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Radar Level Measurement

Reliable Radar Level Measurement under Harsh Conditions Thanks to 80-GHz Sensors

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Turbulence and Inlet Tubes Make Measurement More Difficult

In the flotation tank, the level of the flotation liquid containing the enriched material has to be precisely measured. However, this is far from easy because of the harsh environment and the internal components of the tank. The medium is fed into the flotation tank through pipes from different directions. These pipes cause extreme turbulence and water splashing inside the tank. An older radar sensor with a transmission frequency of 26 GHz, which was installed there a few years ago, always had problems. For example, it displayed the built-in pipes as the level, which was totally incorrect.

Another difficulty was the accumulation of dust and debris on the antenna, which resulted in false readings again and again. Although radar technology is a non-contact measuring method and therefore ideal for dirty environments, the sensor no longer worked optimally because of these extreme ambient conditions. Due to the resulting signal attenuation and interfering reflections, the measuring point could only be kept in operation through constant servicing.

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80-GHz Technology Brings Stable Measurement

Last spring, when the first 80-GHz radar level sensor for liquids was introduced to the market, Vega’s South African subsidiary quickly suggested replacing the existing technology with the new Vegapuls 64. The previous 26 GHz sensor, with its 80 mm antenna, had a beam angle of 10°. It was mainly the narrower beam angle of Vegapuls 64, only 3°, that promised a solution to the problems caused by the inlet pipes. This considerably tighter focusing of the radar beam made it possible to better distinguish the actual measurement signal from the interference signals.

The new radar sensor also has significant advantages because of its higher dynamic range of 120 dB. What is more, Vegapuls 64 provides higher accuracy, reproducibility and reliability in general within the application.

The measuring process itself is completely independent of process conditions, which is one of the greatest advantages of radar technology. Varying temperatures and pressures affect the measuring results just as little as the properties of the liquid to be measured, e.g. density or viscosity. This is important, especially in the inhospitable temperatures that prevail in the diamond mine. Vegapuls 64 measures under pressures from -1 bar to +20 bar and process temperatures between -40 °C and +200 °C.

Despite the considerably shorter wavelength of the 80-GHz sensor, it is hardly affected at all by deposits or condensation. This is achieved mainly through special signal processing in the area close to the sensor. The distance-dependent dynamic adaptation reduces the effects of interference directly in front of the antenna system and at the same time allows a very high signal sensitivity at a greater distance. The measuring distance can be up to 30 m and measurement accuracy still remains at ±2 mm.

Problems in the Mud Bath?

None whatsoever! Besides the exceptional stability of its measuring signal, the radar sensor is also characterized by mechanical robustness, i.e. it is virtually wear and maintenance free. Even if the sensor has to be freed of large quantities of mud now and then, the process can go on unhindered. Cleaning is fast and uncomplicated.

A Real Godsend for the Mine

Conclusion: The extraction and processing of diamond ore definitely has nothing to do with the glittery glamor world where the diamonds later make their grand appearance. The environment in the mine is harsh and forbidding. But what really matters here is the efficiency of the process. For the mine operators, the very idea that a process would have to be interrupted just because of a defective measuring instrument is unacceptable. They are keenly aware that most of the mining and extraction processes are interconnected and depend heavily on each other.

The first 80-GHz radar measuring instrument for liquids proved to be a real godsend for the mine. Everything in the flotation tank has been running smoothly since Vega­puls 64 was installed.

Why is the application in diamond mining interesting for the chemical industry? Read an interview with Jürgen Skowaisa, Product Manager Radar at Vega, on the next page.

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