Lafarge produces a range of granite roadstone from dust to 63mm at its Mountsorrel quarry, conveying the aggregate either as single sizes or a blend via a long conveyor into a bank of ten 300 tonne capacity silos, each of which is ten metres deep. Each silo is filled from a central shuttle conveyor discharging to each side, so each can have twin peaks of material, and each side discharges to a separate belt conveyor, so can be considered as two separate measurement points. Lafarge needed to control the filling of the silos automatically and at the same time maintain stock control, so approached Pulsar for a solution. An abrasive material like granite would wear away a contacting sensor very quickly, so Pulsar’s non-contacting ultrasonic technology was ideal in that respect. The on-site SCADA system was to handle the display of levels and control of the silo loading, so there was no need for a local display of level, just a reliable signal through Profibus. Pulsar’s solution was to offer their Blackbox component ultrasonic system, which has been designed for exactly this scenario. The blackbox is compact and easy to install. Lafarge chose the ‘Blackbox Display’ model with local display and an integral keyboard. Other versions are also available with no display or controls on the device itself, reducing costs. A useful timesaver at Lafarge was the ability to ‘clone’ several units using the same programming parameters. As the silos are all a similar size, they could all be pre-programmed before installation, which reduced process down time. The 20 Blackbox units, two for each silo, were mounted in a control cabinet and each connected to a Pulsar dB15 transducer mounted on an aiming kit so that it could be directed towards the silo draw-off point. The blackbox units were then multiplexed through a Profibus connection to the site SCADA system.
Blackbox in cases