctuation monitoring is carried out by arranging the integrating cavity and the surface-mounted Si photodiode detector, the surface-mounted Si photodiode detector is used as a reference detector, the fluctuation change of the LED light source is recorded in the actual detection process, and the final calculation result is calibrated by adopting data processing, so that the measurement performance of the sensor and the accuracy of the result are improved.
According to the invention, the upper computer is preferably arranged on a ship, the absorbance sensor is fixed at one end of the drag chain, the other end of the drag chain is fixed on the ship, and data acquired by the absorbance sensor is transmitted to the upper computer through the drag chain.
The absorbance sensor is thrown to the sea area to be tested through the drag chain, seawater in the test sea area flows through the absorption pool along with the movement of the ship, the absorbance three-dimensional profile data of the test sea area can be detected in real time, and the overflow sampling of a water pump is avoided. The water pump is used for overcurrent sampling, so that the weight and the volume of the towing system are increased, and the real-time measurement of a certain area cannot be realized by the overcurrent sampling.
According to the invention, the system control module comprises a multi-channel AD acquisition unit and a single chip microcomputer,
the multi-channel AD acquisition unit is respectively connected with the photoelectric receiver and the reference detector, realizes the real-time acquisition of data and transmits the acquired data to the singlechip;
the multi-channel AD acquisition unit acquires signals acquired by the photoelectric receiver and the reference detector and transmits the signals to the upper computer, and the upper computer processes the signals based on the digital phase locking technology of the FPGA and then calculates to obtain the absorbance of the solution to be detected.
According to the invention, the first collimated light source and the plurality of second collimated light sources are preferably LEDs with different wave bands.
Preferably, according to the present invention, the first and second photoreceivers are each a photodiode detector.
The photodiode detector is an excellent optical measurement device, has high sensitivity in a wide band range from visible light to near infrared, and realizes multiband measurement corresponding to the light source module; compared with a spectrometer, the photodiode detector has great advantages in cost and volume of the instrument, and can also receive signals with high signal-to-noise ratio; the method is favorable for realizing the miniaturization, multi-channel and high precision of the absorbance sensor.
According to the invention, preferably, a narrow-band filter and a focusing lens are arranged between the first photoelectric receiver and the second dichroic mirror or between the second photoelectric receiver and the second dichroic mirror, and the bandwidth of the narrow-band filter is 10-20 nm.
A narrow-band filter is added in front of the photodiode detector to filter out stray light outside the band, and the focusing lens converges collimated light beams to the photodiode detector for signal detection.
The working method of the absorbance sensor for the underwater dragging system comprises the following specific steps:
(1) the system control module drives the multi-channel collimation light source to emit light, and measures the absorbance A of the calibration solutionCalibrationThen taking the seawater in the dragging area as a solution to be measured, and measuring the absorbance A of the solution to be measured in an absorbance sensorTo be measured；
Measuring the calibration solution, wherein the process can also be finished in a laboratory, and then measuring the seawater absorbance of the dragging area;
(2) the LED is synchronously detected through a reference detector, signals of a photoelectric receiver and the reference detector are transmitted to a multi-channel AD acquisition unit by a signal collection module, then the signals are synchronously transmitted to a single chip microcomputer of a system control module, data are transmitted to an upper computer through a drag chain, and signal processing is carried out in the upper computer by using a digital phase locking technology based on an FPGA;
the FPGA is a low-cost large-scale digital signal processing chip, the upper computer uses the FPGA as a data processing platform to process signals transmitted by the singlechip, the FPGA can complete a high-precision digital phase-locking algorithm through programming, the digital phase-locking technology is based on a cross-correlation detection principle and can extract weak signals to be detected from background noise, because light field signals in seawater are weak and change slowly, background light signals can be well filtered by using the digital phase-locking technology to realize bright field detection of absorbance signals, the singlechip modulates signals of an LED light source, the digital phase-locking technology realizes extraction and demodulation of modulation signals, the digital phase-locking technology of the FPGA realizes absorbance signal detection with high signal-to-noise ratio, and the sensitivity of the sensor is improved;
(3) and in the upper computer, carrying out self-correction processing on the absorbance of the solution to be detected to obtain the absorbance AU of the solution to be detected relative to the calibration solution.
According to the present invention, preferably, in the step (3), the absorbance of the solution to be measured is subjected to self-calibration, specifically:
the absorbance value AU of the solution to be detected relative to the calibration solution is as follows:
in the formula (IV), m is a self-correcting factor,
VcalibrationThe transmission signal of the solution is calibrated, namely the signal intensity of the transmission signal detected by the photoelectric receiver after being processed by the FPGA-based digital phase locking technology; vref1In order to measure the light source signal intensity measured by the reference detector when calibrating the solution, the reference detector receives the light source signal intensity and transmits the data to the singlechipA host computer; vTo be measuredThe transmission signal of the solution to be detected, namely the signal intensity V of the transmission signal detected by the photoelectric receiver after being processed by the digital phase locking technology of the FPGAref2The light source signal intensity measured by the reference detector when the solution to be measured is represented, and the reference detector receives the light source signal intensity and transmits data to the upper computer through the single chip microcomputer.
In the detection process, the signal collection module monitors the fluctuation signal V of the LED light source through the reference detectorref2Synchronously acquiring a signal V of a photoelectric receiver signal processed by a digital phase locking technologyTo be measuredAnd the calculation result of the absorbance is corrected by using the correction factor m, so that high-precision and accurate measurement is realized.
The invention has the beneficial effects that:
1. the invention relates to an absorbance sensor for an underwater dragging system.A light source module uses an LED, a small-hole diaphragm, a collimating lens and a dichroic mirror to combine to achieve a compact light path structure, and multi-channel measurement of absorbance is realized by sharing an absorption cell, namely, 1 absorption cell is shared by multi-channel light sources to realize the miniaturization and the light weight of an instrument; compared with a C-Star transmission meter for realizing multi-channel and multi-band simultaneous measurement, the absorbance sensor is greatly improved in volume and weight, and has important significance for miniaturization and light weight of an ocean exploration instrument.
2. The invention relates to an absorbance sensor for an underwater dragging system, which is characterized in that a system control module synchronously detects an LED light source signal and a signal transmitted by a light transmission solution; for the signals received by the photodiode detector after the light penetrates through the solution, the invention filters background noise by using a digital phase-locking technology, improves the signal-to-noise ratio, thereby obtaining high-quality signals and improving the measurement precision of absorbance; meanwhile, the system control module synchronously detects light source signals through a surface-mounted Si photodiode detector on the side face of the LED light source, and self-correction of absorbance results is achieved through data processing in the later period.
3. The absorbance sensor for the underwater towing system can realize miniaturization, light weight and high-precision detection of an ocean detection sensor system, the towing system can realize omnibearing real-time detection of a towing area, and the towing system is combined with other sensors to be beneficial to acquiring comprehensive ocean water body data and promoting the development of the ocean detection technical field.
Drawings
FIG. 1 is a schematic diagram of the system architecture of an absorbance sensor provided by the present invention;
fig. 2 is a three-dimensional simulation structure diagram of an optical path Zemax of the absorbance sensor provided by the invention.
1. The device comprises a light source module, 2, LEDs, 3, an integration cavity, 4, an aperture diaphragm, 5, a surface-mounted Si photodiode detector, 6, a collimating lens, 7, a first dichroic mirror, 8, window protective glass, 9, an absorption cell, 10, a signal collection module, 11, a second dichroic mirror, 12, a narrow-band optical filter, 13, a focusing lens, 14, a first photoelectric receiver, 15, a first shell, 16, a second shell, 17, a single chip microcomputer, 18, an LED drive control interface, 19, a reference detector signal receiving port, 20, a photodiode detector signal receiving port, 21 and a second photoelectric receiver.
Detailed Description
The invention is further described below, but not limited thereto, with reference to the following examples and the accompanying drawings.
Example 1
An absorbance sensor for an underwater dragging system, as shown in fig. 1 and 2, comprises a light source module 1, an absorption cell 9, a signal collection module 10, a system control module and an upper computer,
a light source module 1 is arranged at one end of the absorption tank 9, a signal collection module 10 is arranged at the other end of the absorption tank 9, the light source module 1 and the signal collection module 10 are both connected with a system control module, and the system control module is connected with an upper computer;
the light source module 1 comprises a plurality of collimation light sources which are respectively a first collimation light source and a plurality of second collimation light sources and are used for transmitting multichannel signals, a plurality of first dichroic mirrors 7 are arranged on an emergent light path of the first collimation light source, one side of each first dichroic mirror 7 is provided with one second collimation light source, and the first dichroic mirrors 7 are also positioned on an emergent light path of the second collimation light sources, so that emergent light of the second collimation light sources shares the same emergent light path with the first collimation light sources after passing through the first dichroic mirrors 7; (ii) a And the light source module 1 is enclosed in a first case 15, and a window protective glass 8 is further provided on the first case 15 so that the outgoing light is incident into the absorption cell 9 from the window protective glass 8.
The signal collection module 10 includes a plurality of photoelectric receivers, which are a first photoelectric receiver 14 and a plurality of second photoelectric receivers 21, respectively, and are configured to receive a multichannel signal, the first photoelectric receiver 14 is disposed on a transmission light path of the absorption cell 9, a plurality of second dichroic mirrors 11 are disposed between the first photoelectric receiver 14 and the absorption cell 9, and a second photoelectric receiver 21 is disposed on a reflection light path of each second dichroic mirror 11, so that the second photoelectric receivers 21 receive transmission light signals of a second collimated light source penetrating through the absorption cell 9; the first collimation light source and the first photoelectric receiver 14 are symmetrically arranged around the absorption cell 9, the second collimation light source and the second photoelectric receiver 21 are in one-to-one correspondence, and the second collimation light source and the second photoelectric receiver 21 are symmetrically arranged around the absorption cell 9; and the signal collection module 10 is enclosed in a second case 16, and a window protective glass 8 is further provided on the second case 16 so that the transmitted light from the absorption cell 9 is incident from the window protective glass 8 into the signal collection module 10.
The system control module is used for driving the light source module 1 to emit light signals, collecting the signals of the signal collection module 10 and transmitting the collected signals to the upper computer;
and the upper computer processes the signals acquired by the system control module based on the FPGA digital phase locking technology and then calculates to obtain the absorbance of the solution to be detected.
The absorbance sensor provided by the invention adopts the first dichroic mirror 7 matched with the light source at the light source emitting end, the emission of multi-channel collimated light is realized by using a compact design, the LED2 collimated light with multiple wave bands shares one absorption cell 9, and the multi-channel and multi-band measurement is greatly optimized in the aspects of the volume and the weight of the instrument compared with the C-Star measurement. The light source module 1 provides high-quality collimated light for signal detection by the LED 2. The first dichroic mirror 7 realizes the reflection of light source signals in corresponding wave bands, and the transmission of light source signals in other wave bands can realize that multi-channel light sources enter the absorption cell 9 simultaneously through reasonable arrangement without mutual interference; the second dichroic mirror 11 reflects corresponding band signals, transmits other band signals, and correspondingly arranges the multi-channel signals to enter the photoelectric receiver at the same time without mutual interference. The absorption cell 9 is filled with a solution for absorbance measurement, and the absorption cell 9 realizes measurement of the underwater free three-dimensional space through a dragging system.
Example 2
An absorbance sensor for an underwater towed system is provided according to embodiment 1, except that:
the first collimation light source and the second collimation light source respectively comprise an LED2, an aperture diaphragm 4 and a collimation lens 6 which are sequentially arranged, an integration cavity 3 is arranged outside the LED2, a reference detector is arranged on the outer surface of the integration cavity 3, and the reference detector is connected with the system control module;
the reference detector is a surface-mounted Si photodiode detector 5.
The emitted light of the LED2 passes through the aperture stop 4 and the collimating lens 6 to generate parallel light. The LED2 is selected as the light source, and the LED2 has the advantages of long service life, small volume and low cost. The aperture stop 4 structure provides a good-quality LED2 point light source, and then collimated light is obtained through the collimating lens 6 and enters the absorption cell 9 as an emitting end light source.
In the actual detection process, the LED2 light source has the fluctuation problem, the LED2 light source fluctuation monitoring is carried out by arranging the integrating cavity 3 and the surface-mounted Si photodiode detector 5, the surface-mounted Si photodiode detector 5 is used as a reference detector, the fluctuation change of the LED2 light source is recorded in the actual detection process, and the final calculation result is calibrated by adopting data processing, so that the measurement performance of the sensor and the accuracy of the result are improved.
The absorbance sensor is fixed in the one end of dragging the chain, and the other end of dragging the chain is fixed on the ship, and the data that the absorbance sensor gathered are transmitted to the host computer on the ship through dragging the chain.
The absorbance sensor is thrown to the sea area to be tested through the drag chain, seawater in the test sea area flows through the absorption pool 9 along with the movement of the ship, the absorbance three-dimensional profile data of the test sea area can be detected in real time, and the overflow sampling of a water pump is avoided. The water pump is used for overcurrent sampling, so that the weight and the volume of the towing system are increased, and the real-time measurement of a certain area cannot be realized by the overcurrent sampling.
The system control module comprises a multi-channel AD acquisition unit and a singlechip 17,
the multi-channel AD acquisition unit is respectively connected with the photoelectric receiver and the reference detector, realizes the real-time acquisition of data and transmits the acquired data to the singlechip 17;
the single chip microcomputer 17 is connected with the LED2 light source, and the single chip microcomputer 17 is used for driving the LED2 light source to emit light signals, processing data collected by the multi-channel AD collection unit and transmitting the data to the upper computer for processing, so that the absorbance of the solution to be detected is obtained.
The LED2 light source is connected with the single chip microcomputer 17 through an LED drive control interface 18, the reference detector is connected with the multi-channel AD acquisition unit through a reference detector signal receiving port 19, and the photodiode detector is connected with the multi-channel AD acquisition unit through a photodiode detector signal receiving port 20;
the light source module 1 comprises at least two collimated light sources, each collimated light source adopts an LED2 with different wave bands, and multi-band absorbance signal measurement is realized; the signal collection module 10 comprises at least two photo receivers.
The first and second photoreceivers 14 and 21 are each a photodiode detector.
The photodiode detector is an excellent optical measurement device, has high sensitivity in a wide band range from visible light to near infrared, and realizes multiband measurement corresponding to the light source module 1; compared with a spectrometer, the photodiode detector has great advantages in cost and volume of the instrument, and can also receive signals with high signal-to-noise ratio; the method is favorable for realizing the miniaturization, multi-channel and high precision of the absorbance sensor.
A narrow-band filter 12 and a focusing lens 13 are arranged between the first photoelectric receiver 14 and the second dichroic mirror 11 and between the second photoelectric receiver 21 and the second dichroic mirror 11, and the bandwidth of the narrow-band filter 12 is 10-20 nm.
A narrow-band filter 12 is added in front of the photodiode detector to filter out-of-band stray light, and a focusing lens 13 converges collimated light beams to the photodiode detector for signal detection.
Example 3
According to embodiment 2, there is provided an absorbance sensor for an underwater towed system, distinguished in that:
in this embodiment, the light source module 1 includes three collimated light sources, which are a first collimated light source and two second collimated light sources, respectively, the signal collection module 10 includes three photoelectric receivers, which are a first photoelectric receiver 14 and two second photoelectric receivers 21, respectively, and the first photoelectric receiver 14 receives a transmission light signal after the emergent light of the first collimated light source passes through the absorption cell 9; the second photoelectric receiver 21 receives a transmission light signal of the emergent light of the second collimation light source after passing through the absorption cell 9;
the absorbance sensor can realize three channels to measure the absorbance value of the solution.
The absorbance sensor for the underwater towing system provided by the invention has the volume of about 20cm multiplied by 4cm multiplied by 6cm, wherein the length of the absorption pool 9 is 10cm, and the space below the absorption pool 9 can be matched with other sensors to be shared in the towing system, so that more comprehensive ocean water body data measurement is realized; dilution experiments prove that the precision of the absorbance sensor provided by the invention can reach 0.0006 A.U.
Example 4
The working method of the absorbance sensor for the underwater dragging system, provided by any one of embodiments 1 to 3, comprises the following specific steps:
(1) the system control module drives the collimated light source in any channel to measure the absorbance of the calibration solution, then the seawater in the dragging area is used as the solution to be measured, and the absorbance of the solution to be measured is measured in the absorbance sensor;
measuring the calibration solution, wherein the process can also be finished in a laboratory, and then measuring the seawater absorbance of the dragging area;
(2) the LED2 light source signals are synchronously detected through a reference detector, the signals of the photoelectric receiver and the reference detector are transmitted to a multi-channel AD acquisition unit by a signal collection module 10, then the signals are synchronously transmitted to a single chip microcomputer 17 of a system control module, then data are transmitted to an upper computer through a drag chain, and the signals are processed in the upper computer by using a digital phase locking technology based on an FPGA;
the FPGA is a large-scale digital signal processing chip with low cost, the digital phase-locking technology is based on the cross-correlation detection principle, weak signals to be detected can be extracted from background noise, since light field signals in seawater are weak and change slowly, the digital phase-locking technology can well filter background light signals, bright field detection of absorbance signals is realized, the digital phase-locking technology of the FPGA is used for realizing absorbance signal detection with high signal-to-noise ratio, and the sensitivity of the sensor is improved;
(3) in the upper computer, carrying out self-correction processing on the absorbance of the solution to be detected to obtain the absorbance AU of the solution to be detected relative to the calibration solution; the specific process is as follows:
the absorbance a is defined as:
in the formula (I), VIntoIndicating the intensity of the optical signal, V, before entering the solutionGo outIndicates the intensity of an optical signal after passing through the solution, and T indicates the transmittance of the solution, i.e.
Absorbance A of calibration solutionCalibration：
In the formula (II), VCalibrationThe transmission signal of the calibration solution, namely the signal intensity of the transmission signal detected by the photodiode detector after being processed by the FPGA-based digital phase-locking technology,Vref1representing the intensity of the light source signal measured by the reference detector when measuring the calibration solution;
absorbance A of the solution to be measuredTo be measured：
In the formula (III), VTo be measuredThe transmission signal representing the solution to be measured, i.e. the signal intensity V of the transmission signal detected by the photodiode detector after being processed by the digital phase locking technology of the FPGAref2Representing the intensity of the light source signal measured by the reference detector when measuring the solution to be measured;
the absorbance value AU of the solution to be detected relative to the calibration solution is as follows:
in formula (IV), m is a self-correcting factor, and generally, the transmission signal V of the selected calibration solutionCalibrationAnd a reference signal VrefIs proportionally variable, i.e.
The signal collection module 10 monitors the fluctuation signal V of the LED2 light source through the reference detector during the detection processref2Synchronously acquiring a signal V of a signal of a photodiode detector processed by a digital phase locking technologyTo be measuredAnd the calculation result of the absorbance is corrected by using the correction factor m, so that high-precision and accurate measurement is realized.
Claims (10)
1. An absorbance sensor for an underwater dragging system is characterized by comprising a light source module, an absorption cell, a signal collecting module, a system control module and an upper computer,
a light source module is arranged at one end of the absorption tank, a signal collection module is arranged at the other end of the absorption tank, the light source module and the signal collection module are both connected with a system control module, and the system control module is connected with an upper computer;
the light source module is used for transmitting a multichannel signal and comprises a first collimation light source and a plurality of second collimation light sources, a plurality of first dichroic mirrors are arranged on an emergent light path of the first collimation light source, one side of each first dichroic mirror is provided with one second collimation light source, and the first dichroic mirrors are also positioned on an emergent light path of the second collimation light sources, so that emergent light of the second collimation light sources shares emergent light of the same emergent light path with the first collimation light sources after passing through the first dichroic mirrors;
the signal collection module is used for receiving multi-channel signals and comprises a first photoelectric receiver and a plurality of second photoelectric receivers, wherein the first photoelectric receiver is arranged on a transmission light path of the absorption cell and used for receiving transmission light signals of a first collimation light source penetrating through the absorption cell; a plurality of second dichroic mirrors are arranged between the first photoelectric receiver and the absorption cell, and a second photoelectric receiver is arranged on a reflection light path of each second dichroic mirror, so that the second photoelectric receiver receives a transmission light signal of a second collimation light source penetrating through the absorption cell; enabling the absorbance sensor to realize multi-channel measurement;
the system control module is used for driving the light source module to emit light signals, collecting the signals of the signal collection module and transmitting the collected signals to the upper computer;
and the upper computer processes the signals acquired by the system control module based on the FPGA digital phase locking technology and then calculates to obtain the absorbance of the solution to be detected.
2. The absorbance sensor for the underwater dragging system according to claim 1, wherein the first collimating light source and the second collimating light source each comprise an LED, an aperture diaphragm and a collimating lens, which are sequentially arranged, an integrating cavity is arranged outside the LED, and a reference detector is arranged on the outer surface of the integrating cavity and connected with the system control module.
3. The absorbance sensor for an underwater dragging system according to claim 2, wherein the reference detector is a surface-mounted Si photodiode detector.
4. The absorbance sensor for the underwater dragging system according to claim 2, wherein the upper computer is arranged on a ship, the absorbance sensor is fixed at one end of a dragging chain, the other end of the dragging chain is fixed on the ship, and data collected by the absorbance sensor is transmitted to the upper computer through the dragging chain.
5. The absorbance sensor for the underwater dragging system according to claim 2, wherein the system control module comprises a multi-channel AD acquisition unit and a single chip microcomputer,
the multi-channel AD acquisition unit is respectively connected with the photoelectric receiver and the reference detector, realizes the real-time acquisition of data and transmits the acquired data to the singlechip;
the multi-channel AD acquisition unit acquires signals acquired by the photoelectric receiver and the reference detector and transmits the signals to the upper computer, and the upper computer processes the signals based on the digital phase locking technology of the FPGA and then calculates to obtain the absorbance of the solution to be detected.
6. The absorbance sensor for an underwater dragging system according to claim 2, wherein the first collimated light source and the plurality of second collimated light sources use different wavelength band LEDs.
7. The absorbance sensor for an underwater dragging system according to claim 2, wherein the first and second photoelectric receivers are each a photodiode detector.
8. The absorbance sensor for the underwater dragging system according to claim 2, wherein a narrow-band filter and a focusing lens are arranged between the first photoelectric receiver and the second dichroic mirror or between the second photoelectric receiver and the second dichroic mirror, and the bandwidth of the narrow-band filter is 10-20 nm.
9. The working method of the absorbance sensor for the underwater dragging system according to any one of the claims 2 to 8, characterized by comprising the following concrete steps:
(1) the system control module drives the multi-channel collimation light source to emit light, and measures the absorbance A of the calibration solutionCalibrationThen taking the seawater in the dragging area as a solution to be measured, and measuring the absorbance A of the solution to be measured in an absorbance sensorTo be measured；
(2) The LED is synchronously detected through a reference detector, signals of a photoelectric receiver and the reference detector are transmitted to a multi-channel AD acquisition unit by a signal collection module, then are synchronously transmitted to a system control module, data are transmitted to an upper computer through a drag chain, and signal processing is carried out in the upper computer by using a digital phase locking technology based on an FPGA;
(3) and in the upper computer, carrying out self-correction processing on the absorbance of the solution to be detected to obtain the absorbance AU of the solution to be detected relative to the calibration solution.
10. The operating method of the absorbance sensor for the underwater dragging system according to claim 9, wherein in the step (3), the absorbance of the solution to be measured is self-corrected, specifically:
the absorbance value AU of the solution to be detected relative to the calibration solution is as follows:
in the formula (IV), m is a self-correcting factor,
VcalibrationFor calibrating the transmission signal of the solution, i.e. the transmission signal detected by a photoelectric receiver, via an FPGA-based systemSignal intensity after digital phase locking technology processing; vref1The intensity of a light source signal measured by a reference detector when a calibration solution is measured; vTo be measuredThe transmission signal of the solution to be detected, namely the signal intensity V of the transmission signal detected by the photoelectric receiver after being processed by the digital phase locking technology of the FPGAref2Indicating the intensity of the light source signal measured by the reference detector when measuring the solution to be measured.
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