Operating Instructions
LMS500 Product Family
Product description
8013796/UL20/2010-09-27 © SICK AG · Division Auto Ident · Germany · Subject to change without notice 19
Chapter 3
Distance measurement
The LMS emits pulsed laser beams using a laser diode. If such a laser pulse is incident on
an object or a person, it is reflected at its surface. The reflection is detected in the laser
measurement system’s receiver using a photodiode.
Fig. 4: Principle of operation for pulse propagation time measurement
The distance to the object is calculated from the propagation time that the light requires
from emission to reception of the reflection at the sensor. This principle of “pulse
propagation time measurement” is used by radar systems in a similar manner (see also
section 3.7.4 “Measured value output for a 5-echo reflected pulse” on page 29).
Direction measurement
The emitted laser beams are deflected using a mirror and scan the surroundings in a
circular manner. The measurements are triggered at regular angular steps using an angular
encoder.
The LMS scans with a scanning frequency of 25, 35, 50, 75 or 100 Hz. During this process,
a laser pulse and therefore a measurement is triggered after an angular step of 0.167°,
0.25°, 0.33°, 0.5°, 0.66° or 1°.
Influences of object surfaces on the measurement
The signal received from a perfectly diffuse reflecting white surface corresponds to the
definition of a remission of 100%. As a result of this definition, the remissions for surfaces
that reflect the light bundled (mirrored surfaces, reflectors), are more than 100%.
Fig. 5: Reflection of the laser beam at the surface of an object
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