by Gregory Tischler, Product Manager, VEGA Americas
For years, radar sensors have had a bad reputation for powder level measurement. Frankly, radar earned that bad rap. While the technology has always worked brilliantly with coal, grains, and plastic pellets, it was never compatible with powders for a variety of reasons including size and chemical composition. Users who tried to make radar sensors work because they are low-maintenance, long-lasting, and durable in difficult conditions ended up disappointed. If radar technology were a restaurant, powders users would drive by its parking lot without a second look. But now is the time for users to give radar another try.
Modern sensors with 80 GHz transmission frequency have put radar technology back on the menu as it concerns measuring the level of powders. This paper will examine how increasing the frequency makes radar viable in powders applications, and discuss advantages radar has always had over other level technologies.
Particle size is no longer a problem
Radar sensors were always a good fit for measuring the level of plastic pellets, but there was a time in the not-too-distant past when radar level measurement was a non-starter for fine powders.
80 GHz radar sensors emit higher-energy, 3.5-4.0 mm microwaves that can detect particles smaller than one millimeter in diameter. The rake’s teeth are closer together, so contacting a lone fertilizer pellet is easier than ever. High-frequency radar sensors with large dynamic range (more on that to come) are now a proven level solution in plastic powder applications.
Any dielectric will do
While available for years, large dynamic range came at a prohibitive cost. It made no financial sense for instrumentation manufacturers to double the cost of sensors to narrowly expand the application scope for users. That expanded scope is now easy to achieve at a reasonable price. The most sensitive radar sensors on the market have a dynamic range of 120 dB, five times greater than that of its 26 GHz predecessors. These sensors can measure virtually any product, no matter how low the dielectric constant. This is quite a paradigm shift; as dK value used to be the most important question when determine whether or not a radar sensor will work. Now, the dielectric value of a powder doesn’t determine if radar will work, but rather which radar will work.
Non-contact instruments have longer service life
Non-contact instruments, including radar and ultrasonic sensors, maximize user investment. They may be more expensive on the front end, but the initial cost is negated by reduced (and in most cases, eliminated) maintenance costs and a longer service life. With the ability to set and forget the level measurement, plant operators can allocate more resources to improving overall process efficiency. When buildup encroaches upon a radar antenna, its presence is neutralized in modern sensors that include software that filters out close-range signals. For longer sensor life and accuracy through buildup, there is no better investment than a non-contact level sensor.
Radar is not disturbed by dust
Radar sensors emit electromagnetic radio waves that are unaffected by dust. Unlike with sound waves, dust does not inhibit a radar signal’s transmission or its propagation. In fact, it has no effect on any radar sensor, regardless of transmission frequency. This is due to wavelength. The diameter of dust particles is in the 0.5-to-1.0-micrometer range. 80 GHz radar sensors have the shortest wavelength on the market, and dust is about 1,000 times too small to affect these waves as they travel through the airspace. This means that inside an industrial plant, radar can accurately measure the level of bulk solids and powders when dust is rampant and/or during a filling cycle. This is a major advantage in automated processes.
Anyone who invested in a radar sensor to measure powder, only to have the sensor fail has every right to hesitate to try it again. But 80 GHz transmission frequency changes everything. These sensors have the wavelength to detect smaller particles and the dynamic range to measure weak signals from low-dielectric products. Plus, all of radar’s established strengths apply. Non-contact measurement extends a sensor’s life and the presence of dust has no bearing on measurement accuracy. It’s time to reconsider radar level measurement for powder storage and handling.
As radar sensor transmission frequency has increased, wavelength has decreased, allowing for more accurate measurement of small particles.
Gregory Tischler is a Product Manager at VEGA Americas responsible for radar and guided wave radar sensors. He has almost 20 years of experience in the Industrial Automation industry, all with VEGA Americas. He is a voting member of the ASME-BPE Process Instrumentation subcommittee responsible for writing instrumentation standards for Bioprocessing Equipment, and he was also an active member of the MCAA committee that was responsible for shaping new FCC rules for Tank Level Probing Radars (Section 15.256) that was released at the beginning of 2014. Learn more about VEGA radar sensors at vega.com/radar.