Unit II – Sensors and Actuators (Simple English Notes)

1. Sensor

A Sensor is a device that detects or measures a physical quantity and converts it into a signal that can be processed.

Examples

Temperature sensor
Humidity sensor
Pressure sensor
Light sensor
Motion sensor

Formula Definition

Sensor = Sensing Element + Signal Processing Unit

Applications

Smart homes
Healthcare
Agriculture
Industrial automation

2. Basic Components of a Sensor Node

A Sensor Node is a small device used in IoT and Wireless Sensor Networks (WSN).

Components

1. Sensor Unit

Collects data from environment

2. Processing Unit

Processes collected data
Usually contains a microcontroller

3. Communication Unit

Sends and receives data
Uses Wi-Fi, ZigBee, Bluetooth, etc.

4. Power Unit

Battery or power source

Diagram


Sensor
   ↓
Processor
   ↓
Communication Module
   ↓
Network

3. Challenges of a Sensor Node

1. Limited Battery Power

Batteries drain quickly

2. Limited Memory

Small storage capacity

3. Limited Processing Power

Cannot perform heavy computations

4. Communication Issues

Signal loss and interference

5. Security Problems

Risk of unauthorized access

6. Environmental Conditions

Heat, dust, moisture may affect sensors

4. Sensor Features

Important characteristics of a sensor:

Accuracy

Closeness to actual value

Precision

Ability to produce same reading repeatedly

Sensitivity

Ability to detect small changes

Range

Minimum and maximum measurable value

Response Time

Time taken to produce output

Reliability

Ability to work consistently

5. Sensor Resolution

Resolution is the smallest change in input that a sensor can detect.

Example

If a temperature sensor measures:

25.0°C, 25.1°C, 25.2°C

Resolution = 0.1°C

Important Point

Higher resolution = Better measurement accuracy

6. Sensor Classes

A) Analog Sensor

Produces continuous output values.

Examples

Temperature sensor
Pressure sensor

Output:


0V → 5V

Advantages

High accuracy
Continuous readings

B) Digital Sensor

Produces discrete (0 or 1) output.

Examples

Motion sensor
Digital temperature sensor

Output:


ON / OFF
1 / 0

Advantages

Easy processing
Less noise

C) Scalar Sensor

Measures only magnitude.

Examples

Temperature sensor
Humidity sensor

Example:


Temperature = 30°C

D) Vector Sensor

Measures magnitude and direction.

Examples

Accelerometer
Magnetometer

Example:


Wind speed + direction

7. Sensor Types

Temperature Sensor

Measures temperature.

Pressure Sensor

Measures pressure.

Humidity Sensor

Measures moisture in air.

Light Sensor

Measures light intensity.

Motion Sensor

Detects movement.

Gas Sensor

Detects gases.

Proximity Sensor

Detects nearby objects.

8. Bias Error

Bias is a constant difference between actual value and measured value.

Example

Actual Temperature = 30°C

Sensor Reading = 32°C

Bias Error = 2°C

Causes

Calibration errors
Manufacturing defects

9. Drift Error

Drift is the gradual change in sensor output over time.

Example

A sensor gives different readings even when the actual value remains constant.

Causes

Aging
Temperature changes
Environmental effects

10. Hysteresis Error

Hysteresis occurs when the sensor gives different outputs for the same input depending on whether the value is increasing or decreasing.

Example

Input = 50 units

Increasing value → Output = 51

Decreasing value → Output = 49

Result

Different outputs for same input.

11. Quantization Error

Occurs during Analog-to-Digital Conversion (ADC).

Continuous values are rounded to nearest digital value.

Example

Actual Value = 4.67

Digital Value = 5

Quantization Error = 0.33

Cause

Limited number of digital levels.

12. Actuator

An Actuator is a device that converts electrical signals into physical action.

Function

Sensor detects → Controller processes → Actuator performs action

Examples

Motor
Pump
Valve
Relay

13. Actuator Types

A) Hydraulic Actuator

Uses liquid pressure to produce movement.

Features

High force
High power

Applications

Excavators
Hydraulic lifts

B) Pneumatic Actuator

Uses compressed air.

Features

Fast operation
Clean system

Applications

Industrial automation
Air brakes

C) Electrical Actuator

Uses electrical energy.

Examples

DC Motor
Servo Motor
Stepper Motor

Applications

Robots
Smart devices

D) Thermal/Magnetic Actuator

Thermal Actuator

Uses heat energy.

Examples:

Thermostat
Temperature-controlled valves

Magnetic Actuator

Uses magnetic force.

Examples:

Solenoid
Electromagnetic relay

E) Mechanical Actuator

Produces movement through mechanical mechanisms.

Examples

Gears
Springs
Levers

Applications

Machines
Industrial equipment

F) Soft Actuator

Made from flexible materials.

Features

Flexible
Lightweight
Safe for humans

Applications

Soft robotics
Medical devices
Wearable technology

Comparison of Actuator Types

Actuator Type	Energy Source	Example
Hydraulic	Liquid Pressure	Hydraulic Lift
Pneumatic	Compressed Air	Air Cylinder
Electrical	Electricity	DC Motor
Thermal	Heat	Thermostat
Magnetic	Magnetic Field	Solenoid
Mechanical	Mechanical Force	Gear System
Soft Actuator	Flexible Materials	Soft Robot

Important Short Notes (Exam Revision)

Sensor: Device that converts physical quantity into electrical signal.
Sensor Node Components: Sensor, Processor, Communication Unit, Power Unit.
Resolution: Smallest detectable change in input.
Analog Sensor: Continuous output.
Digital Sensor: Discrete output (0/1).
Scalar Sensor: Measures only magnitude.
Vector Sensor: Measures magnitude and direction.
Bias Error: Constant measurement error.
Drift Error: Change in output over time.
Hysteresis Error: Different output for same input.
Quantization Error: Error during ADC conversion.
Actuator: Converts electrical signal into physical action.
Hydraulic Actuator: Uses liquid pressure.
Pneumatic Actuator: Uses compressed air.
Electrical Actuator: Uses electricity.
Soft Actuator: Flexible actuator used in robotics.