2. Working Principles and Applications of Common Sensors

Temperature Sensors:
- Working Principle: Temperature sensors, such as thermocouples and thermistors, operate based on the principle that materials change their electrical resistance with temperature. Thermocouples generate a voltage when two different metals are joined and exposed to different temperatures.
- Applications: Temperature sensors are used in HVAC systems, refrigerators, and industrial processes to monitor and control temperature.

Pressure Sensors:
- Working Principle: Pressure sensors, such as piezoelectric sensors, work by converting pressure into an electrical signal. When pressure is applied to a piezoelectric material, it generates an electrical charge.
- Applications: Pressure sensors are used in automotive systems (e.g., tire pressure monitoring), medical devices (e.g., blood pressure monitors), and industrial equipment.

Light Sensors:
- Working Principle: Light sensors, such as photodiodes and phototransistors, detect light levels and convert them into electrical signals. The intensity of light hitting the sensor changes its conductivity, which is then measured as an output signal.
- Applications: Light sensors are used in automatic lighting systems, digital cameras, and environmental monitoring.

Motion Sensors:
- Working Principle: Motion sensors, such as passive infrared (PIR) sensors, detect infrared radiation emitted by objects. When an object moves within the sensor's range, it detects the change in infrared radiation and triggers a response.
- Applications: Motion sensors are used in security systems, automatic doors, and smart home devices.

Example Problem:
Describe the working principle of a thermocouple and its application in industrial temperature measurement.

Solution:
A thermocouple consists of two different metals joined at one end. When this junction is heated or cooled, it generates a voltage proportional to the temperature difference between the junction and the other ends of the metals. This voltage is measured and converted into a temperature reading. Thermocouples are widely used in industrial applications for temperature measurement due to their wide temperature range and durability.