A programmable logic controller (PLC) is an industrial computer used to control manufacturing processes, offering flexibility, reliability, and ease of programming. It processes data from input devices and manages outputs, making it suitable for various applications, with multiple programming languages including ladder diagrams. PLCs support a range of configurations and communication protocols, allowing integration with systems like SCADA for enhanced monitoring and management.

1. PLC LADDER DIAGRAM
BY
NALINI MC
20GAEL1008
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2. PROGRAMMABLE LOGIC CONTROLLER
• It is an industrial computer that has been adapted for the control of manufacturing processes, such
as assembly lines, machines, robotic devices, or any activity that requires high reliability, ease of
programming, and process fault diagnosis.
• Dick Morley is considered as the father of PLC as he had invented the first PLC, the Modicon 084,
for General Motors in 1968.
• PLCs can range from small modular devices with tens of inputs and outputs (I/O), to large rack-
mounted modular devices with thousands of I/O, and which are often networked to other PLC
and SCADA systems.
• They can be designed for many arrangements of digital and analog I/O, extended temperature
ranges, immunity to electrical noise, and resistance to vibration and impact.
• PLCs were first developed in the automobile manufacturing industry to provide flexible, rugged and
easily programmable controllers to replace hard-wired relay logic systems.
• A PLC is an example of a hard real-time system since output results must be produced in response
to input conditions within a limited time
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3. How does a PLC work?
• The PLC receives information from
connected sensors or input devices,
processes the data, and triggers outputs
based on pre-programmed parameters.
Depending on the inputs and outputs, a
PLC can monitor and record run-time data
such as machine productivity or operating
temperature, automatically start and stop
processes, generate alarms if a machine
malfunctions, and more.
• Programmable Logic Controllers are a
flexible and robust control solution,
adaptable to almost any application.
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4. 1. I/O – The PLC’s CPU stores and processes program data, but input and output modules connect the
PLC to the rest of the machine these I/O modules are what provide information to the CPU and trigger
specific results.
 I/O can be either analog or digital
 Input devices might include sensors, switches, and meters.
 Output devices might include relays, lights, valves, and drives.
 Users can mix and match a PLC’s I/O in order to get the right configuration for their application.
2. Communications – In addition to input and output devices, a PLC might also need to connect with
other kinds of systems; for example, users might want to export application data recorded by the PLC to
a supervisory control and data acquisition (SCADA) system, which monitors multiple connected devices.
 PLCs offer a range of ports and communication protocols to ensure that the PLC can communicate with
these other systems.
3. HMI – In order to interact with the PLC in real time, users need an HMI, or Human Machine
Interface.
 These operator interfaces can be simple displays, with a text-readout and keypad, or large touchscreen
panels more similar to consumer electronics, but either way, they enable users to review and input
information to the PLC in real time.
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5. PLC Programming Languages
The five types of different PLC Programming
Languages are:
1.Ladder Diagram(LD)
2.Function Block Diagram(FBD)
3.Structured Text(ST)
4.Instruction List(IL)
5.Sequential Function Chart(SFC)
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6. LADDER DIAGRAM
• It is a graphical PLC programming
language which expresses logic
operations with symbolic notation.
• Ladder logic is made out of rungs of
logic, forming what looks like a ladder –
hence the name ‘Ladder Logic’.
• A ladder diagram is executed or read
from left to right and top to bottom as
shown in figure
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7. LADDER DIAGRAM SYMBOLS
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8. LADDER DIAGRAM FOR BASIC GATES
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9. Advantages of Ladder Diagram(LD):
• Easy to learn, understand and follow
• More reliable than electronic circuit controller
• A most convenient way to represent the discrete logic
• Easy to fault diagnose
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10. THANK YOU!
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