Level Measurement the Easy Way – How Radar Measures Plastic, Concrete and Other Bulks

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The speed of propagation of the microwave pulse is dependent upon the surrounding dielectric. Since the microwave pulse propagates through the bulk solid at a slower rate than in air, the signal from the probe end appears to be coming from a greater distance when the silo is full. The higher the level climbs on the probe, the greater the distance the probe end signal seems to be coming from. Since, Vegaflex 82 knows its correct probe length and measures this shift, it can continuously determine the dielectric constant of the bulk material.

Particularly in bulk materials, the reflectivity (dielectric constant) of the medium is often very small. If the level echo itself is not detectable, the sensor automatically switches over to probe end tracking (indirect level measurement). It then measures the distance to the end of the probe and calculates the level using the most recently determined dielectric constant. If the level echo becomes visible again, the instrument switches back to the direct measurement mode.

With this method, the specific limits of guided radar are greatly extended. Plastic granules or powders with very low reflectivity (small dielectric constant) can be measured without restrictions. One example is PE or PP powder. Thanks to its probe end tracking function, Vegaflex 82 can take the initiative to continue the measurement.

Be Aware at All Times

This method is also applied when the medium is fluidized with compressed air, which generally takes place in the conical part of a silo. Due to the injection of air, the dielectric constant of the medium is considerably reduced. Standard instruments often simply drop out in these conditions and report that the container is empty. Other methods, such as ultrasonic measurement, also fail in this application due to the huge amounts of dust generated.

Vegaflex 82 acts quite differently, because it has the ability to determine the dielectric constant at all times. If the instrument loses the level signal in this area of the silo, it automatically switches to the indirect mode and measures the level down to the end of the probe. Since the dielectric constant is continuously detected, it can also be transmitted as an additional measurement and processed in the control system. This can be particularly useful as the dielectric constant is related to the moisture content of the bulk material, which allows the moisture content to be measured continuously as well.

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