Level measurement and monitoring in plastic raw materials

Modern, high-quality technologies ensure a continuous stress-free manufacturing process in plants


When it comes to detecting fill levels in silos and material processing operations, sensors with a high level of compatibility for different process containers provide the optimum support for a smooth process. Depending on the processing stage, the material to be controlled can be of very different nature and place different demands on the measurement technology to be used. Users from different industries with a number of scattered storage silos consider it increasingly necessary for their plants to be equipped with automated visualisation and monitoring of the data in addition to continuous measurement of the fill levels.


Modern solutions for efficient storage processes

Measurement technology Rotonivo® and NivoBob® combined with data visualisation NivoTec®

In order to guarantee a professional solution in terms of precision and process reliability for content measurement during the various stations in the manufacturing process to support a production facility, it is necessary to react to the respective process requirements with sophisticated measuring solutions. When configuring the sensor technology, individual phenomena of the respective process environment must be taken into account so that the sensor integrates perfectly into the containers and silos. To ensure a continuous value chain, a modernisation of the storage processes of a plastics processor for its raw materials was realised in the production plant in Portugal.

The fill levels of 21 storage silos with raw materials for plastic products were to be monitored more precisely and an additional overfill protection implemented in the silos. The project was realized with a combined installation of a NivoBob® NB 4200 continuous level measurement system and a Rotonivo® RN 3002 rotary vane level sensor system with the local UWT partner ZEBEN Sistemas Electrónicos Lda.. The NivoBob® NB 4200 with Modbus RTU interface continuously measures the level of the various plastics in the silos, independent of bulk density and DK value. The Rotonivo® RN 3002 full silo alarm with rope extension protects against overfilling. The extension arms can be flexibly set to the right length and switching point. Both sensors are all-rounders in the plastics industry and can be used in all solids, granulates and powders. They are cost-effective and easy to set up.

Level determination with an electromechanical solder sensor is one of the most customer-friendly technologies due to its simplicity and comprehensibility. The basis of this measuring method is the tape or rope coil driven by an electric motor and the sensing weight attached to it. This can be adjusted to the bulk density of the medium. Electromechanical plumb bob sensors are mounted on the container roof. A sensor weight is lowered into the container. The sensing weight is attached to the end of a measuring cable/tape, which is wound on a spool driven by an electric motor. When the sensing weight hits the product, the direction of the spool is changed and the weight returns to its original position. During the downward movement of the sensing weight, the distance is measured electronically by the rotation of the rope/tape reel. The microprocessor converts the measured distance into a volume-specific output signal that depends on the silo geometry. The output signal is updated after the sensing weight hits the product. The NivoBob® 4000 series is the low-cost version of the electromechanical plumb bob sensors. In addition to a cable version, a belt version is also available. Mechanically somewhat simpler in design, the level sensors are suitable for all common bulk solids applications in various industrial sectors. In addition, the swivel flange, which can be selected for this series, enables flexible mounting on sloping silo roofs.


The Rotonivo® RN 3000 rotating paddle detector has a compact, small electronics housing and can be configured with different probe arms depending on the application. It is used as a full, demand and empty detector. For process vessels, there is the short version with correspondingly small wings. For larger storage tanks and silos, there are Maxmelder variants with cable booms and booms with shaft and protective tube. All can be flexibly configured in terms of length. For mechanically demanding applications, versions with stable angled booms or with protective tube and double shaft bearing can be used. Rotating paddle detectors of the Rotonivo® RN 3000 series are used up to a process temperature of 1100°C and a vessel overpressure of 10 bar. The great advantage of these bulk solids limit switches is that they function smoothly in almost any type of solid. Independent of adhering products and dust formation, they operate for a long time and are cost-effective in relation to other measuring principles. The Rotonivo® RN 3000 rotating paddle detector has international StaubEx approvals as well as EHEDG approval for the food sector. The all-rounder for level limit measurement in bulk material applications.


In addition, the NivoTec® NT 3500 visualisation system was combined within the storage silos for monitoring and control. The detected levels are retrieved via remote enquiry and trends are analysed, which ultimately rounds off the logistics management optimally. The hardware is a Wago web controller with Modbus RTU interface, which communicates with the sensors and provides all the data needed to monitor the fill level and demand. Remote access via the Internet and level information via e-mail could be implemented in parallel.

Due to the individually thought-out measuring solutions for the storage area, the plant operator could be guaranteed effective support for a continuous production process.