PLC COMMUNICATION -Industrial Automation in India | PLC SCADA DCS Training in Chennai,

PLC COMMUNICATION -Industrial Automation in India | PLC SCADA DCS Training in Chennai,

Access, protocol, and modulation functions of LANs. By using standard interfaces and protocols, LANs allow a mix of devices (PLCs, PCs, mainframe computers, operator interface terminals, etc.) from many different vendors to communicate with others on the network. Access.

NETWORK CABLING COLOR CODE -Industrial Automation in India | PLC SCADA DCS Training in Chennai,

NETWORK CABLING COLOR CODE -Industrial Automation in India | PLC SCADA DCS Training in Chennai,

A crossover cable has different ends. A straight-thru is used as a patch cord in Ethernet connections. A crossover is used to connect two Ethernet devices without a hub or for connecting two hubs. A crossover has one end with the Orange set of wires switched with the Green set.

Industrial Automation in India | PLC SCADA DCS Training in Chennai

Atmel Automotive Applications provides a touch solution for all automotive microcontrollers in the automotive environment :

Atmel Automotive Applications is an application that covers a wide range of products, ranging from electronics body, engine components, and access to the system elements and entertainment lighting. It support small design provide a high level of integration, to fit the limited space available in the automotive environment. 

THE BEST ATMEL AUTOMOTIVE APPLICATIONS WITH STRICT AUTOMOTIVE QUALIFICATION REQUIREMENTS

To meet the diverse needs of a wide range of Atmel Automotive Applications, developers need a solution that provides: 

1. The strict automotive qualification requirements, including industry standards and the quality of the Beatles cars

2. Flexible interface to the various capacities HMI Options with standards-based connectivity solutions for smart networks

3. Protection and compatibility of products of high-voltage, including strong electromagnetic compatibility (EMC); Electrostatic Discharge (ESD) protection; and OEM approvals

4. High temperature resistance hassle-free environments in the automotive process

5. Security tight to get a car with low power consumption for maximum efficiency

6. A complete solution set for cars

ATMEL AUTOMOTIVE APPLICATIONS SOLUTIONS TO MAKES CARS SAFER, MORE ECONOMICAL AND CONVENIENT

Atmel Automotive Applications provide a comprehensive set of products for automotive applications. It meets the strict quality requirements of the automotive and makes cars safer, more economical and convenient. The solutions include:

1. Body and leisure

These functions provide for branding and differentiation is a unique opportunity for OEMs cars. This includes control functions such as door and window control, and monitors the sunroof, controls the steering column, and climate control

2. The arrival of a car

Atmel Automotive Applications Auto Electronic efforts focus not only on large complex electronic systems, but also on smaller independent applications. Atmel built on decades of experience in the design of automotive electronics, and offers a range of stand-alone solutions uniquely designed.

3. Information and entertainment / HMI / connection

Category & Media and HMI link many of the functions that allow the driver and passengers to interact with the car to provide convenient service, information, and entertainment that you want in the cabin car safely and smoothly involved.

4. Under the Hood

Atmel does not focus on electronic efforts only on large complex electronic systems, but also on smaller independent applications. Atmel built on decades of experience in the design of automotive electronics, and offers a range of stand-alone solutions uniquely designed.

ATMEL AUTOMOTIVE APPLICATIONS FEATURE

Atmel Automotive Applications has demonstrated a strong commitment to the automotive market. Their company has more than 25 years of experience designing automotive electronics, a market leader in several areas of the car. They offer a wide range of customized automotive technologies.

Comprehensive portfolio and a wide range of Atmel ranging from car radios and navigation devices, and the interim standards electronics body, including high temperature, Lin / CAN and motor driver IC, and a solution for system access, car RKE / internal key chains for Atmel AVR us ® microcontrollers cars, memories, capacitive and customer-specific ICs. 

CONCLUSION

Atmel Automotive Applications is touch solutions forward from the proximity sensor for door keyless entry with the touch screen on the GPS. Touch-screen interface gives the driver and passengers a sense of luxury, quality and excellence. With the industry the most comprehensive portfolios, Atmel provides a touch solution for all automotive microcontrollers in the automotive environment. 

BLOCK DIAGRAM OF PLC

A simplified block diagram of a PLC shown in above Fig. It has three major units/sections.

• I/O (Input/Output) Modules.
• CPU (Central Processing Units).
• Programmer/Monitor.   

     The input section converts the field signals supplied by input devices/sensors to logic-level signals that the PLC's CPU can read.
     The Processor Section reads these inputs, Processes the signal, and prepares the output signals.
     The output section converts the logic level output signals coming from processor section to high level signals and used to actuate various output field devices.
     The programmer/monitor is used to enter the user's program into memory and to monitor the execution of the program.

1) I/O Section:-

          The I/O section establish the interfacing between physical devices in the real world outside the PLC and the digital arena inside the PLC.

          The input module has bank of terminals for physically connecting input devices, like push buttons, limit switches etc. to a PLC. the role of an input module is to translate signals from input devices into a form that the PLC's CPU can understand.

          The Output module also has bank of terminals that physically connect output devices like solenoids, motor starters, indicating lamps etc. to a PLC. The role of an output module is to translate signals from the PLC's CPU into a form that the output device can use.

The tasks of the I/O section can be classified as:

• Conditioning
• Isolation 
• Termination
• Indication

           An electronic system for connecting I/O modules to remotely located I/O devices can be added if needed. The actual operating process under PLC Control can be thousands of feet from the CPU and its I/O modules.

2) CPU Section:-

            The Central Processing Unit, the brain of the system is the control portion of the PLC. It has three Subparts.

• Memory System
• Processor
• Power Supply    

Memory System:-

The memory is the area of the CPU in which data and information is stored and retrieved.The total memory area can be subdivided into the following four Sections.

• I/O Image Memory

         The input image memory consists of memory locations used to hold the ON or OFF states of each input field devices, in the input status file.

         The output status file consists of memory locations that stores the ON or OFF states of hardware output devices in the field. Data is stored in the output status file as a result of solving user program and is waiting to be transferred to the output module's switching device.

• Data Memory

         It is used to store numerical data required in math calculation, bar code data etc.

• User Memory

         It contains user's application program.

• Executive Memory

         It is used to store an executive program or system software . An operating system of the PLC is a special program that controls the action of CPU and consequently the execution of the user's program. A PLC operating system s designed to scan image memory, interprets the instruction of user's program stored in main memory, and executes the user's application program the operating system is supplied by the PLC manufacturer and is permanently held in memory.

Processor:-  

                  The processor, the heart of CPU is the computerized part of the CPU in the form of Microprocessor / Micro controller chip. It supervises all operation in the system and performs all tasks necessary to fulfill the PLC function.

• It reads the information i.e status of externally connected input devices with input module.
• It stores this information in memory for later use.
• It carries out mathematical and logic operations as specified in application program.
• After solving the user's program, it writes the result values in the memory.
• It sends data out to external devices like output module, so as to actuate field hardware.
• It performs peripheral and external device communication.
• It Performs self diagnostics.

 Power Supply:-  

                        The power supply provides power to memory system, processor and I/O Modules.

• It converts the higher level AC line Voltage to various operational DC values.
• for electronic circuitry.
• It filters and regulates the DC voltages to ensure proper computer operations. 

 

3) Programmer/Monitor:-

                           The Programmer/Monitor (PM) is a device used to communicate with the circuits of the PLC.The programming unit allows the engineer/technicians toenter the edit the program to be executed.

                           In its simplest form it can be hand-held device with membrane keypad for program entry, and a display device (LED or LCD) for viewing program steps of functions.

                           More advanced systems employ a separate industrial terminal or personal computers with type-writer type keyboard and CRT monitors. With the help of proprietary software, it allows programmer to write, view and edit the program and download it into the PLC. It also allows user to monitor the PLC as it is running the program. With this monitoring systems, such things as internal coils, registers, timers and other items not visible externally can be monitored to determine proper operation. Also,internal register data can be altered, if required. to fine tune program operation while debugging.communication between PM and PLC is done via a cable connected to a special programming port on PLC. connection to the personal computer can be through a serial port or from a dedicated card installed in the computer.

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SIMATIC Industrial Automation Software provides maximum efficiency, flexibility and wide and high cost effectiveness - in every application :

SIMATIC Industrial Automation Software can achieve maximum efficiency for all automation software tasks to achieve new heights in efficiency resulting from our unified and integrated platform and utilization of open interfaces and modules are reusable. 

ADVANCED INDUSTRIAL AUTOMATION SOFTWARE PROVIDES ADVANCED SOLUTIONS THAT HAVE BEEN DESIGNED WITH PROPER ATTENTION

From the field level to the enterprise management level, there are a wide range of automation software within SIMATIC software provides advanced solutions that have been designed with proper attention given to every detail. Function and selection of our industry-specific software ensures that you achieve maximum efficiency in a wide range of processes and tasks. 

The continued development of the SIMATIC Industrial Automation Software makes sure that all integrated automation components in the latest level. Select the appropriate license to get the most benefit from your product. Automation solutions today must deal with different challenges. It calls for high-performance software - efficiency, flexibility and reliability as possible, now and in the future alike. And select the appropriate license for your applications to maintain effective programs in terms of cost yet. 

SIMATIC INDUSTRIAL AUTOMATION SOFTWARE PROGRAM HELP YOU MANAGE YOUR LICENSES COMFORTABLE AND KEEP THIS SOFTWARE UP TO DATE

The challenge of the field of automation is keeping your software up to the latest standard. Up to the date of the program is important if you want to work efficiently and to obtain reliable results. But even for the Industrial Automation Software program, it must remain transparent and cost explained. That is why SIMATIC program offers you not only the different types of licenses, but a useful tool to help you manage your licenses comfortable and keep this software up to date. 

INDUSTRIAL AUTOMATION SOFTWARE SIMATIC UPDATE SERVICE LICENSES

If you need a license for an area of one business, a small team or an international company, Siemens has the proper license for your application. So you can use your software SIMATIC effective in terms of cost only in the way that is right for your needs. Program from Siemens Industrial Automation Software is constantly updated and improved. 

Provides Software Update Service (SUS) latest version of the program you're right where you work - with no additional commands and immediately after its release. Online delivery program (OSD) software license makes you faster - whether it is a new system or delivery of SUS. You can download software licenses and SIMATIC from the Internet. It will be faster than ever before. 

Industrial Automation Software systems provide you with the answers to the requirements of plant and machinery and protective of the future are increasingly demanding. Engineering to meet the needs of all sectors of industry in the almost infinite variety of its tasks, the superiority of our systems provides maximum efficiency, flexibility and wide and high cost effectiveness - in every application. 

CONCLUSION

Industrial Automation Software of SIMATIC system is synonymous with excellence for our commitment to engineering and superior technology. For more than 50 years, Siemens has continuously evolving technological advances in automation. The system includes all the needs of the industry and set the standard in its field of competence. 

Allen-Bradley Servo Motor

Allen-Bradley Servo Motor, Best To Provide Motion In Automation Solution; Product Acknowledgement And Beneficial Approach :

Servo Motor is part of industrial movement facilities, both in laterally and based on the fact. There are so many equipment, device and other stuff which is need and used as moving function. For the example, the conveyor belt which used to move some stuff or product from one departement to other department. Another function of this conveyor belt is to move several parts which is need to be assemble by worker or co-bots. 

At the other hands, Servo Motor was run with automation solution, motor and automation motion controller. All was doing for single purposes as the industrial kindness and increas the productivity. But there is an answer with it, what kind manufacture which is create best motor models and so with several functional utilities to complete it? There are lots of, but one of the best come from best manufacture or developer called the servo motor from Allen-Bradey products. Here in this article we would go further more with couple of Allen Bradley Servo motor product divers. 

BROAD OF LINEAR AND ROTARY MOTOR, ALLEN-BRADLEY SERVO MOTOR CAME WITH BEST PRODUCT FOR INDUSTRIAL KINDNESS

Allen-Bradley has provide the industries with varies of great product, for the servo motor models there are at least three main component which create and offered by Allen-Bradley for the public and here it them; SpeedTec DIN
a
conectors Kinetix Cable, LDL and LDC series Linear Servo Motors, and The Rotary Motors, which comes by diferent utilities such as; Kinetix VP and MP Series servo motor also the RDD Series Direct Drive. Each of that has been designed with great features, and here it the summary. 

1. SpeedTec DIN conectors Kinetix Cable

This flexing cable came from Allen Bradley called with Buletin 2090 Kinetix Cables, design to quick and easier connect with servo connection, available from 2 AWG to 16 AWG available with brakes option. At the drives end, it build with molded conector (D-sub) and flying leads. Also small diameter cable jacket, so it would be easier to channeling through conduits.

2. LDL and LDC series Linear Servo Motors

This design as precise linear positioning even in high operating speed, this model has been developed with several features that give benefits such as; full setup programming with RSLogix™ 5000 software, designed compact with no bearings, gears or belts, and best way in quick maintain movement even handling many motion profiles.

3. The Rotary Motors

Designed to be high performance motion systems, this Allen Bradley product came with many models, such as; VP Kinetix Servo Motors, MP Series, also the RDD Series Direct Drive. Each has been designed with great capabilites such as integrated motion on IP™/EtherNet, food grade function, low or medium inertia also rapid acceleration and deceleration.

For Allen-Bradley companies, product and qualities of the product can’t be compromised. The quality of the product came in single way with inovation and development. By that idea, in motion control department of Servo Motor Allen-Bradley has been offered each of that great product. 

CONCLUSION

Allen-Bradley servo motors series, has been created and offered as great motion control component. With many capabilites such as; VP-Low Inertia motor, food grade, build with stainless steel material. Each of the parts also certified with latest globals certified standard such as IP67 rating, UL and DESINA, it can found in the product from Allen Bradley such as Buletin 2090 Kinetix Cables that was design as one of servo motor in Allen Bradley motion controller product. 

"Leading industrial automation companies in India providing PLC SCADA DCS training in Chennai. Best PLC training center in Chennai. Automation in India

What is a VFD?

A Variable Frequency Drive (VFD) is a type of motor controller that drives an electric motor by varying the frequency and voltage supplied to the electric motor. Other names for a VFD are variable speed drive, adjustable speed drive, adjustable frequency drive, AC drive, microdrive, and inverter.  Frequency (or hertz) is directly related to the motor’s speed (RPMs). In other words, the faster the frequency, the faster the RPMs go. If an application does not require an electric motor to run at full speed, the VFD can be used to ramp down the frequency and voltage to meet the requirements of the electric motor’s load. As the application’s motor speed requirements change, the VFD can simply turn up or down the motor speed to meet the speed requirement. 

How does a Variable Frequency Drive work?

 The first stage of a Variable Frequency AC Drive, or VFD, is the Converter. The converter is comprised of six diodes, which are similar to check valves used in plumbing systems. They allow current to flow in only one direction; the direction shown by the arrow in the diode symbol. For example, whenever A-phase voltage (voltage is similar to pressure in plumbing systems) is more positive than B or C phase voltages, then that diode will open and allow current to flow. When B-phase becomes more positive than A-phase, then the B-phase diode will open and the A-phase diode will close. The same is true for the 3 diodes on the negative side of the bus. Thus, we get six current “pulses” as each diode opens and closes. This is called a “six-pulse VFD”, which is the standard configuration for current Variable Frequency Drives. 

Let us assume that the drive is operating on a 480V power system. The 480V rating is “rms” or root-mean-squared. The peaks on a 480V system are 679V. As you can see, the VFD dc bus has a dc voltage with an AC ripple. The voltage runs between approximately 580V and 680V. 

We can get rid of the AC ripple on the DC bus by adding a capacitor. A capacitor operates in a similar fashion to a reservoir or accumulator in a plumbing system. This capacitor absorbs the ac ripple and delivers a smooth dc voltage. The AC ripple on the DC bus is typically less than 3 Volts. Thus, the voltage on the DC bus becomes “approximately” 650VDC. The actual voltage will depend on the voltage level of the AC line feeding the drive, the level of voltage unbalance on the power system, the motor load, the impedance of the power system, and any reactors or harmonic filters on the drive.

The diode bridge converter that converts AC-to-DC, is sometimes just referred to as a converter. The converter that converts the dc back to ac is also a converter, but to distinguish it from the diode converter, it is usually referred to as an “inverter”. It has become common in the industry to refer to any DC-to-AC converter as an inverter.

When we close one of the top switches in the inverter, that phase of the motor is connected to the positive dc bus and the voltage on that phase becomes positive. When we close one of the bottom switches in the converter, that phase is connected to the negative dc bus and becomes negative. Thus, we can make any phase on the motor become positive or negative at will and can thus generate any frequency that we want. So, we can make any phase be positive, negative, or zero. 

Notice that the output from the VFD is a “rectangular” wave form. VFD’s do not produce a sinusoidal output. This rectangular waveform would not be a good choice for a general purpose distribution system, but is perfectly adequate for a motor.

If we want to reduce the motor frequency to 30 Hz, then we simply switch the inverter output transistors more slowly. But, if we reduce the frequency to 30Hz, then we must also reduce the voltage to 240V in order to maintain the V/Hz ratio (see the VFD Motor Theory presentation for more on this). How are we going to reduce the voltage if the only voltage we have is 650VDC?

This is called Pulse Width Modulation or PWM. Imagine that we could control the pressure in a water line by turning the valve on and off at a high rate of speed. While this would not be practical for plumbing systems, it works very well for VFD’s. Notice that during the first half cycle, the voltage is ON half the time and OFF half the time. Thus, the average voltage is half of 480V or 240V. By pulsing the output, we can achieve any average voltage on the output of the VFD.

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What is an HMI?

HMI is the acronym for Human Machine Interface, and can be designed as just that; an interface between the user and the machine. An HMI is considered an interface; a very broad term that can include MP3 players, industrial computers, household appliances, and office equipment. However, an HMI is much more specific to manufacturing and process control systems. An HMI provides a visual representation of a control system and provides real time data acquisition. An HMI can increase productivity by having a centralized control center that is extremely user-friendly. 

HMI Block Diagram;

A Human Machine Interface (HMI) is exactly what the name implies; a graphical interface that allows humans and machines to interact. Human machine interfaces vary widely, from control panels for nuclear power plants, to the screen on an iPhone. However, for this discussion we are referring to an HMI control panel for manufacturing-type processes. An HMI is the centralized control unit for manufacturing lines, equipped with Data Recipes, event logging, video feed, and event triggering, so that one may access the system at any moment for any purpose. For a manufacturing line to be integrated with an HMI, it must first be working with a Programmable Logic Controller (PLC). It is the PLC that takes the information from the sensors, and transforms it to Boolean algebra, so the HMI can decipher and make decisions.

Basic Types of HMIs :

There are three basic types of HMIs: the pushbutton replacer, the data handler, and the overseer. Before the HMI came into existence, a control might consist of hundreds of pushbuttons and LEDs performing different operations. The pushbutton replacer HMI has streamlined manufacturing processes, centralizing all the functions of each button into one location. The data handler is perfect for applications requiring constant feedback from the system, or printouts of the production reports. With the data handler, you must ensure the HMI screen is big enough for such things as graphs, visual representations and production summaries. The data handler includes such functions as recipes, data trending, data logging and alarm handling/logging. Finally, anytime an application involves SCADA or MES, an overseer HMI is extremely beneficial. The overseer HMI will most likely need to run Windows, and have several Ethernet ports. 

How to Select an HMI :

An HMI is a substantial purchase, so it is important to know exactly what is required of it. An HMI is used for three primary roles: a pushbutton replacer, data handler, and overseer. The pushbutton replacer takes the place of LEDs, On/ Off buttons, switches or any mechanical device that performs a control function. The elimination of these mechanical devices is possible because the HMI can provide a visual representation of all these devices on its LCD screen, while performing all the same functions. The Data Handler is used for applications that require constant feedback and monitoring. Often these Data Handlers come equipped with large capacity memories. The last of the HMI three types is referred to as the overseer, because it works with SCADA and MES. These are centralized systems that monitor and control entire sites or complexes of large systems spread out over large areas. An HMI is usually linked to the SCADA system's databases and software programs, to provide trending, diagnostic data, and management information

Physical Properties of a HMI :

The actual physical properties of an HMI vary from model to model and among manufacturers. It is important that one makes the appropriate selection. An HMI that is located in a water plant might have various water seals around its perimeter, as opposed to an HMI that is located in a pharmaceutical warehouse. The actual size of an HMI is also a key physical property that will vary, because not all applications require a large, high-resolution monitor. Some applications may only require a small, black and white touch screen monitor. When it comes to selecting an HMI, the physical properties are extremely important because one must take into consideration the operating environment, and what safety measures the HMI needs to protect itself. Also, a specific size may be needed due to space limitations. Lastly, physical properties include the processor and memory of the HMI. It is important to make sure that the processor and memory capabilities are sufficient enough to control a system. 

How does an HMI Work?  

First consider the other components that are necessary to make a manufacturing control system operate. The production line consists of all the machinery that performs the work required in the production of the product. Next, consider the various input/output sensors that monitor temperature, speed, pressure, weight and feed rate. Third, decide on the programmable logic controller (PLC) that will receive the data from the input/output sensors, and converts the data into logical combinations.

How can a PLC be controlled without ladder logic?

How can a PLC be controlled without ladder logic?

What Programming Software to Choose?

When considering which programming software to use, there are three main categories to choose from: proprietary, hardware independent and open software. Proprietary software is the software that the manufacturer provides, which is typically easy to use and allows for quick development. The drawback is that proprietary software will only run on that specific hardware platform. Hardware-independent software is third party software developed to program on several different types of HMIs. This type of software gives the developer much more freedom for the HMI selection. The downside to hardware independent software is that it is not as user-friendly as the proprietary. Open Software should only be selected by the advanced programmer. It allows the developer to have complete openness in the design process.

HMI Applications :

The HMI is used throughout various industries including manufacturing plants, vending machines, food and beverage, pharmaceuticals, and utilities, just to name a few. HMIs along with PLCs are typically the backbone of the production line in these industries. The integration of the HMI into manufacturing has vastly improved operations. The HMI allows for supervisory control and data acquisition in the entire system, so parameter changes are feasible as the operator's choosing. For example, in metals manufacturing, an HMI might control how metal is cut and folded, and how fast to do so. An HMI offers improved stock control and replenishment, so the fewer journeys are required out to the vendors. HMIs are used in bottling processes to control all aspects of the manufacturing line, such as speed, efficiency, error detection and error correction. Utility companies may use HMIs to monitor water distribution and waste water treatment.  

Advantages of an HMI :

The greatest advantage of an HMI is the user-friendliness of the graphical interface. The graphical interface contains color coding that allows for easy identification (for example: red for trouble). Pictures and icons allow for fast recognition, easing the problems of illiteracy. HMI can reduce the cost of product manufacturing, and potentially increase profit margins and lower production costs. HMI devices are now extremely innovative and capable of higher capacity and more interactive, elaborate functions than ever before. Some technological advantages the HMI offers are: converting hardware to software, eliminating the need for mouse and keyboard, and allowing kinesthetic computer/human interaction. 

Advantage of an HMI over a PLC alone :

The advantage to using an HMI over using just a PLC is the fact that there are no disadvantages! Using just a PLC will not provide any real-time feedback, cannot set off alarms nor modify the system without reprogramming the PLC. The key advantage to an HMI is it functionality; an HMI can be used for simple tasks such as a coffee brewing controller, or a sophisticated control unit of a nuclear plant. With new HMI designs emerging every day, we are now seeing HMIs that offer remote access, allowing for access of the terminal while away. Another advantage of an HMI is that the user can personally design the user interface.


HMI/PLC Combination  :
How can a PLC be controlled without ladder logic? How does an HMI replace the standard software a PLC comes with? Ladder logic is simply conditional programming. For example, if input 1 is energized, then coil 1 will be powered. A statement has to be true for the output to be executed. The same can be achieved with C programming. However, in order to program an HMI to operate a PLC properly, all the registers of the PLC must be known. A good way to learn how to program a PLC via an HMI is to first start working with the PLC and the software it came with. This helps build an understanding of how to operate the PLC without the HMI. That knowledge will easily transfer over when the user is ready to connect the two units together.

SCADA system components

SCADA system components :

A SCADA system usually consists of the following main elements:

Supervisory computers

This is the core of the SCADA system, gathering data on the process and sending control commands to the field connected devices. It refers to the computer and software responsible for communicating with the field connection controllers, which are RTUs and PLCs, and includes the HMI software running on operator workstations. In smaller SCADA systems, the supervisory computer may be composed of a single PC, in which case the HMI is a part of this computer. In larger SCADA systems, the master station may include several HMIs hosted on client computers, multiple servers for data acquisition, distributed software applications, and disaster recovery sites. To increase the integrity of the system the multiple servers will often be configured in a dual-redundant or hot-standby formation providing continuous control and monitoring in the event of a server malfunction or breakdown.

Remote terminal units

Further information: Remote terminal unit

Remote terminal units, also known as (RTUs), connect to sensors and actuators in the process, and are networked to the supervisory computer system. RTUs are "intelligent I/O" and often have embedded control capabilities such as ladder logic in order to accomplish boolean logic operations.

Programmable logic controllers

Further information: Programmable logic controller

Also known as PLCs, these are connected to sensors and actuators in the process, and are networked to the supervisory system in the same way as RTUs. PLCs have more sophisticated embedded control capabilities than RTUs, and are programmed in one or more IEC 61131-3 programming languages. PLCs are often used in place of RTUs as field devices because they are more economical, versatile, flexible and configurable.

Communication infrastructure

This connects the supervisory computer system to the remote terminal units (RTUs) and PLCs, and may use industry standard or manufacturer proprietary protocols. Both RTUs and PLCs operate autonomously on the near-real time control of the process, using the last command given from the supervisory system. Failure of the communications network does not necessarily stop the plant process controls, and on resumption of communications, the operator can continue with monitoring and control. Some critical systems will have dual redundant data highways, often cabled via diverse routes.

Human-Machine Interface (HMI)

Further information: Graphical user interface

An important part of most SCADA implementations is alarm handling. The system monitors whether certain alarm conditions are satisfied, to determine when an alarm event has occurred. Once an alarm event has been detected, one or more actions are taken (such as the activation of one or more alarm indicators, and perhaps the generation of email or text messages so that management or remote SCADA operators are informed). In many cases, a SCADA operator may have to acknowledge the alarm event; this may deactivate some alarm indicators, whereas other indicators remain active until the alarm conditions are cleared.

Alarm conditions can be explicit—for example, an alarm point is a digital status point that has either the value NORMAL or ALARM that is calculated by a formula based on the values in other analogue and digital points—or implicit: the SCADA system might automatically monitor whether the value in an analogue point lies outside high and low- limit values associated with that point.

Examples of alarm indicators include a siren, a pop-up box on a screen, or a coloured or flashing area on a screen (that might act in a similar way to the "fuel tank empty" light in a car); in each case, the role of the alarm indicator is to draw the operator's attention to the part of the system 'in alarm' so that appropriate action can be taken.

PLC/RTU PROGRAMMING

"Smart" RTUs, or standard PLCs, are capable of autonomously executing simple logic processes without involving the supervisory computer. They employ standardized control programming languages such as under, IEC 61131-3 (a suite of 5 programming languages including function block, ladder, structured text, sequence function charts and instruction list), is frequently used to create programs which run on these RTUs and PLCs. Unlike a procedural language such as the C programming language or FORTRAN, IEC 61131-3 has minimal training requirements by virtue of resembling historic physical control arrays. This allows SCADA system engineers to perform both the design and implementation of a program to be executed on an RTU or PLC.

A programmable automation controller (PAC) is a compact controller that combines the features and capabilities of a PC-based control system with that of a typical PLC. PACs are deployed in SCADA systems to provide RTU and PLC functions. In many electrical substation SCADA applications, "distributed RTUs" use information processors or station computers to communicate with digital protective relays, PACs, and other devices for I/O, and communicate with the SCADA master in lieu of a traditional RTU.

SCADA AND PLC COMMERCIAL INTEGRATION

Since about 1998, virtually all major PLC manufacturers have offered integrated HMI/SCADA systems, many of them using open and non-proprietary communications protocols. Numerous specialized third-party HMI/SCADA packages, offering built-in compatibility with most major PLCs, have also entered the market, allowing mechanical engineers, electrical engineers and technicians to configure HMIs themselves, without the need for a custom-made program written by a software programmer. The Remote Terminal Unit (RTU) connects to physical equipment. Typically, an RTU converts the electrical signals from the equipment to digital values such as the open/closed status from a switch or a valve, or measurements such as pressure, flow, voltage or current. By converting and sending these electrical signals out to equipment the RTU can control equipment, such as opening or closing a switch or a valve, or setting the speed of a pump.

COMMUNICATION INFRASTRUCTURE AND METHODS

SCADA systems have traditionally used combinations of radio and direct wired connections, although SONET/SDH is also frequently used for large systems such as railways and power stations. The remote management or monitoring function of a SCADA system is often referred to as telemetry. Some users want SCADA data to travel over their pre-established corporate networks or to share the network with other applications. The legacy of the early low-bandwidth protocols remains, though.

SCADA protocols are designed to be very compact. Many are designed to send information only when the master station polls the RTU. Typical legacy SCADA protocols include Modbus RTU, RP-570, Profibus and Conitel. These communication protocols, with the exception of Modbus (Modbus has been made open by Schneider Electric, and is now managed by the modbus.org), are all SCADA-vendor specific but are widely adopted and used. Standard protocols are IEC 60870-5-101 or 104, IEC 61850 and DNP3. These communication protocols are standardized and recognized by all major SCADA vendors. Many of these protocols now contain extensions to operate over TCP/IP. Although the use of conventional networking specifications, such as TCP/IP, blurs the line between traditional and industrial networking, they each fulfill fundamentally differing requirements.

With increasing security demands (such as North American Electric Reliability Corporation (NERC) and Critical Infrastructure Protection (CIP) in the US), there is increasing use of satellite-based communication. This has the key advantages that the infrastructure can be self-contained (not using circuits from the public telephone system), can have built-in encryption, and can be engineered to the availability and reliability required by the SCADA system operator. Earlier experiences using consumer-grade VSAT were poor. Modern carrier-class systems provide the quality of service required for SCADA.

RTUs and other automatic controller devices were developed before the advent of industry wide standards for interoperability. The result is that developers and their management created a multitude of control protocols. Among the larger vendors, there was also the incentive to create their own protocol to "lock in" their customer base. A list of automation protocols is compiled here.

OLE for process control (OPC) can connect different hardware and software, allowing communication even between devices originally not intended to be part of an industrial network.