The upgrading of the Temba Water Treatment Plant had to include a telemetry system to enable automatic control of the high lift pumps delivering water to the distribution system.
Telemetry system requirements
The system had to be able to integrate into the Modbus TCP/IP PLC network on the treatment plant. The radio network system had to be able to incorporate multiple master configuration. This was necessary because monitoring from the main station at the treatment had to run together with a master slave control between outstation 4 and 3 and also master slave control between the master station and outstation 2. The system needed full PLC programming capabilities as the control in the pump station involved complicated pump set control together with level control in outstation 3. The telemetry had to be able to be programmed and set up remotely and for this store and forward was necessary.
System description
The master station at the treatment plant must update and monitor all information at all of the outstations and make this information available on the PLC/scada Modbus TCP/IP network. This in turn displays and trends the relevant information of all the outstations. The outstation 4 must control pump sets according to a level in outstation 3.
Remote programming capabilities
The ScadaPack 32 PLC provides remote terminal unit (RTU) functionality with flexible remote programming options. The unit is programmable in Relay Ladder Logic, IEC 61131-3 and multitasking C/C++ languages and provides an unlimited number of PID controllers for use in feedback control applications.
Remote control functions running locally at outstations independent of scada monitoring functions
As PLCs were used more often to replace relay switching logic control systems, telemetry was used more and more with PLCs at the remote sites. It became desirable to influence the program within the PLC through the use of a remote signal. Where only a simple local control program was required, it became possible to store this program within the RTU and perform the control within that device.
Multiple master configuration
The ScadaPack 32 controller can be used in either Master or Slave configurations. A comprehensive set of features has been added, including unsolicited reporting, event logging with/without timestamps, support for multiple masters, select-before-operate control of output points, and pulsed digital outputs.
Store and forward within multiple master network configuration
For maximum versatility, the ScadaPack series controllers provide store-and-forward capability, which allows Modbus messages to be received and retransmitted to other slaves.
Integration of the telemetry RTUs into a Modbus TCP/IP PLC network
Local networks connect the RTUs directly to the scada central host computer if there is no need for a WAN connection. Like the WAN, the local network may comprise cable, radio, or satellite data communications links depending on the geographic distribution of the scada system.
The ScadaPack can be programmed and monitored over the network from a central point.
The ScadaPack Solution
ScadaPack PLC/RTU was chosen because of the wide variety of functions that was needed in this application. The master station was fitted with a ScadaPack controller incorporating Modbus TCP/IP. Multiple peripheral ports on this controller ensured that serial radio communication and the Modbus TCP/IP protocol could be serviced. The PLC Modbus TCP/IP network was used in order to interlock high lift pump sets on the treatment plant with reservoir level at outstation 2. The radio communication runs on a Modbus RTU protocol via FreeWave serial data radios.
The outstation 3 used the multiple serial ports available on the ScadaPack controllers in order to enable slave communication to the master station via outstation 2. The repeating through outstation 2 is implemented using only one radio, using the store and forward capabilities of the ScadaPack controllers and the FreeWave radios. The second serial port was used to enable slave communication to the master at the pump station (outstation 4).
Lastly, the store and forwarding was used to enable remote programming of any of the outstation controllers. The ScadaPack controller at outstation 4 was set up as a master to enable to communicate to the slave controller at outstation 3. The controller also used the extension programming capabilities of the ScadaPack controllers to control the pump station.
System Integrator, Artiflex Engineering, made extensive use of FreeWave radios and ScadaPack PLC/RTU, which were obtained through sole supplier Supervisory and Control Expertise.
For more information contact Jaco Hoogenboezem, Supervisory and Control Expertise, 016 982 3700 [email protected]
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