According to Vega, ultrasonic sensors and hydrostatic pressure transmitters are the primary devices used in water and sewage applications today. Radar, however, can offer considerable advantage over ultrasonics. For instance, measurement with radar is less affected by the influences of temperature, wind, fog or rain, and, due to their high sensitivity, most radar sensors can still detect water levels even under a thin layer of foam.
Winds of change in sewage measurement technology
For these reasons Vega has launched a new radar sensor especially developed for the areas of water and sewage. “Vegapuls WL 61 boasts high precision, is easy to use and is a real alternative to ultrasonic instruments when it comes to cost,” said Jürgen Skowaisa, product manager for radar and ultrasonics at Vega. “The price differential between ultrasonic and radar measurement technology used to be very high. Today, radar measurement technology is only slightly more expensive, so it is actually the better solution for these applications.”
The sensor has an accuracy of 2 mm over its measuring range that extends to 15 metres. Other decisive features include the plastic antenna with a diameter of 80 mm for good focusing characteristics, high protection rating of IP66/68 (1 bar) made possible by the moulded cable and robust housing, as well as the variety of mounting options for easy integration into existing infrastructure.
Application parameters have been optimised for the intended areas of use. “Users in this industry do not need parameters for application in large tanks or storage bins or for solvents as the measured medium. The new sensor therefore includes only applications such as pumping station, flow-rate measurement in open channels or similar applications typical of this sector,” explained Skowaisa. “Measurement data can be transmitted either directly to an existing control system, 4-20 mA, FF or Profibus PA, or via a suitable signal conditioning instrument. Linearisation curves can be stored in the sensor itself, to allow for example, direct indication of the flow in open channels.”
Reliable data despite difficult conditions
In flow-rate measurement in open channels, measurement errors can arise very quickly with ultrasonic sensors due to solar radiation on the transducer. According to Skowaisa, most users do not even realise that ultrasonic technology delivers inaccurate measuring results. “Users simply trust that the values stated in the manual are correct. But in reality, these only apply under ideal measuring conditions. Municipalities charge for the registered sewage quantities on the basis of these values. Radar technology gives them far more accurate measurement data, as it is completely independent of weather effects.”
To relieve the channel network and the sewage plant during heavy rains, the fast-rising water is collected in on-site pre-flooders and rain overflow basins and then forwarded to the sewage plant. Here, the user benefits greatly from the small mounting height of the sensor. “Radar technology knows no blocking distance, which means measurement can continue even with very high water levels.” said Skowaisa. “Even flooding is no problem because the sensors have a protection rating of IP68.”
Outlook
Sewage treatment will continue to be an important topic in the future, as it will always place new challenges on measurement technology. Meeting the requirements of the immensely different markets in this sector is in itself a challenge: in Germany, for example, spare parts and services for existing plants are mainly in demand, while in other countries, like China and Brazil, new sewage plants with communication systems based on the latest Fieldbus technology are being built almost daily. The approvals and norms in the individual countries are also quite different. “Future market requirements can be met quickly when one has a well-functioning core technology. Our radar based instruments will play a major role here in almost all cases,” concluded Skowaisa.
For more information contact John Groom, Vega Instruments SA, +27 (0)11 958 1901, [email protected], www.vega.com
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