Lesson: Industrial Discrete Control Input Switches
1. Introduction to Industrial Discrete Control Input Switches
What are Discrete Control Input Switches?
Discrete control input switches are devices used in industrial control systems to send signals
(on/off) to control machinery, processes, or systems. These switches play an essential role in
ensuring the safe, efficient, and reliable operation of machines by either activating or deactivating
specific functions.
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Discrete Signals: These are binary signals, meaning they have only two possible states: ON
or OFF.
These switches help operators and control systems make decisions about machine operations. In
an industrial setting, such as a factory or production line, these switches ensure that systems
function properly and safely.
2. Types of Discrete Control Input Switches
Here are some common types of switches used in industrial control systems:
1. Limit Switches
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Function: Detects the position of a moving part and sends a signal when the part reaches a
preset limit.
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Example: A limit switch can stop a conveyor when the belt reaches a certain position.
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Application: Used in machines where specific positions need to be detected, such as
robotic arms or automated doors.
2. Pushbutton Switches
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Function: Simple buttons used to start or stop a process or operation.
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Example: A pushbutton is pressed to start a motor or to reset a machine.
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Application: Used in control panels for operators to manually control machinery.
3. Rocker Switches
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Function: A switch that toggles between ON and OFF by rocking back and forth.
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Example: A rocker switch can be used to control a light or a simple machine.
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Application: Often found in industrial control panels, lighting systems, or HVAC controls.
4. Proximity Sensors
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Function: Detects objects without physical contact and sends a signal when an object is
within range.
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Example: A proximity sensor detects a metal part on an assembly line and triggers a stop
signal.
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Application: Used in automated systems to detect the presence of objects, such as in
material handling systems.
5. Rotary Switches
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Function: Allows selection between multiple positions by rotating a knob.
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Example: A rotary switch can change a machine's operational mode from automatic to
manual.
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Application: Commonly used in control panels for selecting between different operational
settings.
6. Toggle Switches
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Function: A mechanical switch that moves between ON and OFF positions, typically with a
toggle lever.
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Example: A toggle switch is used to turn on/off a light or activate a fan.
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Application: Common in many industrial applications like simple on/off controls in
machinery.
7. Emergency Stop Buttons
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Function: Used to immediately stop a machine or process in case of an emergency.
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Example: A red emergency stop button stops a conveyor belt when a safety hazard is
detected.
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Application: Found in all industrial environments to ensure safety by providing an
immediate way to halt dangerous operations.
3. How Discrete Control Input Switches Work in Control Systems
Understanding the Basics of On/Off Signals
When a discrete control input switch is activated, it either sends an "ON" signal (1) or an "OFF"
signal (0) to the control system. The control system interprets these signals and takes action based
on the current state of the switch.
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Normally Open (NO): The circuit remains open (OFF) until the switch is activated, allowing
the signal to flow.
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Normally Closed (NC): The circuit remains closed (ON) until the switch is activated,
interrupting the flow and turning the signal OFF.
Example:
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A limit switch in a conveyor system may have a normally open contact. When the conveyor
reaches a certain position, the switch closes, sending an ON signal to the control system to
stop the conveyor.
4. Practical Applications of Discrete Control Input Switches
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Manufacturing: Limit switches are used to stop machines when parts reach a certain
position.
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Safety: Emergency stop buttons are used to halt machinery in the event of a malfunction or
dangerous situation.
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Automation: Pushbutton switches or rotary switches are used to control machine modes or
start/stop processes.
5. Summary of Key Points
.
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Discrete control input switches are essential for controlling the operation of machinery in
industrial settings.
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They come in various types, such as limit switches, pushbuttons, and emergency stop
buttons, each serving a unique function.
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These switches help maintain the safety, efficiency, and functionality of industrial systems.
LABORATORY 1: Drawing and Labeling Industrial Control Switches
Objective:
To help you visually understand the different types of industrial discrete control input switches and
how they fit into control circuits.
Instructions:
1. Draw the following types of switches and their connections in a basic control circuit.
2. Label the key parts of the switches, including the terminals and connections to the load.
3. For each switch, provide a brief description of its function.
1. Draw and Label a Limit Switch
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Include:
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The limit switch with its Normally Open (NO) contact.
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A simple load (e.g., a light bulb or motor).
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The power source and wiring.
Label the following:
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Normally Open contact (NO)
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Common terminal
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Load (e.g., light bulb or motor)
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Power supply (positive and negative terminals)
Description:
A limit switch is used to detect the position of a moving part and sends a signal when the
part reaches a preset limit.
2. Draw and Label a Pushbutton Switch
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Include:
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A simple circuit with a pushbutton switch and load.
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Label the ON and OFF states of the switch.
Label the following:
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Common terminal
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Normally Open terminal (NO)
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Load (e.g., motor or light bulb)
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Power supply (positive and negative terminals)
Description:
A pushbutton switch is used to start or stop a process. It is usually in the OFF state and
turns the circuit ON when pressed.
3. Draw and Label a Toggle Switch
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Include:
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A toggle switch controlling a light bulb or motor.
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Show the ON and OFF positions of the toggle switch.
Label the following:
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Common terminal
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Normally Open terminal (NO)
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Load (light bulb or motor)
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Power supply
Description:
A toggle switch has two positions (ON and OFF) to control a load. It is often used for simple
ON/OFF functions in industrial control panels.
4. Draw and Label an Emergency Stop Button
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Include:
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Emergency stop button in a simple circuit with a load.
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Show how pressing the button cuts power to the load.
Label the following:
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Normally Closed contact (NC)
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Emergency stop button
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Load (e.g., light bulb or motor)
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Power supply
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Description:
The emergency stop button is designed to immediately halt operations in case of an
emergency by breaking the circuit.
5. Bonus: Draw a Circuit with Multiple Switches
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Include:
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A circuit that uses a combination of at least two different switches (e.g., a
pushbutton and toggle switch) to control a load.
Label the following:
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Each switch type (pushbutton, toggle, etc.)
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Common terminal
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Load (light bulb or motor)
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Power supply
Description:
Explain how these switches interact with each other and control the load in the circuit.
After completing the drawings and labels, write a brief explanation of each type of switch, how it
works in a control system, and what happens when the switch is activated.
This activity will help reinforce your understanding of industrial control input switches by visually
connecting the theory to practical applications.
Lesson: Industrial Discrete Control Output Devices
Objective:
By the end of this lesson, learners will understand the role, types, and applications of industrial
discrete control output devices. They will also be able to identify and describe how these devices
operate within an automation system.
1. Introduction to Discrete Control Output Devices
In industrial automation, discrete control refers to the use of binary signals—either ON (1) or OFF
(0)—to control various devices. These devices can turn equipment on or off, activate machinery, or
alert operators to system status changes. Discrete control systems are critical in manufacturing,
process control, and safety applications.
Discrete control output devices are the hardware components that perform these actions based
on input signals from controllers like PLCs (Programmable Logic Controllers).
2. Types of Discrete Control Output Devices
A. Relays
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Definition: A relay is an electrically operated switch that uses a control signal to open or
close contacts, thus controlling larger electrical currents.
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Operation: When the relay coil is energized, it creates a magnetic field that pulls in the relay
contacts, allowing current to flow through the connected load (like a motor or light).
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Applications: Used in controlling low-voltage circuits, switching loads such as motors,
lights, or alarm systems.
B. Solid-State Relays (SSRs)
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Definition: A solid-state relay is similar to a traditional relay but operates using
semiconductor components instead of mechanical contacts.
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Operation: When a control signal is applied, the semiconductor switches the load on or off
without moving parts.
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Advantages: Faster response times, higher reliability, no mechanical wear, and no noise
during operation.
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Applications: Used in systems where durability and speed are critical, like in highfrequency switching or environments with vibration.
C. Contactors
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Definition: A contactor is a heavy-duty relay used to switch high current loads, such as
motors or industrial heaters.
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Operation: The contactor has an electromagnet that closes or opens high-current contacts
when the coil is energized.
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Applications: Motor control circuits, HVAC systems, and industrial power systems.
D. Motor Starters
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Definition: A motor starter is a device that helps start and protect electric motors. It often
includes a contactor and overload protection in one package.
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Operation: The motor starter can start or stop the motor, and the overload protection helps
prevent motor damage due to excessive current.
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Applications: Used in manufacturing and industrial applications where electric motors are
common, such as conveyors, pumps, and fans.
E. Solenoids
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Definition: A solenoid is an electromechanical device used to convert electrical energy into
linear motion (push or pull).
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Operation: When current flows through a coil of wire, it generates a magnetic field that
moves a plunger or armature, which can open a valve or activate a mechanical device.
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Applications: Opening or closing valves, locking mechanisms, and controlling fluid
systems.
F. Actuators
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Definition: An actuator is a device that converts electrical energy into mechanical motion.
Actuators can be electric, pneumatic, or hydraulic.
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Operation: Electric actuators use an electric motor to produce rotational motion, while
pneumatic or hydraulic actuators use pressure to create linear or rotary motion.
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Applications: Valve control, robotics, automated assembly lines, and any application that
requires movement in response to a control signal.
G. Light Indicators
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Definition: Light indicators, often LED-based, are used to visually communicate the status
of equipment or systems.
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Operation: A PLC or controller sends a signal to the light, which will turn on or off based on
the system’s status (e.g., green for "OK", red for "fault").
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Applications: Used in control panels, machinery, and safety systems for operator alerts.
H. Buzzers/Alarms
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Definition: Buzzers or alarms are output devices used to alert operators to a condition that
requires attention.
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Operation: When a controller detects a specific condition (e.g., a fault), it triggers the
buzzer or alarm to produce a sound or visual indication.
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Applications: Used for safety or to warn operators of faults, critical events, or maintenance
requirements.
3. Key Features of Discrete Control Output Devices
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Binary Operation: These devices operate on a binary (on/off) signal, making them easy to
integrate into digital control systems like PLCs.
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Speed and Reliability: Devices like solid-state relays and contactors are designed to
operate at high speeds with high reliability, ensuring the control system’s stability.
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Safety and Protection: Many of these devices, like motor starters and relays, include
features like overload protection to prevent system damage.
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Application-Specific Design: Output devices are often chosen based on the voltage,
current rating, and specific needs of the machinery or process.
4. Application Examples
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Motor Control: A motor starter controls the motor in a conveyor belt system. When the
controller signals to start, the starter energizes the contactor, allowing power to the motor. If
the motor draws too much current, the overload protection will disconnect power to
prevent damage.
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Valve Control: A solenoid is used to control the opening and closing of a valve in a fluid
system. When a signal is sent, the solenoid moves the valve mechanism.
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System Status: An operator might monitor a system using indicator lights—green for
operational, red for fault. If the PLC detects a failure, it will trigger the red light, signaling the
need for maintenance.
5. Conclusion
Discrete control output devices play a crucial role in industrial automation by controlling
machinery, providing feedback, and ensuring safe operations. By understanding how each type of
device works and its application, operators and engineers can design more efficient, reliable, and
safe automated systems.
LABORATORY 2: Drawing and Labeling Industrial Discrete Control Output Devices
Objective:
The purpose of this activity is to help students or trainees become familiar with the physical
appearance and function of industrial discrete control output devices by drawing and labeling
them.
Instructions:
1. Materials Needed:
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Paper
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Pencil
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Reference images of each output device (optional but helpful)
2. Task: You are to draw and label the following industrial discrete control output devices.
Label each component clearly and include a brief description of how the device functions.
Devices to Draw and Label:
1. Relay
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Description: A relay is an electrically operated switch used to control higher voltage
circuits with a lower voltage control signal. It includes a coil and a set of contacts
that open or close when energized.
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Task: Draw the coil, the armature, and the contacts. Label each part (e.g., coil,
armature, normally open contact, normally closed contact).
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Additional Detail: Indicate the direction of current flow when the relay is activated.
2. Solid-State Relay (SSR)
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Description: A solid-state relay operates similarly to a mechanical relay but uses
semiconductor devices to switch on or off. It has no moving parts.
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Task: Draw a simple diagram of a solid-state relay, showing the control input and the
output terminals. Label the key components (e.g., control input, output,
semiconductor components).
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Additional Detail: Show how it switches a load without physical contact.
3. Contactor
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Description: A contactor is used for switching high-current devices, such as
motors. It consists of an electromagnet and a set of contacts.
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Task: Draw a contactor with the electromagnet coil, movable contacts, and
stationary contacts. Label each component (e.g., coil, normally open contacts,
fixed contacts).
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Additional Detail: Indicate how the contacts close when the coil is energized.
4. Motor Starter
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Description: A motor starter combines a contactor and overload protection to
safely start and stop motors.
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Task: Draw a motor starter system showing the contactor, overload relay, and motor
connections. Label each component (e.g., contactor, overload relay, motor
terminals).
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Additional Detail: Indicate how the overload relay protects the motor from
excessive current.
5. Solenoid
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Description: A solenoid is an electromechanical device used for linear motion,
such as pushing or pulling a mechanical part.
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Task: Draw a solenoid, showing the coil, plunger, and the mechanical part it moves.
Label each component (e.g., coil, plunger, actuator).
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Additional Detail: Indicate how the solenoid operates when energized.
6. Actuator
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Description: An actuator converts electrical energy into mechanical motion, such
as for controlling valves or moving robotic arms.
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Task: Draw an electric actuator, showing the motor and the movement mechanism
(linear or rotary). Label each component (e.g., motor, drive shaft, housing).
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Additional Detail: Indicate the motion direction and how it is controlled.
7. Light Indicator
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Description: Light indicators provide visual status feedback (e.g., green for "on", red
for "fault").
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Task: Draw a basic light indicator system with LED lights or signal lamps. Label each
component (e.g., LED, circuit, power supply).
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Additional Detail: Show how the light turns on based on the input signal.
8. Buzzer/Alarm
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Description: A buzzer or alarm is used to alert operators about a system status or
error, typically with sound.
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Task: Draw a buzzer circuit with a power source and buzzer. Label each part (e.g.,
power source, buzzer, control input).
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Additional Detail: Show how the alarm is triggered by an input signal from the
control system.
Completion Instructions:
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Step 1: Draw each device on a separate piece of paper or on a whiteboard.
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Step 2: Label each part of the device and provide a short description of its function below
the diagram.
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Step 3: For each device, include one real-world example or application where it might be
used in an industrial automation system.
Example:
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Relay Drawing Example:
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Draw the relay coil, contacts (both normally open and normally closed), and the
armature. Label each part.
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Write: "A relay is used to control circuits by opening or closing contacts when the
coil is energized. Example: Switching on a motor from a control panel."