Robust level measurement you can build on.
The challenge was to find a system which can measure reliably even in this extremely dusty environment. Together with UWT a free-radiating continuous level measurement was configured. In addition to that a vibrating fork was installed for overfill protection within the truck transporters.
- Smart non-contact continuous radar determination
Due to the fast development of the building and quarry industry in many European countries during the past years, the demand for more solution approaches for applications of cement plants has increased. Solutions of appropriate sensor technology for content and point level measurement have to be found in order to support the process flow of the cement production in the most reliable way.
A manufacturer of concrete and plaster products for the building industry in Italy wanted to modernize his process flow with a redesign of the measuring equipment. Pre-dosed products are mainly offered, which are supposed to make life on the construction site easier. The manufacturer was amongst others looking for a reliable level measurement system for his new cement storage silos. The requirements for the sensor were not easy. The environment is very dusty and sticky and the surface of the cement is after filling or during emptying with a steep angle of repose.
When it comes to cement product storage the technology needs also to deal with moisture prone to clumping of sticky materials and low density and low dielectric constant. Further there occurs condensation in winter that might affect the measurement. There is a need for the equipment to be safe and reliable, with high availability, easy to install, no leakage, maintenance-free and certified.
Together with the local partner SMERI S.R.L the team from UWT Level Control thus tested by actual application conditions different technologies that have been already successfully applied in extremely dusty process environments. The configuration of measurement technology for the storage silos was finally made with the free-radiating radar sensor NivoRadar® NR 3100 that has to fit to the special installation demands. The measuring device has to cope with measuring distances up to 19 meters and DK values of 3 - 4. During filling processes there are extremely dusty, polluted environments. There were process temperatures of up to 80°C (176°F) with 0,8bar (11,6psi) pressure.
The 80 GHz technology of the radar sensor has a 4° narrow radar beam and guarantees a reliable level signal in the single chamber silos. Also during filling the reflection from the surface of the material has a high echo confidence.
Electromagnetic waves form the basis of level measurement with radar. A radar sensor emits a focused electromagnetic wave that is reflected by objects as an echo and is then 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 sensors 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, the chosen free-radiating radar sensors also work with 80 GHz technology.
The combination of a high dust generation and adhering material characteristic were no challenge for the radar transmitter as the air purge connection allows regular, cyclical cleaning of the lens antenna. The commissioning with the quick start wizard was simple and intuitive. That makes the NR 3100 the right choice of instruments in the cement storing application. The integrated aiming flange allowed the sensor to be perfectly aligned to the desired position on the roof of the silo.
- Universal voltage electronic and no calibration
Further the manufacturer looks for a reliable sensor to detect the max-level in several truck transporters. Despite the cement other different solids are filled in these tanks. It should be a robust sensor for this harsh environment with a dusty atmosphere and buildup.
Depending on these requirements, vibrating level limit switches are suggested as full, demand and empty detectors as they are especially suitable for use in sticky, fine media. The main component of the vibrating level limit switch is a piezo stack which is electrically excited and thereby vibrates. The design of this piezo stack largely defines the range of application. With the vibrating fork electronically stimulated piezos cause the fork to vibrate. As soon as the sensor is covered with material, the vibration is dampened and the resulting electrical current change causes the output signal to switch. Once the material level falls below the sensor, it is free to vibrate again and the output signal is reset.
The vibrating fork Vibranivo® VN 2020 was an ideal solution with high sensitivity regardless of dusty environment and limited installation space. The devices were equipped with an aluminum diecast housing and robust stainless steel extensions for a long-lasting precise point level measurement in the truck transporters. They have all required international approvals for use in hazardous locations (gas and dust). The switch is a plug and play sensor and was simple in installation and commissioning. It is equipped with universal voltage electronics and could be put into operation without calibration.
- Planning security with level visualization
The building material manufacturer additionally requested an economical and practical solution in the form of a central level-remote system. Background was to save unnecessary logistics costs caused by multiple deliveries and make the storage management more transparent and efficient through continuous level control, improved truck routing and detailed planning.
Therefore a level visualization system was connected. Because of the wide range of different level control solutions within the UWT NivoTec® series, it could be found a proper economical model for the plant. The level signals of the installed sensors were bundled by the visualization software combined with a Wago WebController. The information received was passed to the Internet using an Ethernet connection via a routed IP address. The plant could securely access this information (password-protected) via any internet browser at any time of the day over a pre-defined IP address). It is possible to include any number of other silos or tans in the visualization system - without additional hardware or costs. If the priority is to keep installation at the plant silos to a minimum a GSM modem can be used to remotely access the data. In this case for the data transmission no Ethernet connection is required, but only a SIM card in the WAGO to pass the modem. This modem collects all level signals and sends them in an encrypted log via mobile phone over the Internet to the appropriate controller.
The benefits of the whole system for the producer were besides the simplification of the material disposition processes leading to a reduction of costs, the installation of the system was straightforward and could be carried out by the plant own service engineers. Control cabinets only had to be set-up once; afterwards no additional IT support was necessary. All levels can be now visualized at the same time which leads to more material planning security and the material flow finally follows a standard process with much greater planning security. The system can be dismantled at one location and installed again at another without new costs.
Plant operators are busy keeping pace of the wide range of challenges presented by raw materials of the building sector, the changing operating conditions in silos or pipelines or the need for ex-certificates. Precise and robust continuous and point level measurement has to deal with high temperature, adhesion, different measuring ranges, corrosion of the probe, mechanical impact - And of course dusty atmosphere.
Such requirements call for technology solutions that are versatile, whilst representing a cost-effective investment and offering versions fully equipped to meet a wide variety of these requirements.
