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

OAK RIDGE NATIONAL LABORATORYU. S. DEPARTMENT OF ENERGY

Fiber Optic Strain Gages

8-17-06


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


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)


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.


Path forward:

Qualify FISO gages at LN temperature Test Coil C5 with FISO gages Specify instrumentation for all other coils


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


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 thesame 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 ,


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-2000-2 10639, Deccmbrr 2000.

Influenced by EMI at Cryo


Prior work done on FISO gages at NASA - Down to -100 oC

20040000044 NASA Stennis Space Center, Bay Saint Louis, MS, USAExperimental Evaluation of White Light Fabry-Perot Interferometry Fiber-Optic Strain Gages when Measuring Small StrainsSt.Cyr, William; Figueroa, Fernando; VanDyke, David; McVay, Greg; Mitchell, Mark; January 10, 2002; 17 pp.; In EnglishContract(s)/Grant(s): NAS13-650Report No.(s): SE-2002-01-00001-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 2.4 - 11.2%, 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.


Prior work done on FISO gages at NASA (2) small deformations at -100 oC20040050782 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): NAS13-650

Report No.(s): SE-2003-12-00109-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.


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 1994. pp. 260-263.

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 1995. pp. 882-885.

“The ability of the fiber optic sensor system to survive in a cryogenic environment under high pressure has been demonstrated.”


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.


Cyclic strain test requires new fixture/chamber

Seal weld

tank

Fiber Optic Strain Gage

Data Acquistion

Wedge Grip

Cylindrical GRIP

1.5 in

Clevis

Clevis pin

Threded rod possibly with steps

MTS Fluid machine at ORNL Stress Lab


Qualify FISO gages - cost and scheduleFISO gage - test plan cost estimate

start finish labor hrs labor $materials

$ S/CPlanningprepare plan, cost est. 4-Aug-06 18-Aug-06 12 $1,800peer review 18-Aug-06 18-Aug-06 14 $2,450

ProcuringS/C for Jim Tsai 15-Aug-06 22-Aug-06 4 $700talk to FISO 18-Aug-06 25-Aug-06 8 $1,100specify/order gages 19-Aug-06 23-Aug-06 4 $400 $6,600buy special fixtures 1-Sep-06 15-Sep-06 4 $700 $2,500buy test coupons 23-Aug-06 30-Aug-06 4 $700 $2,000

LN2 Adhsesion testwrite test plan 21-Aug-06 28-Aug-06 8 $1,400design LN2 adhesion test 21-Aug-06 28-Aug-06 20 $3,200set up LN2 adhesion test 23-Aug-06 30-Aug-06 18 $2,550 $250perform LN2 adhesion tests 30-Aug-06 15-Sep-06 24 $3,600 $50write report 15-Sep-06 22-Sep-06 16 $2,800

Strain cycle testwrite test plan 18-Aug-06 25-Aug-06 8 $1,400design strain cycle test 11-Aug-06 1-Sep-06 48 $7,800set up strain test 1-Sep-06 22-Sep-06 32 $5,000 $250perform strain cycle test 22-Sep-06 13-Oct-06 24 $3,600 $50write report 13-Oct-06 20-Oct-06 18 $3,150

Total 266 $42,350 $11,700

contingency 40% $16,940 $4,680

Grand total $75,670


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


Proposed Instrumentation for C5 test

16 strain gages - FOS-N-BA-C1-F1-M2-RX-ST - $195 each

range of – 7 000 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.


Strain Gage InstallationStarin Gage # Shell Hole Number Side Location Measuring Direction

1 7 A winding pack Winding direction

2 7 A casting Winding direction

3 7 A winding pack Transverse direction


5 33 A casting Transverse direction

6 68 B winding pack Winding direction

7 68 B casting Winding direction

8 68 B winding pack Transverse direction

9 68 B casting Transverse direction

10 50 B casting Winding direction

11 50 B casting Transverse direction

12 50 B winding pack Winding direction



15 Near Leads Near A Casting Perpendicular to lead holes

21 Outer shell Near A Casting Perpendicular to outer flange

22 Outer shell Near B Casting Perpendicular to outer flange

16 7

17 7

18 68

19 68

20 42

Redunanat for gage # 7





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


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

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