Applications - Level measurement - Level monitoring - Technology insights

Silos are going digital: Sensors to provide accurate level measurement

A critical task for most businesses is to maintain stock levels. This can be challenging, particularly when ‘stock’ consists of large containers such as silos full of large volumes of solids, powders, or liquids. A fast, cost-effective and safe alternative to manual monitoring is digital level measurement. The latest technologies in automated level measurement are outlined in this article.
Silo Level Monitoring Solution

Suddenly realizing you do not have enough stock for customer demand or that you have nowhere to store incoming stock as the storage containers are full are both equally problematic and frustrating scenarios. To maintain necessary stock levels, many businesses are rapidly adopting digital level measurements and automation.1

Monitoring Bulk Materials is Challenging

Silos, bins or hoppers are commonly used to store grains, animal feed, corn, pellets, seeds, and oats in the agricultural sector. Similar storage methods are also used for food, construction materials, mining products, municipal waste, recycling, plastic ingredients, and fuels.

Checking the stock levels of such large containers often involves climbing the side of the container and measuring the stock level from the top, which puts workers at risk of falling. It is of high priority to make routine processes like level measurement as safe as possible, particularly in the agriculture industry, which has one of the highest rates of work-based fatalities. Furthermore, manual stock checks are not only time-consuming but also inaccurate.2

Accurate Level Measurement is Essential for Safe and Efficient Operation

It is possible to reduce storage and transport costs by optimizing stock levels and deliveries using reliable data provided with digital stock monitoring. It also enables a quick resolution to any leaks in stock supply by providing alerts if there is a sudden drop in stock. 3

Accurate level measurement sensors are used in digital systems to detect how much stock is remaining in a silo. However, automatic measurements are challenging in silos, as levels are often uneven with irregular build-up and lots of dust.
programmable distance sensor

A Range of Sensors are Available for Accurate Level Measurements

Mechanical techniques provide the simplest stock sensors. One example is to drop a probe attached to a cable until it touches the material in the container, then to measure the distance dropped to provide a stock level measurement. 4,5

Traditional mechanical stock measurements are cheap and straightforward, yet they have several drawbacks. Frequent maintenance is required for moving parts and they can quickly wear out, particularly in dusty silo environments. Contamination is also a concern in many industries, particularly the food industry, meaning that contact between the probe and the material is undesirable. 5

Ultrasound sensors are used in many newer stock monitoring solutions. The sensors send ultrasound waves at the material in the silos and detect the reflected signal. It is then possible to calculate the distance between the material and the sensor. Optical and radar sensors work similarly, and both provide alternative solutions. If the stock levels are distributed unevenly, then multiple sensors can be used to give a 3D surface mesh of the material. 5,6

Continuous level monitoring can be achieved with ultrasound sensors and these do not have the drawbacks of contact and maintenance of moving parts. However, the signal can bounce around, causing less accurate readings of content volume.

Most affordable ultrasound sensors below the 100 EUR price tag are unsuitable for large storage units as they only provide a limited range of approximately 7-8 m. Alternative sensors are available such as those using lasers, but these are expensive and have high power consumption, limiting their compatibility with battery-powered systems. 5,6,7

Time-of-Flight (ToF) Level Measurement Sensors Provide Unrivaled Accuracy

A compact, low-cost solution are optical Time-of-Flight (ToF) sensors. These can provide continuous, accurate level measurements, with no risk of contact between the sensor and material. Even the largest silos are covered with the long-range measurements provided by ToF sensors and they are rarely affected by the effects of signal bouncing or absorption. Optical ToF is currently the most accurate technology to monitor stock available on the market. 7,8

ToF sensors work by sending pulsed infrared light at the material surface and detecting the reflected light. The sensor measures the time taken for light to travel to and from the material. The distances to the surface of the material can be calculated from these measurements.8,9

At a competitive market price, ToF sensors can optimize stock delivery and storage, increase automation, improve efficiency, and reduce operating costs.

Terabee are the ToF experts

A wide range of ToF sensors are provided by Terabee from the TeraRanger Evo 60m, which provides reliable long-range measurements for tall containers, to the Evo 3m sensor, which is the ideal solution for smaller tanks. 10,11

Sensor modules provided by Terabee can integrate with existing frameworks. Rapid prototyping projects and integration work for volume production are enabled with the available interfaces, which include USB, UART, and I2C. Fast connectivity to manufacturing systems is possible with industrial interfaces like RS-485.

Terabee level measurement sensors can be used in battery-powered devices and other low-energy solutions as they have low power requirements compared to laser ToF sensors. Terabee is committed to working together with customers to optimize solutions to meet their needs. As such, Terabee ToF technology can be deployed in a plug and play manner and easily customized.

Terabee can also build complete solutions on top of raw sensor data for customers who require the development of new level measurement applications.
structured light sensor camera

References and Further Reading

1. ‘The Internet of Things in the Industrial Sector’ — Mahmood Z, Springer, 2019.
2. ‘Global Estimates of Occupational Accidents and Work-related Illnesses 2017’ — Hämäläinen P, Takala J, Kiat TB, Workplace Safety and Health Institute, 2017.
3. ‘Smart feeding in farming through IoT in silos’ — Agrawal H, Prieto J, Ramos C, Corchado JM, Intelligent Systems Technologies and Applications, 2016.
4. ‘What’s new in smart weight-and-cable bin level sensors’ — Lewis J, Powder and Bulk Engineering, 2006.
5. ‘Sensor Technology Handbook’ — Wilson JS, Elsevier, 2005.
6. ‘Level sensing of liquids and solids ‐ a review of the technologies’ — Hunt JA, Sensor Review, 2007.
7. ‘Time-of-flight level monitoring for silos, water and more’
8. ‘An Overview of Depth Cameras and Range Scanners Based on Time-of-Flight Technologies’ — Horaud R, Hansard M, Evangelidis G, Ménier C, Machine Vision and Applications, 2016.
9. ‘Time of Flight Principle’
10. ‘TeraRanger Evo 60m’
11. ‘TeraRanger Evo 3m’
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