„RECENT ISSUES IN THE CALIBRATION OF MATERIAL TESTING MACHINES“ (Future Developments from Static to Dynamic Forces, from Single to Multicomponent Forces and from Large to Small Forces in respect to Applications like in the Field of Material Testing, ....) Rolf Kumme Physikalisch-Technische Bundesanstalt, Germany WG 1.21 + WG 1.23
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„RECENT ISSUES IN THE CALIBRATION OF MATERIAL TESTING MACHINES“
(Future Developmentsfrom Static to Dynamic Forces,
from Single to Multicomponent Forcesand from Large to Small Forces
in respect to Applications like in the Fieldof Material Testing, ....)
Rolf Kumme
Physikalisch-Technische Bundesanstalt, Germany
WG 1.21 + WG 1.23
Applications of Force Measurement
metrology in medicine
1 N10 N
100 N1 kN
10 kN100 kN
1 MN10 MN
100 MN
aircraft industry
open cut mining
space industry
off-shore industry
materials testing / safety technique
automobile industry
automation technology
(Atomic Force Microscopes)
103Force in Newton
10-9 10-6 10-5 10-4 10-3 10-2 10-1 100 101
Coordinate measuringmach.
Hardness measuring devices
102
AFM
Stylus systems
Typical Applications
New Facility
FSM of PTB
Needs for extension of PTB´s FSM to smallforces
Microsystem and nanotechnology
demand of traceability of smallforces
Calibration of Material Testing MachinesThe verification and calibration of the tension/compression testing machineis in general performed on site at the place of installation of the testingmachine, according to the procedure described in ISO 7500-1. The standard specifies the criteria for the classification of the testingmachine by way of the on-site calibration of its force-measuring system. The class of the transfer standard (force-proving instrument, specified in ISO 376) shall be equal to or better than the class for which the testingmachine is to be classified. Conformity with respect to the classification of a testing machineaccording to ISO 7500-1 thus implies that the uncertainties of forcesassociated with the transfer standard have been taken into account.
=> „UNCERTAINTY OF MEASUREMENT IN THE VERIFICATION AND CALIBRATION OF THE FORCE-MEASURING SYSTEMS OF TESTING MACHINES“ by Amritlal Sawla, PTBIn: PROCEEDINGS OF THE ASIA-PACIFIC SYMPOSIUM ON MEASUREMENT OF FORCE, MASS AND TORQUE (APMF 2000) TSUKUBA, JAPAN - NOVEMBER, 2000.
Acrobat-Dokument
Force Standard Machines of PTB20 kN
5 MN
1 MN200 N
2 kN100 kN
2 MN16,5 MN
Set-Up based on a compensation balance
Piezoelectricaladjustment device
Force transducer(to be investigated)
Electrodynamic force compensation balance
Levermecha-
nismCoil
Magnet
Positionsensor
16,5-MN-hydraulic amplification-FSM
Fg
A1 A2
oil pressure p
m
F1 F2
force transduceroiloil
loadframe
piston piston
1
2 3
5
4
6 7 8
11
10
9
12
13
14
15
16
17
18
19
PTB‘s „new“ 2 MN Deadweight FSM
Measurement Uncertainty of 2 MN Deadweight Force Standard Machine
m mass of deadweightsgloc local gravity at the position of deadweightρm density of the deadweightsρL density of air∆1 relative deviation due to magnetic forces∆2 relative deviation due to influences of the compensation lever∆3 relative deviation due to other effects like force introduction
(verified by ideal force transducers)
( ) ( ) ( ) ( ) ( )∑=
∆+
+
−++=
3
1
222
22
22)(i
imm
LL
m
Lloc wwwgwmwFw ρ
ρρρ
ρρ
( )∏=
∆−⋅−⋅⋅=3
1
1)1(i
im
LlocgmF
ρρ
=> Rel. Uncertainty: W <= 2*10-5 (k=2)
Comparison of stack 5 (10 x 100 kN) with stack combination 4, 3, 2, 1 by using a 2 MN force transducer.
-2
-1
0
1
2
1 2 3 4 5 6 7 8 9 10 11 12
No. of measurement
Rel
. dev
iatio
n in
10-6
Stack
No.5 10x
100kN
No.410x
50kN
No.310x
20kN
No.210x
20kN
No.110x
10kN
Stack 4,3,2,1 Stack 4,3,2,1Stack 5 Stack 5
2 MN Transducer1050 kN Force
Rotation effect in the 2 MN force standard machine measuredin 2 rotations according key comparison procedure.
Inluences on the Uncertainty of Force CalibrationThe Measurement Uncertainty is determinded by: - Force Calibration Machine Wbmc- Calibration Procedure- Force Transducer to be calibrated Wtra
MU is calculated as follows:
EA10/04 describes the calculation only for ISO 376 and for the Force Measuring Device (Transducer+Indicator)
New Uncertainty Annex for ISO 376 under discussion.
The relative expanded uncertainty of calibration W will be determined by considering the best measurement capability of the force calibration machine as follows:
22bmctra wwkW +⋅=
Contibution for fixed loading profile (Key Comparison)
0
500
1000
1500
0 6 12 18
time in minutes
forc
e in
kN
start of rotationmeasurement
measurement
measurement
measurement
222222revresinprotrepzertra wwwwwww +++++=
Calibration Procedures of Force Measuring Devices
1. Key ComparisonComparison of Force Standard Machines with rel. Uncertainties of < 0,002% (Deadweight)
2. Traceability of Accreditatied Laboratories forCalibration of Force Measuring Devices
DKD Procedure to verify the Traceability of Force Calibration Machines with rel. Uncertainties down to 0,005% (Deadweight)
3. Procedure according IS0 376 for Calibration of Material Testing Machines
4. Simplified Procedures according DKD 3-3
5. Continous Procedures according DKD 3-9
6. Special Procedures which have to be evaluated.
Influences in the calibration of force transducersMU according EA10/04 :
Comments to MU:
- MU components of indicator has to be taken intoaccount if indicator is changed.
- MU according loading procedure is missing.
- MU valid only for parts of force introduction used in calibration.
=> User has to take additional influences into account.
222222revresinprotrepzertra wwwwwww +++++=
Contibutions according EA10/04 Table 7.1: Probability distributions assumed for the different input quantities(a: relative half-width of the maximum deviation of the input quantity)
Uncertainty contributions Probability distribution Estimated relative(input quantities) variance
zero deviation rectangular distribution 32
32zer
20
2
==f
aw
reproducibility without rotation rectangular distribution 32'
32rep
2
2
==b
aw
reproducibility with rotation U-shaped distribution 22
22rot
2
2
==b
aw
interpolation deviation triangular distribution 62
62inp
2
2
==cf
aw
resolution rectangular distribution 32/
32res
2
2
==Fr
aw
reversibility (hysteresis) rectangular distribution 32
32rev
2
2
==ν
aw
Probable changes in ISO 376 New ISO 376 Annex prepared by ISO/TC 164/SC 1 WG3:
1. The Annex will be independent off EA10/04.
2. The uncertainty should be independent of the classification.
3. The uncertainty for increasing and decreasing forces should becalculated seperately.
For example:
Case 1
Case 2
222222revresinprotrepzertra wwwwwww +++++=
22222resinprotrepzertra wwwwww ++++=
Table 9.2: Limits for the expanded relative uncertainty fordifferent classes of (EN 10002-3) ISO 376
Combination of the 17,8 kN shaker system with laser vibrometer.
Extension of the calibration to large dynamic forces with the comparison method.
Forc
e
Load cycle time tc=1000 s
a) Stepwise Load Cycle
Forc
e
Load cycle time tc=10 s
b) Continuous Load Cycle
Forc
etc=1....0,0001 s
c) Sinusoidal Load CycleControlsystem
Amplifier
Amplifier
Up to 100 kN
Servohydraulicforce generation
FT
FT
Conclusion: Calibration of force transducers.
- Different calibration procedures are possible:
static (continous or stepwise)
dynamic (sinusoidal, impact, ....)
- Different influences have to be taken into account:
static and quasistatic influences:
nonlinearity, hysteresis, creep...
=> sensitivity
dynamic influences:
frequency response of amplifier, force transducer, coupling of load mass to transducer
=> dynamic sensitivity
Conclusion for dynamicapplications.
1. Static and dynamic calibration of the force sensorDeviations between the static sensitivity determined bystepwise calibration methods and the dynamic sensitivityindicate the limits of the use of static sensitivity.
2. Analysis of the mechanical applicationAnalysis of the vibration behaviour
3. Compensation of systematic influencesCompensation of inertia forces and consideration of theresonance behaviour.
Future developments in force measurementin
respect to applications and material testing.1. Investigation and calibration of force measuringdevices with static, quasistatic, coninuous, periodical and impact forces.
2. Extension of the range of force standardsaccording the needs in industry like in the field of material testing machines.
3. Development and investigation of transferstandards for dynamic forces, multicomponent measurements and small forces.
=> Additional Procedures for Calibration of Material Testing Machines.