FBGS - Strain Gauge Technology

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FBGS - Strain Gauge Technology

Transcript of FBGS - Strain Gauge Technology

  • Strain Gauge Technology

    mbZSE

  • Contents

    FBG / DTG principle

    Strain gauge technology

    Strain gauge performance

    Temperature compensation

    Product overview strain gauge technology

  • Contents

    FBG / DTG principle

    Strain gauge technology

    Strain gauge performance

    Temperature compensation

    Product overview strain gauge technology

  • FBG principle

    B = 2 n 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 nBragg 2 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 (< mm)

    High integration and imbedding capabilities

    Advantages

  • DTG process

    FBGS has a unique industrial process to automatically produce FBGs

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

    )

  • DTG process

    FBGS has a unique industrial process to automatically produce FBGs

    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 200C

    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

    FBG / DTG principle

    Strain gauge technology

    Strain gauge performance

    Temperature compensation

    Product overview strain gauge technology

  • 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 900m 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

    FBG / DTG principle

    Strain gauge technology

    Strain gauge performance

    Temperature compensation

    Product overview strain gauge technology

  • 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 e/Million cycles

    Fatigue testing > 2 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 ( 2 Million cycles

  • -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 +90C

    Temperature response of strain gauge attached to metal

    - X-axis: Applied temperature

    - Y- Left axis: Wavelength DTG

    - Y- Right axis: Wavelength deviation from fit

    Repeatability < 5pm = 4e 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 e / 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 m 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

    FBG / DTG principle

    Strain gauge technology

    Strain gauge performance

    Temperature compensation

    Product overview strain gauge technology

  • 5 cycles between

    -45 and +130C

    Temperature response of temperature sensor

    - X-axis: Applied temperature

    - Y- Left axis: Wavelength DTG

    - Y- Right axis: Wavelength deviation from fit

    Repeatability < +/-2pm = 0,2C

    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

    FBG / DTG princ