The main elements that make up the complete SCADA system are:
- SCADA (graphical interface, alarming and trending) - Outpost 2
- Historian (datastore and reporting interface)
- MTU (the master telemetry unit, which communicates with the field hardware)
- RTU (the remote telemetry units, with optional pump controller module and user interface)
MultiTrode SCADA - Outpost 2 - is built on open protocols.
OPC is used for communicating between the HMI, the historian and the MTU.
DNP3 is used for communicating between the MTU and the field hardware.
DNP3 is an open and public protocol specifically designed for the requirements of telemetry. It has great flexibility and is widely used in the electricity industry, but
the main benefits for the water industry are:
- Date/time stamping - each event and alarm has a native date/time stamp. So if data is received by the SCADA system or historian either minutes or hours later the event is logged as occurring at the original time, not the time when the SCADA received it. This means if a radio failed and was not replaced for several hours, all of the data from that period would still make it to the SCADA and historian - not the case with a protocol like Modbus
- Different classes of data - for example, you can nominate critical alarms to be sent immediately, and event data (eg pump on/off times and level changes) to be sent every 30 minutes, or when polled by the SCADA system. And because the original date/time is always kept, the SCADA has a perfect record. This kind of arrangement ensures that bandwidth is used effectively, rather than having to send every event as it occurs (as happens with MODBUS protocol).
- Guaranteed delivery - The protocol supports acknowledgements from the SCADA (or other master unit) to ensure that alarms are never lost.
- Supported by many suppliers worldwide - because no manufacturer owns it, the customers don't get locked in to one supplier, giving customers peace of mind and a better choice of equipment.
For more information, visit the website for the DNP3 users group, www.dnp.org
OPC is the most widely used open protocol in the SCADA industry. OPC allows different vendor products to communicate with each other without needing to write
drivers from one product to another.
One of the best features of OPC is the way an OPC server "publishes" tags to the network, so an OPC client can view the tags in a Windows Explorer style hierarchy, rather than having to know the obscure naming convention for the tags from that manufacturer.
The Genesis32 platform is "OPC to the core" meaning that each component - the trend system, the alarm system and the graphics HMI all have OPC interfaces.
This means the system is totally open and you will never be locked into one supplier.
For more information see the website for the OPC foundation, www.opcfoundation.org
