Plant operators need to continuously measure bulk material levels/weight in their silos and hoppers to ensure their processes are running safely, efficiently, and without bottlenecks. Measuring these levels allows operators to automate vessel filling, verify material consumption, and prevent overfilling.
How do you measure bulk material levels/weights in silos and hoppers?
The two ways to measure bulk material quantity in silos/hoppers are level indicators (laser, ultrasonic, radar) and weight measurements (load cells, strain gauges). Weight measurements are more accurate, safer to install, and can be installed during operation. Of the types of weight measurements, ITM prefers to implement strain gauge-based solutions since they do not require structural modification of the vessel.
An ITM silo monitoring system typically consists of weatherproofed strain gauges for each silo leg and a NI CompactRIO embedded controller to acquire data, process signals, and output results. Systems are scalable to accommodate all the silos at the plant.
The graph above shows a typical trend of real silo data during unloading. Weight levels are sent directly to factory DCS systems and historians via common communication protocols like Ethernet/ip and Modbus, or they can be viewed on the system’s webpage or a local/remote workstations and panels.
What are the challenges when measuring bulk material levels/weights?
Most bulk material storage is outside, so temperature and other environmental factors must be accounted for not only in the durability of the equipment, but in the sensor design and data processing. Changes in temperature, wind, and humidity can result in changes to the load path in silo legs. Load changes are account for by instrumenting all or most of the silo legs and selecting the appropriate strain gauge bridge design which results in continuously accurate weight measurements.
While other systems require calibrating the system with known loads (point calibration), ITM calibrates the system using a shunt voltage across the strain gauge bridge. This process automatically calibrates the system and eliminates the requirement of having pre-known material weight added to the vessel.