LASER :
Measurement
of distance is fundamental to hundreds of industrial, defense, and consumer
needs. Of course, the measurement of level is a distance measurement.
With
ranges extended up to a mile or more or as short as small fractions of an inch,
they typically find applications in such disparate fields as collision
avoidance systems, military target ranging, tanker car load-out, truck
positioning, robotics, laser measuring tapes and industrial level control.
PSI's expertise and emphasis is level measurement, however, we can and
do address a wide range of laser applications.
To
accurately measure distance, the time required for light to make a round trip
between the measuring device and the object is measured. PSI offers two different laser measurement methods.
The right
choice for your application is dependent upon a variety of parameters.
The
simplest, conceptually, is the time-of-flight approach that measures the
elapsed time between when a short pulse of light leaves the instrument and when
the returning reflected or scattered pulse is detected.
Conceptually
more complex, but electronically simpler, is to measure the phase of a
modulated light beam when it leaves the instrument, and then compare that phase
to the phase of the return light.
VARIOUS LA SERS OFFERED
PRINCIPLES
OF OPERATION
There are three physical
properties of laser light that can be exploited in the measurement of distance:
Light travels in a
straight line. |
This
property makes feasible a variety of possible geometric methods for measuring
distance, most of which depend on some form of triangulation. These methods are
limited in that they require at least two spatially separate reference points.
Laser light is coherent. |
The use of
diffraction (destructive and constructive interference) of the light is an
excellent method for measuring very short distances (inches or less) with
sub-micron accuracy. The technique, however, is not easily usable for greater
distances.
Light propagates through space with a very well-known velocity. |
In principle, this offers an extremely accurate way to
determine distances of any required length. It is technically difficult,
though, to accurately time the departure/return of a light pulse traveling ~ 1
ft/ns. Resolution of 1/8 in., e.g., requires a temporal accuracy of
~ 10 ps.