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Technews Industry Guide - IIoT 2018

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Through-air radar for level measurement
June 2018, Level Measurement & Control


Radar is one of the most common level measurement technologies in the instrumentation market. Whether measuring liquids or solids, from chemical plants to wastewater facilities to ready-mix cement manufacturers, radar provides accurate, reliable level measurement without ongoing maintenance and frequent recalibration. Radar sensors are not only a trusted means of pinpoint level control, they are easy to use as well.

Radio microwaves are transmitted by the antenna system of the sensor to the measured product, reflected by the product surface, and received by the antenna system. The microwaves travel through the air, hence the label, through-air radar. The time of flight from emission to reception of the signals is proportional to the distance to the product surface. The longer the time of flight, the greater the distance. This distance is inversely proportional to the level in the tank. The greater the distance, the lower the level.

Many parameters determine the strength of the signal returned to a radar sensor. An agitated, turbulent surface will affect signal strength, as will distance to the product surface. Even normal process conditions like build-up on the antenna system may influence a return signal. Signal strength also depends partially on chemical composition, as not every product reflects microwaves equally.

Conductive products reflect almost all microwave energy and non- conductive products reflect only a portion of the energy. Non-conductive products with low dielectric constant, oil for instance, produce weaker signals than those with high dielectric constant, like water. The range of signals a radar sensor can detect is called its dynamic range.

The focus of the microwave beam depends on a radar transmitter’s antenna size and its transmission frequency. The smaller the antenna, the wider and less focused the beam. The larger the antenna, the more focused the beam. This is why the development of liquid level sensors operating at 80 GHz transmission frequency was such enormous news in process automation.

VEGA has seen the practical benefits of 80 GHz level sensors, the VEGAPULS 64 and VEGAPULS 69, in over 70 000 installations worldwide per year. In containers and silos with many internal installations, enhanced focusing helps reduce the influence of noise created by microwave energy reflecting back to the antenna from something other than the product surface. Noise is commonplace in vessels with agitators, baffles, or heating coils, and it is sometimes created by the walls of the vessel itself. Noise is a problem because it distorts level measurement, but it can be overcome.

The most obvious advantage to using a through-air radar sensor is that it is a non-contact level measurement that requires less maintenance due to a lack of moving parts and a lack of contact with corrosive product. Through-air radar sensors are unaffected by fluctuating product properties or by changing process conditions such as temperature, pressure or intense dust generation because they use radio waves to make a measurement. Few process variables can disturb the flight of a radio wave, making through-air radar sensors a reliable option for level measurement.

Radar level transmitters are used for non-contact level measurement of liquids and bulk solids, even under high pressure and extreme temperatures. They can be used in simple as well as in aggressive liquids and are suitable for applications with stringent hygiene requirements. Radar level sensors measure light as well as heavy bulk solids with absolute reliability, even in the presence of dust and noise, without being affected by build-up or condensation.

Through-air radar has tremendous capabilities and offers many benefits to users. However, through-air radar is not a level measurement panacea; it is not applicable for use with every product. In applications with rampant, heavy foam, radar is sometimes not the right solution because microwaves can be absorbed right into the foam. Another limitation is that in order to use radar for level, a user must have a connection at the top of the tank. The connection can be small, but it has to be present. Through-air radar is a great fit for the vast majority of applications, even those with foam, but not all of them. Users should discuss the specifics of their level application with their instrument providers before choosing a technology.

Through-air radar instruments are more focused than ever before, making them a reliable option in vessels with obstructions or applications that require isolation valves. Some instrumentation manufacturers are pairing this hyper-focus with incredible sensitivity and intelligent software so that users can measure non-conductive products and suppress noise from false signals. High transmission frequency sensors have made antenna sizes smaller than ever, so retrofitting and mounting are less costly and less burdensome than ever before. Any users who have shied away from radar in the past should rethink their position; any users relying on an older radar sensor should consider an upgrade. The instruments are just that good.

More information contact Chantal Groom, VEGA Controls SA, +12 (0)11 795 3249, chantal.groom@vega.com, www.vega.com


Credit(s)
Supplied By: VEGA Controls SA
Tel: +27 11 795 3249
Fax: +27 11 795 2422
Email: info.za@vega.com
www: www.vega.com
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Further reading:

  • Contents measurement in silos
    January 2019, Morton Controls, Level Measurement & Control
    Each industry provides its own challenges with regard to accurate process control. In the mining and metal processing industry, accurate level measurement is a challenge due to the increased volume of ...
  • A wavelength for all situations
    January 2019, Endress+Hauser, Level Measurement & Control
    113 GHz: the best fitting radar frequency for every level application.
  • SIL2 for UWT’s rotating paddle ­series
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    The terms ‘functional safety’ and ‘safety integrity level’ (SIL) have occurred more frequently since the publication of the international standard IEC 61508/IEC61511. Particularly in systems with hazard-causing ...
  • Level measurement is becoming more sophisticated
    October 2018, KROHNE, Level Measurement & Control
    Since radar was developed and deployed during WW II, its use has expanded enormously. As technology advances, these uses are also advancing. For example, radar technology is used in the motor industry ...
  • VEGA launches VIS in South Africa
    September 2018, VEGA Controls SA, News
    VEGA Controls SA announced the local launch of the VEGA Inventory System (VIS) at a function held at Montecasino on 24 July. With VIS, VEGA combines its expertise in level measurement technology with ...
  • The right wavelength
    September 2018, Endress+Hauser, Level Measurement & Control
    113 GHz: the best fitting radar frequency for every level application.
  • SIL2 for rotating paddle level switch
    September 2018, Morton Controls, Level Measurement & Control
    The terms functional safety and safety integrity level (SIL) have occurred more frequently since the publication of the international standard IEC 61508/IEC 61511. Particularly in systems with hazard-causing ...
  • Pushing the pulper towards maximum efficiency
    August 2018, VEGA Controls SA, Level Measurement & Control
    Non-contact measuring methods have become well established in the paper industry.
  • Reliable wastewater treatment
    July 2018, Siemens Digital Factory & Process Indust. & Drives, Level Measurement & Control
    To update and optimise its wastewater disposal system, the authorities of the City of Edmonton in Alberta, Canada, opted to use level measurement technology from Siemens. Installing the Sitrans LUT400 ...
  • Slurry control valves for level control
    July 2018, eDART Group, Level Measurement & Control
    In order to improve the froth level control at a flotation concentrator in Rustenburg, eDART was recently commissioned to replace the froth level control valves on the secondary cleaner. Froth level ...
  • Enhanced pressure vessel level measurement
    May 2018, EOH Process Automation Solutions, Level Measurement & Control
    The traditional approach to level measurement in a pressurised vessel, such as a boiler, has been to use a conventional differential pressure (DP) transmitter with external water-filled ‘wet’ legs connecting ...
  • Reliable wastewater treatment with ultrasonic level controller
    April 2018, Siemens Digital Factory & Process Indust. & Drives, Level Measurement & Control
    To update and optimise its wastewater disposal system, the authorities of the City of Edmonton in Alberta, Canada, opted to use level measurement technology from Siemens. Installing the Sitrans LUT400 ...

 
 
         
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