US1834875A - Acoustic testing apparatus for detecting irregularities of machines of any type - Google Patents

Description

w SCHAAFHAUSEN ACOUSTIC TESTING APPARATUS FOR DETECTING Dec. 1, 1931.

IRREGULARITIES OF MACHINES OF ANY TYPE Filed Oct. 7, 1930 Patented Dec; 1', 1931 UNITED-STATES PATENT? mm.

wrmmI-u scnzAArnAusnn, or HAMBURG, GERMANY, Assrenoza 'ro EEBOLD AKTIENGESELLSOEAI'T, or HAMBURG, ennmm- I Acousrro rnsrme ArrAaA'rUs ron nnmo'rme mnEeULAnrrms or or ANY ma Application med October 7, 1930, serial No.

My invention relates to improvements in acoustic testing apparatus for detecting irregularities of machines of any type. For this purpose testing apparatus have been 5 used in which the acoustic vibrations of machines are transmitted through a hollow or solid rod to adiaphragm for rendering the same audible, so that the irregularities and the source-thereof may be ascertained by the abnormal tones. Apparatus of this type are objectionable for the reason that all the noises caused by the machine are transmitted to the ear, sothat it is-frequentlydiflicult to find out the abnormal tones and their source, 1 the intensity of the said tones being ordinarily very small. The object of the improvements is to provide a system in which this objection is obviated. A Y

The resonators proposed by Helmholtz re- 90 produce a certain fundamental tone depending on the size of the apparatus, and in addition very high overtones. If the fundamental tone of a resonator of this type is transmitted, the air of the resonator is made to resound, 2! and the sound thus intensified is directly transmitted to'the ear of the attendant bearing on the resonator, while other flmdamental tones are not perceived. If the other ear of the attendant is closed the said foreign fundamental'tones are not perceived at all.

If between the diaphragm of the acoustic testing apparatus and the ear of the attendant a resonator is provided, the attendant perceives only those tones of the noises of the 85 machine the vibrations of which correspond to the vibrations of the resonator. Thus the individual tone of the noise of the machine may be isolated. By using a set of resonators of different vibrations the whole noise of the machine may be subdivided into tones of different oscillations, and finally the tone may be isolatedwhich is to be specifically investi gated as to its character and its source.

To provide a large number of resonators of different numbers or vibrations is objectionable, and therefore I: prefer to provide a single resonator the cavity of which may be en larged or reduced in size so as to vary the fundamental tone of the resonator. For ex- 5Q ample, the size of the cavity may be varied by tubular member having an opening f for the uAcmn'Es 487,085, and in Germany August 20, 1929. v

A resonator of this type may be tuned; by

gradually enlarging the same or opening the holes thereof to a-large number of fundamental tones, so that by examining the noises of the machine and simultaneously tuning the resonator the tone to be investigatedmay be isolated.

Another object of the improvements is to provide a system in which the resonator and the testing device are combined into a single apparatus, which is simple in construction. Further the resonator may be constructed so that asingle apparatus comprises several octaves. For the purpose of explaining the inven tion several examples embodying the same have been shown in the accompanying drawings in which the same reference characters have been used in all theviews to indicate corresponding'parts. In said drawings,

Fig; 1 is a sectional elevationshowing a resonator adapted to be connected with the receiver of an acoustic testing device, and

' Fig. 2 is a sectional elevation showing an acoustic testing apparatus combined with a. resonator.

a is the receiver of the acoustic testing -ap- .paratus and b-the diaphragm thereof.

a is the outer cylindrical wall of the Helm holtz resonator having anopening d for the admission of the sound.

e is a tubular member in telescoping engagement with the cylindrical wall, the said delivery of the sound.

The said tubular member is held with its opening 7 on the ear.

In such parts of the machine which are readily accessible the testing apparatus as 1 such may be omitted and the resonator may be directly-placed on the machine to be tested. Further the use of the resonator, which'may 'or may/not be provided with a testing ap pa atus, isnot limited to machines, and it may be used whereverit is desired to isolate 'and test tones.

In the modification shown in Fig. 2 1 is the outer box having a'lid 4 and a bottom 2 provided with a central opening 3 for the admission of thesound and for the passage of the conducting pipe. 5 is an inner box hav- .ing a bottom 6 the outer diameter of which is equal to the inner diameter of the box 1. The bottom is equipped with a central opening for the admission of thesound, the d1ameter of'the said opening being such that when-pulling the box 5 outwardly the bottom sounds.

9 of the box 8 is carried along. 7 is the lid of the box 5. 8 is a third box having a bottom 9 the outer diameter -of which is equal to the inner diameter of the .box 5. 10 is a conducting pipe shiftable within the box ,8. 11, 12 and 13 are rings provided with handles for As'shown in broken lines, the conuctingpipe 10 has been shifted inwardly so farthat it bears on .the main conducting .pipe 15. "The apparatus is applied with the upper end of the conducting pipe to the ear of the attendant. The main conducting pipe is placed on the machine to be tested. The noise of the machine is transmitted to the ears through the system of pipes, so that the attendant is enabled to ascertain whether or not there is an irregularity in the machine. Thereafter the conducting pipe 10 is drawn outwardly until its bottom end coincides with the bottom end of the innermost box. There'- a'fter, at first the box5 is pulled outwardly by means of the ring 11, the whole contents of the resonator following this movement so that the volume of the box 1 within the space confined between the bottom 2 thereof and the bottom 6 of the box 5 acts as a resonator chamber. By withdrawing the 'box 5 the said lresonator chamber is gradually enlarged;

until the bottom 6 bears ,on the lid 4. If by this operation no resonance of the sound to be. isolated is obtained, the box 5 is pushed inwardly again, and the inner box 8 is shiftedoutwardly,- Now the volume of the box 5 provides the resonator chamber. 1 The dimensions. and the number of the boxes 'are "such that theresonance chambers provided thereby have fundamental tones'of the octaves comprisingthe normal'noise of stood to the resonator.

the machine and the irregular tone to be exass octave and the first and second descant octaves. will be s'uflicient.

From the foregoing detailed description of the apparatus the following will be under- At its bottom the resonator is provided with a sound box made from a material which does not transmit the sound, and to the bottom of the said sound box a main conducting pipe is fixed which is adapted to be extended at will, and which may be placed on the machine to be tested. The sound is transmitted through the column of air confined within the said pipe in a perfectly satisfactory way. A second conducting pipe is within the resonator, and for the first testing operation it is directly connected with the main conducting pipe by inserting the pipes one into the other, so that the sound waves are conducted to the upper delivery end of the conducting pipe without being interrupted. The sound waves act at the said delivery end directly on the ear of the attendant. In this case there is no resonance. If it is desired to isolate a certain tone the conducting pipe connected with r the resonator is pulled upwardly, until its bottom end coincides with the bottom of-the inner box, so that the direct connection between the ear, and the main conducting pipe is interrupted. Now the sound waves expand within the sound box, and they have access To prevent the sounds which should not produce resonance from dis turbing the resonance by interference the wall of the sound box is provided with openings permitting the said sound waves to escape. I

The resonator consists of several telescoping boxes disposed and constructed so that the bottom of each box is the resonance board of the box surroundinggthe same. By this construction and by providing a suitable number of difl'erentboxes resonance chambers of different diameters are provided, so

become loose or broken under the same conditions and therefore while producing the same. sound correspondingto the disturbance of the machine. If the said critical point is equipped with a resonator tuned to the fre- 'quency of the expected sound of the disturb ance, the slightest disturbance will produce at the beginning within the resonator a resonance sound which will be directly audible. Therefore it is preferred continuously to equip, apparatus of any type at each critical I point with a fixed tuned resonator. To prevent such supervision resonators from being i made to sound by tones having the same frequency and coming from other parts of the system without being caused by disturbances, it is preferred to isolate the resonators in such a way that they can be affected only from the critical point.

I claim: 1. In acoustic apparatus for detecting vibrations of different frequency in machinery, the combination with a resonator comprising a plurality of nested chambers, means whereby said chambers may be telescoped to vary the effective volume of the chamber for altering the natural frequency of vibration 7 thereof, one of said chambers being provided with a wall portion movable therewith and extending within a second chamber to constitute a sounding board for said second chamber.

2. In acoustic apparatus for detecting vibrations of different frequency in machinery,

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