Calibration Accelerometers

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.


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


Calibration Business Group (CBG)CBG

Jesper Bo Vedel

Vibration SystemsTorben R. Licht

Instrument SystemsJesper Bo Vedel

Microphone SystemsErling Frederiksen

Additionally 4 engineers/calibration specialists


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


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 ..


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


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


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.


Frequency Response of an OK Accelerometer159.16 Hz


Frequency Response of Damaged Accelerometer

Piezo crackedConnection failure

159.16 Hz

Mechanical failure


Runs on PULSE

Fifth Generation Vibration and Shock

Transducer Calibration System Type 3629


System Configuration

Vibration Transducer Calibration System Type 3629


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


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).


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


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)


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


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


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)


Calibration by substitution


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


Precautions and Verifications

zSystem verification to check system stability

zCharge verification to check

(Working Standard)/(Reference Transducer) stability

zCoherence check

zCorrection formulas applied


Let us now look at the real thing!


Main Screen at start up, procedure manager

Sortable list of results

Type/procedure selection tree


Select the Type to be Calibratedfrom an existing type or define a new


Enter DUT specific data like customer etc ..


Execute test


Customer/Type/DUT selection


View and print the Calibration Certificate in Word


Calibration Certificate


Search for test results


View the result as at the test or print/view


System Configuration


Setting up the system, Reference Transducer


Setting up the system, Reference Capacitor


Setting up the system, Conditioners, Calibration


Setting up the system, Exciters, Characterization


Setting up the system, Working Standards, Transfer Cal.


% 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


Shock Calibration


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


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


Real World Vibration Levels

1 000 000

1000

1

0.001

0.000 001

240

180

120

60

0

ms-2 dB


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


Shock parameters

Polynomial fit, 15 points.

Peak at:

T

levelatSensREFpeakREFpeakDUTySensitivitDUT ___

___ =

2)( ctbtatA ++=

cbt2

=

cbaApeak 4

2

=

ARef

t

ADUT

Tt


Shock parameters

ADUT

Duration=T

10% of maxPost-shock averagePre-shock average

T/2T/2 T/2T/2

[ ] %100)()(% ReRe =

peakDUT

prefpostfpreDUTpostDUT

aaaaa

Zeroshift


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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Calibration Accelerometers