CN113189196B - Method for detecting gas concentration based on ultrasonic phase difference technology - Google Patents

Method for detecting gas concentration based on ultrasonic phase difference technology Download PDF

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CN113189196B
CN113189196B CN202110384059.5A CN202110384059A CN113189196B CN 113189196 B CN113189196 B CN 113189196B CN 202110384059 A CN202110384059 A CN 202110384059A CN 113189196 B CN113189196 B CN 113189196B
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phase difference
frequency
ultrasonic
low
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CN113189196A (en
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孙慧
丁喜波
丁欣
施云波
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Harbin University of Science and Technology
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
    • G01N29/02—Analysing fluids
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
    • G01N29/44—Processing the detected response signal, e.g. electronic circuits specially adapted therefor
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2291/00—Indexing codes associated with group G01N29/00
    • G01N2291/01—Indexing codes associated with the measuring variable
    • G01N2291/012—Phase angle

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Abstract

The invention discloses a gas concentration detection method based on an ultrasonic phase difference technology, and belongs to the technical field of gas concentration detection. The invention deduces and utilizes the conclusion that the phase difference before and after mixing is the same, and the frequency is slightly smaller than the original x by selecting 1 (t) and x 2 Rectangular wave signals y (t) of (t), respectively associated with x 1 (t) and x 2 After mixing, obtaining two low-frequency signals, and obtaining the phase difference of the two low-frequency signals, thereby realizing the conversion of the original detection of the phase difference of the two high-frequency ultrasonic signals into the detection of the extremely low-frequency phase difference. The invention can realize the conversion of original phase difference detection of two high-frequency ultrasonic signals into extremely low-frequency phase difference detection, thereby meeting the requirement of improving the detection precision and solving the problem that a system has enough high working frequency when measuring low-concentration gas in the traditional method.

Description

Method for detecting gas concentration based on ultrasonic phase difference technology
Technical Field
The invention relates to a gas concentration detection method based on an ultrasonic phase difference technology, and belongs to the technical field of gas concentration detection.
Background
The gas concentration detection by using the acoustic technology has the advantages of low cost, low power consumption, applicability to complex environments and the like. When the concentration of the measured gas is very low, the receiving time difference delta T of the two ultrasonic signals in the two-channel measuring cavity and the reference cavity is very small, so that the corresponding phase difference is causedIf the system counting frequency is not high, the measured phase difference error is too large, and the gas concentration measurement accuracy is seriously affected. In the prior art, no method can well solve the problem.
Disclosure of Invention
The invention aims to provide a gas concentration detection method based on an ultrasonic wave phase difference technology, which converts a high-frequency signal phase difference into a low-frequency signal phase difference for extraction by providing an ultrasonic wave mixing technology, thereby realizing higher measurement precision requirement by using a lower working frequency system and solving the problems in the prior art.
The method for detecting the gas concentration based on the ultrasonic phase difference technology comprises the following steps:
step one, obtaining a conclusion: the phase difference before mixing is the same as the phase difference after mixing;
step two, using the conclusion, selecting rectangular wave signals y (t) with frequencies close to those of the known rectangular wave signals x1 (t) and x2 (t), and enabling y (t) to be respectively equal to x 1 (t) and x 2 And (t) mixing and low-pass filtering to obtain two low-frequency signals, and obtaining the phase difference of the two low-frequency signals to realize the conversion of the original detection of the phase difference of the two high-frequency ultrasonic signals into the detection of the extremely low-frequency phase difference.
Further, in step one, the conclusion is reached by the following method:
setting the frequency of the ultrasonic signal as f, and measuring the time domain rectangular wave signal as x after ultrasonic receiving processing in the cavity 1 (T) period of T 1 Pulse width τ 1 The time domain rectangular wave signal after ultrasonic wave receiving processing in the reference cavity is x 2 (T) since the ultrasonic waves of the reference cavity and the measuring cavity are the same ultrasonic source signal with phase difference, the ultrasonic wave time domain waveform signal received by the reference cavity is also of period T 1 Pulse width τ 1 ，
Assuming that the time difference of the received signal in the reference cavity is delta t and the angular frequency omega is measured by lagging the signal in the measurement cavity 1 The phase difference of the received signals of the reference cavity and the measuring cavityComparing the ultrasonic time domain signals to convert them into rectangular wave signals, setting x 1 (t) and x 2 The duty cycle of (t) is +.>Taking the frequency y (t), angular frequency omega of another rectangular wave signal 2 Let omega 2 Slightly less than omega 1 Duty cycle is +.>Let y (t) be equal to x in magnitude 1 (t) and x 2 Amplitude K of (t):
from Fourier seriesWherein-> It is known that the number of the components,
x 1 (t) fourier series:
and:there is->Then: />Due to x 1 (t) is an even function, b n ＝0，
Corresponding x 1 The fourier series expansion of (t) is:
handle x 2 (t) is regarded as x 1 (t) a function obtained by right shifting x in the time domain,
then x 2 The fourier series expansion of (t) is:
the fourier series expansion of the same theory y (t) is:
let x 1 (t) and x 2 (t) are multiplied by y (t) mixing respectively to obtain a new function K 1 (t) and K 2 (t)，
Wherein the method comprises the steps of
And (3) finishing to obtain:
wherein cos (omega) 1 -ω 2 ) t and cos [ (omega) 1 -ω 2 )t-ω 1 Δt]Respectively K 1 (t) and K 2 The Fourier of (t)The low frequency term in the inner leaf series term is far higher than (omega) 1 -ω 2 ) And K 1 (t) and K 2 (t) after low frequency filtering, respectively, leaving only the low frequency term, and therefore,
x 1 (t) and x 2 (t) mixing with y (t) and low-pass filtering to obtain new signal function K 1 (t) and K 2 (t) the phase difference is stillAnd K is 1 (t) and K 2 (t) angular frequency conversion to ω 1 -ω 2 Is a low frequency signal, and thus concludes: the phase difference before and after mixing is the same.
The invention has the following advantages: the gas concentration detection method based on the ultrasonic wave phase difference technology can realize the conversion of original phase difference detection of two high-frequency ultrasonic signals into extremely low-frequency phase difference detection, thereby meeting the requirement of improving detection precision and solving the problem that a system has enough high working frequency when measuring low-concentration gas in the traditional method.
Drawings
FIG. 1 is a basic schematic diagram of an ultrasonic wave phase difference gas concentration detection technology.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
The basic principle of the ultrasonic wave phase difference gas concentration detection technology is shown in figure 1. The ultrasonic signals are loaded at the input ends of two channels close to the same path, the reference channel in the two channels is closed air, and the measuring channel is the gas with the concentration to be measured. When the ultrasonic signals pass through the two channels, the sound wave transmission speeds are different due to different gas concentrations, and the two output ends receive unsynchronized sound wave signals, so that the signals are reflected to have phase differences. The phase difference is extracted by a phase detection technology and calculated to obtain the concentration of the gas to be detected.
Ultrasonic waves have definite propagation speeds in different gases in different environments. The ultrasonic sound velocity formula in the gas under normal pressure is as follows,
wherein R is a universal gas constant, T is an ambient absolute temperature, M is the molar molecular weight of the measured gas, gamma is the specific heat ratio of the gas,
when the air is mixed with the gas to be measured, M and gamma in the formula (1) can be regarded as weighted average values of the mixed gas, and when the concentration u of the gas to be measured in the air is determined and the molecular weight and specific heat ratio of the mixed gas are determined, the formula (1) is corrected at this time,
wherein u is the concentration of the measured gas, M 1 For background air molar mass, M 2 Gamma, the molar weight of the gas to be measured 1 Gamma is the specific heat capacity ratio of air 2 To be the specific heat ratio of the gas to be measured,
the relation between the phase difference and the gas concentration after finishing can be written as:
wherein the method comprises the steps of T is the absolute temperature of the environment, M 1 Is of air molecular weight, M 2 For purifying the molecular weight of the detected gas, f is the ultrasonic frequency of the loaded and input end, and the phase difference of the two-channel ultrasonic receiving signals is +.>The measurement channel and reference channel are L in acoustic path.
Further, let the frequency of the ultrasonic signal be f, and the time domain rectangular wave signal after ultrasonic receiving processing in the measuring cavity be x 1 (T) period of T 1 Pulse width τ 1 The time domain rectangular wave signal after ultrasonic wave receiving processing in the reference cavity is x 2 (T) since the ultrasonic waves of the reference cavity and the measuring cavity are the same ultrasonic source signal with phase difference, the ultrasonic wave time domain waveform signal received by the reference cavity is also of period T 1 Pulse width τ 1 ，
Assuming that the time difference of the received signal in the reference cavity is delta t and the angular frequency omega is measured by lagging the signal in the measurement cavity 1 The phase difference of the received signals of the reference cavity and the measuring cavityComparing the ultrasonic time domain signals to convert them into rectangular wave signals, setting x 1 (t) and x 2 The duty cycle of (t) is +.>Taking the frequency y (t), angular frequency omega of another rectangular wave signal 2 Let omega 2 Slightly less than omega 1 Duty cycle is +.>Let y (t) be equal to x in magnitude 1 (t) and x 2 Amplitude K of (t);
from Fourier series
Wherein the method comprises the steps of
x 1 (t) fourier series:
and:there is->Then: />Due to x 1 (t) is an even function, b n ＝0，
Corresponding x 1 The fourier series expansion of (t) is:
handle x 2 (t) is regarded as x 1 (t) a function obtained by right shifting x in the time domain,
then x 2 The fourier series expansion of (t) is:
the fourier series expansion of the same theory y (t) is:
let x 1 (t) and x 2 (t) are multiplied by y (t) mixing respectively to obtain a new function K 1 (t) and K 2 (t)，
Wherein the method comprises the steps of
And (3) finishing to obtain:
wherein cos (omega) 1 -ω 2 ) t and cos [ (omega) 1 -ω 2 )t-ω 1 Δt]Respectively K 1 (t) and K 2 The low frequency term in the Fourier series term of (t) is far higher than (omega) 1 -ω 2 ) And K 1 (t) and K 2 (t) after low frequency filtering, respectively, leaving only the low frequency term, and therefore,
it can be concluded that: x is x 1 (t) and x 2 (t) mixing with y (t) and low-pass filtering to obtain new signal function K 1 (t) and K 2 (t) the phase difference is stillAnd K is 1 (t) and K 2 (t) angular frequency conversion to ω 1 -ω 2 Is a low frequency signal, thus a conclusion is drawn that the phase difference before and after mixing is the same, and the conclusion is utilized by selecting a frequency slightly less than the original x 1 (t) and x 2 Rectangular wave signals y (t) of (t), respectively associated with x 1 (t) and x 2 After mixing, two low-frequency signals can be obtained, and the original detection of the phase difference of two high-frequency ultrasonic signals can be converted into the detection of the phase difference of the extremely low frequency by obtaining the phase difference of the two low-frequency signals, so that the requirement of improving the detection precision is met.
The specific embodiments described in this patent are merely illustrative of one type of parameter design and are not intended to limit the invention in any way. Many possible variations and modifications may be made to the disclosed method and apparatus, or equivalents may be modified by those skilled in the art, without departing from the scope of the invention. Therefore, any simple modification, equivalent variation and modification of the above embodiments according to the technical substance of the present invention are still within the scope of the technical solution of the present invention.

Claims (1)

1. The method for detecting the gas concentration based on the ultrasonic phase difference technology is characterized by comprising the following steps of:
step one, obtaining a conclusion: the phase difference before mixing is the same as the phase difference after mixing; the conclusion is obtained by the following method:
setting the frequency of the ultrasonic signal as f, and measuring the time domain rectangular wave signal as x after ultrasonic receiving processing in the cavity 1 (T) period of T 1 Pulse width τ 1 The time domain rectangular wave signal after ultrasonic wave receiving processing in the reference cavity is x 2 (T) since the ultrasonic waves of the reference cavity and the measuring cavity are the same ultrasonic source signal with phase difference, the time domain waveform signal of the acoustic wave received by the reference cavity is also of period T 1 Pulse width τ 1 ，
Assuming that the time difference of the received signal in the reference cavity is delta t and the angular frequency omega is measured by lagging the signal in the measurement cavity 1 The phase difference of the received signals of the reference cavity and the measuring cavityComparing the ultrasonic time domain signals to convert them into rectangular wave signals, setting x 1 (t) and x 2 The duty cycle of (t) is +.>Taking the frequency y (t), angular frequency omega of another rectangular wave signal 2 Let omega 2 Slightly less than omega 1 Duty cycle is +.>Let y (t) be equal to x in magnitude 1 (t) and x 2 Amplitude K of (t):
from Fourier seriesWherein-> It is known that the number of the components,
x 1 (t) fourier series:
and:there is->Then: />Due to x 1 (t) is an even function, b n ＝0，
Corresponding x 1 The fourier series expansion of (t) is:
handle x 2 (t) is regarded as x 1 (t) a function obtained by right shifting x in the time domain,
then x 2 The fourier series expansion of (t) is:cos2ω 1 (t-Δt)+...
the fourier series expansion of the same theory y (t) is:
let x 1 (t) and x 2 (t) are multiplied by y (t) mixing respectively to obtain a new function K 1 (t) and K 2 (t)，
Wherein the method comprises the steps of
And (3) finishing to obtain: k (K) 1
Wherein cos (omega) 1 -ω 2 ) t and cos [ (omega) 1 -ω 2 )t-ω 1 Δt]Respectively K 1 (t) and K 2 The low frequency term in the Fourier series term of (t) is far higher than (omega) 1 -ω 2 ) And K 1 (t) and K 2 (t) after low frequency filtering, respectively, leaving only the low frequency term, and therefore,
x 1 (t) and x 2 (t) mixing with y (t) and low-pass filtering to obtain new signal function K 1 (t) and K 2 (t) the phase difference is stillAnd K is 1 (t) and K 2 (t) angular frequency conversion to ω 1 -ω 2 Is a low frequency signal, and thus concludes: the phase difference before mixing is the same as the phase difference after mixing;
step two, selecting the frequency and the known rectangular wave signal x by utilizing the conclusion 1 (t) and x 2 (t) rectangular wave signal y (t) with close frequency, lety (t) is respectively equal to x 1 (t) and x 2 And (t) mixing and low-pass filtering to obtain two low-frequency signals, and obtaining the phase difference of the two low-frequency signals to realize the conversion of the original detection of the phase difference of the two high-frequency ultrasonic signals into the detection of the extremely low-frequency phase difference.
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Publication number Priority date Publication date Assignee Title
CN1431496A (en) * 2003-01-30 2003-07-23 南京大学 Difference method for measuring change of ultrasonic gases in microscale and its control and evaluation system
JP2008256485A (en) * 2007-04-04 2008-10-23 Ebara Corp Device for detecting gas component
CN101813673A (en) * 2010-05-07 2010-08-25 河海大学常州校区 Acoustic signal processing device and method for detecting concentration of trace binary-component gas
CN203148896U (en) * 2013-04-16 2013-08-21 哈尔滨理工大学 Device based on phase difference method for measuring gas concentrations through ultrasonic waves
CN103543333A (en) * 2013-10-22 2014-01-29 哈尔滨理工大学 High-frequency signal phase difference measurement method and device
CN206177890U (en) * 2016-10-26 2017-05-17 哈尔滨理工大学 Combustible gas concentration detection device with remote alarm function

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN1431496A (en) * 2003-01-30 2003-07-23 南京大学 Difference method for measuring change of ultrasonic gases in microscale and its control and evaluation system
JP2008256485A (en) * 2007-04-04 2008-10-23 Ebara Corp Device for detecting gas component
CN101813673A (en) * 2010-05-07 2010-08-25 河海大学常州校区 Acoustic signal processing device and method for detecting concentration of trace binary-component gas
CN203148896U (en) * 2013-04-16 2013-08-21 哈尔滨理工大学 Device based on phase difference method for measuring gas concentrations through ultrasonic waves
CN103543333A (en) * 2013-10-22 2014-01-29 哈尔滨理工大学 High-frequency signal phase difference measurement method and device
CN206177890U (en) * 2016-10-26 2017-05-17 哈尔滨理工大学 Combustible gas concentration detection device with remote alarm function

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