Chapter 3: Monitoring and control

Question 1

Basic sensor steps

Answer 1

1) sensor constantly monitor surroundings
2) data reading from sensor analogue
3) ADC digital signal
4) digital signal processed my micro processor
5) compared with preset values
6) signal to actuator (if value out of range)

Question 2

Passive motion sensor

Answer 2

• reads energy in room, detect changes caused by movement
• no work in harsh environment
• no detect slow motion
• passive infrared sensor
• security

Question 3

Active motion sensor

Answer 3

• emits energy into environment
• microwave sensor
• emit microwave, detect change in reflection, bounce off
• security
• work in harsh environments
• prone to false alarm (e.g object gets blown by wind)

Question 4

Motion sensor E.g

Answer 4

1) CCTV
2) doors
3) lights
4) car park barriers

Question 5

Pressure sensor

Answer 5

• use piezoresistance
• specific level of pressure to a level of charge in a substance (crystal)
• change in level of charge is a change in level of pressure

Question 6

Pressure sensor: uses

Answer 6

1) Airbag safety system
2) Liquid/ gas pipes , not flow too fast (nuclear plant), safet
3) pressure placed on accelerator / brake
4) aviation/ marine : atmosphere, breathing condition
5) touch screen , signal tell where pressure is applied

Question 7

Uses of humidity sensor

Answer 7

• agriculture
• allergy
• manufacturing
• meteorological station

Question 8

Uses of temp sensor

Answer 8

• washing machine
• dish washer
• dryer
• fridge
• AC

Question 9

Uses of light sensors

Answer 9

Photo resistor: change its resistance based on intensity of light

• street light
• camera
• phone

Question 10

Sensor application: traffic

Answer 10

Induction loop

• detect car overhead
• metal changes magnetic field induced in the loop

Sounds sensor

Camera

Push button