Continuous level measurement between double filling: Optimum echo quality & dust-tight design make it possible
Many an inconspicuous component part can quickly become a problem if it does not function reliably. In the case of level monitoring, for example, cost-causing silo overfilling or running empty, which can result in a production standstill, are avoided. In order to integrate sensors perfectly into plants, the highest process compatibility is required for the individual production stages, as well as a certified design. For an animal feed producer in Chile, it should also be a non-contact measurement technology for the storage of powdered raw materials, which operates under high dust generation during the dynamic filling process.
When configuring a suitable sensor system for the plant operator, the focus was on process reliability, durability and simplicity. Furthermore, the requirements for the special installation situation had to be taken into account.
Continuous level measurement between double filling
Optimum echo quality & dust-tight design make it possible
Level sensors detect the exact level of a medium in real time. The user is thus informed at all times about the current, percentage content of the container, which optimizes processes in warehousing in particular and reduces costs. There are different technologies and measuring principles for continuous level measurement, which have their advantages and disadvantages depending on the application. For the selection, numerous process conditions have to be taken into account, which have to be mastered for the sensor technology. In addition, the requirements for installations in bulk solids differ from those in liquids.
When it came to content measurement, one of the largest manufacturers of animal feed products in Chile wanted to optimize its manufacturing process in several production facilities with a professional and modern solution in terms of precision and process reliability. The production process includes the manufacture of different types of feed for livestock and pets as well as the breeding sector. For various powdered basic materials, which are stored in silos for the production of the feed, a corresponding level monitoring system was configured on site together with UWT's partner Sensorica Industrial SpA.The measurement technology was to operate without contact and cope with the dynamic filling process via two filling lines. In the application area, a very dust-intensive atmosphere and process temperatures of up to 80°C prevail. Metal struts inside the containers, which can additionally complicate the installation and function of a level sensor, had to be taken into account.
For the 15 meter high storage silos, a precise measurement solution for continuous level measurement was implemented with the NivoRadar® NR 3000 radar sensor from UWT GmbH. Electromagnetic waves form the basis of level measurement with radar. A radar sensor emits a bundled electromagnetic wave that is reflected by objects as an echo and evaluated by the sensor. In addition to free-radiating radar sensors, the radar category also includes those based on guided microwave technology, which are referred to as guided radar, TDR (Time Domain Reflectometry) or also GWR (Guided Wave Radar) sensors. The fundamental difference between free-radiating and guided radar sensors is the way the electromagnetic waves reach the medium to be measured. While free-radiating radar sensors use special types of antennas to transmit the waves in the direction of the material without contact, guided radar sensors require a probe (rod or cable) as a waveguide along which the signal is guided to the medium. The probe is in contact with the medium.
Free-radiating radar sensors are generally characterized by their frequency, since this is important for non-contact level determination in process or storage vessels. Radar sensors with high frequencies can be built more compactly, have smaller radiation angles and better reflection properties, which ultimately leads to precise and reliable measurement results. Therefore, UWT's free-radiating radar sensors also work with 78 GHz technology. They are preferably used in storage processes and, due to their high sensitivity, can be used in almost all bulk materials and solids (be it powder, granulate, small and coarse-grained bulk material). For signal processing, Process Intelligence software is used, which has proven itself in numerous applications worldwide. A lens antenna focuses the high-frequency signal into a 4° narrow beam lobe, which allows use in narrow tall silos and greatly simplifies installation and alignment of the sensor.
This beam lobe of only 4° results in a diameter of the beam of only approx. 1 meter for the measurement of the feed meal at a distance of 15 meters. The ATEX ta (dust) certified sensor could be optimally placed and aligned to the silo discharge with the flexible adjustment flange. This also meant that the metal struts were not within the measuring range of the beam lobe. The high frequency of the sensor also provides an optimum echo quality in this very dusty application. The standard air purge device for the lens antenna has not yet had to be activated. (This air purge prevents material buildup on the lens antenna, which could cause a loss of energy in the transmitted signal). With the help of the local display, the sensor could be easily and quickly calibrated and put into operation. Easy-to-understand echo data informs the user about the status as well as the measurement reliability of the sensor.
By implementing the safe solution for continuous functional level measurement according to the high requirements and standards of the animal feed producer, smooth plant operation is optimally supported.