DE3245484A1 - METHOD FOR MEASURING THE SWITCHING POWER OF LOW-FREQUENCY SOUND GENERATORS - Google Patents

Description

NAQHeERElQHT-I

attorney and lawyer.:! ..:!. .: ..:!. ^: .. ^: .: I. 3 Z 4 S 4 8 * 4

DipL-lng. Joachim Boecker 6 Frankfurt / Main 1, December 3, 1982

Rathenauplatz 2-8 21 212 P.

Telephone: (0811) '2823 55 Telex: 4189060 itaxd

- 3 Infrasonic AB, Stockholm / Sweden

Procedure for measuring the breaking power of low frequency sound generators

The invention relates to a method for measurement and for possible control or regulation of the sound power of low-frequency sound generators according to the preamble of Claim 1.

Low-frequency sound is used when cleaning industrial and power station boilers. In particular, infrasound with a frequency of 20 Hz is used. Such a sound cleaning device is described in Swedish patent application 7807473-9.

In order to be able to generate low-frequency sound with high power, it is necessary to use the sound generator to provide a resonator. In most cases, a quarter-wave resonator is best for this. Such a Resonator consists of a tube that is closed at one end and open at the other end. the Length corresponds to a quarter of the wavelength of the sound generated.

When cleaning boilers with low-frequency sound the opening of the resonator is connected to the boiler room to be cleaned. In order for the sound to have a cleaning effect, a certain minimum sound pressure is required. The level of the achievable sound pressure depends on the size and construction of the boiler as well as on the size of the generated sound power.

When the sound is made with the help of air pulses of high pressure

December 3, 1982 21 212 P.

which are fed from a feed unit to a quarter-wave generator, the sound power is determined by the air flow ₍ the type of feed of the air impulses and the type of connection of the sound generator to the boiler.

It is of great interest to know how large the sound power emitted by the sound generator is so that one can can judge whether the sound generator is installed correctly and the setting is optimal. To get an idea of To get the performance development of the sound generator, the air pressure in the boiler can be measured. It is however, because of the high temperature of the flue gases, it is often difficult or even impossible to control the air pressure in the boiler measure up. In addition, the pressure of the flue gases is often higher than the external surrounding pressure. Even if it is possible, the To measure air pressure, it is difficult to convert a measure of the performance development of the sound generator to obtain.

The invention is based on the object of developing a method of the type mentioned above, with which the Sound power of the sound generator can be measured in a simple manner while avoiding the aforementioned difficulties can.

To solve this problem, a method according to the preamble of claim 1 is proposed, which according to the invention has the features mentioned in the characterizing part of claim 1.

Advantageous further developments of the invention are mentioned in the subclaims.

The invention is based on the knowledge that there is a certain relationship between the sound power generated by the generator and the sound pressure at the closed end of the

December 3, 1982 21 212 P.

324

- There is 5 resonance pipe of the sound generator.

At the closed end of a quarter-wave resonator, the following equation applies to the sound pressure amplitude:

whereby

P ₀ = the amplitude of the sound pressure p _Q at the closed

End of the quarter-wave resonator in {jPaJ, ψ = the density of the gas at the opening of the sound generator in

c = the speed of sound of the gas at the opening of the sonic generator in [m / sj. '

k = the wave number in Qa "J, a = the radius of the resonance tube in (jnj ρ = the generated sound power in

When the sound generator by compressed air with eir? It is operated temperature of 20 ⁰ C, so is the Produktj? C £ i 410 kg / (ms). The value changes somewhat with temperature; there

2D the temperature fluctuations of the compressed air are usually relatively small and since the sound pressure is also proportional to the square root of the value yc, the value for 'f c can be regarded as constant with sufficient accuracy,

The sizes k and a depend entirely on the structural design of the sound generator. k can also be given as the number of waves per meter - ~ -, where Λ is the wavelength in meters.

For a certain, given construction of the sound generator, the following applies:

ic

December 3, 1982 21 212 P.

where the constant K depends essentially on the dimensions of the sound generator.

The invention is to be explained in more detail with the aid of the figure. 5

In the figure, 1 denotes a resonance tube of a sound generator, e.g. a quarter wave resonator. A feed unit 3 is supplied with compressed air via a line 7. The feed unit 3 generates high pressure air pulses which are fed to the quarter wave resonator. The opening of the resonance pipe 1 is connected to the room to be cleaned, e.g. a boiler 2. So here's a definite one Minimum sound pressure required. The sound power P is determined by the air flow, the type of supply of the air impulses and the type of connection of the resonance pipe to the room to be cleaned.

The sound pressure P is at the inner closed end of the Resonator measured by a pressure gauge 4, which emits an alternating voltage as an output variable. This alternating voltage is converted into a DC voltage signal via a filter and a rectifier 5, at the cathode of which is a capacitor 8 converted, which is proportional to the amplitude ρ. This DC voltage signal is from a Display device 6 displayed. The sound power can be read directly on the display device 6.

Of course, the alternating voltage can also be displayed directly and converted into the sound power P if necessary.

The output signal can be analog and / or digital, and it can possibly be used as a measured value in a control arrangement (not shown) for the sound power (P., -,).

December 3, 1982 21 212 P.

- 7 -

After the value P of the sound power signal has been obtained, the desired sound power can also be set manually will.

The method described above can be used in many ways within the scope of the general inventive concept disclosed Way can be varied.

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Claims (5)

Claims ί 1 J Yerf ahren for the measurement and possible control or regulation of the sound power of low-frequency sound generators, for example sound cleaning generators, which contain a quarter-wave resonator with a closed and an open end, characterized in that to obtain a measure for the output line (P) des Sound generator the sound pressure amplitude (p _o ) is measured at the inner closed end of the resonance tube (1) of the sound generator. 2. The method according to claim 1, characterized in that the output power (P) according to the formula is calculated, where = the amplitude of the sound pressure ρ at the inner closed End of quarter wave resonator in [PaJ, = the density of the gas at the opening of the sound generator in [kg / m- ^ J, = the speed of sound of the gas at the opening of the sound generator in fm / sj, = the wave number in J_m ~ J, = the radius of the resonance pipe in £ mj = the generated sound power in 30th 3. The method according to claim 1, characterized in that the output power (P) according to the formula P. is calculated, where K is a constant depending essentially on the measurements from the sound generator. 21 212 P. I NACHQEREIOHT - 2 - 4. The method according to any one of the preceding claims, characterized in that the measurement signal (p _Q ) is fed to a conversion element whose analog or digital output signal indicates the output power (P). 5. The method according to any one of the preceding claims, characterized in that one of the aforementioned measurement signals (p _o > P ₀ t P) is fed to a control device or regulating device for setting or regulating the desired output power (P _{sol -i).} / 3