Ultrasonic Sensors for Fill Level Monitoring in Gravel Silos

Gravel open-cast mines contain construction materials such as sand, crushed rock, and gravel. These materials are excavated at depths of up to 50 m and must be appropriately stored until they can be transported from the site. Conveyor belts transport the construction materials to silos. Ultrasonic sensors determine when the maximum fill level of a silo is reached. The F260 Series ultrasonic sensors are particularly suitable for this application.

By means of ultrasonic time-of-flight measurement, the ultrasonic sensors determine the distance to the surface of the filled material and transmit this value to the control room for the gravel silo. There, further filling can be stopped and overfilling prevented. The analog output of the ultrasonic sensor controls this process. In addition, the devices feature two switching outputs. One output provides an advance warning that the maximum fill level of the silo will soon be reached. The other switching output provides for final shutdown as soon as the silo is completely filled.

The detection range of these ultrasonic sensors is up to 10 m. The sensors can monitor continuous filling of the silo at all times. This series is especially characterized by the wide temperature range of -25 °C … +70 °C. When used in crushed rock silos that generate high amounts of dust, the maximum detection range of the 10 m sensors may be reduced to 6 m.

The F260 Series offers the following versions for the analog output (including 2 switching outputs in NO or NC contact version):

 4 mA … 20 mA, UCxxx-F65-IE..-V15

 0 V … 10 V, UC10000-F260-UE..-V15

Furthermore, the 3RX4000-PF programming interface including "SONPROG for Windows" software is available for the commissioning and parameterization of all versions.

Mount the  ultrasonic sensor right in the center of the silo so that the projection cone does not reach the sides of the container walls. Otherwise, the sensor may inadvertently detect the sides of the walls themselves or slag sticking to the walls.

To ensure adequate sound reflection as the fill level increases, align the ultrasonic sensor's projection cone at a slight angle toward the center of the material cone. The F260 can be swiveled up to 10° in its bracket.

The blind zone between the sensor head (white) and the start of the measuring range (80 cm) must also be taken into account. If the fill level is located in this area, measurement errors may result. If two probes are installed, multiplex operation must be set using SONPROG and the ultrasonic sensors connected via the "XI" synchronization connector.

• Extremely robust design with high excess gain
• Mounting flange with swiveling bracket for optimum alignment of the sensor head
• Simple commissioning through viewing with SONPROG + 3RX4000-PF
• Continuous fill status monitoring
• Reliable shutdown of the conveyor belt prevents overfilling