IS 14736-1: Vibration and Shock - Experimental Determination of Mechanical Mobility, Part 1: Basic Definitions and Transducers

29 Pages·1999·2.5 MB·English

by  Bureau of Indian Standards

इंटरनेट मानक
Disclosure to Promote the Right To Information
Whereas the Parliament of India has set out to provide a practical regime of right to
information for citizens to secure access to information under the control of public authorities,
in order to promote transparency and accountability in the working of every public authority,
and whereas the attached publication of the Bureau of Indian Standards is of particular interest
to the public, particularly disadvantaged communities and those engaged in the pursuit of
education and knowledge, the attached public safety standard is made available to promote the
timely dissemination of this information in an accurate manner to the public.
“जान1 का अ+धकार, जी1 का अ+धकार” “प0रा1 को छोड न’ 5 तरफ”
Mazdoor Kisan Shakti Sangathan Jawaharlal Nehru
“The Right to Information, The Right to Live” “Step Out From the Old to the New”
IS 14736-1 (1999): Vibration and Shock - Experimental
Determination of Mechanical Mobility, Part 1: Basic
Definitions and Transducers [MED 28: Mechanical Vibration
and Shock]
“!ान $ एक न’ भारत का +नम-ण”
Satyanarayan Gangaram Pitroda
““IInnvveenntt aa NNeeww IInnddiiaa UUssiinngg KKnnoowwlleeddggee””
“!ान एक ऐसा खजाना > जो कभी च0राया नहB जा सकता हहहहै””ै”
Bhartṛhari—Nītiśatakam
“Knowledge is such a treasure which cannot be stolen”

Indian Standard
NOITARBIV DNA KCOHS - LATJhEMIREPXE
NOITANIMRETED OF LACINAHCEM YTILIBOM
PART 1 BASIC DEFINITIONS AND TRANSDUCERS
SCI 061.71

0 SIB 9991
BUREAU OF INDIAN STANDARDS
KANAM ,NAVAHB 9 RUDAHAB HAHS RAFAZ GRAM
NEW IHLED 200011
October 9991 Price Group 9
lacinahceM noitarbiV dna kcohS lanoitceS Committee, ML 40
LANOITAN FOREWORD
sihT naidnI dradnatS hcihw si lacitnedi htiw 0SI 6891:1-6267 noitarbiV‘ dna kcohs - latnemirepxE
noitanimreted fo lacinahcem ytilibom -- traP 1 : cisaB snoitinifed dna ’srecudsnart deussi yb eht
lanoitanretnI noitazinagrO rof noitazidradnatS )OSI( saw detpoda yb eht uaeruB fo naidnI sdradnatS no
eht noitadnemmocer fo lacinahceM noitarbiV dna kcohS lanoitceS Committee dna lavorppa fo eht thgiL
lacinahceM gnireenignE noisiviD .licnuoC
ehT txet fo 0SI dradnatS sah neeb sadevorppa elbatius rof noitacilbup sa naidnI dradnatS tuohtiw
.snoitaived nI eht detpoda dradnats niatrec snoitnevnoc era ton lacitnedi ot esoht desu ni naidnI .sdradnatS
noitnettA si yllaicepse nward ot eht :gniwollof
a) Wherever eht sdrow lanoitanretnI‘ ’dradnatS raeppa gnirrefer ot siht ,dradnats yeht dluohs eb daer
sa naidnI‘ .’dradnatS
b) Comma (,) sah neeb desu sa a lamiced marker elihw ni naidnI ,sdradnatS eht tnerruc ecitcarp si
ot esu a lluf tniop (.) sa eht lamiced marker.
nI siht detpoda ,dradnats ecnerefer sraeppa ot niatrec lanoitanretnI sdradnatS rof hcihw naidnI sdradnatS
osla .tsixe ehT gnidnopserroc naidnI sdradnatS hcihw era ot eb detutitsbus ni rieht eraecalp detsil woleb
gnola htiw rieht eerged fo ecnelaviuqe rof eht snoitide :detacidni
In terna tional Corresponding Indian Standard Degree of
Standard Equivalence
0SI 1402 SI 9991:71711 yralubacoV no noitarbiv dna kcohs (first revision) lacitnedI
ehT denrecnoc lacinhcet com.mittee sah deweiver eht snoisivorp fo eht gniwollof lanoitanretnI sdradnatS
derrefer ni siht detpoda dradnats dna sah dediced taht yeht era elbatpecca rof esu ni noitcnujnoc htiw siht

:dradnats
International Standard Title
0SI 5684 noitarbiV dna kcohs - sdohteM rof sisylana dna noitatneserp fo atad
0SI 7435 noitarbiV dna -kcohs sdohteM fo noitarbilac fo noitarbiv dna kcohs spukcip
CEI noitacilbuP elacS dna sezis rof gnittolp ycneuqerf scitsiretcarahc dna ralop smargaid
362
IS 14736 ( Part 1 ) : 1999
IS0 7626-l : 1986
Indian Standard
NOITARBIV DNA KCOHS - LATNEMIREPXE
NOITANIMRETED OF LACINAHCEM YTILIBOM
PART 1 BASIC DEFINITIONS AND TRANSDUCERS
0 Introduction For most practical applications, it is ton yrassecen ot wonk eht
entire N6 x N6 matrix. Often it is sufficient ot measure eht
driving-point mobility dna a wef transfer mobilities yb gniticxe
0.1 General introduction to IS0 7626 on mobility with a force ta a single point in a single direction dna measuring
measurement eht translational response motions ta yek pojnts no eht struc-
.erut nI rehto applications, ylno rotational mobilities yam eb fo
interest.
Dynamic characteristics fo structures can eb determined as a
function fo ycneuqerf from mobility measurements or measure-
nI order ot simplify eht use fo eht suoirav parts fo 0SI 6267 in
ments fo eht related esnopser-ycneuqerf functions, nwonk as
eht suoirav mobility measurement tasks deretnuocne in prac-
accelerance dna dynamic compliance. hcaE fo these -ycneuqerf
tice, 0SI 6267 will eb published as a set fo evif separate parts.
response functions is eht phasor fo eht motion response ta a
point no a structure eud ot a unit force (or moment) .noitaticxe
0SI 7626/l (this part fo 0SI )6267 srevoc basic definitions dna
The magnitude dna eht phase fo these functions are -ycneuqerf
transducers. The information nevig in this part fo 0SI 6267 is
.tnedneped
common ot most mobility measurement tasks.
Accelerance dna dynamic compliance differ from mobility ylno
0SI 2/6267 srevoc mobility measurements using single-point
in taht eht motion response is desserpxe in terms fo acceler-
translational noitaticxe with na dehcatta .reticxe
ation or displacement, ,ylevitcepser instead fo in terms fo -olev
.ytic nI order ot simplify eht suoirav parts fo 0SI ,6267 ylno eht
0SI 3/6267 srevoc mobility measurements using single-point
term “mobility” will eb used. tI is dootsrednu taht all test pro-
rotational noitaticxe with na dehcatta .reticxe This information
cedures dna requirements described are also applicable ot eht
is primarily dednetni for rotor system rotational resonance
determination fo accelerance dna dynamic compliance.
predictions.
Typical applications for mobility measurements are for 0SI 4/6267 srevoc measurements fo eht entire mobility matrix
using dehcatta exciters. This includes eht translational, ro-
a) predicting eht dynamic response fo structures ot nwonk tational dna combination terms required for eht 6 x 6 matrix
or assumed input ;noitaticxe for each location no eht structure.
b) determining eht modal properties fo a structure (natural 0SI 5/6267 srevoc mobility measurements using impact -aticxe
frequencies, mode shapes dna damping ratios); tion with na reticxe which is ton dehcatta ot eht structure.
c) predicting eht dynamic interaction fo interconnected
Mechanical mobility is denifed as eht esnopser-ycneuqerf func-
structures;
tion formed yb eht ratio fo eht phasor fo eht translational or
rotational response yticolev ot eht phasor fo eht applied force
d) checking eht ytidilav dna improving eht ycarucca fo
or moment .noitaticxe fI eht response is measured with na ac-
mathematical models dna structures;
celerometer, noisrevnoc ot yticolev is required ot obtain eht
e) determining dynamic properties (i.e. eht complex mobility. ,ylevitanretlA eht ratio fo acceleration ot force, wonk
modulus fo elasticity) fo materials in erup or composite as accelerance, yam eb used ot characterize a structure. nI
forms. rehto cases, dynamic compliance, eht ratio fo displacement ot
force, yam eb used.
For some applications, a complete description fo eht dynamic
characteristics yam eb required using measurements fo transla- NOTE - Historically, frequency-response functions of structures have
tional forces dna motions along eerht mutually perpendicular often been expressed in terms of the reciprocal of one of the above-
sexa as well as measurements fo moments dna rotational mo- named dynamic characteristics. The arithmetic reciprocal of
mechanical mobility has often been called mechanical impedance. It
tions tuoba these eerht .sexa This set fo measurements results
should be noted, however, that this is misleading because the
in a 6 x 6 mobility matrix for each location fo interest. For N
arithmetic reciprocal of mobility does not, in general, represent any of
locations no a structure, eht system thus has na llarevo mobility
the elements of the impedance matrix of a structure. This point is
matrix fo size N6 x .N6 elaborated upon in annex A.
1
1s 14736 (Part 1 ) : 1999
IS0 7626-l : 1966
Mobility test data cannot be used directly as part of an im- 3 Symbols and units
pedance model of the structure. In order to achieve compatibi-
lity of the data and the model, the impedance matrix of the Symbol Quantity St unit
model shall be converted to mobility or vice-versa (see
a Acceleration m/s2
clause A.3 for limitations).
ailFj Accelerance m/(N.s2)
E Transducer output V
0.2 Introduction to this part of IS0 7626
f Frequency HZ
Before carrying out mobility measurements, it is necessary to F Force N
evaluate the characteristics of the force and response k Stiffness N/m
transducers to be used in order to ensure that accurate
m Mass kg
amplitude and phase information can be obtained over the
s Sensitivity V/units of
entire frequency range of interest.
input variable
This part of IS0 7626 is primarily a guide for the selection, V Velocity m/s
calibration and evaluation of the transducersand instruments X Displacement m
for their suitability in making mobility measurements.
x,/F, Dynamic compliance m/N
Yij Mobility m/fNs)
z Free impedance N.s/m
1 Scope and field of application
=ij Blocked impedance N.s/m
This part of IS0 7626 provides basic definitions with comments
and identifies the calibration tests, environmental tests and
4 Definitions
physical measurements necessary to determine the suitability
of impedance heads, force transducers and response
transducers for use in measuring mechanical mobility. For the general terms and their definitions used in this part of
IS0 7636, see IS0 2041. Several of the more important defi-
This part of IS0 7626 is limited to information which is basic to nitions used in the measurement and presentation of mecha-
various types of driving point and transfer mobility, accelerance nical mobility data are listed below to emphasize their use in
and dynamic compliance measurements. Blocked impedance this part of IS0 7636.
(see 4.3) measurements are not dealt with.
4.1 frequency-response function: The frequency depen-
NOTE - Procedures for carrying out mobility measurements in various
circumstances will be dealt with in IS0 7626/2, IS0 7626/3, dent ratio of the motion-response phasor to the phasor of the
IS0 7626/4 and IS0 7626/5. excitation force.
NOTES

1 Frequency-response functions are properties of linear dynamic
2 References systems which do not depend on the type of excitation function. Ex-
citation can be harmonic, random or transient functions of time. The
test results obtained with one type of excitation can thus be used for
IS0 2041, Vibration and shock - Vocabulary
predicting the response of the system to any other type of excitation.
Phasors and their equivalents for random and transient excitation are
IS0 4865, Vibration and shock - Methods for analysis and discussed in annex B.
presentation of data. 1)
2 Linearity of the system is a condition which, in practice, will be met
only approximately, depending on the type of system and on the
IS0 5347, Vibration and shock - Methods of calibration of
vibration and shock pickups. 1) magnitude of the input. Care has to be taken to avoid non-linear ef-
fects, particularly when applying impulse excitation. Structures which
are known to be non-linear (e.g. certain riveted structures) should not
IEC Publication 263, Scales and sizes for plomhg frequency be tested with impulse excitation and great care is required when using
characteristics and polar diagrams. random excitation for testing such structures.

1) At present at the stage of draft.
2
IS 14736 (Part 1 ) : 1999
IS0 7626-l : 1986
3 Motion may be expressed in terms of either velocity, acceleration or 2 The primary usefulness of blocked impedance is in the
displacement; the corresponding frequency-response function mathematical modelling of a structure using lumped mass, stiffness
designations are mobility, accelerance and dynamic compliance, and damping elements or finite element techniques. When combining
respectively. or comparing such mathematical models with experimental mobility
data, it is necessary to convert the analytical blocked impedance matrix
into a mobility matrix, or vice versa, as discussed in annex A.
4.2 mobility, Y,,: The esnopser-ycneuqerf function formed
yb eht ratio fo eht esnopser-yticolev phasor ta point i ot eht -xe
citation force phasor ta point j, with all rehto measurement 4.4 free impedance: The ratio fo eht applied noitaticxe
force phasor ot eht resulting yticolev phasor, with all rehto con-
points no eht structure allowed ot respond yleerf without yna
nection points fo eht system free (i.e. gnivah orez restraining
constraints rehto naht those constraints which represent eht
forces). Free impedance is eht arithmetic reciprocal fo a single
normal support fo eht structure in its dednetni application. A
element fo eht mobility matrix, as denifed in .2.4
lacipyt hparg is nevig in figure .1
NOTES
NOTES
1 The yticolev response can be either translational or rotational, and 1 Historically, no distinction has often been made between blocked
impedance and free impedance. Caution should, therefore, be exer-
the excitation force can be either a rectilinear force or a moment.
cised in interpreting published data.
2 If the velocity response measured is a translational one and if the
2 While experimentally determined free impedances could be
excitation force applied is a rectilinear one, rhe mobility term should be
assembled into a matrix, this matrix would be quite different from the
expressed in metres per newton second in the SI system.
blocked impedance matrix resulting from mathematical modelling of
the structure and, therefore, would not conform to the requirements
4.3 blocked impedance, Z,,: The frequency-responsefunc- discussed in annex A for using mechanical impedance in an overall
tion formed yb eht ratio fo eht phasor fo eht blocking or -gnivird theoretical analysis of the system.
point force response ta point i ot eht phasor fo eht applied -xe
citation yticolev ta point j, with all rehto measurement points 4.5 Other frequency-response functions related
no eht structure “blocked” (i.e. constrained ot evah tero -olev
to mobility
.)ytic All forces dna moments required ot constrain ylluf all
points fo interest no eht structure shall eb measured in order ot There are lareves rehto structural response ratios which are
obtain a dilav blocked impedance matrix. dekcolB impedance sometimes used instead fo mechanical mobility. These are
measurements (see )1311 are, ,erofereht seldom made dna are summarized in table .1
ton dealt with in eht suoirav parts fo 0SI .6267
Careful eton should eb nekat fo eht comments no each epyt fo
NOTES ratio. Typical magnitude graphs for accelerance dna for
dynamic compliance, corresponding ot eht mobility hparg
1 Any changes il the number of measurement points or their location
will change the blocked impedances at all measurement points. shown in figure ,1 are shown in figures 2 dna ,3 .ylevitcepser
Table 1 - Equivalent definitions to be used for various kinds of measured frequency response functions
related to mechanical mobility

Motion expressed Motion expressed Motion expressed
as velocity as acceleration as displacement
Term Mobility Accelerance Dynamic compliance
lobmyS Y,, = vJF, aIF, x,lF;
Unit m/(N.s) m/(N& = kg~’ m/N
Boundary conditions Fk = 0 ; k t j kF = 0 ; k s j FL = 0;k #,;
See figure 1 2 3
,
Comment Boundarv conditions are easy to achieve experimentally
____..___
Term Blocked impedance Blocked effective mass Dynamic stiffness
Symbol Z,, = F/v, F,fa, F,lX,
Unit IN.s)/m (N.s2)im = kg N/m
;
Boundary conditions vk = 0 ; k f j ak = 0;k *j _Y* = 0 k -f .i
Comment Boundary conditions are very difficult or impossible to achieve experimentally
--__-
Term Free impedance Effective mass (free effective mass)) Free dynamic stiffness
Symbol F,/v, = -;- ,al,F F I \-
8-I
(Ns)im"
Unit fN.sJ)im = kg N/m
Boundary conditions Fk = 0;k #j Fk = 0; k s,, Fk = 0;k *.j
I I
Comment yradnuoB conditions are ysae ot ,eveihca tub results shall eb used with taerg caution in system modelling
IS 14736 (Part 1 ) : 1999
IS0 7626-l : 1966
NOTES 5.2.1 The motion transducer should be of lightweight (or non-
contacting) design so as to minimize structural kading of the
1 Dynamic compliance is called “receptance” by several authors.
structure under test.
2 Accelerance has, regrettably, been called “inertance” in some
publications. This term is not a standard term and should be avoided
because it is in conflict with the common definition of “acoustic iner- 5.2.2 The attachment of the transducer to the structure under
tance” and also contrary to the implication carried by the term “iner- test should be stiff in the direction of the primary measurement
tance”. axis of the transducer.
4.5 frequency range of interest: Span, in hertz, from the 5.2.3 The attachment should have a sufficiently small contact
lowest frequency to the highest frequency at which mobility area to prevent stiffening or damping of the structure by the
data are to be obtained in a given test series. transducer or its mounting fixture.
5.2.4 When applying impulse excitation, zero drift of
piezoelectric accelerometers due to the ,pyro-electric effect is
5 Basic requirements for force- and likely to occur and this will limit the accuracy of the measure-
ment at low frequencies. Other types of motion transducers
motion-measurement transducers
(e.g. piezoresistive, electrodynami,car some shear type piezo-
electronic accelerometers) can provide the solution to this
5.1 General problem.
The basic characteristics of all measurement transducers which
are important in acquiring adequate mobility data are as 5.3 Requirements for force-measurement
follows: transducers
a) Transducers shall have sufficient sensitivity and low
noise in order to obtain a signal-to-noise ratio of the Some of the characteristics outlined in 5.1 are more important
measurement chain which is adequate to cover the dynamic than others in the selection of a force-measurement transducer
range of the mobility of the structure. Since lightly damped to be used for mechanical mobility measurements. Since com-
structures require a larger dynamic range than structures promises in design have to be made, the items outlined in 5.3.1
with considerable damping, transducer noise is of particular to 5.3.3 shall be considered as being of prime importance.
concern when testing lightly damped structures.
b) If the frequency-response function of the measurement 5.3.1 The effective end mass (mass between the force-
transducer is not compensated by suitable signal process- sensing element of the transducer and the structure) should be
ing, the natural frequency of the response transducer shall small enough to minimize extraneous inertial signals related to
be far enough below or above the frequency range of in- such mass. (See 8.4 for further details.)
terest that no unacceptable phase shift will occur.

c) Transducer sensivity shall be stable with time and have 5.3.2 The stiffness of the force transducer and its com-

negligible d.c. drift. ponents should be selected so that no resonances involving this
d) Transducers shall be insensitive to extraneous en- stiffness occur within the frequency range of interest. As a
vironmental effects, such as temperature, humidity, compromise, the effect of such resonances on the signal from
magnetic fields, electrical fields, acoustical fields, strain and the force-sensing element should be compensated for by
cross-axis inputs. suitable signal processing.
e) Transducer mass and rotational inertia shall be small so
as to avoid dynamic loading of the structure under test, or 5.3.3 The static preload shall be adequate for the range of ex-
at least small enough so that a correction can be made for citation forces required by the test application. Transducers
the loading. with built-in preload are available to minimize this problem.
Low susceptibility of the measurement system to the effects of
electrical ground loops and other extraneous signals is also im- 5.4 Requirements for impedance heads and
portant. attachments to the structure under test
A device which combines an accelerometer and a force
5.2 Requirements for motion-measurement
transducer in one assembly for the purpose of mobility
transducers
measurement is traditionally called an “impedance head”. The
design is a compromise based on the characteristics outlined in
Although motion-measurement transducers require the 5.2 and 5.3. However, certain characteristics of prime import-
characteristics outlined in 5.1, certain of these characteristics ance, given in 5.4.1 to 5.4.4, should be borne in mind.
are more important than others. Motion transducers used in
mechanical mobility measurements are most commonly ac-
celerometers; however, displacement or velocity transducers 5.4.1 The total compliance between the structure and the in-
are sometimes use,d. The major characteristics to be considered ternal accelerometer should be small, because a large com-
in transducer selection are outlined in 5.2.1 to 5.2.4. pliance will cause errors in acceleration measurements.
4
IS 14736 (Part 1 ) : 1999
IS0 7626-l : 1986
NOTE - The total compliance is the sum of the attachment com- used for mobility measurements, and the accelerometer is of a low
pliance and the internal compliance of the impedance head. The at- damping design. However, it is good practice to display the phase
tachment compliance includes the localized “die effect” compliance of angle between the force transducer and accelerometer outputs on a
the structure under test The total compliance can be measured as phase meter and record any deviations from the proper phase angle be-
described in annex C. tween the force transducer and accelerometer outputs while carrying
out the operational calibration.
5.4.2 The effective end mass (mass between the force-
sensing element of the transducer and the structure) should be 6.2 Basic and supplementary transducer
small in relation to the free effective mass of the structure calibrations
under test.
The basic and supplementary calibrations (see table 2) are in-
tended for determining the suitability of the transducers for
5.4.3 The moment of inertia of the impedance head, relative
mobility measurements. Piezoelectric transducers are very fre-
to an axis in the plane of attachment, should be small enough
quently used. If other types of transducers are used, the pro-
to minimize structural loading due to rotational motion about
cedures may have to be modified to determine the suitability of
that axis.
such transducers.
NOTE - Further guidelines for avoiding loading of the structure under
Transducers exhibiting changes in basic or supplementary
test by the attachment of impedance heads will be given in IS0 762612.
calibrations should not be used if the changes are unac-
ceptable, as indicated in the appropriate clauses in this part of
5.4.4 In the design of an impedance head, care is required to IS0 7626.
avoid cross-sensitivity of the acceleration transducer to the ap-
plied force. Table 2 - Summary of transducer calibrations and tests
T
Force
Accelerometer
Calibration transducer
6 Calibration or test 1! Supple. Supple-
Basic r nentarl Basic mentary
Calibrations fall into three categories:
Sensitivity ,7.2.1 7.2.2
a) operational calibration of the combined measurement
Electrical impedance 7.3 7.3
and analysis system;
b) basic transducer calibrations; Dimensions 8.2 8.2
c) supplementary transducer calibrations. Mass 8.3 8.3
Effective end mass 8.4
6.1 Operational calibrations
Transducer
Operational calibrations of the combined measurement and compliance 8.5
analysis system shall be carried out at the begi n ning and end of
Polarity 8.6 8.6
each measurement series (and at intermediate times, as re-
quired). Detailed procedures will be covered in the relevant
Frequency
parts of IS0 7626 pertaining to the various types of mobility response 8.7.1 8.7.2
measurements, as outlined in clause 0.
Linearity 8.8.1 8.8.2
Combined system calibrations are easier to perform, more ac-
curate and in wider use than the basic calibrations discussed in Temperature 8.9.1 8.9.1
clause 7. These system calibrations are achieved by driving, in sensitivity rnd 8.9. 3nd 8.9.2
free space, a known free mass while the acceleration and force
Transverse
channel gains are set at the values that will be used in later
sensitivity 8.9.4
measurements. The ratio output shall follow the appropriate
mass line on the resulting mobility graph. If any difficulties are
Strain
experienced in combined system calibrations, basic calibrations sensitivity 8.9.5
should be carried out. L
The accuracy of the frequency scale of the response graph or Transducers intended for use with specific amplifiers or signal
other data output should always be checked during the oper- conditioners should have the calibration performed under the
ational calibration. conditions of intended use. For example, piezoelectric force
transducers, impedance heads and accelerometers are in-
NOTES
tended for use with either charge amplifiers or high impedance
1 An example of the resulting mobility graph, showing the effect of voltage amplifiers and should be calibrated with the intended
the impedance head attachment compliance, is shown in annex C. amplifier. For these transducers, the capacitance of the cables
2 It is usually unnecessary to perform a phase-shift calibration provid- used between transducer and amplifier is important and the
ed that the accelerometers, force transducers and amplifiers are transducers should be calibrated together with the intended
selected to have nearly flat response throughout the frequency range cable. Other types of transducers should be calibrated with
5