This is presentation of Mechatronics class.

1. Intro to Sensors

2. Overview
• Sensors?
• Commonly Detectable Phenomenon
• Physical Principles – How Sensors Work?
• Need for Sensors
• Choosing a Sensor
• Examples

3. Sensors?
• American National Standards Institute
– A device which provides a usable output in response to a specified measurand
• Nowadays common sensors convert measurement of physical
phenomena into an electrical signal
• Active element of a sensor is called a transducer
Sensor
Input Signal Output Signal

4. Transducer?
A device which converts one form of energy to another
When input is a physical quantity and output electrical → Sensor
When input is electrical and output a physical quantity → Actuator
Actuators
Sensors
Physical
parameter
Electrical
Output
Electrical
Input
Physical
Output
e.g. Piezoelectric:
Force -> voltage
Voltage-> Force
=> Ultrasound!
Microphone, Loud Speaker

5. Commonly Detectable Phenomena
•Biological
•Chemical
•Electric
•Electromagnetic
•Heat/Temperature
•Magnetic
•Mechanical motion (displacement, velocity, acceleration, etc.)
•Optical
•Radioactivity

6. Common Conversion Methods
•Physical
–thermo-electric, thermo-elastic, thermo-magnetic, thermo-optic
–photo-electric, photo-elastic, photo-magnetic,
–electro-elastic, electro-magnetic
–magneto-electric
•Chemical
–chemical transport, physical transformation, electro-chemical
•Biological
–biological transformation, physical transformation

7. Commonly Measured Quantities
Stimulus Quantity
Acoustic Wave (amplitude, phase, polarization), Spectrum, Wave
Velocity
Biological & Chemical Fluid Concentrations (Gas or Liquid)
Electric Charge, Voltage, Current, Electric Field (amplitude, phase,
polarization), Conductivity, Permittivity
Magnetic Magnetic Field (amplitude, phase, polarization), Flux,
Permeability
Optical Refractive Index, Reflectivity, Absorption
Thermal Temperature, Flux, Specific Heat, Thermal Conductivity
Mechanical Position, Velocity, Acceleration, Force, Strain, Stress,
Pressure, Torque

8. Physical Principles: Examples
• Amperes’s Law
– A current carrying conductor in a magnetic field experiences a force (e.g.
galvanometer)
• Curie-Weiss Law
– There is a transition temperature at which ferromagnetic materials exhibit
paramagnetic behavior
• Faraday’s Law of Induction
– A coil resist a change in magnetic field by generating an opposing
voltage/current (e.g. transformer)
• Photoconductive Effect
– When light strikes certain semiconductor materials, the resistance of the material
decreases (e.g. photoresistor)

9. Choosing a Sensor

10. Need for Sensors
• Sensors are pervasive. They are embedded in
our bodies, automobiles, airplanes, cellular
telephones, radios, chemical plants, industrial
plants and countless other applications.
• Without the use of sensors, there would be no
automation !!
– Imagine having to manually fill Poland Spring
bottles

11. Temperature Sensors

12. Types of Temperature Sensors
 Thermocouples
 Resistance
Temperature Detectors
(RTDs)
 Thermistors
 Infrared Sensors
 Semiconductors

13. Thermocouples
A thermocouple is a temperature-measuring device
consisting of two dissimilar conductors that contact each
other at one or more spots. It produces a voltage when the
temperature of one of the spots differs from the reference
temperature at other parts of the circuit.

14. Misconception in Thermoelectricity
The EMF generated by the Seebeck effect is due to the temperature
gradient along the wire.
The EMF is not generated at the junction between two dissimilar wires.

15. Principle of operation

17. Thermocouples: Seebeck effect
The Seebeck effect is the conversion of thermal energy/temperature differences directly
into electrical energy or electricity.
This effect measures the ease at which excess electrons will circulate in an electrical circuit
under the influence of thermal difference.
The change in the voltage is proportional to the temperature difference between the
junctions when the ends are connected to form a loop.

18. A thermoelectric circuit composed of materials of different Seebeck coefficient
(p-doped and n-doped semiconductors), configured as athermoelectric generator.
If the load resistor at the bottom is replaced with avoltmeter the circuit then
functions as a temperature-sensing thermocouple.

19. Seebeck Effect

20. Circuit construction

21. Material EMF versus Temperature
With reference to
the characteristics
of pure Platinum
emf
Temperature
Chromel
Iron
Copper
Platinum-Rhodium
Alumel
Constantan

22. Thermocouple temperature vs.Voltage graph

23. Seebeck coefficient vs. Temperature

24. applications
1.Steel industry
2.Gasappliance safety
3.Thermopile radiation sensors
4.Manufacturing
5.Power production
6.Thermoelectric cooling
7.Process plants
8.Thermocouple asvacuum gauge

25. A thermocouple (the right most tube) inside the burner
assembly of a water heater.

26. Thermocouple connection in gas appliances. The end ball (contact) on the left is insulated
from the fitting by an insulating washer. The thermocouple line consists of copper wire,
insulator and outer metal (usually copper) sheath which is also used as ground.

27. Type

29. Thermocouple insulation

30. Advantages