CN111351551A - Accurate temperature compensation ultrasonic liquid level detection method and system - Google Patents
Accurate temperature compensation ultrasonic liquid level detection method and system Download PDFInfo
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- G01F23/00—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm
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Abstract
The invention discloses a precise temperature compensation ultrasonic liquid level detection method and a system, wherein the precise temperature compensation ultrasonic liquid level detection method comprises the steps of generating PWM excitation waves, transmitting a beam of ultrasonic waves to a detected liquid, receiving the ultrasonic waves reflected by the detected liquid, recording transmitting and receiving time, and calculating propagation time; the width time t is obtained by measuring the signal intensity of the pulse and adjusting the gain of the circuitvAnd the mean transit time of the ultrasonic wave
Obtaining the temperature values of the ultrasonic transducer and the measured liquid repeatedly measured for x times, and calculating to obtain a first temperature average value
Corresponding first value of speed of sound vclSecond average temperature value
And a corresponding second value of velocity vcr(ii) a Based on temperature drift compensation factor delta0Establishing a temperature compensation formula according to the harmonic speed difference delta v; calculating to obtain a target liquid level measurement distance l based on the measured liquid level measurement distance l without temperature compensation and the temperature compensation distance lGeneral assembly. The purpose of accurate temperature compensation is achieved in an outdoor complex environment, and the measurement accuracy of the liquid level meter is guaranteed.
Description
Technical Field
The invention relates to the technical field of liquid level detection, in particular to an accurate temperature compensation ultrasonic liquid level detection method and system.
Background
The ultrasonic liquid level meter has the advantages of clear characteristics, no contact with the liquid to be measured and convenient installation and maintenance, but is also easily influenced by the environment, such as the temperature change of air, which can cause the transmission speed of ultrasonic waves in the air to change and finally cause the fluctuation of measured data; data fluctuation caused by temperature drift is an important reason for influencing the precision of the ultrasonic liquid level meter, the temperature measurement module is mainly arranged at the probe end of the liquid level meter at present, and temperature compensation is carried out by measuring the air temperature at the probe, so that the method can play a certain temperature compensation role in a scene with stable environment, such as an inspection well and a closed container; when the liquid level meter is installed outdoors, the environment is complex, and meanwhile, the air has the problem of temperature stratification along with different heights, so that the temperature compensation effect is not ideal, the phenomenon of obvious temperature drift can still occur during measurement, and the measurement precision is influenced. Therefore, a more accurate temperature compensation scheme is urgently needed to be provided, so that the measurement accuracy of the liquid level meter can be ensured when the liquid level meter is used in complex environments such as outdoor environments and the like.
Disclosure of Invention
The invention aims to provide an accurate temperature compensation ultrasonic liquid level detection method and system, which can accurately compensate temperature in an outdoor complex environment and ensure the measurement accuracy of a liquid level meter.
In order to achieve the above object, in a first aspect, the present invention provides a precise temperature compensation ultrasonic liquid level detection method, including:
outputting a control signal, generating a beam of PWM excitation wave matched with the frequency of the ultrasonic transducer, and amplifying;
outputting an excitation signal, transmitting a beam of ultrasonic waves to the liquid to be detected, receiving the ultrasonic waves reflected by the liquid to be detected, generating an oscillation signal, and recording the ultrasonic wave transmitting time t1And ultrasonic wave reception time t2Calculating the propagation time delta t of the ultrasonic wave and generating an echo signal, wherein the delta t is t2-t1；
Receiving echo signal, measuring the signal strength of pulse, automatically regulating the gain of circuit to make the pulse signal strength meet the threshold requirement and obtain the width time t when the pulse signal exceeds the thresholdvAnd the mean transit time of the ultrasonic wave
Obtaining the air temperature value at the ultrasonic transducer which is repeatedly measured for x times, and calculating to obtain a first temperature average value
And a corresponding first value of speed of sound vcl；
Obtaining the surface temperature value of the measured liquid repeatedly measured for x times, and calculating to obtain a second temperature average value
And a corresponding second value of velocity vcr；
Based on temperature drift compensation factor delta0Establishing a temperature compensation formula according to the harmonic speed difference delta v;
calculating to obtain a target liquid level measurement distance l based on the measured liquid level measurement distance l without temperature compensation and the temperature compensation distance lGeneral assembly。
In one embodiment, an echo signal is received, the signal strength of a pulse is measured, and the gain of a circuit is automatically adjusted to enable the pulse signal strength to meet the threshold requirement, so that the width time t when the pulse signal exceeds the threshold is obtainedvAnd the mean transit time of the ultrasonic wave
The method comprises the following specific steps:
comparing the voltage of the echo signal with the reference threshold voltage v' of the circuit, and recording the time t when the signal exceeds the thresholdiAnd a time t less than a thresholdjCalculating the width time t of the pulse signal exceeding the thresholdvWherein t isv＝tj-tj。
In one embodiment, an echo signal is received, the signal strength of a pulse is measured, and the gain of a circuit is automatically adjusted to enable the pulse signal strength to meet the threshold requirement, so that the width time t when the pulse signal exceeds the threshold is obtainedvAnd the mean transit time of the ultrasonic wave
The method comprises the following specific steps:
the n echo signals are sorted in ascending order according to the signal intensity, and m data which are sorted in the front are selected, wherein the m data are respectively tv1、tv2……tvmKeeping the corresponding m time data as Δ t1、Δt2……ΔtmWherein m is less than n;
calculating the average transmission time of ultrasonic waves
In one embodiment, the air temperature value at the ultrasonic transducer is obtained by repeating the measurement for x times, and the first temperature average value is calculated
And a corresponding first value of speed of sound vclThe method comprises the following specific steps:
obtaining x times of measured first temperature values to calculate first temperature average value
According to the formula of temperature and sound velocity, calculating a corresponding first sound velocity value vcl：
Wherein v is0The velocity of ultrasonic waves in air at 0 ℃ v0＝331.45m/s。
In one embodiment, the surface temperature value of the measured liquid is obtained by repeating the measurement for x times, and the second temperature average value is calculated
And a corresponding second value of velocity vcrThe method comprises the following specific steps:
obtaining x times of measured second temperature values to calculate second temperature average value
According to the formula of temperature and sound velocity, calculating the corresponding second sound velocity value vrl；
Wherein v is0The velocity of ultrasonic waves in air at 0 ℃ v0＝331.45m/s。
In one embodiment, the surface temperature value of the measured liquid is obtained by repeating the measurement for x times, and the second temperature average value is calculated
And a corresponding second value of velocity vcrThereafter, the method further comprises:
based on the first value of speed of sound vclAnd a second value of velocity vcrCalculating the difference in sound velocity Δ v, where Δv＝vcl-vcr。
In one embodiment, the compensation factor δ is based on the temperature drift0Establishing a temperature compensation formula according to the harmonic speed difference delta v, wherein the temperature compensation formula comprises the following specific steps:
wherein, a0、b0Is the environmental coefficient, e is the natural constant.
In one embodiment, the target liquid level measurement distance l is calculated based on the measured liquid level measurement distance l without temperature compensation and the temperature compensation distance lGeneral assemblyThe method comprises the following specific steps:
lgeneral assembly＝l±l'；
In a second aspect, the present invention provides a precision temperature compensated ultrasonic liquid level detection system comprising:
the ultrasonic temperature measurement device comprises a central processing module, a signal generation module, an ultrasonic transduction module, a signal processing module, a signal comparison module, a local temperature measurement module and an infrared temperature measurement module, wherein the central processing module, the signal generation module, the ultrasonic transduction module, the signal processing module and the signal comparison module are sequentially connected, and the signal comparison module, the local temperature measurement module and the infrared temperature measurement module are all connected with the central processing module; wherein,
the central processing module is used for outputting a control signal to the signal generating module after receiving a command of measuring the liquid level;
the signal generating module is used for receiving the control signal to generate a beam of PWM excitation wave matched with the frequency of the ultrasonic transducer, carrying out amplification processing and outputting an excitation signal to the ultrasonic transducer module;
the ultrasonic wave transduction module is used for receiving the excitation signal, transmitting a beam of ultrasonic wave to the liquid to be detected, receiving the ultrasonic wave reflected by the liquid to be detected and generating an oscillation signal;
the central processing module is also used for recording the ultrasonic wave emission time t1And ultrasonic wave reception time t2Calculating the propagation time delta t of the ultrasonic wave and generating an echo signal, wherein the delta t is t2-t1；
The signal processing module is used for receiving the echo signal, automatically adjusting the gain of the circuit by measuring the signal intensity of the pulse, and enabling the pulse signal intensity to meet the threshold requirement;
the signal comparison module is used for comparing the obtained pulse signal with the threshold voltage and recording the width time t when the pulse signal exceeds the thresholdv；
The local temperature measurement module is used for repeatedly measuring the air temperature value at the ultrasonic transducer for x times;
the infrared temperature measurement module is used for repeatedly measuring the surface temperature value of the measured liquid for x times;
the central processing module is also used for calculating and obtaining the average transmission time of the ultrasonic wave
First temperature average value
Corresponding first value of speed of sound vclSecond average temperature value
And a corresponding second value of velocity vr(ii) a Based on temperature drift compensation factor delta0Establishing a temperature compensation formula according to the harmonic speed difference delta v, and calculating a target liquid level measurement distance l based on a measured liquid level measurement distance l without temperature compensation and a temperature compensation distance lGeneral assembly。
In an embodiment, the central processing module is further configured to determine a first sound velocity value v based on the first sound velocity valueclAnd a second value of velocity vcrCalculating a difference in sound velocity Δ v, where Δ v ═ vcl-vcr。
According to the method and the system for detecting the accurate temperature compensation ultrasonic liquid level, a beam of PWM (pulse width modulation) excitation wave matched with the frequency of an ultrasonic transducer is generated; transmitting a beam of ultrasonic waves to the liquid to be measured, receiving the ultrasonic waves reflected by the liquid to be measured, generating an oscillation signal, and recording the ultrasonic wave transmitting time t1And ultrasonic wave reception time t2Calculating the propagation time delta t of the ultrasonic wave to generate an echo signal; receiving echo signal, measuring the signal strength of pulse, automatically regulating the gain of circuit to make the pulse signal strength meet the threshold requirement and obtain the width time t when the pulse signal exceeds the thresholdvAnd the mean transit time of the ultrasonic wave
Obtaining the air temperature value at the ultrasonic transducer which is repeatedly measured for x times, and calculating to obtain a first temperature average value
And a corresponding first value of speed of sound vcl(ii) a Obtaining the surface temperature value of the measured liquid repeatedly measured for x times, and calculating to obtain a second temperature average value
And a corresponding second value of velocity vcr(ii) a Based on temperature drift compensation factor delta0Establishing a temperature compensation formula according to the harmonic speed difference delta v; calculating to obtain a target liquid level measurement distance l based on the measured liquid level measurement distance l without temperature compensation and the temperature compensation distance lGeneral assembly. When the liquid level meter is installed in an outdoor environment, the problem that air is layered along with different heights is considered, temperature compensation is carried out in a complex environment, the purpose of accurate temperature compensation is achieved, and the measurement accuracy of the liquid level meter is guaranteed.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
FIG. 1 is a schematic flow diagram of a method for accurate temperature compensated ultrasonic level detection provided by an embodiment of the present invention;
FIG. 2 is a schematic diagram of a configuration of a precision temperature compensated ultrasonic level detection system provided by an embodiment of the present invention;
FIG. 3 is a graph of echo signal intensity;
FIG. 4 is a graphical representation of the sound velocity difference versus measurement error.
In the figure: 100-accurate temperature compensation ultrasonic liquid level detection system, 10-central processing module, 20-signal generating module, 30-ultrasonic transducing module, 40-signal processing module, 50-signal comparing module, 60-local temperature measuring module and 70-infrared temperature measuring module.
Detailed Description
Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to the same or similar elements or elements having the same or similar function throughout. The embodiments described below with reference to the drawings are illustrative and intended to be illustrative of the invention and are not to be construed as limiting the invention.
Referring to fig. 1, fig. 1 is a schematic flow chart of an ultrasonic liquid level detection method with accurate temperature compensation according to an embodiment of the present invention. Specifically, the precise temperature compensation ultrasonic liquid level detection method may include the following steps:
s101, outputting a control signal to generate a beam of PWM (pulse-width modulation) excitation wave matched with the frequency of the ultrasonic transducer, and amplifying;
in the embodiment of the invention, after receiving the liquid level measurement command, the central processing unit outputs a control signal to control the high-speed digital-to-analog converter and the amplifying circuit to generate a beam of PWM excitation wave matched with the frequency of the ultrasonic transducer, and the PWM excitation wave is amplified and then transmitted to the ultrasonic transducer.
S102, outputting an excitation signal, transmitting a beam of ultrasonic waves to the liquid to be detected, receiving the ultrasonic waves reflected by the liquid to be detected, generating an oscillation signal, and recording the ultrasonic wave transmitting time t1And ultrasonic wave reception time t2Calculating the propagation time delta t of the ultrasonic wave to generate an echo signal;
in the embodiment of the invention, the ultrasonic transducer receives the excitation signal, transmits a beam of ultrasonic waves to the liquid to be detected, receives the ultrasonic waves reflected by the liquid to be detected, generates an oscillation signal, and the central processing unit records the ultrasonic wave transmission time t1And ultrasonic wave reception time t2Calculating the propagation time delta t of the ultrasonic wave to generate an echo signal; where Δ t ═ t2-t1。
S103, receiving the echo signal, automatically adjusting the gain of the circuit by measuring the signal intensity of the pulse to enable the pulse signal intensity to meet the threshold requirement, and obtaining the width time t when the pulse signal exceeds the thresholdvAnd the mean transit time of the ultrasonic wave
In the embodiment of the invention, a signal conditioning and amplifying circuit receives an echo signal, automatically adjusts the gain of the circuit by measuring the signal intensity of a pulse to enable the pulse signal to meet the threshold requirement of a signal comparator, specifically, the voltage of the echo signal is compared with the reference threshold voltage v' of the circuit, timing is started when the signal intensity exceeds a threshold, timing is stopped when the signal intensity is less than the threshold, and the time t when the signal exceeds the threshold is recordediAnd a time t less than a thresholdjReferring to fig. 3, fig. 3 is a schematic diagram of the intensity of the echo signal, and the width time t of the pulse signal exceeding the threshold is calculatedvAs the signal quality value of the present measurement, where tv＝tj-tj. Repeating the above measurement process n times, and recording the propagation time and signal quality value of each ultrasonic wave to obtain n ultrasonic wave transmission time differences of Δ t1、Δt2……ΔtnThe corresponding n signal intensities are respectively tv1、tv2……tvn. The n echo signals are sorted in ascending order according to the signal intensity, and m data which are sorted in the front are selected, wherein the m data are respectively tv1、tv2……tvmKeeping the corresponding m time data as Δ t1、Δt2……ΔtmIf the measured data is used as the current measurement data, the ultrasonic propagation time measurement is finished, wherein m is less than n; calculating the average transmission time of ultrasonic waves
S104, obtaining the air temperature value of the ultrasonic transducer repeatedly measured for x times, and calculating to obtain a first temperature average value
And a corresponding first value of speed of sound vcl；
In the embodiment of the invention, the local temperature sensor is started to measure the air temperature at the ultrasonic transducer, and the temperature obtained by local measurement is recorded as clRepeating the measurement x times to obtain x temperatures cl1、cl2……clxObtaining x times of measured first temperature values to calculate first temperature average value
According to the formula of temperature and sound velocity, calculating a corresponding first sound velocity value vcl：
Wherein v is0The velocity of ultrasonic waves in air at 0 ℃ v0＝331.45m/s。
S105, obtaining surface temperature values of the liquid to be measured which are repeatedly measured for x times, and calculating to obtain a second temperature average value
And a corresponding second value of velocity vcr；
In the embodiment of the invention, the infrared temperature sensor is started to measure the air temperature of the surface of the measured liquid surface, and the measured air temperature is marked as crRepeating the measurement x times to obtain x temperatures cr1、cr2……crxObtaining x times of measured second temperature values to calculate second temperature average value
According to the formula of temperature and sound velocity, calculating the corresponding second sound velocity value vrl；
Wherein v is0The velocity of ultrasonic waves in air at 0 ℃ v0＝331.45m/s。
S106, based on the temperature drift compensation factor delta0Establishing a temperature compensation formula according to the harmonic speed difference delta v;
in the embodiment of the invention, the first sound velocity value v is used as the basisclAnd a second value of velocity vcrCalculating a difference in sound velocity Δ v, where Δ v ═ vcl-vcr. When the delta v is larger than 0, the ambient temperature of the ultrasonic transducer is higher, the sound velocity is higher, the air temperature around the liquid surface is lower, the sound velocity is lower, and negative compensation should be performed; when Δ v < 0, the ambient temperature of the ultrasonic transducer is low, the air temperature around the liquid surface is high, and positive compensation should be performed.
Wherein, a0、b0Is the environmental coefficient, e is the natural constant.
In particular to the air temperature at the ultrasonic transducerMeasuring the temperature, and recording the temperature obtained by local measurement as c1At this temperature, the corresponding speed of sound in air is s1(ii) a Then measuring the surface temperature of the measured liquid or object, and recording the temperature as c2At this temperature, the corresponding speed of sound in air is s2(ii) a Let the temperature difference be Δ c ═ c2-c1I, the ultrasonic velocity difference is Δ v ═ v2-v1L. Experiments show that the sound velocity difference value formed by the temperature difference of the liquid level meter and the measurement error of the liquid level meter generated by the temperature difference are in an exponential relationship, the temperature drift is larger when the difference value is larger, and FIG. 4 is a schematic diagram of the relationship between the sound velocity difference and the measurement error; as shown in fig. 4, therefore, a new temperature difference compensation algorithm is introduced from here, and the temperature drift compensation factor δ is calculated as follows:
δ＝a(eb·Δv-1)； (1)
wherein e is a natural constant, coefficients a and b are related to the installation environment of the liquid level meter, and Δ v is a sound velocity difference formed by temperature difference. The formula for the temperature difference compensation is as follows:
l'＝δ·ts； (2)
wherein, delta is a temperature drift compensation factor, tsThe propagation time of the ultrasonic wave obtained when the liquid level meter measures is obtained.
Finally, the liquid level is calculated in such a way that m data measurement results with the maximum signal intensity are reserved in n measurement results, the measurement time obtained from the m measurement results is averaged, and the average propagation time of the ultrasonic wave is tsThen, according to the formula:
distance-time-velocity
The measured distance of the measured liquid level without temperature compensation is:
after temperature compensation is performed, the liquid level distance obtained by the final liquid level meter is as follows:
thus, the liquid level measurement of the ultrasonic liquid level meter is completed.
S107, calculating to obtain a target liquid level measurement distance l based on the measured liquid level measurement distance l without temperature compensation and the temperature compensation distance lGeneral assembly。
In the embodiment of the invention, the actual liquid level is laThe propagation time of the ultrasonic wave measured by the liquid level meter is taThe liquid level obtained without temperature compensation is la', local temperature is claRemote temperature of craIf the error due to temperature drift is Δ l ═ la-la'; from the formula (2), it can be obtained
Similarly, when the local temperature is clβRemote temperature of crβThen can obtain
The two modes are simultaneous, and the coefficient a under the current environment can be obtained0And b0. Then in this liquid level measurement, the measured value is represented by a0、b0And the sound velocity difference delta v can obtain the temperature compensation factor delta of the measurement according to the formula (1)0Comprises the following steps:
averaging the m ultrasonic wave transmission times with the maximum reserved echo signal quality to obtain
Then, according to the distance calculation formula, the liquid level data before temperature compensation can be obtained as follows:
according to equation (2), the distance for temperature compensation is:
the resulting liquid level measurement distance of the ultrasonic liquid level meter can be expressed as follows according to the local temperature and the infrared temperature:
thus, after one complete measurement and temperature compensation process of the ultrasonic liquid level meter is finished, the measurement result l is obtainedGeneral assemblyAnd (6) outputting.
According to the method and the system for detecting the accurate temperature compensation ultrasonic liquid level, a beam of PWM (pulse width modulation) excitation wave matched with the frequency of an ultrasonic transducer is generated; transmitting a beam of ultrasonic waves to the liquid to be measured, receiving the ultrasonic waves reflected by the liquid to be measured, generating an oscillation signal, and recording the ultrasonic wave transmitting time t1And ultrasonic wave reception time t2Calculating the propagation time delta t of the ultrasonic wave to generate an echo signal; receiving echo signal, measuring the signal strength of pulse, automatically regulating circuit gain to make pulse signal meet threshold requirement and obtain width time t of pulse signal over thresholdvAnd the mean transit time of the ultrasonic wave
Obtaining the air temperature value at the ultrasonic transducer which is repeatedly measured for x times, and calculating to obtain a first temperature average value
And a corresponding first value of speed of sound vcl(ii) a Obtaining the surface temperature value of the measured liquid repeatedly measured for x times, and calculating to obtain a second temperature average value
And a corresponding second value of velocity vcr(ii) a Based on temperature drift compensation factor delta0Establishing a temperature compensation formula according to the harmonic speed difference delta v; distance l and temperature compensation distance l' meter based on measured liquid level without temperature compensationCalculating the target liquid level measurement distance lGeneral assembly. When the liquid level meter is installed in an outdoor environment, the problem that air is layered along with different heights is considered, temperature compensation is carried out in a complex environment, the purpose of accurate temperature compensation is achieved, and the measurement accuracy of the liquid level meter is guaranteed.
Referring to fig. 2, a schematic structural diagram of an accurate temperature compensation ultrasonic liquid level detection system 100 according to an embodiment of the present invention is shown. Specifically, the precise temperature compensation ultrasonic liquid level detection system 100 includes:
the ultrasonic temperature measurement device comprises a central processing module 10, a signal generation module 20, an ultrasonic transduction module 30, a signal processing module 40, a signal comparison module 50, a local temperature measurement module 60 and an infrared temperature measurement module 70, wherein the central processing module 10, the signal generation module 20, the ultrasonic transduction module 30, the signal processing module 40 and the signal comparison module 50 are sequentially connected, and the signal comparison module 50, the local temperature measurement module 60 and the infrared temperature measurement module 70 are all connected with the central processing module 10; wherein,
the central processing module 10 is a central processing unit, and is configured to output a control signal to the signal generating module 20 after receiving a command for measuring a liquid level;
the signal generating module 20 is a high-speed digital-to-analog converter and an amplifying circuit, and is configured to receive a control signal, generate a beam of PWM excitation wave matching the frequency of the ultrasonic transducer, amplify the PWM excitation wave, and output an excitation signal to the ultrasonic transducer module 30;
the ultrasonic transducer module 30 is an ultrasonic transducer, and is configured to receive an excitation signal, transmit a beam of ultrasonic waves to the liquid to be measured, receive the ultrasonic waves reflected by the liquid to be measured, and generate an oscillation signal;
the central processing module 10 is further configured to record the ultrasonic emission time t1And ultrasonic wave reception time t2Calculating the propagation time delta t of the ultrasonic wave and generating an echo signal, wherein the delta t is t2-t1；
The signal processing module 40 is a signal conditioning and amplifying circuit, and is used for receiving an echo signal, and automatically adjusting the gain of the circuit by measuring the signal intensity of a pulse, so that the pulse signal meets the threshold requirement;
the signal comparison module 50 is a signal comparator for comparing the pulse signal with a threshold voltage and recording the width time t of the pulse signal exceeding the thresholdv；
The local temperature measurement module 60 is a local temperature sensor, and is configured to repeatedly measure the air temperature value at the ultrasonic transducer for x times;
the infrared temperature measuring module 70 is an infrared temperature sensor and is used for repeatedly measuring the surface temperature value of the measured liquid for x times;
the central processing module 10 is further configured to calculate and obtain an average transmission time of the ultrasonic wave
First temperature average value
Corresponding first value of speed of sound vclSecond average temperature value
And a corresponding second value of velocity vr(ii) a Based on temperature drift compensation factor delta0Establishing a temperature compensation formula according to the harmonic speed difference delta v, and calculating a target liquid level measurement distance l based on a measured liquid level measurement distance l without temperature compensation and a temperature compensation distance lGeneral assembly。
The central processing module 10 is further configured to determine a first sound velocity value v based on the first sound velocity valueclAnd a second value of velocity vcrCalculating a difference in sound velocity Δ v, where Δ v ═ vcl-vcr。
For the specific implementation of the embodiment of the present invention, please refer to the specific implementation of the precise temperature compensation ultrasonic liquid level detection method of the first aspect, which is not described herein again.
While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.
Claims (10)
1. An accurate temperature compensation ultrasonic liquid level detection method is characterized by comprising the following steps:
outputting a control signal to generate a beam of PWM excitation wave matched with the frequency of the ultrasonic transducer, and amplifying;
outputting an excitation signal, transmitting a beam of ultrasonic waves to the liquid to be detected, receiving the ultrasonic waves reflected by the liquid to be detected, generating an oscillation signal, and recording the ultrasonic wave transmitting time t1And ultrasonic wave reception time t2Calculating the propagation time delta t of the ultrasonic wave and generating an echo signal, wherein the delta t is t2-t1；
Receiving echo signal, measuring the signal strength of pulse, automatically regulating the gain of circuit to make the pulse signal strength meet the threshold requirement and obtain the width time t when the pulse signal exceeds the thresholdvAnd the mean transit time of the ultrasonic wave
Obtaining the air temperature value at the ultrasonic transducer which is repeatedly measured for x times, and calculating to obtain a first temperature average value
And a corresponding first value of speed of sound vcl；
Obtaining the surface temperature value of the measured liquid repeatedly measured for x times, and calculating to obtain a second temperature average value
And a corresponding second value of velocity vcr；
Based on temperature drift compensation factor delta0Establishing a temperature compensation formula according to the harmonic speed difference delta v;
calculating to obtain a target liquid level based on the measured liquid level measurement distance l and the temperature compensation distance l' which are not subjected to temperature compensationMeasuring the distance lGeneral assembly。
2. The method of claim 1 wherein the echo signal is received and the gain of the circuit is automatically adjusted by measuring the signal strength of the pulse to meet a threshold requirement to obtain a time t when the pulse signal exceeds the threshold widthvAnd the mean transit time of the ultrasonic wave
The method comprises the following specific steps:
comparing the voltage of the echo signal with the reference threshold voltage v' of the circuit, and recording the time t when the signal exceeds the thresholdiAnd a time t less than a thresholdjCalculating the width time t of the pulse signal exceeding the thresholdvWherein t isv＝tj-tj。
3. The method of claim 2 wherein the echo signal is received and the gain of the circuit is automatically adjusted by measuring the signal strength of the pulse to meet a threshold requirement to obtain a time t when the pulse signal exceeds the threshold widthvAnd the mean transit time of the ultrasonic wave
The method comprises the following specific steps:
the n echo signals are sorted in ascending order according to the signal intensity, and m data which are sorted in the front are selected, wherein the m data are respectively tv1、tv2……tvmKeeping the corresponding m time data as Δ t1、Δt2……ΔtmWherein m is less than n;
calculating the average transmission time of ultrasonic waves
4. The method of claim 3, wherein the obtaining of the air temperature value at the ultrasonic transducer is repeated x times, and the calculating of the first temperature average value
And a corresponding first value of speed of sound vclThe method comprises the following specific steps:
obtaining x times of measured first temperature values to calculate first temperature average value
According to the formula of temperature and sound velocity, calculating a corresponding first sound velocity value vcl：
Wherein v is0The velocity of ultrasonic waves in air at 0 ℃ v0＝331.45m/s。
5. The method of claim 4, wherein the surface temperature of the liquid is measured x times and the second temperature average is calculated
And a corresponding second value of velocity vcrThe method comprises the following specific steps:
obtaining x times of measured second temperature values to calculate second temperature average value
According to the formula of temperature and sound velocity, calculating the corresponding second sound velocity value vrl；
Wherein v is0The velocity of ultrasonic waves in air at 0 ℃ v0＝331.45m/s。
6. The method of claim 5, wherein the obtaining of the surface temperature value of the liquid is repeated x times, and the calculating of the second temperature average value is performed
And a corresponding second value of velocity vcrThereafter, the method further comprises:
based on the first value of speed of sound vclAnd a second value of velocity vcrCalculating a difference in sound velocity Δ v, where Δ v ═ vcl-vcr。
7. The method of claim 6, wherein the temperature drift compensation factor δ is based0Establishing a temperature compensation formula according to the harmonic speed difference delta v, wherein the temperature compensation formula comprises the following specific steps:
wherein, a0、b0Is the environmental coefficient, e is the natural constant.
8. The method of claim 7, wherein the target level measurement distance/' is calculated based on the measured level measurement distance/' and the temperature compensated distance/' without temperature compensationGeneral assemblyThe method comprises the following specific steps:
lgeneral assembly＝l±l'；
9. An accurate temperature compensated ultrasonic liquid level detection system, comprising:
the ultrasonic temperature measurement device comprises a central processing module, a signal generation module, an ultrasonic transduction module, a signal processing module, a signal comparison module, a local temperature measurement module and an infrared temperature measurement module, wherein the central processing module, the signal generation module, the ultrasonic transduction module, the signal processing module and the signal comparison module are sequentially connected, and the signal comparison module, the local temperature measurement module and the infrared temperature measurement module are all connected with the central processing module; wherein,
the central processing module is used for outputting a control signal to the signal generating module after receiving a command of measuring the liquid level;
the signal generating module is used for receiving the control signal to generate a beam of PWM excitation wave matched with the frequency of the ultrasonic transducer, carrying out amplification processing and outputting an excitation signal to the ultrasonic transducer module;
the ultrasonic wave transduction module is used for receiving the excitation signal, transmitting a beam of ultrasonic wave to the liquid to be detected, receiving the ultrasonic wave reflected by the liquid to be detected and generating an oscillation signal;
the central processing module is also used for recording the ultrasonic wave emission time t1And ultrasonic wave reception time t2Calculating the propagation time delta t of the ultrasonic wave and generating an echo signal, wherein the delta t is t2-t1；
The signal processing module is used for receiving the echo signal and automatically adjusting the gain of the circuit by measuring the signal intensity of the pulse to enable the pulse signal to meet the threshold requirement;
the signal comparison module is used for comparing the obtained pulse signal with the threshold voltage and recording the width time t when the pulse signal exceeds the thresholdv；
The local temperature measurement module is used for repeatedly measuring the air temperature value at the ultrasonic transducer for x times;
the infrared temperature measurement module is used for repeatedly measuring the surface temperature value of the measured liquid for x times;
the central processing module is also used for calculating and obtaining the average transmission time of the ultrasonic wave
First temperature average value
Corresponding first value of speed of sound vclSecond average temperature value
And a corresponding second value of velocity vr(ii) a Based on temperature drift compensation factor delta0Establishing a temperature compensation formula according to the harmonic speed difference delta v, and calculating a target liquid level measurement distance l based on a measured liquid level measurement distance l without temperature compensation and a temperature compensation distance lGeneral assembly。
10. The precision temperature compensated ultrasonic liquid level detection system of claim 9,
the central processing module is further used for basing on the first sound velocity value vclAnd a second value of velocity vcrCalculating a difference in sound velocity Δ v, where Δ v ═ vcl-vcr。
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