Millimeter wave radar water level gauge and algorithm thereof

Abstract

The millimeter wave radar water level gauge comprises a main control module, the main control module is connected with a power module, a level shifter and a communication module, the level shifter is connected with a radar sensor, the radar sensor is connected with the power module, and the communication module is connected with the power module. The power supply module is also connected with the level translator and the communication module. The radar sensor sends detected data to the master control module through the level translator, the master control module processes the detected data, then discharges invalid data, outputs valid data and transmits the data to the upper computer for display through the communication module, and the system has the advantages of high measurement precision, stable anti-interference capability, good false alarm control capability, low cost and high reliability. The device is suitable for water level measurement in agricultural irrigation, facilitates improvement of irrigation efficiency and crop yield, and meanwhile reduces waste of water resources.

Description

Technical Field

[0001] The invention relates to a millimeter wave radar water level meter and an algorithm thereof in the technical field of water level measurement. Background Art

[0002] In agricultural irrigation applications, traditional water level meters, such as float type, pressure type and capacitive type water level meters, require direct contact with water. This limits their service life and measurement accuracy when faced with complex field environments such as large water level fluctuations and poor water quality. Therefore, their usage rate in agricultural irrigation applications is relatively low.

[0003] However, with the continuous development and maturity of ultrasonic and ordinary radar water level meter technology, it has been widely used in the field of irrigation. However, there are also problems such as low accuracy and unstable false alarm rate in the application. Its anti-interference ability is insufficient and it cannot effectively distinguish the target signal and environmental noise. Therefore, the interference factor has a great influence on the accuracy of the measurement results, and it cannot be applied to the irrigation system in the long-term complex environment in the field. Summary of the invention

[0004] The purpose of the present invention is to provide a millimeter wave radar water level meter and its algorithm, which have high measurement accuracy, stable anti-interference ability and good false alarm control ability, and are low in cost. The water level meter is suitable for water level measurement in agricultural irrigation, which helps to improve irrigation efficiency and crop yield, and reduce the waste of water resources.

[0005] To achieve the above-mentioned purpose, the present invention provides a millimeter-wave radar water level meter, including a main control module, the main control module is respectively connected to a power module, a level converter and a communication module, the level converter is connected to a radar sensor, the radar sensor is connected to the power module, and the power module is also connected to the level converter and the communication module.

[0006] Compared with the prior art, the beneficial effect of the present invention lies in that the radar sensor sends the detected data to the main control module through the level converter, and after being processed by the main control module, invalid data is discharged, valid data is output, and the data is transmitted to the host computer for display through the communication module. It has high measurement accuracy, stable anti-interference ability and good false alarm control ability, and the cost is low. It is suitable for water level measurement in agricultural irrigation, which helps to improve irrigation efficiency and crop yield, and reduce the waste of water resources.

[0007] As a further improvement of the present invention, the main control module includes a chip STM32L431, the drive module includes a chip A111, the level converter uses a chip TXS0108, and pins 1, 3, 4, 5, 6, and 9 of the chip TXS0108 are respectively connected to the F10 pin, K2 pin, K3 pin, K6 pin, J2 pin, and K8 pin of the chip STM32L431, and pins 12, 15, 16, 17, 18, and 20 of the chip TXS0108 are respectively connected to pins 33, 37, 36, 35, 34, and 38 of the chip A111.

[0008] In this way, since the operating voltage of the chip STM32L431 is 3.3V and the operating voltage of the chip A111 is 1.8V, the two cannot communicate directly through SPI. By adding a signal level conversion chip between the two, that is, the chip TXS0108EPWR, normal data communication between the two is achieved.

[0009] As a further improvement of the present invention, the power module includes a voltage stabilizing chip U9 and a voltage stabilizing chip U6, pin 1 of the voltage stabilizing chip U9 is grounded, pin 2 of the voltage stabilizing chip U9 is connected to the external power supply VIN via a fuse F2, capacitor C6 and diode D4 are connected in parallel between pin 2 and pin 1 of the voltage stabilizing chip U9, capacitor C3, capacitor C40 and capacitor C41 are connected in parallel between pin 3 and pin 1 of the voltage stabilizing chip U9, pin 3 of the voltage stabilizing chip U9 is respectively connected to pin 1, pin 32, pin 48 and pin 64 of the chip STM32L431, and pin 3 of the voltage stabilizing chip U9 is also connected to the chip TXS0108 19; Pin 1 of the voltage regulator chip U6 is respectively connected to one end of the capacitor C32 and the pin 3 of the voltage regulator chip U9, the other end of the capacitor C32 is grounded, Pin 2 of the voltage regulator chip U6 is grounded, Pin 3 of the voltage regulator chip U6 is connected to the pin 3 of the voltage regulator chip U9, Pin 4 of the voltage regulator chip U6 is grounded via capacitor C30, Pin 5 of the voltage regulator chip U6 is grounded via capacitor C31, Pin 3 of the voltage regulator chip U6 is respectively connected to Pin C2, Pin D1, Pin C9, Pin D10, Pin J9 and Pin K9 of chip A111, and Pin 3 of the voltage regulator chip U6 is also connected to Pin 2 of the chip TXS0108.

[0010] In this way, a self-recovery fuse protection circuit is added at the power input end, the 3.3V voltage domain uses the HT7133LDO voltage regulator chip, and the 1.8V voltage domain uses the TPSPX3819M5-L-1-8 linear voltage regulator chip, thereby ensuring that the required stable voltage is provided to each module.

[0011] As a further improvement of the present invention, the communication module includes a chip SP3485EN-L / T, pin 1 and pin 4 of the chip SP3485EN-L / T are respectively connected to pin 17 and pin 16 of the chip STM32L431, pin 2 and pin 3 of the chip SP3485EN-L / T are connected and are respectively connected to one end of the resistor R11 and the collector of the transistor Q1, the other end of the resistor R11 is connected to pin 3 of the voltage stabilizing chip U9, the emitter of the transistor Q1 is grounded, the collector of the transistor Q1 is connected to pin 16 of the chip STM32L431 via a resistor R14, and the chip SP3485EN-L / T Pin 5 is grounded; Pin 6 of chip SP3485EN-L / T is respectively connected to one end of resistor R15 and pin 1 of TVS tube D2, the other end of resistor R15 is connected to pin 3 of voltage regulator chip U9, Pin 7 of chip SP3485EN-L / T is respectively connected to one end of resistor R9 and pin 2 of TVS tube D2, the other end of resistor R9 is grounded, resistor R12 is connected in parallel between pin 1 and pin 2 of TVS tube D2, pin 3 of TVS tube D2 is grounded, Pin 8 of chip SP3485EN-L / T is respectively connected to pin 3 of voltage regulator chip U9 and one end of capacitor C27, the other end of capacitor C27 is grounded.

[0012] In this way, RS485 is used for communication, and the chip uses the 485 bus transceiver SP3485EN-L / T. Among them, PSM712-LF-T7 is a TVS tube for anti-static and surge protection. The sending end uses SS8050 to form a switch circuit.

[0013] In order to achieve the above object, the present invention also provides an algorithm for a millimeter wave radar water level meter, comprising the following steps:

[0014] Step 1, obtain the height from the water surface to the bottom of the water, that is, the water level;

[0015] Step 2, the signal transmitted by the A111 chip is processed to obtain the background clutter power level Z;

[0016] Step 3, obtaining the threshold sensitivity factor T;

[0017] Step 4, obtaining the detection threshold V;

[0018] Step 5: Output the comparison results.

[0019] Compared with the prior art, the beneficial effect of the present invention is that by setting the detection threshold and realizing high-precision measurement of the water level, the distribution and use of irrigation water can be accurately monitored to ensure that the crops get the right amount of water. Due to the low power consumption performance of the hardware structure, it is particularly important in field irrigation applications and can reduce its operating and production costs.

[0020] As a further improvement of the present invention, the A111 chip measures the distance of an object based on the time of signal propagation, and its formula is

[0021]

[0022] Where t is the time interval between the radar sending and receiving pulses, d is the distance between the water surface and the radar, and v is the propagation speed of radio in the air. Since the dielectric constant of the radio with a frequency of 60 GHz in the air is 1, the speed of v is 3×10 8 m / s;

[0023] The distance between the height of the radar installation and the bottom of the water measured in advance is b, and bd is the water level height.

[0024] In this way, the distance between the height of the radar installation and the water bottom is measured in advance, and then the height from the water surface to the water bottom (i.e., the water level) is obtained by measuring the height from the water surface to the radar installation, thereby obtaining the water level height through an indirect measurement method.

[0025] As a further improvement of the present invention, the specific content of step 2 is as follows:

[0026] Step 2.1, set the sampling of the unit to be detected to M, there are several samples of the protection unit on both sides of the unit to be detected, and there are L / 2 samples of the reference unit outside the protection unit, with a total of L reference units; X is the sum of the L / 2 reference units in front of the protection unit, and Y is the sum of the L / 2 reference units behind the protection unit;

[0027] Step 2.2, assuming that the total background clutter power level of the sample M of the unit to be detected is Z, then the background clutter power level Z=(X+Y) / L.

[0028] In this way, the signal transmitted by the A111 chip is processed to obtain the reference unit size and the window to be detected, and the background clutter power level Z is calculated.

[0029] As a further improvement of the present invention, the specific content of step 3 is as follows

[0030] Step 3.1. After the signal is detected by the square law, the noise distribution model obeys the exponential distribution, so the probability density function of the corresponding detection threshold is:

[0031]

[0032] Where λ is the parameter of the exponential function;

[0033] Step 3.2. Using the Neyman-Pearson criterion, the probability density distribution function corresponding to the false alarm probability is obtained as

[0034]

[0035] Integrating the above formula, we can get the false alarm probability as:

[0036]

[0037] Step 3.3. From the above formula, we can see that the false alarm probability is only related to the threshold coefficient and the length of the reference unit, where the threshold coefficient is the threshold sensitivity factor T. After the specific values ​​of the two are determined, the false alarm probability remains unchanged; under the premise that the false alarm probability is constant and the reference unit length is determined, the calculation of the threshold sensitivity factor T is as follows:

[0038]

[0039] In this way, a constant false alarm probability is defined in the program, and finally the threshold sensitivity factor T is obtained under the premise that the false alarm probability is constant and the reference unit length is determined.

[0040] As a further improvement of the present invention, V=Z·T.

[0041] Thus, V is the detection threshold (also called threshold value), and the unit to be detected M can be compared with the value of the detection threshold (threshold value) to determine whether the unit to be detected is a target or clutter.

[0042] As a further improvement of the present invention, the specific content of step 5 is as follows:

[0043] When the calculated threshold V is less than or equal to the sample M of the unit to be detected, it means that the target is detected, so the distance between the radar and the target is output, and this distance is the result we need; but when the calculated threshold V is greater than the unit to be detected M, it means that clutter is detected. At this time, the calculated distance is the distance between the radar and the clutter, and the distance result should be discarded.

[0044] This way, even in environments with strong winds or large water surface fluctuations, water level changes can still be effectively identified, avoiding false alarms caused by interference echoes. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 It is the overall block diagram of the system of the present invention.

[0046] Figure 2 Detailed circuit diagram of the present invention.

[0047] Figure 3 It is a schematic diagram of the data detection principle of the present invention.

[0048] Figure 4 This is a schematic diagram of the algorithm of the present invention.

[0049] Figure 5 This is a diagram showing the upper computer software of the present invention. DETAILED DESCRIPTION

[0050] The present invention is further described below in conjunction with the accompanying drawings:

[0051] like Figure 1-2 A millimeter-wave radar water level meter shown includes a main control module, which is respectively connected to a power module, a level converter and a communication module, the level converter is connected to a radar sensor, the radar sensor is connected to the power module, and the power module is also connected to the level converter and the communication module.

[0052] The main control module includes the chip STM32L431, the driving module includes the chip A111, the level converter uses the chip TXS0108, the pin 1, pin 3, pin 4, pin 5, pin 6 and pin 9 of the chip TXS0108 are respectively connected to the pin F10, pin K2, pin K3, pin K6, pin J2 and pin K8 of the chip STM32L431, and the pin 12, pin 15, pin 16, pin 17, pin 18 and pin 20 of the chip TXS0108 are respectively connected to the pin 33, pin 37, pin 36, pin 35, pin 34 and pin 38 of the chip A111.

[0053] The power supply module includes a voltage regulator chip U9 and a voltage regulator chip U6. Pin 1 of the voltage regulator chip U9 is grounded, and pin 2 of the voltage regulator chip U9 is connected to the external power supply VIN through a fuse F2. Capacitor C6 and diode D4 are connected in parallel between pin 2 and pin 1 of the voltage regulator chip U9. Capacitor C3, capacitor C40 and capacitor C41 are connected in parallel between pin 3 and pin 1 of the voltage regulator chip U9. Pin 3 of the voltage regulator chip U9 is respectively connected to pin 1, pin 32, pin 48 and pin 64 of the chip STM32L431, and pin 3 of the voltage regulator chip U9 is also connected to pin 19 of the chip TXS0108.

[0054] Pin 1 of the voltage regulator chip U6 is respectively connected to one end of the capacitor C32 and pin 3 of the voltage regulator chip U9, the other end of the capacitor C32 is grounded, pin 2 of the voltage regulator chip U6 is grounded, pin 3 of the voltage regulator chip U6 is connected to pin 3 of the voltage regulator chip U9, pin 4 of the voltage regulator chip U6 is grounded via capacitor C30, pin 5 of the voltage regulator chip U6 is grounded via capacitor C31, pin 3 of the voltage regulator chip U6 is respectively connected to pin C2, pin D1, pin C9, pin D10, pin J9 and pin K9 of chip A111, and pin 3 of the voltage regulator chip U6 is also connected to pin 2 of the chip TXS0108.

[0055] The communication module includes a chip SP3485EN-L / T, wherein pins 1 and 4 of the chip SP3485EN-L / T are respectively connected to pins 17 and 16 of the chip STM32L431, pins 2 and 3 of the chip SP3485EN-L / T are connected and are respectively connected to one end of a resistor R11 and a collector of a transistor Q1, the other end of the resistor R11 is connected to pin 3 of a voltage regulator chip U9, the emitter of the transistor Q1 is grounded, the collector of the transistor Q1 is connected to pin 16 of the chip STM32L431 via a resistor R14, and pin 5 of the chip SP3485EN-L / T is grounded.

[0056] Pin 6 of chip SP3485EN-L / T is respectively connected to one end of resistor R15 and pin 1 of TVS tube D2, the other end of resistor R15 is connected to pin 3 of voltage regulator chip U9, pin 7 of chip SP3485EN-L / T is respectively connected to one end of resistor R9 and pin 2 of TVS tube D2, the other end of resistor R9 is grounded, resistor R12 is connected in parallel between pin 1 and pin 2 of TVS tube D2, pin 3 of TVS tube D2 is grounded, pin 8 of chip SP3485EN-L / T is respectively connected to pin 3 of voltage regulator chip U9 and one end of capacitor C27, the other end of capacitor C27 is grounded.

[0057] like Figure 3-5 The algorithm of a millimeter wave radar water level meter shown in FIG. includes the following contents:

[0058] Step 1, obtain the height from the water surface to the bottom of the water, that is, the water level;

[0059] The A111 chip measures the distance of an object based on the time it takes for a signal to propagate. The formula is:

[0060]

[0061] Where t is the time interval between the radar sending and receiving pulses, d is the distance between the water surface and the radar, and v is the propagation speed of radio in the air. Since the dielectric constant of the radio with a frequency of 60 GHz in the air is 1, the speed of v is 3×10 8 m / s;

[0062] The distance between the height of the radar installation and the bottom of the water measured in advance is b, and bd is the water level height.

[0063] Step 2, the signal transmitted by the A111 chip is processed to obtain the background clutter power level Z;

[0064] Step 2.1, set the sampling of the unit to be detected to M, there are several samples of the protection unit on both sides of the unit to be detected, and there are L / 2 samples of the reference unit outside the protection unit, with a total of L reference units; X is the sum of the L / 2 reference units in front of the protection unit, and Y is the sum of the L / 2 reference units behind the protection unit;

[0065] Step 2.2, assuming that the total background clutter power level of the sample M of the unit to be detected is Z, then the background clutter power level Z=(X+Y) / L.

[0066] Step 3, obtaining the threshold sensitivity factor T;

[0067] Step 3.1. After the signal is detected by the square law, the noise distribution model obeys the exponential distribution, so the probability density function of the corresponding detection threshold is:

[0068]

[0069] Where λ is the parameter of the exponential function;

[0070] Step 3.2. Using the Neyman-Pearson criterion, the probability density distribution function corresponding to the false alarm probability is obtained as

[0071]

[0072] Integrating the above formula, we can get the false alarm probability as:

[0073]

[0074] Step 3.3. From the above formula, we can see that the false alarm probability is only related to the threshold coefficient and the length of the reference unit, where the threshold coefficient is the threshold sensitivity factor T. After the specific values ​​of the two are determined, the false alarm probability remains unchanged; under the premise that the false alarm probability is constant and the reference unit length is determined, the calculation of the threshold sensitivity factor T is as follows:

[0075]

[0076] Step 4, obtaining the detection threshold V;

[0077] V = Z·T.

[0078] Step 5: Output the comparison results.

[0079] When the calculated threshold V is less than or equal to the sample M of the unit to be detected, it means that the target is detected, so the distance between the radar and the target is output, and this distance is the result we need; but when the calculated threshold V is greater than the unit to be detected M, it means that clutter is detected. At this time, the calculated distance is the distance between the radar and the clutter, and the distance result should be discarded.

[0080] In the present invention, the hardware part includes a main control module, a power module, a level converter, a communication module and a radar sensor.

[0081] The main control module uses the STM32L4 chip: as the core of the control system, it contains a wealth of peripherals and interfaces, is responsible for processing sensor data and executing algorithms, has low power consumption, can achieve low-power operation, and is suitable for long-term operation in the wild, especially in environments powered by solar panels or lithium batteries.

[0082] The radar sensor uses the A111 chip for transmitting and receiving millimeter-wave radar signals and is a key sensor for achieving accurate measurement. It integrates modules such as RF, signal processing, and microprocessor, reduces the complexity and cost of the system, can quickly and accurately process radar signals, and provide reliable data output, making it suitable for applications in complex environments.

[0083] The power module adds a self-recovery fuse protection circuit at the power input end. The 3.3V voltage domain uses the HT7133LDO voltage regulator chip, and the 1.8V voltage domain uses the TPSPX3819M5-L-1-8 linear regulator. It is connected to the external power supply to power the internal modules of the sensor, provide a stable power supply for the system, and ensure the stability of the hardware under different working conditions.

[0084] Since the microcontroller operates at 3.3V and the A111 sensor operates at 1.8V, the two cannot communicate directly through SPI. A signal level conversion circuit needs to be added between the two. The level conversion chip uses TXS0108EPWR, which has a 1.8V voltage domain on one side and a 3.3V voltage domain on the other side. It is used to convert signals between different voltage domains to ensure that the various parts of the system can communicate correctly.

[0085] The communication module is used to realize data communication between the water level meter and other systems or host computers. RS485 is used for communication. The chip uses the 485 bus transceiver SP3485EN-L / T, of which PSM712-LF-T7 is a TVS tube for anti-static and surge protection. The sending end uses SS8050 to form a switch circuit.

[0086] The radar water level measurement used in the present invention is obtained by an indirect measurement method. The distance between the height of the radar installation and the water bottom is measured in advance, and then the height from the water surface to the water bottom (ie, the water level) is obtained by measuring the height from the water surface to the radar installation.

[0087] The A111 chip used for transmitting and receiving millimeter-wave radar signals is a pulse coherent radar chip with a radio frequency of 60GHz, which measures the distance of objects based on the time it takes for the signal to propagate.

[0088] The basic formula is

[0089]

[0090] Where t is the time interval between the radar sending and receiving pulses, d is the distance between the object and the radar, and v is the propagation speed of radio in the air. Since the dielectric constant of a 60GHz radio in the air is 1, v is equivalent to the speed of light 3×10 8 m / s.

[0091] Since the distance to the water surface is measured and the background clutter on the water surface is relatively average, a mean-type algorithm is used. The principle of the algorithm is as follows: first sample the reference unit near the unit to be detected, then use these sampled values ​​to estimate the clutter background level of the unit to be detected according to certain criteria, and finally determine the detection threshold in combination with the preset false alarm rate. If the signal strength of the detection unit is higher than this threshold, it is considered that the target is detected. The core idea of ​​the mean class is to use the processing result of the reference window mean as the background power level estimate, multiply it by the threshold multiplication factor to obtain the detection threshold, and make a comparison to determine whether there is a target. Its detection principle is as follows Figure 3 shown.

[0092] Where M is the sampling of the unit to be detected, there are several samples of protection units on both sides of the unit to be detected, and there are L / 2 samples of reference units on the outside of the protection unit, with a total of L reference units. Where X is the sum of the L / 2 reference units in front of the protection unit, and Y is the sum of the L / 2 reference units behind the protection unit. Where Z is the estimate of the total background clutter power level of the unit to be detected M, and the background clutter power level Z of CA-CFAR is (X+Y) / L; T is the threshold sensitivity factor (also called threshold coefficient), V is the detection threshold (also called threshold), V=Z·T. By comparing the value of the unit to be detected M and the detection threshold (threshold), it is determined whether the unit to be detected is a target or clutter. When M>V, it is considered that there is a target and the output is H1, otherwise it is considered that there is no target and the output is H0.

[0093] Usually, after the signal is detected by the square law, the noise distribution model obeys the exponential distribution. Therefore, the probability density function of the corresponding detection threshold is: where λ is the parameter of the exponential function.

[0094]

[0095] By using the Neyman-Pearson criterion, the probability density distribution function of the corresponding false alarm probability is obtained as follows:

[0096]

[0097] Integrating the above formula, we can get the probability of false alarm as:

[0098]

[0099] From the above formula, we can know that the false alarm probability is only related to the threshold coefficient and the length of the reference unit. After the specific values ​​of the two are determined, the false alarm probability remains unchanged. Under the premise that the false alarm probability is constant and the reference unit length is determined, the calculation of the threshold coefficient is as follows.

[0100]

[0101] The signal transmitted by the A111 chip is processed to obtain the reference unit size and the window to be detected, and the background clutter power level Z is calculated by using the above algorithm. A constant false alarm probability is defined in the program. Finally, the threshold sensitivity factor T is obtained under the premise of constant false alarm probability and determined reference unit length. The calculated threshold V of the input signal uses the result obtained by multiplying the threshold sensitivity factor of the detector by the background clutter power level Z. Therefore, dynamically adjusting the threshold is to dynamically adjust the threshold sensitivity factor.

[0102] If the radar detects an abnormal echo intensity, the algorithm can avoid misjudgment by setting a dynamic threshold to ensure the stability of target detection. In this way, even in an environment with strong winds or large water surface fluctuations, it can still effectively identify water level changes and avoid false alarms caused by interference echoes.

[0103] like Figure 4 As shown in the figure, when the calculated threshold value V is less than or equal to the unit to be detected M, it means that the target is detected, so the distance between the radar and the target is output, and this distance is the result we need. However, when the calculated threshold value V is greater than the unit to be detected M, it means that clutter is detected. At this time, the calculated distance is the distance between the radar and the clutter, and the distance result should be discarded.

[0104] Due to the low power consumption and strong anti-interference performance of the hardware structure, the present invention can set the detection threshold by the average background threshold of the front and rear window data to achieve high-precision measurement of the water level, accurately monitor the distribution and use of irrigation water, and ensure that crops get the right amount of water. It can work stably under various environmental conditions, provide stable and reliable data, and can adapt well to the changeable weather conditions often encountered in precision agriculture and agricultural irrigation. The installation of the water level meter is relatively simple, does not require complex civil engineering, can be quickly deployed in the farmland irrigation system, and can reduce its operating and production costs.

[0105] The present invention is not limited to the above-mentioned embodiments. On the basis of the technical solution disclosed herein, technicians in this field can make some substitutions and deformations to some technical features therein according to the disclosed technical content without creative labor, and these substitutions and deformations are all within the protection scope of the present invention.

Claims

1. A millimeter wave radar water level meter, characterized in that: It includes a main control module, which is respectively connected to a power module, a level converter and a communication module, the level converter is connected to a radar sensor, the radar sensor is connected to the power module, and the power module is also connected to the level converter and the communication module.

2. A millimeter wave radar water level meter according to claim 1, characterized in that: The main control module includes the chip STM32L431, the driving module includes the chip A111, the level converter uses the chip TXS0108, the pin 1, pin 3, pin 4, pin 5, pin 6 and pin 9 of the chip TXS0108 are respectively connected to the pin F10, pin K2, pin K3, pin K6, pin J2 and pin K8 of the chip STM32L431, and the pin 12, pin 15, pin 16, pin 17, pin 18 and pin 20 of the chip TXS0108 are respectively connected to the pin 33, pin 37, pin 36, pin 35, pin 34 and pin 38 of the chip A111.

3. A millimeter wave radar water level meter according to claim 2, characterized in that: The power module includes a voltage regulator chip U9 and a voltage regulator chip U6. Pin 1 of the voltage regulator chip U9 is grounded, and pin 2 of the voltage regulator chip U9 is connected to an external power supply VIN via a fuse F2. A capacitor C6 and a diode D4 are connected in parallel between pin 2 and pin 1 of the voltage regulator chip U9. A capacitor C3, a capacitor C40, and a capacitor C41 are connected in parallel between pin 3 and pin 1 of the voltage regulator chip U9. Pin 3 of the voltage regulator chip U9 is respectively connected to pin 1, pin 32, pin 48, and pin 64 of the chip STM32L431. Pin 3 of the voltage regulator chip U9 is also connected to pin 19 of the chip TXS0108. Pin 1 of the voltage regulator chip U6 is respectively connected to one end of the capacitor C32 and pin 3 of the voltage regulator chip U9, the other end of the capacitor C32 is grounded, pin 2 of the voltage regulator chip U6 is grounded, pin 3 of the voltage regulator chip U6 is connected to pin 3 of the voltage regulator chip U9, pin 4 of the voltage regulator chip U6 is grounded via capacitor C30, pin 5 of the voltage regulator chip U6 is grounded via capacitor C31, pin 3 of the voltage regulator chip U6 is respectively connected to pin C2, pin D1, pin C9, pin D10, pin J9 and pin K9 of chip A111, and pin 3 of the voltage regulator chip U6 is also connected to pin 2 of the chip TXS0108.

4. A millimeter wave radar water level meter according to claim 3, characterized in that: The communication module includes a chip SP3485EN-L / T, wherein the pin 1 and pin 4 of the chip SP3485EN-L / T are respectively connected to the pin 17 and pin 16 of the chip STM32L431, the pin 2 and pin 3 of the chip SP3485EN-L / T are connected and are respectively connected to one end of a resistor R11 and a collector of a transistor Q1, the other end of the resistor R11 is connected to the pin 3 of a voltage stabilizing chip U9, the emitter of the transistor Q1 is grounded, the collector of the transistor Q1 is connected to the pin 16 of the chip STM32L431 via a resistor R14, and the pin 5 of the chip SP3485EN-L / T is grounded; Pin 6 of chip SP3485EN-L / T is respectively connected to one end of resistor R15 and pin 1 of TVS tube D2, the other end of resistor R15 is connected to pin 3 of voltage regulator chip U9, pin 7 of chip SP3485EN-L / T is respectively connected to one end of resistor R9 and pin 2 of TVS tube D2, the other end of resistor R9 is grounded, resistor R12 is connected in parallel between pin 1 and pin 2 of TVS tube D2, pin 3 of TVS tube D2 is grounded, pin 8 of chip SP3485EN-L / T is respectively connected to pin 3 of voltage regulator chip U9 and one end of capacitor C27, the other end of capacitor C27 is grounded.

5. An algorithm for a millimeter wave radar water level meter, characterized in that: Include the following: Step 1, obtain the height from the water surface to the bottom of the water, that is, the water level; Step 2, the signal transmitted by the A111 chip is processed to obtain the background clutter power level Z; Step 3, obtaining the threshold sensitivity factor T; Step 4, obtaining the detection threshold V; Step 5: Output the comparison results.

6. The algorithm of a millimeter wave radar water level meter according to claim 5, characterized in that: The A111 chip measures the distance of an object based on the time it takes for a signal to propagate. The formula is: Where t is the time interval between the radar sending and receiving pulses, d is the distance between the water surface and the radar, and v is the propagation speed of radio in the air. Since the dielectric constant of the radio with a frequency of 60 GHz in the air is 1, the speed of v is 3×10 8 m / s; The distance between the height of the radar installation and the bottom of the water measured in advance is b, and bd is the water level height.

7. The algorithm of a millimeter wave radar water level meter according to claim 6, characterized in that: The specific contents of step 2 are as follows: Step 2.1, set the sampling of the unit to be detected to M, there are several samples of the protection unit on both sides of the unit to be detected, and there are L / 2 samples of the reference unit outside the protection unit, with a total of L reference units; X is the sum of the L / 2 reference units in front of the protection unit, and Y is the sum of the L / 2 reference units behind the protection unit; Step 2.2, assuming that the total background clutter power level of the sample M of the unit to be detected is Z, then the background clutter power level Z=(X+Y) / L.

8. The algorithm of the millimeter wave radar water level meter according to claim 7, characterized in that: The specific contents of step 3 are as follows Step 3.

1. After the signal is detected by the square law, the noise distribution model obeys the exponential distribution, so the probability density function of the corresponding detection threshold is: Where λ is the parameter of the exponential function; Step 3.

2. Using the Neyman-Pearson criterion, the probability density distribution function corresponding to the false alarm probability is obtained as Integrating the above formula, we can get the false alarm probability as: Step 3.

3. From the above formula, we can see that the false alarm probability is only related to the threshold coefficient and the length of the reference unit, where the threshold coefficient is the threshold sensitivity factor T. After the specific values ​​of the two are determined, the false alarm probability remains unchanged; under the premise that the false alarm probability is constant and the reference unit length is determined, the calculation of the threshold sensitivity factor T is as follows:

9. The algorithm of a millimeter wave radar water level meter according to claim 8, characterized in that: V = Z·T.

10. The algorithm of a millimeter wave radar water level meter according to claim 9, characterized in that: The specific contents of step 5 are as follows: When the calculated threshold V is less than or equal to the sample M of the unit to be detected, it means that the target is detected, so the distance between the radar and the target is output, and this distance is the result we need; but when the calculated threshold V is greater than the unit to be detected M, it means that clutter is detected. At this time, the calculated distance is the distance between the radar and the clutter, and the distance result should be discarded.

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