for ECE students

1. SENSOR
TECHNOGY
Presented by Apurba Chatterjee

2. • What is sensor
• Type of sensor
• Some quantities that can be sensed
• Working of some sensor
• Application
• Advantage & disadvantage’s
• How sensor made easy to human life
• Summary

3. • Transducer convert one form of energy into another
• Sensors/Actuators are input/output transducers
• Sensors can be passive (e.g. change in resistance) or active (output is a voltage or current
level)
• Sensors can be analog (e.g. thermocouples) or digital (e.g. digital tachometer)

4. Types of Sensor
Direct
A sensor that can convert a non-electrical stimulus into an electrical signal with
intermediate stages.
Thermocouple (temperature to voltage)
Indirect
A sensor that multiple conversion steps to transform the measured signal into an
electrical signal.
A fiber-optic displacement sensor:
Current >> photons >>current

5. What are some quantities
that can be sensed?
• Motion, position, displacement
• Velocity and acceleration
• Force, strain
• Pressure
• Flow
• Sound
• Moisture
• Light
• Radiation
• Temperature
• Chemical presence

6. Working of some sensor’s
example

7. Temperature Sensors
• Bimetallic switch (electro-mechanical) – used in thermostats. Can be “creep” or
“snap” action.
• Thermistors (thermally sensitive resistors): Platinum Resistance Thermometer
(PRT), very high accuracy

8. Thermocouples
Two dissimilar metals induce voltage difference (few mV per 10K) – electro-
thermal or Seebeck effect
Use op-amp to process/amplify the voltage
Absolute accuracy of 1K is difficult

10. Light sensors: photoconductive cells
• Light dependent resistor (LDR) cell

11. Light level sensitive switch

12. Photojunction devices
• Photodiode • Phototransistor

13. Photovoltaic Solar Cells
• Can convert about 20% of light power into electricity
• Voltage is low (diode drop, ~0.6V)

14. Distance Measurement Sensor
• Ultrasonic Sensor :As the name indicates, ultrasonic sensors measure
distance by using ultrasonic waves. The sensor head emits an ultrasonic wave and
receives the wave reflected back from the target. Ultrasonic Sensors measure the
distance to the target by measuring the time between the emission and reception.

15. Application

16. Transportation Sensor Applications
• Controlled Atmosphere Monitoring
Controlled or modified atmospheres can considerably increase the storage life of
certain fruit and vegetable cargoes. Slowing down their metabolic rate delays the
natural ripening of the produce without effecting its flavour and eating quality.
SST’s OXY-COMM Oxygen Sensor is designed to prolong the life of perishable
food within refrigerated, controlled and modified atmospheres by accurately
measuring the oxygen concentration.

17. Sensor Applications In Home Automation
Home automation or domestics is building automation for a home, called a smart
home or smart house. A home automation system will control lighting, climate,
entertainment systems, and appliances. It may also include home security such as
access control and alarm systems. When connected with the Internet, home devices
are an important constituent of the Internet of Things.

18. Industrial Sensor Applications
• Boiler Combustion Efficiency
• Protecting Robotic Process Automation Systems
• Gas Nitriding and O2 Measurement

19. Advantage & Disadvantage
Sensors Advantages Disadvantages
Limit Switch Sensor High Current Capability
Low Cost
Familiar “Low- Tech" Sensing
Very Slow Response
Contact Bounce
Photoelectric
Sensor
Senses all Kinds of Materials
Long Life
Longest Sensing Range
Lens Subject to
Contamination
Sensing Range
Inductive
Sensor
Very Predictable
Long Life
Easy to Install
Distance
Limitation
Capacitive
Sensor
Detects Through Some Containers Very Sensitive
Ultrasonic
Sensor
Senses all Materials Resolution

20. How Sensor Made Easy to
Human Life

22. Summary
• We’ve only briefly touched on most basic types
• Many other transducers are used/common, almost for any physical quantity one
can think of
• Processing electronics is often essential: output of many sensors is not linear,
needs impedance transform, filtering, etc.
• For additional references see
• http://www.electronics-tutorials.ws/io/io_1.html
• Handbook of Transducers by H.N. Norton
• http://www.sparkfun.com