DMI in South Africa recently completed the electronic and electrical design and manufacture of a control system for NAMCO's new 190 ton sub-sea diamond mining tool.
The mining tool is fitted with a 1,8 MW submersible dredge pump for pumping gravel to the surface processing plant via a riser system. The tool is a tracked vehicle with a movable boom and knuckle to control the position of the suction nozzle. The tool is fitted with a 500 kW hydraulic power pack and a 500 kW jetting motor. An umbilical cable fed through a slip-ring assembly provides electrical power and control signals to the tool. There are approximately 140 field instruments fitted to the tool for monitoring various pressures, temperatures, forces, positions and fluid levels. It also has a sonar system, a gyrocompass, lights and underwater cameras.
A Pilot controls the tool from the surface control room. The surface control room has a 7-bay console with a pilot and a co-pilot operating position. Each operator position has a chair fitted with two 3-axis joysticks in the armrests for control. The seven bays have various sonar and navigation displays as well as the main operating screens. The main operating screens were developed using the Rockwell RSView scada software. The screens include graphical animation as well as system mimics and maintenance information.
The control system is based on Allen Bradley PLC5 equipment. This was chosen for its reliability and ruggedness. There are two PLCs - one PLC is installed into an electronic bottle which is mounted on the mining tool and another is installed in the vessel's control room.
DMI has been involved with the project together with NAMCO's design team, from the concept phase to final hand-over. DMI's main areas of responsibility were for the development of the control software, the design and manufacture of the underwater and surface electrical hardware, including underwater cables, junction boxes and sensors. DMI was also responsible for integration and interfacing to equipment supplied by specialist vendors.
Fibre optics is used as the primary communications medium between the vessel and the mining tool. This provides immunity against interference generated by the variable frequency drive of the 1,8 MW dredge motor. Standard wire communications is also incorporated as a back-up.
The mining tool's electronic equipment is housed in an electronics bottle. This includes the PLC, its I/O modules, power supplies and amplifiers for hydraulic solenoid valves, roll and pitch sensors, lighting control cards, insulation monitoring cards (AC and DC), and water ingress detection cards. These special purpose electronic cards were designed and manufactured in-house by DMI. The mining tool was designed to operate to depths of 300 m and was commissioned in December 2000. The complete system is now operational and mining.
DMI is an electronic and electrical systems engineering and manufacturing company operating from Cape Town and has the capability to meet the customers' requirements for specialised and underwater control systems.
DMI
(021) 762 0216
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