A GOOD example of modern ultrasonic level measurement in action is a shiploading station at Imerys Quarries’ site in Cornwall, in the United Kingdom, undertaken by Pulsar Process Measurement. The Australian supplier is Bintech Products .
Imerys is the UK’s largest producer of china clay, operating 17 pits, 14 of which are in Cornwall. The vast majority of the china clay produced is exported, primarily to Nordic countries; 70 percent of the exported clay is shipped via the deepwater port of Fowey.
Clay emerges from the clay pit driers in granular form, with 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 unit is non-contacting and uses a sound pulse to measure the level of clay. A relay closure is provided when the level of clay is low enough to accept the next load.
The complicating factor 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 able to track the level through the grid without losing it. This inevitably means that the grid itself will provide the largest echo. Added to this is the 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 past few years this sort of application would have been unachievable using ultrasonic (or any other sort of) continuous level measurement. Datem software analyses the echo that returns from the whole target area, uses 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.