Basics of Programmable Logic Controller and Its Functionality

Basics of Programmable Logic Controller and Its Functionality

“PLC” means “Programmable Logic Controller”. The word “Programmable” differentiates it from the conventional hard-wired relay logic. It can be easily programmed or changed as per the application’s requirement. The PLC also surpassed the hazard of changing the wiring. The PLC as a unit consists of a processor to execute the control action on the field data provided by input and output modules. In a programming device, the PLC control logic is first developed and then transferred to the PLC.

FUNCTIONS and Features OF PLC

• It can perform relay-switching tasks.

• It can conduct counting, calculation and comparison of analog process values.

• It offers flexibility to modify the control logic, whenever required, in the shortest time.

• It responds to the changes in process parameters within fractions of seconds.

• It improves the overall control system reliability.

• It is cost effective for controlling complex systems.

BASIC BLOCK DIAGRAM OF THE PLC

As shown in the Fig, the heart of the “PLC” is the center, i.e., the Processor or CPU (Central Processing Unit).

• The CPU regulates the PLC program, data storage, and data exchange with I//O modules.

• Input and output modules are the media for data exchange between field devices and CPU.

• It tells CPU the exact status of field devices and also acts as a tool to control them.

• A programming device is a computer loaded with programming software, which allows a user to create, transfer and make changes in the PLC software.

• Memory provides the storage media for the PLC program as well as for different data.

COMPONENTS OF THE PLC SYSTEM

CPU or processor: The main processor (Central Processing Unit or CPU) is a microprocessor-based system that executes the control program after reading the status of field inputs and then sends commands to field outputs.

I/O section: I/O modules act as “Real Data Interface” between field and PLC CPU. The PLC reads the real status of field devices, and controls the field devices by means of the relevant I/O cards.

Programming device: A CPU card can be connected with a programming device through a communication link via a programming port on the CPU.

Operating station: An operating station is commonly used to provide an "Operating Window" to the process. It is usually a separate device (generally a PC), loaded with HMI (Human Machine Software).

AUTOMATION USING A PLC with applications

AUTOMATION USING A PLC

PLCs are electronic devices that work on the basic principle of logic gates. It was a major leap from sequencing automation with rotating cams or with series of electrical relay switches, to using micro processor based PLC sequencers. With micro processors, the sequencers could be programmed to follow different sequences under different conditions.
The physical structure of a PLC is as important as a feature as its computerized inwards. The central component, the CPU, contains the digital computer and plugs into a bus or a rack. Other PLC modules can be plugged into the same bus. Optional interface modules are available for just about any type of sensor or actuator.
The PLC user buys only the modules needed, and thus avoids having to worry about compatibility between sensors, actuators and the PLC. Most PLCs offer communication modules now, so that the PLC can exchange data with at least other PLCs of the same make.

AUTOMATED CAR PARKING SYSTEM:
Automated parking is a method of automatically parking and retrieving cars typically using a computerized system of lifts and carriers. As the system removes the need for driveways and ramps, the floor area and the volume of the parking station itself can be more efficiently used.
For the driver, the process is very simple. They park their car at an entrance point then leave the vehicle. From there, the car is automatically moved through the parking system. It's returned to the driver in the same fashion using a signaling device (similar to a credit card) or for a public car park a ticket and payment system in a designated waiting zone.
Automated parking systems can be designed to fit above or below ground, allowing for flexible usage of land space; this means the footprint can be reduced to one-third of the land required by conventional car parking solutions. Cost-effective on a number of fronts, automated parking also offers significantly improved service to the customer.

These automated car parking systems are suitable for installation in basements, open floors or open spaces outside commercial buildings, residential buildings, shopping malls, and other public places. Such multi-level automated car parking systems have been installed all around the world, especially in Europe, Korea, Japan and some other parts of South-East Asia.
There is an overwhelming need for these systems because of increasing traffic and non-availability of adequate parking spaces, especially in urban cities. The most unique feature of such systems is that they increase the parking space available on the ground by more than 30%, depending upon the kind of system installed and the contours of the space available.
Multi-level parking systems require careful planning and assessment of the space available, traffic flows, and the capacity utilization within that space. These systems can be integrated within concrete (RCC) structures.