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IS 14917-1 (2001): Mechanical Vibration - Laboratory Method

for Evaluating Vehicle Seat Vibration, Part 1: Basic
Requirements [MED 28: Mechanical Vibration and Shock]

“!ान $ एक न' भारत का +नम-ण”

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है”
ह
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“Knowledge is such a treasure which cannot be stolen”
 IS 14917 (Part 1): 2001
ISO 10326-1:1992
( Reaffirmed 2005 )

Indian Standard
MECHANICAL VIBRATION — LABORATORY
METHOD FOR EVALUATING VEHICLE
SEAT VIBRATION
PART 1 BASIC REQUIREMENTS

ICS 13.160

@ BIS 2001
BUREAU OF IN DI AN STAN DARDS
MANAK BHAVAN, 9 BAHADUR SHAH ZAFAR MARG
NEW DELHI 110002

January 2001
Price Group 4
Mechanical Vibration and Shock Sectional Committee, ME 28

NATIONAL FOREWORD

This Indian Standard (Part 1) which is identical with ISO 10326-1 : 1992 ‘Mechanical vibration —
Laboratory method for evaluating vehicle seat vibration — Patt 1: Basic requirements’ issued by the
International Organization for Standardization (ISO) was adopted by the Bureau of Indian Standards
on the recommendations of the Mechanical Vibration and Shock Sectional Committee and approval of
the Mechanical Engineering Division Council.

The text of ISO Standard has been approved as suitable for publication as Indian Standard without
deviations. In the adopted standard, certain conventions are not identical to thos,e used in Indian
Standards. Attention is especially drawn to the following:

a) Wherever the words ‘International Standard’ appear referring to this standard, they should be
read as ‘Indian Standard’.

b) Comma (,) has been used as a decimal marker while in Indian Standards, the current practice
is to use a full point (.) as the decimal marker.

In this adopted standard, reference appears to certain International Standards for which Indian
Standards also exist. The corresponding” Indian Standards which are to be substituted in their place
are listed below along with their degree of equivalence for the editions indicated:

/ntemafiona/ Corresponding Degree of

Standard Indian Standard Equivalence

ISO 263 -1:1997 IS 13276 (Part 1) :2000 Evaluation of human Identical

exposure to whole body vibration: Part 1
General requirements

ISO 804 :1990 Is 14737 : 1999 Human res~onse to do

vibration — Measuring instrumenta~ion

For the purpose of deciding whether a particular requirement of this standard is complied with, the
final value, observed or calculated, expressing the result of test or analysis shall be rounded off in
accordance with IS 2 : 1960, ‘Rules for rounding off numerical values ( reviseo)’. The (number of
significant places retained in the rounded off value should be the same as that of the specified value in
this standard.
 IS 14917 (Partl ):2001
ISO 10326-1 :1992

Indian Standard
MECHANICAL VIBRATION — LABORATORY
METHOD FOR EVALUATING VEHICLE
SEAT VIBRATION
PART 1 BASIC REQUIREMENTS

1 Scope ISO 2631-1:1985, Evaluation of human exposure to

whole-body vibration — Part 1: General require-
This part of ISO 10326 specifies basic requirements
ments.
for the laboratory testing of vibration transmission
ISO 5347-0 :1987,. Methods for the calibration of vi-
through a vehicle seat to the’ occupant. These
bration and shock pick-ups – Part O: Basic
methods for measurement and analysis make it
concepts.
possible to compare test results from different lab-
oratories.
ISO 8041:1990, Human response to vibration –
It specifies the test method, the instrumentation re- Measuring instrumentation.
quirements, the measuring assessment method and
the way to report the test result.

This part of ISO 10326 applies to specific laboratory

seat tests which evaluate vibration transmission to
the occupants of any type of seat used in vehicles
3 General
and mobile off-road machinery.

The measurement and assessment methods given

Application standards for specific vehicles should
in this part of ISO 10326 comply with the present
refer to this part of ISO 10326 when defining the test
input vibration that is typical for the vibration practice standardized in ISO 2631-1. The measuring
characteristics of the type or class of vehicle or equipment and the frequency weighings shall be in
machinery in which the seat is to be fitted. accordance with ISO 8041.

The primary test for the vibration characteristics of

the seat involves measurements under conditions
which simulate the range of actual uses of a vehicle
or machine. For some applications, a secondary test
is used to ensure that the seat responds acceptably
2 Normative references
to occasional severe shocks or transient vibraiion.
Given the present state of knowledge, a test to
The following standards contain provisions which, evaluate the damping of the seat suspension is pro-
through reference in this text, constitute provisions posed for this purpose. The seat to be tested shall
of this part of ISO 10326. At the time of publication, be mounted on a horizontal platform of a vibration
the editions indicated were valid. All standards are simulator, which shall have movements in the verti-
subject to revision, and parties to agreements based cal and/or one of the horizontal directions, as
on this part of ISO 10326 are encouraged to investi- specified in application standards.
gate the possibility of applying the most recent edi-
tions of the standards indicated below. Members of NOTE 1 In order to make tests in both horizontal di-
IEC and ISO maintain registers of currently valid in- rections, x and y, the seat may be turned 90° on the plat-
ternational Standards. form.

1
IS 14917 ( Part 1 ) :2001
ISO 10326-1 :1992

Dimensions in millimetres
4 Instrumentation

4.1 Acceleration transducers

The measuring systems selected for the evaluation

of vibration at the seat mounting base or platform
of tbe vibration simulator and that selected for the
evaluation of vibration transmitted to the seat occu-
pant, or to an inert mass when used, shall have
similar characteristics.

The characteristics of the vibration measuring sys-

tem, accelerometers, signal conditioning and data
acquisition equipment, including recording devices,
shall be specified in the relevant application stan-
dard, especially the dynamic range, sensitivity, ac-
curacy, linearity and overload capacity.

4.2 Transducer mounting

One accelerometer shall be located on the platform

(P) at the place of the vibration transmission to the
seat. The other accelerometer(s) shall be located at
the interface between the human body and the seat,
at either the seat pan (S) and/or the backrest (B)
(see figure 1). Figure 1 – Location of the accelerometers on the
piatform (P), on the seat pan (S) and on the backrest
(B)
4.2.1 Transducer mounting on the platform

The accelerometer on the platform shall be located When tests are performed without a person sitting
within a circle with a diameter of 200 mm centred on the seat, e.g. during damping tests, the disc shall
directly below the seat accelerometer. The measur- be placed in the same position as if a per%on were
ing directions shall be aligned parallel to the move- seated in the seat.
ment of the platform,
If measurements are made on the backrest, the ac-
celerometers shall be (horizontally) located in the
4,2,2 Transducer mounting on the seat pan andlor vertical longitudinal plane through the centre-line of
backrest the seat. The relevant application standards shall
specify the vertical position of the accelerometers.
The accelerometers on the seat pan shall be at- The measurement axes shall be aligned parallel to
tached in the centre of a mounting disc with a total the basicentric coordinate system.
diameter of 250 mm + 50 mm. The disc shall be as
thin as possible (see figure 2). The height shall not NOTES
be more than 12 mm. This semi-rigid mounting disc
2 Besides the semi-rigid mounting disc recommended
of approximately 80 to 90 durometer units (A-scale)
for soft or highly contoured cushions, a rigid disc with a
moulded rubber or plastics material shall have a
generally flat surface or an individual-form design may be
centre cavity in which to place the accelerometers. used. Such discs may be, for instance, required for testing
The accelerometers shall be attached to a thin metal rail vehicle passenger seats. The transducer mounting
disc with a thickness of 1,5 mm t 0,2 mm and a di- should be made of low-mass materials, so that the res-
ameter of 75 mm + 5 mm. onant frequency of the mounting is at least four times the
highest frequency specified for the test.
The mounting disc shall be placed on the surface of
the seat pan and taped to the cushion in such a way 3 For practical reasons, it is usually not possible to align
that the accelerometers are located midway be- perfectly the accelerometers in the disc with the axes of
motion of the platform. In a tolerance range within 15° of
tween the ischial tuberosities of the seat occupant
the appropriate axes, the accelerometers may be con-
with a tolerance to be defined in the relevant appli- sidered as aligned parallel to the axes of interest. For
cation standards. Alternative positioning of the disc deviations greater than 15“, acceleration should be
may be recommended for certain applications. Any measured along two axes and the acceleration vector sum
variation from the position here defined shall be along the axis of interest should be calculated.
specified in application standards.

2
 Is 14s17(F%wt 1 ] :2001
ISO 10326-1:1992

Dimensions in mllllmetres

Thin metal disc for accelerometer Appropriate cavity

mount andaddedmntre rlgldlty tar accelerometer(s)
\ r

Figure 2 – A semi-rigid mounting disc

4.3 Frequency weighting Application standards shall specl~ requirements for

test stand dimensions and equipment to ensure that
Frequency weighting shall be in accordance with these are adequate for each particular application.
ISO 8041.
NOTE 4 It has been observed that the use of certain
equipment (e.g. a steering wheel, pedals, etc.) may lower
the repeatability of the results.
4.4 Calibration

The instrumentation shall be calibrated in accord- 5.2 Control system

ance with ISO 5347-O and, depending on the type of
measuring system used, to the relevant part of The frequency response characteristics of the vi-
1s0 53471). bration test system shall be compensated for to en-
sure that the power spectral density (PSD) and the
It is recommended to check the whole measuring probability density function (PDF) of the acceleration
chain following the specifications given in ISO 8041.
amplitudes of the vibration at the seat mounting
Calibration shall be made before and afler each test
base comply with the requirements of the specified
series.
test input vibration.

Where necessary, the output from each acceler-

ometer amplifier shall be zeroed after mounting the 6 Safety requirements
accelerometers in the test position.
Safety requirements with regard to tests in which
people are exposed to mechanical vibration and re-
peated shock will be the subject of a future inter-
5 Vibration equipment national Standard.

Specific safety requirements shall be considered

5.1 Physical characteristics when the relevant application standard is being de-
veloped.
The minimum equipment required is a vibrator ca-
pable of driving the platform in the vertical and/or
horizontal directions. The dynamic response of the 7 Test conditions
exciter’ shall be capable of exciting the seat with the
seated test person and additional equipment, in ac-
cordance with the specified test input vibration. 7.1 Test seat

Attributes of performance to be specified include

frequel}cy range and displacement capability in 7,1,1 General
each of the required directions.
The seat to be tested shall be representative of ac-
Application standards shall specify the lowest ac- tual or intended production models with regard to
ceptable resonance frequency of the platform, the design, construction, mechanical and geometrical
acceptable cross-axis motion of the platform and the characteristics, and any other factors which may af-
frequency range for which this applies, fect the vibration test results.

1) Parts 1 to 20 are to be published.

IS 14917 ( Part 1 ) :2001
ISO 10326-1 :1992

NOTE 5 The performance may vary between seats of The application standards shall also define a pos-
the same type. Therefore, it i-srecommended to test more ture appropriate to the application. This could in-
than one seat. clude some relationship between seat height and
longitudinal footrest position, absence or presence
7.1.2 Run-in periods for suspension seats of a steering wheel (and its position), and some
guidance as to how the correct posture can be as-
Suspension seats require a run-in period prior to sured, e.g. by measurement of certain limb or joint
exposure to vibration in order to free the moving angles.
parts of the suspension. This period shall be long
The test persons shall be trained in preliminary tests
enough for the seat performance to stabilize.
until they have become accustomed to maintaining
Any required air, hydraulic or electric power shall a normal, inactive behaviour and posture with re-
be supplied to the seat at the pressure and flow rate, spect to the seat throughout the test.
or voltage, recommended by the seat manufacturer
and shall be connected to the seat in the manner 7.3 Other possibilities
recommended by the seat manufacturer. The test
seat shall be loaded with an inert mass of In order to avoid the exposure of human beings to
75 kg ~ 1 % placed 6n the seat cushion, and the testing, it may in future application standards be
seat sh@l be adjusted according to the’ manufac- possible to recommend other solutions.
turer’s hwtructions for a nominal value of 100 kg
operator mass.
8 Test input vibration
NOTE 6 A suitable inert mass consists of lead shot. The
lead shot can be contained within thin cushions which are The application standards shall specify one or more
sewn so as to form a quilt. About ten such cushions are dynamic tests, designed to ensure that a seat is
sufficient to obtain a 75 kg mass. suitable for the intended purpose. As a minimum,
there shall be a test using an input representative
During the run-in period, the test seat sha[l be ex- of severe but not abnormal use, in the course of
cited by a sinusoidal input vibration at approxi- which the vibration transmitted to the interface be-
mately the natural frequency of the suspension. The tween the seat and the operator is measured, as the
amplitude of the applied sinusoidal vibration shall basic performance parameter of the seat.
be 75 O/. of the full amplitude of the seat suspension.
In order to specify the transmission characteristics
The dampef may over-heat during the run-in period. of seats with regard to different input frequencies
Therefore, use an automatic shut-down and monitor (e.g. for tuning the vibration response of seats on
the temperature of the damper. different types of vehicle, such as foam seats in
passenger cars), an alternative method is rec-
If additional vibration tests in the horizontal direction
ommended in 8.2 for the determination of the trans-
are planned, the run-in procedure shall be followed
fer function for the relevant frequency range with a
under the same conditions separately for each di-
sinusoidal vibration input.
rection.
For seats with suspension systems used in off-road
NOTE 7 Deviations from this run-in method for the seat
machinery, there should be a test of the effective-
suspension may be specified in relevant application stan-
ness of the suspension damper in controlling oc-
dards for individual seat tests.
casional large-amplitude vibrations or shocks. This
can take the form of a sinusoidal test to determine
the maximum response of the seat at a frequency
7.2 Test persons
close to its resonant frequency when carrying a
simple load equivalent to an average operator (e.g.
Application standards shall specify the masses of
the inert mass as specified in 7.1.2).
two test persons to be used for the test. These
masses will normally be based on the 5th and the
NOTE 9 In some case, a further or alternative test may
95th percentile masses of the population of vehicle be needed to ensure that, under conditions of excessive
or machinary users for which the seat is intended. suspension travel, the suspension end stops are so con-
The tolerance shall be low, preferably _~ % of the structed as to keep the resulting shock acceleration at an
required mass for the low-mass test person. For the acceptable level. Application standards should specify this
heavy test person, a greater tolerance is permiss- additional test if needed.
ible, up to ‘~ 0/0 of the required mass.
8.1 Simuiated input vibration test
NOTE 8 To meet the required mass of the test persons,
added masses may be used. The use of added masses
and other optional possibilities (such as carrying out the The simulated input test vibration shall be specified
test with only one test person) should be dealt with in in accordance with the vehicle or machinery groups
application standards. defined either by the acceleration power spectral

4
 IS 14917 (Partl ):2001
ISO 10326-1 :1992

density function or by the time history of an actual available. All measurements shall be made with an
and representative signal. inert mass of 75 kg + 1 0/0 on the seat, adjusted in
accordance with 7.1.2.
When the input vibration is defined by PSD, the rel-
evant application standard should give the equation
describing the PSD and its tolerance. The equation
8.3.2 Other seats
for the PSD may be in the form of filter equations,
which should be those of a low-pass filte”r and a
Application standards may specify damping tests for
high-pass filter (the pair constituting a band-pass
non-suspension seats in a manner similar to that
filter), both of the Butterworth type. The cut-off fre-
described above, with appropriate modifications.
quencies and the slopes of the filters shall be clearly
defined.

When the input vibration is defined by a time history,

the application standard shall specify the number of
9 Test procedure
measured (calculated) points, frequency and ampli-
tude spacing and the sampling rate.
Mount the seat to be tested on the platform of the
A tolerance on this level shall also be specified vibration simulator, in accordance with the specified
when the input vibration is defined by a time history. test seat arrangement. Check the safety require-
ments and calibrate the instruments. Prior to the
The probability density function of the random vi- damping test and simulated input vibration test,
bration at the mqunting base of the seat during the carry out the run-in procedure on the test seat (see
test may be required in application standards. 7.1.2).

For both types of input vibration, the required root

mean square (r. m.s.) acceleration on the platform,
CQ, shall be specified in application standards. 9.1 Simulated input vibration test

9.1.1 Position a test person in the seat. Operate the

vibration simulator to produce the appropriate test
8.2 Transfer function with sinusoidal vibration input vibration.
input
The test input vibration, during each test run, shall
The vibration transfer function test shall be carried be continuous to provide an analysing time sufficient
out with two persons, as specified in 7.2. Input vi- to be specified in application standards.
bration magnitude and phase versus frequency, fre-
quency spacing, transient time and duration of Repeat the test to obtain three consecutive test runs
vibration input per frequency step shall be specified in which the frequency-weighted r.m.s. acceleration
in application standards. values, ~, measured at the seat are within & 5 0/0
of their arithmetic mean. Record this arithmetic
mean as the fequency-weighted r.m.s. acceleration
at the seat, ~s.

For the tests described above, the vibration at’the

8.3 Damping test platform during each test shall be within the PSD
tolerances mentioned in 8.1. The arithmetic mean
of the three test values measured at the platform
shall be recorded as the frequency-weighted r.m.s.
8.3.1 Suspension seats acceleration values at the platform, ~p.

Application standards shall specify the charac-

teristics of either a sinusoidal vibration or a random 9,1.2 If the purpose of the simulated input vibration
vibration to be used to assess the damping of sus-
test of the relevant application standard is to obtain
pension seats. The sine-wave test shall be con-
the seat effective amplitude transmissibility factor
ducted at the resonance frequency of the seat
(SEAT) of the seat, calculate the ratio of the re-
suspension. This resonance frequency shall be de-
corded values as follows:
termined by exciting the seat in the frequency range
from 0,5 to 2,0 times the expected resonance fre-
SEAT =%
quency. This displacement amplitude for both the
damping test and the determi.nation of the reson-
ance frequency shall be (75 + 5) 0/0 of the full travel where Q and cqP are as defined in 9.1.1.

5
IS 14917 ( Part 1 ) :2001
ISO 10326-1 :1992

9.1.3 If the purpose of the simulated input vibration The acceptance value for the simulated input vi-
test is to obtain the absolute magnitude for vibration bration test shall be given either as the maximum
to be transmitted to a person in a vehicle or ma- value of the SEAT or the maximum corrected m.a9-
chinery, the magnitude on the seat, ~s, shall be nitude on the seat, u&. To pass the test, lower val-
corrected according to the ratio between the meas- ues than this maximum shall be obtained for each
ured test input magnitude, ~p, and the intended in- test person.
put value &. The corrected magnitude on the seat,
&$, is given by The acceptance value for the damping test shall be
defined as transmissibility at resonance.
%s’f&P
4s = qp

or

~s = SEAT.&p
11 Test report

The test report should contain the following:

where SEAT is as defined in 9.1.2.
a) name and address of seat manufacture~
9.2 Damping test
b) model of seat, product and serial numbec
Load the seat with an inert mass of 75 kg & 1 V.
(see 7.1.2).
c) date of test;
Apply the required peak-to-peak displacement am-
d) duration of run-in period, in hours;
plitude to the base of the seat at the resonance fre-
quency. ~, of the suspension.
e) type of measurement equipment and mounting
Repeat the test to obtain three consecutive test runs disc used (semi-rigid or rigid);
in which the r.m.s. acceleration values, u&), meas-
ured at the disc are within + 5 0/0 of their arithmetic 9 characteristics of the simulated input vibration
mean. Record this arithmetic mean, u.#J. test;

Note the arithmetical mean of the three values of the 9) vibration transmission to the test persons during
r.m. s. acceleration values, +~r), measured on the the simulated input vibration test
platform.
— mass of test persons, in kilograms,
Calculate the transmissibility, T, at resonance of the
seat as the ratio of the registered values, as follows: – SEAT-factor, andlor

— corrected magnitude on the seat surface;

h) transmissibility at resonance during the damping

10 Acceptance test and the resonance frequency (alternatively,
the transfer function with sinusoidal-vibration in-
Under the test procedures of this part of ISO 10326, put) ;
acceptance values from the simulated input vi-
bration test ardior damping test can be defined. i) name of person responsible for the test;
Application standards shall state the acceptance
values relevant to the specific seat test. j) identification of test laboratory.

6
 IS 14917 (Partl ):2001
ISO 10326-1 :1992

Annex A
(informative)

Bibliography

[2] ISO 5805:– 2), Mechanjca/ vibration and shock

[1] 1S02041:1990, Vibration andshock– Vocabu-
Iary. affecting man — Human exposure –
Vocabulary.

2) To be published. (Revision, of ISO 5805:1981)

7
Bureau of Indian Standards

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Enquiries relating to copyright be addressed to the Direetor (publications), BIS.

Review of Indian Standards

Amendments are issued to standards as the need arises on the basis of comments. Standards are also reviewed
periodically; a standard along with amendments is reaffied when such review indicates that no changes are
needed; if the review indicates that changes are needed, it is taken up for revision. Users of Indian Standards
should ascertain that they are in possession of the latest amendments or edition by m,ferring to the latest issue of
‘BIS Catalogue’ and ‘Standards: Monthly Additions’.

This Indian Standard has been developed from Doc : No. ME 28 (0543).

Amendments Issued Since Publication

Amend No. Date of Issue Text Affeeted

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