MTS Series LX Laser Extensometer - Manual (Page 30)

LX Laser Extensometer
Mechanical Mounting
Installation 30
Mechanical Mounting
Proper installation of the unit is essential for best performance. It is important
that the instrument be solidly mounted on a flat surface and that the scanning
laser beam be properly positioned on the target; see
“Tripod Mounting Adapter”
on page 31. It is recommended that the laser extensometer be mounted on four
machined spacers 12.7 mm (0.500 in) diameter by 12.7 mm (0.500 in) long, with
1/4-20 bolts using the four threaded mounting holes located in the base of the
unit. The purpose of these spacers is to provide 4 solid contact areas between the
bottom of the Laser Extensometer and the mounting surface. The spacers and the
mounting surface must be fabricated using good machining practice such that,
with the mounting bolts loose, the laser extensometer rests flat contacting all 4
spacers simultaneously.
Choose the mounting location of the laser extensometer such that the specimen to
be measured ends up at the appropriate target distance from the instrument,
where target distance refers to the distance between the front panel of the laser
extensometer and the targeted surface of the specimen. Try to locate the LX500
so that a 304 mm (12 in) target distance results; for the LX1500, try for a target
distance of 381 mm (15 in). If this is not a practical distance for the intended
application, then choose another distance: for the LX500, 381 mm (15 in); for the
LX1500, 457 mm (18 in).
Important Calibration is a function of target distance, and the instrument must
be calibrated at the target distance (or distances) it will be operated
at. Contact factory for details.
Orient the laser extensometer so that the scan line is aligned parallel with the
specimen's axis of elongation; see
“Scan Line Orientation on Specimen” on page
32. It is important to position the laser extensometer properly with respect to the
specimen in order to avoid possible spurious reflections. These reflections
usually result from scanning orthogonally across a bright, shiny surface. This
happens in situations where the plane of the scan line is orthogonal to the plane
containing the surface of a shiny specimen. The presence of spurious reflections
is suspected when unstable or invalid readings occur. These reflections can
typically be eliminated by rotating the offending surface of the specimen a small
amount (
≈5° to 10°) about the axis of the scan line; see
“Scan Line Orientation on
Specimen” on page 32.