A method and system for measuring liquid level of a guided wave radar liquid level meter

Abstract

A kind of liquid level measurement method and system of guided wave radar liquid level meter, to solve the problem that the accuracy of actual liquid level measurement result is not high when guided wave radar liquid level meter measures the liquid level of asphalt reaction kettle due to installation or steam and temperature in the reaction kettle, the echo signal of guided wave radar liquid level meter is smoothed and filtered;Generate echo signal-time curve, obtain peak information of reflected echo;Select the shortest transmission time of reflected echo peak segment and its coordinate position;Measure the temperature at a certain time in the reaction kettle, calculate the original liquid level distance using the relative speed of electromagnetic wave and coordinate position;Assume that the force is gravity, calculate the inclination angle of the top of guided wave radar liquid level meter and liquid level horizontal plane by three-axis acceleration;Obtain the actual liquid level distance by using trigonometric function;Obtain the function relationship of temperature, inclination angle and actual liquid level measurement value in the reaction kettle by using MATLAB software to calculate the actual measurement distance.

Description

Technical Field

[0001] This invention relates to a measurement method and system, specifically to a precise measurement method and system for a guided wave radar level gauge used to measure the liquid level in an asphalt reactor, belonging to the field of industrial level measurement. Background Technology

[0002] In recent years, due to its wide application and high measurement accuracy, radar-based level gauges have experienced rapid growth. As the price of radar-type instruments decreases and technology is upgraded, radar has become one of the most important level measurement technologies, especially in traditional industrial fields such as metallurgy, building materials (cement), petroleum, and chemicals. It will increasingly replace other types of instruments and become the mainstream product in the level gauge industry.

[0003] Guided wave radar level gauges are a new level measurement technology that emerged with the development of level measurement and radar technologies. They overcome the shortcomings of traditional instrument principles and are increasingly used in power plants. Guided wave radar is a product of combining non-contact radar and a guided wave antenna. This instrument transmits electromagnetic wave signals onto a waveguide, using the waveguide as the signal transmission medium. When the electromagnetic wave reaches the surface of the measured medium, part of the pulse is reflected to form an echo. The distance between the transmitting device and the measured liquid level is proportional to the pulse propagation time.

[0004] When guided wave radar level gauges are used for level measurement in asphalt reactors, the electromagnetic pulses of the guided wave radar level gauges propagate along the waveguide rod at the speed of light. When they encounter the asphalt surface, part of the pulse is reflected to form an echo and returns to the pulse transmitting device along the same path. The distance between the transmitting device and the asphalt surface is proportional to the propagation time of the pulse. The liquid level height of the asphalt in the reactor can be calculated.

[0005] Because the process temperature in the asphalt reactor reaches as high as 400℃, close to the upper limit of the applicable temperature range of the guided wave radar level gauge, the gauge is easily damaged under prolonged high-temperature conditions. Furthermore, the large amount of asphalt vapor generated in the reactor can easily obscure the radar transmitter, causing false echoes and, in severe cases, rendering the measurement impossible. This leads to a deviation between the measured and actual liquid level values, resulting in distorted level measurements. Additionally, the non-transparent design of the asphalt reactor introduces installation errors into the guided wave radar level gauge, causing a slight tilt angle between the top of the gauge and the asphalt surface, affecting the true liquid level height and contributing to measurement errors. Due to these factors, the accuracy of guided wave radar level gauge measurements is not high. Summary of the Invention

[0006] To address the problem that the accuracy of liquid level measurement results is low when guided wave radar level gauges are used to measure the liquid level in asphalt reactors due to installation issues or the steam and temperature inside the reactor, this invention proposes a liquid level measurement method and system using guided wave radar level gauges.

[0007] The technical solution adopted in this invention is:

[0008] It includes the following steps:

[0009] Step 1: Obtain the echo signal of the guided wave radar level gauge when measuring the liquid level in the asphalt reactor, and smooth and filter the echo signal.

[0010] Step 2: Generate an echo signal-time curve based on the smoothed and filtered echo signal, and obtain the peak information of the reflected echo in the echo signal-time curve;

[0011] Step 3: Select the peak segment of the reflected echo with the shortest transmission time within the echo signal detection range and its corresponding coordinate position;

[0012] Step 4: Measure the temperature inside the asphalt reactor at a certain moment, obtain the relative velocity of the electromagnetic wave of the guided wave radar level gauge at that temperature, and calculate the original liquid level distance of the asphalt using the relative velocity and coordinate position.

[0013] Step 5: Assuming the force acting throughout the entire time period is gravity, calculate the tilt angle between the top plane of the guided wave radar level gauge and the horizontal liquid level using triaxial acceleration.

[0014] Step 6: Based on the tilt angle and the original liquid level distance, use trigonometric function formulas to obtain the actual liquid level distance;

[0015] Step 7: Use MATLAB software to fit the temperature, tilt angle and actual liquid level at different stages inside the asphalt reactor to obtain the functional relationship between the measured values ​​of temperature, tilt angle and actual liquid level inside the reactor, and calculate the actual measurement distance based on the functional relationship.

[0016] Further, in step one, the echo signal of the guided wave radar level gauge when measuring the liquid level in the asphalt reactor is acquired, and the echo signal is smoothed and filtered. The specific process is as follows:

[0017] The echo signal of the guided wave radar level gauge is sampled according to the oversampling setting sampling frequency to obtain the echo signal when the guided wave radar level gauge measures the liquid level of the asphalt reactor. The echo signal is smoothed by the IIR zero phase shift elliptic bandpass filtering algorithm to obtain the smoothed echo signal.

[0018] Furthermore, the echo signal is smoothed using an IIR zero-phase-shift elliptic bandpass filter algorithm. The specific process is as follows:

[0019] The waveform of the echo signal is forward filtered, the waveform after forward filtering is inverted in the time domain, the inverted waveform is then backward filtered, and the waveform after backward filtering is inverted in the time domain.

[0020] Furthermore, in step two, an echo signal-time curve is generated based on the smoothed and filtered echo signal, and the peak information of the reflected echo in the echo signal-time curve is obtained. The specific process is as follows:

[0021] An echo signal-time curve is generated based on the smoothed and filtered echo signal. Information about each peak segment in the echo signal-time curve and the information feature value of the echo signal are obtained. Then, the thresholds for the number of continuously rising data points, the absolute maximum value threshold, the relative maximum value threshold, and the maximum number of peaks in the reflected echo are defined. Echo signal-time curve segments that meet the above thresholds are selected. The peak information of the reflected echo in the echo signal-time curve segment is obtained based on the information about each peak segment and the corresponding information feature value of the echo signal.

[0022] Further, in step four, the relative velocity V of the electromagnetic wave from the guided wave radar level gauge at the stated temperature is obtained. The specific process is as follows:

[0023] The electromagnetic waves from the guided wave radar level gauge propagate from the top of the waveguide rod to the asphalt surface at approximately the speed of light.

[0024]

[0025] K is the speed of light in a vacuum, α is the relative permittivity of air at the stated temperature, and β is the relative permeability of air at the stated temperature.

[0026] Furthermore, the dielectric constant of asphalt vapor varies at different temperatures, resulting in different relative velocities of electromagnetic waves.

[0027] Further, in step four, the temperature inside the asphalt reactor at a certain moment is measured to obtain the relative velocity of the electromagnetic wave from the guided wave radar level gauge at that temperature. The original liquid level distance of the asphalt is calculated using the relative velocity and coordinate position. The specific process is as follows:

[0028]

[0029] Where L represents the initial liquid level distance; V represents the relative velocity; and A represents the coordinate position.

[0030] Furthermore, in step five, assuming the force acting throughout the entire time period is gravity, the tilt angle between the top plane of the guided wave radar level gauge and the horizontal liquid level is calculated using triaxial acceleration. The specific process is as follows:

[0031] A coordinate system is established with the top of the guided wave radar level gauge as the origin. The upward gravity output values ​​of the acceleration along the x, y, and z axes are measured, and the vertical tilt angle is obtained using the axial tilt angle calculation formula.

[0032]

[0033] Where δ is the tilt angle of the vertical z-axis, tan -1 Let g be the arctangent function. x g y g z This represents the upward gravity output values ​​along the x, y, and z axes.

[0034] Furthermore, in step six, the actual liquid level distance is obtained using trigonometric function formulas based on the tilt angle and the original liquid level distance. The specific process is as follows:

[0035] L′=L·cosδ

[0036] Where L′ represents the actual liquid level distance.

[0037] A liquid level measurement system for a guided wave radar level gauge 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 performs any step of the liquid level measurement method for a guided wave radar level gauge.

[0038] Beneficial effects:

[0039] This invention filters the obtained echo signal to obtain a regular and clean echo signal; it generates an echo signal-time curve based on the smoothed and filtered echo signal to obtain the peak information of the reflected echo; it selects the peak segment of the reflected echo with the shortest transmission time within the echo signal detection range and its corresponding coordinate position; it uses steam compensation and tilt angle compensation through corresponding compensation algorithms to obtain the true liquid level position, thereby improving the measurement accuracy of the radar level gauge; this invention performs real-time tilt compensation calculation and steam compensation calculation on the guided wave radar level gauge, and finally obtains the true liquid level distance, thereby eliminating errors caused by installation and realizing high-precision measurement of the radar level gauge. After multiple training and verifications, MATLAB software is used to fit the temperature, tilt angle, and actual liquid level at different stages in the asphalt reactor to obtain the functional relationship between the reactor temperature, tilt angle, and actual liquid level measurement values, and the actual measurement distance under any conditions is calculated based on the functional relationship. Attached Figure Description

[0040] Figure 1 This is a flowchart of the present invention; Detailed Implementation

[0041] Specific implementation method one: Combining Figure 1 This embodiment describes a liquid level measurement method using a guided wave radar level gauge, which includes the following steps:

[0042] Step 1: Sample the echo signal from the guided wave radar level gauge in the asphalt reactor according to the oversampling setting frequency to obtain the echo signal when the guided wave radar level gauge measures the liquid level in the asphalt reactor. Since the echo signal may have irregularities, filtering is first used to eliminate glitches or irregularities in the echo signal. Specifically, the IIR zero-phase-shift elliptic bandpass filtering algorithm is used to smooth the echo signal. This involves first performing forward filtering on the waveform of the echo signal, then inverting the waveform in the time domain, then performing backward filtering on the inverted waveform, and finally inverting the waveform in the time domain to obtain the smoothed echo signal.

[0043] Step 2: Generate an echo signal-time curve based on the smoothed and filtered echo signal. Obtain information about each peak segment in the echo signal-time curve, as well as the information feature values ​​of the echo signal. Then, customize the thresholds for the number of continuously rising data points, the absolute maximum value threshold, the relative maximum value threshold, and the maximum number of reflected echo peaks in the echo signal-time curve according to actual conditions. Select echo signal-time curve segments that meet the above thresholds. Obtain information about multiple peaks that may be reflected echoes in the echo signal-time curve segments based on the information about each peak segment and the corresponding information feature values ​​of the echo signal.

[0044] Step 3: Select the peak segment of the reflected echo with the shortest transmission time within the echo signal detection range and its corresponding coordinate position A.

[0045] Step 4: Since the electromagnetic wave velocity of a guided wave radar level gauge varies depending on the dielectric constant of the measurement environment, in the high-temperature, high-pressure steam environment of an asphalt reactor, to reduce the influence of asphalt steam on the electromagnetic wave velocity, traditional steam compensation technology adds a steam compensation target at a fixed position on the guided wave radar rod. The true velocity of the electromagnetic wave is calculated based on the time it takes for the electromagnetic wave to reach the steam compensation target. However, in practical engineering applications, due to changes in operating conditions, the internal temperature and pressure of the asphalt reactor will change accordingly. At this time, saturated steam easily condenses into condensate, and the condensate adheres to the guided wave radar rod, causing a deviation between the steam compensation and the actual value, thus leading to distorted level measurement. Therefore, this invention proposes a compensation or correction method for the temperature and steam inside the asphalt reactor. The specific process is as follows:

[0046] The temperature inside the asphalt reactor at a certain moment is measured, and the relative velocity V of the electromagnetic wave from the guided wave radar level gauge at that temperature is obtained. The initial liquid level distance of the asphalt is calculated using the relative velocity V and the coordinate position A, as shown in the following formula:

[0047]

[0048] Since the electromagnetic wave propagates from the top of the waveguide rod of the guided wave radar level gauge to the asphalt surface at approximately the speed of light, then...

[0049]

[0050] K is the speed of light in a vacuum, α is the relative permittivity of air at the stated temperature, and β is the relative permeability of air at the stated temperature. Based on the permittivity of asphalt vapor at different temperatures, the relative velocities of different electromagnetic waves can be calculated.

[0051] Step 5: Since guided wave radar level gauges may exhibit slight tilting, and it is impossible to observe whether they are level within an opaque reactor, if they are tilted, the accuracy of the reflected echo signal will be low, leading to deviations in the final level measurement results and affecting the overall operation of the unit or device. Therefore, this invention proposes a compensation or correction method for the tilt angle between the guided wave radar level gauge and the liquid surface, as follows:

[0052] If the force acting throughout the entire time period is gravity, then the static angle of tilt can be measured using acceleration. The tilt angle is determined using the gravity vector and its projection onto the acceleration axis. In this invention, the tilt angle refers to the tilt angle between the top plane of the guide wave radar level gauge and the liquid level plane, obtained through triaxial acceleration.

[0053] A coordinate system is established with the top of the guided wave radar level gauge as the origin. The upward gravity output values ​​of the acceleration along the x, y, and z axes are measured, and the vertical tilt angle is obtained using the axial tilt angle calculation formula.

[0054]

[0055] Where δ is the tilt angle of the vertical z-axis, tan -1 Let g be the arctangent function. x g y g z This represents the upward gravity output values ​​along the x, y, and z axes.

[0056] Step Six: Based on the obtained tilt angle δ and the original liquid level distance L, use trigonometric function formulas to calculate the actual liquid level distance after adjusting the tilt angle:

[0057] L′=L·cosδ

[0058] This invention provides accurate measurement results from the guided wave radar level gauge. It takes into account the temperature during measurement and the tilt angle during installation, and improves the measurement method by performing real-time tilt angle compensation calculation, thereby obtaining more accurate measurement results, eliminating errors caused by installation, and improving the measurement accuracy of the guided wave radar level gauge.

[0059] Step 7: Using MATLAB software, the temperature, tilt angle, and actual liquid level at different stages inside the asphalt reactor are fitted to obtain a functional relationship between the measured values ​​of temperature, tilt angle, and actual liquid level. Based on this functional relationship, the actual measurement distance of the guided wave radar level gauge can be calculated in real time. The actual measurement distance under any conditions can be calculated based on the function.

[0060] Specific Implementation Method Two: Combining Figure 1 This embodiment describes a liquid level measurement system for a guided wave radar level gauge, which 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 step of the liquid level measurement method for a guided wave radar level gauge.

Claims

1. A liquid level measurement method using a guided wave radar level gauge, characterized in that: It includes the following steps: Step 1: Obtain the echo signal of the guided wave radar level gauge when measuring the liquid level in the asphalt reactor, and smooth and filter the echo signal. Step 2: Generate an echo signal-time curve based on the smoothed and filtered echo signal, and obtain the peak information of the reflected echo in the echo signal-time curve; Step 3: Select the peak segment of the reflected echo with the shortest transmission time within the echo signal detection range and its corresponding coordinate position; Step 4: Measure the temperature inside the asphalt reactor at a certain moment, obtain the relative velocity of the electromagnetic wave of the guided wave radar level gauge at that temperature, and calculate the original liquid level distance of the asphalt using the relative velocity and coordinate position. Step 5: Assuming the force acting throughout the entire time period is gravity, calculate the tilt angle between the top plane of the guided wave radar level gauge and the horizontal liquid level using triaxial acceleration. Step 6: Based on the tilt angle and the original liquid level distance, use trigonometric function formulas to obtain the actual liquid level distance; Step 7: Use MATLAB software to fit the temperature, tilt angle and actual liquid level at different stages inside the asphalt reactor to obtain the functional relationship between the measured values ​​of temperature, tilt angle and actual liquid level inside the reactor, and calculate the actual measurement distance based on the functional relationship.

2. The liquid level measurement method of a guided wave radar level gauge according to claim 1, characterized in that: In step one, the echo signal of the guided wave radar level gauge when measuring the liquid level in the asphalt reactor is obtained, and the echo signal is smoothed and filtered. The specific process is as follows: The echo signal of the guided wave radar level gauge is sampled according to the oversampling setting sampling frequency to obtain the echo signal when the guided wave radar level gauge measures the liquid level of the asphalt reactor. The echo signal is smoothed by the IIR zero phase shift elliptic bandpass filtering algorithm to obtain the smoothed echo signal.

3. The liquid level measurement method of a guided wave radar level gauge according to claim 2, characterized in that: The echo signal is smoothed using an IIR zero-phase-shift elliptic bandpass filter algorithm. The specific process is as follows: The waveform of the echo signal is forward filtered, the waveform after forward filtering is inverted in the time domain, the inverted waveform is then backward filtered, and the waveform after backward filtering is inverted in the time domain.

4. The liquid level measurement method of a guided wave radar level gauge according to claim 3, characterized in that: In step two, an echo signal-time curve is generated based on the smoothed and filtered echo signal, and the peak information of the reflected echo in the echo signal-time curve is obtained. The specific process is as follows: An echo signal-time curve is generated based on the smoothed and filtered echo signal. Information about each peak segment in the echo signal-time curve and the information feature value of the echo signal are obtained. Then, the thresholds for the number of continuously rising data points, the absolute maximum value threshold, the relative maximum value threshold, and the maximum number of peaks in the reflected echo are defined. Echo signal-time curve segments that meet the above thresholds are selected. The peak information of the reflected echo in the echo signal-time curve segment is obtained based on the information about each peak segment and the corresponding information feature value of the echo signal.

5. The liquid level measurement method of a guided wave radar level gauge according to claim 4, characterized in that: Step four obtains the relative velocity V of the electromagnetic wave from the guided wave radar level gauge at the stated temperature. The specific process is as follows: The electromagnetic waves from the guided wave radar level gauge propagate from the top of the waveguide rod to the asphalt surface at approximately the speed of light. K is the speed of light in a vacuum, α is the relative permittivity of air at the stated temperature, and β is the relative permeability of air at the stated temperature.

6. The liquid level measurement method of a guided wave radar level gauge according to claim 5, characterized in that: The dielectric constant of asphalt vapor varies at different temperatures, resulting in different relative velocities of electromagnetic waves.

7. The liquid level measurement method of a guided wave radar level gauge according to claim 6, characterized in that: In step four, the temperature inside the asphalt reactor at a certain moment is measured to obtain the relative velocity of the electromagnetic wave from the guided wave radar level gauge at that temperature. The initial liquid level distance of the asphalt is calculated using the relative velocity and coordinate position. The specific process is as follows: Where L represents the initial liquid level distance; V represents the relative velocity; and A represents the coordinate position.

8. The liquid level measurement method of a guided wave radar level gauge according to claim 7, characterized in that: Step five assumes that the force acting throughout the entire time period is gravity. The tilt angle between the top plane of the guided wave radar level gauge and the horizontal liquid level is calculated using triaxial acceleration. The specific process is as follows: A coordinate system is established with the top of the guided wave radar level gauge as the origin. The upward gravity output values ​​of the acceleration along the x, y, and z axes are measured, and the vertical tilt angle is obtained using the axial tilt angle calculation formula. Where δ is the tilt angle of the vertical z-axis, tan -1 Let g be the arctangent function. x g y g z This represents the upward gravity output values ​​along the x, y, and z axes.

9. The liquid level measurement method of a guided wave radar level gauge according to claim 8, characterized in that: In step six, the actual liquid level distance is obtained using trigonometric function formulas based on the tilt angle and the original liquid level distance. The specific process is as follows: L′=L·cosδ Where L′ represents the actual liquid level distance.

10. A liquid level measurement system for a guided wave radar level gauge, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that: When the processor executes the computer program, it implements the steps of the method as described in any one of claims 1-9.

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