Over three decades, radar level transmitters have become an accepted form of non-contact measurement in the process industry.
The use of the radar level transmitter for the process industry started back in 1991. These were extremely large units and operated with a 6 GHz frequency. The units were sold generally into liquid applications and were only ever considered when no other technology would work. Each unit weighed in at several kilograms and operated only from an air conditioning supply.
In 1997, VEGA released the world’s first true loop-powered radar level transmitter. The company was able to offer a more suitable transmitter for typical process applications but once again it had its limitations. By 1999, a 26 GHz radar level transmitter was released, offering a smaller unit with a reduced antenna size and a narrower beam angle (a downside to lower frequencies is the larger beam angle).
VEGA continued to develop and improve radar level transmitter performances through the first decade of 2000. The main changes were in the software, an area where, thanks to customer feedback, the parameters for set-up were improved and much more descriptive and user-friendly.
As with all developments, a point is reached where the components and physics of the technology are maximised. At this stage, VEGA commenced research on the 80 GHz frequency range. This frequency was not new to the market as it was – and still is – quite common in the automotive industry with reversing sensors.
During the research and development of this frequency, VEGA carried out numerous real life customer trials and the results of these opened up many more opportunities for the use of the radar that had never been practical before. It also allowed for the first time for antenna sizing and adaptation to many typical process fittings that exist in industry. One of the things to note about radar frequencies is that as you increase the frequency the antenna size and the beam angle reduce.
Radar level transmitters work on the reflection of the signal from the product being measured and the strength of that returned signal is based in the dielectric constant (conductivity). As a result, applications with a relatively low DK value radar in the past were considered to be not suitable. The 80 GHz transmitters now allowed these measurements to take place but, of course, there are other considerations. As well as the high frequency, you also need quality components that provide very good sensitivity or dynamic range, as it is commonly known.
Typically, up to this point, radar level transmitters had a dynamic range of around 90 decibels (dB) – at least until the VEGAPULS 64 (liquids) and the VEGAPULS 69 (solids) were developed. VEGA now manufactured a radar level transmitter with a dynamic range of 120 dB. So what does this mean, given that with audio for every increase of 3 dB, you get a doubling of the power? An increase of 30 dB over previous and existing radar frequencies achieved an increase of more than 1000 times in the sensitivity of the VEGA 80 GHz radar level transmitters. For this increase, VEGA transmitters were now able to measure extremely low DK products such as plastics.
Radar level transmitters, like all instruments, have their limitations, many of which are determined by the physics of the technology. It is very important to take into account not just the frequency but all the data when evaluating whether a transmitter is suitable for the application. At VEGA, 80 GHz has proven to be a large step forward in solving difficult applications but the company has developed a model for liquid applications and a model for solids applications, as you need different algorithms for the types of process medium.
Radar level transmitters are now a very accepted form of non-contact level measurement and the use of these units has increased many times over in the past decade. However, as with all developments, it has not finished yet and VEGA will continue to improve the transmitters so that in the near future we can again break the barriers faced previously and open up the opportunities for radar to solve more and more applications.
Source: VEGA Australia