In the pharmaceutical, building materials, and food industries, as well as in applications like platforms, dosing, and even kitchen and personal scales, weight measurement is of central importance. Especially in industrial applications, the level measurement of containers and silos is of great interest. There are various methods for determining the level, including optical, hydrostatic, ultrasonic, microwave, and radar measurements, as well as mechanical, capacitive, and gravimetric methods.
What is Gravimetry?
The term gravimetry is derived from the Latin "gravitas" for "weight" and the Greek "τὸ μέτρον" for "measure". In gravimetric measurement, the weight of the mass is linked to a meaningful value through the gravitational force, whereby the level is determined by weighing containers. This method is an essential part of weighing technology.
Applications of Gravimetric Level Measurement
Gravimetric level measurement is particularly suitable in situations where there may be spillages within containers, such as in the distribution of bulk goods in silos.
Advantages of Gravimetric Level Measurement
This type of weighing offers several advantages:
- External Force Sensors: The measuring sensors are located outside the container and do not come into contact with the contents. This prevents contamination and makes cleaning much easier.
- High Accuracy: A relative linearity deviation of only 0.02% of the nominal load is not uncommon. This allows for precise dosing, as is necessary, for example, when filling food products.
- Independence from the Contents: The measurement is not affected by the nature of the contents. Solids, liquids, viscous and foaming substances, as well as toxic or aggressive materials, can be measured gravimetrically.
- Avoidance of Measurement Distortion: Even with heap cones or voids inside the silo, the entire content is weighed, resulting in precise results.
- Easy Installation: Thanks to suitable mounting modules, the gravitational force is ideally directed into the force sensors, simplifying installation. These modules and sensors are characterized by their low height and small installation volume.
Challenges and Disadvantages
Gravimetric level measurement also has its drawbacks:
- Force Shunts: Mechanical decoupling of the container is ideal but often difficult to implement in practice, especially if bracing is necessary. The accuracy of the measurement can be affected by the support effect.
- High Carrying Weight: The accuracy of the measurement decreases if the weight of the container is high compared to the contents.
- Environmental Influences: Freestanding outdoor containers can be affected by wind pressure or snow loads, reducing measurement accuracy.
Typical Load Cells for Weighing
Depending on the application, different load cells are used:
- Platform Load Cells: Ideal for scales, they offer high accuracy and are cost-effective.
- Bending or Shear Beams: Installed under tanks, silos, or containers that stand on supports. They divide the nominal load by the number of supports.
- Compression Load Cells: For high nominal loads over 10 t, with capacities up to 300 t. Containers up to 1,200 t can be weighed with them.
- S-Type Load Cells and Strain Gauges: For containers that can be hung from these sensors or equipped with them.
