Modern ultrasonic devices supplied by Pulsar are able to tackle applications that would have been impossible even a few years ago. Pulsar's Level Star unit (now in Ultra units) was installed to improve loading efficiency for a large Imerys china clay pit when they feed clay to ships for export around Europe. The unit had to accurately measure level even through a large metal grid. Pulsar's DATEM (Digital Adaptive Tracking of Echo Movement) echo processing software allowed the system to handle the application successfully, improving efficiency and speeding the operation.
A great example of modern ultrasonic level measurement in action is the ship loading station at Imerys Quarries site at Fowey, Cornwall undertaken by Pulsar Process Measurement.
Imerys is the UK's largest producer of china clay and operates seventeen china clay pits in the UK, fourteen of which are in Cornwall. The vast majority of the china clay produced goes for export, primarily to the Nordic Countries, and 70% of the exported clay is exported via the deep water port of Fowey.
Clay emerges from the clay pit driers in a granular form with a high dust content. From the driers, trucks transport the clay into a 30 tonne hopper. This then feeds onto a conveyor and out onto the waiting ship. To minimise dust, the hopper is enclosed. The capacity of the truck feeding the hopper is close to the hopper capacity so there is a need for a "traffic light" that tells the truck driver when the hopper is ready to accept the next load.
Pulsar supplied a Level Star ultrasonic controller coupled with a 15 metre range dB15 transducer. The Pulsar unit is non-contacting and uses a sound pulse to measure the level of clay. A relay closure is then provided when the level of clay is low enough to accept the next load.
The complicating factor, as can be seen from the photograph, is that the vehicle loads through a heavy grid. The level of the clay will sometimes be above the level of the grid and other times below, so the ultrasonic unit must be capable of tracking the level through the grid without losing it. This will inevitably mean that the grid itself will provide the largest echo. Added to this is a high dust level in the air.
In order to be successful, the DATEM software in the Pulsar system has to offer superb echo discrimination. Up until the last few years this sort of application would have been achievable using ultrasonic (or any other sort of) continuous level measurement. The DATEM software analyses the echo that returns from the whole target area, uses advanced echo processing algorithms to identify the clay level from all competing echoes and then maintains contact with the correct echo, disregarding all other echoes, even when the clay level goes below the level of the metal grid.
Posted from the Pulsar Archives - May 2005