Powerline Communication (PLC)
It is a fact that there are some places in the world where there is not constant supply of power. Elsewhere in the western part of the world, not only do they have continuous supply of power but they can also transport Internet and many more through the powerlines. Unbelievable is it? Read through.
Powerline Communication or just PLC, is a method of transporting telephony and high data rate services such as the Internet over the electricity supply network. That means you would be supplied Internet, from the transformer station right through to every main socket in a building. Get the picture?
Network industry projections say that powerline communication (plc) technology is going to be a multi-billion dollar industry and of course would be very popular. The impact might be as strong as the television had in the 1950's. So can it be. Because powerlines are ubiquitous. There is at least one power outlet in every room in a home. In comparison, the phoneline solution offers far fewer installed connection points. While wireless solutions can reach most locations within the home, they are probably more expensive than a powerline solution.
Without doubt the powerline represents the most challenging medium over which to transmit signals. The electricity supply network is a noisy environment because of the switching actions of household appliances. In addition, it suffers problems because it is part of an unterminated network with many outlets. Therefore, it has not merited a great deal of serious attention in comparison with RF and phoneline solutions. Security of information is also an issue, especially in multi-unit housing.
Every powerline company has a proprietary approach to networking. None of these methods are interoperable, nor can they coexist. Each company believes that it can effectively create a de facto technology based upon its own approach.
The many different approaches differ from the type of technique used to transmit the information (spread spectrum vs. orthogonal frequency division multiplexing, or OFDM), to the implementation of Quality of Service (QoS), to the frequency bands are used in operation. These unique approaches are a direct result of the need to solve the specific challenges that the powerline poses.
Generally speaking, some of those firms with powerline control backgrounds have been using spread spectrum technology, which is the basis of the CEBus home automation protocol. However, other players believe in OFDM since it offers scalability to higher data rates significantly beyond 10Mbps. However, OFDM is generally perceived as a more expensive solution.
The basic question as to whether the electricity supply network could be used for communication applications has been the subject for research for many years. Narrowband technologies in the kbit/s range have already been available for some time.
Suman Benedicta,
Content Team – BSNL Portal, Intelligroup Asia Pvt Ltd,
content@bsnl.in
http://portal.bsnl.in/Knowledgebase.asp?intNewsId=19635&strNewsMore=more
International Cell-Phone Service
Different wireless service providers, in different countries, use different technologies for their customers. GSM (Global System for Mobile communications) has been picked up as an international standard in most European, African and Asian countries. In this part of the world, GSM operates in the 900-MHz and 1800-MHz frequency ranges. In the United States, there are CDMA, TDMA and iDEN, among others & GSM operates at the 1900 frequency.The standard U.S phones aren't compatible with the international GSM standard.
Varied technology around the world creates problem with international roaming. Different countries use different systems, so there's a chance that the user's phone won't function at all in some parts of the world.
In countries that use GSM 900 MHz and 1800 MHZ, cell phone users can use the same cell phone to connect to the specific service providers in these different countries, GSM-users simply needs to switch subscriber identification module (SIM) cards.
SIM cards are small removable disks that slip in and out of GSM cell phones. They store all the connection data and identification numbers you need to access a particular wireless service provider.
In addition to international compatibility, the GSM standard supports a number of useful features, including
Encryption technology that makes phone calls more secure
Data networking
Group III facsimile services
Short Message Service (SMS) for text messages and paging
Call forwarding
Caller ID
Call waiting
Multi-party conferencing
If the user uses the local service provider’s services, the advantage of using that he gets a local phone number and can pay all the bills at home, just as he would with the domestic cell phone service. But, these service plans are more expensive and will have to pay for incoming calls as well as outgoing calls. In most cases, it's probably easier to get prepaid international SIM cards instead. These prepaid cards incoming calls are free and are charged the local service rate, even though the cards connect you to local wireless providers.
Madhavi Chalamalasetti
Content Team - BSNL Portal, Intelligroup Asia Pvt Ltd,
content@bsnl.in
Charge mobiles while on the move
Mobiles are being used for many purposes. Though they are primarily meant for communication, with many essential features being incorporated in them, it has become necessary to carry these gadgets everywhere. It is also necessary to charge the phones regularly so that communication remains uninterrupted. But, it is also possible for a person to be in a place such as a proverbial Timbuktu, where it may not be possible to find an electrical connection to charge the phone. A new battery-enabled charger from Energizer may help the user charge his mobile anywhere.
Energizer Holdings, Inc., US, is a leading manufacturer of batteries, battery-powered gadgets and flashlights. The company released a portable battery charger called ‘Energi To Go’ that can be used to charge cell phones, iPods and gaming devices, with disposable e2 lithium AA batteries. There are two such battery models - a two-battery charger for mobile phones and a four-battery charger for gadgets such as iPods, PlayStstion Portable and Nintendo DS. According to market research firm Roper ASW, almost 20 per cent of cell phones lose charge at least once a week. This charger lets the users make a call in about 30 seconds of activating ‘Energi To Go’.
With a view to offering greater mobility to its subscribers, Sprint, US, announced that it is bringing ‘Energi To Go’ charger into the market for the first time. The charger has a single-barrel design made from durable aluminium and a patented intelligent control chip that ensures maximum power transfer from the charger to the phone. The charger is also useful for 80 per cent of Sprint Nextel phones. This provides greater flexibility to the customers to charge their mobile phones while on the move.
The power requirements of mobile gadgets have gone up. The ‘Energi To Go’, which is available from Sprint Stores, can be used to access the Internet, send emails, capture photos, play music and listen to radio on a number of models of mobiles. These chargers come with ‘smart tip’ technology that optimises power transfer from the battery to the charger. The ‘smart tip’ assesses the power levels in the AA batteries and the battery in the mobile gadget, adjusting the rate of transfer to appropriate level for each of the gadgets. Many organisations are bringing out cells that are functioning as a link between the present day batteries and the future fuel cells. The Energizer batteries are part of the transition. As of now, Energizer has a strong presence in the alkaline and lithium cylindrical cell market. The company is optimistic that it would be able to experience substantial growth in the years to come with new models of batteries.
Content Team -- BSNL Portal -- Intelligroup Asia Pvt. Ltd.
content@bsnl.co.in
To power mobiles without chargers...
The mobile phone industry has been making efforts to introduce user-friendly features. One such attempt is to power cell phones wirelessly. Splashpower, UK, specialises in wireless power for portable devices. The company has introduced two devices - the Multi SplashPad and the Single SplashPad. These products are based on Paraflux, the patented technology from the company. With this product range, the possibility of provisioning wireless power to a wider range of gadgets has gone up. This technology can be harnessed to offer interoperable and universal wireless charging capacity. The company is making intensive efforts to provide solutions to the power crunch faced by the latest mobile devices that have greater power requirements.
Splashpower's Multi SplashPad allows the users to power many gadgets at the same time just by placing them on the surface of the pad. This device can be used to power mobile phones, PDAs, MP3 players and digital cameras. There is no need to plug in the charger and the process of charging does not consume more time than other plugged charging devices. The Single SplashPad charges one gadget at a time and is capable of working with a wide range of devices. It is thin, light and easy to carry. It is a worthy innovation that can be offered by OEMs to the consumers. Electromagnetic induction is used by the pads to charge mobile devices. The process is similar to that used in charging electric toothbrushes.
The company has also developed receiver modules in order to enable manufacturers to incorporate wireless capacity straight into their mobile products. Splashpower also introduced some accessories that can be used to charge the existing mobile devices. These accessories enable the user to power NTT DoCoMo's FOMA 3G phones and Apple iPod. 'Resonance' is the phenomenon used in these devices by the research team at Massachusetts Institute of Technology. Resonance makes an object vibrate when energy of a particular frequency is applied. When two resonant objects of the same frequency are close, they tend to bond strongly. In this instance, instead of using acoustic vibrations, they exploited the resonance of electromagnetic waves. Electromagnetic radiation includes radio waves, infrared and X-rays.
Systems such as radio antennae that use electromagnetic radiation are not appropriate for the effective transfer of energy because they disperse energy in all directions, wasting it. Hence, the team came up with 'non-radiative' objects that have what is referred to as 'long-lived resonances'. When energy is applied to them, it does not escape and remains bound to them. 'Tails' of energy blink over the surface. When another resonant object with the same frequency comes nearer to the tails, the energy gets transferred from that gadget to the other. A copper antenna designed to possess long-lived resonance is capable of transmitting power to a laptop, which has an antenna resonating at similar frequency. The energy not passed onto the gadget will be reabsorbed. These systems would be capable of transferring energy over a distance of three to five metres.
Reference:
BSNL, India.
Monday, July 23, 2007
Thursday, July 19, 2007
SCADA SYSTEM
An industrial SCADA system will be used for the development of the controls of the four LHC experiments. This paper describes the SCADA systems in terms of their architecture, their interface to the process hardware, the functionality and the application development facilities they provide. Some attention is also paid to the industrial standards to which they abide, their planned evolution as well as the potential benefits of their use.
What does SCADA MEAN?
SCADA stands for Supervisory Control And Data Acquisition. As the name indicates, it is not a full control system, but rather focuses on the supervisory level. As such, it is a purely software package that is positioned on top of hardware to which it is interfaced, in general via Programmable Logic Controllers (PLCs), or other commercial hardware modules.
SCADA systems are used not only in industrial processes: e.g. steel making, power generation (conventional and nuclear) and distribution, chemistry, but also in some experimental facilities such as nuclear fusion. The size of such plants range from a few 1000 to several 10 thousands input/output (I/O) channels. However, SCADA systems evolve rapidly and are now penetrating the market of plants with a number of I/O channels of several 100 K: we know of two cases of near to 1 M I/O channels currently under development.
SCADA systems used to run on DOS, VMS and UNIX; in recent years all SCADA vendors have moved to NT and some also to Linux.
Architecture
This section describes the common features of the SCADA products that have been evaluated at CERN in view of their possible application to the control systems of the LHC detectors
1 Hardware Architecture
One distinguishes two basic layers in a SCADA system: 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 (e.g. Siemens H1), or non-proprietary (e.g. Profibus). Data servers are connected to each other and to client stations via an Ethernet LAN. The data servers and client stations are NT platforms but for many products the client stations may also be W95 machines. Fig.1. shows typical hardware architecture.
2 Software Architecture
The products are multi-tasking and are based upon a real-time database (RTDB) located in one or more servers. Servers are responsible for data acquisition and handling (e.g. polling controllers, alarm checking, calculations, logging and archiving) on a set of parameters, typically those they are connected to.
However, it is possible to have dedicated servers for particular tasks, e.g. historian, datalogger, alarm handler. Fig. 2 shows a SCADA architecture that is generic for the products that were evaluated.
3 Communications
Internal Communication
Server-client and server-server communication is in general on a publish-subscribe and event-driven basis and uses a TCP/IP protocol, i.e., a client application subscribes to a parameter which is owned by a particular server application and only changes to that parameter are then communicated to the client application.
Access to Devices
The data servers poll the controllers at a user defined polling rate. The polling rate may be different 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 products will support this too.
The products provide communication drivers for most of the common PLCs and widely used field-buses, e.g., Modbus. Of the three fieldbuses that are recommended at CERN, both Profibus and Worldfip are supported but CANbus often not [3]. Some of the drivers are based on third party products (e.g., Applicom cards) and therefore have additional cost associated with them. VME on the other hand is generally not supported.
A single data server can support multiple communications protocols: it can generally support as many such protocols as it has slots for interface cards.
The effort required to develop new drivers is typically in the range of 2-6 weeks depending on the complexity and similarity with existing drivers, and a driver development toolkit is provided for this.
Interfacing
Application Interfaces / Openness
The provision of OPC client functionality for SCADA to access devices in an open and standard manner is developing. There still seems to be a lack of devices/controllers, which provide OPC server software, but this improves rapidly as most of the producers of controllers are actively involved in the development of this standard. OPC has been evaluated by the CERN-IT-CO group
The products also provide an Open Data Base Connectivity (ODBC) interface to the data in the archive/logs, but not to the configuration database,
an ASCII import/export facility for configuration data,
a library of APIs supporting C, C++, and Visual Basic (VB) to access data in the RTDB, logs and archive. The API often does not provide access to the product's internal features such as alarm handling, reporting, trending, etc.
The PC products provide support for the Microsoft standards such as Dynamic Data Exchange (DDE) which allows e.g. to visualise data dynamically in an EXCEL spreadsheet, Dynamic Link Library (DLL) and Object Linking and Embedding (OLE).
Database
The configuration data are stored in a database that is logically centralised but physically distributed and that is generally of a proprietary format.
For performance reasons, the RTDB resides in the memory of the servers and is also of proprietary format.
The archive and logging format is usually also proprietary for performance reasons, but some products do support logging to a Relational Data Base Management System (RDBMS) at a slower rate either directly or via an ODBC interface.
Scalability
Scalability is understood as the possibility to extend the SCADA based control system by adding more process variables, more specialised servers (e.g. for alarm handling) or more clients. The products achieve scalability by having multiple data servers connected to multiple controllers. Each data server has its own configuration database and RTDB and is responsible for the handling of a sub-set of the process variables (acquisition, alarm handling, archiving).
Redundancy
The products often have built in software redundancy at a server level, which is normally transparent to the user. Many of the products also provide more complete redundancy solutions if required.
Functionality
1 Access Control
Users are allocated to groups, which have defined read/write access privileges to the process parameters in the system and often also to specific product functionality.
2 MMI
The products support multiple screens, which can contain combinations of synoptic diagrams and text.
They also support the concept of a "generic" graphical object with links to process variables. These objects can be "dragged and dropped" from a library and included into a synoptic diagram.
Most of the SCADA products that were evaluated decompose the process in "atomic" parameters (e.g. a power supply current, its maximum value, its on/off status, etc.) to which a Tag-name is associated. The Tag-names used to link graphical objects to devices can be edited as required. The products include a library of standard graphical symbols, many of which would however not be applicable to the type of applications encountered in the experimental physics community.
Standard windows editing facilities are provided: zooming, re-sizing, scrolling... On-line configuration and customisation of the MMI is possible for users with the appropriate privileges. Links can be created between display pages to navigate from one view to another.
3 Trending
The products all provide trending facilities and one can summarise the common capabilities as follows: the parameters to be trended in a specific chart can be predefined or defined on-line
a chart may contain more than 8 trended parameters or pens and an unlimited number of charts can be displayed (restricted only by the readability)
real-time and historical trending are possible, although generally not in the same chart historical trending is possible for any archived parameter
zooming and scrolling functions are provided
parameter values at the cursor position can be displayed
The trending feature is either provided as a separate module or as a graphical object (ActiveX), which can then be embedded into a synoptic display. XY and other statistical analysis plots are generally not provided.
4 Alarm Handling
Alarm handling is based on limit and status checking and performed in the data servers. More complicated expressions (using arithmetic or logical expressions) can be developed by creating derived parameters on which status or limit checking is then performed. The alarms are logically handled centrally, i.e., the information only exists in one place and all users see the same status (e.g., the acknowledgement), and multiple alarm priority levels (in general many more than 3 such levels) are supported.
It is generally possible to group alarms and to handle these as an entity (typically filtering on group or acknowledgement of all alarms in a group). Furthermore, it is possible to suppress alarms either individually or as a complete group. The filtering of alarms seen on the alarm page or when viewing the alarm log is also possible at least on priority, time and group. However, relationships between alarms cannot generally be defined in a straightforward manner. E-mails can be generated or predefined actions automatically executed in response to alarm conditions.
5 Logging/Archiving
The terms logging and archiving are often used to describe the same facility. However, logging can be thought of as medium-term storage of data on disk, whereas archiving is long-term storage of data either on disk or on another permanent storage medium. Logging is typically performed on a cyclic basis, i.e., once a certain file size, time period or number of points is reached the data is overwritten. Logging of data can be performed at a set frequency, or only initiated if the value changes or when a specific predefined event occurs. Logged data can be transferred to an archive once the log is full. The logged data is time-stamped and can be filtered when viewed by a user. The logging of user actions is in general performed together with either a user ID or station ID. There is often also a VCR facility to play back archived data.
6 Report Generation
One can produce reports using SQL type queries to the archive, RTDB or logs. Although it is sometimes possible to embed EXCEL charts in the report, a "cut and paste" capability is in general not provided. Facilities exist to be able to automatically generate, print and archive reports.
7 Automation
The majority of the products allow actions to be automatically triggered by events. A scripting language provided by the SCADA products allows these actions to be defined. In general, one can load a particular display, send an Email, run a user defined application or script and write to the RTDB.
The concept of recipes is supported, whereby a particular system configuration can be saved to a file and then re-loaded at a later date.
Sequencing is also supported whereby, as the name indicates, it is possible to execute a more complex sequence of actions on one or more devices. Sequences may also react to external events.
Some of the products do support an expert system but none has the concept of a Finite State Machine (FSM).
Application Development
1 Configuration
The development of the applications is typically done in two stages. First the process parameters and associated information (e.g. relating to alarm conditions) are defined through some sort of parameter definition template and then the graphics, including trending and alarm displays are developed, and linked where appropriate to the process parameters. The products also provide an ASCII Export/Import facility for the configuration data (parameter definitions), which enables large numbers of parameters to be configured in a more efficient manner using an external editor such as Excel and then importing the data into the configuration database.
However, many of the PC tools now have a Windows Explorer type development studio. The developer then works with a number of folders, which each contains a different aspect of the configuration, including the graphics.
The facilities provided by the products for configuring very large numbers of parameters are not very strong. However, this has not really been an issue so far for most of the products to-date, as large applications are typically about 50K I/O points and database population from within an ASCII editor such as Excel is still a workable option.
On-line modifications to the configuration database and the graphics is generally possible with the appropriate level of privileges.
2 Development Tools
The following development tools are provided as standard:
a graphics editor, with standard drawing facilities including freehand, lines, squares circles, etc. It is possible to import pictures in many formats as well as using predefined symbols including e.g. trending charts, etc. A library of generic symbols is provided that can be linked dynamically to variables and animated as they change. It is also possible to create links between views so as to ease navigation at run-time.
a data base configuration tool (usually through parameter templates). It is in general possible to export data in ASCII files so as to be edited through an ASCII editor or Excel. a scripting language an Application Program Interface (API) supporting C, C++, VB a Driver Development Toolkit to develop drivers for hardware that is not supported by the SCADA product.
3 Object Handling
The products in general have the concept of graphical object classes, which support inheritance. In addition, some of the products have the concept of an object within the configuration database. In general the products do not handle objects, but rather handle individual parameters, e.g., alarms are defined for parameters, logging is performed on parameters, and control actions are performed on parameters. The support of objects is therefore fairly superficial.
Evolution
SCADA vendors release one major version and one to two additional minor versions once per year. These products evolve thus very rapidly so as to take advantage of new market opportunities, to meet new requirements of their customers and to take advantage of new technologies.
As was already mentioned, most of the SCADA products that were evaluated decompose the process in "atomic" parameters to which a Tag-name is associated. This is impractical in the case of very large processes when very large sets of Tags need to be configured. As the industrial applications are increasing in size, new SCADA versions are now being designed to handle devices and even entire systems as full entities (classes) that encapsulate all their specific attributes and functionality. In addition, they will also support multi-team development.
As far as new technologies are concerned, the SCADA products are now adopting:
Web technology, ActiveX, Java, etc.
OPC as a means for communicating internally between the client and server modules. It should thus be possible to connect OPC compliant third party modules to that SCADA product.
Engineering
Whilst one should rightly anticipate significant development and maintenance savings by adopting a SCADA product for the implementation of a control system, it does not mean a "no effort" operation. The need for proper engineering can not be sufficiently emphasised to reduce development effort and to reach a system that complies with the requirements, that is economical in development and maintenance and that is reliable and robust. Examples of engineering activities specific to the use of a SCADA system are the definition of:
a library of objects (PLC, device, subsystem) complete with standard object behaviour (script, sequences, ...), graphical interface and associated scripts for animation,
templates for different types of "panels", e.g. alarms,
instructions on how to control e.g. a device ...,
a mechanism to prevent conflicting controls (if not provided with the SCADA),
alarm levels, behaviour to be adopted in case of specific alarms, ...
Potential benefits of SCADA
The benefits one can expect from adopting a SCADA system for the control of experimental physics facilities can be summarised as follows:
a rich functionality and extensive development facilities. The amount of effort invested in SCADA product amounts to 50 to 100 p-years!
the amount of specific development that needs to be performed by the end-user is limited, especially with suitable engineering.
reliability and robustness. These systems are used for mission critical industrial processes where reliability and performance are paramount. In addition, specific development is performed within a well-established framework that enhances reliability and robustness.
technical support and maintenance by the vendor.
For large collaborations, as for the CERN LHC experiments, using a SCADA system for their controls ensures a common framework not only for the development of the specific applications but also for operating the detectors. Operators experience the same "look and feel" whatever part of the experiment they control. However, this aspect also depends to a significant extent on proper engineering.
REFERENCES
http://ref.web.cern.ch/ref/CERN/CNL/2000/003/scada/
OTHER RESOURCES:
www.tech-faq.com/scada.shtml
www.roseindia.net/technology/scada/index.shtm
www.rel.co.in/aboutus/scada.asp
wikipedia.org/wiki/SCADA
What does SCADA MEAN?
SCADA stands for Supervisory Control And Data Acquisition. As the name indicates, it is not a full control system, but rather focuses on the supervisory level. As such, it is a purely software package that is positioned on top of hardware to which it is interfaced, in general via Programmable Logic Controllers (PLCs), or other commercial hardware modules.
SCADA systems are used not only in industrial processes: e.g. steel making, power generation (conventional and nuclear) and distribution, chemistry, but also in some experimental facilities such as nuclear fusion. The size of such plants range from a few 1000 to several 10 thousands input/output (I/O) channels. However, SCADA systems evolve rapidly and are now penetrating the market of plants with a number of I/O channels of several 100 K: we know of two cases of near to 1 M I/O channels currently under development.
SCADA systems used to run on DOS, VMS and UNIX; in recent years all SCADA vendors have moved to NT and some also to Linux.
Architecture
This section describes the common features of the SCADA products that have been evaluated at CERN in view of their possible application to the control systems of the LHC detectors
1 Hardware Architecture
One distinguishes two basic layers in a SCADA system: 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 (e.g. Siemens H1), or non-proprietary (e.g. Profibus). Data servers are connected to each other and to client stations via an Ethernet LAN. The data servers and client stations are NT platforms but for many products the client stations may also be W95 machines. Fig.1. shows typical hardware architecture.
2 Software Architecture
The products are multi-tasking and are based upon a real-time database (RTDB) located in one or more servers. Servers are responsible for data acquisition and handling (e.g. polling controllers, alarm checking, calculations, logging and archiving) on a set of parameters, typically those they are connected to.
However, it is possible to have dedicated servers for particular tasks, e.g. historian, datalogger, alarm handler. Fig. 2 shows a SCADA architecture that is generic for the products that were evaluated.
3 Communications
Internal Communication
Server-client and server-server communication is in general on a publish-subscribe and event-driven basis and uses a TCP/IP protocol, i.e., a client application subscribes to a parameter which is owned by a particular server application and only changes to that parameter are then communicated to the client application.
Access to Devices
The data servers poll the controllers at a user defined polling rate. The polling rate may be different 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 products will support this too.
The products provide communication drivers for most of the common PLCs and widely used field-buses, e.g., Modbus. Of the three fieldbuses that are recommended at CERN, both Profibus and Worldfip are supported but CANbus often not [3]. Some of the drivers are based on third party products (e.g., Applicom cards) and therefore have additional cost associated with them. VME on the other hand is generally not supported.
A single data server can support multiple communications protocols: it can generally support as many such protocols as it has slots for interface cards.
The effort required to develop new drivers is typically in the range of 2-6 weeks depending on the complexity and similarity with existing drivers, and a driver development toolkit is provided for this.
Interfacing
Application Interfaces / Openness
The provision of OPC client functionality for SCADA to access devices in an open and standard manner is developing. There still seems to be a lack of devices/controllers, which provide OPC server software, but this improves rapidly as most of the producers of controllers are actively involved in the development of this standard. OPC has been evaluated by the CERN-IT-CO group
The products also provide an Open Data Base Connectivity (ODBC) interface to the data in the archive/logs, but not to the configuration database,
an ASCII import/export facility for configuration data,
a library of APIs supporting C, C++, and Visual Basic (VB) to access data in the RTDB, logs and archive. The API often does not provide access to the product's internal features such as alarm handling, reporting, trending, etc.
The PC products provide support for the Microsoft standards such as Dynamic Data Exchange (DDE) which allows e.g. to visualise data dynamically in an EXCEL spreadsheet, Dynamic Link Library (DLL) and Object Linking and Embedding (OLE).
Database
The configuration data are stored in a database that is logically centralised but physically distributed and that is generally of a proprietary format.
For performance reasons, the RTDB resides in the memory of the servers and is also of proprietary format.
The archive and logging format is usually also proprietary for performance reasons, but some products do support logging to a Relational Data Base Management System (RDBMS) at a slower rate either directly or via an ODBC interface.
Scalability
Scalability is understood as the possibility to extend the SCADA based control system by adding more process variables, more specialised servers (e.g. for alarm handling) or more clients. The products achieve scalability by having multiple data servers connected to multiple controllers. Each data server has its own configuration database and RTDB and is responsible for the handling of a sub-set of the process variables (acquisition, alarm handling, archiving).
Redundancy
The products often have built in software redundancy at a server level, which is normally transparent to the user. Many of the products also provide more complete redundancy solutions if required.
Functionality
1 Access Control
Users are allocated to groups, which have defined read/write access privileges to the process parameters in the system and often also to specific product functionality.
2 MMI
The products support multiple screens, which can contain combinations of synoptic diagrams and text.
They also support the concept of a "generic" graphical object with links to process variables. These objects can be "dragged and dropped" from a library and included into a synoptic diagram.
Most of the SCADA products that were evaluated decompose the process in "atomic" parameters (e.g. a power supply current, its maximum value, its on/off status, etc.) to which a Tag-name is associated. The Tag-names used to link graphical objects to devices can be edited as required. The products include a library of standard graphical symbols, many of which would however not be applicable to the type of applications encountered in the experimental physics community.
Standard windows editing facilities are provided: zooming, re-sizing, scrolling... On-line configuration and customisation of the MMI is possible for users with the appropriate privileges. Links can be created between display pages to navigate from one view to another.
3 Trending
The products all provide trending facilities and one can summarise the common capabilities as follows: the parameters to be trended in a specific chart can be predefined or defined on-line
a chart may contain more than 8 trended parameters or pens and an unlimited number of charts can be displayed (restricted only by the readability)
real-time and historical trending are possible, although generally not in the same chart historical trending is possible for any archived parameter
zooming and scrolling functions are provided
parameter values at the cursor position can be displayed
The trending feature is either provided as a separate module or as a graphical object (ActiveX), which can then be embedded into a synoptic display. XY and other statistical analysis plots are generally not provided.
4 Alarm Handling
Alarm handling is based on limit and status checking and performed in the data servers. More complicated expressions (using arithmetic or logical expressions) can be developed by creating derived parameters on which status or limit checking is then performed. The alarms are logically handled centrally, i.e., the information only exists in one place and all users see the same status (e.g., the acknowledgement), and multiple alarm priority levels (in general many more than 3 such levels) are supported.
It is generally possible to group alarms and to handle these as an entity (typically filtering on group or acknowledgement of all alarms in a group). Furthermore, it is possible to suppress alarms either individually or as a complete group. The filtering of alarms seen on the alarm page or when viewing the alarm log is also possible at least on priority, time and group. However, relationships between alarms cannot generally be defined in a straightforward manner. E-mails can be generated or predefined actions automatically executed in response to alarm conditions.
5 Logging/Archiving
The terms logging and archiving are often used to describe the same facility. However, logging can be thought of as medium-term storage of data on disk, whereas archiving is long-term storage of data either on disk or on another permanent storage medium. Logging is typically performed on a cyclic basis, i.e., once a certain file size, time period or number of points is reached the data is overwritten. Logging of data can be performed at a set frequency, or only initiated if the value changes or when a specific predefined event occurs. Logged data can be transferred to an archive once the log is full. The logged data is time-stamped and can be filtered when viewed by a user. The logging of user actions is in general performed together with either a user ID or station ID. There is often also a VCR facility to play back archived data.
6 Report Generation
One can produce reports using SQL type queries to the archive, RTDB or logs. Although it is sometimes possible to embed EXCEL charts in the report, a "cut and paste" capability is in general not provided. Facilities exist to be able to automatically generate, print and archive reports.
7 Automation
The majority of the products allow actions to be automatically triggered by events. A scripting language provided by the SCADA products allows these actions to be defined. In general, one can load a particular display, send an Email, run a user defined application or script and write to the RTDB.
The concept of recipes is supported, whereby a particular system configuration can be saved to a file and then re-loaded at a later date.
Sequencing is also supported whereby, as the name indicates, it is possible to execute a more complex sequence of actions on one or more devices. Sequences may also react to external events.
Some of the products do support an expert system but none has the concept of a Finite State Machine (FSM).
Application Development
1 Configuration
The development of the applications is typically done in two stages. First the process parameters and associated information (e.g. relating to alarm conditions) are defined through some sort of parameter definition template and then the graphics, including trending and alarm displays are developed, and linked where appropriate to the process parameters. The products also provide an ASCII Export/Import facility for the configuration data (parameter definitions), which enables large numbers of parameters to be configured in a more efficient manner using an external editor such as Excel and then importing the data into the configuration database.
However, many of the PC tools now have a Windows Explorer type development studio. The developer then works with a number of folders, which each contains a different aspect of the configuration, including the graphics.
The facilities provided by the products for configuring very large numbers of parameters are not very strong. However, this has not really been an issue so far for most of the products to-date, as large applications are typically about 50K I/O points and database population from within an ASCII editor such as Excel is still a workable option.
On-line modifications to the configuration database and the graphics is generally possible with the appropriate level of privileges.
2 Development Tools
The following development tools are provided as standard:
a graphics editor, with standard drawing facilities including freehand, lines, squares circles, etc. It is possible to import pictures in many formats as well as using predefined symbols including e.g. trending charts, etc. A library of generic symbols is provided that can be linked dynamically to variables and animated as they change. It is also possible to create links between views so as to ease navigation at run-time.
a data base configuration tool (usually through parameter templates). It is in general possible to export data in ASCII files so as to be edited through an ASCII editor or Excel. a scripting language an Application Program Interface (API) supporting C, C++, VB a Driver Development Toolkit to develop drivers for hardware that is not supported by the SCADA product.
3 Object Handling
The products in general have the concept of graphical object classes, which support inheritance. In addition, some of the products have the concept of an object within the configuration database. In general the products do not handle objects, but rather handle individual parameters, e.g., alarms are defined for parameters, logging is performed on parameters, and control actions are performed on parameters. The support of objects is therefore fairly superficial.
Evolution
SCADA vendors release one major version and one to two additional minor versions once per year. These products evolve thus very rapidly so as to take advantage of new market opportunities, to meet new requirements of their customers and to take advantage of new technologies.
As was already mentioned, most of the SCADA products that were evaluated decompose the process in "atomic" parameters to which a Tag-name is associated. This is impractical in the case of very large processes when very large sets of Tags need to be configured. As the industrial applications are increasing in size, new SCADA versions are now being designed to handle devices and even entire systems as full entities (classes) that encapsulate all their specific attributes and functionality. In addition, they will also support multi-team development.
As far as new technologies are concerned, the SCADA products are now adopting:
Web technology, ActiveX, Java, etc.
OPC as a means for communicating internally between the client and server modules. It should thus be possible to connect OPC compliant third party modules to that SCADA product.
Engineering
Whilst one should rightly anticipate significant development and maintenance savings by adopting a SCADA product for the implementation of a control system, it does not mean a "no effort" operation. The need for proper engineering can not be sufficiently emphasised to reduce development effort and to reach a system that complies with the requirements, that is economical in development and maintenance and that is reliable and robust. Examples of engineering activities specific to the use of a SCADA system are the definition of:
a library of objects (PLC, device, subsystem) complete with standard object behaviour (script, sequences, ...), graphical interface and associated scripts for animation,
templates for different types of "panels", e.g. alarms,
instructions on how to control e.g. a device ...,
a mechanism to prevent conflicting controls (if not provided with the SCADA),
alarm levels, behaviour to be adopted in case of specific alarms, ...
Potential benefits of SCADA
The benefits one can expect from adopting a SCADA system for the control of experimental physics facilities can be summarised as follows:
a rich functionality and extensive development facilities. The amount of effort invested in SCADA product amounts to 50 to 100 p-years!
the amount of specific development that needs to be performed by the end-user is limited, especially with suitable engineering.
reliability and robustness. These systems are used for mission critical industrial processes where reliability and performance are paramount. In addition, specific development is performed within a well-established framework that enhances reliability and robustness.
technical support and maintenance by the vendor.
For large collaborations, as for the CERN LHC experiments, using a SCADA system for their controls ensures a common framework not only for the development of the specific applications but also for operating the detectors. Operators experience the same "look and feel" whatever part of the experiment they control. However, this aspect also depends to a significant extent on proper engineering.
REFERENCES
http://ref.web.cern.ch/ref/CERN/CNL/2000/003/scada/
OTHER RESOURCES:
www.tech-faq.com/scada.shtml
www.roseindia.net/technology/scada/index.shtm
www.rel.co.in/aboutus/scada.asp
wikipedia.org/wiki/SCADA
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