Laser Level Measurement Technology in IndustryLaser Level Measurement Technology in Industry

October 23, 2014

4 Min Read
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Today, laser products are managing bulk solids applications across the mining, power, food and beverage, pulp and paper, petrochemical, and chemicals industries. Typical applications include level sensing and control in bins or silos, positioning of conveyors/tripper cars, height control, level control in crushers or shredders, movement detection, anti-collision of overhead cranes, block chute detection, and positioning of machinery. These level measurement instruments serve a broad range of companies in the mining, power generation, manufacturing, and many other industries.
    The laser (light amplification by stimulated emission of radiation) was a remarkable technical breakthrough, but in its early years it was something of a technology without a purpose. Almost immediately, though, engineers began to find uses for it. Among them were the military weapons laser rangefinder and land surveying. From these early developments the current laser level measurement technology emerged.
    Laser technology in level/positioning measurement brings a number of unique advantages to the table. First, its short wavelength results in a narrow beam (approximately 5-cm diam) with extremely low divergence (<0,5°). This enables the instrument to measure accurately into silo cones or chutes, to see through narrow openings in protective grids, and to be completely unaffected by obstacles close to or moving in its area of operation. It is also unaffected by electrical noise, wind, pressure or temperature fluctuations. Laser instruments measure distance off any surface, from black coal to brown wood chips to reflective plastics, at any angle, and with no false echoes.
    The non-contact laser level transmitters can easily measure distances up to 60 ft on coal and up to 500 ft on positioning applications using a reflector plate. Some other type of lasers having enhanced optics can read at least 100 ft on coal and up to 1312 ft on positioning applications using a reflector plate. The instruments give a reading in centimeters or inches through a 4-20 mA output and are accurate within 25 mm across the measuring range and are rated as Class 3R and are completely safe.
    The laser level transmitter on-board microprocessor calculates distance by multiplying the speed of light by the time it takes for a laser pulse to travel from the instrument to a target and back. The measuring laser uses invisible, infrared light. There is a second, visible aiming laser to help with the alignment of the measuring laser. The laser beams have little divergence so that accurate targeting is easy even in silos or vessels that have internal structures.
    Using a time-of-flight calculation, and knowing the height of the vessel, the laser level instrument accurately measures the distance to the target surface using the equation below:

    The unique characteristics of laser light give the laser level instrument significant performance advantages over other technologies. The narrow, long-range beam can measure both near and far distances while the optical wavelength makes it easy to evaluate applications. If you can see the surface clearly, the laser can measure the level.
    In applications where dust may be present (even in small quantities) a dust tube accessory can be used. The dust tube is a simple and effective device, designed to prevent dust settling on the lenses by creating a static airspace. When abundant dust is present the dust tube can additionally be purged with dry oil free air to further reduce any dust settling on the lens.
    The laser level technology is a plug-and-play instrument. The user-friendly menu makes for a quick setup on commissioning through a handheld programmer or laptop. It requires no calibration or special configuration. The laser pointer provides precise alignment and a number of mounting options providing accurate, fast, reliable level and positioning measurement.
    Christian Vallieres is director of sales for the laser level & volume products at ABB Measurement Products Business Unit. He joined ABB eight years ago, holding a position as business development manager in the space division. He has more than 18 years of experience in related electro-optical technologies, has a BS degree in Mechanical Engineering from the University of Quebec in Canada, and is the co-author of several scientific papers on remote sensing and hyper-spectral technologies.

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