Laser beta lasermike LS8000-3 - Manual (Page 21)

LaserSpeed 8000-3 Instruction Handbook
Installing the System
Part No. 93463 / Drawing No. 0921-01561 Page 21 of 221 Revision A (Sep 2007)
Aligning the Gauge
Once the gauge is mounted at the proper standoff distance, the critical
alignment angles need to be checked. To obtain accurate results, the LS8000-
3 must be mounted so the surface being measured is perpendicular to the
optical axis. The best method to ensure this is to place a level alongside the
gauge. The material being measured should be parallel to the front face of the
gauge and the material motion should be parallel to the base of the gauge.
The velocity measurement, which is made in the plane of the two laser beams,
is the rate at which the material passes the fringes of the beams. When the
motion of the material is perpendicular to the fringes, the velocity
measurement is considered calibrated. If the fringes are at an angle to the
motion of the material (angular rotation), measurement errors occur. The
measured velocity equals the actual velocity multiplied by the cosine of the
angle by which the alignment deviates from the direction of material
movement.
Three types of misalignment are possible. Two of the three are responsible for
measurement errors: rotation about the optical axis and tilt in the plane of the
beams. The errors are proportional to the sine of the misalignment angle.
Misalignment will always make the gauge measure velocities and lengths that
are too low.