Micron Optics os3610 User manual

I n s t a l l a t i o n G u i d e | R e v . A
Surface Mount Strain Sensor | os3610
Micron Optics Inc.
1852 Century Place NE
Atlanta, GA 30345 USA
phone [phone]
fax [phone]
www.micronoptics.com

Long Gage Strain Sensor | os3610
C o p y r i g h t © 2 0 1 2 M i c r o n O p t i c s , I n c .
o s 3 6 1 0 I n s t a l l a t i o n G u i d e , R e v i s i o n A 2
Introduction:
The os3610 Surface Mount Strain Sensor measures average strain over the length of the sensor
while providing integrated temperature compensation. It is based on fiber Bragg grating (FBG)
technology. The os3610 is intended exclusively for surface mounting. Each end of an os3610 is
attached to a structure via rigid brackets that are either welded, bolted, epoxied, or grouted to the
surface of a concrete, rock, steel, composite, or other structure. The os3610 strain sensor
measures the relative movement of the two mounting brackets along the axis of the sensor. It is
important that the mounting brackets be securely attached to the surface to be tested if accurate
results are to be obtained. Several installation tools are available from Micron Optics to aid in
installation. Note that tools are available for Grout-in and Bolt-on applications of gage length
25.4 cm and 100 cm.
Installation Tools:
Grout-in Drill Guide (25.4 cm)
Grout-in Drill Guide (100 cm)
Bolt-on Drill Guide (25.4 cm)
Bolt-on Drill Guide (100 cm)
Setting Bar (25.4 cm)
Setting Bar (100 cm)
Mounting To Steel (Weldable Brackets):
The first step in installing the os3610 strain sensor is welding the two mounting brackets to the
surface to be measured. The end brackets are made of 316 stainless steel. Each mounting bracket
has two ¼-20 set screws installed as shown in Figure 1. Use a 1/8 inch Hex-Key to tighten set
screws.
Figure 1 –Mounting Bracket
It is important that mounting brackets are properly spaced and axially aligned prior to welding. If
axial alignment is not maintained, the sensor may bind leading to reduced sensor accuracy. The
setting bar shown in Figure 2 is used to hold the mounting brackets in alignment and properly

Long Gage Strain Sensor | os3610
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spaced during welding. The Setting Bar has flats cut into each end that properly position the end
brackets.
Figure 2 –os3610 Setting Bar
The Setting Bar is inserted in both mounting bracket and held in place with the set screws shown
in Figure 3.
Figure 3 –Close up of mounting bracket & Setting Bar
The steel surface should be cleaned to remove scale, rust, dirt, and oil. Position the Setting Bar
with the attached mounting brackets on the steel surface to be measured. Align the axis of the
Setting Bar with the axis of strain to be measured. While holding the mounting brackets firmly
against the surface, weld the edges shown in Figure 4 in the indicated sequence.

Long Gage Strain Sensor | os3610
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Figure 4 –Weld Location / Sequence
Allow the weld to cool and remove the Setting Bar. Clean off welding slag and inspect weld.
Mounting To Steel (Bold-On Brackets):
An alternative mounting bracket shown in Figure 5 is available as an option that can be fastened
to the test specimen using two ¼-20 screws. Button head cap screws are recommended to allow
clearance for set screw Hex-Key. It is important that mounting brackets are properly spaced and
axially aligned prior to mounting. If axial alignment is not maintained, the sensor may bind
leading to reduced sensor accuracy. The Setting Bar shown in Figure 2 is available to hold the
mounting brackets in alignment and properly spaced while the mounting holes are transferred to
the specimen surface. The Setting Bar has flats cut into each end that properly position the end
brackets. Alternatively, the Bolt-on drill guide listed in the “Installation Tools” section can be
used. To use the Drill Guide, securely clamp it to the surface. Drill the four holes using the Drill
Guide to guide the drill bit. After both brackets are bolted securely to the surface, check the
alignment by verifying that the Setting Bar will drop into the brackets.
Figure 5 –Bolt-On Mounting Bracket
Mounting To Concrete:
The concrete mounting brackets shown in Figure 6 may be attached to concrete by inserting the
concrete mounting bracket stud into a drilled hole and securing with anchoring cement or epoxy.

Long Gage Strain Sensor | os3610
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Figure 6 –Concrete Mounting Bracket
Prepare the test surface by drilling two ½ inch [13mm] diameter holes properly spaced. To
maintain hole spacing and alignment it is necessary to use the Grout-in Drill Guide listed in the
“Installation Tools”section. The distance between the holes is determined by the gage length
purchased. The distance between the holes is equal to the gage length. Standard gage lengths are
25.4 cm and 100 cm. The holes should be a minimum of 3 ½ inches [64 mm] deep. To use the
Drill Guide, clamp it to the surface. Place hammer-drill in hole on one end of drill guide and drill
hole. Place 1/2 inch round bar through drill guide into hole just drilled. This will help hold Drill
Guide in place while second hole is drilled. Now Place hammer-drill in hole on other end of Drill
Guide and drill hole. Clean out holes with vacuum or compressed air. Attach the mounting
brackets to the Setting Bar as shown in Figure 3 to maintain proper alignment and spacing. Grout
the mounting bracket studs into place in the drilled holes using an anchoring cement or high
strength epoxy. Allow the grout or epoxy to cure before removing the Setting Bar.
Sensor Installation:
Once the mounting brackets are attached to the surface to be studied, the sensor may be set in
place and pre-tension adjusted. An interrogation unit attached to the sensor may be helpful in
adjusting pre-tension.
Notice that one end of the sensor has two windows cut into the steel tube (Active-end). The other
end has a hex crimp (Fixed-end). Set the sensor in place by placing by aligning the sensor flats
into the mounting brackets as shown in Figure 7.

Long Gage Strain Sensor | os3610
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Figure 7 –Mounted Sensor
Using a torque wrench fitted with a 1/8 hex key, torque the two set screws on the Fixed-end of
the sensor. Tighten the two screws to a torque of 75 inch-pounds [8.5 Nm]. The two set screws
on the Active-end of the sensor should remain loose.
Figure 8 –Sensor
Adjust pretension as required for the particular application. For example, if the application
requires the sensor to operate equally in tension and compression, the sensor should be installed
centered within its range. The pre-Strain can be visually adjusted by monitoring the two gaps
shown in Figure 9. The sensor can be centered or biased to one side of its range.
The sensor pretension and corresponding wavelength can be adjusted by gently grasping the
Active-end of the sensor and sliding it in the mounting bracket.
If desired, the sensor can also be connected to an interrogator and adjusted while observing the
interrogated wavelength. For example to center the sensor, adjust the Active-end until the
wavelength is halfway between the minimum and maximum wavelength value. The wavelength
should increase as the sensor is extended. The wavelength should decrease as the sensor is
compressed.

Long Gage Strain Sensor | os3610
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Figure 9 –Pre-Strain Adjustment
While holding the sensor in position, torque the remaining two set screws on the Active-end of
the sensor. Continue tightening the two screws to a torque of 75 inch-pounds [8.5 Nm].
Sensor Protection:
When installing a strain sensor it is important to consider how to insulate and physically protect
the sensor in order to improve the accuracy and longevity of the sensor. There are many ways to
insulate and protect a sensor depending on the particular installation. One method that may be
applicable to civil structures is detailed here. This method utilizes expanded polystyrene (EPS)
foam insulation and a stainless steel cover shown in Figure 10. These parts are available from
Micron Optics as an accessory.
Sensor Accessories:
os3610 Protective Cover and Insulation Kit (25.4 cm)
Universal Connector Protection Fitting “PF” Kit
This method may not be applicable to all installations due to size or other considerations;
however, the general principles demonstrated here can be adapted for the particular installation.
Figure 10 also shows a Non-metallic conduit and fitting. (Hubbell Part Numbers: G1050,
P050NGYA)
Figure 10 –Sensor Cover
Figure 11 show the EPS foam insulation that is part of the kit. The insulation is designed to
thermally insulate the sensor from the effects of wind and sun exposure. Notice the “stepped”

Long Gage Strain Sensor | os3610
C o p y r i g h t © 2 0 1 2 M i c r o n O p t i c s , I n c .
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interior of the foam insulator. The insulation is designed so that the fiber can be spliced and
excess fiber coiled and stored above the sensor.
Figure 11 –EPS Frame
Plan ahead and determine where the fiber will enter and exit the stainless steel cover shown in
Figure 13. The foam insulation can be cut with a knife as needed to provide fiber access. The
EPS foam insulation can be attached to a variety of surface materials using a silicone sealant
(such as 3M Super Silicone Sealant, Part No. 08663), or other compatible adhesive. Complete
the insulation assembly by attaching the EPS foam cover to the base using silicone sealant or
other compatible adhesive. The completed foam insulation is shown in Figure 12.
Figure 12 –EPS Lid

Long Gage Strain Sensor | os3610
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The kit also contains the stainless steel cover shown in Figure 13. This cover provides additional
protection to the sensor from weather and physical damage. Notice the cover is supplied with 4
knockout holes to provide a variety of fiber routing configurations. The knockout holes are .88
inch [22.4 mm] in diameter and will accept conduit fittings such as Hubbell Part Numbers
P050NGYA.
Figure 13 –Stainless Steel Cover

Long Gage Strain Sensor | os3610
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The drawings for the stainless steel cover and EPS insulation are provided for those preferring to
modify or provide their own covers.
Figure 14 –Cover Lid Drawing
Figure 15 –Cover Base Drawings

Long Gage Strain Sensor | os3610
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Figure 16 –Insulation Frame

Long Gage Strain Sensor | os3610
C o p y r i g h t © 2 0 1 2 M i c r o n O p t i c s , I n c .
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Figure 17 –Insulation Lid

Long Gage Strain Sensor | os3610
C o p y r i g h t © 2 0 1 2 M i c r o n O p t i c s , I n c .
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In addition to the sensor itself, the connector or splice on the end of the sensor cable also needs
to be protected from the elements. If the cable end is not protected, the cable could become a
path for moisture to enter the sensor. One method of protecting sensors supplied with FC/APC
connectors is to use the Universal Connector Protection Fitting “PF” Kit from Micron Optics.
The Kit shown in Figure 18 contains everything needed to protect an FC/APC connection.
Figure 18 –Universal Connector Protection Fitting