Articles & Case Studies

ABB solves level measurement problem for wastewater plant

Posted: Monday 2nd April 2012

An ABB K-TEK LM200 laser level transmitter is helping a well-known wastewater plant return to reliable level measurement, after issues with a competitor’s hydrostatic level transmitter.

The company uses level measurement to activate pumps to a pre-treatment plant when the water reaches a pre-determined volume. Previous measurement techniques failed to cope with the amount of debris and grit present in the effluent, which clogged up sensors, causing inaccurate readings and making them difficult to re-calibrate.

The ABB K-TEK LM200 laser transmitter is ideal for this application and was purposefully designed for the measurement of dry bulk solids, opaque liquids, and slurries at distances of up to 200 feet. It features an advanced timing system and sophisticated, self-correcting signal processing function that allows it to accurately and reliably measure level, distance, and position in the harshest of conditions.

A key feature of the LM200 is its ability to work in the presence of dust, vapours, or turbulence. A rugged, powder coated aluminium enclosure, rated for IP65 or NEMA 4X, with CL II and III, Div 1 and 2, Gr E, F, G dust ignition proof ratings to FM and CSA, ensures operation in a variety of challenging environments. Stainless steel dust tubes prevent dust build-up and protect the optical lens from being coated.

Non-contact measurement technologies, such as ultrasonic and open air radar, have an inherent ‘beam spread’ nature (up to 24˚) and find it hard to deal with issues such as dust, vibration and constantly changing levels. However, the LM200 overcomes these by combining accurate, long distance laser measurements with no beam divergence (less than 0.2˚).

The system design allows the software to perform distance measurements quickly, dedicating more time for sophisticated signal processing, data analysis, and distance display. An intelligent ‘Last pulse’ capability means the LM200 can select true signals from among the many that are reflected from dust clouds, agitator blades, or other obstacles. Colour compensation corrects for weak or excessive return signals. Variable gain allows the LM200 to select the best return signal in quickly changing visibility conditions, such as dust, vapors, and materials of different colours.

The LM200 transmitter takes measurements using a laser with an extremely small wavelength of ~1 micrometer. As a result, the unit has virtually no angle divergence, even over long distances. It can be narrowly focused, ensuring that it does not pick up interference from surrounding objects. The system can also measure oblique angles with pinpoint accuracy. This allows it to operate within complex vessels, even if they contain internal structures.

The LM200 is also immune to reflections and echoes, thus providing consistent performance on solids and total immunity to “cone up” and “cone down” variations in the material being measured.

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