Optical path delay-based liquid level measurement method, device, equipment and storage medium

Abstract

This invention relates to the field of photoelectric sensing and measurement technology, specifically disclosing a liquid level measurement method, device, equipment, and storage medium based on optical path delay. This invention, based on the principle of optical path delay, controls a laser emitting device to emit a measurement laser beam that penetrates the liquid surface and enters the internal medium. The propagation time delay of the laser beam in the internal medium is obtained, and the round-trip path length is calculated by combining this with the refractive index of the medium. The liquid level is then calculated using the reflection characteristics of the target reflection interface. This avoids irregular scattering interference caused by foam layers, viscous liquid films, or suspended particles on the liquid surface, and solves the problems of echo signal attenuation and measurement value jumps under complex operating conditions in the liquid surface reflection method, thereby improving the reliability and long-term operational stability of liquid level measurement.

Description

Technical Field

[0001] This invention relates to the field of photoelectric sensing and measurement technology, and in particular to a liquid level measurement method, apparatus, device, and storage medium based on optical path delay. Background Technology

[0002] Laser level measurement technology has wide applications in industrial scenarios such as chemical storage and transportation, petroleum refining, and food processing. Currently, most mainstream laser level gauges use the liquid surface reflection method for measurement. This method works by utilizing the reflection of a laser pulse after it propagates through the air to the liquid surface. By accurately measuring the time difference between the emitted and echo signals and combining this with the speed of light constant, the optical path length in the air segment is calculated, and thus the liquid level height is estimated. Under ideal conditions, this method can achieve non-contact, rapid measurement. However, when the surface of the measured liquid contains a foam layer, a viscous film, or suspended particles, the liquid surface reflection interface will exhibit irregular scattering characteristics, leading to drastic fluctuations or even complete attenuation of the echo signal intensity. This easily causes jumps in the measured value and false level readings, severely restricting the long-term stable operation and measurement reliability of level monitoring devices under complex conditions.

[0003] Therefore, there is an urgent need to provide a technical solution to address the above problems. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a liquid level measurement method, apparatus, device, and storage medium based on optical path delay.

[0005] In a first aspect, the present invention provides a liquid level measurement method based on optical path delay, the technical solution of which is as follows: A laser emitting device is controlled to emit a measuring laser beam toward the surface of the liquid to be tested, and at least a portion of the energy of the measuring laser beam penetrates the liquid surface and enters the internal medium of the liquid to be tested; The laser beam that propagates along the internal propagation path in the internal medium and is reflected back by the target reflection interface is received as an echo signal. Obtain the propagation time difference from the emission of the measurement laser beam to the receipt of the echo signal; Based on the refractive index of the internal medium and the propagation time difference, the round-trip path length of the measuring laser beam in the internal medium is calculated; The measured liquid level value of the liquid under test is calculated based on the geometric relationship between the round-trip path length and the depth of the target reflective interface relative to the liquid surface.

[0006] The beneficial effects of the liquid level measurement method based on optical path delay of the present invention are as follows: The method of this invention, based on the principle of optical path delay, controls a laser emitting device to emit a measurement laser beam that penetrates the liquid surface and enters the internal medium. The propagation time delay of the laser beam in the internal medium is obtained, and the round-trip path length is calculated by combining the refractive index of the medium. The liquid level is calculated by utilizing the reflection characteristics of the target reflection interface. This avoids irregular scattering interference caused by foam layers, viscous liquid films, or suspended particles on the liquid surface, and solves the problems of echo signal attenuation and measurement value jumps under complex working conditions in the liquid surface reflection method, thereby improving the reliability of liquid level measurement and long-term operational stability.

[0007] Based on the above scheme, the liquid level measurement method based on optical path delay of the present invention can be further improved as follows.

[0008] In one alternative approach, the step of controlling the laser emitting device to emit a measuring laser beam toward the surface of the liquid to be measured includes: Configure the emission wavelength of the measurement laser beam, wherein the light absorption coefficient of the emission wavelength in the internal medium is lower than a predetermined threshold; The laser emitting device is controlled to emit the measuring laser beam according to the emission wavelength, and the measuring laser beam is adjusted to be incident perpendicular to the liquid surface; The measuring laser beam changes its propagation speed at the liquid surface according to the refractive index of the internal medium, and at least a portion of the energy of the measuring laser beam enters the internal medium.

[0009] The advantages of using the above-mentioned optional method are: by further selecting an emission wavelength with an absorption coefficient lower than a predetermined threshold, the transmission loss of the laser in the internal medium is reduced, ensuring that the energy of the measurement laser beam stably penetrates the liquid surface and enters the liquid interior, providing an optical basis for subsequent accurate calculation of the round-trip path length.

[0010] In one alternative approach, the step of receiving a laser beam that propagates along an internal propagation path in the internal medium and returns after being reflected by a target reflecting interface as an echo signal includes: The laser beam reflected from the target reflective interface is received by a photodetector, and the optical signal of the laser beam is converted into an analog electrical signal by the photodetector. The analog electrical signal is subjected to bandpass filtering to remove noise outside the preset frequency band, resulting in a filtered signal. Based on the emission time of the measured laser beam and the estimated reflection time window of the target reflection interface, a signal segment corresponding to the estimated reflection time window is extracted from the filtered signal; The pulse signal with an amplitude exceeding a preset threshold in the signal segment is identified as the echo signal; The target reflective interface is the interface between the liquid to be tested and the bottom wall of the container holding the liquid to be tested.

[0011] The advantages of adopting the above-mentioned optional method are as follows: by combining bandpass filtering with time window truncation, the echo signal of the target reflection interface can be extracted from the complex noise environment, avoiding signal interference caused by non-target reflection, ensuring that the liquid level calculation is based on the stable bottom wall reflection signal, and improving the measurement anti-interference capability.

[0012] In one alternative approach, the step of obtaining the propagation time difference from the emission of the measuring laser beam to the receipt of the echo signal includes: The emission time of the measurement laser beam is recorded as the first timestamp, and the time when the pulse signal in the echo signal is identified is recorded as the second timestamp; wherein, the first timestamp and the second timestamp are generated based on the same clock source; The time interval between the first timestamp and the second timestamp is determined as the propagation time difference.

[0013] The advantages of adopting the above-mentioned optional method are as follows: by recording the transmission and reception times through a unified clock source, the drift error between different clock sources is eliminated, the measurement accuracy of the propagation time difference is improved, thereby reducing the liquid level calculation error caused by time measurement deviation and improving the accuracy of the measurement results.

[0014] In one alternative approach, the step of calculating the round-trip path length of the measuring laser beam in the internal medium based on the refractive index of the internal medium and the propagation time difference includes: Obtain the refractive index of the internal medium at the emission wavelength of the measuring laser beam; Based on the refractive index and the speed of light in vacuum, the propagation speed of the measured laser beam in the internal medium is calculated; Based on the reflective or penetrating optical path structure, and considering the relationship between the total height of the container, the liquid level, and the optical path length of the air section and the liquid section, the round-trip path length of the measuring laser beam in the internal medium is calculated using the propagation time difference.

[0015] The advantages of adopting the above-mentioned optional method are as follows: by combining the refractive index of the internal medium with the speed of light in a vacuum, a mathematical conversion relationship between optical path delay and geometric path length is established, and the time domain measurement results are accurately mapped to the round-trip path length in the spatial domain, providing an accurate physical quantity basis for liquid level calculation.

[0016] In one alternative approach, the step of calculating the measured liquid level value of the liquid under test based on the geometric relationship between the round-trip path length and the depth of the target reflective interface relative to the liquid surface includes: Based on the geometric relationship, the round-trip path length is converted into the depth of the target reflective interface relative to the liquid surface; Obtain the installation reference height of the bottom wall of the container holding the liquid to be tested; The measured liquid level value of the liquid to be tested is obtained by superimposing the installation reference height and the depth.

[0017] The advantages of adopting the above optional method are: by further converting the round-trip path length into the depth of the target reflective interface relative to the liquid surface and superimposing it with the installation reference height of the container bottom wall, the accurate conversion from optical measurement value to actual liquid level height can be achieved, meeting the liquid level measurement needs under different installation scenarios.

[0018] In one alternative approach, it also includes: Within a single measurement cycle, the laser emitting device is controlled to emit the measuring laser beam at least twice, and at least two measuring liquid level values ​​are obtained accordingly. Calculate the statistical distribution parameters of the at least two measured liquid level values; When the statistical distribution parameters meet the preset consistency conditions, the arithmetic mean of the at least two measured liquid level values ​​is used as the final liquid level output value.

[0019] The advantages of adopting the above-mentioned optional method are as follows: by performing multiple samplings within a single measurement cycle and judging measurement consistency based on statistical distribution parameters, the influence of random fluctuations is suppressed by using the arithmetic mean, thereby improving the stability and repeatability of the liquid level output results and avoiding misjudgments caused by single measurement anomalies.

[0020] Secondly, the present invention provides a liquid level measuring device based on optical path delay, the technical solution of which is as follows: The control module is used to control the laser emitting device to emit a measuring laser beam toward the surface of the liquid to be tested, wherein at least a portion of the energy of the measuring laser beam penetrates the liquid surface and enters the internal medium of the liquid to be tested; The receiving module is used to receive the laser beam that propagates along the internal propagation path in the internal medium and returns after being reflected by the target reflection interface as an echo signal. An acquisition module is used to acquire the propagation time difference from the emission of the measurement laser beam to the receipt of the echo signal; The calculation module is used to calculate the round-trip path length of the measuring laser beam in the internal medium based on the refractive index of the internal medium and the propagation time difference; The measurement module is used to calculate the measured liquid level value of the liquid to be measured based on the geometric relationship between the round-trip path length and the depth of the target reflective interface relative to the liquid surface.

[0021] The beneficial effects of the liquid level measuring device based on optical path delay of the present invention are as follows: The device of this invention controls a laser emitting device to emit a measurement laser beam that penetrates the liquid surface and enters the internal medium based on the principle of optical path delay. It obtains the propagation time delay of the laser beam in the internal medium and calculates the round-trip path length by combining it with the refractive index of the medium. It uses the reflection characteristics of the target reflection interface to calculate the liquid level, avoiding irregular scattering interference caused by liquid surface foam layers, viscous liquid films or suspended particles. It solves the problem of echo signal attenuation and measurement value jump in the liquid surface reflection method under complex working conditions, thereby improving the reliability of liquid level measurement and long-term operational stability.

[0022] Thirdly, the technical solution of an electronic device according to the present invention is as follows: It includes a memory, a processor, and a program stored in the memory and running on the processor, wherein the processor executes the program to implement the steps of the liquid level measurement method based on optical path delay as described in this invention.

[0023] Fourthly, the technical solution of a computer-readable storage medium provided by the present invention is as follows: The computer-readable storage medium stores instructions that, when read, cause the computer-readable storage medium to perform the steps of the optical path delay-based liquid level measurement method of the present invention.

[0024] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, and in order to make the above and other objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention are described below. Attached Figure Description

[0025] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings: Figure 1 This is a schematic flowchart of an embodiment of a liquid level measurement method based on optical path delay according to the present invention; Figure 2 This is one of the schematic diagrams illustrating the principle of liquid level measurement. Figure 3 This is the second schematic diagram of the liquid level measurement principle; Figure 4 This is a schematic diagram of an embodiment of the liquid level measuring device based on optical path delay according to the present invention; Figure 5 This is a schematic diagram of an embodiment of an electronic device according to the present invention. Detailed Implementation

[0026] Exemplary embodiments of the invention will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the invention are shown in the drawings, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein.

[0027] Figure 1 This diagram illustrates a flowchart of an embodiment of a liquid level measurement method based on optical path delay provided by the present invention. This method can be executed by an electronic device such as a terminal device or a server. The terminal device can be any fixed or mobile terminal, such as a user equipment (UE), mobile device, user terminal, terminal, cellular phone, cordless phone, personal digital assistant (PDA), handheld device, computing device, vehicle-mounted device, or wearable device. The server can be a single server or a server cluster consisting of multiple servers. Any electronic device can implement the liquid level measurement method based on optical path delay by having its processor call computer-readable instructions stored in its memory. Figure 1 As shown, it includes the following steps: S1. Control the laser emitting device to emit a measuring laser beam toward the surface of the liquid to be tested, wherein at least a portion of the energy of the measuring laser beam penetrates the liquid surface and enters the internal medium of the liquid to be tested.

[0028] The laser emitting device refers to a device that generates and directionally emits coherent light pulses for liquid level measurement; for example, a laser installed on the top of a storage tank emits a pulsed laser beam with a wavelength of 1550 nm. The liquid to be measured refers to the target liquid substance whose liquid level needs to be measured; for example, industrial diesel fuel stored in a cylindrical vertical storage tank. The measuring laser beam refers to a light pulse emitted by the laser emitting device specifically for performing liquid level measurement; for example, a laser beam with a center wavelength of 1550 nm and a pulse width of 10 ns is directed towards the diesel fuel surface. The internal medium refers to the liquid to be measured itself within which the laser beam propagates after penetrating the liquid surface; for example, diesel fuel inside a storage tank is the medium through which the laser beam propagates after entering.

[0029] S2. Receive the laser beam that propagates along the internal propagation path in the internal medium and returns after being reflected by the target reflection interface as an echo signal.

[0030] The internal propagation path refers to the actual optical path traversed by the laser beam within the internal medium, from the point of incidence to the target reflecting interface and back to the point of incidence. For example, after the laser beam enters the diesel fuel vertically, it propagates downwards in a straight line to the bottom of the tank and then returns in a straight line along the same path. The laser beam refers to a highly coherent and directional light beam; for example, light reflected from the target reflecting interface and returning to the receiving optical window. The echo signal refers to the signal of the laser beam reflected from the target reflecting interface and returning to the receiving device; for example, a laser pulse reflected back from the bottom wall of the storage tank received by a photodetector.

[0031] S3. Obtain the propagation time difference from the emission of the measurement laser beam to the receipt of the echo signal.

[0032] The propagation time difference refers to the time difference between the emission time of the measured laser beam and the time when its corresponding echo signal is effectively identified; for example, the interval Δt between the laser pulse emission time and the time when the peak pulse returned from the bottom of the tank is received is 200ns.

[0033] S4. Calculate the round-trip path length of the measuring laser beam in the internal medium based on the refractive index of the internal medium and the propagation time difference.

[0034] The refractive index, denoted as n, is the ratio of the speed of light in a vacuum to its speed of light in a specific medium. For example, the refractive index n of diesel fuel at 20°C for a 1550nm wavelength laser is approximately 1.45. The round-trip path length, denoted as L, is the total geometric path length of the laser beam as it travels through the internal medium from the point of incidence to the target reflecting interface and back. For example, the calculated total distance L traveled by the laser beam in diesel fuel is 27.6m.

[0035] S5. Based on the geometric relationship between the round-trip path length and the depth of the target reflective interface relative to the liquid surface, calculate the measured liquid level value of the liquid to be measured.

[0036] The depth of the target reflective interface relative to the liquid surface refers to the vertical distance, denoted as h, between the target reflective interface and the upper surface of the liquid being measured; for example, the vertical distance h from the upper surface of diesel fuel to the bottom wall of the tank. Geometric relationship refers to the defined mathematical correlation between various geometric quantities under a specific spatial configuration; for example, under conditions of perpendicular laser incidence, the relationship between the round-trip path length L and the depth h is L = 2h. The measured liquid level value refers to the numerical value of the height of the upper surface of the liquid being measured relative to a specified reference plane, calculated using the aforementioned method; for example, the calculated height of the diesel fuel level relative to the reference point at the bottom of the tank is 10.5m.

[0037] The technical solution of this embodiment uses the principle of optical path delay to control a laser emitting device to emit a measurement laser beam that penetrates the liquid surface and enters the internal medium. The propagation time delay of the laser beam in the internal medium is obtained and the round-trip path length is calculated by combining the refractive index of the medium. The liquid level is calculated by using the reflection characteristics of the target reflection interface. This avoids irregular scattering interference caused by foam layers, viscous liquid films or suspended particles on the liquid surface, and solves the problem of echo signal attenuation and measurement value jumps under complex working conditions in the liquid surface reflection method. This improves the reliability of liquid level measurement and the stability of long-term operation.

[0038] In one alternative approach, S1 specifically includes: Configure the emission wavelength of the measurement laser beam, wherein the light absorption coefficient of the emission wavelength in the internal medium is lower than a predetermined threshold.

[0039] The emission wavelength, denoted as λ, refers to the center wavelength of the measured laser beam. For example, to reduce medium absorption, the emission wavelength λ is configured to 1550 nm. The optical absorption coefficient, denoted as α, is a quantitative parameter representing the ability of a medium to absorb and attenuate light of a specific wavelength. For example, diesel fuel has a low optical absorption coefficient α for 1550 nm laser light, less than 0.1 nm. -1 A predetermined threshold refers to a numerical limit set in advance to achieve a specific technical purpose; for example, to ensure signal strength, the wavelength selection must satisfy the requirement that the light absorption coefficient α < 0.2m. -1 .

[0040] The laser emitting device is controlled to emit the measuring laser beam according to the emission wavelength, and the measuring laser beam is adjusted to be incident perpendicular to the liquid surface.

[0041] The measuring laser beam changes its propagation speed at the liquid surface according to the refractive index of the internal medium, and at least a portion of the energy of the measuring laser beam enters the internal medium.

[0042] It should be noted that at least part of the energy refers to the portion of the total energy of the measured laser beam that successfully penetrates the liquid surface and enters the internal medium; for example, more than 90% of the laser energy penetrates the liquid surface and enters the diesel fuel.

[0043] In the above-mentioned optional methods, by further selecting an emission wavelength with an absorption coefficient lower than a predetermined threshold, the transmission loss of the laser in the internal medium is reduced, ensuring that the energy of the measurement laser beam stably penetrates the liquid surface and enters the liquid interior, providing an optical basis for subsequent accurate calculation of the round-trip path length.

[0044] In one alternative approach, S2 specifically includes: The laser beam reflected from the target reflective interface is received by a photodetector, and the optical signal of the laser beam is converted into an analog electrical signal by the photodetector.

[0045] In this context, a photodetector refers to a sensor that converts incident light signals into corresponding electrical signals; for example, a photodiode with a response wavelength of 1550 nm is used to receive reflected laser light. An optical signal refers to a signal that carries information in the form of light waves; for example, a laser pulse reflected from the bottom wall of a storage tank and illuminating the photosensitive surface of a photodetector. An analog electrical signal refers to a voltage or current signal output by a photodetector whose amplitude changes continuously with time; for example, a microvolt-level voltage pulse output by a photodiode that is proportional to the intensity of the received light.

[0046] The analog electrical signal is subjected to bandpass filtering to remove noise outside the preset frequency band, resulting in a filtered signal.

[0047] Bandpass filtering refers to an electronic processing procedure that allows signals within a specific frequency range to pass through while suppressing signals outside that range. For example, an electronic filter may only allow signals with a certain bandwidth and a center frequency close to the laser pulse repetition frequency (e.g., 10 kHz) to pass through. The filtered signal refers to the signal obtained after the original analog electrical signal has undergone bandpass filtering. For example, after filtering, low-frequency and high-frequency noise in a voltage signal is suppressed, and the pulse profile becomes clearer.

[0048] Based on the emission time of the measured laser beam and the estimated reflection time window of the target reflective interface, a signal segment corresponding to the estimated reflection time window is extracted from the filtered signal.

[0049] Here, the emission time refers to the precise time point at which the laser beam leaves the laser emitting device, denoted as t0; for example, recording the rising edge trigger time of the laser driving current as t0. The estimated reflection time window refers to the range of time the echo signal is likely to arrive, estimated in advance based on known parameters; for example, estimating that the echo signal will arrive within a time interval of 100ns to 300ns after emission. A signal segment refers to a data segment corresponding to a specific time interval extracted from a continuous time-domain signal; for example, a voltage data segment extracted from a filtered signal between t0+100ns and t0+300ns.

[0050] The pulse signal with an amplitude exceeding a preset threshold in the signal segment is identified as the echo signal.

[0051] The preset threshold refers to the amplitude threshold set in advance to determine the validity of a signal; for example, a voltage threshold of 50mV is set, and signal peaks exceeding this value are identified as valid signals. A pulse signal refers to an electrical signal with a pulse-like shape, where the amplitude rises sharply and then falls within a short period of time; for example, a sharp voltage peak in a signal segment with an amplitude far exceeding the background noise.

[0052] It should be noted that the target reflective interface is the interface between the liquid to be tested and the bottom wall of the container holding the liquid to be tested.

[0053] The container bottom wall refers to the bottom structure of the container holding the liquid to be tested; for example, the flat bottom of a steel storage tank for diesel fuel. The interface refers to the boundary formed by the contact between two substances with different physical properties; for example, the interface formed by the contact between diesel fuel and the steel bottom wall of a storage tank.

[0054] In the above-mentioned optional methods, the echo signal of the target reflection interface is further extracted from the complex noise environment by combining bandpass filtering and time window truncation, so as to avoid signal interference caused by non-target reflection, ensure that the liquid level calculation is based on the stable bottom wall reflection signal, and improve the measurement anti-interference capability.

[0055] In one alternative approach, S3 specifically includes: The emission time of the measurement laser beam is recorded as the first timestamp, and the time when the pulse signal in the echo signal is identified is recorded as the second timestamp; wherein the first timestamp and the second timestamp are generated based on the same clock source.

[0056] The first timestamp refers to the time stamp data recording the emission time (t0) of the measured laser beam; for example, a 64-bit digital code representing time t0 recorded and output by a clock circuit. The second timestamp refers to the time stamp data recording the moment the pulse signal in the echo signal is identified; for example, a 64-bit digital code representing the arrival time of the pulse peak recorded and output by the same clock circuit. The same clock source refers to a clock generator that provides a unified time reference for multiple units in the system that require time synchronization; for example, a high-stability crystal oscillator simultaneously provides clock signals for both the transmission time recording unit and the reception time recording unit.

[0057] The time interval between the first timestamp and the second timestamp is determined as the propagation time difference.

[0058] The time interval refers to the duration between two time points, i.e., the propagation time difference Δt; for example, the difference between the second timestamp and the first timestamp calculated by the time-to-digital converter is Δt = 200 ns.

[0059] In the above-mentioned optional methods, the transmission and reception times are further recorded by a unified clock source to eliminate drift errors between different clock sources, improve the measurement accuracy of propagation time difference, thereby reducing the liquid level calculation error caused by time measurement deviation and improving the accuracy of measurement results.

[0060] In one alternative approach, S4 specifically includes: Obtain the refractive index of the internal medium at the emission wavelength of the measuring laser beam.

[0061] Based on the refractive index and the speed of light in vacuum, the propagation speed of the measured laser beam in the internal medium is calculated.

[0062] The speed of light in a vacuum refers to the speed at which light travels in a vacuum, denoted as c, where c ≈ 299,792,458 m / s. The propagation speed refers to the speed at which light travels in a specific medium, denoted as v; for example, the propagation speed of a laser beam in diesel fuel is v = c / n ≈ 206,753,419 m / s.

[0063] Based on the reflective or penetrating optical path structure, and considering the relationship between the total height of the container, the liquid level, and the optical path length of the air section and the liquid section, the round-trip path length of the measuring laser beam in the internal medium is calculated using the propagation time difference.

[0064] In the above-mentioned optional methods, by combining the refractive index of the internal medium with the speed of light in a vacuum, a mathematical conversion relationship between optical path delay and geometric path length is established, which accurately maps the time-domain measurement results into the round-trip path length in the spatial domain, providing an accurate physical quantity basis for liquid level calculation.

[0065] In one alternative approach, S5 specifically includes: Based on the geometric relationship, the round-trip path length is converted into the depth of the target reflective interface relative to the liquid surface.

[0066] Obtain the installation reference height of the bottom wall of the container holding the liquid to be tested.

[0067] The installation reference height refers to the height of a fixed horizontal reference surface that serves as the zero point reference for liquid level measurement; for example, the height value of the upper surface of a fixed flange at the bottom of the storage tank, determined by measurement.

[0068] The measured liquid level value of the liquid to be tested is obtained by superimposing the installation reference height and the depth.

[0069] In the above-mentioned optional methods, the round-trip path length is further converted into the depth of the target reflective interface relative to the liquid surface and superimposed with the installation reference height of the container bottom wall to achieve accurate conversion from optical measurement value to actual liquid level height, thus meeting the liquid level measurement needs under different installation scenarios.

[0070] In one alternative approach, it also includes: Within a single measurement cycle, the laser emitting device is controlled to emit the measuring laser beam at least twice, and at least two measuring liquid level values ​​are obtained accordingly.

[0071] The single measurement cycle refers to the time required to complete a full measurement process from laser emission to liquid level calculation and output; for example, the entire process from triggering the first laser emission to outputting the liquid level result takes 50ms.

[0072] Calculate the statistical distribution parameters of the at least two measured liquid level values.

[0073] Among them, the statistical distribution parameter refers to a statistic used to describe the distribution characteristics of a set of measurement data; for example, the standard deviation σ of a set of liquid level values ​​obtained from multiple measurements within a single measurement cycle.

[0074] When the statistical distribution parameters meet the preset consistency conditions, the arithmetic mean of the at least two measured liquid level values ​​is used as the final liquid level output value.

[0075] The preset consistency condition refers to the logical conditions set in advance to determine the reliability and consistency of a set of measurement results; for example, the set condition is: the range R of five measurement values ​​≤ 2mm. The final liquid level output value refers to the liquid level value output as the final result of this measurement after verification, screening, or fusion processing; for example, when multiple measurement values ​​meet the consistency condition, their arithmetic mean of 10.502m is taken as the final liquid level output value.

[0076] In the above-mentioned optional methods, further sampling is performed multiple times within a single measurement cycle, and the measurement consistency is judged based on statistical distribution parameters. The influence of random fluctuations is suppressed by using the arithmetic mean, thereby improving the stability and repeatability of the liquid level output results and avoiding misjudgments caused by single measurement anomalies.

[0077] In this embodiment, it should be noted that: based on the physical principle of optical path delay, the propagation speed of laser light in the medium With the refractive index of the medium Inversely proportional, the relationship is ,in The speed of light in a vacuum. When a laser beam passes perpendicularly through both air and liquid media, the total propagation time is... It is the sum of the propagation time of the laser in the air segment and the liquid segment. Due to the refractive index of the liquid... Greater than the refractive index of air When a laser beam propagates through a liquid, an optical path delay occurs, the amount of which is related to the liquid level. They are in a linear proportional relationship.

[0078] The apparatus for implementing the above method mainly includes a laser emitting device, a high-precision timing unit, a receiving device, and a computing module. The laser emitting device is mounted on the top of the container and is used to emit a pulsed measurement laser beam vertically downwards. The high-precision timing unit is a circuit with picosecond-level time resolution, such as a time-to-digital converter. The receiving device is used to receive the laser signal, and there are two optional implementation schemes. Scheme A is a reflective reception, where the receiving device is mounted on the top of the container to receive the echo signal reflected back from the bottom of the container. Scheme B is a penetrating reception, where the receiving device is mounted on the bottom of a transparent container to directly receive the laser beam after it penetrates the liquid. The computing module is used to calculate the propagation time... Calculate liquid level height .

[0079] The optical path and formulas for the two implementation schemes are derived in detail: The first implementation scheme uses a reflective optical path. For example... Figure 2 As shown, both the laser emitting and receiving devices are located at the top of the container. The measuring laser beam is emitted from the top, passes through the air layer, penetrates the surface of the liquid to be measured, enters the internal medium, and is reflected at the target reflection interface on the bottom wall of the container, returning along the same path to the receiving device at the top. In this scheme, the receiving device ignores the liquid surface reflection signal and only receives the echo signal from the bottom wall of the container. Let the total vertical installation height of the laser emitting device from the bottom wall of the container be... The liquid level height of the liquid to be measured is air refractive index Approximately 1, the refractive index of the liquid is The speed of light in a vacuum is Assume that when there is no liquid, the time it takes for the receiving device to receive the signal is... The time it takes to receive a signal when there is liquid is Based on the principle of optical path delay, the following formula is established: The total time t when there is liquid consists of the round-trip time of the air segment and the round-trip time of the liquid segment: Air segment distance: Time spent in the air: ; Liquid segment distance: Time spent in liquid: ; therefore: Total time without liquid for: Combining the above formulas, the formula for calculating the liquid level height h is as follows: The second implementation scheme uses a through-type optical path. For example... Figure 3 As shown, the laser emitting device is installed at the top of the container, and the receiving device is installed at the bottom of the transparent container. The laser beam is emitted from the top, passes through the air layer and the liquid layer in a single path, and is directly received by the receiving device at the bottom. Based on the principle of optical path delay, the following formula is established: The total time t when liquid is present consists of the one-way travel time of the air segment and the one-way travel time of the liquid segment: Air segment distance: Time spent in the air: ; Liquid segment distance: Time spent in liquid: ; therefore: Total time without liquid for: By combining the above formulas, the formula for calculating the liquid level height h can be obtained as follows: The following is a specific implementation example to verify the reflection scheme. This example uses formula ( The time is calculated, and the sensitivity of liquid level change is derived by time difference to verify the time resolution and measurement accuracy of this embodiment.

[0080] Set installation height The height is set to 500mm. The value is 10.0 mm, and the target measurement accuracy is 1 mm. Taking water as an example, the liquid refractive index... Set to 1.33. Speed ​​of light. Values mm / s, or 300 mm / ns. The core hardware uses a time-to-digital converter with a time resolution of [missing information]. It is 100 ps. When the liquid level is high When the length is 10mm, substitute the values ​​into the reflection formula to calculate the total propagation time. : When the liquid level rises by 1mm to When mm, calculate the total propagation time. : Time difference caused by a 1mm change in liquid level Since the original time resolution of the time-to-digital converter used is 100 ps, ​​which is higher than the required 2.2 ps time difference, an averaging method based on multiple measurements is needed to improve the equivalent resolution. Equivalent resolution With average number of times The relationship follows: in The original hardware resolution is 100ps. Given an effective resolution of 2.2 ps, solve for... get: This means that, in order to effectively distinguish the 2.2ps time difference corresponding to a 1mm liquid level change on a timing unit with a raw resolution of 100ps, theoretically each set of valid data needs to be averaged from at least approximately 2100 raw measurements.

[0081] The method in this embodiment is based on penetration measurement and does not rely on the specular reflection characteristics of the liquid surface. Even if there are slight fluctuations in the liquid surface or it is covered by a semi-transparent film, as long as the measuring laser beam can penetrate the liquid surface and reach the reflection interface at the bottom of the container, the measurement can be completed. Its stability is superior to the traditional liquid surface reflection method. This method obtains liquid level information by calculating the entire optical path delay, avoiding signal loss problems caused by liquid surface scattering or defocusing, and has stronger anti-interference capabilities. In addition, the method has a flexible structural design, supporting the installation of the transmitting and receiving devices on the same side or opposite sides, and can adapt to the liquid level measurement needs of containers with different transparency.

[0082] Figure 4 A schematic diagram of an embodiment of a liquid level measuring device 200 based on optical path delay provided by the present invention is shown. Figure 4 As shown, the liquid level measuring device 200 based on optical path delay includes: Control module 201 is used to control the laser emitting device to emit a measuring laser beam toward the surface of the liquid to be tested, wherein at least a portion of the energy of the measuring laser beam penetrates the liquid surface and enters the internal medium of the liquid to be tested; The receiving module 202 is used to receive the laser beam that propagates along the internal propagation path in the internal medium and returns after being reflected by the target reflection interface as an echo signal. Acquisition module 203 is used to acquire the propagation time difference from the emission of the measurement laser beam to the receipt of the echo signal; The calculation module 204 is used to calculate the round-trip path length of the measuring laser beam in the internal medium based on the refractive index of the internal medium and the propagation time difference. The measurement module 205 is used to calculate the measured liquid level value of the liquid to be measured based on the geometric relationship between the round-trip path length and the depth of the target reflective interface relative to the liquid surface.

[0083] In an alternative embodiment, the control module 201 is specifically used for: Configure the emission wavelength of the measurement laser beam, wherein the light absorption coefficient of the emission wavelength in the internal medium is lower than a predetermined threshold; The laser emitting device is controlled to emit the measuring laser beam according to the emission wavelength, and the measuring laser beam is adjusted to be incident perpendicular to the liquid surface; The measuring laser beam changes its propagation speed at the liquid surface according to the refractive index of the internal medium, and at least a portion of the energy of the measuring laser beam enters the internal medium.

[0084] In one alternative embodiment, the receiving module 202 is specifically used for: The laser beam reflected from the target reflective interface is received by a photodetector, and the optical signal of the laser beam is converted into an analog electrical signal by the photodetector. The analog electrical signal is subjected to bandpass filtering to remove noise outside the preset frequency band, resulting in a filtered signal. Based on the emission time of the measured laser beam and the estimated reflection time window of the target reflection interface, a signal segment corresponding to the estimated reflection time window is extracted from the filtered signal; The pulse signal with an amplitude exceeding a preset threshold in the signal segment is identified as the echo signal; The target reflective interface is the interface between the liquid to be tested and the bottom wall of the container holding the liquid to be tested.

[0085] In an alternative embodiment, the acquisition module 203 is specifically used for: The emission time of the measurement laser beam is recorded as the first timestamp, and the time when the pulse signal in the echo signal is identified is recorded as the second timestamp; wherein, the first timestamp and the second timestamp are generated based on the same clock source; The time interval between the first timestamp and the second timestamp is determined as the propagation time difference.

[0086] In an alternative embodiment, the computing module 204 is specifically used for: Obtain the refractive index of the internal medium at the emission wavelength of the measuring laser beam; Based on the refractive index and the speed of light in vacuum, the propagation speed of the measured laser beam in the internal medium is calculated; Based on the reflective or penetrating optical path structure, and considering the relationship between the total height of the container, the liquid level, and the optical path length of the air section and the liquid section, the round-trip path length of the measuring laser beam in the internal medium is calculated using the propagation time difference.

[0087] In an alternative embodiment, the measurement module 205 is specifically used for: Based on the geometric relationship, the round-trip path length is converted into the depth of the target reflective interface relative to the liquid surface; Obtain the installation reference height of the bottom wall of the container holding the liquid to be tested; The measured liquid level value of the liquid to be tested is obtained by superimposing the installation reference height and the depth.

[0088] In an alternative embodiment, the method further includes: a verification module; the verification module is used for: Within a single measurement cycle, the laser emitting device is controlled to emit the measuring laser beam at least twice, and at least two measuring liquid level values ​​are obtained accordingly. Calculate the statistical distribution parameters of the at least two measured liquid level values; When the statistical distribution parameters meet the preset consistency conditions, the arithmetic mean of the at least two measured liquid level values ​​is used as the final liquid level output value.

[0089] It should be noted that the beneficial effects of the optical path delay-based liquid level measuring device 200 provided in the above embodiments are the same as those of the optical path delay-based liquid level measuring method described above, and will not be repeated here. Furthermore, the device provided in the above embodiments is only illustrated by the division of the above functional modules. In practical applications, the above functions can be assigned to different functional modules as needed, that is, the device can be divided into different functional modules according to the actual situation to complete all or part of the functions described above. In addition, the device and method embodiments provided in the above embodiments belong to the same concept, and their specific implementation process is detailed in the method embodiments, and will not be repeated here.

[0090] The optical path delay-based liquid level measuring device 200 of the present invention can be a computer program (including program code) running on a computer device. For example, the optical path delay-based liquid level measuring device 200 of the present invention is an application software that can be used to execute the corresponding steps in the optical path delay-based liquid level measuring method of the present invention.

[0091] In some embodiments, the optical path delay-based liquid level measuring device 200 of the present invention can be implemented in a combination of hardware and software. As an example, the optical path delay-based liquid level measuring device 200 of the present invention can be a processor in the form of a hardware decoding processor, which is programmed to execute the optical path delay-based liquid level measuring method of the present invention. For example, the processor in the form of a hardware decoding processor can be one or more application-specific integrated circuits (ASICs), DSPs, programmable logic devices (PLDs), complex programmable logic devices (CPLDs), field-programmable gate arrays (FPGAs), or other electronic components.

[0092] The modules described in the embodiments of this invention can be implemented in software or hardware. The names of the modules are not, in some cases, limiting the scope of the module itself.

[0093] An electronic device according to an embodiment of the present invention includes a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, it implements any of the above-mentioned liquid level measurement methods based on optical path delay. That is, an electronic device according to an embodiment of the present invention may include, but is not limited to: a processor and a memory; the memory is used to store the computer program; the processor is used to execute the liquid level measurement method based on optical path delay shown in any embodiment of the present invention by calling the computer program.

[0094] In one alternative embodiment, an electronic device is provided, such as Figure 5 As shown, Figure 5 The illustrated electronic device 4000 includes a processor 4001 and a memory 4003. The processor 4001 and the memory 4003 are connected, for example, via a bus 4002. Optionally, the electronic device 4000 may further include a transceiver 4004, which can be used for data interaction between the electronic device and other electronic devices, such as sending and / or receiving data. It should be noted that in practical applications, the transceiver 4004 is not limited to one type, and the structure of the electronic device 4000 does not constitute a limitation on the embodiments of the present invention.

[0095] Processor 4001 may be a CPU (Central Processing Unit), a general-purpose processor, a DSP (Digital Signal Processor), an ASIC (Application Specific Integrated Circuit), an FPGA (Field Programmable Gate Array), or other programmable logic devices, transistor logic devices, hardware components, or any combination thereof. It can implement or execute the various exemplary logic blocks, modules, and circuits described in conjunction with the disclosure of this invention. Processor 4001 may also be a combination that implements computational functions, such as including one or more microprocessor combinations, a combination of a DSP and a microprocessor, etc.

[0096] Bus 4002 may include a path for transmitting information between the aforementioned components. Bus 4002 may be a PCI (Peripheral Component Interconnect) bus or an EISA (Extended Industry Standard Architecture) bus, etc. Bus 4002 can be divided into address bus, data bus, control bus, etc. For ease of representation, Figure 5 The bus 4002 is represented by only one thick line, but this does not mean that there is only one bus or one type of bus.

[0097] The memory 4003 may be ROM (Read Only Memory) or other types of static storage devices capable of storing static information and instructions, RAM (Random Access Memory) or other types of dynamic storage devices capable of storing information and instructions, or EEPROM (Electrically Erasable Programmable Read Only Memory), CD-ROM (Compact Disc Read Only Memory) or other optical disc storage, optical disc storage (including compressed optical discs, laser discs, optical discs, digital universal optical discs, Blu-ray discs, etc.), magnetic disk storage media or other magnetic storage devices, or any other medium capable of carrying or storing desired program code in the form of instructions or data structures and accessible by a computer, but not limited thereto.

[0098] The memory 4003 stores application code (computer program) for executing the present invention, and its execution is controlled by the processor 4001. The processor 4001 executes the application code stored in the memory 4003 to implement the content shown in the foregoing method embodiments.

[0099] Among them, electronic devices can also be terminal devices. A terminal device can be any terminal device that can install applications and access web pages through applications, including at least one of smartphones, tablets, laptops, desktop computers, smart speakers, smartwatches, smart TVs, and smart in-vehicle devices.

[0100] It should be noted that, Figure 5 The electronic device shown is merely an example and should not be construed as limiting the functionality and scope of use of the embodiments of the present invention.

[0101] An embodiment of the present invention provides a computer-readable storage medium storing a computer program, which, when executed by a processor, implements any of the above-described liquid level measurement methods based on optical path delay.

[0102] Alternatively, the computer-readable storage medium may be a read-only memory (ROM), a random access memory (RAM), a compact disc read-only memory (CD-ROM), magnetic tape, a floppy disk, and an optical data storage device, etc.

[0103] In an exemplary embodiment, a computer program product or computer program is also provided, which includes computer instructions stored in a computer-readable storage medium. A processor of an electronic device reads the computer instructions from the computer-readable storage medium and executes the computer instructions, causing the electronic device to perform the aforementioned liquid level measurement method based on optical path delay.

[0104] Computer program code for performing the operations of this invention can be written in one or more programming languages ​​or a combination thereof, including object-oriented programming languages ​​such as Java, Smalltalk, and C++, and conventional procedural programming languages ​​such as C or similar languages. The program code can be executed entirely on the user's computer, partially on the user's computer, as a standalone software package, partially on the user's computer and partially on a remote computer, or entirely on a remote computer or server. In cases involving remote computers, the remote computer can be connected to the user's computer via any type of network—including a local area network (LAN) or a wide area network (WAN)—or can be connected to an external computer (e.g., via the Internet using an Internet service provider).

[0105] It should be understood that the flowcharts and block diagrams in the accompanying drawings illustrate the architecture, functionality, and operation of possible implementations of methods and computer program products according to various embodiments of the present invention. In this regard, each block in a flowchart or block diagram may represent a module, segment, or portion of code containing one or more executable instructions for implementing the specified logical function. It should also be noted that in some alternative implementations, the functions indicated in the blocks may occur in a different order than those indicated in the drawings. For example, two consecutively indicated blocks may actually be executed substantially in parallel, and they may sometimes be executed in reverse order, depending on the functions involved. It should also be noted that each block in the block diagrams and / or flowcharts, and combinations of blocks in the block diagrams and / or flowcharts, may be implemented using dedicated hardware-based means to perform the specified function or operation, or using a combination of dedicated hardware and computer instructions.

[0106] The computer-readable storage medium provided in this invention can be, but is not limited to, an electrical, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any combination thereof. More specific examples of a computer-readable storage medium may include, but are not limited to: an electrical connection having one or more wires, a portable computer disk, a hard disk, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), optical fiber, portable compact disk read-only memory (CD-ROM), optical storage device, magnetic storage device, or any suitable combination thereof. In this invention, a computer-readable storage medium can be any tangible medium containing or storing a program that can be used by or in conjunction with an instruction execution system, apparatus, or device.

[0107] The aforementioned computer-readable storage medium carries one or more programs, which, when executed by the electronic device, cause the electronic device to perform the method shown in the above embodiments.

[0108] The above description is merely a preferred embodiment of the present invention and an explanation of the technical principles employed. Those skilled in the art should understand that the scope of disclosure in this invention is not limited to technical solutions formed by specific combinations of the above-described technical features, but should also cover other technical solutions formed by arbitrary combinations of the above-described technical features or their equivalents without departing from the above-disclosed concept. For example, technical solutions formed by substituting the above features with (but not limited to) technical features with similar functions disclosed in this invention.

[0109] It should be noted that the terms "first," "second," etc., used in the specification and claims of this application are used to distinguish similar objects and represent a limitation on a specific order or sequence. Where appropriate, the order of use for similar objects can be interchanged so that the embodiments of this application described herein can be implemented in an order other than that shown or described.

[0110] Those skilled in the art will recognize that this invention can be implemented as an apparatus, method, or computer program product. Therefore, this invention can be specifically implemented in the following forms: it can be entirely hardware, entirely software (including firmware, resident software, microcode, etc.), or a combination of hardware and software, generally referred to herein as a "circuit," "module," or "apparatus." Furthermore, in some embodiments, this invention can also be implemented as a computer program product contained in one or more computer-readable media, which includes computer-readable program code.

[0111] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A liquid level measurement method based on optical path delay, characterized in that, include: A laser emitting device is controlled to emit a measuring laser beam toward the surface of the liquid to be tested, and at least a portion of the energy of the measuring laser beam penetrates the liquid surface and enters the internal medium of the liquid to be tested; The laser beam that propagates along the internal propagation path in the internal medium and is reflected back by the target reflection interface is received as an echo signal. Obtain the propagation time difference from the emission of the measurement laser beam to the receipt of the echo signal; Based on the refractive index of the internal medium and the propagation time difference, the round-trip path length of the measuring laser beam in the internal medium is calculated; The measured liquid level value of the liquid under test is calculated based on the geometric relationship between the round-trip path length and the depth of the target reflective interface relative to the liquid surface.

2. The liquid level measurement method based on optical path delay according to claim 1, characterized in that, The steps of controlling the laser emitting device to emit a measuring laser beam toward the surface of the liquid to be measured include: Configure the emission wavelength of the measurement laser beam, wherein the light absorption coefficient of the emission wavelength in the internal medium is lower than a predetermined threshold; The laser emitting device is controlled to emit the measuring laser beam according to the emission wavelength, and the measuring laser beam is adjusted to be incident perpendicular to the liquid surface; The measuring laser beam changes its propagation speed at the liquid surface according to the refractive index of the internal medium, and at least a portion of the energy of the measuring laser beam enters the internal medium.

3. The liquid level measurement method based on optical path delay according to claim 2, characterized in that, The step of receiving a laser beam that propagates along an internal propagation path in the internal medium and returns after being reflected by a target reflecting interface as an echo signal includes: The laser beam reflected from the target reflective interface is received by a photodetector, and the optical signal of the laser beam is converted into an analog electrical signal by the photodetector. The analog electrical signal is subjected to bandpass filtering to remove noise outside the preset frequency band, resulting in a filtered signal. Based on the emission time of the measured laser beam and the estimated reflection time window of the target reflection interface, a signal segment corresponding to the estimated reflection time window is extracted from the filtered signal; The pulse signal with an amplitude exceeding a preset threshold in the signal segment is identified as the echo signal; The target reflective interface is the interface between the liquid to be tested and the bottom wall of the container holding the liquid to be tested.

4. The liquid level measurement method based on optical path delay according to claim 3, characterized in that, The step of obtaining the propagation time difference from the emission of the measurement laser beam to the receipt of the echo signal includes: The emission time of the measurement laser beam is recorded as the first timestamp, and the time when the pulse signal in the echo signal is identified is recorded as the second timestamp; wherein, the first timestamp and the second timestamp are generated based on the same clock source; The time interval between the first timestamp and the second timestamp is determined as the propagation time difference.

5. The liquid level measurement method based on optical path delay according to claim 4, characterized in that, The step of calculating the round-trip path length of the measuring laser beam in the internal medium based on the refractive index of the internal medium and the propagation time difference includes: Obtain the refractive index of the internal medium at the emission wavelength of the measuring laser beam; Based on the refractive index and the speed of light in vacuum, the propagation speed of the measured laser beam in the internal medium is calculated; Based on the reflective or penetrating optical path structure, and considering the relationship between the total height of the container, the liquid level, and the optical path length of the air section and the liquid section, the round-trip path length of the measuring laser beam in the internal medium is calculated using the propagation time difference.

6. The liquid level measurement method based on optical path delay according to claim 5, characterized in that, The step of calculating the measured liquid level value of the liquid under test based on the geometric relationship between the round-trip path length and the depth of the target reflective interface relative to the liquid surface includes: Based on the geometric relationship, the round-trip path length is converted into the depth of the target reflective interface relative to the liquid surface; Obtain the installation reference height of the bottom wall of the container holding the liquid to be tested; The measured liquid level value of the liquid to be tested is obtained by superimposing the installation reference height and the depth.

7. The liquid level measurement method based on optical path delay according to any one of claims 1 to 6, characterized in that, Also includes: Within a single measurement cycle, the laser emitting device is controlled to emit the measuring laser beam at least twice, and at least two measuring liquid level values ​​are obtained accordingly. Calculate the statistical distribution parameters of the at least two measured liquid level values; When the statistical distribution parameters meet the preset consistency conditions, the arithmetic mean of the at least two measured liquid level values ​​is used as the final liquid level output value.

8. A liquid level measuring device based on optical path delay, characterized in that, include: The control module is used to control the laser emitting device to emit a measuring laser beam toward the surface of the liquid to be tested, wherein at least a portion of the energy of the measuring laser beam penetrates the liquid surface and enters the internal medium of the liquid to be tested; The receiving module is used to receive the laser beam that propagates along the internal propagation path in the internal medium and returns after being reflected by the target reflection interface as an echo signal. An acquisition module is used to acquire the propagation time difference from the emission of the measurement laser beam to the receipt of the echo signal; The calculation module is used to calculate the round-trip path length of the measuring laser beam in the internal medium based on the refractive index of the internal medium and the propagation time difference; The measurement module is used to calculate the measured liquid level value of the liquid to be measured based on the geometric relationship between the round-trip path length and the depth of the target reflective interface relative to the liquid surface.

9. An electronic device, characterized in that, The electronic device includes a processor coupled to a memory storing at least one computer program, which is loaded and executed by the processor to enable the electronic device to implement the liquid level measurement method based on optical path delay as described in any one of claims 1 to 7.

10. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores at least one computer program, which, when executed by a processor, implements the liquid level measurement method based on optical path delay as described in any one of claims 1 to 7.

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