Campbell Scientific ST350 Strain Transducer for Structural Testing - Manual (Page 15)

Section 5. Mounting of Sensor to
Various Surfaces
5.1 General
In most situations, other than reinforced concrete, the most efficient method of
mounting a transducer is using the tab/glue method. This method is the least
invasive and is truly a “non-destructive testing” technique. Below is an outline
for implementing the glue/tab technique. Tips and alternative mounting
techniques for different mounting surfaces can be found in the following
sections.
1. Place two tabs in mounting jig (if available, if not simply hold with vice
grips). Place transducer over mounts and tighten the 1/4-20 nuts until
tight. Be sure that the transducer calibration number is facing up. This
procedure allows the tabs to be mounted without putting stress on the
transducer itself.
2. Mark the centerline of the transducer location on the structure. Place
marks 1-1/2 inch on both sides of the centerline and using a grinder,
remove paint or scale from these areas. For steel structures, a power
grinder is recommended for the initial cleaning. If available, use a
portable grinder (a Makita Model 9500D battery-powered grinder with a
46-grit wheel works very well) to “touch up” the newly-cleaned surface.
If attaching to concrete, lightly grind the surface with the portable grinder
to remove any scale and remove dust with a shop rag or paint brush.
3. Using the portable grinder, very lightly grind the bottom of the transducer
tabs to remove any oxidation and/or other contaminants. Before
mounting, set the transducer in the location it is to be attached, and ensure
that the tabs seat uniformly on the member and that the transducer doesn’t
“rock”. This is important for a good bond.
4. Apply a thin line of adhesive to the bottom of each transducer tab (Loctite
410 Black Toughened Adhesive, Part # 41045 in 0.7oz containers)
about 1/4” wide. If bonding to concrete, slightly more adhesive is
necessary to allow some to flow out and around the tabs. Mount the
transducer in the marked location, and then pull it away. This action will
apply adhesive to the structural member at the tab locations.
5. Spray each adhesive contact area on the structural member (just one “light
shot”) with the adhesive accelerator (Loctite Tak Pak 7452, Part # 18637
in 0.7oz aerosol spray container).
6. Very quickly, mount transducer in its proper location and apply a light
force to the top of the tabs (not the center of the transducer) for
approximately 15-20 seconds.
If the above steps are followed, it should be possible to mount each
transducer in approximately five minutes.
5-1