Sensors and Actuators: Differences, DAQ, Types & Applications
Q1: Sensors vs Actuators — Detailed Explanation
Definition of Sensor
A sensor is a device that detects, measures, or senses a physical quantity such as temperature, pressure, displacement, light, humidity, flow, etc., and converts it into a usable electrical signal (voltage, current, resistance).
Sensors act as the input element of any measurement or control system.
They form the first stage of data acquisition.
Without sensors, a system cannot perceive real-world conditions.
Definition of Actuator
An actuator is a device that converts an electrical control signal into a physical action such as motion, force, rotation, or displacement.
Actuators act as the output element of a control system.
They execute decisions taken by controllers.
Actuators physically influence the environment.
Energy Conversion
Sensor: Physical energy → Electrical energy
Actuator: Electrical energy → Mechanical / Thermal / Hydraulic energy
Detailed Comparison Table
| Parameter | Sensor | Actuator |
|---|---|---|
| Basic function | Measures physical quantity | Produces physical action |
| Role in system | Input device | Output device |
| Energy conversion | Physical → Electrical | Electrical → Physical |
| Signal flow | Environment → System | System → Environment |
| Examples | Temperature sensor, Pressure sensor, LVDT | DC motor, Solenoid, Valve |
| IoT role | Data collection | Control and execution |
| Feedback role | Provides feedback | Executes control signal |
Conclusion
Sensors and actuators are complementary devices. Sensors sense and report, while actuators respond and act. Together, they enable automation, control systems, and IoT applications.
Q2: Data Acquisition System (DAQ) Block Diagram
Definition
A Data Acquisition System (DAQ) is a system that measures physical parameters, converts them into electrical signals, processes them, and stores or displays the information in digital form for monitoring and control.
Need for DAQ
Physical quantities are analog and cannot be directly processed by digital systems.
DAQ bridges the gap between real-world signals and digital processing systems.
DAQ Block Diagram — Block-wise Explanation
1. Sensor / Transducer
Converts physical quantity (temperature, pressure, displacement) into an electrical signal.
Output may be voltage, current, or resistance.
Example: Thermocouple, Strain gauge
2. Signal Conditioning Unit
Improves signal quality.
Functions include:
Amplification (boosts weak signals)
Filtering (removes noise)
Isolation (protects system)
Linearization (corrects non-linearity)
3. Multiplexer
Selects one signal from multiple sensor outputs.
Reduces hardware cost by using one ADC for many sensors.
4. Sample and Hold Circuit
Samples analog signal at a specific time.
Holds the value constant during conversion.
5. Analog-to-Digital Converter (ADC)
Converts conditioned analog signal into digital binary data.
Resolution and speed determine accuracy.
6. Processor / Computer
Processes digital data.
Performs:
Data analysis
Storage
Decision making
Control logic
7. Output / Display / Storage
Displays data on screen.
Stores data in memory.
Sends control commands to actuators.
Applications of DAQ
Industrial process control
Biomedical monitoring
Environmental monitoring
IoT systems
Automotive testing
Q3: Types of Sensors and Classifications
Sensors can be classified based on multiple criteria as follows:
A. Classification Based on Power Requirement
1. Active Sensors
Require external power supply.
Output signal depends on excitation.
High accuracy and sensitivity.
Examples:
RTD
Strain gauge
LVDT
2. Passive Sensors
Do not require external power.
Generate output by themselves.
Examples:
Thermocouple
Piezoelectric sensor
Photovoltaic cell
B. Classification Based on Output Signal
1. Analog Sensors
Provide continuous output.
Suitable for precise measurements.
Examples:
Potentiometer
LVDT
Thermistor
2. Digital Sensors
Provide discrete or binary output.
Easy to interface with microcontrollers.
Examples:
Optical encoder
Digital temperature sensor
C. Classification Based on Measured Quantity
Temperature sensors
Pressure sensors
Flow sensors
Level sensors
Position sensors
Proximity sensors
D. Classification Based on Contact
Contact Sensors
Physically touch the object.
Example: Strain gauge
Non-contact Sensors
Measure without physical contact.
Example: Ultrasonic sensor
Q4: Types of Actuators
1. Electrical Actuators
Use electrical energy.
Convert electrical signal into motion.
Examples:
DC motors
Stepper motors
Servo motors
Advantages:
High precision
Easy control
Clean operation
2. Pneumatic Actuators
Use compressed air.
Provide linear or rotary motion.
Advantages:
Fast response
Simple construction
Limitations:
Limited force
Air leakage
3. Hydraulic Actuators
Use pressurized fluid.
Suitable for high-force applications.
Applications:
Heavy machinery
Industrial presses
4. Smart Material Actuators
Respond to electrical or thermal input.
High precision and compact size.
Examples:
Piezoelectric actuators
Shape memory alloys
Q5: Working of Electric Actuators
Principle
Electric actuators operate on electromagnetic induction and the Lorentz force principle.
Working
Electrical power is applied to the actuator.
A magnetic field is generated.
Interaction of magnetic field produces force.
Rotor or armature moves.
Motion is transmitted as:
Linear motion
Rotary motion
Types
DC motor actuator
Stepper motor actuator
Servo actuator
Advantages
High accuracy
Fast response
Easy integration with controllers
Q6: Role of Sensors in IoT Applications
Role
Sensors are the foundation of IoT systems.
They collect real-world data and convert it into digital information.
Functions
Environment monitoring
Real-time data acquisition
Triggering automated actions
Data-driven decision making
Examples
Temperature sensor → Smart AC control
Soil moisture sensor → Smart irrigation
Gas sensor → Safety systems
Importance
Without sensors, IoT systems become blind and ineffective.
Q7: Actuators in Industrial & Home Automation
Industrial Automation
Control valves
Operate robotic arms
Conveyor belt movement
Machine positioning
Home Automation
Automatic lighting
Smart door locks
HVAC systems
Motorized curtains
Conclusion
Actuators transform digital intelligence into physical reality.
Q8: Selection Criteria for Sensors and Actuators
Sensor Selection Criteria
Measurement range
Accuracy
Sensitivity
Resolution
Response time
Environmental conditions
Cost and reliability
Actuator Selection Criteria
Load capacity
Speed
Power requirement
Control precision
Duty cycle
Operating environment
Q9: Interaction with Control Systems
Closed Loop Operation
Sensor measures output variable.
Signal is sent to controller.
Controller compares with reference value.
Error signal is generated.
Actuator receives control signal.
Actuator corrects system output.
Feedback is continuously monitored.
Importance
Improves accuracy
Reduces error
Enhances stability
Q10: Industrial Applications of Sensors & Actuators
Industrial Applications
Manufacturing automation
Process control
Robotics
Automotive systems
Medical devices
Power plants
Aerospace systems
Q11: Smart Material Actuators & Piezoelectric Transducer
Smart Material Actuators
Materials that change properties when stimulated.
Provide high-precision actuation.
Piezoelectric Transducer
Principle:
When mechanical stress is applied → electrical charge is generated. When voltage is applied → mechanical deformation occurs.
Applications
Precision positioning
Ultrasonic devices
Sensors and actuators
Medical imaging