CN109883997B - High-precision intelligent turbidity detection device and calibration method and use method thereof - Google Patents
High-precision intelligent turbidity detection device and calibration method and use method thereof Download PDFInfo
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Abstract
The invention discloses a high-precision intelligent turbidity detection device and a calibration and use method thereof, wherein the device is divided into three layers, a probe structure at the bottom layer comprises a photodiode and two light-emitting diodes on the same horizontal plane, one of the two light-emitting diodes is over against the photodiode, and the other light-emitting diode is vertical to the photodiode; the top layer is a circuit board which comprises a constant current source driving circuit and a range switching circuit electrically connected with the constant current source driving circuit, and the range switching circuit is respectively and electrically connected with two light emitting diodes in the probe structure at the bottom layer. The high-precision intelligent turbidity detection device disclosed by the invention integrates two measurement modes of a 90-degree scattering method and a transmission method, has high measurement precision and wide measurement range, and can be used in various measurement occasions. The device with high cost performance is selected, the cost is low, the practicability is high, and the device has good application prospect and popularization value in the field of water quality detection.
Description
Technical Field
The invention belongs to the field of water quality detection devices, and particularly relates to a high-precision intelligent turbidity detection device, a calibration method and a use method thereof.
Background
Turbidity is a unit for representing the turbidity degree of a water body, and is an important physical index in water quality monitoring. Whether domestic or foreign, the turbidity parameter index is detected for domestic water of people and process water in other industries, and the turbidity of sewage generated in rivers, lakes, seas and human production and life is also required to be detected.
The measurement method of turbidity is classified into a transmission method and a 90 ° scattering method according to the measurement principle of turbidity. The current international universal measuring method is a 90-degree scattering method, the measuring method is good in linearity and high in measuring accuracy, but when the turbidity of the water body is high, the influence of secondary scattering is caused, 90-degree scattered light cannot accurately reflect the turbidity, and therefore the measuring range of the measuring method is generally 0-200 NTU. The transmission method reflects the turbidity of the water body by measuring the absorbance of the water body, has good linearity within the range of 200-1000 NTU and above, and is more suitable for measuring medium and high turbidity. Most of turbidity meters in the current market adopt a 90-degree scattering method, and have low precision and high price.
Disclosure of Invention
The invention aims to solve the technical problem of providing a high-precision intelligent turbidity detection device and a calibration method and a use method thereof.
The invention adopts the following technical scheme:
a high-precision intelligent turbidity detection device is improved in that: the device is divided into three layers, the probe structure at the bottom layer comprises a photodiode and two light-emitting diodes on the same horizontal plane, one of the two light-emitting diodes is over against the photodiode, and the other light-emitting diode is vertical to the photodiode; the top layer is a circuit board which comprises a constant current source driving circuit and a range switching circuit electrically connected with the constant current source driving circuit, the range switching circuit is respectively and electrically connected with two light emitting diodes in the bottom probe structure, the circuit board also comprises an I/V conversion circuit electrically connected with a photodiode in the bottom probe structure, the I/V conversion circuit is electrically connected with a pre-amplification circuit through an amplification filter circuit, the pre-amplification circuit and a temperature compensation circuit are both electrically connected with an AD conversion circuit, the AD conversion circuit is electrically connected with a main control circuit, the main control circuit is electrically connected with a storage circuit and a communication circuit, and the communication circuit is connected with a human-computer interaction interface for communication; the power module in the middle layer supplies power for the device.
Furthermore, the device is of a black shell structure; the bottom surface of the bottom probe is an inclined plane and is inwards sunken, the light emitting diode is arranged in the light emitting diode mounting hole sealed by the optical window, the photodiode is arranged in the photodiode mounting hole sealed by the lens, and the centers of the light emitting diode mounting hole and the photodiode mounting hole are on the same horizontal plane.
Furthermore, the constant current source driving circuit is a high-precision controllable constant current source; the I/V conversion circuit is an adjustable gain I/V conversion circuit; the range switching circuit is a two-channel analog switch; the temperature compensation circuit is a high-precision constant current source driving PT 1000; the main control circuit is STM32F103CBT 6; the storage circuit is an SD card and adopts a FatFs file system; the communication circuit is for Lora wireless communication.
Furthermore, the adjustable gain I/V conversion circuit comprises an operational amplifier, wherein the input end of the operational amplifier is electrically connected with a photodiode, filter capacitors C1, C2, C3, C4 and C5, the output end of the operational amplifier is electrically connected with an LC pi-type filter circuit, the LC pi-type filter circuit consists of capacitors C7 and C8 and an inductor L1, two precise resistors R2 and R3 and a capacitor C6 are connected between the input end and the output end in parallel, and the precise resistors R2 and R3 are gated by a master control circuit to control an analog switch.
Furthermore, the power module is a linear voltage-stabilized power supply and adopts a mode of connecting a tantalum capacitor and a ceramic capacitor in parallel to filter the voltage output end of the power module; and magnetic beads are used for digital-analog isolation between the main control circuit and the AD conversion circuit, and a 0 omega resistor is used for single-point grounding.
The calibration method using the high-precision intelligent turbidity detection device is improved by comprising the following steps of:
(1) preparing 11 kinds of turbidity standard solutions in the range of 0-200 NTU every 20 NTU;
(2) preparing 16 kinds of turbidity standard solutions in the range of 200-1000 NTU every 50 NTU;
(3) placing a probe at the bottom layer of the device into a turbidity standard solution in a constant temperature box, wherein the temperature T of the constant temperature box is 20 ℃, a 90-degree scattering method is selected within the range of 0-200 NTU, a transmission method is selected within the range of 200-1000 NTU, and collecting and recording photoelectric voltage signals corresponding to different turbidity standard solutions;
(4) in the range of 0-100 NTU and 100-200 NTU, a least square method is used for calculating a fitting expression, and a calibration model of the natural logarithm of the turbidity and the photovoltage signals is established:
(5) in the range of 200-600 NTU and 600-1000 NTU, using least square method to calculate fitting expression, establishing calibration model of turbidity and light voltage signal natural logarithm:
(6) placing a probe at the bottom layer of the device into a turbidity standard solution in a thermostat, changing the temperature T of the thermostat when the turbidity of the turbidity standard solution is 400NTU at 20 ℃, acquiring temperature information by using a temperature compensation circuit, and recording turbidity measurement values of the device to the turbidity standard solution at different temperatures;
(7) selecting T-20 ℃ as x1Absolute error, i.e. turbidity measurement-400 NTU is y1Calculating a fitting expression by using a least square method, and establishing a temperature compensation model of the device: y is1＝mx1+n；
(8) Assuming that the turbidity value measured at this time is Q, the temperature compensation model can be converted into: q-400 ═ c · 400 · (T-20) + n, where m ═ c · 400, so that the haze increases c times with each 1 ℃ change in temperature;
(9) the calibration model after temperature compensation can be obtained by bringing the temperature compensation model into the corresponding calibration model:
in the above formula, Y is the measured value of turbidity after temperature compensation; x-the natural logarithm of the photovoltage signal; a, calibrating a model slope value, b, calibrating a model intercept; n is the temperature compensation model intercept; c-coefficient.
The use method of the high-precision intelligent turbidity detection device is improved by comprising the following steps:
(1) placing a probe at the bottom layer of the device into a solution to be detected, then performing power-on reset, and initializing parameters;
(2) the measuring range switching circuit defaults to select a 90-degree scattering method gear, namely, a light emitting diode vertical to a photodiode is switched on, the light emitting diode which is switched on is driven by a constant current source driving circuit to emit light, the light emitted by the light emitting diode enters the photodiode after being scattered by a solution to be detected, the current is induced by the photodiode, the current is converted into a mV-level voltage signal through an I/V conversion circuit, the voltage signal enters a main control circuit through an amplifying filter circuit, a pre-amplifying circuit and an AD conversion circuit, the main control circuit sets the voltage signal as a current voltage signal, the main control circuit preliminarily calculates a turbidity value according to the current voltage signal, if the preliminarily calculated turbidity value is more than 200NTU, the measuring range switching circuit needs to be controlled to be switched to a transmission method gear, namely, the light emitting diode opposite to the photodiode is switched on, and the light emitted by the light emitting, the current is induced again by the photodiode, the re-induced current is converted into a new mV level voltage signal through the I/V conversion circuit, the new voltage signal enters the main control circuit through the amplifying filter circuit, the pre-amplifying circuit and the AD conversion circuit, and the main control circuit sets the new voltage signal as a current voltage signal;
(3) the temperature compensation circuit sends the acquired current temperature signal to the main control circuit through the AD conversion circuit, and the main control circuit calculates the turbidity value after temperature compensation according to the current voltage signal and the current temperature;
(4) the turbidity value is transmitted to a human-computer interaction interface for display through a communication circuit.
Further, in the step (2), the light emitting frequency of the light emitting diode is controlled through PWM; the photodiode operates in a photoconductive mode; the I/V conversion circuit has a high gain in the 90 ° scattering method and a low gain in the transmission method.
Furthermore, the main control circuit filters data by adopting moving average filtering in the calculation process, and the circuit board filters the data by adopting an LC pi-type filtering mode.
Furthermore, a system kernel selected by the main control circuit is a real-time operating system FreeRTOS, the FreeRTOS tasks comprise an initialization task, a communication task, a turbidity acquisition task, a temperature acquisition task, a data processing task, a data storage task and a data display task, and the FreeRTOS task scheduler is used for scheduling uniformly according to task priorities.
The invention has the beneficial effects that:
the high-precision intelligent turbidity detection device disclosed by the invention integrates two measurement modes of a 90-degree scattering method and a transmission method, has high measurement precision and wide measurement range, and can be used in various measurement occasions. The device with high cost performance is selected, the cost is low, the practicability is high, and the device has good application prospect and popularization value in the field of water quality detection.
The high-precision intelligent turbidity detection device disclosed by the invention adopts a black shell structure, so that the influence of stray light during measurement can be avoided; the bottom surface of the bottom probe is an inclined surface and is inwards concave to facilitate the water flow to enter; the FatFs file system is adopted, so that the risk of loss of stored data is reduced; and a Lora wireless communication mode is adopted, the transmission distance is long, and remote real-time online detection can be realized. The power module adopts a linear voltage-stabilized power supply, the ripple of the output voltage of the power module is small, and hardware filtering is performed at the voltage output end, so that the quality of the power supply is improved.
The calibration method disclosed by the invention uses a least square method to perform segmented fitting, different fitting formulas are selected for different measurement ranges, a temperature compensation circuit is used for measuring the temperature of the solution to be measured, then a temperature compensation model is used for performing temperature compensation on the calibration model, the turbidity data at the current temperature is converted into the turbidity data at 20 ℃, and the device is ensured to still have higher precision at different temperatures.
The use method disclosed by the invention controls the light emitting frequency of the light emitting diode through PWM, solves the problem of unstable light source caused by long-time heating of the light emitting diode, and improves the measurement precision of the device. The I/V conversion circuit has high gain in the 90-degree scattering method and low gain in the transmission method, so that the measurement range is expanded, and the measurement precision and the intelligent level of the device are improved. The combination of the moving average filtering (software filtering) and the LC pi-type filtering (hardware filtering) improves the anti-interference capability of the device. The method selects a lightweight operating system FreeRTOS with strong real-time performance as a system kernel, can well shield the bottom hardware of a microprocessor, and has the characteristics of multi-task type, cuttability, real-time performance, stable and reliable application codes and the like. A plurality of tasks are established based on the FreeRTOS, and then are uniformly scheduled by a FreeRTOS task scheduler, so that the hierarchy is clear, and the stability and reliability of the system are enhanced.
Drawings
FIG. 1 is a schematic structural diagram of an apparatus disclosed in embodiment 1 of the present invention;
FIG. 2 is a block diagram of the circuit components of the top circuit board in the device disclosed in embodiment 1 of the present invention;
FIG. 3 is a schematic circuit diagram of an I/V conversion circuit in the device disclosed in embodiment 1 of the present invention;
FIG. 4 is a schematic flow chart of the application method disclosed in embodiment 1 of the present invention;
fig. 5 is a schematic diagram of task scheduling of FreeRTOS in the use method disclosed in embodiment 1 of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in further detail below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
In this embodiment, the device has a black housing structure; the bottom surface of the bottom probe is an inclined surface and is recessed inwards, the light emitting diodes are mounted in light emitting diode mounting holes 5 and 8 sealed by optical windows 6 and 7 (the optical windows can also be used for converting optical signals into parallel light), the photodiodes are mounted in a photodiode mounting hole 3 sealed by a lens 4 (the lens can also be used for collecting optical signals), and the centers of the light emitting diode mounting holes and the centers of the photodiode mounting holes are on the same horizontal plane.
In this embodiment, the light emitting diode is an infrared diode, and the constant current source driving circuit is a high-precision controllable constant current source; the I/V conversion circuit is an adjustable gain I/V conversion circuit; the range switching circuit is a two-channel analog switch; the temperature compensation circuit is a high-precision constant current source driving PT 1000; the main control circuit is STM32F103CBT 6; the storage circuit is an SD card and adopts a FatFs file system; the communication circuit is for Lora wireless communication. The power module is a lithium battery.
As shown in fig. 3, the adjustable gain I/V conversion circuit includes an operational amplifier, an input terminal of the operational amplifier is electrically connected to a photodiode, filter capacitors C1, C2, C3, C4 and C5, the filter capacitors can improve the quality of the power supply of the operational amplifier, and an output terminal of the operational amplifier is electrically connected to an LC pi filter circuit, and the LC pi filter circuit is composed of capacitors C7, C8 and an inductor L1, and is used to enhance the anti-interference capability of the apparatus and improve the measurement accuracy. Two precision resistors R2 and R3 and a capacitor C6 are connected in parallel between the input end and the output end, wherein the precision resistors R2 and R3 are gated by a master control circuit control analog switch to realize gain adjustability, and the capacitor C6 can eliminate stray noise on the precision resistors R2 and R3 to improve the stability of signals.
In this embodiment, the power module is a linear voltage-stabilized power supply and filters a voltage output end of the power module in a manner of parallel connection of a tantalum capacitor and a ceramic capacitor; and magnetic beads are used for digital-analog isolation between the main control circuit and the AD conversion circuit, and a 0 omega resistor is used for single-point grounding.
The embodiment also discloses a calibration method, which uses the high-precision intelligent turbidity detection device, and comprises the following steps:
(1) preparing 11 kinds of turbidity standard solutions in the range of 0-200 NTU every 20 NTU;
(2) preparing 16 kinds of turbidity standard solutions in the range of 200-1000 NTU every 50 NTU;
(3) placing a probe at the bottom layer of the device into a turbidity standard solution in a constant temperature box, wherein the temperature T of the constant temperature box is 20 ℃, a 90-degree scattering method is selected within the range of 0-200 NTU, a transmission method is selected within the range of 200-1000 NTU, and collecting and recording photoelectric voltage signals corresponding to different turbidity standard solutions;
(4) in the range of 0-100 NTU and 100-200 NTU, a least square method is used for calculating a fitting expression, and a calibration model of the natural logarithm of the turbidity and the photovoltage signals is established:
(5) in the range of 200-600 NTU and 600-1000 NTU, using least square method to calculate fitting expression, establishing calibration model of turbidity and light voltage signal natural logarithm:
(6) placing a probe at the bottom layer of the device into a turbidity standard solution in a thermostat, changing the temperature T of the thermostat when the turbidity of the turbidity standard solution is 400NTU at 20 ℃, acquiring temperature information by using a temperature compensation circuit, and recording turbidity measurement values of the device to the turbidity standard solution at different temperatures;
(7) selecting T-20 ℃ as x1Absolute error, i.e. turbidity measurement-400 NTU is y1Calculating a fitting expression by using a least square method, and establishing a temperature compensation model of the device: y is1＝mx1+n；
(8) Assuming that the turbidity value measured at this time is Q, the temperature compensation model can be converted into: q-400 ═ c · 400 · (T-20) + n, where m ═ c · 400, so that the haze increases c times with each 1 ℃ change in temperature;
(9) the calibration model after temperature compensation can be obtained by bringing the temperature compensation model into the corresponding calibration model:
in the above formula, Y is the measured value of turbidity after temperature compensation; x-the natural logarithm of the photovoltage signal; a, calibrating a model slope value, b, calibrating a model intercept; n is the temperature compensation model intercept; c-coefficient.
As shown in fig. 4, the present embodiment further discloses a using method, using the above high-precision intelligent turbidity detecting apparatus, including the following steps:
(1) placing a probe at the bottom layer of the device into a solution to be detected, then performing power-on reset, and initializing parameters;
(2) the measuring range switching circuit defaults to select a 90-degree scattering method gear, namely, a light emitting diode vertical to a photodiode is switched on, the light emitting diode which is switched on is driven by a constant current source driving circuit to emit light, the light emitted by the light emitting diode enters the photodiode after being scattered by a solution to be detected, the current is induced by the photodiode, the current is converted into a mV-level voltage signal through an I/V conversion circuit, the voltage signal enters a main control circuit through an amplifying filter circuit, a pre-amplifying circuit and an AD conversion circuit, the main control circuit sets the voltage signal as a current voltage signal, the main control circuit preliminarily calculates a turbidity value according to the current voltage signal, if the preliminarily calculated turbidity value is more than 200NTU, the measuring range switching circuit needs to be controlled to be switched to a transmission method gear, namely, the light emitting diode opposite to the photodiode is switched on, and the light emitted by the light emitting, the current is induced again by the photodiode, the re-induced current is converted into a new mV level voltage signal through the I/V conversion circuit, the new voltage signal enters the main control circuit through the amplifying filter circuit, the pre-amplifying circuit and the AD conversion circuit, and the main control circuit sets the new voltage signal as a current voltage signal;
(3) the temperature compensation circuit sends the acquired current temperature signal to the main control circuit through the AD conversion circuit, and the main control circuit calculates the turbidity value after temperature compensation according to the current voltage signal and the current temperature;
(4) the turbidity value is transmitted to a human-computer interaction interface for display through a communication circuit.
In the step (2), controlling the light emitting frequency of the light emitting diode through PWM; the photodiode works in a light guide mode, so that the measurement precision of the device can be improved; the I/V conversion circuit has a high gain in the 90 ° scattering method and a low gain in the transmission method. In the calculation process of the main control circuit, the data is filtered by adopting the moving average filtering, and the circuit board is filtered by adopting an LC pi-type filtering mode.
As shown in fig. 5, the system kernel selected by the main control circuit is a real-time operating system, namely, a FreeRTOS, and the FreeRTOS tasks include an initialization task, a communication task, a turbidity acquisition task, a temperature acquisition task, a data processing task, a data storage task and a data display task, and are uniformly scheduled by a FreeRTOS task scheduler according to task priorities.
Claims (8)
1. The utility model provides a high accuracy intelligence turbidity detection device which characterized in that: the device is divided into three layers, the probe structure at the bottom layer comprises a photodiode and two light-emitting diodes on the same horizontal plane, one of the two light-emitting diodes is over against the photodiode, and the other light-emitting diode is vertical to the photodiode; the top layer is a circuit board which comprises a constant current source driving circuit and a range switching circuit electrically connected with the constant current source driving circuit, the range switching circuit is respectively and electrically connected with two light emitting diodes in the bottom probe structure, the circuit board also comprises an I/V conversion circuit electrically connected with a photodiode in the bottom probe structure, the I/V conversion circuit is electrically connected with a pre-amplification circuit through an amplification filter circuit, the pre-amplification circuit and a temperature compensation circuit are both electrically connected with an AD conversion circuit, the AD conversion circuit is electrically connected with a main control circuit, the main control circuit is electrically connected with a storage circuit and a communication circuit, and the communication circuit is connected with a human-computer interaction interface for communication; the power supply module of the middle layer supplies power to the device; the constant current source driving circuit is a high-precision controllable constant current source; the I/V conversion circuit is an adjustable gain I/V conversion circuit; the range switching circuit is a two-channel analog switch; the temperature compensation circuit is a high-precision constant current source driving PT 1000; the main control circuit is STM32F103CBT 6; the storage circuit is an SD card and adopts a FatFs file system; the communication circuit is Lora wireless communication; the adjustable gain I/V conversion circuit comprises an operational amplifier, wherein the inverting input end of the operational amplifier is electrically connected with a grounded photodiode, the non-inverting input end of the operational amplifier is electrically connected with a filter capacitor C1 and a resistor R1 which are grounded in parallel, a positive power supply pin is electrically connected with filter capacitors C4 and C5 which are grounded in parallel, a negative power supply pin is electrically connected with filter capacitors C2 and C3 which are grounded in parallel, the output end of the operational amplifier is electrically connected with an LC pi-type filter circuit, the LC pi-type filter circuit comprises an inductor L1, two sides of the inductor L1 are respectively electrically connected with the capacitors C7 and C8 which are grounded in parallel, two precise resistors R2 and R3 and a capacitor C6 are connected between the inverting input end and the output end in parallel, and the precise resistors R2 and R3 are gated by a.
2. The high-precision intelligent turbidity detecting device according to claim 1, wherein: the device is of a black shell structure; the bottom surface of the bottom probe is an inclined plane and is inwards sunken, the light emitting diode is arranged in the light emitting diode mounting hole sealed by the optical window, the photodiode is arranged in the photodiode mounting hole sealed by the lens, and the centers of the light emitting diode mounting hole and the photodiode mounting hole are on the same horizontal plane.
3. The high-precision intelligent turbidity detecting device according to claim 1, wherein: the power supply module is a linear voltage-stabilized power supply and filters the voltage output end of the power supply module in a way of connecting a tantalum capacitor and a ceramic capacitor in parallel; and magnetic beads are used for digital-analog isolation between the main control circuit and the AD conversion circuit, and a 0 omega resistor is used for single-point grounding.
4. A calibration method using the high-precision intelligent turbidity detecting apparatus of claim 1, comprising the steps of:
(1) preparing 11 kinds of turbidity standard solutions in the range of 0-200 NTU every 20 NTU;
(2) preparing 16 kinds of turbidity standard solutions in the range of 200-1000 NTU every 50 NTU;
(3) placing a probe at the bottom layer of the device into a turbidity standard solution in a constant temperature box, wherein the temperature T of the constant temperature box is 20 ℃, a 90-degree scattering method is selected within the range of 0-200 NTU, a transmission method is selected within the range of 200-1000 NTU, and collecting and recording photoelectric voltage signals corresponding to different turbidity standard solutions;
(4) in the range of 0-100 NTU and 100-200 NTU, a least square method is used for calculating a fitting expression, and a calibration model of the natural logarithm of the turbidity and the photovoltage signals is established:
(5) in the range of 200-600 NTU and 600-1000 NTU, using least square method to calculate fitting expression, establishing calibration model of turbidity and light voltage signal natural logarithm:
(6) placing a probe at the bottom layer of the device into a turbidity standard solution in a thermostat, changing the temperature T of the thermostat when the turbidity of the turbidity standard solution is 400NTU at 20 ℃, acquiring temperature information by using a temperature compensation circuit, and recording turbidity measurement values of the device to the turbidity standard solution at different temperatures;
(7) selected from T-20 ℃ tox1Absolute error, i.e. turbidity measurement-400 NTU is y1Calculating a fitting expression by using a least square method, and establishing a temperature compensation model of the device: y is1＝mx1+n；
(8) Assuming that the turbidity value measured at this time is Q, the temperature compensation model can be converted into: q-400 ═ c · 400 · (T-20) + n, where m ═ c · 400, so that the haze increases c times with each 1 ℃ change in temperature;
(9) the calibration model after temperature compensation can be obtained by bringing the temperature compensation model into the corresponding calibration model:
in the above formula, Y is the measured value of turbidity after temperature compensation; x-the natural logarithm of the photovoltage signal; a, calibrating a model slope value, b, calibrating a model intercept; n is the temperature compensation model intercept; c-coefficient.
5. A method of use using the high-precision intelligent turbidity detecting apparatus of claim 1, comprising the steps of:
(1) placing a probe at the bottom layer of the device into a solution to be detected, then performing power-on reset, and initializing parameters;
(2) the measuring range switching circuit defaults to select a 90-degree scattering method gear, namely, a light emitting diode vertical to a photodiode is switched on, the light emitting diode which is switched on is driven by a constant current source driving circuit to emit light, the light emitted by the light emitting diode enters the photodiode after being scattered by a solution to be detected, the current is induced by the photodiode, the current is converted into a mV-level voltage signal through an I/V conversion circuit, the voltage signal enters a main control circuit through an amplifying filter circuit, a pre-amplifying circuit and an AD conversion circuit, the main control circuit sets the voltage signal as a current voltage signal, the main control circuit preliminarily calculates a turbidity value according to the current voltage signal, if the preliminarily calculated turbidity value is more than 200NTU, the measuring range switching circuit needs to be controlled to be switched to a transmission method gear, namely, the light emitting diode opposite to the photodiode is switched on, and the light emitted by the light emitting, the current is induced again by the photodiode, the re-induced current is converted into a new mV level voltage signal through the I/V conversion circuit, the new voltage signal enters the main control circuit through the amplifying filter circuit, the pre-amplifying circuit and the AD conversion circuit, and the main control circuit sets the new voltage signal as a current voltage signal;
(3) the temperature compensation circuit sends the acquired current temperature signal to the main control circuit through the AD conversion circuit, and the main control circuit calculates the turbidity value after temperature compensation according to the current voltage signal and the current temperature;
(4) the turbidity value is transmitted to a human-computer interaction interface for display through a communication circuit.
6. Use according to claim 5, characterized in that: in the step (2), controlling the light emitting frequency of the light emitting diode through PWM; the photodiode operates in a photoconductive mode; the I/V conversion circuit has a high gain in the 90 ° scattering method and a low gain in the transmission method.
7. Use according to claim 5, characterized in that: in the calculation process of the main control circuit, the data is filtered by adopting the moving average filtering, and the circuit board is filtered by adopting an LC pi-type filtering mode.
8. Use according to claim 5, characterized in that: the system kernel selected by the main control circuit is a real-time operating system FreeRTOS, the FreeRTOS tasks comprise an initialization task, a communication task, a turbidity acquisition task, a temperature acquisition task, a data processing task, a data storage task and a data display task, and the FreeRTOS task scheduler is used for scheduling uniformly according to task priorities.
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| CN111239079B (en) * | 2020-03-09 | 2022-11-11 | 上海交通大学 | Time-varying turbid field simulation device with fixed optical depth |
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