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Filename, 1www.bksv.com_Accel_cal, 1
Calibration of Accelerometers - Teleconference Two
possibilities:1. Use VoIP. Use headphones or
loudspeakers. Listening only.
To ask questions or make comments use the Chat window.
2. Call Brel & Kjr HQ on +45 45 800 500 and ask for this
meeting. Listening and talking.
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Filename, 2www.bksv.com_Accel_cal, 2
Calibration of Accelerometers
or
Introduction to
Shock and vibration transducer calibration
using
Vibration Transducer Calibration System Type 3629.
Torben R. Licht & Jesper Bo VedelJanuary 2006
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Filename, 3www.bksv.com_Accel_cal, 3
Calibration Business Group (CBG)CBG
Jesper Bo Vedel
Vibration SystemsTorben R. Licht
Instrument SystemsJesper Bo Vedel
Microphone SystemsErling Frederiksen
Additionally 4 engineers/calibration specialists
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Filename, 4www.bksv.com_Accel_cal, 4
Calibration Business GroupOur tasks:z Specification,
development, building, testing, installation and
marketing of customized and (partly) standard calibration
systems.
z Support to international calibration centers (B&K and
others)z DPLA (Danish Primary Laboratory of Acoustics)
activities
Our customers:z Larger companies (typically aerospace &
defense or
automotive)z National and other Governmental Metrology
Institutesz Calibration Service Centersz B&K Calibration
Service Centers
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Calibration
In general terms for us at B&K:measurements performed to
ensure that sound and
vibration transducers and instruments measure correctly
Calibration defined by BIPM, IEC, ISO, ..... :
.. a set of operations that establish, under specified
conditions, the relationship between values of quantities indicated
by a measuring instrument or system and the corresponding values
realised by standards ..
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Calibration Levels
z Primary calibration Normally performed as absolute
calibration that means as close as possible to the fundamental
physical units (MKSA in the SI system)
z Secondary calibration (comparison to a reference)
Transducers, calibrators, instruments
z Field calibration Field calibrators like 4231, 4294 etc
z Field measurements
I
II
III
IV
Measurements must be traceable and measurement uncertainty
known
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B&K Calibration Systems
Instruments Accelerometers Microphones
Dose meter
Octave Filter
Calibrator
Laser
Comparison
Shock 10k
Reciprocity
Comparison
Fr. Resp. Act.
Phase Comp.
Dyn. Linearity
Reciprocity
Hydrophones
ComparisonDirectional R.
SLM
Low-frequency
Fr. Resp. Coup.
Turn-key Systems- instructions on screen- printing of
certificates- uncertainty budgets
Shock 100k
Low-frequencyComparison
TransversePrimary PULSE based
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Calibration of Vibration Transducers todayBasically we are
looking for information about:
z Sensitivity in pC/(m/s2) or pC/g or mV/(m/s2) or mV/g at a
reference frequency.
ANDz Frequency response in the useable frequency range.
This is the most sensitive parameter to detect early failures.
Many points are needed.
And maybe the resonance peakz Some laboratories want the system
to handle the ISO
17025 requirements for customer, due dates etc.z In special
cases also parameters like
linearity transverse sensitivity temperature dependence etc.
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Frequency Response of an OK Accelerometer159.16 Hz
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Frequency Response of Damaged Accelerometer
Piezo crackedConnection failure
159.16 Hz
Mechanical failure
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Runs on PULSE
Fifth Generation Vibration and Shock
Transducer Calibration System Type 3629
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System Configuration
Vibration Transducer Calibration System Type 3629
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Back to Back Calibration System
Test TransducerWA0567 Calibration Fixture4371 Working
Standard
Accelerometer4808 Exciter / WH26514809 Exciter
3560C 3560C Pulse Sound & Vibration
Analyzer
10/100M LAN Interface 10/100M LAN Interface
Generator Signal
2719 2719 Power Amplifier
5308 Vibration Transducer Calibration S/W3629-CTI 3629 system
Traceable Initial Calibration
2647 2647 Charge to Deltatron Converter
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Vibration & Shock Transducer Calibration System Type
3629
z Fast and accurate amplitude and phase calibration of vibration
transducers.z Comparison calibration according to ISO 16063-21
(former ISO 5347 3)z Primary calibration (optional) according to
ISO 16063-11 (former ISO 5347 1) method 3 including phase.z
Calibration of Voltage and Charge conditioning amplifiers
(optional)z Comparison shock calibration to 10,000 g according to
ISO 16063-22. (optional)z Automated electrical system calibration
including conditioners for highest accuracy and traceability (all
data stored and used for correction).z Calculation, reading and
writing of TEDS (transducer electronic data sheet) coefficients.z
Very low expanded calibration uncertainty (e.g. 0.3% @ 10 Hz with
0.2% reference). Spreadsheet for calculation supplied.z Automated
calibration provides ease of use yet fault-proof results.z
Frequency range 0.1 Hz to 25 or 100 kHz, depending on shaker,
reference and front-end.z Calibrates practically all transducer
types: Charge, DeltaTron (constant current supplied
transducers), Piezoresistive and Variable capacitance with 2697
(optional), Voltage, Servo and Electrodynamic (Velocity
pick-ups).
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What is Type 3629?
z Type 3629 is a calibration system for vibration transducers
developed by Brel & Kjr
z Type 3629 combines the best ideas from Brel & Kjr's9610
and PULSE
z Type 3629 has a much lower cost than the former solutions
z Type 3629 uses the Brel & Kjr PULSE multifunction analyser
and this can be used separately
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Type 3629 Software Elementsz PULSE Labshop softwarez Calibration
Software Type 5308
Automated calibration control Comparison by substitution for
highest accuracy and flexibility Procedure editor System and Charge
verification for highest reliability Type description and automated
characterization of different
exciters Automated transfer calibration of working
standards,
(reference spectra). Automated calibration of PULSE front-ends
using high
precision voltmeter (hp3458A) Traceability control of components
Customer database to fulfil ISO 17025 Report generator using MSWord
and templates changeable
by customer (using keywords)
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Type 3629 Hardware Elements
z PULSE multifunction analyser (Portable PULSE)z PCz
Shaker/Power amplifier
existing or our recommendation easy to adopt to any shaker/power
amplifier
z Reference accelerometer and charge to DeltaTronconverter (or
optionally any charge conditioner)
z Differential conditioning amplifier Type 2697(optional for
calibration of PR and VC accelerometers)
z System calibration by means of HP/Agilent 3458A DMM for
highest accuracy and traceability
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Front-end Calibration
z PULSE can be calibrated using an external voltmeter
(HP/Agilent 3458A)
z Or PULSE can be calibrated in a B&K Service centre
z In either case correction values are stored in the
database
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Comparison calibration, Back to back
By back-to back mounting of the accelerometers, both
accelerometers are subjected to the same vibration. This is assumed
to be a perfectly linear motion perpendicular to the accelerometers
common mounting surface.
The sensitivity in this direction of the DUT accelerometer can
then be calculated
Suut = Sref x (Vuut / Vref) x (G ref /G uut)
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Calibration by substitution
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Measurement results and formulas
H is the frequency response function
S is the sensitivity
)()(
)(*)()(*)(*
)(*)()(*)(
fHfH
fHfSfHfS
fHfSfHfS
r
u
Br
Ax
Ax
Bu =
)()(*)()(
fHfHfSfS
r
uru =
giving the result
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Precautions and Verifications
zSystem verification to check system stability
zCharge verification to check
(Working Standard)/(Reference Transducer) stability
zCoherence check
zCorrection formulas applied
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Let us now look at the real thing!
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Main Screen at start up, procedure manager
Sortable list of results
Type/procedure selection tree
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Select the Type to be Calibratedfrom an existing type or define
a new
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Enter DUT specific data like customer etc ..
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Execute test
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Customer/Type/DUT selection
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View and print the Calibration Certificate in Word
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Calibration Certificate
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Search for test results
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View the result as at the test or print/view
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System Configuration
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Setting up the system, Reference Transducer
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Filename, 35www.bksv.com_Accel_cal, 35
Setting up the system, Reference Capacitor
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Setting up the system, Conditioners, Calibration
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Setting up the system, Exciters, Characterization
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Setting up the system, Working Standards, Transfer Cal.
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% Uncertainty under different conditionsf-
range160 Hz
> 2 to 5 Hz
>5 to 10 Hz
> 10 to 20
Hz
> 20 to 40
Hz
> 40 to 500
Hz
> 0.5 to 1,25 kHz
> 1,25 to 2 kHz
> 2 to 4 kHz
> 4 to 5 kHz
> 5 to 7 kHz
> 7 to 10 kHz
PTB-DUT4809
0.35 0.42 0.42 0.36 0.42 0.42 0.42 0.57 0.57 0.65
PTB-DUT4808
0.36 0.34 0.36 0.43 0.43 0.43 0.48 0.48 0.48 0.85 0.85
DPLA-DUT4808
0.58 0.60 0.62 0.63 0.63 0.63 0.63 0.63 0.88 1.09 1.25
DPLA-DUT4809
0.58 0.62 0.62 0.58 0.58 0.58 0.85 0.90 1.08 1.58
DPLA+DUT4809
0.68 0.72 0.72 0.72 0.72 0.72 0.95 1.08 1.24 1.77
+/- DUT means with or without transverse and temperature
influencePTB means PTB cal. at all points, DPLA means DPLA cal.
only at 160 Hz
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Shock Calibration
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Filename, 41www.bksv.com_Accel_cal, 41
Shock Calibration (POP)
Runs on PULSE
The shaker has been replaced bythe ENDEVCO POP machine Type
2925(Pneumatically Operated Projectile)A pendulum can also be used
for low levels
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Filename, 42www.bksv.com_Accel_cal, 42
Shock Calibration (POP)
1 Cushioned restraint2 Transducer under test
and reference transducer3 Optional mass4 Anvil and pad5 Piston6
Barrel7 Valve8 Pressure regulator9 Pressurized air source
After ISO/DIS 16063-22
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Real World Vibration Levels
1 000 000
1000
1
0.001
0.000 001
240
180
120
60
0
ms-2 dB
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Examples of Shocks and Their Spectra
a)
b)
c)
A
m
p
l
i
t
u
d
e
A
T Time
A
m
p
l
i
t
u
d
e
A
T Time
A
m
p
l
i
t
u
d
e
A
T Time
1
Frequency
Frequency
Frequency
1/T 2/T 3/T
0.5
F(f)AT
1
1/T 2/T 3/T
0.5
F(f)AT
1
1/T 2/T 3/T
0.5
F(f)AT F f
ATAT ft
ft( ) = sin
F(f)AT
= +ATft ft
fTft
fT2
1 1 1 2 1 sin sin
F fAT
AT ftf T
( ) = 2
1 4 2 2cos
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Shock parameters
Polynomial fit, 15 points.
Peak at:
T
levelatSensREFpeakREFpeakDUTySensitivitDUT ___
___ =
2)( ctbtatA ++=
cbt2
=
cbaApeak 4
2
=
ARef
t
ADUT
Tt
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Shock parameters
ADUT
Duration=T
10% of maxPost-shock averagePre-shock average
T/2T/2 T/2T/2
[ ] %100)()(% ReRe =
peakDUT
prefpostfpreDUTpostDUT
aaaaa
Zeroshift
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Shock parameters, linearity
g
Sensitivity pC/g
x
xx x
x x
x
x
bgagS +=)(
agS == )0( ( ) bggpCSlope =)//(0.0 g
=i
iCurveiMeasured gSgSR22 ))()((Quality of fit:
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Filename, 48www.bksv.com_Accel_cal, 48
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