Strain Gauge Technology

Transcription

1 Strain Gauge Technology

2 Contents FBG / DTG principle Strain gauge technology Strain gauge performance Temperature compensation Product overview strain gauge technology

3 Contents FBG / DTG principle Strain gauge technology Strain gauge performance Temperature compensation Product overview strain gauge technology

4 FBG principle P Incident spectrum l FBG P P Typical 8 mm Transmitted spectrum l Reflected spectrum l The reflection and transmission properties of a Fibre Bragg Grating. BRAGG CONDITION: λ B = 2 n Λ

5 FBG principle P 2n Bragg L Unstrained FBG l P ' Bragg 2n' ' L' Strained FBG l Strain sensing principle of an FBG

6 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 electromagnetic 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

7 DTG process FBGS has a unique industrial process to automatically produce FBG s during the fiber drawing process, named Draw Tower Gratings (DTG TM )

8 DTG process Preform KrF 248nm Fibre winder FBGS has a unique industrial process to automatically produce FBG s during the fiber drawing process, named Draw Tower Gratings (DTG TM )

9 Advantages DTGs compared to FBGs Classical recoated FBG DTG Relative breaking probability [F]] Breaking force [N] high strength DTG fiber compared to standard recoated telecom fiber.

10 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

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

12 Contents FBG / DTG principle Strain gauge technology Strain gauge performance Temperature compensation Product overview strain gauge technology

13 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

14 Patented fixation methodology 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 Highly controllable curing process Patent WO (A1)

15 Patented fixation methodology Highly controllable curing process Patent WO (A1)

16 Comparison with electrical strain gauges Features Fibre Optic Electric EM-radiation Immune EM-sensitive Lightning / electric discharge Lightning and discharge proof May cause damage or complete failure Electric conductivity Explosion Safety Non-conductive and hence no special precautions needed for outdoor use or usage under water Spark-free and hence safe in potentially explosive atmospheres All wiring needs to be hermetically sealed for outdoor use or usage under water Hazardous in explosive atmospheres Measurement distance THANK Up to tens of kilometers YOU! Limited in range without any additional amplification Multiplexing Weight Protective coating Fatigue resistance Transverse sensitivity Price (sensor + read-out) Temperature sensitivity Other Temperature Induced Effects Possible to multiplex, i.e. multiple sensors can be allocated within the same optical fibre fibres are lightweight and number of cables can be limited 1 No protective coating required for operation Excellent fatigue resistance: negligible effects for at least 2 million cycles for +/ % straining Negligible. The FO gages measure basically only in the direction of the fibre. Becomes more cost-effective for more sensors 1. Break even point already for 20 sensors Relatively high temperature sensitivity. Temperature compensation required. None No multiplexing capability in series configuration Becomes heavy for large numbers of sensors because of the copper wiring Protective coating required (electric conductivity, corrosion, ) Similar performance not possible with electrical gages Of the order of a few percent. Needs to be accounted for in many cases. Price scales linearly with the number of sensors since every sensor needs a separate read-out channel Relatively low temperature sensitivity. Temperature compensation required. Resistive heat generation can occur for gages installed on materials with low thermal conductivity, resulting into measurement errors.

17 Contents FBG / DTG principle Strain gauge technology Strain gauge performance Temperature compensation Product overview strain gauge technology

18 Fatigue testing > 2 Million cycles Calibration curve of one cycle for FP525 material. - X-axis: Electrical extensometer - Y- Left axis: Wavelength DTG - Y- Right axis: Wavelength deviation from fit

19 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

20 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 (<< 1%)

21 T [ C] Fatigue testing - Temperature Temperature response of strain gauge attached to metal - X-axis: Applied temperature - Y- Left axis: Wavelength DTG - Y- Right axis: Wavelength deviation from fit t [h] 5 cycles between -45 and +90 C Repeatability < 5pm = 4µe over 5 cycles

22 Specifications strain gauge Parameter Unit Value Gage factor (k) (typical) Relative statistical error on gage factor % 0.5 Transverse sensitivity 1 - < Temperature coefficient of gage factor 2 C Strain range (tension / compression) % 0.5 Fatigue shift 3 µe / 10 6 cycles 4 S 1 (linear temperature sensitivity) 10-6 C (typical) S 2 (quadratic temperature sensitivity) 10-9 C (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 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 % to % up to 2 million cycles.

23 Contents FBG / DTG principle Strain gauge technology Strain gauge performance Temperature compensation Product overview strain gauge technology

24 Method 1: Temperature probe 5 cycles between -45 and +130 C Temperature response of temperature sensor - X-axis: Applied temperature - Y- Left axis: Wavelength DTG - Y- Right axis: Wavelength deviation from fit Repeatability < +/-2pm = 0,2 C

25 Method 2: Compensating 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: e mech ' 1, s ln ln ' k 0 0 SG-01 mounted on structure under test SG-01 mounted on TC-plate

26 Contents FBG / DTG principle Strain gauge technology Strain gauge performance Temperature compensation Product overview strain gauge technology

27 Strain Gauge Kit SGK-01 Contains 20 Strain gauge sensors, 2 temperature probes and all necessary installation materials with exception of the UV light source Patent WO (A1) 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

28 Strain gage SG-01 Strain gauges SG-01 are packaged per 5 in one box and are connectorised at both sides: Box containing 5 SG-01 sensors Parameter Value Strain resolution µe Strain precision µe Strain range 1 %(long term) 5 %(short term) Operating temperature range 2-50 C to +130 C Active gage length 3 8 mm Overall gage length 4 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

29 Temperature probe TC-probe Compact temperature sensor for temperature compensation of strain measurements High accuracy and excellent long-term stability Wide temperature operating range Single ended configuration Parameter Temperature resolution 1 Temperature precision 1 Value 0.1 C 0.2 C Temperature range 2,3-20 C to +110 C Sensor length Housing diameter Housing material Pigtail diameter Pigtail length 3 Pigtail material Connector type 58 mm 5 mm SS mm 1 m PVDF 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.

30 UV light source: Omnicure series W 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

31 Compact measurement device for FBG strain sensors: FBG interrogator: FBG-Scan x00 High dynamic range / High sampling rate / External triggering / High number of sensors / Excellent wavelength precision Parameter Value Wavelength range 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 Delivered standard with ILLumisense Strain software: fast set-up and easy to use software for strain experiments.