User Manual

11
• Aspect
The aspect of the target, or its orientation to the sensor, affects the
observable cross section and, therefore, the amount of returned signal
decreases as the aspect of the target varies from the normal.
• Reectivity
Reectivity characteristics of the target’s surface also affect the amount
of returned signal (How does the device work with reective surfaces?,
page 11).
In summary, a small target can be very difcult to detect if it is distant, poorly
reective, and its aspect is away from the normal. In such cases, the returned
signal strength may be improved by attaching infrared reectors to the target,
increasing the size of the target, modifying its aspect, or reducing distance
from the sensor.
How does the device work with reective surfaces?
Reective characteristics of an object’s surface can be divided into three
categories:
• Diffuse Reective
• Specular
• Retro-reective
Diffuse Reective Surfaces
Purely diffuse surfaces are found on materials that have a textured quality
that causes reected energy to disperse uniformly. This tendency results in a
relatively predictable percentage of the dispersed laser energy nding its way
back to the device. As a result, these materials tend to read very well.
Materials that fall into this category are paper, matte walls, and granite. It
is important to note that materials that t into this category due to observed
reection at visible light wavelengths may exhibit unexpected results in other
wavelengths. The near infrared range used by the device may detect them
as nearly identical. For example, a black sheet of paper may reect a nearly
identical percentage of the infrared signal back to the receiver as a white
sheet.
Specular Surfaces
Specular surfaces, are found on materials that have a smooth quality that
reect energy instead of dispersing it. It is difcult or impossible for the
device to recognize the distance of many specular surfaces. Reections
off of specular surfaces tend to reect with little dispersion which causes
the reected beam to remain small and, if not reected directly back to the
receiver, to miss the receiver altogether. The device may fail to detect a
specular object in front of it unless viewed from the normal.
Examples of specular surfaces are mirrors and glass viewed off-axis.
How does liquid affect the signal?
There are a few considerations to take into account if your application requires
measuring distances to, or within, liquid:
• Reectivity and other characteristics of the liquid itself
• Reectivity characteristics of particles suspended in the liquid
• Turbidity
• Refractive characteristics of the liquid
Reectivity of the liquid is important when measuring distance to the surface of
a liquid or if measuring through liquid to the bottom of a container (How does
the device work with reective surfaces?, page 11).
Measuring distance with the device depends on reected energy from the
transmitted signal being detected by the receiver in the sensor. For that
reason, the surface condition of the liquid may play an important role in
the overall reectivity and detectability of the liquid. In the case of a at,
highly reective liquid surface, the laser’s reected energy may not disperse
adequately to allow detection unless viewed from the normal. By contrast,
small surface ripples may create enough dispersion of the reected energy to
allow detection of the liquid without the need to position the sensor so that the
transmitted beam strikes the liquid’s surface from the normal.
Reectivity of suspended particles is a characteristic that may help or hinder,
depending on the application.
Turbidity, or the clarity of a liquid created by the presence or absence of
suspended particles, can similarly help or hinder measurement efforts. If
the application requires detecting the surface of the liquid, then suspended
particles may help by reecting more of the transmitted beam back to the
receiver, increasing detectability and permitting measurements to be taken.
Attempting to measure through suspended particles in a liquid will only be
successful if the transmitted beam is allowed to reect off of the desired target
without rst being absorbed or reected by the suspended particles.
When the near infrared energy transmitted by the device transitions from the
atmosphere to a liquid, the energy may be bent, or refracted, and absorbed
in addition to being dispersed. The degree to which the transmitted beam is
refracted and absorbed is dened by its refraction index. That being said, the
most important criteria impacting successful measurement through a liquid
is the amount of dispersion of the transmitted beam and whether any of the
dispersed beam makes its way back to the receiver on the device.
Electromagnetic energy travels slower through a liquid and may affect
accuracy of the nal measurement output.