1. Sensor (application to measurement)
Lecture 3
(Chapter 2)

2. Sensor is a Transducer: What is a transducer ?
An electromechanical device that converts a mechanical change into a change in an electrical signal
Sensors
Physical parameter
Electrical Output
Electrical Input
Physical Output
e.g. Piezoelectric:
Force -> voltage
Actuators
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SME3252: Mechatronics Lecture 3

3. Essential Elements Input Instrumentation System Output Sensing Element
True value of variables
Instrumentation
System
Output
Measured value of variables
Sensing Element
Conditioning Element
Processing Element
Displaying Element
Chapter 2
Chapter 3
Chapter 4,5,6
4/21/2017
SME3252: Mechatronics Lecture 3

4. Example of Instrumentation System
4/21/2017
SME3252: Mechatronics Lecture 3

5. 2.1: Sensor Measurement in mechanical engineering:
Displacement, position and proximity
Velocity and motion
Force
Pressure
Fluid flow
Liquid level
Temperature
Light intensity

6. 2.2 Performance terminology
Range and span
Error
Accuracy
Sensitivity
Hysteresis error
Nonlinearity error
Repeatability / reproducibility
Stability – zero drift
Resolution
Output impedence

7. Examples - Ranges: 70 to 1000kPa, 2000 to 70000 kPa
Supply voltage: 10 V d.c or a.c. rms
Full range output: 40 mV
Nonlinearity and hysteresis:±0.5% full range output
Temperature range: -540C to +1200C when operating
Thermal zero shift: 0.030% full range output /0C

8. 2.3: Displacement, position and proximity
Displacement – how much the object has been moved
Position – position of an object with a reference point
Proximity – position sensor to detect when an object has moved
2 basic types of displacement / position sensor – contact and noncontact

9. Displacement measurement
Examples of application:
Location & position of object on a conveyor
Orientation of steel plate in a rolling mill
Liquid/solid level measurement
Location or position of work piece in milling operation

10. Application : Bottle sensing. Type : Photoelectric Sensor
Location & position of object on a conveyor
Application : Bottle sensing. Type           : Photoelectric Sensor

11. Rolling of steel plate

12. Application : Liquid level indicator. Type           : Capacitive Sensor

13. Milling process

14. Translational and Rotational Potentiometers
Translational or angular displacement is proportional to resistance.
Taken from luennot/Luento3.pdf

15. high alternating stresses that cause damage to blade
2.3.2: Strain-gage
high alternating stresses that cause damage to blade
Strain gages allow monitoring of dynamic torsional motions

16. 2.3.3: Capacitive sensor

17. How does it works: Capacitive
A capacitive touchscreen consists of a glass panel with a capacitive (charge storing) material coating its surface. Circuits located at the corners of the screen measure the capacitance of a person touching the overlay. Frequency changes are measured to determine the X and Y coordinates of the touch command. The touchscreen controller sends data via serial port to the host
computer and emulates a mouse.

18. 2.3.4: LVDT

19. Inductive Sensors - LVDT
An LVDT is used as a sensitive displacement sensor: for example, in a cardiac assist device or a basic research project to study displacement produced by a contracting muscle.
LVDT
Linear Variable Differential Transformer
Taken from

20. 2.3.6: Inductive sensor

21. 2.3.7: Optical encoder
Provide digital output from linear and angular displacement

22. 2.3.9: Proximity switch simplest form of digital displacement sensor
many forms: lever or push-rod operated microswitches; float switches; pressure switches; etc.
A limit switch
A float switch

23. Lim Kim Fung, PSM 2006/2007

24. 2.4: Velocity sensor A) Linear velocity measurement
Linear velocity transducer or LVT
Based on inductive transducer principle
Magnetic field associated with velocity to be measured moves w.r.t fixed conductor

25. B) Angular velocity measurement
Many common machine have rotating shafts – angular velocity or shaft speed
Stroboscopic – flashing light, mark on pulley, rpm
Photoelectric – used photodetector

26. 2.5: Force measurement - Load Cell
Performance
Load range: to 250 lbs
Non-Linearity: 0.05% F.S.
Hysteresis: 0.03% F.S.
Non-Repeatability: 0.03% F.S.
Output: 3 mV/V
Resolution: Infinite
Environmental
Temp. operating: 0 to 130 °F
Temp. compensated: 30 to 130 °F
Mechanical
Static overload: 50% over capacity
Full
Scale P eT eL R3
, R4
, R1 R2

27. 2.6: Fluid pressure
hydraulic pressure is used to measure force applied to diaphragm
when force F applied, pressure is developed in fluid (normally oil),device to measure normally Bourdon gage

28. What is piezoelectricity ?
2.6.1: Piezoelectric Sensors
What is piezoelectricity ?
Strain causes a redistribution of charges and results in a net electric dipole (a dipole is kind of a battery!)
A piezoelectric material produces voltage by distributing charge (under mechanical strain/stress)
Discovered in 1880 by Pierre Curie in quartz crystals. The greek word “piezein”, which means “to press”
Examples --- Quartz, Barium titanate, tourmaline

29. 2.7: Liquid flow
The most common principals for fluid flow metering are: 
Differential pressure flowmeter
Velocity flowmeter
Positive displacement flowmeter
Open channel flowmeter

30. The most common types of differential pressure flowmeters are:
Orifice Plates
Flow Nozzles 
Venturi Tubes
Variable Area - Rotameters

31. 2.9: Temperature
RTD
Thermistor
Thermocouple

32. 2.10: Photoelectric sensor
Photodiode
Phototransistor
Photocell
Solar cell

33. Presence of object
Samsul Tongaji, PSM 2006/2007

34. Exercises (Textbook)
Identify / suggest suitable sensors for the following applications:
Control system for a furnace to monitor rate of heating oil flows along a pipe line
Control system to determine difference of liquid levels in two container
Control system to control thickness of rolled sheet that emerges from rollers

35. End of Lecture 3