Scada
SCADA stands for Supervisory Control and Data Acquisition. It is a software package used for the Supervisory Control and Data Acquisition of industrial processes. SCADA systems are widely used in various industries for controlling and monitoring their processes. The systems are positioned on top of hardware, in general via Programmable Logic Controllers (PLCs), or other commercial hardware modules. The hardware architecture of a SCADA system consists of two basic layers, the "client layer" which caters for the man-machine interaction and the "data server layer" which handles most of the process data control activities. The data servers communicate with devices in the field through process controllers. Process controllers, e.g. PLCs, are connected to the data servers either directly or via networks or fieldbuses that are proprietary or non-proprietary. The software architecture of a SCADA system is multi-tasking and is based upon a real-time database (RTDB) located in one or more servers. Servers are responsible for data acquisition and handling, such as polling controllers, alarm checking, calculations, logging, and archiving on a set of parameters, typically those they are connected to.
The internal communication within a SCADA system is generally based on a publish-subscribe and event-driven model, and uses a TCP/IP protocol. The server-client and server-server communication is event-driven, meaning that only changes to a subscribed parameter are communicated to the client application. The data servers in a SCADA system poll the controllers at a user-defined polling rate, and the polling rate may differ for different parameters. The controllers pass the requested parameters to the data servers. Time stamping of the process parameters is typically performed in the controllers, and this time-stamp is taken over by the data server. If the controller and communication protocol used support unsolicited data transfer, then the SCADA system products will support this too. The products provide communication drivers for most common PLCs and widely used field-buses, such as Modbus, Profibus, and Worldfip, but generally do not support VME. A single data server can support multiple communication protocols, and new drivers can be developed using a driver development toolkit provided by the SCADA system. The effort required to develop new drivers typically ranges from 2-6 weeks, depending on the complexity and similarity with existing drivers.
SCADA (Supervisory Control and Data Acquisition) systems, which are used for monitoring and controlling industrial processes. The passage describes the key features of SCADA systems, including communication protocols, access to devices, interfacing options, scalability, redundancy, access control, MMI (man-machine interface), trending, alarm handling, logging/archiving, report generation, automation, and object handling. The passage also discusses the development of SCADA applications and the potential benefits of using SCADA systems in experimental physics facilities.
In terms of communication protocols, SCADA systems use a publish-subscribe and event-driven basis with TCP/IP protocol for server-client and server-server communication. Access to devices is provided through communication drivers for most PLCs and widely used field-buses, although some drivers require additional costs. SCADA systems offer various interfacing options, including OPC client functionality, ODBC interface to archive/logs, ASCII import/export facility, APIs supporting C, C++, and Visual Basic (VB), and support for Microsoft standards like DDE, DLL, and OLE.
SCADA systems achieve scalability by having multiple data servers connected to multiple controllers, with each data server responsible for handling a subset of process variables. Built-in software redundancy at the server level is also provided by many SCADA systems, and some products offer more complete redundancy solutions.
Access control is provided by allocating users to groups with defined read/write access privileges to process parameters and specific product functionality. MMI is supported with multiple screens containing combinations of synoptic diagrams and text, and a library of standard graphical symbols is provided, but not all of them are applicable to experimental physics applications. Trending facilities are provided to trend predefined or on-line defined parameters, with real-time and historical trending possible, and zooming and scrolling functions provided.
Alarm handling is based on limit and status checking and performed in the data servers, and multiple alarm priority levels are supported. Logging/archiving facilities are provided for medium-term and long-term storage of data, with time-stamping and filtering options. Report generation is possible using SQL type queries to the archive, RTDB, or logs. Automation is supported with a scripting language and the concept of recipes and sequencing.
The development of SCADA applications is typically done in two stages, with process parameters and associated information defined through parameter definition templates and graphics developed, including trending and alarm displays linked to process parameters. SCADA vendors release one major version and one to two additional minor versions once per year, with SCADA products adopting web technology, ActiveX, Java, and OPC as a means for communicating internally.
The potential benefits of using SCADA systems in experimental physics facilities include rich functionality and extensive development facilities, limited specific development needed by the end-user with suitable engineering, reliability and robustness, and technical support and maintenance by the vendor. However, proper engineering is necessary to ensure that the SCADA system complies with the requirements, is economical in development and maintenance, and is reliable and robust.