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ROCTEST FOS Series Manual

Sensoptic fiber-optic sensors fabry perot strain gauge
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I
M
NSTRUCTION
ANUAL
SENSOPTIC FIBER-OPTIC SENSORS
FABRY PEROT STRAIN GAUGE
FOS Series
 Roctest Limited, 2000. All rights reserved.
This product should be installed and operated only by qualified personnel. Its misuse is potentially dangerous. The Company makes no
warranty as to the information furnished in this manual and assumes no liability for damages resulting from the installation or use of this
product. The information herein is subject to change without notification.
Tel.: 1.450.465.1113 • 1.877.ROCTEST (Canada, USA) • 33.1.64.06.40.80 (France) • 41.91.610.1800 (Switzerland)
www.roctest.com
E10190-000816

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Summary of Contents for ROCTEST FOS Series

  • Page 1 The information herein is subject to change without notification. Tel.: 1.450.465.1113 • 1.877.ROCTEST (Canada, USA) • 33.1.64.06.40.80 (France) • 41.91.610.1800 (Switzerland) www.roctest.com...

  • Page 2: Table Of Contents

    TABLE OF CONTENTS PRODUCT ....................... 1 Introduction ....................... 1 Description ......................1 Specifications ....................3 INSTALLATION ....................... 4 Gauge installation ..................... 4 2.1.1 Metal surface preparation................5 2.1.2 Bonding method ..................6 2.1.3 Rebar installation ..................11 2.1.4 Installation of sensors with composite laminates on concrete structures .. 11 Mating gauges to the readout unit ..............

  • Page 3: Product

    The FOS can be surface-mounted on a variety of materials including steel, concrete and composite materials using suitable industrial quality adhesives. The gauge is intended for long-term, precise strain measurements and can be read by all ROCTEST's fiber-optic readout units which displays readings directly in units of microstrains (see separate instruction manual for operation of the readout unit).
  • Page 4 E10190-000816 Figure 1 Fabry-Perot strain gauge schematic principle Page 2...

  • Page 5: Specifications

    Minus 55°C to +350°C; operating temperature is fiber- optic cable dependent EMI/RFI susceptibility: Intrinsic immunity Combatibility:: All ROCTEST's fiber-optic readout units and data loggers Cable length: 1.5 meter length. Custom length up to 5 km available Gauge dimensions: 310 microns diameter Fiber-Optic Cable: 4.0 mm O.D.

  • Page 6: Installation

    E10190-000816 2 INSTALLATION 2.1 GAUGE INSTALLATION The steps for bonding the fiber optic strain gauges depend upon the adhesive used. Epoxy and ceramic adhesives and even metal arc spraying can be used to bond gauges. As with conventional strain gauges, high residual compression strains occur when adhesives are heat cured at elevated temperatures.

  • Page 7: Metal Surface Preparation

    E10190-000816  Cotton tipped applicators (Cotton Swabs);  Waterproof tape (Aquaseal);  Nitrile and butyl rubber sealants;  M-Coat Protective Coating (from Measurements Group) - Optional. Note: The manufacturer can provide a complete Gauge Installation Kit which includes the adhesive with all the accessories and products mentioned above.

  • Page 8: Bonding Method

    E10190-000816 400-grit silicon-carbide paper. Rewet the surface with Conditioner A (or the equivalent compound) and scrub with cotton tipped applicators until a clean applicator is no longer discolored by the scrubbing. Remove the residue and Conditioner by slowly wiping through the gauge area with clean Kimwipes. The final step is to apply a liberal amount of M-Prep Neutralizer 5A from Micro- Measurements to the gauge area.
  • Page 9 E10190-000816 With a flashbreaker or an electrical tape, create a channel into which the fiber sensor will be installed. The width of this channel must be approximately 2 mm. 2 mm Place the gauge between the channel of electrical tape and hold it in place by applying tape ("scotch"...
  • Page 10 E10190-000816 The incoming optical fiber must be secured on the specimen with a very small drop (less than 1 mm) of 5-minutes epoxy about 3 mm away from the micro capillary. To ensure that the 5-minutes epoxy will not flow to the micro-capillary, we recommend letting the epoxy cure slightly before applying it on the fiber in order to increase viscosity.
  • Page 11 E10190-000816 DON'T AE-10 epoxy Risk of air bubbles Side view Side view Immediately after applying the adhesive, a Mylar or high temperature adhesive tape (a "scotch" tape may also be used if curing temperature is low) may be installed over the adhesive in the gauge sensitive region in order to keep the gauge in good contact with the specimen.
  • Page 12 E10190-000816 After curing you may apply 5-minutes epoxy (if the gauge is used at low temperature) over the remaining unprotected optical fiber up to the fiber jacket. Then use electrical tape to attach the fiber-optic cable to the structure. You may also apply a protective coating like the M-Coat Protective Coating (from Measurements Group) over the adhesive for improved protection against chemical attack, moisture, etc.

  • Page 13: Rebar Installation

    E10190-000816 2.1.3 REBAR INSTALLATION To install instrumented rebar into a new structure as part of the reinforcement cage, a portion of the surface of rebar 70-80 mm long should be milled flat. This forms a perfect surface on which to bond a sensor and the installation procedure is the same as described in section 2.1.2.
  • Page 14 E10190-000816 2. Primer application A primer should be applied in order to increase the strength of concrete surface and improve bounding. Different types of primers can be used (CAPHARD E30, EPOTHERM, …). 3. Putty application If the concrete surface has not been sanded, it is recommended to apply putty to smooth pores and gaps on the concrete surface.

  • Page 15: Mating Gauges To The Readout Unit

    Kimwipes. The input connectors of ROCTEST's fiber-optic readouts unit must be clean as well. Use the specially designed 2.5 mm mini foam swab for cleaning the input connectors of your readout unit.

  • Page 16: Data Readings And Analysis

    Initial length of the Fabry-Perot cavity, in nanometers Total strain measurement, in strains Total strain  Total strain  is the raw strain obtained directly from FOS readings with all ROCTEST's fiber-optic readout units after the gauge factor has been defined in readout memory and selected.
  • Page 17 16 m/m/°C for steel. The  expansion factor can be known from laboratory test. Numerical example: 2200.2 units, initial reading of FOS with the ROCTEST's fiber-optic readout unit 2407.8 units, current reading of FOS with ROCTEST's fiber-optic readout unit 20.2°C, initial temperature reading 26.2°C, current temperature reading...

  • Page 18: Miscellaneous

    E10190-000816       135.6 microstrains 207 6 26 2 20 2 Note: Positive values of  represent tensile strains and negative values represent compressive strains. 4 MISCELLANEOUS 4.1 CONVERSION FACTORS To Convert From Multiply By Microns Inches 3.94E-05 LENGTH...

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