Precise interface measurement of different solids in liquids

Project planning options for interface detection with electromechanical lot system for continuous level measurement or vibrating fork for point level detection


There are several industries where sludge levels or solids in liquids need to be measured. For example, in sediment containers or basins, filters or lamella separators in the metal industry, chemical plants, lime or gravel works and the waste water industry. The measuring accuracy and durability of the sensor technology is important. Dirt, chemicals and gases often affect the sensors and require special resistance. The NivoBob® series NB 3300/3400 meet the requirements of many interface measurements and are very reliable due to the simple measuring principle. For level evaluation an analogue signal 4-20mA and a Modbus RTU/Profibus DP interface are available.

Vibrating forks of the Vibranivo® series VN 1000 or VN 5000 can be used to measure the point level of sludge and solids in liquids. The parts in contact with the medium are made of resistant stainless steel. With the versions VN 1030 and VN 5030 even depths of approx. 4 m (13,12 feet) are realizable when installed from above in a silo or basin. The high sensitivity required for the respective solids detection can be easily adjusted on the electronics.


Robust design of the electromechanical plumb line system for reliable measurement results

The multifunctional technologies NivoBob®  NB 3300 in rope version and  NB 3400 as tape version are specially modified plumb line systems of UWT for interface measurements. They are used, among other things, for continuous measurement of salt or sludge levels in tanks for polluted water or settling silos. Material resistance of the devices is of decisive importance in order to withstand the corrosive process conditions and achieve reliable measurement results. All installed device parts are therefore additionally coated and made of corrosion-resistant materials. The housing and the process connection, which are made of aluminum IP 66, are immune even to chemically aggressive and corrosive media. Due to the increased corrosion resistance and insensitivity to dirt, the NivoBob® versions measure very precisely even under challenging process conditions, such as use in sewage sludge or salt water.

Accordingly, the installation of the lot system within a sewage treatment plant in Europe was recently completed without any problems. The plant operator had the requirement to measure the height of the settled sludge in a bed load chute. The addition challenge here is to reliably determine the separation layer in flowing, heavily polluted water.

An extra PA coating of the stainless steel cable also allows installation in very corrosive materials. To avoid slippage, the cable or tape pulley is provided with a further special rubber coating. Due to the individual fine adjustment of the sensor weight in the rope version, whereby this is exactly adjusted to the sludge layer, a high precision of the measurements can be achieved with the NB 3300. Integrated metal disks in the PVC sensor weight also allow individual adjustment of the sensitivity and even allow interface measurement in very light sludge.

In addition to a 0/4-20mA signal, the bob sensors also offer communication via Modbus or Profibus DP. The appropriate NivoTec® visualization software provides options for intelligent level monitoring and, for example, height and volume-related values for controlling the sludge pump. After installation and simple programming, the plumb line systems are immediately ready for operation and completely maintenance-free, according to the "install and forget" principle.


Project planning options for interface detection with vibrating forks

Due to its high sensitivity, the fork measures light media from 5g/l, such as wood dust, polystyrene, plastic powder, flour, milk powder, salt, lime or silicic acid as well as pasty materials. Thus, a wide range of applications can be found in plant processes of different industries. Within the vibrating fork family there are five series, each of which can be adapted to customer-specific application requirements.

The models of the Vibranivo® VN 1000 and  VN 5000 are predestined for interface level measurement, such as sand sediments in seawater or sludge in liquid. Even challenging installations, such as those for measuring the sludge level in a lamella separator, can be flexibly configured with the UWT fork. Here the polluted water came from an iron foundry. The sludge level measurement should control a pump that pumps the sludge on to a press. Thanks to the specially developed electronics of this series with an adjustable sensitivity, the probe could be set to the desired switching point, which made it possible to use it in this application.