ISO/TS 21476:2018

Road vehicles — Displacement calibration method of IR-TRACC devices

This document establishes a procedure to calibrate IR-TRACC displacement transducers. Like all other sensors used on dummies, calibration is required. The calibration is carried out with the sensor disassembled from the dummy. The procedure is valid for sensors with analogue as well as digital output.

Véhicules routiers — Méthode d'étalonnage de déplacement des dispositifs IR-TRACC

General Information

• Status: Published
• Publication Date: 11-Dec-2018
• ICS: 43.020 - Road vehicles in general
• Technical Committee: ISO/TC 22/SC 36 - Safety and impact testing
• Drafting Committee: ISO/TC 22/SC 36/WG 3 - Instrumentation
• Current Stage: 9093 - International Standard confirmed
• Completion Date: 18-Aug-2022

Standards Content (Sample)

TECHNICAL ISO/TS
SPECIFICATION 21476
First edition
2018-12
Road vehicles — Displacement
calibration method of IR-TRACC devices
Véhicules routiers — Méthode d'étalonnage de déplacement des
dispositifs IR-TRACC
Reference number
ISO/TS 21476:2018(E)
©
ISO 2018

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ISO/TS 21476:2018(E)

COPYRIGHT PROTECTED DOCUMENT
© ISO 2018
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
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ISO/TS 21476:2018(E)

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and abbreviated terms . 3
5 Displacement Calibration Procedure . 5
5.1 Preparations . 6
5.2 Test equipment set-up, power supply, voltmeter . 6
5.3 Establish starting point . 6
5.4 Forced Lateral Manipulation Test . 7
5.5 Displacement Calibration Data Collection. 8
5.6 Parameter optimization and data review . 9
6 Displacement Calibration Data Processing .10
6.1 General .10
6.2 Linearization over calibration range with nominal exponent .10
6.3 Linearization optimization .10
6.4 Data analysis and pass criteria calculations .11
6.4.1 Optimized Nominal Linearity Error .11
6.4.2 Tubes In-Out Variation .11
6.4.3 Pass–fail tests and limits .12
6.4.4 Forced Lateral Manipulation variation .12
6.5 Example Data .12
Annex A (informative) Sensor Model Numbers .14
Annex B (informative) Example Calibration Template .15
Bibliography .19
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ISO/TS 21476:2018(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
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ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
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Attention is drawn to the possibility that some of the elements of this document may be the subject of
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.org/iso/foreword .html.
This document was prepared by Technical Committee ISO/TC 22, Road vehicles, Subcommittee SC 36,
Anthropomorphic test devices.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/members .html.
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ISO/TS 21476:2018(E)

Introduction
This document was written to address the need of the automotive crash testing community for a well-
defined calibration method of non-linear telescopic displacement sensors known as IR-TRACC. This
device is commonly used on crash dummies to measure the chest deflection as injury an assessment
parameter. Various aspects specific to this type of sensors are addressed in this procedure, among
others linearization of the exponential voltage output and the sensitivity to tubes position of the
telescopic devices.
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TECHNICAL SPECIFICATION ISO/TS 21476:2018(E)
Road vehicles — Displacement calibration method of IR-
TRACC devices
1 Scope
This document establishes a procedure to calibrate IR-TRACC displacement transducers. Like all
other sensors used on dummies, calibration is required. The calibration is carried out with the sensor
disassembled from the dummy. The procedure is valid for sensors with analogue as well as digital output.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 6487, Road vehicles — Measurement techniques in impact tests — Instrumentation
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https: //www .iso .org/obp
— IEC Electropedia: available at http: //www .electropedia .org/
3.1
IR-TRACC
Infra-Red Telescoping Rod for the Assessment of Chest Compression
non-ratiometric displacement transducer used to measure chest deflection in crash dummies
[1]
Note 1 to entry: The technology of the transducer was described in a paper by Rouhana et al. [1998] . The
measurement principle is based on emission of infra-red light by an LED and a phototransistor sensitive to
irradiance. The transducer is a non-linear device, as the irradiance and output voltage is proportional to
the inverse square of the distance between the emitter and the phototransistor. The distance between the
phototransistor and the LED is theoretically proportional to the inverse square root of the phototransistor
output voltage: d = C/√U . The inverse square root of the output voltage can also be written as the output voltage
IR
−0,5
to the power of minus 0,5, therefore d = C × U
IR
3.2
Displacement Calibration
classic compression method where the zero mm starting point is defined close to the extended range of
the sensor
Note 1 to entry: When the IR-TRACC overall length decreases (IR-TRACC compresses), its calibrated mm
output increases. The IR-TRACC linearized output is negatively proportional to its length. During displacement
calibration components are used to fix the transducer to a calibration fixture. These components do not
necessarily belong to the final assembly of the sensor as used in the dummy. The displacement calibration
therefore is not an absolute point to point (distance) calibration against a fixed reference. This is not necessary
as the chest deflection of the dummy is calculated with respect to the IR-TRACC displacement at time zero. The
[2]
IR-TRACC displacement output is associated with the ISO MME Code DS for Displacement.
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ISO/TS 21476:2018(E)

3.3
Displacement Calibration Fixture
fixed head to which the large diameter end of the IR-TRACC is attached through an interface, and a
moveable cross head parallel to the sensitive axis of the IR-TRACC to which the small diameter end of
the IR-TRACC is attached through another interface
Note 1 to entry: An example of a displacement calibration fixture is shown in Figure 1. The maximum allowable
1)
axis parallelism deviation is 1,5 mm . The minimum distance between the moveable and fixed head interface is
less than the collapsed interface distance of the smallest sensor (currently 55 mm) and the maximum exceeds
the fully extended interface distance of the largest displacement sensor (currently 201 mm). The interfaces
have freedom of rotation about the two axis perpendicular to sensitive axis. The moveable head position is
accurately adjustable by means of, for instance, a hand or motor operated screw; the moveable head is linked to a
displacement measurement gage parallel to the sensitive axis with a resolution of at least 0,01 mm. The moveable
head is linked to the displacement gage without mechanical play. A lateral loading fixture is mounted about half
way between the fixed and moving cross head to execute the forced lateral manipulation test.
Key
1 Lateral loading fixture
2 Screw to position cross head
3 Interfaces
4 Fixed head
5 IR-TRACC
6 Moving cross head
7 Linear gauge
Figure 1 — Example Displacement Calibration Fixture (exploded view)
1) Generally a 1,5 mm crosshead parallelism deviation causes less than 0,01 mm displacement deviation.
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ISO/TS 21476:2018(E)

3.4
Nominal Linearization Exponent
theoretical parameter to linearize the phototransistor voltage output as an inverse square root
function, or the voltage output U to the power of −0,5
IR
Note 1 to entry: See 3.1. The theoretical linearization exponent is -0,5 [−]. During inception of the IR-TRACC it
was found based on a certain quantity of examples or prototypes that in practise the exponent to linearize IR-
TRACCs was not −0,5, but was close to −0,428 57.
−0,428 57
Note 2 to entry: d = C * U
IR
Note 3 to entry: This value has been used for some time as a fixed exponent to linearize the voltage output,
but due to minimal individual differences of IR-TRACC components, this fixed value did not give the smallest
linearization error for each individual transducer. Up to this date this value is now applied as a starting exponent
for optimization of the exponent (see 3.5 and 3.6).
3.5
Optimized Linearization Exponent
calibration parameter based on the actual calibration data (output voltage over calibration range) of
one individual sensor, giving the least linearization error over the entire calibration range
3.6
Exponent Optimization
optimization of the Linearization Exponent by applying data processing, for instance (but not limited
to) numerical optimization
Note 1 to entry: The method finds the best linearization exponent that minimises the linearization errors over
the entire calibration range. The result of the process is the optimized linearization exponent EXP, Calibration
Factor C , Displacement Intercept I , Sensitivity S and Displacement Intercept Voltage I . The optimization
IR DS IR DSV
method is explained in 6.3.
3.7
Forced Lateral Manipulation Test
test implemented to ensure an IR-TRACC is not overly sensitive to bending of the tubes in a direction
perpendicular to the axis of displacement measurement
Note 1 to entry: The test is executed at the zero displacement point. A force of 4,45 N ± 0,15 N is exerted to the
IR-TRACC tube pulling perpendicular to the axis of compression about halfway between the fixed head and the
moving cross head (the distance of the lateral loading point does not have to be exact, as the applied force is
adequate to manipulate the tubes in bending extremes). The IR-TRACC lateral test output voltages (U ) are
IR-LAT
recorded pulling in four directions spaced 90 degrees.
3.8
Tubes In-Out Calibration Method
calibration procedure that takes two extreme tube position conditions into account at each calibration
interval (tubes-in and tubes-out position) to ensure an IR-TRACC is not overly sensitive to the individual
positions of the telescope tubes
Note 1 to entry: Tubes-in: all free tubes are moved to the largest diameter end (to fixed cross head); Tubes-out: all
free tubes are moved to the smallest diameter end (to moving cross head).
Note 2 to entry: In any length of the IR-TRACC displacement range (except fully extended/fully collapsed) the
intermediate telescope tubes are free to move position.
4 Symbols and abbreviated terms
A list of symbols, abbreviated terms, units and definitions is given in Table 1. The output of analogue
sensors in V and the output of digital sensors in LSB (Least Significant Bit) are handled in the same
way, hence the same parameters and symbols apply to analogue and digital sensors throughout this
document. The only difference is the amount of decimals used to express the values, as the analogue
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ISO/TS 21476:2018(E)

output are generally low values (0,060 0 - 2,000 0 V) and digital output are generally high values
(1 000,0 - 32 000,0 LSB).
Table 1 — List of symbols
Nr Parameter Symbol Unit Definition/Description
1 Zero d mm Starting point of displacement
S
displacement calibration d=0 (fully compressed +
point calibration range + 2 mm)
2 Calibration d mm End point of displacement calibration
e
range
3 Displacement d mm Displacement from zero displacement
point
4 Lateral mm Calculated displacement under forced
d
LAT
manipulation lateral manipulation, maximum and
d
LAT-MAX
displacement minimum
d
LAT-MIN
5 IR-TRACC output U V (LSB) IR-TRACC output voltage (or digital
IR
output)
6 Tubes-IN voltage U V (LSB) (Digital) output voltage at certain
IR-IN
displacement with all floating tubes
pushed IN
7 Tubes-OUT U V (LSB) (Digital) output voltage at certain
IR-OUT
voltage displacement with all floating tubes
pushed OUT
8 Average In-Out U V (LSB) Average of Tubes-IN and Tubes-OUT
IR-AVE
voltage (Digital) voltage
9 Forced lateral U V (LSB) (Digital) output voltage at forced
IR-LAT
manipulation lateral manipulation
voltage
10 Nominal EXP — IR-TRACC Linearization optimization
NOM
Linearization routine starting value: -0,428 57
exponent (fixed)
11 Optimized EXP — IR-TRACC linearization exponent
exponent resulting from optimization routine
12 Linearized U (V ) IR-TRACC output voltage (or digital
LIN
LIN
voltage (or output) to power of exponent (The
(LSB )
LIN
linearized linearized voltage (digital output)
digital output) is a calculated parameter, not a
physical quantity)
13 Calculated d mm Displacement calculated using average
NOM
nominal In-Out voltage (or digital output)
displacement
14 Nominal E % Error of calculated displacement
NOM
linearity error using average in-out voltage w.r.t.
calibration displacement
15 Calculated Δ mm Deviation calibration displacement
IN
deviation-In and calculated displacement using
Tubes-In voltage
16 Calculated Δ mm Deviation calibration displacement
OUT
deviation-Out and calculated displacement using
Tubes-Out voltage
17 Maximum Δ mm Difference calculated deviation-In
MAX
variation and calculated deviation-Out
18 Maximum Var % Maximum variation divided by
MAX
Variation error calibration range
The measurement techniques applied in this procedure shall be in accordance with ISO 6487.
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ISO/TS 21476:2018(E)

Table 1 (continued)
Nr Parameter Symbol Unit Definition/Description
19 Maximum E % Maximum error of calculated
MAX
Linearity error displacement using tubes-in voltage
or tubes-out voltage (highest error
from the two) w.r.t. calibration
displacement
20 Maximum Δ mm Maximum variance of lateral
LAT
variance displacement:
lateral
Δ minus Δ
LAT-MAX LAT-MIN
displacement
21 Maximum Lateral E % Maximum error of lateral variance
LAT
Variance Error w.r.t. calibration range
22 Calibration C IR-TRACC mm displacement per
(mm/V )
IR
LIN
factor linearized voltage (or linearized
(mm/LSB )
LIN
digital output) pertaining to
optimized exponent
23 Sensitivity S (V /mm) IR-TRACC linearized voltage (or
IR LIN
(LSB /mm) linearized digital output) per 1mm
LIN
displacement pertaining to optimized
exponent
24 Sensitivity S (V /mm) IR-TRACC linearized voltage (or
NOM LIN
(LSB /mm) linearized digital output) per 1 mm
LIN
displacement pertaining to nominal
exponent EXP
NOM
25 Displacement I mm Calculated displacement at U = 0
DS LIN
Intercept
26 Displacement I Linearized Voltage (or linearized
(V )
DSV
LIN
intercept digital output) at 0 mm displacement
(LSB )
LIN
voltage
The measurement techniques applied in this procedure shall be in accordance with ISO 6487.
5 Displacement Calibration Procedure
This clause describes the procedure for displacement calibration of IR-TRACCs. This calibration is run
according to the classic compression method: the zero mm starting point is defined at the extended
range of the sensor: at full length the compression is close to zero mm and with increasing compression
the IR
...