E-Zine June 2011
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The laser beam travels from the sensor to the material and back. The beam can be attenuated in transit due a number of phenomena, including optical attenuation caused by nature of the vapors in the beam path, and dust/dirt in the beam path to/from the material. Note that the presence of dust/dirt in the path can be temporary, such as when filling occurs and causes a dust cloud to form in the path of the beam.
The surface of the material can cause the intensity of the reflected laser beam to degrade when it exhibits poor reflective qualities, such as when the material itself or contaminants cause the laser beam to reflect poorly.
In addition, accuracy can be degraded based upon the surface on which the laser beam is reflected. For example, the laser beam may measure the top of a layer of foam by reflecting off the top of the foam. If the foam is transparent to the laser energy, the beam may reflect from the foam/liquid interface and measure the liquid level. Translucent foam might cause the level measurement to represent a location within the foam. Further, the foam conditions may vary over time and cause erratic level measurements,
Many laser level measurement sensors utilize Class 1 lasers that do not generally pose a hazard under normal operating conditions. Other sensors use Class 3 lasers that can pose a risk of eye injury when viewed with the naked eye for more than a moment.
Laser level measurement sensors can be used for sanitary applications where the laser beam enters and leaves the vessel via a sight glass.
Excerpted from The Consumer Guide to Non-Contact Level Gauges