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O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY Fiber Optic Strain Gages 8-17-06.

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Presentation on theme: "O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY Fiber Optic Strain Gages 8-17-06."— Presentation transcript:

1 O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY Fiber Optic Strain Gages

2 O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY Scope  What are we trying to do?  Test one coil to see if it behaves like the analysis says it should  Monitor all coils in operation to see if 1) they are behaving as expected during commissioning and 2) they are not degrading over time  Status  TRC and C1 tested, but strain data inscrutable. Other instr, such as deflect-o-meter, T/C, etc. ok  Problem  Find a reliable way to measure strain and/or deflection in operation

3 O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY Background  FISO gages used successfully on SNS, NSTX TF joint at or above room temperature  Fiber optic gages initially specified for NCSX because they solve known problems with resistance gages – mag field, noise, voltage isolation, etc.  FISO fiber optic gages purchased and glued to stainless sample and dipped in LN2, glue held  FISO gages glued to TF coil beam and tested at LN2 – gages initially worked, then 2 fell off (unknown cause), 1 stopped reading (due to wrong cable sheath material)

4 O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY Background (2)  FISO gages abandoned  EM canceling resistance strain gages used for TRC test, but results were not understandable and this was attributed to use of RTV gage coating  Subsequent tests performed with strain gages on stainless block in compression at LN2 temp, results appeared good  C1 coil test used strain gages, results inconclusive, problem attributed to magnetic field effects.

5 O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY Path forward:  Qualify FISO gages at LN temperature  Test Coil C5 with FISO gages  Specify instrumentation for all other coils

6 O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY Qualify Fiber Optic Gages at LN Temperature  Research FISO gage applications  Buy new FISO gages  Perform adhesion tests at LN2 temps with variety of glues  Select glue system  Perform cyclic strain tests at LN2 temp on sst

7 O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY What is a Fiber Optic Strain Gage?  There are several types of fiber-optic strain gages, two of which comprise the majority of commercially available strain sensors. The most popular manufacturing method produces the Fabry-Perot strain sensor with the second most popular type being the Bragg-grating strain sensor.  The Fabry-Perot interferometer type of sensor uses a phase difference or “shift” between reference and sensing reflections of the fibers for making strain measurements  FISO gages under consideration are Fabry-Perot type Definition: These sensors consist of a multimode optical fiber that transports white light, with the sensing element at the tip. The sensing element is defined by a micro capillary tube that holds the end of the fiber close to another small piece of the same fiber, leaving a cavity in between. The fiber-ends that define the cavity are deposited with mirrors, so that the white light entering the cavity is reflected, and hence frequency- modulated in accordance to this length. When the sensor is bonded to a surface, the length of the cavity in the micro capillary expands or contracts exactly by the same amount of strain experienced by the surface,

8 O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY How do they compare to foil gages? For Traditional Foil gages Fiber Optic Strain Gages Advantages over conventional electrical strain gauges: Immunity to electromagnetic interference Immunity to leakage-to-ground problems No inaccuracies associated with long, multiple, signal lead requirements Reference: Hare, David A., and Moore, Thomas C., “Chamcleristics of Extrinsic Fabry-Perot Inlerfcromc1”nc (EFPI) Fiber-optic Slnin Gages,” NASAKP , Deccmbrr Influenced by EMI at Cryo

9 O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY Prior work done on FISO gages at NASA - Down to -100 o C NASA Stennis Space Center, Bay Saint Louis, MS, USA Experimental Evaluation of White Light Fabry-Perot Interferometry Fiber-Optic Strain Gages when Measuring Small Strains St.Cyr, William; Figueroa, Fernando; VanDyke, David; McVay, Greg; Mitchell, Mark; January 10, 2002; 17 pp.; In English Contract(s)/Grant(s): NAS Report No.(s): SE SSC; No Copyright; Avail: CASI; A03, Hardcopy An experimental study was conducted to evaluate whether fiber optic strain gages (FOSG) are ‘better’ sensors than typical foil gages. A particularly attractive feature of FOSG was their specified resolution of 0.01% of full-scale (0.1 micro strain for 1000 micro strain full-scale). This feature would make FOSG practical tank level sensors, by measuring very small strains on the support structure of a tank. A specific application in mind was to measure liquid oxygen tank level, with support beams that were predicted to contract approximately 11 micro strain as the tank goes from empty to full. Among various fiber optic technologies currently available, Fabry-Perot Interferometry using white light was selected. This technology exhibits highly desirable feature such as absolute strain measurement, linearity over its full-scale, and temperature compensation. However, experiment results suggest that the resolution is 0.8 micro strain, at best, calibration from one sensor to another can be off by %, and that temperature compensation is not fully predictable, with errors of up to 3.5 micro strain over an11C range. Hence, when compared with classic foil gages, FOSG possess less accuracy, similar resolution and repeatability (precision), and superior linearity over their entire operating range. They are immune to EMI and their signals suffer minimal degradation over long distances. It is also expected that drift with time will be minimal in FOSG whereas the gage factor of foil sensors changes over time when exposed to varying environmental conditions. In conclusion, FOSG are ‘better’ than foil gages as long as the application allows calibration of individual units as installed for operation.

10 O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY Prior work done on FISO gages at NASA (2) small deformations at -100 o C NASA Stennis Space Center, Bay Saint Louis, MS, USA Fiber-Optic Strain-Gage Tank Level Measurement System for Cryogenic Propellants Figueroa, Fernando; Mitchell, Mark; Langford, Lester; May 18, 2004; 5 pp.; In English Contract(s)/Grant(s): NAS Report No.(s): SE SSC; No Copyright; Avail: CASI; A01, Hardcopy Measurement of tank level, particularly for cryogenic propellants, has proven to be a difficult problem. Current methods based on differential pressure, capacitance sensors, temperature sensors, etc.; do not provide sufficiently accurate or robust measurements, especially at run time. These methods are designed to measure tank-level, but when the fluids are in supercritical state, the liquid-gas interface disappears. Furthermore, there is a need for a non-intrusive measurement system; that is, the sensors should not require tank modifications and/or disturb the fluids. This paper describes a simple, but effective method to determine propellant mass by measuring very small deformations of the structure supporting the tank. Results of a laboratory study to validate the method, and experimental data from a deployed system are presented. A comparison with an existing differential pressure sensor shows that the strain gage system provides a much better quality signal across all regimes during an engine test. Experimental results also show that the use of fiber optic strain gages (FOSG) over classic foil strain gages extends the operation time (before the system becomes uncalibrated), and increases accuracy. Finally, a procedure is defined whereby measurements from the FOSG mounted on the tank supporting structure are compensated using measurements of a FOSG mounted on a reference plate and temperature measurements of the structure. Results describing the performance of a deployed system that measures tank level during propulsion tests are included.

11 O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY Fiber Optic strain gage worked for S/C accel. magnet  1994 and 1995 papers  LBNL accelerator magnet  CTD-101 and Stycast 2850 FT adhesive  Reliable results  No mention of gage de-bonding  Are continuing attempts to contact authors J.M. van Oort and H.H.J. ten Kate. "A fiber optics sensor for strain and StRSs measurements m superconducting accelerator magnets," IEEE Transactions on Magnetics. Vol. 30. No. 4. July pp J.M. van Oort and H.H.J. ten Kate and Ronald Scanlan. "A Fiber-Optic Strain Measurement and Quech Loacalization System for Use in Superconducting Accelerator Magnets," IEEE Transactions on Applied Superconductivity. Vol. 5. No. 2. June pp “The ability of the fiber optic sensor system to survive in a cryogenic environment under high pressure has been demonstrated.”

12 O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY LN2 adhesion test includes several glue types and applied strain  Glue must be room temp cure, elevated temperature cure is not practical  Stycast 2850 FT is primary candidate, UV cured glue from FISO, and others as identified from literature.  Gages applied to thin strip and put in bending at LN2 temp.

13 O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY Cyclic strain test requires new fixture/chamber MTS Fluid machine at ORNL Stress Lab

14 O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY Qualify FISO gages - cost and schedule

15 O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY C5 test  Repeat of C1 test, but:  FISO strain gages instead of resistance gages  Some FISO temp. gages in addition to T/C  Dial indicator for deflect-o-meter with digital output  Better temperature control in cryostat  Modified base support to provide known deflection constraints

16 O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY Proposed Instrumentation for C5 test  16 strain gages - FOS-N-BA-C1-F1-M2- RX-ST - $195 each  range of – to 3000 µε at – 200 C: extra $100 per gage to get +- 5,000 µε  2 Veloce boxes – VEL-MOD-50 – $38,000 each OR 2 BUS-MOD – $26,000 each  2 Veloce rack mount chassis – VEL CHA – $1995 each  VELOCE System channel modules, up to 8 channels; Upgradeable on number of channels with sliding modules.

17 O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY Strain Gage Installation  16 gages read at a time  Eliminate all winding pack gages due to potential glue adhesive problems  12 on casting (two new gages installed away form tee/windings on outer surface of casting.  4 redundant gages  Numbering is listed the same as before in this table

18 O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY Cost/benefit of A,B coil tests  TRC and Coil C1 tests showed that the thermal and gross deflection of the coils match the analytical models to first order  Tests of Type A and B would add only second order information, we think, with costs of:  Analysis  Cryostat and buswork mods  Coil setup and testing costs  Intermediate option: 15 ka test at room temp would still require analysis but cold check answers at 1/6 max strain


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