The Cadia Mine in NSW Australia is a deposit of very rich copper and zinc and has yielded significant amounts of gold since its opening in 1998. In order to overcome several environmental issues, the ore concentrate needed to be transported via several large slurry pipelines, from the mine at Cadia, 70 km to the nearest rail link at Blayney.
There, the ore would be extracted from the water, which is then pumped back to Cadia to be recycled. Because of the volumes of critical data generated at the Blaney de-watering plant and to ensure that EPA regulations were not breached, it was essential that the field data be continuously transferred to a central DCS system.
The mine is centrally operated using a Yokogawa DCS, while a distributed Allen-Bradley SLC system handles control in the field. To integrate the Allen-Bradley SLC into the Yokogawa DCS system, Modbus was selected as the common communication protocol.
Because the Yokogawa DCS system lacks the ability to send the strings necessary to dial a telephone modem, an intermediate "sub-master" SLC system with a ProSoft Technology MVI46-MCM was added at Cadia. The ProSoft MVI46-MCM is a modified version of the commonly used MVI46-MCM, with the added capability of initiating telephone modem dialing built into the product. The sub-master acts as a transparent link between the Yokogawa DCS and the remote SLC at the Blayney dewatering plant.
In the Cadia sub-master SLC, Port 1 on the MVI46-MCM is configured as a Modbus Master port with dialing and is connected to a telephone modem. Port 2, configured as a Slave, is connected directly to the Yokogawa DCS. The Cadia SLC processor initiates all Read and Write commands to the remote system at Blaney through the dial-up modem. The Yokogawa DCS, acting as the Modbus Master, simply accesses the data out of the local MVI46-MCM module's memory. To provide additional robustness in the system, a watchdog function was added between the SLCs to ensure that the Yokogawa DCS would positively identify a communications failure.
The system has been up and running since June 1998 with no problems.