7 MARKS QUESTION

SUBJECT CODE : 3161714

Explain PLC architecture with suitable diagrams. OR

Draw a block diagram of a PLC showing the main functional items and how buses link them,
explaining the functions of each block.

A programmable Logic Controller(PLC) is a specialized digital computer employed in industrial

settings for automation and control. Acting as the central brain of machinery and processes, PLCs
receive input from sensors, process the data through programmed logic, and generate output signals
to control devices like motors and valves.

It is a hardware device with microprocessor-based control system. PLC is a general-purpose computer

modified specially to perform control tasks.

It is used for industrial automation to automate a specific process, machine function, or even entire
production.

PLCs are developed for electronic replacement for hard-wired relay logic circuit systems for machine
control. They are designed for industrial use to control many automated processes in industries.

Components of PLC :
Their are mainly 6 major part of a PLC that are :
• Processor
• Memory(RAM/ ROM)
• Input device
• Output device
• Power supply
• Programming device
Description of each part of a PLC :
• CPU : CPU is the brain of a PLC, responsible for executing the control program stored in
memory. It performs tasks such as data processing, decision-making and communication
with other devices.
• Memory(RAM/ROM) : RAM is used for storing data and variables temporarily during
the execution of the program. ROM is used to store the operating system of a PLC and
the user program. The program typically consists of two ladder logic, function block
diagrams or other programming languages.
• Input Device : This is responsible for interacting with the machine and the instructor
which can be external sensors, switches etc.
• Output Device : Output device is responsible for interacting with the end point external
device like motor, valve or indicator.
• Power Supply : PLC requires a stable power supply to run its program and match the
voltage levels that needed for a PLC components.
• Programming Device : As PLC is mainly a programmable device, so we need a device
where we can write code and execute it, just like a monitor and keyboard.

Give one application-based example of SCADA. Draw a suitable diagram to explain in detail.
Supervisory Control and Data Acquisition (SCADA) systems are widely used in various industries to
monitor and control complex processes. One common application of SCADA is in the management of
a water treatment plant. In a water treatment plant, SCADA systems help monitor and control processes
such as water purification, distribution, and storage.

Application Example: Water Treatment Plant SCADA System

Diagram:
Components:

1. Field Devices:
• These devices include sensors and actuators deployed in the water treatment plant.
Sensors measure parameters like water flow, pressure, chemical levels, and quality.
• Actuators control valves, pumps, and other equipment.
2. Remote Terminal Unit (RTU):
• RTUs are deployed in the field and act as an interface between the field devices and
the SCADA system.
• RTUs collect data from sensors and send it to the SCADA system for monitoring.
3. Master Terminal Unit (MTU):
• The MTU is the central component of the SCADA system located in the control room
of the water treatment plant.
• It collects data from RTUs, processes the information, and provides a graphical user
interface for operators to monitor and control the entire process.
4. Communication Network:
• A communication network, often based on protocols like Modbus or DNP3, connects
the RTUs and the SCADA system.
5. SCADA Software:
• The SCADA software runs on the MTU and provides a user-friendly interface for
operators and engineers.
• It displays real-time data, historical trends, and alarms. Operators can also send control
commands to adjust processes based on the information provided.
6. Historical Database:
• The SCADA system often includes a historical database to store and retrieve past data
for analysis, reporting, and compliance purposes.

Explain discrete I/O module of PLC. OR

Explain discrete input module of PLC.

The input device provides a signal to an input module. This input module is connected with the CPU for
the initial automated processes. CPU processes all the input data.

After processing by CPU, it gives output data to the output module. The output module provides a
signal to the output device. The singles can be anything like activating or deactivating output devices.
There are two types of PLCs- Compact PLC and Modular PLC.
• In Compact PLC, the capability of the I/O module is fixed.
• In Modular PLC, the capability of the I/O module is not fixed.

1. Digital I/O Module

The digital module is also called Discrete Module.

In this module, the I/O signal work on the binary system i.e. only 0 or 1 value. For the digital input
module, only the 1-bit signal is used.

It is useful in the ON or OFF condition.

Based on Input and Output, the digital module is of two types.

• Digital Input Module

• Digital Output Module

The digital I/O signal gives status in the different form like –

1. High/Low, True/False and 1/0 for General Status

2. ON/OFF for Load Condition
3. Activated/Deactivated for Switching Mechanism
4. Close/ Open for the Switching Contact Status

Examples: Push switch, Toggle switch, Rocker switch, Selector switch, Proximity switch, Limit switch are
the example of the Digital Input Signal.

2. Analog I/O Module

The analog module is called a Continuous Module.

Usually, the voltage or current is given to the input module in the form of an analog signal. For the
analog input module, 12-bit or 13-bit signal is used.
Generally, analog input signals operate in the range of 4-20 mA, 0-20 mA, 1-5 V, etc.

This analog signal provides any intermittent value between the two extreme limits (initial to final range)
for the analog input module.

Again, analog I/O modules are also of two types.

• Analog Input Module

• Analog Output Module

Examples: Temperature Transmitter, Thermocouples, Pressure Transmitter, Flow Transmitter, Level

Transmitter, etc., are the example of the Analog Output Signal.
Describe the different counter function in PLC.

UP Counter (CTU)

The first counter instruction I will introduce you to is the up counter, also known as just CTU. As the

name implies, this PLC counter is used for counting up.

The way is works is that it will set an output, when is has counted a certain amount of times. To be a

little more specific this is how it works.

Down Counter (CTD)

Counting down is another operation that is widely used in PLC programming. In some cases you want

to know how many counts are remaining before the limit is reached. With the up counter you can use

some math to do it. But you can do it easily with a down counter.

Up Down Counter (CTUD)

At last you have the up down counter which can count both ways. Sometimes the combination of the

up and the down counter can be useful. You can count the same number both up and down and set

both an upper and a lower limit.

Explain PLC scanning with suitable diagram.
A PLC operates by executing programs in PLC memory repeatedly. The instructions contained in the
program are executed sequentially from beginning to end and continuously, and when the last
instruction is executed, the operation will return and starting from the initial instructions, this process
will continue as long as the PLC is still running.

PLC Scanning Process:

1. Input Scan: The scanning process begins with the PLC reading the state of its input devices,
such as sensors, switches, and other input modules.
2. Program Execution: After reading the input states, the PLC executes the user program stored
in its memory.
3. Output Update: Once the program execution is complete, the PLC updates the output
devices based on the results of the program logic.
4. Repeat Cycle: After updating the outputs, the PLC repeats the scanning process in a
continuous loop.
Explain ON Delay timer (Ton) with timing diagram and suitable example.
An ON Delay Timer (TON) is a type of timer instruction used in Programmable Logic Controllers (PLCs)
to delay turning on an output after an input condition has been met.

It operates by initiating a timing sequence when the input condition becomes true, and the output
remains off during the delay period. Once the delay period expires, the output is turned on.

• Input Signal: The input signal transitions from false to true at the beginning of the timing
sequence.
• Output State: The output remains off during the delay period (TON), indicated by the gap
between the input becoming true and the output turning on.
• Output Activation: After the delay period (TON) elapses, the output turns on and remains on
as long as the input condition remains true.
Example:
Consider a conveyor belt system where a motor needs to be started after a delay once a start button is
pressed to avoid sudden jerks. We can use an ON Delay Timer (TON) to achieve this:

• Input Condition: Start button pressed (Start signal becomes true).

• Output: Motor control output.
• ON Delay Timer (TON):
• Preset time (TON) set to 5 seconds.
• Operation:
• When the start button is pressed, the ON Delay Timer starts its timing sequence.
• The motor remains off during the delay period (5 seconds).
• After 5 seconds, the motor turns on, ensuring a smooth start after the delay.
• Timing Diagram:
• Start button pressed -> ON Delay Timer starts timing sequence.
• Motor remains off during the delay period (TON).
• After 5 seconds, motor turns on and remains on as long as the start button is pressed.
Explain UP and Down counter of PLC with suitable application.
UP Counter:
An UP counter increments its count value each time a specified event or condition occurs. It starts
counting from a preset value and increments the count value as the events occur.

UP counters are commonly used to track the number of occurrences of an event or to measure the total
quantity of items produced or processed.

Example Application: Bottling Plant

In a bottling plant, an UP counter can be used to count the number of bottles filled with a liquid product.

Each time a bottle is filled, a sensor detects the completion of the filling process and triggers the UP
counter to increment its count value.

Down Counter:
A Down counter decrements its count value each time a specified event or condition occurs. It starts
counting from a preset value and decrements the count value as the events occur.

Down counters are commonly used for applications such as countdown timers, where the remaining
time for a process or operation needs to be monitored.

Example Application: Traffic Signal Control

In a traffic signal control system, a Down counter can be used to implement a countdown timer for
pedestrian crossings. When the pedestrian signal is activated, the Down counter starts counting down
from a preset value (e.g., 30 seconds).

List various shift register functions of PLC and explain any two of them in detail

Types of Shift Registers

• Serial In Serial Out shift register
• Serial In parallel Out shift register
• Parallel In Serial Out shift register
• Parallel In parallel Out shift register
• Bidirectional Shift Register
• Universal Shift Register
• Shift Register Counter

Serial-In Serial-Out Shift Register (SISO):

The shift register, which allows serial input (one bit after the other through a single data line) and
produces a serial output is known as a Serial-In Serial-Out shift register.

The logic circuit given below shows a serial-in serial-out shift register. The circuit consists of four D
flip-flops which are connected in a serial manner. All these flip-flops are synchronous with each other
since the same clock signal is applied to each flip-flop.
Serial-In Parallel-Out Shift Register (SIPO):

The shift register, which allows serial input (one bit after the other through a single data line) and
produces a parallel output is known as the Serial-In Parallel-Out shift register. The logic circuit given
below shows a serial-in-parallel-out shift register.

The circuit consists of four D flip-flops which are connected. The clear (CLR) signal is connected in
addition to the clock signal to all 4 flip flops in order to RESET them.

The output of the first flip-flop is connected to the input of the next flip flop and so on. All these flip-
flops are synchronous with each other since the same clock signal is applied to each flip-flop.

Explain PLC sequencer functions in detail with application.

A PLC (Programmable Logic Controller) sequencer is a fundamental feature in industrial automation
systems. It allows for the sequential execution of tasks or processes based on a predefined logic or
sequence.

PLC sequencers are commonly used in manufacturing, assembly lines, and other automated systems
where tasks need to be performed in a specific order.

Here's a detailed explanation of the functions and applications of PLC sequencers:

1. Sequential Logic Execution: At its core, a PLC sequencer executes a series of steps or tasks in
a predefined order. These steps are programmed into the PLC's logic using ladder logic,
function block diagrams, or other programming languages supported by the PLC.
2. Step Advancement: The sequencer advances from one step to the next based on predefined
conditions or events. These conditions are typically based on input signals from sensors, timers,
counters, or other devices connected to the PLC.
 3. Branching and Conditional Execution: PLC sequencers can incorporate branching logic to
handle different scenarios or conditions. This allows for conditional execution of steps based
on the state of inputs, internal variables, or other factors.
4. Looping and Iteration: PLC sequencers support looping constructs, such as FOR loops or
WHILE-DO loops, to repeat sections of the sequence as needed. This is useful for tasks like
batch processing or continuous operation.
5. Error Handling and Recovery: PLC sequencers can include error handling mechanisms to
detect and respond to faults or abnormal conditions during operation.
6. Interlocking and Safety: Sequencers often incorporate interlocking logic to enforce safety
protocols and prevent hazardous conditions.

What is the importance of SKIP and MCR functions of PLC explain with suitable application.
1. SKIP (Skip Next Scan) Function:

The SKIP function allows programmers to skip the execution of specific rungs or sections of ladder logic
during a PLC scan cycle.

This feature is particularly useful for bypassing certain routine checks or actions under specific
conditions, thus optimizing scan time and improving overall system performance.

Importance of SKIP Function:

• Efficiency Improvement: By selectively skipping unnecessary operations, the SCAN time of

the PLC can be reduced, leading to faster response times and improved system efficiency.
• Conditional Execution: Allows for the conditional execution of ladder logic rungs based on
the state of inputs, internal variables, or other factors, enabling more flexible and dynamic
control of processes.
• Resource Optimization: Helps conserve processing resources by avoiding the execution of
unnecessary instructions, freeing up CPU cycles for other critical tasks.

Application Example: Conveyor System

Suppose a conveyor system has sensors at various points along the conveyor to detect the presence of
objects.

The PLC program controls the operation of motors to start, stop, and reverse the conveyor based on
these sensor inputs.

However, during maintenance or troubleshooting, it may be necessary to bypass certain conveyor

control logic temporarily.

2. MCR (Master Control Relay) Function:

The MCR function is a special relay in ladder logic programming that acts as a master control for
enabling or disabling a group of rungs or sections of ladder logic.
It is typically used to provide centralized control over complex sequences or subroutines within a PLC
program.

Importance of MCR Function:

• Centralized Control: Provides a single point of control for activating or deactivating multiple
rungs or sections of ladder logic, simplifying program organization and maintenance.
• Enhanced Modularity: Facilitates the creation of modular and reusable code segments by
grouping related rungs under the control of an MCR, promoting code reusability and scalability.
• Improved Fault Handling: Allows for easy isolation and troubleshooting of specific sections
of ladder logic by enabling or disabling them using the MCR, aiding in the diagnosis and
resolution of program faults.

Application Example: Batch Processing System

Consider a batch processing system used in a chemical plant where multiple tanks are filled, mixed, and
emptied according to specific recipes.

Each batch consists of a sequence of steps, including filling, mixing, heating, and draining, controlled
by the PLC.

Write and explain ladder logic program for stepper motor control with PLC in forward and
reverse direction.

&

Prepare Ladder Logic Diagram (LLD) to START and STOP reversible Motor which indicates
forward and reverse direction by the Green and Red LED’s.

The Workpiece starts moving on the left side and moves to the right when the start button is pressed.

When it reaches the rightmost limit, the drive motor reverses and brings the workpiece back to the
leftmost position again and the process repeats.

The forward and reverse pushbuttons provides a means of starting the motor in either forward or
reverse so that the limit switches can take over automatic control.
Program Description

RUNG 0000

Latching rung to operate the system through Master Start and Stop PB.

RUNG 0001

When the workpiece is near Limit switch1, It will enable forward motor, for latching forward Motor is
connected in parallel with limit switch 1.

Forward Pushbutton (PB) is also connected in parallel to manually operate forward motor.

RUNG 0002

When the workpiece is near Limit switch2, It will enable reverse motor, for latching reverse Motor is
connected in parallel with limit switch 2.

Reverse Pushbutton (PB) is also connected in parallel to manually operate Reverse motor.
With neat diagram explain Remote Terminal Units as a part of SCADA system.

Remote Terminal Unit (RTU) in SCADA systems is a microprocessor-based electronic device present at
geographically distributed remote locations in order to facilitate communication of various devices
within the distributed SCADA system.

It consists of input-output hardware and communication interface for remote sensing and controlling
of ongoing processes.

The sole purpose of an RTU present at the remote site of the SCADA system is to send all the collected
data and information to the central station with the help of sensors, monitors, production processes,
etc. so that it can be stored and monitored.
The major components of RTU are CPU, Memory (volatile and non-volatile), Power supply module with
battery, Real-time clock, Watchdog Timer, Communication Interface (serial port or onboard modem
with I/O interface).

In the above-shown figure, a hardware module is shown where the I/O modules are placed within the
RTU panel and communication is established with the master station via the communication port.

The I/O modules are connected to the central processor in order to communicate with the master
station.

Explain various input and output devices interfaced to PLC with example in brief.

PLC controller inputs:

An automated system depends to a large extent on the ability of a PLC controller to read signals from
different types of sensors and input devices.

To detect a work piece, see a mechanism in motion, check the pressure or the level of liquid, you need
specific automatic devices such as proximity sensors, marginal switches, photoelectric sensors, level
sensors, etc. Therefore, the input signals can be logical (on / off) or analog.

One of the most frequent analog signals is a current signal of 4 to 20 mA and a millivolt voltage signal
generated by several sensors. The sensors are generally used as inputs for PLCs. You can get sensors for
different purposes. They can feel the presence of some parts, measure temperature, pressure, or some
other physical dimension, etc.

PLC controller output:

the most commonly used devices are motors, solenoids, relays, indicators, sound signaling and the like.

When starting a motor or a relay, the PLC can manage or control a simple system such as the system to
classify products into complex systems such as the service system to position the head of the CNC
machine.

The output can be analog or digital type. The digital output signal works like a switch; The line is
connected and disconnected. The analog output is used to generate the analog signal.

Explain processor memory organization for an SLC 500 controller with program
and data file details.
The SLC 500 controller, produced by Allen-Bradley, is a widely used Programmable Logic Controller
(PLC) in industrial automation.

Its memory organization is crucial for storing both the program logic and data used in automation
processes.

Here's an explanation of its memory organization:

1. Program Memory:
• The program memory in the SLC 500 controller is divided into two primary sections:
 • A) User Program Memory (P File): This section holds the user-written program logic,
typically in ladder logic format. It contains the instructions that dictate the behavior of
the PLC.
• B) System Program Memory: This section contains the operating system and firmware
required for the PLC's operation. It includes functions for communication, diagnostics,
and other system-level operations.
2. User Program Memory (P File):
• The user program memory, also known as the "P File," is where the ladder logic program
is stored.
• The ladder logic program is structured into multiple rungs, with each rung containing
a combination of input instructions, output instructions, and other logical operations.
3. Data Memory:
• The data memory in the SLC 500 controller is used for storing various types of data
required for program execution.
• Data memory is divided into different data files, each serving a specific purpose and
containing different types of data.
• Common data files in the SLC 500 include:
• A) Input Data File (I File): Stores the current states of input devices connected to the
PLC.
• B) Output Data File (O File): Stores the desired states of output devices controlled by
the PLC.
• C) Integer Data File (N File): Used for storing integer values, such as numerical constants
or intermediate calculations.
• D) Binary Data File (B File): Stores binary data, often used for storing status information
or flags.
• E) Timer Data Files (T Files): Store timer values and control timer functions within the
PLC program.
• F) Counter Data Files (C Files): Store counter values and control counter functions within
the PLC program.

Name various forms of PLC counter instructions and explain any one with timing
diagram.
1. Up Counter (CTU - Count Up): The up counter instruction increments its count value when the
input condition turns true. It typically resets when a specified preset value is reached.
2. Down Counter (CTD - Count Down): The down counter instruction decrements its count value
when the input condition turns true. It typically resets when a specified preset value is reached.
3. Up/Down Counter (CTUD - Count Up/Down): This counter instruction allows both counting
up and counting down based on different input conditions. It typically resets when a specified
preset value for either count direction is reached.
4. Bi-Directional Counter: This counter instruction allows counting in both directions (up and
down) simultaneously. It is often used in applications where forward and reverse movements
need to be tracked independently.
5. Ring Counter: A ring counter is a special type of counter where only one bit is high at a time,
and the high bit rotates from one bit position to the next with each clock pulse.
 UP Counter :

Explanation:

• In the timing diagram above, the clock pulses are represented by short vertical lines at regular
intervals.
• The input condition is shown as a continuous line, indicating when it is true (active) and false
(inactive).
• The count value starts from 0 and increments by 1 each time the input condition becomes true
(active).
• When the count value reaches the preset value (in this case, 10), the counter resets back to 0.
• The counter only increments when the input condition is true. If the input condition is false, the
count remains unchanged.
• In this example, the count value increments from 0 to 10 as the input condition becomes true
for 10 clock pulses. Then, it resets back to 0 when the preset value of 10 is reached.

Draw and illustrate two-axis Robot with PLC sequencer control.

Creating a detailed drawing of a two-axis robot with PLC sequencer control would typically involve CAD
software or specialized drawing tools.

Illustration Explanation:

1. Robot Structure: The illustration depicts a simple two-axis robot consisting of a base (Axis 1)
and an arm (Axis 2). The robot is capable of moving horizontally and vertically to perform tasks
such as picking up objects, placing them, or performing specific actions.
2. Actuators: Each axis of the robot is controlled by respective actuators, such as stepper motors,
servo motors, or pneumatic cylinders, depending on the application requirements. These
actuators are responsible for moving the robot along its axes.
3. End Effector: The end effector, represented by the gripper in the illustration, is attached to the
arm of the robot. It is used to interact with objects, such as grasping, lifting, or manipulating
them based on the programmed instructions.
4. PLC (Programmable Logic Controller): The PLC serves as the control unit for the robot. It
coordinates the movement of the robot's axes and executes programmed sequences to perform
specific tasks. The PLC communicates with sensors, actuators, and other devices to monitor
inputs and control outputs.
 5. PLC Sequencer: The PLC sequencer is a program logic component within the PLC that manages
the sequence of operations performed by the robot. It defines the order of actions, conditions
for transitions between steps, and timing requirements for each operation.

Operation Explanation:

1. Initialization: The PLC starts the control program and initializes the robot's position and state.
2. Input Monitoring: The PLC continuously monitors input signals from sensors, such as limit
switches, encoders, or vision systems, to detect the robot's position, the presence of objects, or
environmental conditions.
3. Sequence Execution: Based on the input signals and programmed logic, the PLC sequencer
executes a sequence of actions to perform a specific task.
4. Feedback Control: During operation, the PLC receives feedback signals from sensors or
encoders to verify the robot's position and ensure accurate execution of the programmed
sequence. It may also incorporate error handling routines to address unexpected events or
deviations from the desired behavior.
5. Task Completion: Once the programmed sequence is completed, the PLC may return the robot
to a standby position, await further instructions, or initiate a new sequence based on external
inputs or triggers.

Describe analog signal processing in PLC. Explain PID function of PLC in detail.
Analog signal processing in PLCs involves handling continuous analog signals, such as voltage or
current, to control various processes or systems.

PLCs typically have analog input and output modules that interface with sensors and actuators, allowing
them to measure and control analog signals within a specified range.

Here's a brief overview of analog signal processing in PLCs:

1. Analog Input (AI) Modules:

• Analog input modules allow PLCs to read analog signals from sensors, transmitters, or
other devices.
 • These modules convert analog signals (e.g., voltage or current) into digital values that
can be processed by the PLC's digital circuitry.
• PLCs can read analog signals from various sensors such as temperature sensors,
pressure transducers, flow meters, and level sensors.
2. Analog Output (AO) Modules:
• Analog output modules enable PLCs to generate analog control signals to drive
actuators, valves, motors, or other devices.
• These modules convert digital signals from the PLC into analog signals suitable for
controlling the desired process variables.
• PLCs can output analog signals to control parameters like motor speed, valve position,
temperature setpoints, and fluid flow rates.
3. Scaling and Calibration:
• PLC programs often include scaling and calibration functions to convert raw analog
input values into engineering units (e.g., degrees Celsius, PSI, gallons per minute).
• Scaling ensures that the PLC interprets analog input values correctly and provides
meaningful data for control algorithms or operator displays.
• Calibration allows adjustments to be made to compensate for inaccuracies or variations
in sensor readings.
4. Control Algorithms:
• PLCs can implement various control algorithms to regulate analog process variables
and maintain desired setpoints.
• Common control algorithms include PID (Proportional-Integral-Derivative) control,
which is widely used for controlling continuous processes with feedback.

PID Control Function in PLC:

PID control is a feedback control algorithm widely used in industrial automation to regulate process
variables such as temperature, pressure, flow, position, and speed.

It calculates control output based on three terms: proportional, integral, and derivative.

1. Proportional (P) Term:

• The proportional term generates an output proportional to the error between the
desired setpoint and the actual process variable.
• It provides immediate correction to reduce the error and bring the process variable
closer to the setpoint.
• The proportional gain (Kp) determines the magnitude of the correction based on the
error.
2. Integral (I) Term:
• The integral term integrates the error over time to eliminate steady-state errors that
may persist with proportional control alone.
• It continuously adjusts the output based on the accumulated error over time.
• The integral gain (Ki) determines the rate at which the integral term responds to
accumulated error.
3. Derivative (D) Term:
• The derivative term anticipates future changes in the error by calculating the rate of
change of the error.
 • It provides damping to the control action, reducing overshoot and improving system
stability.
• The derivative gain (Kd) determines the rate at which the derivative term responds to
changes in error.

Draw neat and clean generic functional diagram of PLC and describe each part in details.

Description of Each Part:

1. Inputs:
• Inputs represent signals received from various sensors, switches, or other devices in the
field.
• These signals can be digital (on/off) or analog (continuous).
• Digital inputs are typically represented by discrete binary values (0 or 1), while analog
inputs are represented by continuous voltage or current levels.
2. Logic:
• The logic section of the PLC processes input signals using programmed instructions.
• It executes the user-defined control logic, which may include ladder logic, function
block diagrams, structured text, or other programming languages.
• The logic section determines the behavior of the PLC based on input conditions and
user-defined logic.
3. Outputs:
• Outputs represent signals sent from the PLC to actuators, motors, valves, or other
devices in the field.
• Similar to inputs, outputs can be digital or analog, depending on the type of device
being controlled.
• Digital outputs control devices with binary states (on/off), while analog outputs provide
variable control over devices such as motor speed or valve position.
4. Input Modules:
• Input modules interface with the physical input devices in the field and convert their
signals into a format that the PLC can understand.
 • These modules may include digital input modules for connecting to switches, sensors,
or proximity detectors, as well as analog input modules for connecting to transducers,
temperature sensors, or pressure sensors.
5. Output Modules:
• Output modules interface with the physical output devices in the field and convert
control signals from the PLC into a format suitable for driving these devices.
• Digital output modules control devices such as relays, solenoids, or contactors, while
analog output modules provide voltage or current signals to control devices with
variable outputs.
A Burglar Alarm is activated if an unauthorized intruder detected by a Window Sensor or a
Motion Detector. Consider following
1.Window sensor is a loop of wire that is a piece of thin metal foil this encircles the window. In
Window Sensor, current is always passing until there is a breakage in glass of a window. Hence
output is always true. When alarm system is active and someone tries to break the window,
current does not flow through the metal foil causing output to go false.
2. The motion detector is designed such that when a person is detected, the output of sensor
goes true.
3. Alarm activate/Deactivate (Master) Switch is true when alarm activated otherwise false.
Prepare LLD of the system using Karnaugh(K)-map
To create the ladder logic diagram (LLD) for the burglar alarm system using Karnaugh (K)-map, we need
to first define the input and output conditions. Let's denote:

• WS (Window Sensor): Input representing the state of the window sensor (true if no breakage,

false if breakage).

• MD (Motion Detector): Input representing the state of the motion detector (true if motion

detected, false if no motion).

• MAS (Master Alarm Switch): Input representing the state of the alarm system (true if activated,

false if deactivated).

• AL (Alarm): Output representing the activation of the burglar alarm (true if alarm should be

activated, false otherwise).

• Using the K-map, we can simplify the logic for AL as:

• AL=(WS+MAS)′
Implement ladder logic diagram to total four number of outputs which should be run one by one
with a particular time delay.

1. Generate Master Start and Stop buttons to activate the sequence and define four outputs.

2. Use TON-1 for 5 sec, TON-2 for 3 sec, TON-8 sec and TON-4 for 10 sec.

3. Use Done bit of first timer to energize other output and activate next timer. 4. Repeat this
process until the final output is energized and last timer is activated. Reset timers after the
completion of first cycle if necessary. Use LEDs as output to test the program.

To implement the ladder logic diagram as described, we'll use the TON (Timer On Delay) instruction for
each output.

We'll also utilize the done bit of each timer to trigger the next output and timer. Here's how you can
implement it:
Explanation:

• Master Start: This is the start button for the sequence.

• Outputs: Four outputs are defined, each associated with a timer.
• TON-1 (5s), TON-2 (3s), TON-3 (8s), TON-4 (10s): These are timers with different time delays as
specified.
• Done bit of each timer triggers the next output and timer.
• Once the last output is activated, the last timer is triggered and the sequence completes.
• Resetting timers: Depending on your specific requirements, you may need to add logic to reset
the timers after the completion of the first cycle. This can be achieved by adding reset conditions
to each timer or using a separate reset mechanism.
Prepare LLD to control Traffic light from South to North direction by Turning ON green Lamp for
15 sec, yellow Lamp for 5 sec, and finally Red Lamp for 120 sec. Repeat it continuously.

To design the Low-Level Design (LLD) for controlling traffic lights from South to North direction with
the specified timings, we can break down the system into components and their interactions.

Here's a basic outline:

Components:
1. Traffic Light Controller: Responsible for managing the state transitions of the traffic lights.
2. South to North Traffic Light: Actual physical lights indicating the status of traffic for this
direction.
States:
1. Green: South to North traffic allowed.
2. Yellow: Transitioning between green and red lights.
3. Red: South to North traffic stopped.
LLD Outline:
1. Traffic Light Controller:
• Input: Clock signal or timer interrupt.
• Output: Control signals to the South to North traffic light.
• Operations:
• Initialize state machine with initial state (Red).
• On clock signal:
• Change state according to timing requirements.
• Output corresponding control signals to the traffic light.
2. South to North Traffic Light:
• Inputs: Control signals from the Traffic Light Controller.
• Outputs: Illumination signals for green, yellow, and red lamps.
• Operations:
• Receive control signals.
• Illuminate lamps based on received signals.
• Manage timings of each lamp according to signals received.
3. State Machine (Traffic Light Controller):
• States:
1. Red
2. Green
3. Yellow
• Transitions:
• Red -> Green: After 120 seconds.
• Green -> Yellow: After 15 seconds.
• Yellow -> Red: After 5 seconds.
• Yellow -> Red (transition from Green directly if the 15 seconds are not yet
completed when transitioning): If external interruption occurs (e.g., pedestrian
crossing request).
4. Timing Mechanism:
• Use timers or clock signals to track time intervals for each state.
 • Upon reaching the specified time for each state transition, trigger the transition in the state
machine.
5. Error Handling:
• Handle any potential errors or exceptions such as sensor failures, power outages, etc.
• Implement fault tolerance mechanisms to ensure continuous operation.

Implement the dual Counter to indicate 5th part coming from line A and 11th part from line B in
to main conveyor belt by turning ON Lamps. Do repeat process again.

To implement the functionality of indicating the arrival of every 5th part from Line A and every 11th part
from Line B onto the main conveyor belt using dual counters and lamps, we can follow this design:

Components:
1. Dual Counters: One for Line A and one for Line B.
2. Lamps: Indicate the arrival of the specified parts onto the main conveyor belt.
3. Main Conveyor Belt: Receives parts from Line A and Line B.
Counter Logic:
1. Line A Counter: Counts every part arriving from Line A.
2. Line B Counter: Counts every part arriving from Line B.
Lamps:
1. Line A Lamp: Turns on when the Line A counter reaches a multiple of 5.
2. Line B Lamp: Turns on when the Line B counter reaches a multiple of 11.
LLD Outline:
1. Dual Counters:
• Inputs: Part detection signals from Line A and Line B.
• Outputs: Counts of parts from Line A and Line B.
• Operations:
• Increment Line A counter on each part detection signal from Line A.
• Increment Line B counter on each part detection signal from Line B.
2. Lamps:
• Inputs: Count values from Line A and Line B counters.
• Outputs: Control signals to the Line A and Line B lamps.
• Operations:
• Check if Line A counter value is a multiple of 5.
• If true, turn on Line A lamp.
• Check if Line B counter value is a multiple of 11.
• If true, turn on Line B lamp.
3. Main Conveyor Belt:
• Inputs: Parts from Line A and Line B.
• Operations:
• Receive parts from Line A and Line B.
• Transport parts along the conveyor belt.
4. Reset Logic:
• Reset Line A Counter: Reset Line A counter to zero after reaching a multiple of 5.
• Reset Line B Counter: Reset Line B counter to zero after reaching a multiple of 11.
5. Repeat Process:
• After indicating the arrival of the specified parts onto the main conveyor belt, repeat the process
by continuing to count parts from Line A and Line B.
Describe STAR and RING bus topology networking for PLC operation.
STAR Topology:
In a STAR topology, all devices (PLCs in this case) are connected directly to a central hub or switch. Each
PLC has its own dedicated connection to the central hub. The hub acts as a mediator, managing the
flow of data between PLCs.

1. Central Hub/Switch: This is the central point of connection for all PLCs. It manages
communication between PLCs.
2. PLCs: Each PLC is connected directly to the central hub via an individual cable. They can
communicate with each other through the hub.
RING Topology:
In a RING topology, PLCs are connected in a closed loop or ring configuration. Each PLC is connected
to two neighboring PLCs, forming a continuous ring.

1. PLCs: Each PLC is connected to two neighboring PLCs forming a ring configuration. PLCs
communicate with each other by passing data in a unidirectional or bidirectional manner
around the ring.
Prepare ladder logic diagram for 2-axis pick and place robot.using PLC sequencer Control .

To design a ladder logic diagram for a 2-axis pick and place robot using PLC sequencer control, we'll
break down the process into steps and then translate these steps into ladder logic.

Here's a basic outline of the process:

Steps:
1. Initialization:
• Initialize variables and set initial conditions.
2. Sequence Control:
• Define a sequence of operations for pick and place.
• Utilize a sequencer control to manage the sequence of steps.
3. Pick Operation:
• Move the robot to the pick position.
• Activate the gripper to pick up the object.
4. Place Operation:
• Move the robot to the place position.
• Release the gripper to place the object.
5. Error Handling:
• Implement error handling routines to deal with unexpected events.
Ladder Logic Diagram:

Explanation:
1. Initialization:
• This section initializes variables, timers, counters, etc., and sets initial conditions for the operation
of the pick and place robot.
2. Sequence Control:
• Utilizes a sequencer control to manage the sequence of steps in the pick and place operation.
Each step will be activated sequentially.
3. Pick Operation:
• This section moves the robot to the pick position and activates the gripper to pick up the object.
4. Place Operation:
• This section moves the robot to the place position and releases the gripper to place the object.
5. Error Handling:
• Implements error handling routines to handle any unexpected events or errors that may occur
during the pick and place operation.
Three conveyors fed a main conveyor. The count from each feeder conveyor is fed into an input
register in PLC. Construct a PLC program to obtain the total count of parts on the main conveyor.
Use a timer to update total count every 15 seconds.

To construct a PLC program to obtain the total count of parts on the main conveyor from the count
obtained from each feeder conveyor, and update the total count every 15 seconds using a timer, we
can use ladder logic.

Here's a basic outline of the PLC program:

Steps:
1. Initialization:
• Initialize variables, timers, counters, etc.
2. Read Feeder Conveyor Counts:
• Read the count of parts from each feeder conveyor and store them in separate registers.
3. Calculate Total Count:
• Add the counts obtained from each feeder conveyor to obtain the total count of parts
on the main conveyor.
4. Update Total Count:
• Use a timer to update the total count every 15 seconds.
Explanation:
1. Initialization:
• Initialize variables, timers, counters, etc., required for the program.
2. Read Feeder Conveyor Counts:
• Read the count of parts from each feeder conveyor and store them in separate registers
or memory locations.
3. Calculate Total Count:
• Add the counts obtained from each feeder conveyor to calculate the total count of
parts on the main conveyor.
4. Update Total Count:
• Use a timer to trigger the update of the total count every 15 seconds. When the timer
expires, update the total count with the latest values from the feeder conveyors.
Prepare ladder diagram program for following application: An automatic car parking system,
when the parking area is full with 10 cars the red bulb at entry should ‘ON’ to indicates it is full.
If the number of cars within the parking area is less than 10 the green bulb should ‘ON’ to indicate
that the space for parking is available.

Explanation:
• Parking Area Full (NO Contact):
• This NO (Normally Open) contact represents the condition when the parking area is full
(10 cars).
• When the parking area is full, this contact closes, energizing the coil connected to the
red bulb, turning it ON to indicate that the parking area is full.
• Parking Area Not Full (NC Contact):
• This NC (Normally Closed) contact represents the condition when the parking area is
not full (less than 10 cars).
• When the parking area is not full, this contact opens, de-energizing the coil connected
to the green bulb, turning it OFF to indicate that parking spaces are available.
Design ladder logic diagram for industrial application rated to bottle filling system. The conveyor
system is connected with motor & other suitable mechanisms. The required control actions are
thus; if a bottle is putted on conveyer system at starting node. The motor which is connected to
conveyer is started and when the bottle will reach at valve which mounted for filling the industrial
liquid, then it will be stopped. The solenoid valve is started. When the bottle is full then the valve
is off. And conveyor system is started again and the bottle reach at ending node then conveyor
is stopped. Consider the suitable sensors, indicators and required push buttons for above
application. Prepare ladder diagram program for above with assumptions of suitable inputs and
outputs.

Explanation:
• Bottle Detected on Conveyor (NO Contact):
• This NO (Normally Open) contact represents the condition when a bottle is detected
on the conveyor system.
• When a bottle is detected at the starting node, this contact closes, energizing the coil
connected to the motor, starting the conveyor system.
• Bottle at Filling (NC Contact):
• This NC (Normally Closed) contact represents the condition when a bottle is at the
filling position.
• When a bottle reaches the valve for filling, this contact opens, de-energizing the coil
connected to the solenoid valve, stopping the flow of liquid into the bottle.
• Bottle Detected at End Node (NO Contact):
• This NO (Normally Open) contact represents the condition when a bottle is detected at
the ending node.
• When a bottle is detected at the ending node, this contact closes, de-energizing the
coil connected to the motor, stopping the conveyor system.
What is SCADA? Explain it with suitable diagram in detail.

SCADA stands for Supervisory Control and Data Acquisition. It is a system used for monitoring and controlling
industrial processes, infrastructure, and facilities.

SCADA systems are commonly used in industries such as manufacturing, energy, oil and gas, water treatment, and
transportation, among others.

The primary function of SCADA is to gather and analyze real-time data from various sensors, equipment, and
devices, and provide a centralized interface for operators to monitor and control the processes remotely.

Components of SCADA System:

1. Supervisory Host/Server:
• This is the central component of the SCADA system where data acquisition, processing, and
visualization occur.
• It hosts the SCADA software applications responsible for monitoring and controlling the
industrial processes.
2. Remote Terminal Units (RTUs) / Programmable Logic Controllers (PLCs):
• RTUs or PLCs are devices installed at remote locations within the industrial process.
• They are responsible for interfacing with sensors, actuators, and other field devices to collect data
and control the process locally.
• RTUs/PLCs communicate with the supervisory host/server to send data and receive control
commands.
3. Human-Machine Interface (HMI):
• The HMI is the interface through which operators interact with the SCADA system.
• It provides real-time visualization of the process data through graphical displays, charts, and
alarms.
• Operators can use the HMI to monitor process parameters, view historical trends, acknowledge
alarms, and issue control commands.
4. Communication Infrastructure:
• SCADA systems rely on various communication protocols and networks to exchange data
between the supervisory host, RTUs/PLCs, and other components.
• Communication infrastructure may include wired (Ethernet, serial communication) and wireless
(radio, cellular) networks.
5. Database and Historian:
• SCADA systems often include a database and historian component to store and archive process
data.
• Historical data is valuable for analysis, reporting, and troubleshooting.
 3 / 4 MARKS

List of PLC Manufacturers

1. Siemens
2. Rockwell Automation / Allen Bradley
3. Mitsubishi Electric
4. Schneider Electric
5. Omron
6. Emerson (General Electric)
7. ABB
8. Bosch Rexroth
9. Hitachi
10. Panasonic
11. Delta Electronic
12. Yokogawa Electric

Describe the discrete input module block diagram.

A discrete input module in a PLC (Programmable Logic Controller) typically consists of several key components that
work together to process digital signals from various input devices like switches, sensors, and push-buttons.

Explain the various programming languages of PLC.

Ladder logic

PLCs were introduced into the field, ladder logic PLC programming was designed to mimic the layout of
relay-based circuits. In other words, ladder logic was one of the first PLC programming languages that’s
still used today due to simplicity.

Structured Text PLC Programming

Structured Text is a PLC programming language that closely resembles C or assembly. The user enters lines
of code that execute sequentially, evaluate specific functions, Boolean checks, and energize appropriate
outputs of the PLC.

Function Block Diagrams PLC Programming Language

Function Block Diagram, of FBD, is a programming language developed with chemical processes in mind.
It allows the user to create a visual representation and flow of the process with appropriate transitions
between the instructions.

Sequential Function Charts PLC Programming Language

As the name implies, sequential function charts, or SFC, shine when it comes to a subsequent process.
List eight different types of data files used by an SLC 500 controller.

• Output data file

• Input data file
• Status data file
• Binary data file
• Timer data file
• Counter data file
• Control data file
• Integer data file
• Floating point data file

Explain the various operation modes of PLC.

PROGRAM MODE : In this mode, new programs are entered, and this mode is also used to edit or update the
program and is also used to upload or download files, document programs.
RUN MODE : This mode in the PLC is used to RUN the user program, so while doing this the input devices are
monitored, and also the energy devices are energized as per the requirement.
TEST MODE : This mode is used after editing or creating a program to test the PLC program before the program
is used for real applications like industrial automation etc.
REMOTE MODE : The remote mode will be very useful to control the PLC remotely, so by using this mode, we can
select the program run mode by using a computer connected to the PLC. This mode will be very useful if the
controller is not inaccessible locations.
MONITOR MODE : In this mode, the CPU will be running and the I/O will be processed in the same way as in the
RUN mode, and also the CPU operation status can be monitored.

Draw the ladder logic for following gates: NOR and EX-OR.

NOR Gate :

EX-OR Gate:
List and explain various PLC registers.

1. Input Registers:

• Input registers store data received from input modules connected to the PLC.

2. Output Registers:

• Output registers store data sent to output modules connected to the PLC.

3. Data Registers (M Registers):

• Data registers are used to store intermediate values, status flags, and control information.

4. Timer Registers (T Registers):

• Timer registers are used to implement timers in the PLC program.

5. Counter Registers (C Registers):

• Counter registers are used to implement counters in the PLC program.

Describe various move instructions: BIT, BYTE, WORD DOUBLE WORD, REAL .

1. BIT Move Instruction:

• Description: Moves a single bit from one memory location to another.

2. BYTE Move Instruction:

• Description: Moves a byte (8 bits) of data from one memory location to another.

3. WORD Move Instruction:

• Description: Moves a word (16 bits or 2 bytes) of data from one memory location to another.

4. DOUBLE WORD Move Instruction:

• Description: Moves a double word (32 bits or 4 bytes) of data from one memory location to another.

5. REAL Move Instruction:

• Description: Moves a real number (32 bits or 4 bytes) of data from one memory location to another.
Describe the networking in PLC.
o Networking in PLC (Programmable Logic Controller) systems refers to the communication between
multiple PLCs, as well as between PLCs and other devices such as HMIs (Human-Machine Interfaces),
SCADA (Supervisory Control and Data Acquisition) systems, and remote I/O modules.
o PLC networking allows for data exchange, remote monitoring, and control of distributed control systems.

What is the role of RTU in the SCADA system? Can PLC replace RTU? Which advantages
are offered by PLC?

Role of RTU in SCADA System:

1. Data Acquisition: RTUs collect data from various field devices, such as sensors, meters, and switches,
located in remote or distributed locations.
2. Data Processing: RTUs process the collected data, performing tasks such as scaling, filtering, and
conversion, to prepare it for transmission to the SCADA system.
3. Control Functions: RTUs execute control commands sent from the SCADA system, such as opening or
closing valves, starting or stopping pumps, and adjusting setpoints.
4. Communication: RTUs establish communication links with field devices using different communication
protocols, such as Modbus, Profibus, or DNP3, and transmit the acquired data to the SCADA system.
5. Remote Monitoring and Control: RTUs enable remote monitoring and control of distributed
processes, allowing operators to monitor equipment status, detect faults, and make control decisions from
a centralized location.

Can PLC Replace RTU?

While PLCs (Programmable Logic Controllers) and RTUs share some similarities and can perform similar functions,
they are designed for different applications and have different characteristics.

Advantages Offered by PLCs:

1. Flexibility: PLCs are highly versatile and can be programmed to perform a wide range of control
functions, making them suitable for a variety of industrial applications.
2. Cost-Effectiveness: PLCs are often more cost-effective than RTUs for local control applications,
especially when a large number of I/O points are required.
3. Scalability: PLC systems can be easily expanded or modified by adding additional I/O modules, making
them scalable to accommodate changing process requirements.
4. Integration with SCADA Systems: PLCs can be integrated with SCADA systems using communication
protocols such as Modbus, OPC, or Ethernet/IP, allowing for seamless data exchange and control.
5. Advanced Functionality: PLCs offer advanced features such as motion control, PID control, data
logging, and recipe management, which may not be available in standard RTUs.

Explain the PID control in PLC.

PID (Proportional-Integral-Derivative) control is a control algorithm used to maintain a process variable at a desired
setpoint by adjusting a control output.

In a PLC (Programmable Logic Controller), PID control is implemented using a combination of instructions that
calculate the control output based on the error between the process variable and the setpoint.
List the benefits offer by PLC. Explain at least four in brief.

1. Flexibility:

• PLCs are highly flexible and can be easily reprogrammed or reconfigured to accommodate changes in the
manufacturing process or production requirements.

2. Reliability:

• PLCs are designed for use in harsh industrial environments and are highly reliable and robust.

3. Scalability:

• PLC systems can be easily expanded or upgraded to accommodate changes in system size, complexity, or
functionality.

4. Diagnostics and Troubleshooting:

• PLCs offer advanced diagnostic and troubleshooting capabilities, allowing operators and maintenance
personnel to quickly identify and resolve system faults or errors.

Write a brief note on PLC network communication.

Programmable Logic Controllers (PLCs) are widely used in industrial automation to control machinery and
processes. PLCs can communicate with each other and with other devices over a network, enabling centralized
control and monitoring.

1. Inter-device Communication: PLCs can communicate with each other over a network, allowing for
coordinated control of different parts of a system.
2. Integration with other Devices: PLCs can communicate with other devices such as sensors, actuators,
and human-machine interfaces (HMIs).
3. Data Exchange: PLC network communication facilitates the exchange of data between PLCs and other
devices, allowing for real-time monitoring, control, and data logging.
4. Remote Access and Monitoring: PLC network communication enables remote access and monitoring
of PLCs and automation systems, allowing for troubleshooting, maintenance, and optimization without
physical presence.

Explain any one application of SCADA in brief.

Application: SCADA in Power Grid Management

Brief : SCADA systems are extensively used in power grid management to monitor, control, and optimize the
generation, transmission, and distribution of electrical power.

1. Monitoring: SCADA systems continuously monitor various parameters such as voltage, current,
frequency, and power flow at different points within the power grid.
2. Control: SCADA systems allow operators to remotely control power generation, transmission, and
distribution equipment such as generators, transformers, and switches.
3. Fault Detection and Management: SCADA systems quickly detect faults or abnormalities within the
power grid, allowing operators to take corrective actions promptly to minimize downtime and prevent
widespread power outages.
4. Data Logging and Analysis: SCADA systems collect and log data from various devices within the power
grid.
Input module layout of PLC with suitable diagram. OR

Output module layout of PLC with suitable diagram.

Develop a ladder diagram for 3 input AND and OR logic gates .

State rules for proper construction of ladder diagram.

1. Inputs can be used in Series as well as Parallel to form a connection

2. Outputs (or coil) can be used only in Parallel

3. One Input can be used in multiple times in one program

4. One Output cannot be used multiple times in one program, except in Set/Reset and Latch/ Unlatch functions

5. Input Address cannot be used as an Output Address

6. Outputs Address can be used as Inputs Address

Develop a ladder diagram for 4 to 1 Multiplexer.

Describe instructions: Bit Set, Bit Reset, SET RTC, RS.

Bit Set (SET):

• Syntax: SET <bit>
• Description: Sets the specified bit to 1.
Bit Reset (RS or RES):
• Syntax: RS <bit>
• Description: Resets the specified bit to 0.
SET RTC (Set Real-Time Clock):
• Syntax: SET RTC <time>
• Description: Sets the real-time clock to the specified time.
Reset RTC (Reset Real-Time Clock):
• Syntax: RS RTC
• Description: Resets the real-time clock.

Explain Table-To-Register MOVE function of PLC.

The Table-To-Register (TBLR) MOVE function in PLC programming allows you to move data from a specified
memory table to one or more registers.

Explanation:

• M100: Source memory table where the status of the sensors is stored.
• D0: Destination register where the data will be moved.
• 10: Number of elements (sensors) to move.

List out the key features of SCADA.

• Data acquisition: SCADA collects real-time data from various sensors and devices.

• Visualization: It provides visual representation of data for operators.

• Control capabilities: SCADA allows operators to control industrial processes.

• Monitoring and processing: SCADA monitors, gathers, and processes data.

• Interaction with devices: It interacts directly with devices through HMI (Human-Machine Interface) software.

• Event recording: SCADA records events for analysis and troubleshooting.

Explain instruction: ENI, Real to ASCII, Integer to Byte.
ENI (Enable Input):
• Syntax: ENI <input>
• Description: Enables the specified input.
Real to ASCII:
• Syntax: REAL_TO_ASCII <real_value>, <ASCII_string>
• Description: Converts a real number to an ASCII string.
Integer to Byte:
• Syntax: INT_TO_BYTE <integer_value>, <byte_value>
• Description: Converts an integer to a byte value.

Describe the benefits offered by graphical (Symbolic) based programming language over script
based programming language for the PLC.

• Graphical programming languages use symbols and graphical representations of logic, making it easier
for engineers and technicians to understand the control logic, even without extensive programming
knowledge.
• Graphical programming languages allow for faster development of PLC programs since users can simply
drag and drop predefined function blocks or logic symbols onto the programming interface, rather than
writing out code line by line.
• Graphical programming languages, such as ladder logic, are standardized in the industry, making it easier
for engineers and technicians to share and understand PLC programs across different platforms and
manufacturers.

What are the modules? Discuss its types and function in context to PLC.

• Input modules are used to interface the PLC with input devices such as sensors, switches, and push
buttons.
• They convert the signals from these devices into digital or analog signals that the PLC can process.
• Input modules may include different types of inputs such as digital inputs (DI), analog inputs (AI), high-
speed counter inputs, and temperature inputs.

Draw and describe wiring diagrams for Sink type and Source type Input device to be connected
to input module of PLC.
Describe MVM (Move with mask) instruction with suitable example.

o Address of the mask through which the instruction moves data. The mask acts like a filter for the
destination.
o It is the address where the instruction moves the data.

Ex : When the rung condition goes true,

Case 1 : Output When Mask Bit is not activated,

Case 2 : Output When Mask Bit is activated,

Explain following arithmetic instructions. 1) ADD 2) MUL 3) DIV.

ADD : Adds the value of the source operand to the value of the destination operand and stores the result in the
destination operand.

MUL : Multiplies the value of the source operand by the value of the destination operand and stores the result in
the destination operand.

DIV : Divides the value of the destination operand by the value of the source operand and stores the result in the
destination operand.

Draw and describe timing diagram and operation of OFF-Delay Timer instruction.
Explain how plc is helpful to design SCADA over typical Industrial Application.

1. Data Acquisition:
• PLCs collect real-time data from various sensors and devices on the factory floor.
2. Control Logic:
• PLCs execute control logic based on the data received from sensors and devices.
3. Communication:
• PLCs communicate with SCADA systems using communication protocols such as Modbus,
Profibus, or Ethernet/IP.
4. Data Processing:
• SCADA systems receive data from PLCs and process it to generate real-time graphical
representations of the industrial process.
5. HMI (Human-Machine Interface):
• SCADA systems provide operators with a user-friendly interface to monitor and control industrial
processes.
Types of Logic Gates using PLC Ladder

NOT GATE:
o In electronics, NOT GATE is also called an ‘Inverter’ or ‘Buffer’.

Working: NOT gate works as inversion. It takes one input and gives one output. When the input is high then the
output is low and vice-versa.

Logic Gate Truth Table for NOT Gate:

PLC Ladder :

AND GATE:
Working: In AND Gate, when both inputs (I1 and I2) are high then the output (Q1) will be high. For all
other inputs, output (Q1) will be the low.

Logic Gate Truth Table for AND Gate:

PLC Ladder :

OR GATE:
Working: If both inputs are low in the OR gate, then the output will be low. For all other cases, the output will be
high.
Logic Gate Truth Table for OR Gate:

PLC Ladder :
NAND GATE :
Working: In NAND Gate, the output will be low when both inputs are high. For all other cases, the output will be
high.
Logic Gate Truth Table for NAND Gate:

PLC Ladder :

NOR GATE
o NOR Gate is operated OR Gate followed by the NOT Gate.

Logic Gate Truth Table for NOR Gate:

PLC Ladder :

6. EX-OR GATE:
Working: If both inputs are high or low, the output will become low. For any other input condition, the output
will be high.
Logic Gate Truth Table for EX-OR Gate:

PLC Ladder :
Explain solid state memory organization in PLC with the help of memory map.

1. Input Image Table (I):

• Stores the status of input devices such as sensors, switches, and push buttons.
• The input image table reflects the actual state of the physical input devices.
2. Output Image Table (Q):
• Stores the control signals sent to output devices such as motors, valves, and indicator lights.
• The output image table reflects the control signals generated by the PLC.
3. Data Memory (D):
• Stores data values used by the PLC program.
• Data memory is used for storing intermediate results, counters, timers, and other data values.
4. Timer Memory (T):
• Stores the current value of timers used in the PLC program.
• Timer memory is used for implementing time-based control functions.
5. Counter Memory (C):
• Stores the current value of counters used in the PLC program.
• Counter memory is used for implementing counting and totalizing functions.

Implement the following Boolean equations in PLC ladder diagrams.

(i) Y= (AB’ + A’B) C (ii) Z= (P+Q+R).(D+E).G’.H
Write short note on “Preventive maintenance of PLC.

1. Regular Inspections: These inspections help identify signs of wear and tear, corrosion, loose connections, or
other physical issues that might impact the system’s performance.

2. Cleaning and Housekeeping: A clean environment is crucial for the smooth operation of PLCs. Dust, debris, and
contaminants can accumulate over time, leading to overheating, short circuits, and other problems.

3. Firmware and Software Updates: PLC manufacturers often release firmware and software updates that address
bugs, security vulnerabilities, and performance enhancements.

4. Lubrication and Mechanical Maintenance: In cases where the PLC system interacts with mechanical
components such as conveyors or motors, lubrication and mechanical maintenance.

5. Backup and Documentation: Regularly backing up PLC programs and configurations is a fundamental aspect
of preventive maintenance.

6. Environmental Considerations: PLCs are often deployed in various industrial settings, each with its own
environmental challenges.

7. Predictive Techniques: Incorporating predictive maintenance techniques, such as vibration analysis,

thermography, and oil analysis, can help detect potential issues before they lead to failure.

8. Training and Skill Development: Maintenance personnel and technicians should receive regular training to stay
updated on the latest advancements in PLC technology, maintenance practices, and troubleshooting techniques.