Fiber Optic Sensors:

Transcription

1 Fiber Optic Sensors: Providing Cost-Effective Solutions To Industry Needs Jeffrey D. Muhs Oak Ridge National Laboratory November 2002

2 Properties That Can Be Sensed Using Fiber Optics Acceleration Chemicals/Gases Color Displacement Flow Force Humidity Liquid Level Magnetic/Electric Fields Moisture Motion Position (linear, angular) Pressure (fluid, gas, etc.) Proximity Radiation Sound Speed State-of-Cure Strain Surface Condition Tactile Sensing Temperature Velocity Vibration Viscosity Weight

3 How Does A Fiber Optic Sensor Work? In a fiber optic sensor, one or more of the following characteristics of a propagating lightware is altered and correlated to an externally-induced physical or chemical parameter: Intensity Phase Frequency (color) Polarization state Time-of-flight Modal cross talk

4 Types Of Fiber Optic Sensors Intrinsic Sensors The fiber itself acts as the sensing medium, i.e., the propagating light never leaves the fiber and is altered in some way by an external phenomenon. Extrinsic Sensors The fiber merely acts as a light delivery and collection system, i.e., the propagating light leaves the fiber, is altered in some way, and is collected by the same (or another) fiber.

5 Why Are Some Optic Sensors Becoming So Popular? Small/lightweight Allow access into normally inaccessible areas (often embedded) Passive (non-electrical) In Some Cases, Fiber Optic Sensors Are Also: Inexpensive Rugged/reliable Easy to install Highly sensitive Accurate over a wide dynamic range Resistant to ionizing radiation Capable of being multiplexed Capable of distributed measurements

6 What Are Some Expressed Concerns About Fiber Optic Sensors? New technology Cost Fragility Ingress/Egress difficulty Often have a nonlinear output Complexity Reliability The bottom line is FO sensors vary widely in their composition (glass plastic, rubber), sensitivity, dynamic range, size, shape, etc., each offering different value propositions

7 Issues Relating To Embedded Fiber Optic Sensors Pros Embedded rather than attached Sensitivity/dynamic range Durability In Some Cases Size Cons Connectivity Difficulty in fabrication In Some Cases Strength degradation Size Cost

8 Ex. #1: The Fabry-Perot Fiber Optic Sensor

9 Design of Fabry-Perot strain sensor Fiso, Inc. sensor: see

10 Fabry Perot strain sensors attached to a section of pipe

11 Metal canister instrumented with Fabry Perot strain gauges attached

12 Strain levels on the order of a few microstrain can be easily recorded in time periods of just a few microseconds Microstrain LE1 F2 01 (08-09) post-processed [*normalized] Time (s) p-p (08)* p-p (09)* LE TP LE TP

13 FO Patch Panel Example fiber optic Fabry Perot module and oscilloscope arrangement Veloce Modules

14 Ex. #2: Fiber Optic Bragg Grating Temperature And Strain Sensors

15 Fiber Optic Bragg Grating Sensors Pros Multipoint in-line measurement capability High sensitivity Low-cost sensors Small / lightweight Linear response Cons Sensitive to more than one parameter Require relatively expensive processing equipment

16 Ex. # 3: Fiber Optic Optical Time Domain Reflectometry (OTDR)

17 Optical Time-Domain Reflectometer - Based Strain Monitoring System Mooring rope with integrated polymeric optical fiber containing reflective interfaces.

18 Summary Thoughts Fiber optics is emerging as a mainstream sensor technology capable of measuring numerous physical parameters Care must be taken to match a specific FO sensor technology with a particular application In just the past few yrs. adv. signal processing techniques have made highly sensitive COTS FO sensors a viable option in many applications Embedding fibers can be difficult.. but very rewarding New low-cost sources, detectors, and processing hardware and industry maturity are making FO sensors more costeffective Sensor multiplexing is an attractive value proposition Don t limit yourself to just one type of FO sensor technology