How 80 GHz radar overcomes level measurement challenges in high dust environments

Don Horne   

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This is the third in a series of articles on level management. The entire handbook of level articles can be downloaded here.
Dust, with its infinitesimal size, is disproportionately problematic. A speck of dust is tiny – one-half to one micrometre in diameter on average. And yet, these little particles cause big problems for level measurement instrumentation. Thick dust clouds and buildup have historically prevented level measurement technologies from providing reliable and accurate measurements.
The mining and building materials industries understand these problems all too well because these industries deal with a disproportionate amount of high dust environments. Fortunately, level measurement instrumentation has evolved, and operations willing to adapt to newer technologies like 80 GHz radar are thriving with more efficient processes, less downtime, and higher throughputs.
Modern radar sensors like the VEGAPULS 69, which use an 80 GHz transmission frequency, deliver enhanced focus, higher sensitivity, and smarter electronics that can read through the dust and buildup. This enables users to make measurements in tight spaces, and users receive accurate continuous level measurements, even during fill cycles.
Seeing through the dust
From the crushers at the beginning of their process to the storage silos near the end, mines and quarries have clouds of dust and buildup everywhere. These two factors have made it challenging for level measurement technologies to work effectively and reliably, and that alone has impeded efficiency.
Crushers are loud, dusty machines, so they’ve always been a challenge to measure level in this application. The crusher is typically one of the first steps in the process, and without a level measurement to optimize its operation, it becomes an immediate bottleneck from the start.

The VEGAPULS 69 is an 80 GHz radar sensor specifically designed for the measurement of bulk solids.

Elsewhere, storage silos holding fine particles like cement or lime powder experience many of the same issues. These tall, narrow structures are often filled pneumatically, so the inside looks like a hazy cloud of dust. Without an accurate continuous level measurement here, it’s impossible to know if these vessels are being used to their full capacity.
Initially, level measurements in these applications were made manually. A person kept a watchful eye on the crusher, and another would climb to the top of every silo and look inside. These methods are labor-intensive and inefficient. A lot of downtime is spent waiting for dust to settle just to get a visual. In lieu of waiting, crushers and silos became underutilized and underfilled, and on occasion, too much material would choke the crusher and spill out of silos. Both scenarios require lengthy maintenance, cleanup, and unexpected downtime.
Mechanical contact measurement sensors could see through the dust in storage silos, but it came at the cost of additional maintenance and regular replacements. Then, users are left without a level measurement and additional labor to repair or replace a sensor. Contact sensors were never an option in crushers because of falling product and moving parts. A non-contact solution was needed that could withstand the dust, buildup, and noise.
Non-contact for no mess and longer service life
When non-contact level measurement technologies like ultrasonic transmitters and radar sensors hit the market, there were significant improvements. Sensors could see through a little bit of dust, and they could withstand buildup for longer. Both technologies operate using a similar principle: a signal travels through the air, bounces off the surface of the product being measured and back to the sensor, and the sensor electronics use the time of flight to calculate distance and output a level measurement. Their differences, however, are why 80 GHz radar has become the go-to level measurement technology, especially in high-dust environments.
Ultrasonics use sound waves to make a measurement. Sound waves are mechanical and require a medium – in this case, air – to transmit energy from one place to another. Dust in the air dampens sound waves, interrupts their transmission, mechanically prevents their propagation, and makes level detection nearly impossible. And in the crusher, loud noises can add to the interference. For measuring level during filling, an ultrasonic device won’t do, and users should turn to radar.
All radar level measurement sensors emit electromagnetic radio waves that are unaffected by dust or noise. Unlike sound waves, a radar signal’s transmission or propagation is not inhibited by dust. In fact, it has no effect on any radar sensor, regardless of transmission frequency. This is due to wavelength. Dust particles are about 1,000 times too small to be detected radar sensors with the shortest wavelength on the market – 80 GHz radars. This means radar can accurately measure level during fill cycles when dust is rampant. This is a major advantage for any automated process.
Even though both technologies are non-contact, dust and dirt eventually build up on the face of ultrasonic transmitters and inside the horn of low-frequency radars. Buildup on an ultrasonic transmitter results in a weaker or lost signal relatively quickly, so these sensors need to be cleaned regularly. For radar, the buildup is a slower process as condensation inside the horn attachment glues and cements dust particles into place until a signal can no longer penetrate the solid block of buildup inside. The workaround – build a radar that doesn’t need a horn attachment.
80 GHz radar brings focus and accuracy
Radar beam angle is a matter of antenna size and frequency; they’re inversely proportional. As antenna size or frequency increases, the beam angle decreases. Low-frequency radars get around this by using large antennas or horn attachments to focus the radar signal into a smaller area. With the development of high-frequency 80 GHz radar sensors, users can achieve a narrow focus without the need for a large process connection or a horn attachment.
A radar signal with a better focus enables users to get a precise measurement in a small space. This feature is crucial in crushers and in the narrow silos holding fine powders. Plus, with more of the signal in a confined spot, users will see a larger return signal, giving them a clearer picture of exactly where their level measurement truly is. With the VEGAPULS 69, the improved signal is compounded by the radar sensor’s higher sensitivity.

Radar sensors using a higher 80 GHz frequency have better focus, which helps to provide a more accurate level measurement.

Despite better focusing and improved sensitivity, the 80 GHz VEGAPULS 69 is able to ignore any potential buildup that’s so common in these high dust environments. Smart electronics within the sensor can differentiate between product being measured and any buildup on the face of the sensor. And without a horn attachment, there’s never a chance for excessive buildup to block the signal all together.
Choosing 80 GHz for high dust environments
In high dust environments, visibility and buildup are the two biggest challenges level measurement instrumentation faces. Users have a wide range of technologies to choose from, but the forward-thinking operators who see their level measurement instrumentation as an investment in the efficiency of their entire process will know 80 GHz radar is the right choice. With exceptional focus, improved sensitivity, and intelligent electronics, high-frequency 80 GHz radar sensors like the VEGAPULS 69 are the only sensors that can see through the dust and buildup.

Author: Luis Santiago, Mining and Aggregates Industry Manager, VEGA Americas

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