ISO 15086-2:2000
(Main)Hydraulic fluid power — Determination of the fluid-borne noise characteristics of components and systems — Part 2: Measurement of the speed of sound in a fluid in a pipe
Hydraulic fluid power — Determination of the fluid-borne noise characteristics of components and systems — Part 2: Measurement of the speed of sound in a fluid in a pipe
Transmissions hydrauliques — Évaluation des caractéristiques du bruit liquidien des composants et systèmes — Partie 2: Mesurage de la vitesse du son émis dans un fluide dans une tuyauterie
La présente partie de l'ISO 15086 décrit la procédure d'évaluation de la vitesse du son émis par un fluide contenu dans un tube, par la réalisation de mesurages à partir de capteurs de pression montés sur ledit tube. La présente partie de l'ISO 15086 s'applique à tous les types de circuits hydrauliques fonctionnant dans des conditions de régime établi, indépendamment de leur dimension, pour des impulsions de pression dans une gamme de fréquences comprise entre 25 Hz et 2 500 Hz.
Fluidna tehnika - Hidravlika - Ugotavljanje značilnic tekočinskega hrupa v sestavinah in sistemih - 2. del: Merjenje hitrosti zvoka po tekočini v cevi
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INTERNATIONAL ISO
STANDARD 15086-2
First edition
2000-02-01
Hydraulic fluid power — Determination of
fluid-borne noise characteristics of
components and systems —
Part 2:
Measurement of speed of sound in a fluid in
apipe
Transmissions hydrauliques — Évaluation des caractéristiques du bruit
liquidien des composants et systèmes —
Partie 2: Mesurage de la vitesse du son émis dans un fluide dans une
tuyauterie
Reference number
ISO 15086-2:2000(E)
©
ISO 2000
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ISO 15086-2:2000(E)
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© ISO 2000
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in the country of the requester.
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Printed in Switzerland
ii © ISO 2000 – All rights reserved
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ISO 15086-2:2000(E)
Contents Page
Foreword.iv
Introduction.v
1 Scope .1
2 Normative references .1
3 Terms and definitions .1
4 Symbols and subscripts .2
5 Instrumentation.3
6 Hydraulic noise generator.4
7 Test conditions .5
8 Test rig.5
9 Test procedure for Method 1 .9
10 Test procedure for Method 2 .10
11 Test report .11
12 Identification statement (Reference to this part of ISO 15086) .12
Annex A (normative) Errors and classes of measurement of mean value .13
Annex B (normative) Errors and classes of dynamic measurement.14
Annex C (normative) Data reduction algorithms.15
Annex D (informative) Example of speed of sound calculation in MATLAB® language using three
pressure transducers in a pipe (Method 1) .21
Annex E (informative) Example of speed of sound calculation in MATLAB® language using two
pressure transducers in a closed-end pipe (Method 2) .25
Bibliography .27
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ISO 15086-2:2000(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO
member bodies). The work of preparing International Standards is normally carried out through ISO technical
committees. Each member body interested in a subject for which a technical committee has been established has
the right to be represented on that committee. International organizations, governmental and non-governmental, in
liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical
Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 3.
Draft International Standards adopted by the technical committees are circulated to the member bodies for voting.
Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this part of ISO 15086 may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
International Standard ISO 15086-2 was prepared by Technical Committee ISO/TC 131, Fluid power systems,
Subcommittee SC 8, Product testing.
ISO 15086 consists of the following parts, under the general title Hydraulic fluid power — Determination of fluid
borne noise characteristics of components and systems:
� Part 1: Introduction
� Part 2: Measurement of the speed of sound in a fluid in a pipe
Annexes A, B and C form a normative part of this part of ISO 15086. Annexes D and E are for information only
iv © ISO 2000 – All rights reserved
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ISO 15086-2:2000(E)
Introduction
In hydraulic fluid power systems, power is transmitted and controlled through a liquid under pressure within an
enclosed circuit. During the process of converting mechanical power into hydraulic fluid power, flow and pressure
fluctuations and structure-borne vibrations are generated.
Hydro-acoustical characteristics of hydraulic components can be measured with acceptable accuracy if the speed of
sound in the fluid is precisely known.
The measurement technique for determining the speed of sound in a pipe, as described in this part of ISO 15086, is
based upon the application of plane wave transmission line theory to the analysis of pressure fluctuations in rigid
pipes [1].
Two different measurement approaches are presented, namely the use of:
� three pressure transducers in a pipe,
� acoustic antiresonance in a closed-end pipe system.
The three-pressure-transducer method should be used at any time when the speed of sound is to be measured
under the effective working conditions in a system.
The antiresonance method should be used to produce a table of speed-of-sound data as a function of mean
pressure and temperature for a particular fluid.
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INTERNATIONAL STANDARD ISO 15086-2:2000(E)
Hydraulic fluid power — Determination of fluid borne noise
characteristics of components and systems —
Part 2:
Measurement of the speed of sound in a fluid in a pipe
1 Scope
This part of ISO 15086 describes the procedure for the determination of the speed of sound in a fluid enclosed in a
pipe, by measurements from pressure transducers mounted in the pipe.
This part of ISO 15086 is applicable to all types of hydraulic circuit operating under steady state conditions,
irrespective of size, for pressure pulsations over a frequency range from 25 Hz to 2 500 Hz.
2 Normative references
The following normative documents contain provisions which, through reference in this text, constitute provisions of
this part of ISO 15086. For dated references, subsequent amendments to, or revisions of, any of these publications
do not apply. However, parties to agreements based on this part of ISO 15086 are encouraged to investigate the
possibility of applying the most recent editions of the normative documents indicated below. For undated
references, the latest edition of the normative document referred to applies. Members of ISO and IEC maintain
registers of currently valid International Standards.
ISO 1000:1992, SI units and recommendations for the use of their multiples and of certain other units.
ISO 1219-1:1991, Fluid power systems and components — Graphic symbols and circuit diagrams — Part 1:
Graphic symbols.
ISO 5598:1985, Fluid power systems and components — Vocabulary.
3 Terms and definitions
For the purposes of this part of ISO 15086, the terms and definitions given in ISO 5598 and the following apply.
3.1
flow ripple
fluctuating component of flowrate in a hydraulic fluid, caused by interaction with a flow ripple source within the
system
3.2
pressure ripple
fluctuating component of pressure in a hydraulic fluid, caused by interaction with a flow ripple source within the
system
3.3
fundamental frequency
lowest frequency of pressure ripple measured by the frequency-analysis instrument
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ISO 15086-2:2000(E)
3.4
harmonic
sinusoidal component of the pressure ripple or flow ripple occurring at an integer multiple of the fundamental
frequency
NOTE A harmonic may be represented by its amplitude and phase, or alternatively by its real and imaginary parts.
3.5
hydraulic noise generator
hydraulic component generating flow ripple and consequently pressure ripple in the circuit
3.6
measurement pipe
pipe in which the pressure transducers are mounted
3.7
impedance
complex ratio of the pressure ripple to the flow ripple occurring at a given point in a hydraulic system and at a given
frequency
3.8
entry impedance.
impedance at the entry of a pipe or piping system
3.9
first acoustic antiresonance frequency
lowest frequency at which the magnitude of the entry impedance of the measurement pipe is at a minimum
4 Symbols and subscripts
4.1 Symbols
A, A', a, B, B',b Frequency-dependent wave propagation coefficients (complex numbers)
c Acoustic velocity in the fluid
d Internal diameter of pipe
f Frequency of the wave pulsation harmonic
f Vector of frequencies at which measurements are conducted
i
f First acoustic antiresonance frequency (in hertz)
o
H Transfer function (complex number) between two pressure transducer signals after calibration
correction
H' Transfer function (complex number) between two pressure transducer signals under calibration
H* Transfer function (complex number) between two pressure transducer signals
j �1
L Distance between transducers 1 and 2 (Method 1)
L' Distance between transducers 2 and 3 (Method 1)
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ISO 15086-2:2000(E)
l Distance between pressure transducers (Method 2)
P Pressure ripple of transducer PT1 (complex number)
1
P Pressure ripple of transducer PT2 (complex number)
2
P Pressure ripple of transducer PT3 (complex number)
3
Q Flow ripple at location 1, from 1 to 2 (complex number)
1� 2
Q Flow ripple at location 2, from 2 to 1 (complex number)
2� 1
Q Flow ripple at location 3, from 2 to 3 (complex number)
2� 3
S Coherence function corresponding to measurement frequencies, f
i i
� Error (complex number)
� Conjugate of complex number � (complex number)
� Real part of �
x
� Imaginary part of �
y
� Density of fluid
� Kinematic viscosity of fluid
� 2�f
NOTE H, H', H*, P , P , P , Q , Q , Q are all frequency-dependent terms and hence are designated by upper-
1 2 3 1� 2 2� 1 2� 3
case letters.
Units used in this part of ISO 15086 are in accordance with ISO 1000.
Graphical symbols are in accordance with ISO 1219-1 unless otherwise stated.
4.2 Subscripts
O Index for old value
N Index for new value
5 Instrumentation
5.1 Static measurements
The instruments used to measure
a) mean flow (Method 1 only);
b) mean fluid pressure;
c) fluid temperature;
shall meet the requirements for "industrial class" accuracy of measurement, i.e. class C as given in annex B.
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ISO 15086-2:2000(E)
5.2 Dynamic measurements
The instruments used to measure pressure ripple shall have the following characteristics:
a) resonant frequencyW 30 kHz;
b) linearityW� 1%;
c) preferably include acceleration compensation.
The instruments need not respond to steady-state pressure. It may be advantageous to filter out any steady-state
signal component using a high-pass filter. This filter shall not introduce an additional amplitude or phase error
°
exceeding 0,5 % or 0,5 respectively of the current measurement.
5.3 Frequency analysis of pressure ripple
A suitable instrument shall be used to measure the amplitude and phase of the pressure ripple.
The instrument shall be capable of measuring the pressure ripple from the pressure transducers such that, for a
particular harmonic, the measurements from each transducer are performed simultaneously and synchronised in
time with respect to each other.
The instrument shall have an accuracy and resolution for harmonic measurements of
a) amplitude within � 0,5 %;
°
b) phase within � 0,5 ;
c) frequency within � 0,5 %;
over the frequency range from 25 Hz to 2 500 Hz.
5.4 Uncertainty
Compliance with the above specification will result in an uncertainty in measurement of speed of sound of less than
� 3%.
6 Hydraulic noise generator
6.1 General
Any type of hydraulic noise generator may be used, provided that sufficient pressure ripple is created at the
pressure transducers to allow accurate measurements to be taken.
EXAMPLE Pumps and motors create a pressure ripple consisting essentially of many harmonics of the fundamental
frequency. In these cases, the fundamental frequency is equal to the product of the shaft rotational frequency and the number
of gear teeth, vanes or pistons, etc. (as appropriate to the machine employed).
Suitable alternatives include:
� an auxiliary valve with a rotating spool allowing flow to pass to the return line over part of its rotation;
� an electrohydraulic servo-valve driven by a frequency generator.
� The servo-valve may be operated with a white noise signal in order to obtain significant pressure ripple
measurements at each frequency of interest.
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ISO 15086-2:2000(E)
6.2 Generator vibration
If necessary, the measurement pipe should be structurally isolated from the generator to minimize vibration.
7 Test conditions
7.1 General
The required operating conditions shall be maintained throughout each test within the limits specified in Table 1.
7.2 Fluid temperature
The temperature of the fluid shall be that measured at the entry to the measurement pipe.
7.3 Fluid density and viscosity
The density and viscosity of the fluid shall be known to an accuracy within the limits specified in Table 2.
7.4 Mean fluid pressure
The mean fluid pressure of the fluid shall be that measured at the entry to the measurement pipe.
7.5 Mean flow measurement
The mean flow shall be measured down-stream of the measurement pipe (Method 1 only).
Table 1 — Permissible variations in tests conditions
Test parameter Permissible variation
Mean flow �2%
Mean pressure �2%
Temperature
�2°C
Table 2 — Required accuracy of fluid property data
Property Required accuracy
Density
�2%
Viscosity
�5%
8 Test rig
8.1 General
If, at any test condition, the pressure ripple amplitudes are too small for satisfactory frequency-spectrum analysis to
be performed, an alternative noise generator shall be selected.
The pressure transducers shall be mounted such that their diaphragms are flush, within � 0,5 mm, with the inner
wall of the pipe.
Two alternative specifications for the measurement pipe and transducer position are given, in accordance with the
method employed.
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ISO 15086-2:2000(E)
8.2 Thermal insulation
Temperature shall be measured at both ends of the measurement pipe. The difference in temperature between the
two ends of the measurement pipe shall not exceed 2 °C at any test condition. If necessary, sufficient thermal
lagging shall be applied to the measurement pipe to enable this requirement to be met.
8.3 Method 1: Three-transducer method
8.3.1 This method is suitable when the velocity of sound is to be measured at the same time as other hydro-
acoustical characteristics of hydraulic components, such as impedance, source flow ripple or transfer matrix
coefficients. The measurement pipe shall be installed at the place in the test system where measurement of the
speed of sound is needed. Several measurement pipes may be used simultaneously, if required.
The measurement pipe shall be uniform and straight. Its internal diameter shall be between 80 % and 120 % of the
diameter of the pipes, or component ports, to which it is connected. The pipe should be supported in such a manner
that vibration is minimized.
For cases where other hydro-acoustic properties are not being measured simultaneously, a pump (and if necessary,
a hydraulic noise generator) shall be mounted at one end of the measurement pipe. The other end shall be
terminated by a loading valve without free-moving internal parts, such as a needle valve.
Mean pressure shall be measured at the upstream end of the measurement pipe.
8.3.2 Three pressure transducers are required for Method 1, configured as shown in Figure 1. The transducer
spacing shall be selected according to the standard specifications of hydro-acoustical measurements to be carried
out simultaneously. Otherwise, the distances L and L' between the pressure transducers shall be as specified in
Table 3.
Table 3 — Spacing of transducers: Method 1
L 330 mm �2mm
L'
470 mm �2mm
The distance between each end of the measurement pipe and the nearest pressure transducer shall be at least
10 d, where d is the internal diameter of the pipe. The distances L and L' between the transducers, as shown in
Figure 1, shall be measured to an accuracy of � 0,5 mm.
No other components shall be connected between the inlet port and outlet port of the measurement pipe.
a
Pressure transducers.
b
Distances to end of measurement pipe, x W 10d and x W 10d.
1 2
Figure 1 — Arrangement of three pressure transducers in measurement pipe
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ISO 15086-2:2000(E)
8.4 Method 2: Antiresonance method
8.4.1 This method can be used to produce a data chart of the speed of sound for a particular fluid. Due to the
pressure resonances that are created in the system, this method is not appropriate when other hydro-acoustical
measurements are to be undertaken.
8.4.2 An appropriate test rig is presented schematically in Figure 2 a). The loading valve shall not contain free-
moving parts. A needle valve is an example of a suitable loading valve. The measurement pipe takes the form of a
closed-end side-branch line connected to the pump/pipe/loading-valve circuit as shown. It is important that the fluid
in the measurement pipe is at as uniform a temperature as possible, and does not contain gas bubbles. To achieve
these objectives, the measurement pipe is terminated by a bleed valve. A needle valve is an example of a suitable
bleed valve. Prior to measurements being taken, the bleed valve is opened for a period of time sufficient to flush the
pipe of gas bubbles and to stabilize temperature. The measurement pipe shall be orientated downwards with the
bleed valve below the level of the through-flow pipe to prevent the trapping of air in the measurement pipe during
testing. It is important that the bleed valve does not introduce significant extra volume at the end of the line when
the valve is in the closed position.
The pressure transducers, PT and PT in Figure 2 a), are located at each end of the measurement pipe. It is
1 2
essential that transducer PT is mounted as closely as possible to the end of the pipe. Moreover, the location of
2
transducer PT should be as close as possible to the point where the measurement pipe is connected to the main
1
circuit. Figure 2 b) provides an example of how these requirements may be achieved. In this example, the
measurement pipe is terminated by a purpose-built housing which contains the needle valve assembly.
The hydraulic components necessary to obtain the appropriate test conditions may, inherently, generate sufficient
pressure pulsation levels to allow satisfactory frequency-spectrum analysis to be performed. Should this not be the
case, a separate hydraulic noise generator shall be connected to the circuit, as shown in Figure 2 a).
In order to maximize the pressure pulsation levels, the distance between the pump (or the noise generator if in use)
and the loading valve should not be greater than one-tenth of the measurement pipe length.
8.4.3 The measurement pipe shall be a uniform, rigid, straight metal pipe. The internal diameter of the pipe shall
be between 50 % and 100 % of the diameter of the line where it is connected. This pipe shall be supported in such
a manner that pipe vibration is minimized.
The distance, l, between the pressure transducers shall be defined according to the first acoustic antiresonance
frequency f by equation (1).
o
6
1 B� 10
l � (1)
4 f �
o
The effective bulk modulus B can be estimated using manufacturer’s data for the fluid consistent with the operating
condition of the tests. An accurate value is not required.
The frequency f should be chosen in the range 100 Hz to 200 Hz.
o
The distance between the pressure transducers shall be measured to an accuracy of � 0,5 mm.
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ISO 15086-2:2000(E)
Key
1Pump 6 Loading valve
2 Electric motor 7 Bleed valve
3 Hydraulic noise generator (if used) 8 Measurement pipe
4 Through-flow pipe 9 Temperature transducers
5 Pressure gauge 10 Pressure transducers
a) Circuit layout
Key
1 Through-flow pipe 4 Needle valve adjustment
2 Temperature transducer 5 To reservoir
3 Pressure transducer PT 6 Pressure transducer PT
1 2
b) Example of transducer locations and bleed valve mounting
NOTE Graphical symbols are for illustration purposes and do not conform to ISO 1219-1.
Figure 2 —Typical antiresonance test arrangement
8 © ISO 2000 – All rights reserved
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ISO 15086-2:2000(E)
8.5 Calibration of pressure transducers
Calibration of pressure transducers and signal conditioning is necessary. Perform relative calibration by mounting
the pressure transducers in a common block such that they measure the same pressure ripple. Construct this
common block such that the pressure transducers are at the same axial position and no more than one internal
diameter of the measurement pipe apart.
Measure the amplitude and phase relationship between the pressure transducers for a range of frequencies
spanning the complete range of interest with one transducer used as a reference. For piezoresistive transducers,
the reference transducer can be calibrated statically using, for example, a deadweight testing machine.
If piezoelectric transducers and charge amplifiers are employed, a calibrated piezoresistive transducer may be used
as a reference for dynamic calibration purposes.
If the amplitude or phase difference between the transducers exceeds 1 % or 0,5° respectively, correct for the
differences in the analysis of the test data (see 9.3 and 10.3). Record the transfer functions.
P
1
H� �
12
P
2
and
P
3
H� �
32
P
2
obtained during calibration.
9 Test procedure for Method 1
9.1 Prior to the commencement of tests, operate the hydraulic system for a sufficient period of time to purge air
from the system and to stabilize all variables, including fluid condition, to within the limits given in Table 1. If a speed
of sound test is to be performed at the same time as other hydro-acoustical measurements, conditions to the
standard relevant to those measurements can be used.
9.2 Take the ensemble average of at least 16 time-series pressure transfer functions
P P
3
1
H**��and H
12 32
P P
2 2
and calculate the coherence function S at each frequency f over the frequency range. Typical examples of the
i i
transfer functions H * and H * are given, for the case of broad-band excitation, in Figure 3.
12 32
9.3 Perform the correction of the ensemble-averaged transfer functions H and H using the transfer functions
12 32
obtained from the calibration procedure H' and H' (see 8.5) using equations (2) and (3).
12 32
H *
12
H � (2)
12
H�
12
H *
32
H � (3)
32
H�
32
If correction is not necessary (see 8.5), then H = H* and H = H* .
12 12 32 32
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ISO 15086-2:2000(E)
Key
1 Modulus of transfer functions H* and H* 3 Degree
12 32
4 Phase of transfer functions H* and H*
2 Frequency (Hz) 12 32
Figure 3 — Typical example of transfer functions H* and H*
12 32
9.4 Calculate the speed of sound for each frequency having an associated coherence function S greater than
i
0,95 as described in C.1. The S function is always a positive number less than or equal to 1. The least-squares
i
error procedure given in C.1 allows the speed of sound, averaged over the frequency range investigated, to be
calculated.
9.5 Calculate the mean fluid velocity by dividing the mean flow by the internal cross-sectional area of the
measurement pipe. If the mean fluid velocity is greater than 5 % of any speed of sound measurement, then the
method is invalid and results shall not be reported.
10 Test procedure for Method 2
10.1 Prior to the commencement of a series of tests, operate the hydraulic system and noise generator (if
included) for a sufficient period of time to purge air from the system and to stabilize all variables, including fluid
condition, to within the limits given in Table 1. Particular attention should be given to obtaining a representative fluid
characteristic, especially the bulk modulus.
The bleed valve should be fully open to allow flow through the measurement pipe during this stabilization period.
The restrictor valve downstream of the bleed valve should be adjusted to create a mean pressure approximately
0,5 MPa below the desired test pressure during this phase. Immediately before pressure transducer measurements
are taken, the bleed valve should be closed and, if necessary, the mean pressure re-established through
adjustment of the loading valve.
Warning — No safety valves are included in the system. Personnel performing tests should exercise great
care to ensure that excessive and dangerous pressures are not created when adjusting restrictor valves.
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ISO 15086-2:2000(E)
10.2 Take the ensemble average of at least 16 time-series pressure transfer functions.
P
1
H *�
12
p
2
10.3 Perform the correction of the measured transfer function H* using the transfer function obtained from the
21
calibration procedure of transducers PT and PT , H' = P /P (see 8.5) using equation (4).
1 2 21 2 1
H *
21
H � (4)
21
H�
21
If correction is not necessary (see 8.5), then H = H*
21 21.
10.4 Identify and record the frequencies for which the transfer function H is a maximum. Calculate the speed of
21
sound as described in C.3.
11 Test report
11.1 General information
The test report shall contain the following general information.
a) Name and address of organization performing the test;
b) name of persons performing the test;
c) reference specifications of fluid tested;
d) date and place of tests;
e) conformance statement (see clause 12).
11.2 Test data
The test report shall contain the following test data.
a) Mounting and installation conditions of the measurement pipe:
1) description of measurement pipe (length; internal diameter; wall thickness; material);
2) description of test rig (only for Method 2);
3) nature and characteristics of hydraulic circuit and details of any vibration and thermal insulation treatment;
b) test method adopted (Method 1 or Method 2);
c) instrumentation:
1) class of measurement;
2) details of equipment used for pressure ripple measurements, including type, serial number and
manufacturer;
3) bandwidth of frequency analyser;
4) overall frequency response of instrumentation system and date and met
...
SLOVENSKI STANDARD
SIST ISO 15086-2:2001
01-december-2001
)OXLGQDWHKQLND+LGUDYOLND8JRWDYOMDQMH]QDþLOQLFWHNRþLQVNHJDKUXSDY
VHVWDYLQDKLQVLVWHPLKGHO 0HUMHQMHKLWURVWL]YRNDSRWHNRþLQLYFHYL
Hydraulic fluid power -- Determination of the fluid-borne noise characteristics of
components and systems -- Part 2: Measurement of the speed of sound in a fluid in a
pipe
Transmissions hydrauliques -- Évaluation des caractéristiques du bruit liquidien des
composants et systèmes -- Partie 2: Mesurage de la vitesse du son émis dans un fluide
dans une tuyauterie
Ta slovenski standard je istoveten z: ISO 15086-2:2000
ICS:
17.140.20 Emisija hrupa naprav in Noise emitted by machines
opreme and equipment
23.100.01 +LGUDYOLþQLVLVWHPLQDVSORãQR Fluid power systems in
general
SIST ISO 15086-2:2001 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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SIST ISO 15086-2:2001
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SIST ISO 15086-2:2001
INTERNATIONAL ISO
STANDARD 15086-2
First edition
2000-02-01
Hydraulic fluid power — Determination of
fluid-borne noise characteristics of
components and systems —
Part 2:
Measurement of speed of sound in a fluid in
apipe
Transmissions hydrauliques — Évaluation des caractéristiques du bruit
liquidien des composants et systèmes —
Partie 2: Mesurage de la vitesse du son émis dans un fluide dans une
tuyauterie
Reference number
ISO 15086-2:2000(E)
©
ISO 2000
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SIST ISO 15086-2:2001
ISO 15086-2:2000(E)
PDF disclaimer
This PDF file may contain embedded typefaces. In accordance with Adobe's licensing policy, this file may be printed or viewed but shall not
be edited unless the typefaces which are embedded are licensed to and installed on the computer performing the editing. In downloading
this file, parties accept therein the responsibility of not infringing Adobe's licensing policy. The ISO Central Secretariat accepts no liability in
this area.
Adobe is a trademark of Adobe Systems Incorporated.
Details of the software products used to create this PDF file can be found in the General Info relative to the file; the PDF-creation
parameters were optimized for printing. Every care has been taken to ensure that the file is suitable for use by ISO member bodies. In the
unlikely event that a problem relating to it is found, please inform the Central Secretariat at the address given below.
© ISO 2000
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means, electronic
or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or ISO's member body
in the country of the requester.
ISO copyright office
Case postale 56 � CH-1211 Geneva 20
Tel. + 41 22 749 01 11
Fax + 41 22 734 10 79
E-mail copyright@iso.ch
Web www.iso.ch
Printed in Switzerland
ii © ISO 2000 – All rights reserved
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SIST ISO 15086-2:2001
ISO 15086-2:2000(E)
Contents Page
Foreword.iv
Introduction.v
1 Scope .1
2 Normative references .1
3 Terms and definitions .1
4 Symbols and subscripts .2
5 Instrumentation.3
6 Hydraulic noise generator.4
7 Test conditions .5
8 Test rig.5
9 Test procedure for Method 1 .9
10 Test procedure for Method 2 .10
11 Test report .11
12 Identification statement (Reference to this part of ISO 15086) .12
Annex A (normative) Errors and classes of measurement of mean value .13
Annex B (normative) Errors and classes of dynamic measurement.14
Annex C (normative) Data reduction algorithms.15
Annex D (informative) Example of speed of sound calculation in MATLAB® language using three
pressure transducers in a pipe (Method 1) .21
Annex E (informative) Example of speed of sound calculation in MATLAB® language using two
pressure transducers in a closed-end pipe (Method 2) .25
Bibliography .27
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SIST ISO 15086-2:2001
ISO 15086-2:2000(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO
member bodies). The work of preparing International Standards is normally carried out through ISO technical
committees. Each member body interested in a subject for which a technical committee has been established has
the right to be represented on that committee. International organizations, governmental and non-governmental, in
liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical
Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 3.
Draft International Standards adopted by the technical committees are circulated to the member bodies for voting.
Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this part of ISO 15086 may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
International Standard ISO 15086-2 was prepared by Technical Committee ISO/TC 131, Fluid power systems,
Subcommittee SC 8, Product testing.
ISO 15086 consists of the following parts, under the general title Hydraulic fluid power — Determination of fluid
borne noise characteristics of components and systems:
� Part 1: Introduction
� Part 2: Measurement of the speed of sound in a fluid in a pipe
Annexes A, B and C form a normative part of this part of ISO 15086. Annexes D and E are for information only
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SIST ISO 15086-2:2001
ISO 15086-2:2000(E)
Introduction
In hydraulic fluid power systems, power is transmitted and controlled through a liquid under pressure within an
enclosed circuit. During the process of converting mechanical power into hydraulic fluid power, flow and pressure
fluctuations and structure-borne vibrations are generated.
Hydro-acoustical characteristics of hydraulic components can be measured with acceptable accuracy if the speed of
sound in the fluid is precisely known.
The measurement technique for determining the speed of sound in a pipe, as described in this part of ISO 15086, is
based upon the application of plane wave transmission line theory to the analysis of pressure fluctuations in rigid
pipes [1].
Two different measurement approaches are presented, namely the use of:
� three pressure transducers in a pipe,
� acoustic antiresonance in a closed-end pipe system.
The three-pressure-transducer method should be used at any time when the speed of sound is to be measured
under the effective working conditions in a system.
The antiresonance method should be used to produce a table of speed-of-sound data as a function of mean
pressure and temperature for a particular fluid.
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SIST ISO 15086-2:2001
INTERNATIONAL STANDARD ISO 15086-2:2000(E)
Hydraulic fluid power — Determination of fluid borne noise
characteristics of components and systems —
Part 2:
Measurement of the speed of sound in a fluid in a pipe
1 Scope
This part of ISO 15086 describes the procedure for the determination of the speed of sound in a fluid enclosed in a
pipe, by measurements from pressure transducers mounted in the pipe.
This part of ISO 15086 is applicable to all types of hydraulic circuit operating under steady state conditions,
irrespective of size, for pressure pulsations over a frequency range from 25 Hz to 2 500 Hz.
2 Normative references
The following normative documents contain provisions which, through reference in this text, constitute provisions of
this part of ISO 15086. For dated references, subsequent amendments to, or revisions of, any of these publications
do not apply. However, parties to agreements based on this part of ISO 15086 are encouraged to investigate the
possibility of applying the most recent editions of the normative documents indicated below. For undated
references, the latest edition of the normative document referred to applies. Members of ISO and IEC maintain
registers of currently valid International Standards.
ISO 1000:1992, SI units and recommendations for the use of their multiples and of certain other units.
ISO 1219-1:1991, Fluid power systems and components — Graphic symbols and circuit diagrams — Part 1:
Graphic symbols.
ISO 5598:1985, Fluid power systems and components — Vocabulary.
3 Terms and definitions
For the purposes of this part of ISO 15086, the terms and definitions given in ISO 5598 and the following apply.
3.1
flow ripple
fluctuating component of flowrate in a hydraulic fluid, caused by interaction with a flow ripple source within the
system
3.2
pressure ripple
fluctuating component of pressure in a hydraulic fluid, caused by interaction with a flow ripple source within the
system
3.3
fundamental frequency
lowest frequency of pressure ripple measured by the frequency-analysis instrument
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ISO 15086-2:2000(E)
3.4
harmonic
sinusoidal component of the pressure ripple or flow ripple occurring at an integer multiple of the fundamental
frequency
NOTE A harmonic may be represented by its amplitude and phase, or alternatively by its real and imaginary parts.
3.5
hydraulic noise generator
hydraulic component generating flow ripple and consequently pressure ripple in the circuit
3.6
measurement pipe
pipe in which the pressure transducers are mounted
3.7
impedance
complex ratio of the pressure ripple to the flow ripple occurring at a given point in a hydraulic system and at a given
frequency
3.8
entry impedance.
impedance at the entry of a pipe or piping system
3.9
first acoustic antiresonance frequency
lowest frequency at which the magnitude of the entry impedance of the measurement pipe is at a minimum
4 Symbols and subscripts
4.1 Symbols
A, A', a, B, B',b Frequency-dependent wave propagation coefficients (complex numbers)
c Acoustic velocity in the fluid
d Internal diameter of pipe
f Frequency of the wave pulsation harmonic
f Vector of frequencies at which measurements are conducted
i
f First acoustic antiresonance frequency (in hertz)
o
H Transfer function (complex number) between two pressure transducer signals after calibration
correction
H' Transfer function (complex number) between two pressure transducer signals under calibration
H* Transfer function (complex number) between two pressure transducer signals
j �1
L Distance between transducers 1 and 2 (Method 1)
L' Distance between transducers 2 and 3 (Method 1)
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l Distance between pressure transducers (Method 2)
P Pressure ripple of transducer PT1 (complex number)
1
P Pressure ripple of transducer PT2 (complex number)
2
P Pressure ripple of transducer PT3 (complex number)
3
Q Flow ripple at location 1, from 1 to 2 (complex number)
1� 2
Q Flow ripple at location 2, from 2 to 1 (complex number)
2� 1
Q Flow ripple at location 3, from 2 to 3 (complex number)
2� 3
S Coherence function corresponding to measurement frequencies, f
i i
� Error (complex number)
� Conjugate of complex number � (complex number)
� Real part of �
x
� Imaginary part of �
y
� Density of fluid
� Kinematic viscosity of fluid
� 2�f
NOTE H, H', H*, P , P , P , Q , Q , Q are all frequency-dependent terms and hence are designated by upper-
1 2 3 1� 2 2� 1 2� 3
case letters.
Units used in this part of ISO 15086 are in accordance with ISO 1000.
Graphical symbols are in accordance with ISO 1219-1 unless otherwise stated.
4.2 Subscripts
O Index for old value
N Index for new value
5 Instrumentation
5.1 Static measurements
The instruments used to measure
a) mean flow (Method 1 only);
b) mean fluid pressure;
c) fluid temperature;
shall meet the requirements for "industrial class" accuracy of measurement, i.e. class C as given in annex B.
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5.2 Dynamic measurements
The instruments used to measure pressure ripple shall have the following characteristics:
a) resonant frequencyW 30 kHz;
b) linearityW� 1%;
c) preferably include acceleration compensation.
The instruments need not respond to steady-state pressure. It may be advantageous to filter out any steady-state
signal component using a high-pass filter. This filter shall not introduce an additional amplitude or phase error
°
exceeding 0,5 % or 0,5 respectively of the current measurement.
5.3 Frequency analysis of pressure ripple
A suitable instrument shall be used to measure the amplitude and phase of the pressure ripple.
The instrument shall be capable of measuring the pressure ripple from the pressure transducers such that, for a
particular harmonic, the measurements from each transducer are performed simultaneously and synchronised in
time with respect to each other.
The instrument shall have an accuracy and resolution for harmonic measurements of
a) amplitude within � 0,5 %;
°
b) phase within � 0,5 ;
c) frequency within � 0,5 %;
over the frequency range from 25 Hz to 2 500 Hz.
5.4 Uncertainty
Compliance with the above specification will result in an uncertainty in measurement of speed of sound of less than
� 3%.
6 Hydraulic noise generator
6.1 General
Any type of hydraulic noise generator may be used, provided that sufficient pressure ripple is created at the
pressure transducers to allow accurate measurements to be taken.
EXAMPLE Pumps and motors create a pressure ripple consisting essentially of many harmonics of the fundamental
frequency. In these cases, the fundamental frequency is equal to the product of the shaft rotational frequency and the number
of gear teeth, vanes or pistons, etc. (as appropriate to the machine employed).
Suitable alternatives include:
� an auxiliary valve with a rotating spool allowing flow to pass to the return line over part of its rotation;
� an electrohydraulic servo-valve driven by a frequency generator.
� The servo-valve may be operated with a white noise signal in order to obtain significant pressure ripple
measurements at each frequency of interest.
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6.2 Generator vibration
If necessary, the measurement pipe should be structurally isolated from the generator to minimize vibration.
7 Test conditions
7.1 General
The required operating conditions shall be maintained throughout each test within the limits specified in Table 1.
7.2 Fluid temperature
The temperature of the fluid shall be that measured at the entry to the measurement pipe.
7.3 Fluid density and viscosity
The density and viscosity of the fluid shall be known to an accuracy within the limits specified in Table 2.
7.4 Mean fluid pressure
The mean fluid pressure of the fluid shall be that measured at the entry to the measurement pipe.
7.5 Mean flow measurement
The mean flow shall be measured down-stream of the measurement pipe (Method 1 only).
Table 1 — Permissible variations in tests conditions
Test parameter Permissible variation
Mean flow �2%
Mean pressure �2%
Temperature
�2°C
Table 2 — Required accuracy of fluid property data
Property Required accuracy
Density
�2%
Viscosity
�5%
8 Test rig
8.1 General
If, at any test condition, the pressure ripple amplitudes are too small for satisfactory frequency-spectrum analysis to
be performed, an alternative noise generator shall be selected.
The pressure transducers shall be mounted such that their diaphragms are flush, within � 0,5 mm, with the inner
wall of the pipe.
Two alternative specifications for the measurement pipe and transducer position are given, in accordance with the
method employed.
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8.2 Thermal insulation
Temperature shall be measured at both ends of the measurement pipe. The difference in temperature between the
two ends of the measurement pipe shall not exceed 2 °C at any test condition. If necessary, sufficient thermal
lagging shall be applied to the measurement pipe to enable this requirement to be met.
8.3 Method 1: Three-transducer method
8.3.1 This method is suitable when the velocity of sound is to be measured at the same time as other hydro-
acoustical characteristics of hydraulic components, such as impedance, source flow ripple or transfer matrix
coefficients. The measurement pipe shall be installed at the place in the test system where measurement of the
speed of sound is needed. Several measurement pipes may be used simultaneously, if required.
The measurement pipe shall be uniform and straight. Its internal diameter shall be between 80 % and 120 % of the
diameter of the pipes, or component ports, to which it is connected. The pipe should be supported in such a manner
that vibration is minimized.
For cases where other hydro-acoustic properties are not being measured simultaneously, a pump (and if necessary,
a hydraulic noise generator) shall be mounted at one end of the measurement pipe. The other end shall be
terminated by a loading valve without free-moving internal parts, such as a needle valve.
Mean pressure shall be measured at the upstream end of the measurement pipe.
8.3.2 Three pressure transducers are required for Method 1, configured as shown in Figure 1. The transducer
spacing shall be selected according to the standard specifications of hydro-acoustical measurements to be carried
out simultaneously. Otherwise, the distances L and L' between the pressure transducers shall be as specified in
Table 3.
Table 3 — Spacing of transducers: Method 1
L 330 mm �2mm
L'
470 mm �2mm
The distance between each end of the measurement pipe and the nearest pressure transducer shall be at least
10 d, where d is the internal diameter of the pipe. The distances L and L' between the transducers, as shown in
Figure 1, shall be measured to an accuracy of � 0,5 mm.
No other components shall be connected between the inlet port and outlet port of the measurement pipe.
a
Pressure transducers.
b
Distances to end of measurement pipe, x W 10d and x W 10d.
1 2
Figure 1 — Arrangement of three pressure transducers in measurement pipe
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ISO 15086-2:2000(E)
8.4 Method 2: Antiresonance method
8.4.1 This method can be used to produce a data chart of the speed of sound for a particular fluid. Due to the
pressure resonances that are created in the system, this method is not appropriate when other hydro-acoustical
measurements are to be undertaken.
8.4.2 An appropriate test rig is presented schematically in Figure 2 a). The loading valve shall not contain free-
moving parts. A needle valve is an example of a suitable loading valve. The measurement pipe takes the form of a
closed-end side-branch line connected to the pump/pipe/loading-valve circuit as shown. It is important that the fluid
in the measurement pipe is at as uniform a temperature as possible, and does not contain gas bubbles. To achieve
these objectives, the measurement pipe is terminated by a bleed valve. A needle valve is an example of a suitable
bleed valve. Prior to measurements being taken, the bleed valve is opened for a period of time sufficient to flush the
pipe of gas bubbles and to stabilize temperature. The measurement pipe shall be orientated downwards with the
bleed valve below the level of the through-flow pipe to prevent the trapping of air in the measurement pipe during
testing. It is important that the bleed valve does not introduce significant extra volume at the end of the line when
the valve is in the closed position.
The pressure transducers, PT and PT in Figure 2 a), are located at each end of the measurement pipe. It is
1 2
essential that transducer PT is mounted as closely as possible to the end of the pipe. Moreover, the location of
2
transducer PT should be as close as possible to the point where the measurement pipe is connected to the main
1
circuit. Figure 2 b) provides an example of how these requirements may be achieved. In this example, the
measurement pipe is terminated by a purpose-built housing which contains the needle valve assembly.
The hydraulic components necessary to obtain the appropriate test conditions may, inherently, generate sufficient
pressure pulsation levels to allow satisfactory frequency-spectrum analysis to be performed. Should this not be the
case, a separate hydraulic noise generator shall be connected to the circuit, as shown in Figure 2 a).
In order to maximize the pressure pulsation levels, the distance between the pump (or the noise generator if in use)
and the loading valve should not be greater than one-tenth of the measurement pipe length.
8.4.3 The measurement pipe shall be a uniform, rigid, straight metal pipe. The internal diameter of the pipe shall
be between 50 % and 100 % of the diameter of the line where it is connected. This pipe shall be supported in such
a manner that pipe vibration is minimized.
The distance, l, between the pressure transducers shall be defined according to the first acoustic antiresonance
frequency f by equation (1).
o
6
1 B� 10
l � (1)
4 f �
o
The effective bulk modulus B can be estimated using manufacturer’s data for the fluid consistent with the operating
condition of the tests. An accurate value is not required.
The frequency f should be chosen in the range 100 Hz to 200 Hz.
o
The distance between the pressure transducers shall be measured to an accuracy of � 0,5 mm.
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ISO 15086-2:2000(E)
Key
1Pump 6 Loading valve
2 Electric motor 7 Bleed valve
3 Hydraulic noise generator (if used) 8 Measurement pipe
4 Through-flow pipe 9 Temperature transducers
5 Pressure gauge 10 Pressure transducers
a) Circuit layout
Key
1 Through-flow pipe 4 Needle valve adjustment
2 Temperature transducer 5 To reservoir
3 Pressure transducer PT 6 Pressure transducer PT
1 2
b) Example of transducer locations and bleed valve mounting
NOTE Graphical symbols are for illustration purposes and do not conform to ISO 1219-1.
Figure 2 —Typical antiresonance test arrangement
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ISO 15086-2:2000(E)
8.5 Calibration of pressure transducers
Calibration of pressure transducers and signal conditioning is necessary. Perform relative calibration by mounting
the pressure transducers in a common block such that they measure the same pressure ripple. Construct this
common block such that the pressure transducers are at the same axial position and no more than one internal
diameter of the measurement pipe apart.
Measure the amplitude and phase relationship between the pressure transducers for a range of frequencies
spanning the complete range of interest with one transducer used as a reference. For piezoresistive transducers,
the reference transducer can be calibrated statically using, for example, a deadweight testing machine.
If piezoelectric transducers and charge amplifiers are employed, a calibrated piezoresistive transducer may be used
as a reference for dynamic calibration purposes.
If the amplitude or phase difference between the transducers exceeds 1 % or 0,5° respectively, correct for the
differences in the analysis of the test data (see 9.3 and 10.3). Record the transfer functions.
P
1
H� �
12
P
2
and
P
3
H� �
32
P
2
obtained during calibration.
9 Test procedure for Method 1
9.1 Prior to the commencement of tests, operate the hydraulic system for a sufficient period of time to purge air
from the system and to stabilize all variables, including fluid condition, to within the limits given in Table 1. If a speed
of sound test is to be performed at the same time as other hydro-acoustical measurements, conditions to the
standard relevant to those measurements can be used.
9.2 Take the ensemble average of at least 16 time-series pressure transfer functions
P P
3
1
H**��and H
12 32
P P
2 2
and calculate the coherence function S at each frequency f over the frequency range. Typical examples of the
i i
transfer functions H * and H * are given, for the case of broad-band excitation, in Figure 3.
12 32
9.3 Perform the correction of the ensemble-averaged transfer functions H and H using the transfer functions
12 32
obtained from the calibration procedure H' and H' (see 8.5) using equations (2) and (3).
12 32
H *
12
H � (2)
12
H�
12
H *
32
H � (3)
32
H�
32
If correction is not necessary (see 8.5), then H = H* and H = H* .
12 12 32 32
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Key
1 Modulus of transfer functions H* and H* 3 Degree
12 32
4 Phase of transfer functions H* and H*
2 Frequency (Hz) 12 32
Figure 3 — Typical example of transfer functions H* and H*
12 32
9.4 Calculate the speed of sound for each frequency having an associated coherence function S greater than
i
0,95 as described in C.1. The S function is always a positive number less than or equal to 1. The least-squares
i
error procedure given in C.1 allows the speed of sound, averaged over the frequency range investigated, to be
calculated.
9.5 Calculate the mean fluid velocity by dividing the mean flow by the internal cross-sectional area of the
measurement pipe. If the mean fluid velocity is greater than 5 % of any speed of sound measurement, then the
method is invalid and results shall not be reported.
10 Test procedure for Method 2
10.1 Prior to the commencement of a series of tests, operate the hydraulic system and noise generator (if
included) for a sufficient period of time to purge air from the system and to stabilize all variables, including fluid
condition, to within the limits given in Table 1. Particular attention should be given to obtaining a representative fluid
characteristic, especially the bulk modulus.
The bleed valve should be fully open to allow flow through the measurement pipe during this stabilization period.
The restrictor valve downstream of the bleed valve should be adjusted to create a mean pressure approximately
0,5 MPa below the desired test pressure during this phase. Immediately before pressure transducer measurements
are taken, the bleed valve should be closed and, if necessary, the mean pressure re-established through
adjustment of the loading valve.
Warning — No safety valves are included in the system. Personnel performing tests should exercise great
care to ensure that excessive and dangerous pressures are not created when adjusting restrictor valves.
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10.2 Take the ensemble ave
...
NORME ISO
INTERNATIONALE 15086-2
Première édition
2000-02-01
Transmissions hydrauliques — Évaluation
des caractéristiques du bruit liquidien des
composants et systèmes —
Partie 2:
Mesurage de la vitesse du son émis dans
un fluide dans une tuyauterie
Hydraulic fluid power — Determination of fluid-borne noise characteristics
of components and systems —
Part 2: Measurement of speed of sound in a fluid in a pipe
Numéro de référence
ISO 15086-2:2000(F)
©
ISO 2000
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ISO 15086-2:2000(F)
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ISO 15086-2:2000(F)
Sommaire Page
Avant-propos.iv
Introduction.v
1 Domaine d’application .1
2 Références normatives .1
3 Termes et définitions.1
4 Symboles et souscrits.2
5 Instruments .3
6 Générateur de bruit hydraulique.4
7 Conditions d'essai .5
8 Banc d'essai .6
9 Mode opératoire d'essai de la méthode 1 .10
10 Mode opératoire d'essai de la méthode 2 .11
11 Rapport d'essai .12
12 Phrase d'identification (Référence à la présente partie de l'ISO 15086) .13
Annexe A (normative) Erreurs et classes de mesure de la valeur moyenne.14
Annexe B (normative) Erreurs et classes de mesure dynamique.15
Annexe C (normative) Algorithmes de compression des données .16
®
Annexe D (informative) Exemple de calcul de la vitesse du son en langage MATLAB en utilisant trois
capteurs de pression montés sur le tube (Méthode 1) .22
®
Annexe E (informative) Exemple de calcul de la vitesse du son en langage MATLAB en utilisant deux
capteurs de pression montés sur un tube à extrémité fermée (Méthode 2).26
Bibliographie .27
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ISO 15086-2:2000(F)
Avant-propos
L'ISO (Organisation internationale de normalisation) est une fédération mondiale d'organismes nationaux de
normalisation (comités membres de l'ISO). L'élaboration des Normes internationales est en général confiée aux
comités techniques de l'ISO. Chaque comité membre intéressé par une étude a le droit de faire partie du comité
technique créé à cet effet. Les organisations internationales, gouvernementales et non gouvernementales, en
liaison avec l'ISO participent également aux travaux. L'ISO collabore étroitement avec la Commission
électrotechnique internationale (CEI) en ce qui concerne la normalisation électrotechnique.
Les Normes internationales sont rédigées conformément aux règles données dans les Directives ISO/CEI, Partie 3.
Les projets de Normes internationales adoptés par les comités techniques sont soumis aux comités membres pour
vote. Leur publication comme Normes internationales requiert l'approbation de 75 % au moins des comités
membres votants.
L’attention est appelée sur le fait que certains des éléments de la présente partie de l’ISO 15086 peuvent faire
l’objet de droits de propriété intellectuelle ou de droits analogues. L’ISO ne saurait être tenue pour responsable de
ne pas avoir identifié de tels droits de propriété et averti de leur existence.
La Norme internationale ISO 15086-2 a été élaborée par le comité technique ISO/TC 131, Transmissions
hydrauliques et pneumatiques, sous-comité SC 8, Essais des produits.
L'ISO 15086 comprend les parties suivantes, présentées sous le titre général Transmissions hydrauliques —
Évaluation des caractéristiques du bruit liquidien des composants et systèmes:
� Partie 1: Introduction
� Partie 2: Mesurage de la vitesse du son émis dans un fluide dans une tuyauterie
Les annexes A, B et C constituent des éléments normatifs de la présente partie de l’ISO 15086. Les annexes D et
E sont données uniquement à titre d’information.
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ISO 15086-2:2000(F)
Introduction
Dans les systèmes de transmissions hydrauliques, l'énergie est transmise et commandée par l'intermédiaire d'un
fluide sous pression circulant en circuit fermé. Le processus de transformation de l'énergie mécanique en énergie
hydraulique génère des fluctuations de l'écoulement et de la pression ainsi que des vibrations de la structure.
Les caractéristiques hydro-acoustiques des composants hydrauliques peuvent être mesurées avec une précision
acceptable lorsque la vitesse du son émis par le fluide est connue de façon précise.
La méthode de mesurage pour l'évaluation de la vitesse du son dans un tube, comme décrit dans la présente
partie de l’ISO 15086, est fondée sur l'application de la théorie de la ligne de transmission à onde plane à l'analyse
des fluctuations de pression dans des tubes rigides [1].
Deux méthodes différentes sont présentées, à savoir:
� trois capteurs de pression dans un tube;
� l’antirésonance acoustique dans un système de tubes à extrémité fermée.
Il convient d’utiliser la méthode des trois capteurs de pression chaque fois que la vitesse du son est à mesurer
dans les conditions de service efficaces d'un système.
Il convient d’utiliser la méthode antirésonance pour produire un tableau de vitesse des données acoustiques en
fonction de la pression et de la température moyennes d'un fluide particulier.
© ISO 2000 – Tous droits réservés v
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NORME INTERNATIONALE ISO 15086-2:2000(F)
Transmissions hydrauliques — Évaluation des caractéristiques du
bruit liquidien des composants et systèmes —
Partie 2:
Mesurage de la vitesse du son émis dans un fluide dans une
tuyauterie
1 Domaine d’application
La présente partie de l'ISO 15086 décrit la procédure d'évaluation de la vitesse du son émis par un fluide contenu
dans un tube, par la réalisation de mesurages à partir de capteurs de pression montés sur ledit tube.
La présente partie de l'ISO 15086 s'applique à tous les types de circuits hydrauliques fonctionnant dans des
conditions de régime établi, indépendamment de leur dimension, pour des impulsions de pression dans une
gamme de fréquences comprise entre 25 Hz et 2 500 Hz.
2 Références normatives
Les normes suivantes contiennent des dispositions qui, par suite de la référence qui en est faite, constituent des
dispositions valables pour la présente partie de l'ISO 15086. Au moment de la publication, les éditions indiquées
étaient en vigueur. Toute norme est sujette à révision et les parties prenantes des accords fondés sur la présente
partie de l'ISO 15086 sont invitées à rechercher la possibilité d'appliquer les éditions les plus récentes des normes
indiquées ci-après. Les membres de la CEI et de l'ISO possèdent le registre des Normes internationales en vigueur
à un moment donné.
ISO 1000:1992, Unités SI et recommandations pour l'emploi de leurs multiples et de certaines autres unités.
ISO 1219-1:1991, Transmissions hydrauliques et pneumatiques — Symboles graphiques et schémas de circuit —
Partie 1: Symboles graphiques.
ISO 5598:1985, Transmissions hydrauliques et pneumatiques — Vocabulaire.
3 Termes et définitions
Pour les besoins de la présente partie de l'ISO 15086, les termes et définitions donnés dans l’ISO 5598 et les
suivants s'appliquent.
3.1
onde d'écoulement
composant fluctuant de débit dans le fluide hydraulique, provoqué par l'interaction entre l'onde d'écoulement de la
source et le système
3.2
onde de pression
composant fluctuant de pression dans le fluide hydraulique, provoqué par l'interaction entre l'onde d'écoulement de
la source et le système
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ISO 15086-2:2000(F)
3.3
fréquence fondamentale
fréquence la plus basse d'onde de pression mesurée à l'aide de l'instrument d'analyse de fréquence
3.4
harmonique
composant sinusoïdal de l'onde de pression ou de l'onde d'écoulement se produisant à un multiple entier de la
fréquence fondamentale
NOTE Une harmonique peut être représentée par son amplitude et sa phase, ou bien par ses parties réelle et imaginaire.
3.5
générateur de bruit hydraulique
composant hydraulique générant une onde d'écoulement puis une onde de pression dans le circuit
3.6
tube de mesure
tube dans lequel sont montés les capteurs de pression
3.7
impédance
rapport complexe de l'onde de pression avec l'onde d'écoulement se produisant à un point donné dans un système
hydraulique et à une fréquence donnée
3.8
impédance d'entrée
impédance à l'entrée d'un tube ou d'une tuyauterie
3.9
première fréquence antirésonance acoustique
fréquence la plus basse à laquelle l'amplitude de l'impédance d'entrée du tube de mesurage est minimale.
4 Symboles et souscrits
4.1 Symboles
A, A',a,B,B', b Coefficients de propagation des ondes dépendant de la fréquence (nombres complexes)
c Vitesse acoustique du fluide
d Diamètre intérieur du tube
f Fréquence de l'harmonique d'onde de pulsation
f Vecteur de fréquences auxquelles sont effectués les mesurages
i
f Première fréquence antirésonance acoustique (en hertz)
0
H Fonction transfert (nombre complexe) entre deux signaux de capteurs de pression après
correction de l’étalonnage
H' Fonction transfert (nombre complexe) entre deux signaux de capteurs de pression soumis à
étalonnage
H* Fonction transfert (nombre complexe) entre deux signaux de capteurs de pression après
correction d'étalonnage
j �1
L Distance entre les capteurs 1 et 2 (Méthode 1)
2 © ISO 2000 – Tous droits réservés
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ISO 15086-2:2000(F)
L' Distance entre les capteurs 2 et 3 (Méthode 1)
l Distance entre les capteurs de pression (Méthode 2)
P Onde de pression du capteur PT1 (nombre complexe)
1
P Onde de pression du capteur PT2 (nombre complexe)
2
P Onde de pression du capteur PT3 (nombre complexe)
3
Q Onde d'écoulement à l'emplacement 1, de 1 à 2 (nombre complexe)
1� 2
Q Onde d'écoulement à l'emplacement 2, de 2 à 1 (nombre complexe)
2� 1
Q Onde d'écoulement à l'emplacement 3, de 2 à 3 (nombre complexe)
2� 3
S Fonction de cohérence correspondant aux fréquences de mesure, f
i i
�� Erreur (nombre complexe)
� Conjugué du nombre complexe ��(nombre complexe)
� Partie réelle de �
x
� Partie imaginaire de �
y
� Masse volumique du fluide
� Viscosité cinématique du fluide
� 2�f
NOTE H, H', H*, P , P , P , Q , Q , Q sont tous dépendants, de la fréquence et sont donc représentés par des
1 2 3 1� 2 2� 1 2� 3
lettres majuscules.
Les unités utilisées dans la présente partie de l'ISO 15086 sont conformes à l'ISO 1000.
Les symboles graphiques sont conformes à l'ISO 1219-1, sauf indication contraire.
4.2 Souscrits
O Indice de l'ancienne valeur
N Indice de la nouvelle valeur
5 Instruments
5.1 Mesures statiques
Les instruments utilisés pour mesurer
a) l'écoulement moyen (Méthode 1 uniquement);
b) la pression moyenne du fluide;
c) la température du fluide;
doivent satisfaire l'exigence relative à l’exactitude de mesurage de «classe industrielle», c'est-à-dire la classe C
donnée dans l'annexe B.
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ISO 15086-2:2000(F)
5.2 Mesures dynamiques
Les instruments utilisés pour mesurer l'onde de pression doivent avoir les caractéristiques suivantes:
a) fréquence de résonanceW 30 kHz;
b) linéaritéW� 1%;
c) compensation d'accélération souhaitable.
Il n'est pas nécessaire que les instruments correspondent à une pression en régime établi, et il peut être
avantageux de filtrer toute composante de signal en régime établi à l'aide d'un filtre passe-haut. Ce filtre ne doit
pas générer d'erreur d'amplitude ou de phase supplémentaire supérieure à 0,5 % ou 0,5° respectivement, de la
mesure courante.
5.3 Analyse de fréquence de l'onde de pression
Un instrument approprié doit être utilisé pour mesurer l'amplitude et la phase de l'onde de pression.
L'instrument doit pouvoir mesurer l'onde de pression à partir des capteurs de pression de telle sorte que, pour un
harmonique particulier, les mesures réalisées à partir de chaque capteur soient effectuées simultanément et de
manière synchronisée les unes par rapport aux autres.
La précision et la résolution de l'instrument pour les mesures d'harmonique doivent être les suivantes:
a) amplitude:� 0,5 %;
b) phase:� 0,5°;
c) fréquence:� 0,5 %;
sur une gamme de fréquences comprise entre 25 Hz et 2 500 Hz.
5.4 Incertitude
La conformité à la spécification ci-dessus donnera une incertitude de la vitesse du son inférieure à� 3%.
6 Générateur de bruit hydraulique
6.1 Généralités
Tout type de générateur de bruit hydraulique peut être utilisé à condition qu'il crée une onde de pression suffisante
au niveau des capteurs de pression permettant ainsi la réalisation de mesures exactes.
EXEMPLE Les pompes et les moteurs créent une onde de pression composée principalement de nombreux harmoniques
de la fréquence fondamentale. Dans ces cas, la fréquence fondamentale est égale au produit de la fréquence de rotation de
l’axe et du nombre de dents de l'engrenage, de palettes ou de pistons, etc. (selon la machine utilisée).
Des méthodes alternatives appropriées comprennent:
� un distributeur auxiliaire équipé d'un tiroir tournant permettant au flux de se diriger vers la canalisation de
retour grâce à sa rotation partielle;
� un servodistributeur électro-hydraulique entraîné par un générateur de fréquence. Le servo-distributeur peut
être déclenché par un signal de bruit blanc afin d'obtenir des mesures d'onde de pression significatives à
chaque fréquence intéressante.
4 © ISO 2000 – Tous droits réservés
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ISO 15086-2:2000(F)
6.2 Vibration du générateur
Si nécessaire, il convient que le tube de mesure soit structurellement isolé du générateur afin de minimiser les
vibrations.
7 Conditions d'essai
7.1 Généralités
Les conditions de service requises doivent être maintenues pour chaque essai dans les limites spécifiées dans le
Tableau 1.
7.2 Température du fluide
La température du fluide doit être la température mesurée à l'entrée du tube de mesure.
7.3 Masse volumique et viscosité du fluide
La masse volumique et la viscosité du fluide doivent être connues avec une exactitude définie dans les limites
spécifiées dans le Tableau 2.
7.4 Pression moyenne du fluide
La pression moyenne du fluide doit être celle mesurée à l'entrée du tube de mesure.
7.5 Mesure de l'écoulement moyen
La mesure de l'écoulement moyen doit être effectuée en aval du tube de mesure (Méthode 1 uniquement).
Tableau 1 — Variations admissibles des conditions d'essai
Paramètre d'essai Variation admissible
Écoulement moyen �2%
Pression moyenne
�2%
Température �2°C
Tableau 2 — Exactitude requise des données de propriétés du fluide
Propriété Exactitude requise
Masse volumique �2%
Viscosité
�5%
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ISO 15086-2:2000(F)
8 Banc d'essai
8.1 Généralités
Si, à toute condition d'essai, les amplitudes d'ondes de pression sont trop faibles pour pouvoir réaliser une analyse
satisfaisante du spectre de fréquences, un autre générateur de bruit doit être choisi.
Les capteurs de pression doivent être montés de telle sorte que leurs diaphragmes soient au même niveau que la
paroi intérieure du tube à � 0,5 mm.
Deux spécifications alternatives relatives au tube de mesure et à la position du capteur sont données
conformément à la méthode utilisée.
8.2 Isolation thermique
La température doit être mesurée aux deux extrémités du tube de mesure. La différence de température entre les
deux extrémités du tube de mesure ne doit en aucun cas dépasser 2 °C quelle que soit la condition d'essai. Si
nécessaire, un calorifugeage thermique suffisant doit être appliqué au tube de mesure pour pouvoir satisfaire cette
exigence.
8.3 Méthode 1: Méthode des trois capteurs
8.3.1 Cette méthode peut être utilisée lorsque la vitesse du son doit être mesurée en même temps que les
autres caractéristiques hydro-acoustiques des composants hydrauliques telles que l'impédance, l'onde
d'écoulement de la source ou les coefficients de la matrice-transfert. Le tube de mesure doit être installé dans le
système d'essai à l'endroit où la vitesse du son doit être mesurée. Si nécessaire, plusieurs tubes de mesure
peuvent être utilisés simultanément.
Le tube de mesure doit être uniforme et droit. Son diamètre intérieur doit être compris entre 80 % et 120 % du
diamètre des tubes, ou des orifices de composants, auxquels il est raccordé. Il convient que le tube soit soutenu de
manière à réduire toute vibration.
Dans les cas où les autres propriétés hydro-acoustiques ne sont pas mesurées simultanément, une pompe (et, si
nécessaire, un générateur de bruit hydraulique) doit être montée à une extrémité du tube de mesure. L'autre
extrémité doit avoir la forme d'une soupape de charge ne comportant aucun élément interne libre, telle qu'une
soupape à pointeau.
La pression moyenne doit être mesurée à l'extrémité amont du tube de mesure.
8.3.2 Cette méthode requiert l'utilisation de trois capteurs de pression, configurés comme représenté à la
Figure 1. L'espace entre les capteurs doit être choisi selon les spécifications normalisées des mesures hydro-
acoustiques à effectuer simultanément. Sinon, la distance entre les capteurs de pression L, L' est celle spécifiée
dans le Tableau 3.
La distance entre chaque extrémité du tube de mesure et le capteur de pression le plus proche doit être au moins
égale à 10d,où d est le diamètre intérieur du tube. Les distances L et L' entre les capteurs, comme représenté à la
Figure 1, doivent être mesurées avec une exactitude de � 0,5 mm.
Aucun autre composant ne doit être raccordé entre les orifices d'entrée et de sortie du tube de mesure.
Tableau 3 — Espace entre les capteurs: Méthode 1
L
330 mm �2mm
L'
470 mm �2mm
6 © ISO 2000 – Tous droits réservés
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ISO 15086-2:2000(F)
a
Capteurs de pression
b
Distances par rapport à l'extrémité du tube de mesure, x W 10d et x W 10d
1 2
Figure 1 — Disposition du tube de mesure à trois capteurs de pression
8.4 Méthode 2: Méthode antirésonance
8.4.1 Cette méthode peut être utilisée pour réaliser un organigramme de la vitesse du son d'un fluide particulier.
En raison des résonances de pression créées dans le système, cette méthode ne convient pas lorsque d'autres
mesures hydro-acoustiques doivent être réalisées.
8.4.2 Un banc d'essai approprié est représenté schématiquement à la Figure 2 a). La soupape de charge ne doit
comporter aucun élément libre. Une soupape à pointeau est un exemple de soupape de charge appropriée. Le
tube de mesure prend la forme d'un branchement latéral à extrémité fermée raccordé au circuit
pompe/tube/soupape de charge comme présenté. Il est important que le fluide dans le tube de mesure ait une
température la plus uniforme possible, et qu'il ne contienne pas de bulles de gaz. Pour réaliser ces objectifs,
l'extrémité du tube de mesure est constituée d'un robinet de purge. Une soupape à pointeau est un exemple de
robinet de purge approprié. Avant d'effectuer les mesures, le robinet de purge est ouvert pendant une durée
suffisante pour évacuer les bulles de gaz dans le tube et pour stabiliser la température. Le tube de mesure doit être
orienté vers le bas avec le robinet de purge situé en dessous du niveau du tube d'écoulement de façon à éviter que
de l’air reste piégé dans le tube de mesure durant l’essai. Il est important que le robinet de purge n'achemine pas
un volume supplémentaire significatif à l'extrémité de la conduite lorsque le robinet est fermé.
Les capteurs de pression, PT et PT , représentés à la Figure 2 a), sont situés à chaque extrémité du tube de
1 2
mesure. Il est essentiel que le capteur PT soit monté le plus près possible de l'extrémité du tube. Il convient
2
également que l'emplacement du capteur PT soit le plus proche possible du point de raccordement du tube de
1
mesure au circuit principal. La Figure 2 b) donne un exemple de satisfaction de ces exigences. Dans cet exemple,
l'extrémité du tube de mesure est un logement prévu à cet effet comportant la soupape à pointeau.
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ISO 15086-2:2000(F)
Légende
1 Pompe 6 Soupape de charge
2 Moteur électrique 7 Robinet de purge
3 Générateur de bruit hydraulique (lorsqu'il est utilisé) 8 Tube de mesure
4 Tube d'écoulement 9 Capteurs de température
5 Manomètre 10 Capteurs de pression
a) Disposition du circuit
8 © ISO 2000 – Tous droits réservés
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ISO 15086-2:2000(F)
Légende
1 À travers la conduite d’écoulement 4 Réglage de la soupape à pointeau
2 Capteur de température 5 Vers le réservoir
3 Capteur de pression PT 6 Capteur de pression PT
1 2
b) Exemple d'emplacements de capteur et de montage du robinet de purge
NOTE Les symboles graphiques sont donnés pour illustration et ne sont pas conformes à l'ISO 1219-1.
Figure 2 — Dispositif type de l'essai antirésonance
Les composants hydrauliques nécessaires pour obtenir les conditions d'essai appropriées peuvent,
intrinsèquement, générer des niveaux d'impulsion de pression suffisants pour pouvoir effectuer l'analyse du spectre
de fréquences de façon satisfaisante. Dans le cas contraire, un générateur de bruit hydraulique séparé doit être
raccordé au circuit, comme représenté à la Figure 2 a).
Afin de maximiser les niveaux d'impulsion de pression, il convient que la distance entre la pompe (ou le générateur
de bruit lorsqu'il fonctionne) et la soupape de charge ne soit pas supérieure à un dixième de la longueur du tube de
mesure.
8.4.3 Le tube de mesure doit être un tube métallique uniforme, rigide et droit. Son diamètre intérieur doit être
compris entre 50 % et 100 % du diamètre de la conduite à laquelle il est raccordé. Ce tube doit être soutenu de
telle sorte que les vibrations soient réduites.
La distance entre les capteurs de pression, l, doit être définie selon la première fréquence antirésonance
acoustique f àl'aidedel'équationsuivante:
0
6
1 B�10
l � (1)
4 f �
0
Le coefficient de charge effectif B peut être évalué en utilisant les données du fabricant relatives au fluide adapté
aux conditions de service des essais. Une valeur précise n'est pas requise.
La fréquence f peut être choisie dans la gamme comprise entre 100 Hz et 200 Hz.
0
La distance entre les capteurs de pression doit être mesurée avec une précision de � 0,5 mm.
8.5 Étalonnage des capteurs de pression
L'étalonnage des capteurs de pression et la mise en forme de signaux sont des opérations nécessaires.
L'étalonnage relatif doit être effectué en montant les capteurs de pression sur un bloc commun de telle sorte qu'ils
mesurent la même onde de pression. Ce bloc commun doit être construit de sorte que les capteurs de pression
aient la même position axiale et ne soient pas éloignés du tube de mesure de plus d'un diamètre intérieur.
Mesurer la relation amplitude-phase entre les capteurs de pression pour une gamme de fréquences couvrant la
gamme complète concernée avec un capteur utilisé comme élément de référence. Pour les capteurs piézorésistifs,
le capteur de référence peut être étalonné de manière statique en utilisant, par exemple, une machine d'essais à
contre-poids.
Lorsque l'on utilise des capteurs piézo-électriques et des amplificateurs de charge, un capteur piézorésistif
étalonné peut être pris comme référence pour un étalonnage dynamique.
Lorsque la différence d'amplitude ou de phase entre les capteurs dépasse 1 % ou 0,5° respectivement, les
différences doivent être corrigées dans l'analyse des données d'essais (voir 9.3 et 10.3). Enregistrer les fonctions
transfert
P
1
'
�
H
12
P
2
© ISO 2000 – Tous droits réservés 9
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ISO 15086-2:2000(F)
et
P
3
'
�
H
32
P
2
obtenues au cours de l'étalonnage.
9 Mode opératoire d'essai de la méthode 1
9.1 Avant de commencer les essais, faire fonctionner le système hydraulique pendant une durée suffisante pour
purger l'air contenu dans le système et stabiliser toutes les variables, y compris l'état du fluide, dans les limites
données dans le Tableau 1. Lorsqu'un essai de vitesse du son doit être réalisé en même temps que d'autres
mesures hydro-acoustiques, il est admis d'appliquer les exigences relatives à la norme correspondant à ces
mesures.
9.2 Prendre la moyenne d'ensemble d'au moins 16 séries temporelles de fonctions transfert de pression
P
1
*
�
H
12
P
2
et
P
3
*
�
H
32
P
2
et calculer la fonction de cohérence S à chaque fréquence f sur la gamme de fréquences. Des exemples types de
i i
fonctions transfert H* et H* sont donnés à la Figure 3 pour le cas d'une excitation à large bande.
12 32
9.3 Effectuer la correction de l'ensemble moyennée des fonctions transfert H et H en utilisant les fonctions
12 32
transfert obtenues à partir de la procédure d'étalonnage H' et H' (voir 8.5) en utilisant les équations (2) et (3).
12 32
*
H12
H � (2)
12
'
H
12
*
H
32
H � (3)
32
'
H
32
Lorsque la correction n'est pas nécessaire (voir 8.5), H = H'* et H = H* .
12 32 32
12
10 © ISO 2000 – Tous droits réservés
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ISO 15086-2:2000(F)
Figure 3 — Exemple type des fonctions transfert H* et H*
12 32
9.4 Calculer la vitesse du son pour chaque fréquence ayant une fonction de cohérence associée S supérieure à
i
0,95 comme décrit à l'article C.1. La fonction S est toujours un nombre positif inférieur ou égal à 1. La méthode du
i
carré des erreurs donnée dans l'article C.1 permet de calculer la vitesse du son, moyennée sur la gamme de
fréquences analysée.
9.5 Calculer la vitesse moyenne du fluide en divisant l'écoulement moyen par la superficie de la section interne
du tube de mesure. Lorsque la vitesse moyenne du fluide est supérieure à 5 % de toute mesure de la vitesse du
son, la méthode est alors invalide et les résultats ne doivent pas être consignés.
10 Mode opératoire d'essai de la méthode 2
10.1 Avant de commencer la série d'essais, faire fonctionner le système hydraulique et le générateur de bruit
(lorsqu'il est inclus) pendant une durée suffisante pour purger l'air du système et stabiliser toutes les variables, y
compris l'état du fluide, dans les limi
...
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