Components of PLC
What is PLC?
Programmable Logic Controller, shortly called PLC, is a general-purpose control system that accepts input from various sources like push buttons, temperature, flow sensors, pressure sensors, limit switches, etc. It can send signals to devices like load relays, motor starters, stepping motors, solenoid valves, and even servo drives.
PLC is designed to execute logic functions previously done by electromechanical relays.
Components of PLC
All Programmable Logic Controllers (PLCs) are made up of four basic components. They are
- Power supply
- Input/Output (I/O) Section
- Processor Section
- Programming Section
The programs used in discrete parts manufacturing and process manufacturing are stored in memory and retrieved as needed.
The components of a Programmable Logic Controller are interconnected and work together to allow the controller to accept inputs from various sensors, make logical decisions as programmed, and control outputs like starters of motors, solenoids, drives, and valves.
The power supply offers the essential voltage levels that are needed for the working of PLC. It also provides power for the I/O modules. The power supply can be a separate unit or integrated into the power section. It takes the incoming voltage (normally 120 VAC or 240 VAC) and regulates the voltage as it needed ( normally 5 VDC to 32 VDC).
The power supply has to provide constant output voltage free of transient voltage spikes and other electrical noise. When the power supply is removed or turned off, an internal battery in the Programmable Logic Controller supply charges to prevent memory loss.
Input/output (I/O) Sections
The input/output (I/O) sections act as the eyes, ears, and hands of a programmable logic controller. The input section is designed to receive information from push buttons, temperature switches, pressure switches, photoelectric, proximity switches, and other sensors.
The input section converts the received signal into low power data signal from high voltage and that are sent it into the processor section. The processor receives and compare the incoming signal from input device to the program.
The output section receives the low power-power digital signal from the processor and later converts them into high-power impulses. These high-power impulses can power industrial loads that light, grip, move, rotate, extend, release and do other necessary things.
The I/O sections can either be set on the Programmable Logic Controller or in expansion modules.
The Programmable Logic Controller package includes Onboard I/Os as a permanent part. Expansion modules are modular units that means we can remove the parts. Modular parts include inputs, outputs, or combinations of inputs and outputs.
Onboard I/Os usually have a set of fixed number of inputs and outputs that define the limits of the Programmable Logic Controller. For example, a small Programmable Logic Controller could have up to 16 inputs and eight outputs. This means that the controllers can handle up to 16 inputs and eight outputs.
We can add or extend the number of inputs and outputs of PLC by adding expansion modules
Programmable Logic Controllers that use expansion modules allow the total number of inputs and/or outputs to be changed by changing or adding modules. Individual machines and small systems normally use onboard programmable logic controllers.
The processor section of a Programmable Logic Controller is the section that organises all control activity by receiving inputs, making logical decisions based on the programme, and controlling the outputs.
The processor section, also known as the central processing unit, is the brain of the Programmable Logic Controller (CPU).
Three-wire transistor output sensors use either NPN or PNP transistors to control the load.
Central Processing Unit (CPU)
The processor section makes the decision needed to observe or monitor and control the field devices connected to the Input/Output modules
The plc central processing unit is built into a single element fixed PLC controller, whereas modular frame categories typically use a plug-in unit.
A central processing unit, control system, and computer are all names used by various manufacturers to refer to a similar unit that performs similar tasks.
CPU differs in terms of processing/handling speed and storage options.
The programming section of a Programmable Logic Controller is the section that allows input into the controller via a keyboard.
Exact, step-by-step instructions must be provided to the processor. Load, set, reset, clear, enter in, move, and start timing must all be communicated to the processor.
The size, capability, and function of programming devices vary. Programming devices can be as simple as small text displays or as complex colour displays with monitoring and graphics capabilities.
Programming devices can be as simple as small text displays or as complex colour displays with monitoring and graphics capabilities.