Scada

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SCADA is an acronym for Supervisory Control and Data Acquisition. SCADA systems are used to perform data collection and control at the supervisory level. A SCADA system includes input/output signal hardware, controllers, HMI, networks, communication, database and software. It mainly comes in the branch of Instrumentation Engineering. The term SCADA refers to a central system that monitors and controls a complete site or a system spread out over a long distance. The bulk of the site control is performed by a Remote Terminal Unit (RTU) or by a Programmable Logic Controller (PLC). Data acquisition begins at the RTU or PLC level and includes meter readings and equipment statuses that are communicated to SCADA. Data is then compiled and formatted in such a way that a control room operator using the HMI can make supervisory decisions that may be required to adjust/over-ride normal RTU (PLC) controls. SCADA systems implement a distributed database, called tag database, which contains data elements called tags or points. A point represents a single input or output value monitored/controlled by the system. Points can be "hard" or "soft". A hard point is representative of an actual input or output connected to the system, while a soft point represents the result of logic and math operations applied to other hard and soft points. Human machine interface (HMI) A Human-Machine Interface or HMI is the apparatus which presents processed data to a human operator, and through which the human operator controls the process. The SCADA system gathers information from the PLCs and other controllers via some form of network, and combines and formats the information. An HMI may also be linked to a database, to provide trending, diagnostic data, and management information such as scheduled maintenance procedures, logistic information, detailed schematics for a particular sensor or machine, and expert-system troubleshooting guides. SCADA is popular, due to its compatibility and reliability. It is used in small applications, like controlling the temperature of a room, to large applications, such as the control of nuclear power plants. System components There are three components of a SCADA system: 1. Multiple Remote Terminal Units (also known as RTUs or Outstations).2. Master Station and HMI Computer(s).3. Communication infrastructureRemote Terminal Unit (RTU) The RTU connects to physical equipment, and reads status data such as the open/closed status from a switch, reads measurements such as pressure, flow or voltage. By sending signals to equipment the RTU can control equipment, such as opening or closing a switch or setting the speed of a pump. The RTU can read digital status data or analogue measurement data, and send out digital commands or analogue setpoints. An important part of most SCADA implementations are alarms. An alarm is a digital status point that has either the value NORMAL or ALARM. Alarms can be created in such a way that when their requirements are met, they are activated. Master Station The term "Master Station" refers to the servers/software responsible for communicating with the field equipment (RTUs, PLCs, etc), and then to the HMI software running on workstations in the control room, or elsewhere. In smaller SCADA systems, the master station may be composed of a single PC. In larger SCADA systems, the master station may include multiple servers, distributed software applications, and disaster recovery sites. The SCADA system presents the information to the operating personnel in the form of a mimic diagram. The operator can see a schematic representation of the plant being controlled. For example, a picture of a pump connected to a pipe can show the operator that the pump is running and how much fluid it is pumping through the pipe at the moment. The operator can then switch the pump off. The HMI s oftware will show the flow rate of the fluid in the pipe decrease in real time. Communication infrastructure and methods SCADA systems have traditionally used combinations of radio and direct serial or modem connections to meet communication requirements, although Ethernet and IP over SONET is also frequently used at large sites such as railways and power stations. Typical SCADA protocols include Modbus, RP-570 and Conitel. Standard protocols are IEC 60870-5-101 or 104, Profibus and DNP3. These communication protocols are standardized and recognized by all major SCADA vendors.FIELD OF IMPLEMENTATION? I n d u s t r i a l p r o c e s s e s i n c l u d e : m a n u f a c t u r i n g / p r o d u c t i o n / p o w e r generation/fabrication/refining - continuous, batch, repetitive or discrete.? Infrastructure processes may be public or private and include: water treatment and distribution, wastewater collection and wastewater treatment, oil & gas pipelines, electrical power transmission and distribution and large communication systems. ? Facility processes in private or public facilities including: buildings, airports, ships or space stations in order to monitor and control: HVAC, access control, energy consumption management.