Quarrying is only one of many industries where the detection of blocked feed chutes is important, but the sheer size of most stone quarries and the remoteness of many conveyors means that their monitoring becomes critical.
Contacting solutions such as flap switches are prone to wear and require regular maintenance and frequent replacement.
Pulsar's Blackbox 130 controller with dB3 transducer provide a low cost, non-contacting, zero maintenance ultrasonic solution to the problem. If a chute blocks, an alarm is generated to warn the plant operators of potential blockage.
Quarries use conveyors extensively to feed materials via chutes to stockpiles, screenhouses or crushers, and to transport stone around sites that often extend to several square kilometres. Chutes and transfer points through which the stone is discharged are potential weak points, where a blockage can very quickly cause significant damage to conveyors, creating downtime, expense and delay.
To avoid this, quarries employ a variety of techniques to both warn of blockages and to automatically shut down conveyors and feeders before damage can be done. The most commonly employed technique is a flap switch, signalling from a proximity unit when the angle of the flap changes beyond certain levels. Because the flap is a mechanical contacting system, regular maintenance is required and the flap switches require periodic replacement. An alternative system makes use of microwaves fired across the chute. These are expensive and careful positioning is required to ensure that the microwave path does not cross the normal flow of stone, or spurious alarms may be generated.
The Pulsar solution is to use non-contacting ultrasonic technology to measure "top-down" into the discharge of the conveyor. A robust dB3 transducer fires an ultrasound pulse into the chute and receives the echo from the stone while the associated Blackbox 130 transceiver, which may be up to 1000m from the transducer, analyses the signal received, calculating the materials distance from the transducer. The system is maintenance-free and extremely reliable.
The Blackbox 130 features two relays that can be configured to close or open at a user-programmed level, alerting staff or immediately switching the offending conveyor off before damage can be done. Pulsar's Blackbox family is designed as a component system, reducing cost by removing unnecessary elements of the system such as the unit display.
Following trails, Aggregate Industries has purchased a number of units for their Croft quarry. Another Leicestershire quarry, Midlands Quarry Products's Cliffe Hill site, has installed four systems for use with new conveyors.
Posted from the Pulsar archives - March 2005.