Strain Gauges and Accesories

19.03.2008, Folie 1 Hottinger Baldwin Messtechnik GmbH Nurgül Er

Strain Gauges and Accessories

Nurgül Er

[email protected]

www.hbm.com




How to find the right strain gauge …

a wide range of strain gaugesa wide range of strain gauges



Leads

Cover

Measuring grid

Grid length

carrier

Gri

d w

idth

Strain gauge



Applications of Strain Gauges

Transducers for• Force•Torque• Pressure• Strain• ...

Experimental Test‘s• Exp. stress analysis• Determining Residual Stress • Analysis of loading

(e.g. life-time analysis)

• Determining thermal stress



Strain gauges for transducer manufactures Strain gauges for transducer manufactures



HBM-bending beamHBM-bending beam



Strain gauges for experimental testsStrain gauges for experimental tests



L Type Geometry of the strain gauges

Y Strain Gauges Series Material of the measuring grid and the carrier

1 Connections Leads / solder tabs / …

1 Temperature adjusted to thermal expansion variation coefficient α of an material

6 Measuring grid in mm

120 Measuring grid resistance in Ohm

Strain gauges type designation

Strain gauges type designation (example): LY11-6/120



L one measuring grid (linear strain gauges)

D two measuring grid (direction: parallel)

X two measuring grids (T-rosette (offset by 90°)

R three measuring grids ( rosettes)

V four measuring grids (full bridge strain gauges)

K strain gauges chains for determining strain gradients

M full bridge strain gauges as diaphragm rosettes

Number of measuring grid and their relative position to each other



Typical strain gauges types



εσ=E

Linear strain gauge e.g. LY11-6/120

Calculate the Young's Modulus on a tension / compression bar (Hooke‘s Law)

• measure strain ε• calculate the mechanical stress

AF=σ


F



Dual-element linear strain gauge e.g. DY11-6/350

F

Typical application: bending beam ...

... and the right strain gauge




X-rosettes with 2 measuring grids e.g. XY11-6/120

l

q

εε

=ν

AF=σ

εσ=E


Calculate the Young's Modulus and the Poisson’s ratio on a tension bar

• measure strain ε

• calculate the mechanical stress




X-rosettes with 2 measuring grids e.g. XY41-6/120Example: torque transducer (torsions shaft with strain gauges mounted in the principal strain directions



b

a

c

( ) ( ) ( )2bc

2ba

ca2/1

12

E21

E ε−ε+ε−ε⋅ν+

±ε+ε⋅ν−

=σ

(0º/45º/90º - rosette)


Rosettes with 3 measuring grids e.g. RY11-6/120



determining a biaxial stress state with unknown principal directions

• 0º/45º/90º - rosettes • 0º/60º/120º - rosettes


Rosettes with 3 measuring grids e.g. RY11-6/120(planar)



Strain gauges chains, e.g. KY11-4/120

(for the determination of stress gradients)

Shapes of strain gauges chains:• measuring grids in a direction parallel to the chain‘s

longitudinal axis• measuring grids in a direction perpendicular to the

chain‘s longitudinal axis• measuring grids in a direction alternately parallel and

perpendicular to the chain‘s longitudinal axis• rosette chain




Five 0°/60°/120° - rosette and one compensation strain gauges




strain measurement on a gear wheel

strain measurement on a gear wheel



Diaphragm rosette e.g. MY21-6/120Example: pressure transducer with diaphragm elastic elements




Y carrier polyimide / measuring grid constantan foil

C carrier polyimide / measuring grid CrNi special alloy

G carrier phenolic resin, glass fibre reinforced / measuring grid constantan foil

K carrier phenolic resin, glass fibre reinforced / measuring grid constantan foil, different creep adjustment

V carrier polyimide / measuring grid constantan foil, embedded in plastic resin

Strain gauge series



Strain gauges for harsh environments • embedded in plastic resin

• carrier polyimide / measuring grid constantan foil

• with 3m cable

Strain gauge series



• with leads (aprox. 30mm)• with integrated solder tabs • pre-wired strain gauges

Type and position of connections

new



pre-wired strain gaugesnew!

• no soldering at the measuringpoint

• cable length from 0.5m to 10mavailable

• 2, 3 and 4 wire options

• Teflon insulated wires preventunwanted cable bonding

Type and position of connections



Every strain gauge gives out a value when the temperature varies – without any mechanical load.

Cause:

• Work piece expansion with temperature • Change in specific resistance of strain gauge• Strain gauge grid expansion with temperature

HBM, Thomas Kleckers (Januar 1999)

Temperature compensated strain gauges



1 for ferritic steel α = 10,8 ·10-6/ K

3 for aluminum α = 23 · 10-6/ K

5 for austenitic steel α = 16 · 10-6/ K

6* for quartz α = 0,5 ·10-6/ K

7* for titanium/ gray cast iron α = 9 ·10-6 / K

8* for plastic material α = 65 ·10-6/ K

9* for molybdenum α = 5,4 ·10-6/ K

1 for ferritic steel α = 10,8 ·10-6/ K

3 for aluminum α = 23 · 10-6/ K

5 for austenitic steel α = 16 · 10-6/ K

6* for quartz α = 0,5 ·10-6/ K

7* for titanium/ gray cast iron α = 9 ·10-6 / K

8* for plastic material α = 65 ·10-6/ K

9* for molybdenum α = 5,4 ·10-6/ K

* not for all measuring grid lengths available

Temperature compensated strain gauges



Self Temperature Compensation



Fstrain gauges application

a strain gauges with a long measuring grid giving an averagevalue with inhomogeneous material, e.g. concrete

point values, measured withshort strain gauges (measuringstress peaks)

F not correct

correct

Measuring grid length of an strain gauge



Fstrain gauges application

F

correct

The strain gauges forms an arithmetic mean of the strain conditions existing under its measuring grid.

Measuring grid length of an strain gauge





Typically Values:

• 120Ω ... preferred for stress analysis

• 350Ω ... preferred for transducer manufacturing

• 700Ω ... preferred in combination with telemetriessystems and for the measurement on materialswith low thermal conductivity

and

1000 Ω

The values have an historical origin, but they have proven usefuland so they have been retained.

Resistance of the strain gauges



HBM adhesive programHBM adhesive program



cold curing adhesives

• preferred for experimental stress analysis

• easy to apply and require only little effort

• temperature range is smaller than hot curing adhesives

hot curing adhesives

• preferred in the manufacture of transducers (based on strain gauges)

• can be used where the measured object can be brought up to the curing temperature

• greater temperature range than cold curing adhesives

• contact pressure needed

Adhesives



• single component adhesive, preferred for experimentalstress analysis

• thin liquid

• very easy to handle

• temperature limits: -70°C up to +100°C (+120°C)

• contact pressure: thumb pressure

• curing period: 5°C: 10 minutes20°C: 1 minutes30°C: 0,5 minutes

• Humidity of more than 40% is necessary for curing

Cyano-acrylate Z70



Cyano-acrylate Z70



• two components adhesive, preferred for experimentalstress analysis

• pasty, even on absorbent or uneven surfaces

• easy to handle (mixing to components)


• contact pressure: thumb pressure

• curing period: 0°C: 60 minutes20°C: 10 minutes35°C: 2 minutes

Methacrylate mixture X60



Methacrylate mixture X60



• two components adhesive, preferred for experimentalstress analysis

• for smooth and absorbent surfaces


• contact pressure: 0,05 … 2 N/mm2

• curing period: room temperature: 8 hours 95°C: 1 hour

Epoxy resin X280



Epoxy resin X280



• two components adhesive, preferred in the manufactureof transducer or for stress analyses in a lager temperaturerange

• pasty, even on absorbent or uneven surfaces


• contact pressure: 0,1 … 1,5 N/mm2

• curing period: 95°C: 16 hours 200°C: 0,5 hour

Epoxy resin EP250



Epoxy resin EP250



• two components adhesive, preferred in the manufactureof transducer or for stress analyses in a lager temperature range

• thin liquid, very easy to handle


• contact pressure: 0,1 … 0,5 N/mm2

• curing period: 95°C: 5 hours 200°C: 0,5 hour

Epoxy resin EP310S



Epoxy resin EP310S



Protective coatings



• it is recommended that strain gauges be protectagainst external effects (such as humidity, water, oil,mechanical influences)

• protect the polished metal of our application areaagainst rust

Protective coatings



The cover should be put on immediately after bonding of the strain gauge.

The application area must clean – as for the adhesive.

If bonding the strain gauges in humid ambient conditionsthe applied gauge should be dried with a hot air gun or hair dryer.

Cover a large area surrounding the applied gauges.



• curing conditions: air drying (room temperature …+100°C)

• application method: brush application

• temperature range: -40°C ... +120°C

• suitable for light protection against touching and dust, for normal air humidity; likewise useful as insulating layer under other covers

Polyurethane paint

PU120PU120



Nitrile rubber

NG 150NG 150

• curing conditions: air drying at room temperature

• application method: brush application


• oil and petrol resistance, preferred incontact with liquid gases (excludingoxygen!)



Silicon Rubber

SG 250SG 250

• curingconditions:air drying at room temperature

• transparent, solvent-free

• application method: tube application


• suitable as protection against humidity and weather,against water at room temperature,limited oil resistantvery good mechanical protection



Permanently plastic putty

AK 22AK 22

• curing conditions: -

• application method:kneading on by hand


• very good protection against humidity and weather,can be used under



ABM 75ABM 75

• curing conditions: -

• application method:pressing on by hand

• temperature range:-50°C ... +170°C

• range of application andproperties similar to AK22

Permanently plastic putty with aluminium foil



Accessories

• cleaning agent RMS1

• cleaning pads

• solder terminals

• cables and wires

• …



thank you...

... for your attention

Dikkatiniz icin

tesekkürler…

Hottinger Baldwin Messtechnik GmbH

Im Tiefen See 45

D-64293 Darmstadt

www.hbm.com

Nurgül Er

Technical Support Center

Tel. 06151/803-8352

[email protected]

Strain Gauges and Accesories

Documents

methacrylate mixture x60

epoxy resin ep310s

epoxy resin x280

epoxy resin ep250

wired strain gauges19

hand temperature range

measuring grid length

handle temperature limits