General-purpose laser measurement device

Level Measurement & Control

May 2007 Level Measurement & Control

The popular LM80 Lasermeter from Laser Measurement is a general-purpose level measuring instrument that has been used in hundreds of different applications ranging from straightforward silo monitoring to high-speed crusher control. Like many competitive products the LM80 takes readings at a single point on the surface of the material of interest, however the narrow beam produced by its measuring laser guarantees that the location of this measuring point is clearly defined. Such direct aiming ensures that readings remain reliable and stable even in narrow vessels with restricted access or in silos where measurements all the way down to the exit chute are important.

The recent introduction of multipoint measuring systems, such as the LM150S also from LaserM, now gives customers a choice of three different types of level information. Firstly, 'silo monitoring' describes a range of applications for which a slow, periodic measurement of the level is sufficient. The types of silo for which this approach is applicable are filled and emptied slowly and often have large dimensions. In this case the long-range capability (25 m) and adjustable update rate of the LM80 make it an ideal choice.

The second category of level measurement involves some form of 'control'. This is used when vessels are small in size, can fill or empty quickly and the level information forms part of a control loop (to a feeder conveyor) or an emergency shut off system. Again the LM80 is an ideal choice because the output can be set to update rapidly (12 times per second) and post-processing filters ensure a clean and smoothed control signal.

These two categories of single point measurement give a useful indication of 'how full' a silo is. This has historically been termed the 'level' of the material in the vessel. However, it is well known that the material surface is seldom flat so this 'fullness' value is only indicative of how much material is actually present. Any slope or coning of the material produces errors when the level is compared to the volume.

The third category of level control information is 'volumetric' measurement. Advances in laser technology now make it possible to create three-dimensional maps of the convoluted material surface from which an accurate volume can be calculated. This multipoint information is used for stock control in either small or large vessels but can only be applied when the material is static ie no filling or emptying takes place during the measurement cycle.

Given these three alternatives, the single point measurements made by the LM80 are ideally suited to most process control and basic silo monitoring applications.

For more information contact Natalie Suter, Laser Measurement, +27 (0)11 314 4130, [email protected], www.laserm.co.za

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Level Measurement & Control

General-purpose laser measurement device

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