SENSORS
Detecting the invisible When an MDF manufacturer needed a sensor that could accurately output the level of a silo containing wood flour or wood flakes, VEGA Australia’s Jim Curnow, was confident that the VEGAPULS69 Radar Level Transmitter could handle the job. WOOD FLOUR IS THE VERY FINE wood or particle-board dust that is used to supplement natural gas burners. Wood flakes are further separated into wood fines or wood core to make particleboard. The fines make the particleboard surface while the coarser flakes make the particleboard core. All of these products are stored in separate silos ranging from nine to 30 metres. As part of the manufacturing process D&R Henderson, a particleboard producer, stored the very light, very dry powder in a 21-metre silo. However, it ran into a problem. Because wood flour is so light, fluffy and dry the traditional methods of measuring
the level just simply didn’t work. Sheeshendra Deo, Electrical Manager at D&R Henderson says finding a sensor fit for the job was a process of trial and error. The company first tried using an ultrasonic sensor, which emits acoustic pulses to detect the level in a vessel. The light nature of the wood flour meant the pulse was being absorbed, which made the readings unreliable. On top of this, the ultrasonic sensor was affected by the airborne dust, further attenuating the signal. “We tried a lot of sensors that just didn’t work,” he says. “The material had an extremely low dielectric, which meant it was a poor conductor of electric current.” “Our product is also very dry. Normally these sensors depend on having some moisture there to find an accurate reading.” Jim Curnow, a Business Development Manager at VEGA Australia says radar
The VEGAPULS69 has a dynamic range of 120 decibels and can get a much better return signal from a low dielectric material.
24 І Australian Bulk Handling Review: September/October 2021
systems need at least some conductivity to work. “The wood flour had such a low dielectric, it was basically invisible to the sensor,” he says. The company tried several sensors, but none of them were able to accurately detect the material. One potential solution was to install load cells, but that would be prohibitively expensive and could be affected by the wind and other factors. Attaining an accurate reading in the silo was vital for D&R Henderson. If the company didn’t know how much wood flour it had, it could lead to lost production while refilling the silo. Since the product supplements natural gas in the burners (which run the wood dryers), the gas cost can be huge. Eventually, the manufacturer began testing the VEGAPULS 69, one of VEGA’s most advanced radar sensors. Wood flour was one of the materials VEGA claimed it could accurately measure. Curnow says the 80 gigahertz radar
D&R Henderson stored the very light, very dry powder in a 21-metre silo.
