8. How To Upload From A PLC?
7. How to download to a PLC?
6. Power Supply Module - Front Plate Of PLC S7-200
5. Programming Languages of Programmable Logic Controllers:
FBD: A function block diagram is a diagram that describes a function between input variables and output variables. A function is described as a set of elementary blocks. Input and output variables are connected to blocks by connection lines. An output of a block may also be connected to an input of another block.
LD: Ladder logic is a programming language that represents a program by a graphical diagram based on the circuit diagrams of relay-based logic hardware. It is primarily used to develop software for Programmable Logic Controllers (PLCs) used in industrial control applications. 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.
ST: Structured text is designed for programmable logic controllers (PLCs). It is a high level language that is block structured and syntactically resembles Pascal. All of the languages share IEC61131 (International Electro-technical Commission) Common Elements. The variables and function calls are defined by the common elements so different languages can be used in the same program.
4. Working of a Programmable Logic Controller
3. Building Blocks of a Programmable Logic Controller
2. Program memory: The working of CPU is fully controlled by the instructions and programs stored in the user program memory. The user program directs and controls CPU’s working. This program is prepared by the user based on the control logic required for control and automation task.
3. Process image memory: It is the internal memory of the CPU. It is divided into two parts: Process Input Image (PII) and Process Output Image (PIQ).
4. Internal timers, flags and counters
Output Modules:
The output module acts as a link between the CPU and output devices located in the field. The field devices could be relays, contactors, lamps, actuators, solenoid valves, dampers, etc. the output module on receiving signal from the processor switches voltage to the respective output terminals. Like input module, an output module could be an analog or digital.
Bus System:
The bus system is a path for the transmission of signals. In the programmable controllers, it is responsible for the signal exchange between processor and input / output modules. The bus comprises of several signal lines i.e. wires / tracks.
There are three buses in a PLC:
The power supply module generates the voltages required for the electronic modules of the PLC from the mains supply.
2. Advantages of PLC, need and importance of PLC
1. What is a Programmable Logic Controller?
- Open a project in STEP 7-Micro/WIN to hold the blocks that you are going to upload from the PLC.
- If you want to upload into an empty project, choose File>New or use the New Project toolbar button.
- If you want to upload into an existing project, choose File>Open or use the Open Project toolbar button.
- Choose File>Upload or use the Upload toolbar button to initiate the upload process.
- The Upload box displays checkboxes for the program block, data block, and system block. Ensure that the checkboxes are selected for the blocks that you want to upload and deselected for any blocks that you do not want to upload, and then click OK.
- STEP 7-Micro/WIN displays a message when your blocks upload successfully from the PLC to your personal computer.
7. How to download to a PLC?
- Before downloading to the PLC, verify that the PLC is in Stop mode. Examine the mode indicator light on the PLC. If the PLC is not in Stop mode, click on the Stop button in the toolbar or choose PLC>STOP.
- Click the Download button in the toolbar or choose File>Download. The Download dialog box appears.
- By default, the check boxes for Program Code Block, Data Block, and CPU Configuration (the system block) are selected the first time that you issue the download command. If you do not need to download a particular block, clear its check box.
- Click OK to initiate the download process.
- If the download is successful, a confirmation box displays the following message
- If the value in STEP 7-Micro/WIN for your PLC type does not match your actual PLC, a warning box appears with this message:
- "The PLC type selected for the project does not match the remote PLC type. Continue Download?"
- To correct the PLC type selection, choose No to terminate the download process.
- From the menu bar, choose PLC>Type to bring up the PLC Type dialog box.
- You can either select the correct type from the drop-down list box, or click on the Read PLC button to have STEP 7-Micro/WIN automatically read the correct value.
- Click OK to confirm the PLC type and dismiss the dialog box.
- Re-initiate the download process by clicking on the Download button in the toolbar or choosing File>Download from the menu bar.
- Once you have successfully downloaded, you must switch the PLC from STOP mode back to RUN mode before you can run the program.
6. Power Supply Module - Front Plate Of PLC S7-200
5. Programming Languages of Programmable Logic Controllers:
FBD: A function block diagram is a diagram that describes a function between input variables and output variables. A function is described as a set of elementary blocks. Input and output variables are connected to blocks by connection lines. An output of a block may also be connected to an input of another block.
LD: Ladder logic is a programming language that represents a program by a graphical diagram based on the circuit diagrams of relay-based logic hardware. It is primarily used to develop software for Programmable Logic Controllers (PLCs) used in industrial control applications. 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.
ST: Structured text is designed for programmable logic controllers (PLCs). It is a high level language that is block structured and syntactically resembles Pascal. All of the languages share IEC61131 (International Electro-technical Commission) Common Elements. The variables and function calls are defined by the common elements so different languages can be used in the same program.
4. Working of a Programmable Logic Controller
3. Building Blocks of a Programmable Logic Controller
Input Modules:
The input module acts as an interface between the field control inputs and the CPU. The voltage or current signals generated by the sensors, transducers, limit switches, push buttons, etc., are applied to the terminals of the input module.
The input module helps in the following ways:
- It converts the field signal into a standard control signal for processing by the PLC. The standard control signal delivered by the input module could be 5 V or 9V and the field signal received by it could be 24V DC, 230 V AC or 115V AC.
- If required, it isolates the field signal from the CPU.
- It sends one input at a time to the CPU by multiplexing action.
Depending upon the nature of input signal coming from the field, the input module could be:
- Analog input module
- Digital input module
The CPU consists of the following blocks:
1. Arithmetic and Logical Unit (ALU): ALU is the organizer of the PLC. It organises the input of external signals and data and performs logical operation with data. It stores the signal states of input in the Process Input Image (PII) of the CPU before each program scan cycle. It stores the result of logic operation in the Process Output Image (PIQ) during program cycle.
1. Arithmetic and Logical Unit (ALU): ALU is the organizer of the PLC. It organises the input of external signals and data and performs logical operation with data. It stores the signal states of input in the Process Input Image (PII) of the CPU before each program scan cycle. It stores the result of logic operation in the Process Output Image (PIQ) during program cycle.
2. Program memory: The working of CPU is fully controlled by the instructions and programs stored in the user program memory. The user program directs and controls CPU’s working. This program is prepared by the user based on the control logic required for control and automation task.
3. Process image memory: It is the internal memory of the CPU. It is divided into two parts: Process Input Image (PII) and Process Output Image (PIQ).
4. Internal timers, flags and counters
Output Modules:
The output module acts as a link between the CPU and output devices located in the field. The field devices could be relays, contactors, lamps, actuators, solenoid valves, dampers, etc. the output module on receiving signal from the processor switches voltage to the respective output terminals. Like input module, an output module could be an analog or digital.
Bus System:
The bus system is a path for the transmission of signals. In the programmable controllers, it is responsible for the signal exchange between processor and input / output modules. The bus comprises of several signal lines i.e. wires / tracks.
There are three buses in a PLC:
- Address bus, which enables the selection of a memory location or a module.
- Data bus, which carries the data from modules to processor and vice versa.
- Control bus, which transfers control and timing signals for the synchronization of the CPU’s activities within the programmable controller.
The power supply module generates the voltages required for the electronic modules of the PLC from the mains supply.
2. Advantages of PLC, need and importance of PLC
- Reduced space
- Energy saving
- Ease of maintenance
- Economical
- Greater life
- Greater reliability
- Greater flexibility
- Through using PLCs it became possible to modify an automation process without having to disconnect or reroute a single wire as in the case of conventional logic circuits.
- In industry, there are many tasks which are of a highly repetitive nature. Although monotonous, each step needs careful attention of operator to ensure good quality product.
- Many a times, close supervision of a process can cause high fatigue on operator, resulting in loss of track of control.
- Sometimes it is hazardous also, as in the case of potentially explosive chemical processes. Under all such conditions, PLCs can be used effectively in total elimination of possibilities of human error.
1. What is a Programmable Logic Controller?
A programmable logic controller (PLC) or programmable controller is a digital computer used in many industries and machines, such as packaging and semiconductor machines. Unlike general-purpose computers, the PLC is designed for multiple inputs and output arrangements, extended temperature ranges, immunity to electrical noise, and resistance to vibration and impact. Programs to control machine operation are typically stored in battery-backed or non-volatile memory. A PLC is an example of a real time system since output results must be produced in response to input conditions within a bounded time, otherwise unintended operation will result.
The PLC is basically a programmed interface between the field input elements like limit switches, sensors, transducers, push buttons, etc., and the final control elements like actuators, solenoid valves, dampers, drives, LEDs, hooters, etc.
The PLC is basically a programmed interface between the field input elements like limit switches, sensors, transducers, push buttons, etc., and the final control elements like actuators, solenoid valves, dampers, drives, LEDs, hooters, etc.
There is another though, a Programmable Automation Controller:
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 programmable logic controller (PLC). A PAC thus provides not only the reliability of a PLC, but also the task flexibility and computing power of a PC. PACs are most often used in industrial settings for process control, data acquisition, remote equipment monitoring, machine vision, and motion control. Additionally, because they function and communicate over popular network interface protocols like TCP/IP, Object Linking and Embedding for process control (OPC) and SMTP, PACs are able to transfer data from the machines they control to other machines and components in a networked control system or to application software and databases. A PAC at the core of an automation system can integrate multiple fieldbus networks like RS-485, RS-232, RS-422, CAN, Ethernet, EtherNet/IP, and others.
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