Ancient Greek buoys tank level control
21 Sep 2006
The ancient Archimedes principle - that a body immersed in a fluid is buoyed up by a force equal to the weight of the displaced fluid - is now being used to resolve the problem of accurately measuring and monitoring the liquid contents of vessels and tanks.
Currently, load cell weighing systems are the most widely used systems for level measuring and monitoring. However, these present significant problems when fitting, especially retrofitting, to tanks. The principal alternative level measuring systems are much easier to fit but can give inconsistent and low accuracy results.
Among the companies now employing the 'Archimedes' technology, Weightron has introduced the Displacement Weighing System (DWS), particularly for applications in the food and drink industry. The unit consists of a stainless steel cylinder suspended from a weight transducer mounted in a stainless steel housing. The unit fits to the top of the vessel with the transducer out of contact with the liquid.
A narrow window runs directly through the liquid to the base of the vessel so that the cylinder can hang freely. The force measured by the transducer is directly proportional to the length of the cylinder submersed in the liquid, according to Weightron.
In effect, the transducer measures the decrease or increase in weight of the cylinder through buoyancy as the liquid level rises or falls respectively, the company explains. Calibrating the system when the vessel is both empty and full provides an accurate reading of the weight of liquid in the vessel at any time, it said.
The results, claims Weightron, are not affected by external force shunts and installations offer accuracies of better than +/-0.03%, compared with +/- 0.2% to 1% for standard level measuring systems.
Currently, load cell weighing systems are the most widely used systems for level measuring and monitoring. However, these present significant problems when fitting, especially retrofitting, to tanks. The principal alternative level measuring systems are much easier to fit but can give inconsistent and low accuracy results.
Among the companies now employing the 'Archimedes' technology, Weightron has introduced the Displacement Weighing System (DWS), particularly for applications in the food and drink industry. The unit consists of a stainless steel cylinder suspended from a weight transducer mounted in a stainless steel housing. The unit fits to the top of the vessel with the transducer out of contact with the liquid.
A narrow window runs directly through the liquid to the base of the vessel so that the cylinder can hang freely. The force measured by the transducer is directly proportional to the length of the cylinder submersed in the liquid, according to Weightron.
In effect, the transducer measures the decrease or increase in weight of the cylinder through buoyancy as the liquid level rises or falls respectively, the company explains. Calibrating the system when the vessel is both empty and full provides an accurate reading of the weight of liquid in the vessel at any time, it said.
The results, claims Weightron, are not affected by external force shunts and installations offer accuracies of better than +/-0.03%, compared with +/- 0.2% to 1% for standard level measuring systems.
