Non-Contact Level Sensors for Inventory Management - Laser, Radar or Scanning Sensors?

A large range of different technologies are available for silo and inventory management, with the three most favored using laser, radar or scanning technology. However, the question is, which of these technologies is best for you?

AZoSensors spoke to Scott Hudson, of BinMaster, about the strengths and weaknesses of the different non-contact level sensors, and which technology would deliver the most for your application.

Why is non-contact sensing favorable to contact sensing?

For many process industries it is desirable that no instrumentation comes into contact with the material. This is especially true in the food, feed, and pharmaceutical industries where there is a need for good sanitation.

Non-contact sensors are also favoured because they don’t interfere with other equipment or structures in a silo. Plus, there is no risk of equipment breaking and falling off which could potentially damage equipment that may be present in the bottom of a silo, such as an auger or sweep.

Non-contact sensing is favoured in the pharmaceutical industry where contact with the powder feedstock is avoided for hygiene reasons. Shutterstock | Anna Jurkovska

How do each of the three main non-contact sensing technologies – laser, radar and scanning – work?

A laser sensor mounts on top of the silo using an adjustable 10° mounting flange to aim the laser to the desired output location. Minimum and maximum distances are then set using 4 and 20 inputs configured on the sensor.

The sensor sends timed laser pulses to the material surface in a very narrow 1° beam angle. Distance is then calculated using complex algorithms that convert laser pulses to a data output. A compensation for the “slant range” is made based upon the angle of the beam to ensure accurate level measurement.

From its mounting location on the top of the silo, a non-contact radar emits an electromagnetic pulse through the antenna in a 4° beam angle. The emitted signal is reflected by the material and received by the antenna as an echo of a different frequency.

This frequency difference is proportional to the distance the laser travels (and therefore the height of the material being measured). The sensors then uses algorithmic calculations to convert the measured change in laser frequency into the height of the material.

A 3D scanner is mounted on top of the bin at an optimal location recommended for superior surface coverage. Acoustic pulses – that sound like chirping crickets – are sent to the material surface in a 15°, 30° or 70° beam angle depending on the model used. The acoustic pulses are used to measure and map the material surface.

The distance is then calculated using advanced algorithms that convert the difference in timing of the echo sent and received. Data is sent via 4-20 mA or RS-485 output to software, or an HMI or PLC. Software then records the data and calculates the level, volume, and mass and creates an optional 3D visualisation of the bin contents.

The laser, 3D level, and radar scanners (from left to right) provided by BinMaster

Can laser, radar and scanning sensors all be used for both volume and level sensing? If not, which technologies are most suitable for each application?

Yes, all three can supply very accurate level measurement. However, for measurement reliability in high dust, the 3D scanner and non-contact radar are recommended. If there is very little or no dust, the laser will be a cost-effective sensor alternative.

When it comes to volume accuracy the 3D scanner will provide greater accuracy than the laser or non-contact radar. This is because the 3D scanner measures multiple points across the material surface whereas a laser or non-contact radar measures only one point. This means that only the 3D scanner can take into account variations in the material surface, buildup or cone up or down when calculating volume. So, it is able to calculate volume within 1 to 3 percent of total stored volume.

If material is free flowing and not subject to buildup, the silo is narrow, and precise volume is not needed the laser or non-contact radar sensors are suitable.

An example of the topography and volume calculated using Binmasters 3D level scanner

Are there any situations and applications in which non-contact sensing should not be used?

That depends on the technology used by the non-contact sensor, the material being measured, and the internal structure of the silo.

Laser is not recommended for high dust environments, but is great for narrow vessels.

Non-contact radar also offers precise targeting, but since it only measures a single point will provide less volume accuracy in materials that pile unevenly, such as powders.

The 3D scanner measures multiple points and provides very good volume accuracy in powders, but the material must have a bulk density of at least 12 lb/ft³. Materials with very low dielectrics can sometimes be difficult to measure with non-contact sensors.

What applications are non-contact level sensors used for?

In general, laser, radar, and 3D scanners are used in powders and bulk solids. However, each type of sensor has its sweet spot and may be better suited for some applications over others.

Laser is not recommended for high dust environments. It often used for level control in narrow vessels containing solids, due to its narrow beam angle. It can also be used for plugged chute detection, or in restrictive chutes and hoppers where precise targeting is needed. Monitoring buildup when installed above or pointed to the sidewall is another way that laser is used. Although often used in solids, laser can be used in opaque liquids in applications where the beam must be precisely targeted to avoid walls or structures.

Non-contact radar excels at single point measurement in very tall, narrow silos. It can also be used successfully in segmented silos with narrow compartments. Silos with excessive noise, dust, or high temperatures are good applications for radar.

As non-contact radar has a narrow beam angle, radar is also a great option in silos where precise aiming is needed to avoid internal structures, or flow stream, or sidewall buildup. It can also be mounted over piled material or in flat storage warehouses or over conveyors belts to prevent overloading or to detect when belts are running empty.

As the 3D scanner measures multiple points on the material surface, it is the sensor of choice when precise volume accuracy is needed.

3D scanners also excel in silos with high levels of dust and since they are self-cleaning, they don’t require an air purge. 3D scanning is recommended in silos with irregular material topography or multiple filling and emptying points

With a multiple 3D scanner system, it is possible to get very accurate inventory in very large or wide silos such as those with a 90’, 105’, or 132’ diameter. It provides precise inventory of powders, meals, and flours that don’t flow and pile unevenly. It’s also proven for inventory management in domes or flat storage buildings where material is conveyed or driven into the structure.

Non-contact radar excels at level measurement in tall, narrow silos. Shutterstock | hans engbers

In an ‘ideal’ environment which technology would you say is best?

The best technology to use depends on the application, the physical properties of the vessel and material, the operating environment, and how you want to use the data. Plus, budget almost always comes into play.

The laser is great in narrow silos containing solids or opaque liquids in environments without dust or excessive vapour. The narrow beam can be directed to avoid any obstructions. It is easy to configure in the field using a USB port and the configuration can be done without filling or emptying the vessel.

Laser scanning has a rapid update rate of 8 times per second, which may be desirable in some applications. However, it only measures a single point in the silo, so it won’t provide volume accuracy in materials that pile up or don’t flow freely. Laser technology may also be subject to interference from falling materials during the filling process and it may require an air purge or periodic maintenance to keep the lenses clean.

Non-contact radars using the 80 GHz band spectrum perform much better in solids than 26 GHz technology. It is the best solution for very tall silos with a measuring range of almost 400 feet. Older 26 GHz radars were unreliable in dust, whereby the signals from 80 GHz models can penetrate dust. Radar has a fast reaction time for tracking filling and emptying. There’s also loop power capability which is desirable in some installations.

The downside of radar is it only measures a single point, so it’s not the best choice if you need precise volume for inventory management. It won’t account for variations in material topography or cone up or cone down conditions. In some very extreme conditions, air purge may be needed to keep it clean. Radar can also be pricey, with the cost of options adding up quickly.

3D scanners are the best option if precise volume accuracy is needed. The unique multiple point measurement technology makes it the only sensor that can account for irregular topography. It can provide precision of 1 to 3 percent of total stored volume, detect cone up or down, or sidewall buildup. Plus, it is the only solution that can generate a 3D image of the material topography in the vessel.

The acoustics-based technology also keeps the sensor clean, even in clingy or sticky materials like flours or meals. There’s no air purge needed and minimal maintenance is required. The MultiVision software option also allows for an overview of all vessels with automated alerts, so it’s easy to see where inventory is all the time.

Scanning technology is the most accurate when dealing with materials that can form irregularly shaped piles. Shutterstock |  tishomir

In dusty environments which technology provides the most accuracy?

Both the 3D scanner and 80 GHz non-contact radar will provide accuracy in high dust environments.

The 3D scanner will also provide an average, the highest, and the lowest level detected because it measures more than one point. Again, accuracy is based upon a level measurement versus a volume measurement in which the 3D scanners will excel.

Where can our readers find out more about BinMaster and your level/volume sensing technology?

There’s always our website where there are brochures, web pages, white papers, and tons or articles and newsletter. We’ve also got some video or our youtube channel.

What we like best is to talk with you one-on-one about your situation. It’s the best way to understand and customize the best solution for you. Call us at +1 402-434-9102 and just ask for me or anyone on our sales team.

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About Scott Hudson

Scott Hudson is Executive Vice President of Sales and Marketing at BinMaster.

Scott has over twenty years’ experience in industrial sales and engineering.  He has a BS in Chemical Engineering and an MBA from the University of Nebraska.