PLC/SCADA systems in automation control design for individual quick freezing process in cooling tunnels. Goran Jagetić, Marko Habazin, Tomislav Špoljarić. with Supervisory Control and Data Acquisition (SCADA) systems. SCADA A hybrid version of the RTU contains a PLC that does control local processes and. The First Programmable Logic. Controllers (PLCs). • Introduced in the late 's. • Developed to offer the same functionality as the existing relay logic systems.
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PDF | Automation generally refers to the science and technology of process Key Words: PLC, SCADA, Automation, Case Study-Autoclave. This picture is a screenshot of the pdf version. It includes 3D modelling and provides capabilities such as measurements, changing the light, zoom in, out, angle. The presentation gives an overview of the terms Automation, PLC and SCADA. soundofheaven.info 1 month ago . PC-SCADA – Memory analog/ digital/string tag • PLC-SCADA - I/O analog/digital/string tag 22;
Show related SlideShares at end. Two float switches are used to prevent a 'flutter' a ripple or a wave condition where any water usage activates the pump for a very short time and then deactivates for a short time, and so on, causing the system to wear out faster. They exist as commands in a computer program -- a piece of software only -- that just happens to resemble a real relay schematic diagram. Inside the PLC housing, connected between each input terminal and the Common terminal, is an opto-isolator device Light-Emitting Diode that provides an electrically isolated "high" Logic signal to the computer's circuitry a photo-transistor interprets the LED's light when there is VAC power applied between the respective input terminal and the Common terminal. SCADA systems have made substantial progress over the recent years in terms of functionality, scalability, performance and openness such that they are an alternative to in house development even for very demanding and complex control systems as those of physics experiments.
PLCs contain input and output devices compatible with industrial pilot devices and controls; little electrical design is required, and the design problem centers on expressing the desired sequence of operations in ladder logic or function chart notation. PLC applications are typically highly customized systems so the cost of a packaged PLC is low compared to the cost of a specific custom-built controller design.
For high volume or very simple fixed automation tasks, different techniques are used. Automotive applications are an example; millions of units are built each year, and very few end-users alter the programming of these controllers.
However, some specialty vehicles such as transit busses. PLCs may include logic for single-variable feedback analog control loop, a "proportional, integral, derivative" or "PID controller. Historically PLCs were usually configured with only a few analog control loops; where processes required hundreds or thousands of loops, a distributed control system DCS would instead be used.
Digital or discrete signals behave as binary switches, yielding simply an On or Off signal 1 or 0, True or False, respectively. Pushbuttons, limit switches, and photoelectric sensors are examples of devices providing a discrete signal.
Discrete signals are sent using either voltage or current, where a specific range is designated as On and another as Off. Analog signals are like volume controls, with a range of values between zero and full-scale. These are typically interpreted as integer values counts by the PLC, with various ranges of accuracy depending on the device and the number of bits available to store the data.
Pressure, temperature, flow, and weight are often represented by analog signals. Analog signals can use voltage or current with a magnitude proportional to the value of the process signal. For example, an analog mA or 0 - 10 V input would be converted into an integer value of 0 - Current inputs are less sensitive to electrical noise i. As an example, say the facility needs to store water in a tank.
The water is drawn from the tank by another system, as needed, and our example system must manage the water level in the tank.
Using only digital signals, the PLC has two digital inputs from float switches tank empty and tank full. The PLC uses a digital output to open and close the inlet valve into the tank. If both float switches are off down or only the 'tank empty' switch is on, the PLC will open the valve to let more water in. Once the 'tank full' switch is on, the PLC will automatically shut the inlet to stop the water from overflowing.
If only the 'tank full' switch is on, something is wrong because once the water reaches a float switch, the switch will stay on because it is floating, thus, when both float switches are on, the tank is full. Two float switches are used to prevent a 'flutter' a ripple or a wave condition where any water usage activates the pump for a very short time and then deactivates for a short time, and so on, causing the system to wear out faster.
An analog system might use a load cell scale that weighs the tank, and an adjustable throttling valve. The load cell is connected to an analog input and the valve is connected to an analog output. This system fills the tank faster when there is less water in the tank. If the water level drops rapidly, the valve can be opened wide. If water is only dripping out of the tank, the valve adjusts to slowly drip water back into the tank. A real system might combine both approaches, using float switches and simple valves to prevent spills, and a rate sensor and rate valve to optimize refill rates.
Backup and maintenance methods can make a real system very complicated. Early PLCs, up to the mids, were programmed using proprietary programming panels or special-purpose programming terminals, which often had dedicated function keys representing the various logical elements of PLC programs. Programs were stored on cassette tape cartridges. Facilities for printing and documentation were very minimal due to lack of memory capacity. More recently, PLC programs are typically written in a special application on a personal computer, then downloaded by a direct-connection cable or over a network to the PLC.
The very oldest PLCs used non-volatile magnetic core memory but now the program is stored in the PLC either in battery-backed-up RAM or some other non-volatile flash memory. These PLCs were programmed in "ladder logic", which strongly resembles a schematic diagram of relay logic.
Ladder logic is a method of drawing electrical logic schematics. It was originally invented to describe logic made from relays. The name is based on the observation that programs in this language resemble ladders, with two vertical "rails" and a series of horizontal "rungs" between them. A program in ladder logic, also called a ladder diagram, is similar to a schematic for a set of relay circuits. An argument that aided the initial adoption of ladder logic was that a wide variety of engineers and technicians would be able to understand and use it without much additional.
This argument has become less relevant given that most ladder logic programmers have a software background in more conventional programming languages, and in practice implementations of ladder logic have characteristics — such as sequential execution and support for control flow features — that make the analogy to hardware somewhat imprecise. Ladder logic is widely used to program PLCs, where sequential control of a process or manufacturing operation is required.
Ladder logic is useful for simple but critical control systems, or for reworking old hardwired relay circuits. As programmable logic controllers became more sophisticated it has also been used in very complex automation systems. Ladder logic can be thought of as a rule-based language, rather than a procedural language. A "rung" in the ladder represents a rule. When implemented with relays and other electromechanical devices, the various rules "execute" simultaneously and immediately.
When implemented in a programmable logic controller, the rules are typically executed sequentially by software, in a loop.
By executing the loop fast enough, typically many times per second, the effect of simultaneous and immediate execution is obtained. In this way it is similar to other rule- based languages, like spreadsheets or SQL.
However, proper use of programmable controllers requires understanding the limitations of the execution order of rungs. The language itself can be seen as a set of connections between logical checkers relay contacts and actuators coils.
If a path can be traced between the left side of the rung and the output, through asserted true or "closed" contacts, the rung is true and the output coil storage bit is asserted 1 or true. If no path can be traced, then the output is false 0 and the "coil" by analogy to electromechanical relays is considered "de-energized". The analogy between logical propositions and relay contact status is due to Claude Shannon. Ladder logic has "contacts" that "make" or "break" "circuits" to control "coils.
Unlike electromechanical relays, a ladder program can refer any number of times to the status of a single bit, equivalent to a relay with an indefinitely large number of contacts. Each rung of ladder language typically has one coil at the far right.
Some manufacturers may allow more than one output coil on a rung. The "coil" output of a rung may represent a physical output which operates some device connected to the programmable controller, or may represent an internal storage bit for use elsewhere in the program. If a NC switch is actuated then this instruction will not be true and hence output will not be generated.
Due to high output a 24 volt signal is generated from PLC processor. Here is an example of what one rung in a ladder logic program might look like. In real life, there may be hundreds or thousands of rungs. Typically, complex ladder logic is 'read' left to right and top to bottom.
As each of the lines or rungs are evaluated the output coil of a rung may feed into the next stage of the ladder as an input. In a complex system there will be many "rungs" on a ladder, which are numbered in order of evaluation. This represents a slightly more complex system for rung 2.
After the first line has been evaluated, the output coil S is fed into rung 2, which is then evaluated and the output coil T could be fed into an output device buzzer, light etc.. Note that the contact X on the 2nd rung serves no useful purpose, as X is already a 'AND' function of S from the 1st rung.
This circuit shows two key switches that security guards might use to activate an electric motor on a bank vault door. When the normally open contacts of both switches close, electricity is able to flow to the motor which opens the door. This is a logical AND. Often we have a little green "start" button to turn on a motor, and we want to turn it off with a big red "Stop" button.
Following the program, which shows a normally- open X1 contact in series with a Y1 coil, no "power" will be sent to the Y1 coil. Thus, the PLC's Y1 output remains de-energized, and the indicator lamp connected to it remains dark. If the pushbutton switch is pressed, however, power will be sent to the PLC's X1 input.
Any and all X1 contacts appearing in the program will assume the actuated non-normal state, as though they were relay contacts actuated by the energizing of a relay coil named "X1". In this case, energizing the X1 input will cause the normally-open X1 contact will "close," sending "power" to the Y1 coil.
When the Y1coilof the program "energizes," the real Y1 output will become energized, lighting up the lamp connected to it:. It must be understood that the X1 contact, Y1 coil, connecting wires, and "power" appearing in the personal computer's display are all virtual.
They do not exist as real electrical components. They exist as commands in a computer program -- a piece of software only -- that just happens to resemble a real relay schematic diagram. Once a program has been loaded to the PLC from the personal computer, the personal computer may be unplugged from the PLC, and the PLC will continue to follow the programmed commands. I include the personal computer display in these illustrations for your sake only, in aiding to understand the relationship between real-life conditions switch closure and lamp status and the program's status "power" through virtual contacts and virtual coils.
The true power and versatility of a PLC is revealed when we want to alter the behavior of a control system. Since the PLC is a programmable device, we can alter its behavior by changing the commands we give it, without having to reconfigure the electrical components connected to it. For example, suppose we wanted to make this switch-and-lamp circuit function in an inverted fashion: The "hardware" solution would require that a normally- closed pushbutton switch be substituted for the normally-open switch currently in place.
The "software" solution is much easier: You can see the normally-closed contact X2 appear in a colored block, showing that it is in a closed "electrically conducting" state. If we were to press the "Start" button, input X1 would energize, thus "closing" the X1 contact in the program, sending "power" to the Y1 "coil," energizing the Y1 output and applying volt AC power to the real motor contactor coil.
The parallel Y1 contact will also "close," thus latching the "circuit" in an energized state:. Now, if we release the "Start" pushbutton, the normally-open X1 "contact" will return to its "open" state, but the motor will continue to run because the Y1 seal-in "contact" continues to provide "continuity" to "power" coil Y1, thus keeping the Y1 output energized:.
To stop the motor, we must momentarily press the "Stop" pushbutton, which will energize the X2 input and "open" the normally-closed "contact," breaking continuity to the Y1 "coil: When the "Stop" pushbutton is released, input X2 will de-energize, returning "contact" X2 to its normal, "closed" state.
The motor, however, will not start again until the "Start" pushbutton is actuated, because the "seal-in" of Y1 has been lost:. 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: The data servers communicate with devices in the field through process controllers. Process controllers, e. PLCs, are connected to the data servers either directly or via networks or field buses that are proprietary e.
Siemens H1 , or non-proprietary e. 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.
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. Some of the drivers are based on third party products e. VME on the other hand is generally not supported. A single data server can support multiple communications protocols: The effort required to develop new drivers is typically in the range of weeks depending on the complexity and similarity with existing drivers, and a driver development toolkit is provided for this.
The API often does not provide access to the product's internal features such as alarm handling, reporting, trending, etc. The configuration data are stored in a database that is logically centralized 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. Scalability is understood as the possibility to extend the SCADA based control system by adding more process variables, more specialized servers e.
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. 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.
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. 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.
Standard windows editing facilities are provided: On-line configuration and customization 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. The products all provide trending facilities and one can summarize the common capabilities as follows:. Automation Components 0 Sensor for sensing physical conditions.
Its purpose is to monitor crucial process parameters and adjust process operations accordingly. Memory Optical isolation Optical isolation program data. In an OR gate, the output is high if any one or all of the inputs are high. Therefore the OR gate is equivalent to a parallel combination of normally open switches. The PLC will communicate to the other devices through a network interface. Network PLC interface module. Every manufacturer have there one way communication or follow different protocols.
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