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nita
ICE Master
Joined: June 30, 2006
Posts: 114
Location: Mumbai
Status: Offline
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 Posted:
Feb 17, 2007 - 10:46 AM |
 
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| Post subject: SCADA & RTUs |
SCADA (supervisory control and data acquisition)
Is an industrial measurement and control system consisting of a central host or master (usually called a master station, master terminal unit or MTU); one or more field data gathering and control units or remotes (usually called remote stations, remote terminal units, or RTU's); and a collection of standard and/or custom software used to monitor and control remotely located field data elements. Contemporary SCADA systems exhibit predominantly open-loop control characteristics and utilize predominantly long distance communications, although some elements of closed-loop control and/or short distance communications may also be present.
Systems similar to SCADA systems are routinely seen in factories, treatment plants etc. These are often referred to as Distributed Control Systems (DCS). They have similar functions to SCADA systems, but the field data gathering or control units are usually located within a more confined area. Communications may be via a local area network (LAN), and will normally be reliable and high speed. A DCS system usually employs significant amounts of closed loop control.
SCADA systems on the other hand generally cover larger geographic areas, and rely on a variety of communications systems that are normally less reliable than a LAN. Closed loop control in this situation is less desirable.
This page is intended to help guide you from the basic theory of SCADA systems, to the design of simple SCADA systems, through the selection of vendor hardware and system architecture. Please explore the links and topics below to gain a more complete understanding of this interesting subject!
RTU
A RTU, or Remote Telemetry Unit is a device which interfaces objects in the physical world to a DCS or SCADA system by transmitting telemetry data to the system and/or altering the state of connected objects based on control messages received from the system.
A typical RTU has a network interface , a simple processor, some environmental sensors, some override switches, and a bus which it uses to communicate with devices and/or interface boards. This bus is sometimes called a device bus or a field bus. Standards include the ISO Controller Area Network , MODBUS, and others. Many vendors provide proprietary buses for their equipment; examples include Allen-Bradley's Data Highway and HSQ Technology's MISERnet. Sometimes a device or field bus standard can be used to interconnect RTUs and host systems as well as field devices and RTUs.
Interface boards come in analog and digital flavors, and are typically designed for input only, output only, or both. These main types of interface boards are often abbreviated as "DI" , "AO" , and so forth. These categories are further subdivided based on the range of inputs, the amount of protection against voltage surges, and the amount of intelligence on the interface board. Sometimes an RTU or PLC has integral interfaces used to allow the deployment of only a RTU to monitor or control just a few devices.
The interface boards are in turn connected to physical objects using wires. A typical application found in most SCADA implementations is to connect high current capacity relays to a digital output board to switch power on and off to devices in the field. The DO board switches voltage to the coil in the relay, which closes the high current contacts, which completes the power circuit to the device. Analog inputs are usually 24V with a current range between 4-20 milliamps; the RTU or host system then translates this into the appropriate units such as gallons of water left or temperature before presenting the data to the user via the HMI or MMI.
Modern RTUs are usually capable of executing simple programs autonomously without involving the host computers of the DCS or SCADA system to simplify deployment, and to provide redundancy for safety reasons. A RTU in a modern water management system will typically have code to modify its behavior when physical override switches on the RTU are toggled during maintenance by maintenance personnel. This is done for safety reasons; a miscommunication between the system operators and the maintenance personnel could cause system operators to mistakenly enable power to a water pump when it is being replaced, for example.
RTUs and PLCs are increasingly beginning to overlap in responsibilities, and many vendors sell RTUs with PLC-like features and vice versa. The industry has standardized on the IEC 61131-3 functional block language for creating programs to run on RTUs and PLCs, although nearly all vendors also offer proprietary alternatives and associated development
some links
<a href="http://members.iinet.net.au/~ianw/primer.html">Read Here</a> |
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fundu_instru
ICE Expert
Joined: June 20, 2006
Posts: 164
Location: Singapore
Status: Offline
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Feb 20, 2007 - 08:38 AM |
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nice info. provide information on telemetry measurement and which instruments are deployed ? which vendors are in the markets ? and which are certification for the same. |
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Inst
ICE Newbee
Joined: May 13, 2007
Posts: 2
Location: Sudan
Status: Offline
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May 14, 2007 - 01:05 PM |
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ganesh
ICE Student
Joined: Sep 15, 2006
Posts: 32
Location: Bangalore
Status: Offline
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| Posted:
May 30, 2008 - 12:22 PM |
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ABB is one of the Vendor for RTU |
_________________
Ganesh |
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