Fiber Optic Sensing

Presented by: Jason Kiddy (Aither)

Alan Turner (Micron Optics)

May 13, 2008

Sandia Wind Blade Workshop

Aither Engineering, Inc.4865 Walden LaneLanham, MD 20706(240) 296-1301jkiddy@aitherengineering.com

Micron Optics, Inc.1852 Century PlaceAtlanta, GA 30345(281) 334-3793 aturner@micronoptics.com

Aither Engineering, Inc.

• Maryland Corporation, formed July 2006 as a spin-off from Systems Planning and Analysis (SPA).

• Annual Revenues: $750k-$1M

• Staff: 9 Total, 6 Full Time Engineers

• Secret Facility Security Clearance

• Location: Lanham, Maryland (Washington DC Metro area)

Background

Fiber Optic Monitoring of Wind Turbines - Phase I SBIR -

Instrumented Blade System Concept

• Improve turbine blade reliability through an integrated monitoring system based on fiber Bragg grating sensors

• Predict blade deflections for real-time control to reduce stresses and avoid tower strikes

Phase I SBIR Objectives

• To analyze an existing turbine blade design (TPI CX-100) to determine sensor density and optimal sensor locations for deflection measurements

• Retrofit an existing blade with fiber optic sensors to measure flap bending

• Verify accurate strain measurements and shape prediction during quasi-static load to failure test

Bragg Grating Sensors

• Sensor operates by optically monitoring changes in the grating structure

• Localized, variable length (~ 1 cm)

• Multiplexible

• Sensitive to strain and temperature

P

Λ

CoreCladding

P

Reflected Transmitted

Broadband Source

P

e, T2x2 Coupler

Time Division Multiplexing (TDM)

• Multiplexing occurs based on sensor return time

• Low reflectivity FBG sensors

• Must have a minimum distance between FBG sensors to resolve individual sensors

#1 #2 #3 #n-1 #nPulsedSource Coupler Sensor Array

time

time

#1 #2 #3 #n-1 #n Interrogator

Wavelength Division Multiplexing (WDM)

• Optical filtering based on wavelength of sensors

• Number of sensors limited by channel spacing of WDM— Must consider overall wavelength shift response of sensors

#1 #2 #3 #n-1 #nSource Coupler Sensor Array

1530 1560Wavelength (nm)

Pow

er (a

.u.)

Determines Maximum Measurement Range

l1

l2

l3l4

l5

l8Spectrum Analyzer

Static Deflection Test• FBG sensor data taken throughout load

profiles— 0%-100% in 25% increments

— Above 100% until failure in 10% increments

• Blade failed at ~120% design load at root trailing edge

• All FBG sensors survived test — Low pressure (top) sensors recorded

greatly reduced strains

— Post-test inspection revealed poor epoxy adhesion for unknown reasons

— High pressure (bottom) sensors recorded accurate strains and were used for deflection processing

Static Deflection Results

-0.2

0

0.2

0.4

0.6

0.8

1

0 1 2 3 4 5 6 7 8 9 10

Distance Along Blade (m)

Def

lect

ion

(m)

25% Load50% Load75% Load100% Load120% Load25% Load50% Load75% Load100% Load120% Load

Maximum Error @ 120% Load: 2.4 cm or 3.5%Maximum Error @ 100% Load: 0.53 cm or 0.86%

FBG SensorFiberSplice ProtectorFurcation TubingConnectorFault Detector

Distance Along Blade (m)0.653 1.8 2.55

-1.147- -0.75-

-1934-1591-1428295,593Load 3

-1773-1458-1309500,000Load 2

-1611-1325-11901,010,000Load 1

FBG 3FBG 2FBG 1# Cycles

Fatigue Test Results

Sensor Blade Project

Project Objectives

• Replace retrofitted FBG strain sensors with integral sensors that are embedded in the blade

• To demonstrate the usefulness and robustness of the Micro Optics instrumentation as mounted in the rotating frame

• To demonstrate the accuracy of the tip deflection measurement during operational use

• To test the performance of commercially available strain and temperature sensor from Micron Optics

• To investigate data handling issues

Aither Sensor Layout

• Two arrays of 8 FBGs will be embedded in both HP and LP skins• Two additional redundant strain sensing arrays will be embedded

with the primary arrays• 3 temperature sensors will be retrofit on inside of skin surface

Trailing Edge

0.05 1.2 2.35 3.50 4.65 5.80 6.95 8.10

-1.15-

Distance Along Blade (m)

-1.15- -1.15- -1.15- -1.15- -1.15- -1.15-

Embedded Strain Sensors(8 in LP and HP skins)

Temperature Sensors (x3)

Embedded Sensor Location

• Optical fibers will be embedded in the SARTEX carbon/fiberglass hybrid material

• Six layers of SARTEX at root. Three layers end near center of blade. Three layers end near tip.

• Fiber will egress near the tip at a ply drop off• Fiber return to the root of the blade will occur underneath a single

layer of glass

SARTEX

Composite Sample Test

• 4 point bending samples created to test strain transfer in SARTEX material

• Excellent correlation between FBG and surface-mounted RSG

Aither Temperature Sensor Design

• Conventional ‘loose-tube’design

• FBG sensor will remain strain free inside of SS tube

• Individual sensors will be fusion spliced together to reduce power loss

• SS tubes will be bonded to inside of turbine blade surface after layup and curing

Micron Optics Confidential Slide 18

MICRON OPTICSCompany Profile

• Founded April 1990.• Based in Atlanta, GA.• Manufacturing Facility includes 24,000 sq.

ft. and multiple Clean Rooms.• Consistently won multiple annual US

National Research & Development Awards. • In-House Mirror Coating Operation for Filter

Development & Manufacturing.• Unique, Well-Developed, Seminal,

Core Component and Embedded Opto-Electronics Technology.

• 27 MOI Patents & 3 Trademarks Issued, Additional 5 MOI Patents Pending. Owner of another 32 Patent Licenses.

• 86 Journal and Conference Publications.• Financially Self-Supported.

• Founded April 1990.• Based in Atlanta, GA.• Manufacturing Facility includes 24,000 sq.

ft. and multiple Clean Rooms.• Consistently won multiple annual US

National Research & Development Awards. • In-House Mirror Coating Operation for Filter

Development & Manufacturing.• Unique, Well-Developed, Seminal,

Core Component and Embedded Opto-Electronics Technology.

• 27 MOI Patents & 3 Trademarks Issued, Additional 5 MOI Patents Pending. Owner of another 32 Patent Licenses.

• 86 Journal and Conference Publications.• Financially Self-Supported.

2006 Sales by Territory

54%

21%

25% USEuropeAsia

2006 Sales by Market

52%35%

13%SensingTelecomBioTech

Micron Optics Fiber Bragg Grating Sensor Layout

Fiber Bragg Grating Temperature Sensor (surface mounted) Micron Optics os4300 ( * ≡ optional)T

SS

TT

SS S SS

High Pressure (HP) Skin, Internal Surface

Low Pressure (LP) Skin, Internal SurfaceS

LE

TE

S S T T Te

Fiber Bragg Grating Temperature Sensor (surface mounted) Micron Optics os4200Te

TeSS T

SS S SSS S T T

S

*

* *

Fiber Bragg Grating Strain Gage Sensor (surface mounted)Micron Optics os3200 ( * ≡ optional)S

Micron Optics Fiber Optic Sensing Cable Layout

High Pressure (HP) Skin, Internal Surface

Low Pressure (LP) Skin, Internal Surface

Mounted on the interior surface of the HP skin, Micon Optics will have one fiber optic sensing cable terminating at 8.9-m.

Mounted on the interior surface of the LP skin, Micon Optics will have one fiber optic sensing cable terminating at 8.9-m.

LE

TE

Cable Diameter = 3.0 mm

Strain Gage to be Surface Mounted on Bladeos3200 - Dielectrically Packaged Design

Optical fiber inProtective braided jacket

FBG underneathInside protective groove

Protective plastic carrier& epoxy molding preform

FBGGroove

FiberBonding cavity

Fibergroove

Plastic carrier

Venting holes

Epoxy Filling hole

Top View

CrossSection

Adhesive Backing

Strain Gage to be Surface Mounted on Bladeos3200 - Dielectrically Packaged Design

Temperature Sensor to be Mounted on Blade Tipsos4200 – Temperature Sensor

• Operating temperature range -40 to 120 deg. C

• Temperature Coefficient 9.9 pm/deg. C (+\-10pm)

• Response time 0.3 seconds

• Long Term Accuracy +\-5 deg. C

Equipment to be Utilized in Blade Monitoring

• SP130 utilized to control the SM130 remotely enabling power saving, data logging and web serving capability.

• SM130 interrogates the FBG sensors. Available from 1 to 16 channels. Has a dynamic bandwidth of up to 2 Khz

SP130 Specifications

• SP130 has a 1.4 GHz Pentium, 512 MB DDR, a 100GB 2.5 inch HD and windows XP operating system.

• Peripheral interfaces include USB, Ethernet, RS232/422/485 and a user configurable digital I/O.

• Provides power management through wake-on-LAN and wake-on-clock functions.

• Small foot print, mounts directly onto the SM130.

SM130 Specifications

• 4 channels with a spectral width of 1510 to 1590 nm. Available from 1410 to 1590 nm.

• 1 khz scanning frequency, available to 2 khz.

• Wavelength repeatability 1pm@1khz, 0.05 pm with 1,000 averages.

• Power consumption 25 watts, 50 watts max.

• Operating temperature 0 to 50 degrees C.

• External triggering capability.

Data Acquisition Architecture

• Sandia’s Atlas data system to provide TTL trigger input, to SM130, to synchronize data sets.

• SP130 will host the software that will control the SM130.

• An Ad-Hoc wireless network between the laptop, located in the control room and the SP130 in the hub, will allow for the retrieval of data files through shared resources in the “Wind 2” workgroup.

• SP130 will be configured as a web server allowing for remote control of SM130 software.

Active X container in IE for remote control of SM130