fbgs - strain gauge technology

Strain Gauge Technology

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ZSE

Contents

FBG / DTG® principle

Strain gauge technology

Strain gauge performance

Temperature compensation

Product overview strain gauge technology

FBG principle

λB = 2 n Λ BRAGG CONDITION:

l

P

Typical 8 mm

FBG

Incident spectrum

Reflected spectrum

Transmitted spectrum

l

P l

P

The reflection and transmission properties of a Fibre Bragg Grating.

FBG principle

l

P ''2' nBragg

l

P n

Bragg2 L

L'

Strained FBG

Unstrained FBG

Strain sensing principle of an FBG

Advantages FBGs

Reliable

• Passive component

• Long life time (>20 years) No corrosion

• Stable over time (No calibration required)

• Cables and connectors are telecom grade

Performant

•Up to 40 sensors in 1 fibre

• Less cables

•Easy installation

•High fatigue resistance

• Long distance measurements (20+ km)

Measurement based on light

• Immune for electro-magnetic radiation & radio frequency interference

• Immune for high voltage discharge

•Explosion safe

Size

• Fibre is also the sensor

• Lightweight & small diameter (< ¼ mm)

•High integration and imbedding capabilities

Advantages

DTG process

FBGS has a unique industrial process to automatically produce FBG’s

during the fiber drawing process, named Draw Tower Gratings (DTGTM

)

DTG process

FBGS has a unique industrial process to automatically produce FBG’s

during the fiber drawing process, named Draw Tower Gratings (DTGTM

)

Preform

Fibre winder

KrF 248nm

Advantages DTGs compared to FBGs

high strength DTG fiber compared to standard recoated telecom fiber.

Classical

recoated FBG

DTG

Re

lati

ve b

reak

ing

pro

bab

ility

[F]

]

Breaking force [N]

Advantages DTGs compared to FBGs

1 • High strength: >5% strain

2 • High temperature resistance 200°C

3 • High adhesive coating (direct bonding on coating)

4 • Spliceless sensor chain configurations

5 • Cost effective

6 • Low bending losses

7 • Uniform coating coverage

Draw Tower Gratings DTG-LBL-830/DTG-LBL-1550

Contents






Total strain gauge solution

Fiber optical strain gauges

Fiber optical temperature

probes

Measurement devices

Measurement and

visualisation software

Installation materials

Strain gauge solution to measure strain on multiple locations on objects

UV sensor pad / UV adhesives

•Holding fiber / 28mm fiber in direct contact with surface

•Fiber ends outside pad in 900µm buffered jacket

•Transparent for UV-light

•Pad is not reacting with adhesives / removable after fixation

•Flexible enough to fixate FBG against curved structures

Pressurization 30s pre-cure Removal pad 300s post cure

Patented fixation methodology

Highly controllable curing process – Patent WO 2009106576 (A1)

Highly controllable curing process – Patent WO 2009106576 (A1)

Patented fixation methodology

THANK YOU!

Features Fibre Optic Electric EM-radiation Immune EM-sensitive

Lightning / electric discharge

Lightning and discharge proof May cause damage or complete failure

Electric conductivity Non-conductive and hence no special precautions needed

for outdoor use or usage under water All wiring needs to be hermetically sealed for outdoor use or

usage under water

Explosion Safety Spark-free and hence safe in potentially explosive

atmospheres Hazardous in explosive atmospheres

Measurement distance Up to tens of kilometers Limited in range without any additional amplification

Multiplexing Possible to multiplex,

i.e. multiple sensors can be allocated within the same optical fibre

No multiplexing capability in series configuration

Weight fibres are lightweight and

number of cables can be limited1 Becomes heavy for large numbers of sensors because of the

copper wiring

Protective coating No protective coating required for operation Protective coating required (electric conductivity, corrosion,

…)

Fatigue resistance Excellent fatigue resistance: negligible effects for at least 2

million cycles for +/- 0.24 % straining Similar performance not possible with electrical gages

Transverse sensitivity Negligible. The FO gages measure basically only in the

direction of the fibre. Of the order of a few percent. Needs to be accounted for in

many cases.

Price (sensor + read-out) Becomes more cost-effective for more sensors1. Break even

point already for 20 sensors Price scales linearly with the number of sensors since every

sensor needs a separate read-out channel

Temperature sensitivity Relatively high temperature sensitivity. Temperature compensation required.

Relatively low temperature sensitivity. Temperature compensation required.

Other Temperature Induced Effects

None Resistive heat generation can occur for gages installed on

materials with low thermal conductivity, resulting into measurement errors.

Comparison with electrical strain gauges

Contents






Calibration curve of one cycle for FP525 material.

- X-axis: Electrical extensometer

- Y- Left axis: Wavelength DTG

- Y- Right axis: Wavelength deviation from fit

Fatigue testing > 2 Million cycles

Drift of zero point as function of fatigue cycles

- X-axis: Number of load cycles

- Y- Left axis: Wavelength drift at zero load

Tested for 7 different materials

Drift zero point < 4 µe/Million cycles


Drift of zero point as function of fatigue cycles

- X-axis: Number of load cycles

- Y- Left axis: Change gauge parameter

expressed as a relative shift in [10-3]

- Tested for 7 different materials

No significant drift (<< 1%)


-60

-40

-20

0

20

40

60

80

100

0 10 20 30 40 50 60 70

t [h]

T [

°C]

5 cycles between

-45 and +90°C

Temperature response of strain gauge attached to metal

- X-axis: Applied temperature



Repeatability < 5pm = 4µe over 5 cycles

Fatigue testing - Temperature

Parameter Unit Value

Gage factor (k) - 0.777 (typical)

Relative statistical error on gage factor % 0.5

Transverse sensitivity1 - < 2.5 10-3

Temperature coefficient of gage factor2 °C-1 2.7 10-4

Strain range (tension / compression) % 0.5

Fatigue shift3 µe / 106 cycles ≤ 4

S1 (linear temperature sensitivity) 10-6 °C-1 6.30 (typical)

S2 (quadratic temperature sensitivity) 10-9 °C-2 8.02 (typical)

Active gage length (FBG length) mm 8

Overall gage length (fixation length) mm 28

Operating temperature range °C -45 to +90

Tubing material - PVDF

Tubing diameter µm 900

Tubing length (left and right from strain gage) cm 45

Connector type - FC/APC

1 According to ASTM E 251-92. The transverse strain sensitivity is the ratio of the gage factor of a strain gage mounted

perpendicular to a uniaxial strain field (transverse gage) to the gage factor of a similar gage mounted parallel to the same

strain field (longitudinal gage). 2 The temperature coefficient of the gage factor k expresses the relative variation of k per degree Celsius. 3 The bonding during fatigue cycling was tested by mounting gages on unidirectional glass composite material that was

strained from -0.24 % to +0.24 % up to 2 million cycles.

Specifications strain gauge

Contents






5 cycles between

-45 and +130°C

Temperature response of temperature sensor

- X-axis: Applied temperature



Repeatability < +/-2pm = 0,2°C

Method 1: Temperature probe

'

0

'

0

, lnln1

e

ksmech

SG-01 mounted on structure under test

SG-01 mounted on TC-plate

Compensating plate = cantilever design made of same material

SG-01 mounted on TC-plate is free from mechanical strain

T- compensation can be achieved by taking the difference

in response:

Method 2: Compensating plate

Contents






Detailed contents Quantity Instruction manual 1

Data sheets and safety forms 3

Sensor pads: L =45 mm, W= 8 mm (re-usable) 2

UV-curable adhesive (1 oz. bottle) 1

Z70 cyano-acrylate based rapid adhesive (10 ml bottle) 1

Dosing nozzle for Z70 2

Teflon band 1

Abrasive paper (1 m ribbon) 1

Box with cleaning tissues (90 pieces) 1

Bottle of cleaning agent (85 g) 2

Teflon patches brown (for UV) 24

Teflon patches white (for Z70) 20

Rectangular glass piece 1

Rapid Adhesive component A 1

Rapid Adhesive component B 2

Mixing cups 9

Spoons 2

Wooden stirring sticks 25

Tweezers 1

Scalpel 1

Mechanical protection (90 ml tube) 1

Fibre Optic Strain Gages SG-01* 20

Temperature Compensating probe (TC-probe)* 2

Fibre optic patchcord (6 m) 2

Fibre optic connector adapter 12

Contains 20 Strain gauge sensors,

2 temperature probes and all

necessary installation materials

with exception of the UV light source

Patent WO 2009106576 (A1)

Strain Gauge Kit SGK-01

Strain gauges SG-01 are packaged per 5 in one box

and are connectorised at both sides:

Parameter Value Strain resolution1 0.85 µe

Strain precision1 1.7 µe

Strain range 1 %(long term) 5 %(short term)

Operating temperature range2 -50 °C to +130 °C Active gage length3 8 mm Overall gage length4 28 mm Coating material ORMOCER ® Fibre diameter (coated) 195 µm Tubing material PVDF Tubing diameter 0.9 mm Tubing length (left and right) 45 cm Connector type FC/APC

Box containing 5 SG-01 sensors

Strain gage SG-01

Parameter Value

Temperature resolution1 0.1°C

Temperature precision1 0.2°C

Temperature range2,3 -20 °C to +110 °C

Sensor length 58 mm

Housing diameter 5 mm

Housing material SS316

Pigtail diameter 0.9 mm

Pigtail length3 1 m

Pigtail material PVDF

Connector type FC/APC

1 Taking into account a depolarized measurement device with a 1 pm wavelength resolution and precision. 2 For the sensor and not for the connector. For the extreme temperatures, splicing is recommended. 3 Extendable on request.

• Compact temperature sensor for temperature compensation of strain measurements

• High accuracy and excellent long-term stability

• Wide temperature operating range

• Single ended configuration

Temperature probe TC-probe

• 100W lamp with up to 18W/cm2 of output

• Intelli-Lamp® technology to cool and monitor the

lamp for extended lamp life (typically 2000 hours)

and optimize performance

• Automatic lamp striking with hot strike revention that

will protect lamp life

• Adjustable light output in 1% increments for precise

control

• Selectable bandpass filters to customize light

wavelengths for specific applications

• Easy to use finger touch controls with LED display

UV light source: Omnicure series 1000

Parameter Value

Wavelength range 1515-1590 nm

Number of Bragg sensors 40

Number of channels 2 (same optical line)

Wavelength precision 1 pm

Gain 30 dB with user selectable

control

Scan and report time 2 KHz

Communications USB 2.0

Power supply 5 V

Connector type FC/APC

Dimensions 260mm x 230mm x 60 mm

High dynamic range / High sampling rate / External triggering / High number of sensors / Excellent wavelength precision

Compact measurement device for FBG strain sensors:

Delivered standard with ‘ILLumisense Strain’ software: fast set-up and easy to

use software for strain experiments.

FBG interrogator: FBG-Scan x00

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