CN1587924A - Sound wave liquid level emasuring device and its method - Google Patents

Abstract

Sound wave liquid level measuring device of the invention includes: leading wave tube, signal processing control chip, sound wave generating unit, sound wave receiving unit, and analogy/digit converter, the position of sound wave receiving unit is supposed to be measuring reference point whose distance to liquid level is L; a frequency of lowest acoustic frequency signal is defined by signal processing control chip, control command corresponding to increasing frequency which starts from the lowest frequency is sent by sound wave generating unit, sound signal whose frequency is appointed by control command which has two or more than two period is sent by sound wave generating unit; sound wave is received by sound wave receiving unit and transferred to analogy/digit converter in electric signal form to be transformed into data signal which then is transferred to signal processing control chip to record amplitude of sound with the frequency on the, and the is compared with that recorded last time to find out the first smallest which is stored and the frequency corresponding to the sound wave with the smallest is frequency of standing waves, then calculate the value of L according to sound wave in air, standing waves frequency and equation.

Description

A kind of sound wave liquid level emasuring device and method thereof

Technical field

The present invention relates to the surveying instrument technical field, particularly about a kind of devices and methods therefor of acoustic measurement liquid level.

Background technology

In industrial and agricultural production, the liquid level of various liquid is important parameters.Water level as river, lake is an important parameter of describing water conservancy system, and the oil level of oil depot is a parameter of judging its oil reserve.Therefore how simply, measuring liquid level is the target that people pursue always exactly the measuring technique of liquid level is the research object of fields of measurement.

Present existing liquid level emasuring device mainly divides contact and contactless two big classes.

The contact liquid level emasuring device is common pressure type liquid level sensor and float-type liquid level sensor.

Pressure type liquid level sensor, adopts pressure sensor come measuring liquid level as sensitive element by the pressure of measuring liquid internal.But because this kind liquid level emasuring device contacts with fluid to be measured, can be subjected to alluvial, corrosion and make sensor impaired, simultaneously-measured precision is subjected to the influence of fluid to be measured density and ambient pressure variation, and pressure transducer is on the high side.

The float-type liquid level sensor is suspended in liquid surface by measurement float comes measuring liquid level to the distance of reference point, but this kind liquid level emasuring device volume is big, and accuracy in time prolongation and reduce.

Contactless liquid level emasuring device has ultrasonic liquid level sensor now, owing to do not contact the problem of having avoided contact measuring apparatus such as alluvial, corrosion to exist with fluid to be measured.But, ultrasonic type liquid level emasuring device price height, the precision during measurement is subjected to the influence of extraneous factors such as weather, wave, and has certain measurement blind area.

A kind of existing disclosed on April 24th, 2002 as China national Department of Intellectual Property, application number is 01100503, denomination of invention is the level measuring method and the device of " acoustic water level measuring mehtod and system thereof ", as shown in Figure 1, described sound wave water level measurement mechanism comprises, soundwave generating unit 1,waveguide pipe 2,microphone 3 and 4, the acoustic reflection tube 6 of hollow and with the float 7 of the acoustic reflection tube one of hollow, oscillator and signal Processing control chip, in the prior art the position ofmicrophone 3 is made as the reference point of level measuring, described signal Processing control chip store between themicrophone 3 and 4 apart from l₁And the upper surface of acoustic reflection tube 6 is to water surface spacing l₂, and pass through l respectively by measuring sound wave pulse₁, l₂Time, and upper and lower through the microphone of associating to time of the distance L of water surface, simultaneously, the signal Processing control chip is according to formula:

$L=\frac{{\mathrm{<figure-callout\; label="t"\; filenames="A20041006235500151.png"\; state="\{\{state\}\}">t</figure-callout>}}_1}{2}\&CenterDot;\frac{1}{2\&CenterDot;(\frac{l_1}{{\mathrm{<figure-callout\; label="t"\; filenames="A20041006235500151.png"\; state="\{\{state\}\}">t</figure-callout>}}_1}+\frac{l_2}{t_2})}$

Calculate the value of L.The sound wave liquid level emasuring device of this patent is with respect to existing pressure type sensor and ultrasonic sensor, its cost is low relatively, but the sound wave liquid level emasuring device of this patent is owing to adopt two microphones and the float with hollow reflecting drum, its device is many, cost is higher, and installation procedure is cumbersome; In addition, it will measure two points when work, and two reflection waves, the process of measurement complexity, and the hollow reflecting drum is owing on bubbling through the water column by float, since the ambiguity of ripples, l₂Value be unsettled, measuring accuracy is affected.

At the problems referred to above, be necessary to provide that a kind of device is few, cost is low, easy for installation, quick and sound wave liquid level emasuring device and method thereof that measuring accuracy is high.

Summary of the invention

In order to solve cost height that above-mentioned existing liquid level emasuring device exists, inconvenience and the lower problem of precision to be installed, the invention provides that a kind of device is few, cost is low, easy for installation, quick and sound wave liquid level emasuring device that measuring accuracy is higher.

Program complexity and the lower problem of measuring accuracy in order to solve above-mentioned existing level measuring method the invention provides the sound wave liquid level measuring method that a kind of process of measurement is simple and measuring accuracy is higher.

Sound wave liquid level emasuring device of the present invention comprises: waveguide pipe, signal Processing control chip, sound wave generating unit, sound wave receiving element and analog/digital converter; This waveguide pipe lower end insertion is surveyed in the liquid; The steering order that sound wave generating unit received signal processing controls chip sends, the voice signal of the specified frequency of generation signal Processing control chip also sends in waveguide pipe; The sound wave receiving element is positioned at the below of sound wave generating unit, and is positioned at waveguide pipe, and the position at sound wave receiving element place is made as datum mark, and this point is L with the distance of liquid level; The voice signal that analog/digital converter sends the sound wave receiving element converts digital signal to and sends it back the signal Processing control chip; Described signal Processing control chip is determined the frequency of a lowest audio frequency signal, send the pairing steering order of frequency that begins up to increase from this low-limit frequency to the sound wave generating unit, control sound wave generating unit produces the voice signal of the specified frequency of steering order in two or more cycles; Described sound wave receiving element receives the sound wave of reference point, sends sound wave to analog/digital converter with the form of electric signal and converts digital signal to and deliver to the signal Processing control chip; Described signal Processing control chip is noted the amplitude of the sound of this frequency at reference point, the sound amplitude and the preceding frequency sound amplitude that is once write down of this frequency are compared, find out the minimum amplitude of first appearance, and the amplitude that this is minimum stores, then the pairing frequency of the sound wave of this minimum amplitude is the frequency of standing wave, and according to the frequency and the formula of the aerial velocity of propagation of sound wave, standing wave:

$L=\frac{\mathrm{\&lambda;}}{2}=\frac{\mathrm{<figure-callout\; label="v"\; filenames="A20041006235500151.png"\; state="\{\{state\}\}">v</figure-callout>}}{2\&CenterDot;f}$

Calculate the value of L.

Sound wave liquid level measuring method of the present invention comprises the steps:

(1) provide sound wave receiving element and waveguide pipe, the sound wave receiving element is positioned at waveguide pipe, and the position of setting sound wave receiving element place is a datum mark, and it is L to the distance of liquid level;

(2) provide signal Processing control chip, analog/digital conversion unit and sound wave generating unit, this signal Processing control chip is determined the frequency of the sound signal of a minimum, control sound wave generating unit produces the voice signal of this frequency at least two cycles, and exports waveguide pipe to; Voice signal in the waveguide pipe sends back to the signal Processing control chip by sound wave receiving element and analog/digital conversion unit; The signal Processing control chip is noted the amplitude of the sound of this frequency at reference point;

(3) the signal Processing control chip increases the frequency of sound signal, and control sound wave generating unit produces the voice signal of this frequency at least two cycles, sends back to the signal Processing control chip by sound wave receiving element and analog/digital conversion unit; The signal Processing control chip is noted the amplitude of the sound of this frequency at reference point;

(4) whether the sound amplitude after the signal Processing control chip judgement increase frequency is greater than the sound amplitude under the last frequency.If, finish to measure, be the standing wave frequency with last frequency; If not, repeating step (3);

(5) the signal Processing control chip is according to standing wave frequency, the aerial velocity of propagation of sound wave and formula:

$L=\frac{\mathrm{\&lambda;}}{2}=\frac{\mathrm{<figure-callout\; label="v"\; filenames="A20041006235500151.png"\; state="\{\{state\}\}">v</figure-callout>}}{2\&CenterDot;f}$

Calculate L.

Adopt a plurality of sound wave receiving elements and float with respect to prior art, sound wave liquid level emasuring device of the present invention receives the sound of waveguide pipe by the sound wave receiving element that is positioned at datum mark, and device is less, and cost is low, easy for installation, quick; In addition, the sound wave that the sound wave receiving element received of sound wave liquid level emasuring device of the present invention for the sound wave that reflects at the incident acoustic wave of waveguide pipe with by liquid level at the superimposed sound wave in datum mark place, do not exist the instability that produces because of the fluctuation of float liquid body in the prior art to make the deficiency of measuring accuracy reduction; Simultaneously, the present invention is by the operation of waveguide pipe direct sound waves, and this has been avoided the error that causes because of liquid fluctuation to a great extent, and measuring accuracy is also higher relatively.

Sound wave liquid level measuring method of the present invention, produce the voice signal of its assigned frequency by signal Processing control chip control sound wave generating unit, and the amplitude of the sound of record datum mark, find out the frequency of the sound wave of minimum radius, calculate the distance of datum mark to liquid level according to the condition formula that produces standing wave, process of measurement is simple; In addition, in the sound wave liquid level measuring method of the present invention, the sound wave receiving element is to the sound signal of signal Processing control chip transmission after the analog/digital conversion cell translation, only be incident acoustic wave and the stack of the reflective sound wave that is reflected by liquid level in datum mark, substantially there is not the influence of extraneous factor, the measuring accuracy height.

Description of drawings

Fig. 1 is the structural representation of existing sound wave water level measurement mechanism.

Fig. 2 is the structural representation of sound wave liquid level emasuring device of the present invention.

Fig. 3 is the high-level schematic functional block diagram of sound wave liquid level emasuring device of the present invention.

Fig. 4 is a sound wave liquid level measuring method process flow diagram of the present invention.

Embodiment

The present invention utilizes the incident wave of sound wave and this principle of node amplitude minimum of reflection wave transmits generation in opposite directions in air standing wave to carry out level gauging, and the frequency of standing wave calculates the distance realization level gauging that datum mark arrives liquid level thereby occur for the first time by the sound wave in the searching waveguide pipe in datum mark.

Please refer to Fig. 2, it is the structural representation of sound wave liquid level emasuring device of the present invention, sound wave liquid level emasuring device comprises soundwave generating unit 1, soundwave receiving element 2,waveguide pipe 3, signal Processing control chip 4 (as shown in Figure 3) and analog/digital conversion unit (as shown in Figure 3), and L is the distance of soundwave receiving element 2 to the liquid surface.Describedwaveguide pipe 3 is a hollow tube, and it is fixed to (figure does not show) on the anchor post, and the end portion ofwaveguide pipe 3 inserts the liquid of surveying.Described liquid level emasuring device also comprises ahousing 10, thishousing 10 comprise have cavity,cylindrical body 19, upper/lower terminal alongbody 19 respectively extends cone, lower end cone andbody 19 have the opening that connects, described signal Processing control chip 4 is positioned in the cavity ofbody 19 ofhousing 10, described soundwave generating unit 1 and soundwave receiving element 2 parts are placed in the opening of lower end, and described soundwave receiving element 2 is positioned at the below of sound wave generating unit 1.Described lower end cone has theinterface portion 20 that matches withwaveguide pipe 3, cooperate fixing with the end ofwaveguide pipe 3 by thisinterface portion 20,housing 10 is fixed on the end ofwaveguide pipe 3, and makes described soundwave receiving element 2 just in time be positioned at the center, top of waveguide pipe 3.The top ofwaveguide pipe 3, promptly the position of soundwave receiving element 2 is reference points of level gauging, supposes that reference point has the height H that is higher than surface level₀, the liquid level of being surveyed can be drawn by following formula: H=H₀-L, liquid level emasuring device is fixed among the present invention, i.e. H₀Be fixed value, then liquid level change is directly changed into and is the variation of liquid level to distance between reference L.

The present invention utilizes the locus of seeking the standing wave node to measure the distance L of liquid level to reference point, thereby realizes level gauging, and its principle is as follows:

Because in the communication process of sound wave, to reflect at the interphase of medium, the stack of incident wave and reflection wave forms standing wave under certain condition.When forming standing wave, only change the title antinode of amplitude maximum, the title node of amplitude minimum with the locus cycle along the direction of wave travel amplitude.

Can derive by wave equation: only satisfying transmission range L beIntegral multiple, promptly

$L=n\&CenterDot;\frac{\mathrm{\&lambda;}}{2}$

The time form standing wave (wherein λ is a wave length of sound).

When n=1,$L=\frac{\mathrm{\&lambda;}}{2}=\frac{\mathrm{<figure-callout\; label="v"\; filenames="A20041006235500151.png"\; state="\{\{state\}\}">v</figure-callout>}}{2\&CenterDot;f}$

Wherein v is the speed (constant relatively) that sound wave is propagated in air, and f is the frequency of sound wave.Can calculate L by detecting the frequency f that forms the sound wave of standing wave for the first time.When forming standing wave, in node place acoustic vibration amplitude minimum, the sound wave of detected amplitude minimum, this moment, the frequency of sound wave correspondence was the standing wave frequency.

Signal Processing control chip 4 control soundwave generating units 1 produce the sound wave of certain frequency alongwaveguide pipe 3 incidents among the present invention, reflect up to liquid level and by liquid level, the sound wave that soundwave receiving element 2 receives in thewaveguide pipe 3, and behind the analog/digital conversion unit, deliver to signal Processing control chip 4, signal Processing control chip 4 is noted the acoustic sound amplitude when this frequency.When the wavelength X of the sound wave that is transmitted and L satisfy following the relation:

$L=n\&CenterDot;\frac{\mathrm{\&lambda;}}{2}$

Wherein n is an integer, then incident wave and reflection wave stack, produce standing wave, and satisfy at reference point, the position that is soundwave receiving element 2 is the node of standing wave, and then this moment, then the frequency of this amplitude minimum was the frequency of standing wave in the amplitude minimum of the sound wave at soundwave receiving element 2 places, signal Processing control chip 4 is noted this frequency, and according to formula:

$L=\frac{\mathrm{\&lambda;}}{2}=\frac{\mathrm{<figure-callout\; label="v"\; filenames="A20041006235500151.png"\; state="\{\{state\}\}">v</figure-callout>}}{2\&CenterDot;f}$

Calculate the value of L, promptly measure the distance of soundwave receiving element 2 to liquid level, described v is the speed that sound wave is propagated in air.

Please consulting Fig. 3 simultaneously, is the functional schematic of liquid level emasuring device of the present invention, and measurement mechanism is made up of four functional units: signal Processing and control module, soundwave generating unit 1, soundwave receiving element 2 and analog/digital conversion unit.

Described signal processing control unit is a signal Processing control chip 4, control survey workflow, operating measurement algorithm.

Soundwave generating unit 1 is made up of harmonic signal generator 11, audio-frequency power amplifier 13 and loudspeaker 12.Harmonic signal generator 11 accepts to generate from the instruction that signal Processing control chip 4 transmits the sinusoidal signal of assigned frequency, amplifies rear drive loudspeaker 12 through audio-frequency power amplifier 13, finishes the electroacoustic conversion, sends the voice signal of assigned frequency.

Soundwave receiving element 2 is made up of microphone 21, Mike's power amplifier 22.

The analog/digital conversion unit is an analog/digital converter 7.

Voice signal is amplified to certain amplitude by Mike's power amplifier 22 after microphone 21 is finished the acoustic-electric conversion, convert digital signal to through analog/digital converter 7 then and deliver to signal Processing control chip 4.

Signal Processing control chip 4 and harmonic signal generator 11 are electrical connected by cable, harmonic signal generator 11 and loudspeaker 12 are electrical connected by cable, described microphone 21 is electrical connected with Mike's power amplifier 22, and analog/digital conversion unit 7 is electrically connected between Mike's power amplifier 22 and the signal Processing control chip 4 by cable.

Signal Processing control chip 4 pre-input control programs when working, determine to measure initial minimum frequency at every turn, to guarantee occurring standing wave for the first time in measuring process.Described low-limit frequency is determined by following method: when maximum, incident acoustic wave and reflective sound wave can produce the frequency of the standing wave first time to reference point to the distance L of liquid level, and the frequency of minimum is less than the frequency of above-mentioned first time of standing wave.

Suppose that measurement range is 0～10 meter, promptly the length L ofwaveguide pipe 3 is 10 meters.According to:

$L=\frac{\mathrm{\&lambda;}}{2}=\frac{\mathrm{<figure-callout\; label="v"\; filenames="A20041006235500151.png"\; state="\{\{state\}\}">v</figure-callout>}}{2\&CenterDot;f}$

The speed of sonic propagation is 340 meter per seconds, and corresponding standing wave frequency for the first time is 17Hz, and then minimum frequency is chosen and is slightly less than 17Hz, to guarantee occurring standing wave for the first time in measuring process.

Be provided with the pairing steering order of described low-limit frequency in the signal Processing control chip 4, and the pairing steering order of different frequency that increases gained with constant step size or variable step.Signal Processing control chip 4 is every to send the steering order of an assigned frequency to soundwave generating unit 1, and then it can note the pairing frequency of this steering order.

During work, signal Processing control chip 4 sends the pairing steering order of frequency that begins and increase with constant step size or variable step from described low-limit frequency to soundwave generating unit 1, and control harmonic signal generator 11 produces the sine wave of the specified frequency of steering order in two or more cycles.Described sine wave is after audio-frequency power amplifier 13 amplifies, carry out the electroacoustic conversion through loudspeaker 12, mode with the incident sound tone signal sends to waveguidepipe 3, incident acoustic wave runs into liquid level and is reflected, mode with reflective sound wave returns alongwaveguide pipe 3, and incident acoustic wave and reflective sound wave superpose in waveguide pipe 3.Soundwave receiving element 2 receives the sound wave ofwaveguide pipe 3 top ends; Microphone 21 in the soundwave receiving element 2 carries out the acoustic-electric conversion with the sound wave at received its place, position, sound wave is transmitted to Mike's power amplifier 22 with the form of electric signal, and Mike's power amplifier 22 acoustic signals that it is received is amplified to and sends analog/digital converter 7 after the certain amplitude to and convert digital signal to and deliver to signal Processing control chip 4.Signal Processing control chip 4 is noted at the sound of this frequency amplitude at reference point, the sound amplitude and the preceding frequency sound amplitude that is once write down of this frequency are compared, by mode so, find out and first minimum amplitude occurs, and the amplitude that this is minimum stores, then the pairing frequency of the sound wave of this minimum amplitude is the frequency of standing wave, according to formula:

$L=\frac{\mathrm{\&lambda;}}{2}=\frac{\mathrm{<figure-callout\; label="v"\; filenames="A20041006235500151.png"\; state="\{\{state\}\}">v</figure-callout>}}{2\&CenterDot;f}$

Calculate the value of L.

A kind of sound wave liquid level measuring method as shown in Figure 4, comprises the steps:

(1) determine datum mark above the survey liquid level: sound wave receiving element and waveguide pipe are provided, and the sound wave receiving element is positioned at waveguide pipe, and the position of setting sound wave receiving element place is a datum mark, and its distance to liquid level is L;

(2) provide signal Processing control chip and sound wave receiving element, this signal Processing control chip is determined a certain minimum frequency, the voice signal that control sound wave generating unit produces this frequency exports waveguide pipe to, and the voice signal in the waveguide pipe sends back to the signal Processing control chip by sound wave receiving element and analog/digital conversion unit.The signal Processing control chip is noted the amplitude of the sound of this frequency at reference point;

(3) the signal Processing control chip increases the frequency of sound signal, and control sound wave generating unit produces the voice signal of this frequency, sends back to the signal Processing control chip by sound wave receiving element and analog/digital conversion unit.The signal Processing control chip is noted the amplitude of the sound of this frequency at reference point;

(4) the signal Processing control chip judge to increase sound amplitude after the frequency whether greater than the amplitude of sound under the last frequency.If, finish to measure, be the standing wave frequency with last frequency; If not, repeating step (3);

(5) the signal Processing control chip is according to formula

$L=\frac{\mathrm{\&lambda;}}{2}=\frac{\mathrm{<figure-callout\; label="v"\; filenames="A20041006235500151.png"\; state="\{\{state\}\}">v</figure-callout>}}{2\&CenterDot;f}$

With standing wave frequency computation part L, described v is the speed that sound wave is propagated in air.

In above-mentioned measuring method, described sound wave generating unit comprises a harmonic signal generator, audio-frequency power amplifier and a loudspeaker, described sound wave receiving element comprises microphone and Mike's power amplifier, the harmonious wave generator of described signal Processing control chip is electrical connected, described audio-frequency power amplifier is electrically connected between harmonic signal generator and the loudspeaker, described microphone and Mike's power amplifier are electrical connected, and described analog/digital conversion unit is electrically connected between signal Processing control chip and the Mike's power amplifier.Described microphone is positioned at the below of loudspeaker.

In above-mentioned steps (2), comprise the steps:

(11) the signal Processing control chip sends steering order to the harmonic signal generator, control harmonic signal generator produces the sinusoidal signal of the assigned frequency in two or more cycles at least, this sinusoidal signal is amplified the rear drive loudspeaker through audio-frequency power amplifier, loudspeaker carries out the electroacoustic conversion to the sound signal of this amplification, sends the voice signal of assigned frequency to waveguide pipe.This voice signal transmits downwards along waveguide pipe, is reflected when running into liquid level, and then the be reflected voice signal of returning and the voice signal of incident superpose in waveguide pipe.In the present embodiment, signal Processing control chip control harmonic signal generator produces the sinusoidal signal in five cycles.

(12) microphone that is positioned at the waveguide pipe top receives it and is positioned at the voice signal of waveguide pipe position, after microphone carries out the acoustic-electric conversion to its voice signal that receives, be sent to Mike's power amplifier and be amplified to certain amplitude, convert digital signal to through analog/digital converter then and deliver to the signal Processing control chip.The signal Processing control chip is noted the sound amplitude when this frequency different cycles, such as the sound amplitude of noting five cycles in the present embodiment, calculates the mean value of the sound amplitude in these five cycles, and notes.

In the described step (3), the increase of the frequency of sound signal is that the mode with constant step size increases.

In the described step (3), the increase of the frequency of sound signal is to increase in the mode of fixed step size not.

Described definite minimum frequency in the described step (2) is determined by following method: reference point is during to the distance maximum of liquid level, incident acoustic wave and reflective sound wave can produce the frequency of standing wave for the first time in datum mark, and this minimum frequency is the frequency less than above-mentioned first time of standing wave.

The above only is a preferred implementation of the present invention; should be pointed out that for those skilled in the art, under the prerequisite that does not break away from the principle of the invention; can also make some improvements and modifications, these improvements and modifications also should be considered as protection scope of the present invention.

Claims (17)

1. sound wave liquid level emasuring device comprises:

Waveguide pipe, this waveguide pipe lower end insertion is surveyed in the liquid;

The signal Processing control chip;

The sound wave generating unit, the steering order that received signal processing controls chip sends, the voice signal of the specified frequency of generation signal Processing control chip also sends in waveguide pipe;

The sound wave receiving element is positioned at the below of sound wave generating unit, and is positioned at waveguide pipe, and the position at sound wave receiving element place is made as datum mark, and this point is L with the distance of liquid level;

It is characterized in that: also comprise analog/digital converter, the voice signal that the sound wave receiving element is sent converts digital signal to and sends it back the signal Processing control chip;

Described signal Processing control chip is determined the frequency of a lowest audio frequency signal, send the pairing steering order of frequency that begins up to increase from this low-limit frequency to the sound wave generating unit, control sound wave generating unit produces the voice signal of the specified frequency of steering order in two or more cycles;

Described sound wave receiving element receives the sound wave of reference point, sends sound wave to analog/digital converter with the form of electric signal and converts digital signal to and deliver to the signal Processing control chip;

Described signal Processing control chip is noted the amplitude of the sound of this frequency at reference point, the sound amplitude and the preceding frequency sound amplitude that is once write down of this frequency are compared, find out the minimum amplitude of first appearance, and the amplitude that this is minimum stores, then the pairing frequency of the sound wave of this minimum amplitude is the frequency of standing wave, and according to the frequency and the formula of the aerial velocity of propagation of sound wave, standing wave:

$L=\frac{\mathrm{\&lambda;}}{2}=\frac{v}{2\&CenterDot;f}$

Calculate the value of L.

2. sound wave liquid level emasuring device as claimed in claim 1 is characterized in that: described sound wave generating unit comprises harmonic signal generator, audio-frequency power amplifier and loudspeaker.

3. sound wave liquid level emasuring device as claimed in claim 2 is characterized in that: the steering order that described harmonic signal generator received signal processing controls chip sends, the sinusoidal signal of the specified frequency of generation signal Processing control chip.

4. sound wave liquid level emasuring device as claimed in claim 3 is characterized in that: described sound wave receiving element comprises microphone and Mike's power amplifier.

5. sound wave liquid level emasuring device as claimed in claim 4 is characterized in that: described microphone is positioned at the below of loudspeaker.

6. sound wave liquid level emasuring device as claimed in claim 5 is characterized in that: described microphone is positioned at the top of waveguide pipe.

7. sound wave liquid level emasuring device as claimed in claim 1 is characterized in that: the frequency of described sound signal increases in the mode of constant step size.

8. sound wave liquid level emasuring device as claimed in claim 1 is characterized in that: the frequency of described sound signal increases in the mode of variable step.

9. sound wave liquid level emasuring device as claimed in claim 6 is characterized in that: also comprise a housing, described signal Processing control chip, sound wave generating unit, sound wave receiving element and analog/digital converter are fixed in this housing.

10. sound wave liquid level emasuring device as claimed in claim 9, it is characterized in that: the lower end of described housing has the interface portion that matches with waveguide pipe, cooperate fixingly with the end of waveguide pipe by this interface portion, described sound wave receiving element just in time is positioned at the center, top of waveguide pipe.

11. a sound wave liquid level measuring method is characterized in that, comprises the steps:

(1) provide sound wave receiving element and waveguide pipe, the sound wave receiving element is positioned at waveguide pipe, and the position of setting sound wave receiving element place is a datum mark, and it is L to the distance of liquid level;

(2) provide signal Processing control chip, analog/digital conversion unit and sound wave generating unit, this signal Processing control chip is determined the frequency of the sound signal of a minimum, control sound wave generating unit produces the voice signal of this frequency at least two cycles, and exports waveguide pipe to; Voice signal in the waveguide pipe sends back to the signal Processing control chip by sound wave receiving element and analog/digital conversion unit; The signal Processing control chip is noted the amplitude of the sound of this frequency at reference point;

(3) the signal Processing control chip increases the frequency of sound signal, and control sound wave generating unit produces the voice signal of this frequency at least two cycles, sends back to the signal Processing control chip by sound wave receiving element and analog/digital conversion unit; The signal Processing control chip is noted the amplitude of the sound of this frequency at reference point;

(4) whether the sound amplitude after the signal Processing control chip judgement increase frequency is greater than the sound amplitude under the last frequency.If, finish to measure, be the standing wave frequency with last frequency; If not, repeating step (3);

(5) the signal Processing control chip is according to standing wave frequency, the aerial velocity of propagation of sound wave and formula:

$L=\frac{\mathrm{\&lambda;}}{2}=\frac{v}{2\&CenterDot;f}$

Calculate L.

12. sound wave liquid level measuring method as claimed in claim 11 is characterized in that: described sound wave generating unit comprises a harmonic signal generator, audio-frequency power amplifier and a loudspeaker.

13. sound wave liquid level measuring method as claimed in claim 12, it is characterized in that: described sound wave receiving element comprises microphone and Mike's power amplifier, the harmonious wave generator of described signal Processing control chip is electrical connected, described audio-frequency power amplifier is electrically connected between harmonic signal generator and the loudspeaker, described microphone and Mike's power amplifier are electrical connected, and described analog/digital conversion unit is electrically connected between signal Processing control chip and the Mike's power amplifier; Described microphone is positioned at the below of loudspeaker.

14. sound wave liquid level measuring method as claimed in claim 13 is characterized in that: in above-mentioned steps (2), comprise the steps:

(11) the signal Processing control chip sends steering order to the harmonic signal generator, control harmonic signal generator produces the sinusoidal signal of the assigned frequency in two or more cycles, this sinusoidal signal is amplified the rear drive loudspeaker through audio-frequency power amplifier, loudspeaker carries out the electroacoustic conversion to the sound signal of this amplification, sends the voice signal of assigned frequency to waveguide pipe;

(12) microphone that is positioned at the waveguide pipe top receives its voice signal in the waveguide pipe position, after microphone carries out the acoustic-electric conversion to its voice signal that receives, be sent to Mike's power amplifier and be amplified to certain amplitude, convert digital signal to through analog/digital converter then and deliver to the signal Processing control chip.

15. as claim 11 or 14 described sound wave liquid level measuring methods, it is characterized in that: in above-mentioned described step (3), the increase of the frequency of sound signal is that the mode with constant step size increases.

16. as claim 11 or 14 described sound wave liquid level measuring methods, it is characterized in that: in above-mentioned described step (3), the increase of the frequency of sound signal is to increase in the mode of fixed step size not.

17. as claim 11 or 14 described sound wave liquid level measuring methods, it is characterized in that: the described definite minimum frequency in the described step (2) is determined by following method: reference point is during to the distance maximum of liquid level, incident acoustic wave and reflective sound wave can produce the frequency of standing wave for the first time in datum mark, and this minimum frequency is the frequency less than the above-mentioned generation standing wave first time.

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