RU2186356C2 - Method measuring sound pressure of leak in tested object and gear for its implementation - Google Patents

Abstract

FIELD: measurement technology, test of leak-proofness of examined object, specifically, steam and water pipes in atomic power station and in similar industrial facilities. SUBSTANCE: level of acoustic noise in the form of sound or pulsating pressure and its spectral characteristics are controlled parameters. In this case distances between sensors and sources of leak ( damage ) are found when no reflection from local things and room are present. Level of sound pressure is measured at point of leak in closed small and large rooms with due account of reflection and reverberation phenomena occurring in room. EFFECT: location of emerging leak in object. 2 cl, 4 dwg

Description

 The invention relates to measuring equipment and can be used in the national economy for measuring sound pressure (pressure pulsations) of acoustic origin, in particular for monitoring and diagnosing the tightness of pipelines (with and without thermal insulation) and equipment with RBMK and VVR reactors at nuclear power plants.

 Known leak detector mass spectrometric, containing a sensor, a camera for placing the sensor, pumps for pumping, vacuum gauges, cryoelements. To increase the sensitivity of the leak detector, the sensor chamber is formed by the surfaces of cryoelements.

 The device allows you to search for leaks when placing it in the studied object using the operator (AS USSR 615375 (21), 2375239 / 25-28, 62016529, 1976, G 01 M 3/00. Leak detector. Authors: R.V Bizyaev, V.I. Baryshnikov, S.F. Grishin and others).

 The leak detector has the following disadvantages: the inability to remotely monitor leaks of the investigated object, heavy weight, dimensions, high cost when detecting leaks of the large object under study in normal operation.

 A known method of detecting a leak in a test body being blown using a thermal effect. Moreover, the test object is placed in a chamber in which the same temperature is constantly maintained. The thermal radiation of the object being blown is measured with high accuracy and the areas with reduced thermal radiation on the surface of the object under study are identified as a leak point on a constant thermal image.

 This solution allows you to control leaks from the investigated object by creating thermal radiation on its surface. A change in thermal radiation is indicated by the appearance of a leak (Leak detection system. German patent (DE), UDC 620165.29, G 01 M 3/00, 11/08, 1989, application 053725063, publication 890209 6).

 The disadvantages of this method for determining the location of a leak of a test object are as follows: a stable source of heat radiation is required, it is impossible to determine the location of a leak when the temperature of the test object is much higher than the temperature of the radiated heat source, it is difficult to operate with long-term standard operating conditions of the test object, high cost.

 Closest to the proposed invention, the technical solution is a leak detector containing a sensor. The sensor is placed in the camera. The leak detector also contains a vacuum pump, vacuum gauges, a frozen trap and an electronic system with a wide-range voltage regulator. To simultaneously stabilize the accelerating voltage, it is equipped with an electrostatic cylindrical capacitor. The broadband voltage stabilizer of the electronic system is made with a set of stabilizers corresponding to various test gases. For supplying a test gas with the least amount of impurities to the mass spectrometer chamber, it is equipped with a diffusion pump.

 Such a constructive solution of the device makes it possible to detect leaks by mounting it on the surface of the test object (Mass spectrometric leak detector. A.S. USSR 783611, 2717156 / 25-28 (22), 270179, G 01 M 3/00, (53) 620165.29 ( 72), authors: E. A. Borisov. V. Yu. Brofman and others).

 The disadvantages of this device almost coincide with the disadvantages of a similar device with the difference that this device is bulky and less reliable.

Затем обнаруженную течь преобразуют в электрический сигнал с помощью датчика, согласуют, усиливают с помощью электронных блоков и подают на вход индикатора для обработки. В принципе обнаружения течи заложено соотношение, определенное эмпирической формулой

где Т_кр.ж - температура кипения криогенжидкости, используемой в течеиокателе;

температура кипения жидкого азота; W_диф, - номинальная мощность нагревания диффузионного насоса; W_{доп.диф} - мощность нагревания дополнительного диффузионного насоса; М - масса пробного газа.The closest technical solution is a method for finding leaks. The sensor is mounted on the surface of the object, placed in a chamber and create a vacuum. To stabilize the output signal from the output of the sensor, an electrostatic cylindrical capacitor is used. Select the focus angle of the capacitor

Then, the detected leak is converted into an electrical signal using a sensor, coordinated, amplified by electronic blocks and fed to the input of the indicator for processing. The principle of leak detection is based on the relation defined by the empirical formula

where T _cr.zh is the boiling point of the cryogenic fluid used in the leak detector;

boiling point of liquid nitrogen; W _diff, is the nominal heating power of the diffusion pump; W _add.dif - heating power of an additional diffusion pump; M is the mass of the test gas.

 This method of detecting leaks is carried out by mounting a leak detector on the surface of the object under study (A.S. USSR 783611, 2717156 / 25-28, G 01 M 3/00, 1979 "Mass spectrometric leak detector" Authors: Borisov V.Yu. Bronfman V.P. et al.).

 The disadvantages of the method for detecting leaks of the investigated object are as follows: the lack of the ability to detect leaks at large distances from the object, remotely.

 The objective of the present invention is to increase the reliability of the studied object, (IO), in particular the tightness control of the equipment of heat power plants with high temperature with different reactors of nuclear power plants and other similar installations by detecting leakage of the coolant.

где L - максимальная длина контролируемого исследуемого объекта.The technical result is achieved in that in a device for measuring sound pressure of a leak containing capacitive sound pressure sensors, the output of which is connected to the inputs of matching charge amplifiers, and their outputs through voltage amplifiers are connected to the inputs of the indicator, in it the outputs of the polarization source are respectively connected to the input of the indicator matching amplifiers and voltage amplifiers, moreover, the distance d between the sound leak points and the sensors is chosen to be greater than or equal to d≥2D ² / λ, where D is the maximum sensor size; λ is the wavelength of the leak, and the distance between the sound pressure sources of the leak and reflective objects is d ₁ ≈5 ÷ 6d ₂ , while the distance between the sensors and reflectors d _{2 is} also much greater than the distance d, the distance between the sensors is R≥1 / 6λ, and the number of sensors or monitored points along the entire length of the object is

where L is the maximum length of the controlled object under study.

возникающее в этих точках, затем в условиях эксплуатации при возникновении других течей в точках

на расстояниях между течей R_x<R, при этом каждым датчиком в отдельности измеряют суммарное давление попарно двух течей как: датчик 2 измеряет

датчик 3 измеряет

или

и т.д., причем при наличии отражения от местные предметов на расстоянии d₁, между отражающими предметами и течями, являющимися источниками звука течей в замкнутом небольшом и большом помещениях, датчиками измеряют сумму среднего квадрата прямых и отраженных звуковых давлений течи

затем определяют работоспособность исследуемого объекта по уровням измеряемых звуковых давлений течи, на экране индикатора фиксируют точки повреждения, их количество и их спектральные характеристики, возникающие на поверхности объекта исследования.The technical result is also achieved by the fact that in the method for measuring the sound pressure of a leak, in which a leak pressure is created on the membrane of a capacitive sensor, then pressure is converted into an electrical signal, amplified, processed, stored, recorded, sensors are installed in it from the surface of the object under study at a predetermined distance d, the distance between the sensors R is chosen so that they do not interact with each other, while the sensors measure background acoustic noise and interference, in the event of a leak on top the studied object at points x ₁ , x ₂ , ..., x _{n, the} sensors measure the leak pressure

occurring at these points, then under operating conditions when other leaks occur at the points

at the distances between the leaks R _x <R, while each sensor individually measures the total pressure in pairs of two leaks as: sensor 2 measures

sensor 3 measures

or

etc., moreover, in the presence of reflection from local objects at a distance of d ₁ , between reflecting objects and leaks that are sources of sound leaks in a closed small and large room, the sensors measure the sum of the average square of the direct and reflected sound pressures of the leak

then, the operability of the object under study is determined by the levels of measured sound pressure leaks, damage points, their number and their spectral characteristics that occur on the surface of the object of study are recorded on the indicator screen.

Через объект протекает поток пароводяной смеси "В" с температурой 280^oС и давлением 7•10⁶Па. Устройство содержит емкостные датчики пульсаций давления 2,3,4. Отражатель от местных предметов условно изображен цифрой 5 (отражение от стенок помещения, от конструкций и крепежных средств). Также устройство содержит согласующие усилители заряда 6,7,8, усилители напряжения 9,10,11, индикатор 12 и источник поляризации датчиков и питания усилителей 13.In FIG. 1a, b shows a block diagram of the device and the individual nodes of the test object I, in particular a steam-water pipeline with an outer diameter of 2r (figa). On the surface of the object as a leak, i.e. the source of the emitted sound pressure (pressure pulsations) shows damage in the form of cracks in the shape of an ellipse or a circle at points x ₁ , x ₂ , x ₃ , ..., x _n . Sources of sound power N ₁ , N ₂ , N ₃ , ..., N _n and sound pressure

Through the object flows a stream of steam-water mixture "B" with a temperature of 280 ^o C and a pressure of 7 • 10 ⁶ PA. The device contains capacitive pressure pulsation sensors 2,3,4. The reflector from local objects is conventionally depicted by the number 5 (reflection from the walls of the room, from structures and fasteners). The device also contains matching matching charge amplifiers 6,7,8, voltage amplifiers 9,10,11, indicator 12 and a polarization source of sensors and power amplifiers 13.

Sound pressure from the sources of coolant leak x ₁ , ..., x _n in the form of a steam-water mixture is supplied to the ECH of capacitive sensors 2,3,4. The converted sound pressure in the form of electric voltage from the output of the ECHE is agreed in the charge amplifiers 6,7,8 and through the voltage amplifiers 9,10,11 goes to the indicator 12 for further processing and determining the state of the investigated object 1. The sensors are polarized by a direct current source 13. Block 13 also supplies 6,7,8 charge amplifiers and 9,10,11 voltage amplifiers. Indicator 12, in addition to processing and outputting measurement results, if necessary, also provides regulation of the polarization voltage of the sensors and the gain of normalizing voltage amplifiers when measuring high pressure levels.

The capacitive sound pressure sensor is developed on the basis of well-known thin-film capacitive sensing elements. The sensor membrane is designed on the basis of a high-temperature moisture-resistant alloy. Also, a polyamide film with an operating temperature of -269 ÷ + 300 ^° C was used in the sensor design. In the sensor housing, the EEC is protected from moisture by using a moisture-resistant composite.

The distance between the pipeline and the sensors d provides a measurement of sound pressure in the far field. The distance between the sensors R is chosen so as to exclude interference (interaction) with each other. Moreover, when a random sound source with a power of N _x occurs, i.e. damage X _x power N _x between the leaks x ₁ , x ₂ , ..., x _n , the capacitive sensors can double or even more. Diffraction phenomena from the reflector 5 in the measurement stage from the walls of the room, floor and other installations are shown conditionally. The influence of diffraction on the measurement results is refined and corrected by experimental research.

In practice, the device can be implemented in both single-channel and multi-channel (up to several tens) versions. It is assumed that sound sources at points x _x arise randomly during the operation of pipelines.

1. The method of determining pressure pulsations at the site of damage to the investigated object is implemented as follows:
a. With a fixed arrangement of sensors 2,3,4 ..., measure background, acoustic, thermal noise and interference.

где С - скорость распространения звука; t - текущее время; ф - потенциал скорости. Волновое уравнение при сферическом распространении звука имеет вид:
rФ=f₁(ct-r)+f₂(ct+r)
где f₁(ct-r) - волна, выходящая из источника и бегущая в интересующем нас положительном направлении оси 2. Поскольку нас интересуют расходящиеся от источника волны, то звуковое давление определяют как:

где f' - производная от f=ct-r, тогда f'=С.b. Determine the type of wave (radiation) of sound pressure emanating from the investigated object I. It is known that sound arises when the medium is dynamically disturbed. The fast disturbance of the medium with density ρ, particle velocity V _x and temperature θ affects the sound pressure P. The heat carrier and the object of research have a relatively low heat capacity, the sound propagation is very close to adiabatic even at low frequencies. Sound pressure is dependent on the density of the coolant. In a sound stream, plane and cylindrical waves arise near sources of sounds x ₁ , ..., x _n and emit sound energy N ₁ , ..., N _n in all directions and at large distances from sources x ₁ ..., x _n and all sound waves turn into spherical. In view of the foregoing, the well-known wave equation in spherical coordinates is used as:

where C is the speed of sound propagation; t is the current time; f is the speed potential. The wave equation for spherical sound propagation has the form:
rФ = f ₁ (ct-r) + f ₂ (ct + r)
where f ₁ (ct-r) is the wave emerging from the source and traveling in the positive direction of the axis 2 of interest to us. Since we are interested in waves diverging from the source, the sound pressure is defined as:

where f 'is the derivative of f = ct-r, then f' = C.

скорость частиц в ближнем и дальнем полях как:

где Р_о - постоянная амплитуда давления; ω- угловая частота; ρ- плотность среды; к - волновое число. (Е. Скучик. Простые и сложные колебательные системы. Изд-во "Мир", М., 1971, глава 12. Сферические волны, стр.396-399, фиг. 12.3). Из уравнения V_ближ. cлeдyет, что скорость частиц в ближнем поле отстает по фазе на 90^o от давления и представляет собой звуковое поле.From the results of the known solution, the main parameters are determined in the case of harmonic radiation and have a pressure

particle velocity in the near and far fields as:

where P _about - constant pressure amplitude; ω is the angular frequency; ρ is the density of the medium; k is the wave number. (E. Skuchik. Simple and complex oscillatory systems. Mir Publishing House, Moscow, 1971, chapter 12. Spherical waves, pp. 396-399, Fig. 12.3). From equation V _near It follows that the velocity of particles in the near field is 90 ^° behind the phase in phase pressure and is a sound field.

где Р_а - давление, мм рт.ст.;

абсолютная температура,^oК:
Плотность воздуха при температуре 0^oС и давлении 760 мм рт.ст. равняется ρ=1,2929 кг/м³.The density of gas (air) ρ depending on temperature and atmospheric pressure Ra is defined as:

where R _a - pressure, mm Hg;

absolute temperature, ^o K:
The density of air at a temperature of 0 ^o C and a pressure of 760 mm Hg equals ρ = 1.2929 kg / m ³ .

The wavelength is defined as the distance that a traveling wave travels in one oscillation period: λ = cT = c / f = 2πc / ω, where f is the wave propagation frequency. The wave number is determined through the wavelength as: k = ω / c = 2πf / c = 2π / λ.
It is further shown that the heat capacity C _{p of} air at a constant atmospheric pressure Pa and at a constant volume C _v and temperature (at atmospheric pressure P _a = 10 ⁵ Pa, temperature 0 ^o C, C _p = 0.2398 cal / g ^o С and heat capacity ratio j = C _p / C _v = 1,4032, with an increase in temperature of 100 ^o С С _p -0,2404 cal / g ^o С, j = 1,401; 400 ^o С - С _p = 0,24330 cad / g ^o C, j = 1,993). The effect of viscosity on the propagation of sound pressure in air is expressed through the kinetic coefficient of viscosity V. For air, this coefficient is V = 0.151 cm ² / C at 18 ^o C and atmospheric pressure 760 mm Hg. The coefficient of thermal conductivity of water vapor 100 ^o With is 0,0551 • 10 ^-3 cal / cm s. glad. (L. Beranek. Acoustic measurements. M., 1952, chapter I, p. 7-17. Tab. 1-9).

где j= 1,403 (при P_a=10⁵Па и θ=0^oС). Если температура сильно отличается от 20^oC, то более точную оценку дает формула

в. Измеряют звуковое давление датчиками 2,3,4..., определяют вид волны, излучаемой из точки повреждения исследуемого объекта (ИО) (фиг.1б). Допускают, что размеры ИО и отдельные размеры повреждения на поверхности ИО, по которой распространяются волны звукового давления, будут малы по сравнению с длиной волны, причем давление на выходе отрезка ИО сечением S=const, т.е. на входе ее продолжения и на выходе площадь ИО не изменяется (фиг.1б). При этом в точках повреждения под действием падающей волны возникает отраженная проходящая волна давления и колебательные процессы в импендансе z_σ, на поверхности ИО возникают течи в точках х₁, ..., х₂, ..., x_n. Согласно фиг.1б имеют давление и скорость падающую волну

давление и скорость отраженную волну

давление и скорость проходящую волну
P_{t про} = P_отрcos(ωt-кr);

волну, проходящую в местах повреждений (разветвлений), имеют давление и скорость

В точках повреждений х₁= 0,х₂=0, х₃=0....,х_х=0 течи излучают давление непрерывно, т. e. P_{i пад}+P_{r отр}+P_{t проx.}= P_σ. При этом в местах повреждения ИО отсутствуют перепады давления в связи с отсутствием таких акустических повреждений, как упругого или инерционного импенданса, и объемная скорость распространяется в звуковой волне непрерывно.The dependence of the change in air density ρ on barometric pressure is linear and increases with increasing pressure ρ, and with increasing temperature, the density of air decreases. When the temperature changes from +30 to +300 ^o C and a pressure of 760 mm Hg determine the change in air density ρ 30 ^o C = 1,116 kg / m ³ ; ρ 300 ^o C = 0.615 kg / m ³ . The speed of sound propagation for small amplitudes of sound is determined by the formula

where j = 1,403 (when P _a = 10 ⁵ Pa and θ = 0 ^o C). If the temperature is very different from 20 ^o C, then a more accurate estimate gives the formula

in. Sound pressure is measured by sensors 2,3,4 ..., the type of wave emitted from the point of damage of the object under investigation (IO) is determined (Fig. 1b). It is assumed that the size of the IO and the individual sizes of damage on the surface of the IO, along which sound pressure waves propagate, will be small compared to the wavelength, and the pressure at the output of the IO segment with a section S = const, i.e. at the input of its continuation and at the output, the area of the EUT does not change (Fig.1b). At the same time, a reflected transmitted pressure wave and oscillatory processes in the impedance z _σ arise at the damage points under the influence of the incident wave, and leaks at the points x ₁ , ..., x ₂ , ..., x _n occur on the surface of the IO. According figb have a pressure and velocity of the incident wave

pressure and speed reflected wave

pressure and speed of a passing wave
P _t = P _{pro Neg} cos (ωt-Kr);

the wave passing in the places of damage (branching) have pressure and speed

At the points of damage x ₁ = 0, x ₂ = 0, x ₃ = 0 ...., x _x = 0 leaks emit pressure continuously, i.e. P _{i pad} + P _{r neg} + P _{t prox.} = P _σ . At the same time, there are no pressure drops at the sites of damage to the EUT due to the absence of acoustic damage such as elastic or inertial impedance, and the space velocity propagates continuously in the sound wave.

Next, the sound pressure P _{σ of the} leak, converted into an electric signal, is matched in a charge amplifier, amplified in a voltage amplifier, and fed to an indicator for further analysis.

поступающие на входы датчиков 2,3,4....:
а) Направляют датчики 2,3,4... в предполагаемые места течей и выбирают расстояние R между датчиками таким, чтобы отсутствовало взаимодействие между давлением. При этом каждый датчик регистрирует давление течи

б) В стадии эксплуатации возникают течи (повреждения)

между точками x₁, x₂, x₃, ..., x_n и расстояние между ними R становится таковым R_x, что источники звука течи взаимодействуют между собой. При этом воспользуемся тем, что основные уравнения звукового поля линейны, тогда давление

течи является давлением, создаваемым одним из пары течи источников, а

давлением, создаваемым другим источником течи. При этом на входы датчиков поступают попарно из двух течей

или

Согласно правилу суммирования мощностей получают, что полная мощность звука не равна сумме мощностей излучения каждого из источников течей, а пропорциональна величине

где через Re обозначена действительная часть P = α+jβ; P^* = α-jβ. Взаимодействие между двумя соседними источниками течей характеризуют как

Чтобы из каждого источника звука течи регистрировать давление в отдельности без влияния друг друга, два источника звукового давления течи, возникающего из-за повреждения ИО, должны быть некогерентны. В случае возникновения течи в одной из точек, т.е.

датчик показывает значение давления течи

При этом воспользуемся тем, что излучение звукового давления из двух источников не взаимодействуют, если расстояние R>>R_x, где R≥1/6λ. Тогда количество (число) контролируемых точек течей или количество датчиков выбирают из соотношений

где L - длина ИО. Это условие обеспечивают так. В точке х₁ располагают источники звукового давления (в частности, электродинамик) на расстоянии d от датчика 2 и задают ожидаемое контролируемое давление P_σ. При этом датчик 3 удаляют от датчика 2 на расстояние R и в этом положении на выходе датчика 3 от воздействия источника

регистрируют сигнал, равный нулю, т.е.

В этом положении одновременно градуируют измерительный канал и определяют коэффициенты преобразований. Аналогичным образом поступают с другими источниками, т.е. располагают источник звука в точке x₂ и определяют места расположения датчика 4, и т.д.2. Determine the interaction between radiation sources of sound pressure leakage

arriving at the inputs of the sensors 2,3,4 ....:
a) Direct the sensors 2,3,4 ... to the expected leak points and select the distance R between the sensors so that there is no interaction between the pressure. In this case, each sensor registers leak pressure

b) During operation, leaks (damage) occur

between the points x ₁ , x ₂ , x ₃ , ..., x _n and the distance R between them becomes such that R _x such that the sound sources of the leak interact with each other. In doing so, we take advantage of the fact that the basic equations of the sound field are linear, then the pressure

leak is the pressure created by one of a pair of leak sources, and

pressure created by another leak source. At the same time, the inputs of the sensors come in pairs from two leaks

or

According to the power summation rule, it turns out that the total sound power is not equal to the sum of the radiation powers of each of the leak sources, but is proportional to

where Re denotes the real part P = α + jβ; P ^* = α-jβ. The interaction between two adjacent leak sources is characterized as

In order to record pressure separately from each sound source of a leak without affecting each other, the two sources of leak sound pressure arising due to damage to the EUT should be incoherent. In the event of a leak at one of the points, i.e.

sensor shows leak pressure

In this case, we will use the fact that the sound pressure radiation from two sources do not interact if the distance is R >> R _x , where R≥1 / 6λ. Then the number (number) of monitored leak points or the number of sensors is selected from the relations

where L is the length of the IO. This condition is provided as follows. At point x ₁ , sound pressure sources (in particular, an electrodynamic speaker) are located at a distance d from sensor 2 and the expected controlled pressure P _{σ is set} . In this case, the sensor 3 is removed from the sensor 2 by a distance R and in this position at the output of the sensor 3 from the influence of the source

register a signal equal to zero, i.e.

In this position, simultaneously measure the measuring channel and determine the conversion coefficients. Do the same with other sources, i.e. position the sound source at point x ₂ and determine the location of the sensor 4, etc.

As a rule, the allowable ratio between direct and reflected signals, so that the influence of the reflected signal can be neglected, should be at least 10: 1. Moreover, in order to determine the distance between leaks and reflectors from local objects d ₁ and leaks and sensors d ₂ so that there is no influence by the reflected signal, the value of d _{1 is} chosen as: d ₁ ≈5 ÷ 6d ₂ .

3. Determine the location of the sensors relative to the sources of leaks d at points x ₁ , x ₂ , x ₃ , ... x _n . They use the fact that within small distances the sound propagates according to the law of a spherical wave or the sound pressure varies inversely with the distance. In addition, the distance d between the sources of the sound leaks (at points x ₁ , x ₂ , ... x _n ) and the sensors 2,3,4 is chosen significantly less than the distance d ₁ between the sources of the sound leaks and reflective objects 5. In this case measure the useful signal of leaks more than the reflected signal from local objects 5 (figure 1).

The practically acceptable value between the sensors and sources of sound leaks d is also chosen so that the monitored sound pressure leaks at the site of damage to the EUT differ from the reflected signals, noise and background noise by ~ 20-30 dB (~ 6.3 ... 9.9 time). It is assumed that in the places of damage to the IO, "point" sources of sound leaks arise, creating a spherical wave, and the location of the sensor at a distance d must be such that the curvature of the front of the incident leak wave is insignificant. This condition is satisfied if the distance between the sensors and the sound sources of the leak is chosen (2π / λ) d >> 2. So that there is no reflection from the sensors, the value of d is chosen greater than the maximum size of the sensor D (Fig. 1). Moreover, to preserve the directional action of the sensor, the value of d is chosen as d≥2D ² / λ. In this case, the distance d ₂ between the sensors and reflectors is chosen to be much larger than the distance d between the sound sources and the sensors. This eliminates the reflection or reverb from local objects and premises at a distance of d ₂ .

4. In the case when it is almost impossible to ensure the condition d ₂ >> d, the reverberation effect in the room from local objects occurs and causes interference, then the source of damage, which is the source of sound radiation, perturbes the acoustic field in the room, consisting of controlled sound pressures (measured ) and repeatedly reflected or reverb sounds. Reverb noises before reaching the sensors go through an infinite number of random reflections from the room and local objects.

где

- значения средних квадратов звуковых давлений и течей прямых и отраженных звуков; ρ- плотность среды; N - мощность источника звука; к = α_срS/(1-α_ср) - постоянная помещения; α_ср- средний коэффициент поглощения в помещении; S - площадь ограничивающих поверхностей помещения; α_срS - поглощение помещения; С - скорость звука; D_n, D_m - значения факторов направленности источников звука и датчиков давления. При этом с целью облегчения рассматриваемой задачи пользуются тем, что все источники повреждений ИО имеют одинаковую мощность N₁= N₂= N₃= ...=N_n;

и все перечисленные параметры K, D_n, D_m - одинаковые для каждого контролируемого места повреждения. Из последнего уравнения получают, что средний квадрат звукового давления течи в прямом поле излучений - функция от расстояния d определяется как:

уменьшается обратно пропорционально d₂ и является функцией от направленности источников звука течи и датчиков. Средний квадрат отраженного давления течи

в отраженном звуковом поле определяют как:

который зависит от акустического качества помещения и является определением отраженного и реверберационного фонового шума.a) Based on the static theory of the sound field in a closed small room, determine the dependence of the average square of the sound pressure of the leak of the EUT at a distance d from the sensors as:

Where

- mean square values of sound pressures and leaks of direct and reflected sounds; ρ is the density of the medium; N is the power of the sound source; k = α _cf S / (1-α _cf ) - room constant; α _cf - the average absorption coefficient in the room; S is the area of the bounding surfaces of the room; α _cf S - absorption of the room; C is the speed of sound; D _n , D _m - values of directivity factors of sound sources and pressure sensors. Moreover, in order to facilitate the problem under consideration, they use the fact that all sources of damage to the EUT have the same power N ₁ = N ₂ = N ₃ = ... = N _n ;

and all of the listed parameters K, D _n , D _m are the same for each controlled location of damage. From the last equation it is obtained that the average square of the sound pressure of a leak in a direct radiation field - a function of distance d is defined as:

decreases inversely with d ₂ and is a function of the directivity of the sound sources of the leak and the sensors. The average square of the reflected leakage pressure

in the reflected sound field is defined as:

which depends on the acoustic quality of the room and is the definition of reflected and reverberative background noise.

где

Величину d_o называют радиусом помещения, при котором при равных между собой уровне звукового давления поля прямых звуковых L_пря и поле отраженных звуковых L_отр волн, имеют

показывающее пропорциональность уровня акустического отношения логарифму относительного расстояния

6) В случае распространения звуков в больших помещениях происходит поглощение звука в воздухе, что приводит к нарушению диффузионноcти поля. При нарушении диффузионности поля статическая теория поля замкнутых небольших помещений непригодна для больших помещений. Для больших помещений с учетом поглощения звука в воздухе средний квадрат звуковых давлений прямого и отраженного звука течи в зависимости от радиуса и условий помещения определяют как:

где m - коэффициент поглощения воздуха, который зависит от частоты и относительной влажности; V - объем помещения; S - площадь помещения; d_о - радиус помещения; φ- азимутальный угол; θ- угол возвращения, выражающий отношение интенсивности звука в заданном направлении (φ,θ) к интенсивности, которую измеряют на том же расстоянии для направленного источника с той же самой мощностью N.As the parameter of the acoustic field, the acoustic energy Q is selected in the places of damage, i.e., sound sources of leaking ion sources. To do this, use the known acoustic ratio:

Where

The value d _o called the radius of the room in which the at equal field between a sound pressure level of the direct sound field L _{The direct} and reflected sound waves L _Neg have

showing the proportionality of the level of the acoustic ratio to the logarithm of the relative distance

6) In the case of the propagation of sounds in large rooms, sound is absorbed in the air, which leads to a violation of the diffusion field. If the field diffusion is disturbed, the static field theory of closed small rooms is unsuitable for large rooms. For large rooms, taking into account sound absorption in air, the average square of sound pressures of direct and reflected sound leaks, depending on the radius and room conditions, is determined as:

where m is the absorption coefficient of air, which depends on the frequency and relative humidity; V is the volume of the room; S is the area of the room; d _about - the radius of the room; φ is the azimuthal angle; θ is the angle of return expressing the ratio of the sound intensity in a given direction (φ, θ) to the intensity measured at the same distance for a directional source with the same power N.

In the case of large and small rooms, when d _o = d, this distance is considered as a transition point between the zones of the direct and reflected fields (Methods and techniques of acoustic measurements in wind tunnels. Reviews, abstracts from open foreign press. Publishing House ONTI TsDGI , 1980, pp. 19-21, 2-2. Reflected and reverberation noise of interference).

и отраженных давлений

как:

Таким образом, при определенном расположении датчиков измеряют величину звукового давления течи, его спектральную характеристику. С помощью этих двух параметров определяют состояние работоспособности ИО, нормальное или тревожное положение.Taking into account the reflection from local objects and the walls of the room in closed small and large rooms, the average square of the leak pressure equal to the sum of the direct

and reflected pressures

as:

Thus, at a certain location of the sensors, the magnitude of the sound pressure of the leak is measured, its spectral characteristic. With the help of these two parameters, the state of operability of the EUT, normal or alarming position is determined.

Под действием этих давлений расстояния между обкладками емкостных датчиков 2,3,4 изменяются. В результате прогиба мембраны изменяются начальные емкости емкостных датчиков C, приращение емкости ΔC и относительное изменение емкости

Напряжение поляризации датчиков поступает от источника поляризации 13. Напряжение на выходе датчиков, пропорциональное приращению

и напряжению поляризации. Затем этот сигнал согласуют усилителями заряда 6,7,8, усиливают в нормирующих усилителях 9,10,11 и подают в обработку на индикатор 12.The principle of operation of the device. In case of damage to the EUT at points x ₁ , x ₂ ,. . ., x _n (FIG. 1) there are continuous sources of leakage pressure pulsation

Under the influence of these pressures, the distances between the plates of the capacitive sensors 2,3,4 change. As a result of the deflection of the membrane, the initial capacitances of the capacitive sensors C, the increment of the capacitance ΔC, and the relative change in capacitance change

The polarization voltage of the sensors comes from a polarization source 13. The voltage at the output of the sensors is proportional to the increment

and polarization voltage. Then this signal is coordinated by charge amplifiers 6,7,8, amplified in normalizing amplifiers 9,10,11 and fed to the processing indicator 12.

For this purpose, a model of the device was made at TsAGI for measuring the pressure pulsations of a leak. A charge amplifier was used as a matching amplifier. Further, the signal was amplified by a voltage amplifier in the frequency range from 300 Hz to 20 kHz. The level of measured background noise is 10 ³ μPa in the frequency range from 20 to 100 Hz. When testing high-temperature cable, the KNMS cable was taken with the required maximum length of 44 m; cable capacity 33000-40000 pF.

The dependence of the relative sound pressure level ΔL (d), normalized to the level emitted by the directional power source from the distance d between the sensors and sources, is shown in figure 2, where the solid lines for the directional sensor (Dm = 1) at various values of the constant room K; dashed curves for K = 500 for various values of the axial concentration index of the directional sensor Dm. The distance d = d _o can also be determined from the graphs, figure 2. Each curve asymptotically approaches the level of a characteristic reverberation sound for a given value of total absorption. If the total absorption is known, the intersection of the corresponding horizontal asymptote of the reverberating level and the line - 6 dB to double the distance of the direct sound field will determine the value of d _o . Since the fields of direct and reflected sound are equal in intensity at their intersection, the level of total sound pressure at a distance of the radius of the room will be 3 dB higher than the expected level at the same distance in the absence of reflections. Figure 2 also shows that an increase in the radius of the room can be achieved either by increasing the constant room using the sound-absorbing cladding of the walls of the room, or by using highly directional capacitive pressure pulsation sensors.

In FIG. 3 have the power of sound emitted by each of two identical point sources (dashed curves) and linear sources (solid curves) depending on the distance between them; a is the source of oscillation in the phase; δ is a source oscillating in antiphase. Figure 3 presents the frequency dependence of the ratio N ₂ / N ₃ . At Кd> 1 they have N ₂ ≈N ₃ . Thus, two sound sources do not interact when the distance between them exceeds 1 / 6λ. A similar result is obtained for the sound power of the radiation of two parallel linear sources. The calculation gives the expression N ₂ = N ₃ [1 ± J _o (kd)], where J is the zero-order Bessel function (Fig. 3). It is also known that a vortex layer arises near a solid boundary and sound sources, but this boundary layer is extremely thin (less than 0.001 mm in air at a frequency of 1000 Hz).

Claims (2)

1. A method for measuring the sound pressure of a leak, in which a leak pressure is created on the membrane of a capacitive sensor, then pressure is converted into an electrical signal, amplified, processed, stored, recorded, characterized in that the sensors are installed from the surface of the test object at a given distance d , the distance between the sensors R is chosen so that they do not interact with each other, while the sensors measure background acoustic noise and interference, in the event of a leak on the surface of the investigated object in points x ₁ , x ₂ ,. . . , x _n sensors measure leak pressure

occurring at these points, then under operating conditions when other leaks occur at the points

at distances between leaks R _x <R, while each sensor individually measures the total pressure in pairs of two leaks as: sensor 2 measures

sensor 3 measures

or

moreover, in the presence of reflection from local objects at a distance d between reflective objects and leaks, which are sources of sound leaks in a closed small and large rooms, the sensors measure the sum of the average square of the direct and reflected sound pressures of the leak

then, according to the sound pressure levels of the leak and its spectral characteristics, the state of the object under study is assessed - normal or alarming. 2. A device for measuring the sound pressure of a leak, which contains capacitive sound pressure sensors, the output of which is connected to the inputs of matching charge amplifiers, and their outputs through voltage amplifiers are connected to the indicator inputs, characterized in that the polarization source outputs are respectively connected to the indicator input, matching amplifiers and a voltage amplifier, and the distance d between the sound-leak sources and the sensors is chosen to be greater than or equal to d≥2D ² / λ, where D is the maximum sensor size, λ is the leak wavelength, moreover, the distance between the sound pressure sources of the leak and reflecting objects is d ₁ ≈5 ÷ 6d ₂ , while the distance between the sensors and reflectors d _{2 is} also much greater than the distance d, the distance between the sensors is R≥1 / 6λ, and the number of sensors or monitored points the entire length of the object is

where L is the maximum length of the controlled object under study.

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