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Thursday, 19 January 2017
What is SCADA?
SCADA Defination
SCADA (Supervisory Control And Data Acquisition) is an automation remote monitoring and control system. As stated in its name.
SCADA is applicable in any automation operation that requires supervisory control and real-time data acquisition.
SCADA is applicable in any automation operation that requires supervisory control and real-time data acquisition.
Whereby in this modern world, it is possible to use SCADA in any workplace/home, even though it was first introduced for industrial purpose.
SCADA Working Concept:
On the back-end, sensors will be connected to RTUs (Remote Terminal Units), or PLCs (Programmable Logic Controllers), where signals (such as meter reading and instrument status) will be converted to digital data.
To transport the digital data between RTUs/PLCs and control center, network connection media such as LAN or WAN will be used.
The Data acquisition server shall be required for database storage purpose, as well as trend plotting and report generating.
On the front-end, these digital data will then be accessed by operator on HMI (Human-Machine Interface), where process control and monitor can be done. HMI can be on different platforms, from servers to tablets to even mobile phones.
To transport the digital data between RTUs/PLCs and control center, network connection media such as LAN or WAN will be used.
The Data acquisition server shall be required for database storage purpose, as well as trend plotting and report generating.
On the front-end, these digital data will then be accessed by operator on HMI (Human-Machine Interface), where process control and monitor can be done. HMI can be on different platforms, from servers to tablets to even mobile phones.
Source: Google, Quora, wikipedia
Monday, 16 January 2017
Programming structure for a PLC :-
Programming a PLC :-
In these modern times a PC with specially dedicated software from the PLC manufacturer is used to program a PLC. The most widely used form of programming is called ladder logic. Ladder logic uses symbols, instead of words, to emulate the real world relay logic control, which is a relic from the PLC's history.
These symbols are interconnected by lines to indicate the flow of current through relay like contacts and coils. Over the years the number of symbols has increased to provide a high level of functionality.
The completed program looks like a ladder but in actuality it represents an electrical circuit. The left and right rails indicate the positive and ground of a power supply.
The rungs represent the wiring between the different components which in the case of a PLC are all in the virtual world of the CPU.
So if you can understand how basic electrical circuits work then you can understand ladder logic.
In this simplest of examples a digital input (like a button connected to the first position on the card) when it is pressed turns on an output which energizes an indicator light.
How to Operate a PLC, (PLC Operation) :-
How to Operate a PLC, (PLC Operation) :-
Input Relays:
These are connected to the outside world. They physically exist and receive signals from switches, sensors, etc. Typically they are not relays but rather they are transistors.
Internal Utility Relays:
These do not receive signals from the outside world nor do they physically exist. They are simulated relays and are what enables a PLC to eliminate external relays.
There are also some special relays that are dedicated to performing only
one task.
Timers:
These also do not physically exist. They come in many varieties and increments.
The most common type is an on-delay type.
Others include off-delay and both retentive and non-retentive types. Increments vary from 1ms through 1s.
Counters:
These do not physically exist. They are simulated counters and they can be programmed to count pulses.
Typically these counters can count up, down or both up and down. Since they are simulated they are limited in their counting speed.
Some manufacturers also include high speed counters that are hardware based.
Output Relays:
These are connected to the outside world. They physically exist and send on/off signals to solenoids, lights, etc.
They can be transistors, relays, or triacs depending upon the model chosen.
Data Storage:
Typically there are registers assigned to simply store data. Usually used as temporary storage for math or data manipulation.
They can also typically be used to store data when power is removed from the
PLC.
PLC Hardware Configuration.
Hardware Components of a PLC SystemProcessor unit (CPU), Memory, Input/Output, Power supply unit, Programming device, and other devices.
Power Supply
Most PLC controllers work either at 24 VDC or 220 VAC. Some PLC controllers have electrical supply as a separate module, while small and medium series already contain the supply module.
Central Processing Unit (CPU)CPU – Microprocessor based, may allow arithmetic operations, logic operators, block memory moves, computer interface, local area network, functions, etc.
CPU makes a great number of check-ups of the PLC controller itself so eventual errors would be discovered early.
System BussesThe internal paths along which the digital signals flow within the PLC are called
busses.
The system has four busses:
Programming Device
The programming device is used to enter the required program into the memory of the processor.
The program is developed in the programming device and then transferred to the memory unit of the PLC.
Memory
System (ROM) to give permanent storage for the operating system and the fixed data used by the CPU.
RAM for data. This is where information is stored on the status of input and output devices and the values of timers and counters and other internal devices. EPROM for ROM’s that can be programmed and then the program made permanent.
I/O Sections
Inputs monitor field devices, such as switches and sensors.
Outputs control other devices, such as motors, pumps, solenoid valves, and lights
Power Supply
Most PLC controllers work either at 24 VDC or 220 VAC. Some PLC controllers have electrical supply as a separate module, while small and medium series already contain the supply module.
Central Processing Unit (CPU)CPU – Microprocessor based, may allow arithmetic operations, logic operators, block memory moves, computer interface, local area network, functions, etc.
CPU makes a great number of check-ups of the PLC controller itself so eventual errors would be discovered early.
System BussesThe internal paths along which the digital signals flow within the PLC are called
busses.
The system has four busses:
- – The CPU uses the data bus for sending data between the different elements,
- – The address bus to send the addresses of locations for accessing stored data,
- – The control bus for signals relating to internal control actions,
- – The system bus is used for communications between the I/O ports and the I/O unit.
Programming Device
The programming device is used to enter the required program into the memory of the processor.
The program is developed in the programming device and then transferred to the memory unit of the PLC.
Memory
System (ROM) to give permanent storage for the operating system and the fixed data used by the CPU.
RAM for data. This is where information is stored on the status of input and output devices and the values of timers and counters and other internal devices. EPROM for ROM’s that can be programmed and then the program made permanent.
I/O Sections
Inputs monitor field devices, such as switches and sensors.
Outputs control other devices, such as motors, pumps, solenoid valves, and lights
How PLCs Work...?
Working of PLC:
A programmable logic controller is a specialized computer used to control machines and processes. It therefore shares common terms with typical PCs like central processing unit, memory, software and communications. Unlike a personal computer though the PLC is designed to survive in a rugged industrial atmosphere and to be very flexible in how it interfaces with inputs and outputs to the real world.
The components that make a PLC work can be divided into three core areas.
PLCs come in many shapes and sizes. They can be so small as to fit in your shirt pocket while more involved controls systems require large PLC racks. Smaller PLCs (a.k.a. “bricks”) are typically designed with fixed I/O points. For our consideration, we’ll look at the more modular rack based systems. It’s called “modular” because the rack can accept many different types of I/O modules that simply slide into the rack and plug in.
A programmable logic controller is a specialized computer used to control machines and processes. It therefore shares common terms with typical PCs like central processing unit, memory, software and communications. Unlike a personal computer though the PLC is designed to survive in a rugged industrial atmosphere and to be very flexible in how it interfaces with inputs and outputs to the real world.
The components that make a PLC work can be divided into three core areas.
- The power supply and rack
- The central processing unit (CPU)
- The input/output (I/O) section
PLCs come in many shapes and sizes. They can be so small as to fit in your shirt pocket while more involved controls systems require large PLC racks. Smaller PLCs (a.k.a. “bricks”) are typically designed with fixed I/O points. For our consideration, we’ll look at the more modular rack based systems. It’s called “modular” because the rack can accept many different types of I/O modules that simply slide into the rack and plug in.
Introduction and fundamental Concept of Programmable Logic Controller.
the machine is like any kind of industrial and Home based devices like any Motor, Controller, Lights or any kind of other instruments.
Knowing the basics of PLCs
Programmable logic controllers provide dependable, high-speed control and monitoring demanded by a wide variety of automated applications.
Programmable logic controllers(PLCs) have gained a substantial hold in the industrial manufacturing arena, and we would be remiss if this technology were not given the due attention it has earned.
As such, we are featuring a series of articles based on the fundamentals of PLCs in this new EC&M department covering the technology of solid-state industrial automation. Throughout this series on PLC fundamentals, we'll cover PLC hardware modules; software capabilities; current applications; installation parameters; testing and troubleshooting; and hardware/software maintenance.
What is a PLC?
The National Electrical Manufacturers Association (NEMA) defines a PLC as a "digitally operating electronic apparatus which uses a programmable memory for the internal storage of instructions by implementing specific functions, such as logic, sequencing, timing, counting, and arithmetic to control through digital or analog I/O modules various types of machines or processes."
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