Laser
A laser sensor is mounted on top of the silo using an adjustable 10° mounting flange for aiming the laser beam to the desired output location. Minimum and maximum measuring distances are set using 4 and 20 inputs configured on the sensor. The sensor sends timed laser pulses to the material surface. Distance is calculated using complex algorithms that convert the laser pulses to a data output. A compensation for “slant range” is made based upon the angle of the beam to ensure accurate level measurement.
Laser is for low or no dust environments, as it does not perform reliably in high dust. It is ideal for level control in narrow vessels containing solids or plugged chute detection. It can also be used in restrictive chutes and hoppers where precise targeting is needed. Another use is to monitor buildup when installed above or pointed to the sidewall. Laser sensors may be applied in opaque liquids in vessels where the beam must be precisely targeted to avoid walls or structure.
Pros
The laser sensor:
- Has a narrow beam that can be directed to avoid obstructions
- Is easily configured in the field using a USB port
- Can be configuration without filling or emptying the vessel
- Features a fast update rate of 8 times per second
- Has integrated dust protection for minimal maintenance
- Can also be used in opaque liquids
Cons
The laser sensor:
- Does not measure reliably in dusty environments
- Only measures a single point on the material surface
- Is subject to interference from falling materials
- May need an air purge option to keep lenses free of dust for reliable performance
- Is not recommended for liquids with excessive vapor that is too opaque for the laser to “see through”
3D Scanners
Unlike any other continuous level sensor, the acoustics-based 3D scanner sensor takes measurements at multiple points within the vessel. The sensor uses three independent transducers, which convert electric energy into acoustic sound pulses. The sound pulses bounce off the material in multiple locations on the material surface, and the sensor measures the time it takes for the pulses to return (or echo) back to the transducer. The multiple measuring points take into account the material’s irregular surface topography.
The 3D scanner has a measuring range of up to about 200 feet (approx. 61 meter) and a 19-inch (approx. 480 mm) dead zone. The sensor uses an advanced algorithm that assigns each measuring point a weight to precisely determine the material volume and produce a 3D image of the material level.
Pros
The 3D scanner sensor:
- Provides continuous level measurement
- Is nonintrusive and doesn’t contact the material
- Measures multiple vessel points to create a 3D map of the material’s surface and accurately calculate the material volume
- Can measure uneven material surfaces, including sidewall buildup and cone-up or cone-down formation
- Can report minimum, maximum, and average material levels
- Offers a 3D visualization of the vessel topography
- Can be used in vessels up to about 200 feet (approx. 61 meter meter) tall
- Is available in high-temperature models up to about 350°F (approx. 176°C)
- Isn’t affected by material characteristics
- Works in very dusty conditions
- Is approved for use in hazardous locations
- Self-cleans and requires minimal maintenance
Cons
The 3D scanner sensor:
- Requires time to process multiple sound pulse echoes, limiting its sample rate
- May not perform well in an environment with a lot of background noise
- Isn’t recommended for measuring a material with a bulk density less than 12 lb/ft3 (approx. 192 kg/m3) because such a material will absorb the sound pulse
- Must be carefully located and mounted to accurately map the material surface
- May not perform well in small vessels with corrugated walls, which can create false echoes
- Has a high purchase cost compared to other sensors
| Accuracy of a Multi-Point Inventory Measuring System |
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Unlike standard devices that measure one point and determine a single distance, the 3DLevelscanner takes measurements from multiple points within the silo. These points are used to determine the volume of material in the bin. Measurement points are not averaged to calculate bin volume. Instead, each point is given a “weight” or strength of accuracy rating assigned by an algorithm to determine the true volume of material within the bin. This technology takes into account variations that can occur on material surfaces by mapping the high and low points. The 3DlevelScanner provides an accurate profile of the top surface within a storage vessel. This is beneficial when there are variations in the material surface due to multiple fill and discharge points, or with materials that do not fill/discharge symmetrically. With the 3DLevelScanner the volume accuracy is still dependent upon the accuracy of the vessel dimensions, and sensor placement. When converting the volume to mass there will still be inherent inaccuracies due to bulk density variables. But, the improved accuracy of the volume calculation will improve the accuracy of determining the correct mass calculation. Given correct vessel geometry and proper sensor placement, you can expect a volume accuracy of ±3-5%. With a good average bulk density, the accuracy of the mass may be around ±5-10% |
