When Cyclone Eline lashed eastern South Africa and neighbouring Mozambique early in February 2000, television crews were on hand to capture some of the most dramatic footage of rescue attempts ever recorded. Scenes of trapped villagers being airlifted by SADF helicopters from treetops filled the international media for weeks. However, once the floodwaters had subsided and the spectacular events gave way to the mundane aspects of everyday life, little was reported on the enormous relief effort that was directed to the region.
One of the South African areas hardest hit was the Kruger National Park. Amongst other things damaged, the water purification plants within the world-famous conservatory were all but completely destroyed by the raging floods. As a result, the management team of the park decided to perform a major upgrade to the system that monitored the distribution and purification of water throughout the area. Nelspruit-based Siemens' system integrator, CN Switchboards was awarded the contract to replace the monitoring system.
"Were the system being used for control purposes, a dedicated radio network would have to be installed," explained Steve Luckin, Siemens engineering consultant. "However, as only monitoring takes place on the system, new radios from Spectrum Communications were installed on the park's existing two-way radio network. The data is carried from the various remote points back to the main camp at Skukuza.
"The actual purification plants are controlled by Siemens S7-200 PLCs running 226 CPUs," Luckin continued. "Aside from level and flow (the latter measured using Siemens flowmeters), turbidity and automatic chlorination levels are also measured. The data from the PLCs is connected via ModBus to the two-way radios for relay back to central control."
The Simatic S7-200 has a completely modular design to allow for system expansion at any time in the future. Four CPUs of various memory and built-in I/O sizes are available. A wide range of expansion modules is available with various functions. These include:
* Digital/analog expansions.
* Profibus-DP slave communication.
* AS-Interface master communication.
* Accurate temperature measurement.
* Stepper motor pulse outputs.
* Remote diagnostics.
The central monitoring system is a PC-based HMI system running WinCC. WinCC polls the remote stations, which respond with appropriate data. An integrated OPC server and client and ODBC/SQL database allows for easy integration with third party data sources and MES and ERP systems.
"Kobie van Rensburg from Conhold was contracted to write a special plug-in application for the main scada system," elaborated Siemens technical support and WinCC specialist Tommy Chambers. "The application, written in Visual Basic, generates SMS messages under alarm conditions. For example, should a 'low water' condition be registered, the maintenance staff are called out. Should a 'high water' condition occur, a game ranger is called out. The system also generates and e-mails daily reports to the management team of the park. This allows contingency plans to be put in place should a water crisis occur in any area of the park," Chambers continued.
The high level of data that transferred back to Skukuza has dramatically decreased the workload of the engineering staff. On the original system, support staff would have to transport massive quantities of spares to the remote site should a fault be reported. All to often they would arrive at the breakdown missing some vital spare part. With the new system a far more accurate picture is painted of the problem, allowing exactly the right parts to be taken with on the callout.
Working in the park posed some new problems to the engineering staff. For example, all pipes and cabling had to be buried in extra-deep trenches to prevent hyena from digging them up. A game ranger was also assigned to protect the staff from predators such as lion and hyena. One of the more 'interesting' moments even included being chased by an elephant.
Steve Luckin, Siemens Automation & Drives, 011 652 3672
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