Sensors in IoT systems detect physical quantities and convert them into signals that can be processed and interpreted. These signals are transformed into human-readable formats, such as changes in resistance, capacitance, or impedance.

Transducers

• A transducer converts one type of energy into another (e.g., mechanical to electrical energy).
• Used as actuators in various systems.

Sensor Characteristics

Static Characteristics

• Accuracy: The ability to measure close to the true value, measured by errors.
  • Absolute Error: Measured value - True value
  • Relative Error: Measured value / True value
• Range: The minimum and maximum values a sensor can detect.
• Resolution: The smallest change a sensor can detect.
• Precision: Consistency of measurements under the same conditions.
• Sensitivity: How much the output changes for a small input change.
• Linearity: How closely the sensor's output matches a straight line.
• Drift: Slow changes in measurement over time.
• Repeatability: The consistency of measurements taken under the same conditions.

Dynamic Characteristics

• Zero-order system: No delay in output, no energy storage.
• First-order system: Gradual output change.
• Second-order system: Oscillating output before stabilization.

Sensor Classification

1. Passive Sensors: Cannot independently sense input (e.g., accelerometer, temperature sensors).
2. Active Sensors: Independently sense input (e.g., radar, laser altimeter).
3. Analog Sensors: Provide continuous output based on the input (e.g., temperature sensor).
4. Digital Sensors: Output in binary form with additional electronics for bit conversion (e.g., PIR sensor).
5. Scalar Sensors: Measure the magnitude of an input, not direction (e.g., temperature sensor).
6. Vector Sensors: Measure both magnitude and direction (e.g., accelerometer, gyroscope).

Types of Sensors

• Electrical Sensors: Can be contact or non-contact (e.g., inductive or capacitive sensors).
• Light Sensors: Detect light intensity, typically using LDR (Light Dependent Resistor).
• Touch Sensors: Detect touch, either resistive or capacitive type.
• Range Sensors: Measure distance using non-contact methods (e.g., capacitive, inductive, or energy waves).
• Mechanical Sensors: Use mechanical switches for detection.
• Pneumatic Sensors: Operate by disturbing air flow.
• Optical Sensors: Detect changes in light, often used for proximity sensing.
• Speed Sensors: Measure the speed of moving objects (e.g., wind speed sensors, speedometers).
• Temperature Sensors: Monitor temperature and provide electrical signals proportional to temperature.
• PIR Sensors: Detect motion by measuring infrared light, often used for human motion detection.
• Ultrasonic Sensors: Use sound waves to measure distance (similar to radar or sonar).

These sensors play a crucial role in IoT systems, enabling real-time monitoring, automation, and intelligent decision-making.