Level Detection Measurement Method
Level detection is used to avoid overfilling or downtime in silos and containers. Level limit switches are also used as spillage detectors in pipes or for the measurement of levels in interface applications. The switching point depends on the installation position of the sensor and its configuration. The information is analysed and transmitted via a digital signal to the control unit directly or via a fieldbus. Other operations and alarms such as as a filling stop and start, or demand signal can thus be triggered. Level switches are used in solids, liquids or sticky media.
Level detection / level detection using the rotation principle - rotary paddle switch
A motor-driven shaft causes a vane to rotate. Once the material level reaches the vane, thereby preventing further rotation, a reaction torque is created which is converted into an electrical signal. The motor is thereby turned off. Once the measuring vane is no longer covered by material, a spring moves the motor back into its initial position, the signal is switched and the motor restarts.
The rotary paddle switch can be used in almost all bulk solids as level controllers and can be configured for use in extreme application conditions. The measuring principle is simple, durable, easy and offers the most cost-effective sensors.
Level detection / level detection using the vibration principle - vibrating fork / vibrating rod
Electronically stimulated piezos cause the probe to vibrate. If the probe is covered by 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.
Vibration sensors are very reliable limit indicators and offer high sensitivity for use in very light bulk solids as well as in standard applications. Commissioning is very simple and requires no calibration. The Vibration level detection systems are especially suitable within highly caking media or grain sizes over 10mm. UWT Vibrating probes are mainly used for bulk solids and paste-like media.
Click here for information on the UWT vibrating rod - Mononivo®
Level detection / Limit level measurement using the capacitive principle - capacitive sensor
The electrodes in the sensor make up a capacitor. The value of the capacitance of this capacitor is dependent on the geometry of the probe arm, the container and the dielectric value of the material to be measured by the probe. The integrated electronics evaluate the change in capacity and convert it to a switching signal. In an uncovered state, the dielectric is air with a DK value of about 1 (reference). In a covered state, the change in capacitance is dependent on the DK value of the medium being measured. The Capanivo probes always carry the same geometry within the boom, so no calibration is necessary. The RFnivo probes need to be calibrated for each container because of their flexible cantilever configuration. This is done automatically during the commissioning stage.
Capacitive measuring sensors are the all-rounder of the limit switches. This is because they (the basic version) have the highest application performance. They can be used in extreme conditions in solids, liquids and viscous media and offer the widest range of applications. These sensors are limited only by media with a Dk value of less than 1.5 or a tendency to extreme caking, which cannot be offset by "Active Shield."
What is "Active Shield"?
The Active-Shield technology prevents switching errors caused by caking / buildup on the probe. The Active Shield is located between the two capacitor probes of the boom (Active probe and ground probe) and forms, the same polarity to the active probe, an electromagnetic field to the mass flow meter. As such it constitutes a "protective shield" between the capacitorwhich prevents a change in capacitance with caking on the probe rod. This ensures reliable measurement even in challenging conditions such as caking and build-up.
Level detection with Conductive Level Switches
The level of liquid is detected by the measurement of the conductivity using a conductive probe. The probe is mounted in the side of the container wall at the height of the filling level to be detected. A low measuring circuit voltage is applied at the probe tip. Once the probe comes into contact with the liquid the conductive circuit is completed via the metal container wall and a signal is sent. By using alternating current, any corrosion of the probe and possible electrochemcial reactions are avoided.
The Kondunivo from UWT is popular mainly because of its very robust design for use within building material applications, but also within many liquids and applications with viscous media.