Bulk solids measurement is getting better – and smarter

Heterogeneity, dust, moisture and compaction: measuring the volume and weight of bulk solids is anything but trivial. What methods are there for measuring bulk solids? We present established methods and some new approaches here. And can artificial intelligence perhaps also optimize bulk material measurement?

Written by Marius Schaub

A laptop displaying a computer-generated image of a bulk material bunker and the calculated volume in cubic meters — Lidar measurement technology creates 3D images from laser-supported data, which are used to determine the volume of bulk goods.

Measuring the volume of bulk material is an important process in many industries, particularly in logistics, mining, agriculture and the building materials industry. Whether sand and gravel, grain or ore: the aim is always to determine the quantity of a loosely stored material.

Geometry and texture can interfere

What sounds simple nevertheless poses challenges. For example, piles of bulk material often have an uneven geometry, which makes it difficult to calculate the volume. Bulk material can also become compacted due to its own weight or transportation, causing the volume to vary. Moisture content also plays a role: moist material can clump together and affect the volume.

Depending on the resolution and precision of the sensors or measuring devices, further measurement inaccuracies may arise. Dust formation in industrial environments can also interfere with optical sensors and cameras. When stored in silos, the volume often has to be determined using indirect measurements such as pressure or level sensors.

Established methods for volume measurement

One of the oldest methods is probably level measurement with dipsticks. A long rod – usually made of metal or plastic – is inserted vertically into the bulk material until it reaches the bottom or a certain depth. The material sticks to the contact point of the rod, making the fill level visible. However, the method is relatively imprecise: even hills or depressions can lead to deviations. The method is also time-consuming and often less accurate than modern sensor technology. This is why it is rarely used in industrial applications today.

As the need to measure bulk solids has existed for a long time, various other methods have become established. The most common mechanical method is probably volume measurement: If the bulk density is known, the volume can be determined by weighing in addition to the weight. Today, suppliers such as Sick combine this method with intelligent systems: While a dump truck is being weighed, a measuring system automatically detects the load and the top edge of the loading ramp of the dump truck at the same time and determines the difference in volume. Software then generates a 3D model of the load, which is used to calculate the volume and weight of the load.

A radar measuring device for level measurement of bulk solids or liquids — Classic level measurement: radar measuring devices are mainly used in silos to monitor the fill level of bulk goods.

Radar and ultrasound see more

Radar sensors and ultrasound are also established for level measurement in silos and containers. It is based on the transit time measurement of the reflected radar or ultrasonic waves. The fill level results from the measured fill height of the silo – the volume can be determined based on this. Both methods are contactless and enable continuous monitoring of the fill level. Modern sensor technology makes it possible to measure both bulk solids and liquids with one device, for example with the radar measuring devices from Vega. In the case of dust formation, radar measuring devices are more reliable than optical measuring methods.

Ultrasonic level measurement has also been available for a long time from established suppliers such as Siemens or Endress + Hauser. These devices can also measure both solids and liquids. They are cheaper than radar sensors, but have certain disadvantages in terms of measuring accuracy, for example in the case of dust and moisture or with uneven or highly absorbent surfaces such as bulk powders.

X-rays and computer tomography for high precision

When particularly precise measurement results are required, X-ray or CT technology often comes into play. Level measurement with these methods is based on irradiating the bulk material with high-energy radiation in order to determine the fill level in containers or silos. These methods are primarily used in special applications where other methods such as radar or ultrasound reach their limits, for example with very dense, multi-layered or closed materials. Such applications can be found in the pharmaceutical or food industry, for example. Computed tomography in particular is extremely precise because it enables a complete 3D analysis.

However, X-ray and CT measurement technology is simply too expensive for many applications. Radiation protection regulations must also be observed for X-ray devices.

A production line with measuring devices, in the background an employee checking devices — Manufacturers such as Endress + Hauser produce level measurement devices based on technologies such as ultrasound or radar.

Drone and lidar for an overview of the terrain

Optical methods for measuring bulk solids are the newcomers among the methods for determining volume and fill level. Lidar (Light Detection and Ranging) uses laser beams for this purpose – the basic principle is similar to measurement with radar or ultrasound. With lidar measurement technology, however, a laser beam is sent in the direction of the material surface in order to measure the distance to the surface of the bulk material. This method is particularly precise and is well suited to large silos, warehouses or irregular surfaces. In contrast to methods such as radar or ultrasound, lidar systems can also process irregular surfaces such as hills or hollows in bulk materials: Manufacturers such as Blickfeld offer 3D lidar systems that lay a virtual mesh over the stock to generate very accurate data. However, dust, steam or poor reflection can interfere with the laser signal.

Level measurement with photogrammetry uses camera images to record the surface of a bulk material and calculate the volume or fill level. The method is particularly suitable for large storage areas, stockpiles, gravel and ballast pits, landfills or quarries. For this purpose, one or more cameras – stationary or on a drone – take images of the bulk material from different angles. The images contain reference points for later scaling.

Based on the combined images and through triangulation, a 3D point cloud or a height profile of the surface is created. The calculated height profile is compared with a previously recorded empty container model. The difference in volume ultimately indicates how much material is present. The process, which is offered by companies such as Logxon, can measure complex geometries and very large volumes particularly effectively. However, good lighting conditions are required; wind or dust can make drone measurement more difficult.

AI optimizes bulk solids measurement

Can the level measurement of bulk solids be improved by Artificial intelligence (AI)? Yes: for example, by evaluating measurement data more precisely, better compensating for disturbances or making predictions for material movements. Dust interference, for example, can be compensated for by intelligent noise filtering. Through data fusion, AI can combine different measurement methods to deliver more precise results. And in combination with data from the material flow, measuring systems with AI can even calculate when replenishment is needed based on past consumption data. Corresponding fill level forecasting is already available today from providers such as SLOC.

When it comes to measurement technology, there are often many ways to achieve a goal. Whether mechanically, optically or in other ways: In most cases, the specific application determines which method is most suitable. What is certain is that applications for measuring the volume and fill levels of bulk goods can also benefit greatly from digitalization and AI. Used intelligently, operators can easily avoid suddenly being faced with an empty silo.

Author

Marius Schaub