System Integration & Control Systems Design


Profibus installation running well after four years

May 2002 System Integration & Control Systems Design

One of the first Profibus Installations was at Palabora Mining Company, a copper mine (and industrial minerals processor) in the Limpopo Province. The installation is still running well. Following a comprehensive analysis of all commercially available industrial communication systems, the mine chose Profibus as the most suitable fieldbus system for their open cast and underground operations.

All of the technical requirements for the network were met without limitation. The result of the mine extensions using modern technology has been that the mine's life span is dramatically extended for a further 20 years.

Members of the Profibus User Group were instrumental in assisting with initial training of the mine's engineers, after which mine personnel have successfully maintained and extended this system for their surface and underground plant.

About Profibus

The IT revolution in automation has allowed for increased savings by the optimisation of system procedures, and makes an important contribution towards improved use of resources. Profibus is a fieldbus with an open communication protocol for effecting this communication reliably and safely.

Communication in automation has become direct, both horizontally (at field level) and vertically (through all higher levels). Depending on the application, matching industrial communication systems such as the Ethernet-based PROFInet, the fieldbus Profibus and other systems such as the sensor/actuator bus AS-Interface, offer transparent networking in all areas and levels of the automation process.

At sensor/actuator level, the signals of the binary sensors and actuators are transmitted via a sensor/actuator bus. Here, a particularly simple, low-cost installation technique, through which data and a 24 V power supply for the end devices is transmitted. The data is transmitted purely cyclically. AS-Interface is a suitable bus system for this field of applications.

At field level the distributed peripherals, such as I/O modules, measuring transducers, drive units, valves and operator terminals communicate with the automation systems via an efficient, realtime communication system. The transmission of the process data is effected cyclically, while alarms and diagnostic data are transmitted acyclically if necessary.

On the upper level, programmable control systems communicate with each other. The information flow permits large data packets and a number of powerful communication functions. Smooth integration into company-wide communication systems, such as Intranet and Internet via TCP/IP and Ethernet is provided.

Background

The Palabora mine is one of the largest copper mines in the world. When open cast copper mining first started there in 1966, the original estimate of the mine's lifetime was only 20 years. More economical recovery of the ore-bearing layers allowed the mining operations to be prolonged. Eventually because of the size of the pit and the limitations of open cast mining, this method was no longer feasible.

Studies showed that additional ore-bearing layers were present below the base of the open cast mining. Ore deposits that extend for more than one kilometre were classified as reliable reserves by international specialists. Palabora Mining Company decided to extend the copper mining underground. Subsurface block mining with a daily production of 30 000 tons was considered an economically acceptable way of maximising the recovery from the deposit. This would guarantee operation of the Palabora copper mine for at least another 20 years.

When mining the subsurface deposits, it was planned to increase the efficiency of mining operations even further by using modern automation equipment and digital communication bus controlled devices. An important factor of this equipment was the communication network, which must ensure reliable data transport both in underground areas subject to explosion hazards and in the open cast mining.

Design concept

Palabora Mining Company decided to install an information and data network throughout the mine. The objective was to lengthen the daily operative times, increased productivity, integrate data acquisition and diagnostic features and increase the degree of automation. On the one hand, the system was designed to provide comprehensive information on operations throughout the whole mine for management. The operating personnel at the control panels needed direct control and monitoring of all underground mining activities.

An open communication standard was used at all levels to control the machines and plant. Industrial Ethernet was used at the control level, PROFIBUS-DP and PA at the field level and AS-Interface at the sensor/actuator level.

At the control level, each of the PLC controllers and PCs communicate with each other and with the master controller through Ethernet. The open cast mining, which is not subject to explosion hazards, uses PROFIBUS-DP for the field devices. It connects the remote I/Os, drives, operator panels, motor protection units and control units to the PLCs. Segment connectors and DP/PA links were used to interface the explosion-protected PROFIBUS-PA network for the underground field devices to the DP network.

The subsurface mining extensions proceeded as planned with major cost savings in installation, hardware and engineering. In addition, benefits were obtained from the functional advantages of digital communications. For example, all diagnostics data is transferred directly from the field devices to the control room. This increases reliability and significantly reduces plant downtime. The extensive diagnostic functions allow preventative maintenance and co-ordinated service work. A particular advantage is that operation and configuration of field devices from various manufacturers in the PROFIBUS-PA network are done over the network with a common engineering tool.

Profibus User Group SA

southernafrica@profibus.com

www.profibus.com




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