UNIT-1-SENSOR AND TRANSDUCER- MECHATRONICS-ENGGINERING

Understand the mechatronics systems , differentiate various sensors and transducers

1. 20ME702 -MECHATRONICS
UNIT-1
INTRODUCTION (SENSOR AND TRANSDUCERS)
Prepared by
S.ChandraKumar
AP/MECHANICAL
KongunaduCollege of
Engineering and Technology

2. Sensor
Sensor are devices which produce a proportional
output signal (mechanical, electrical, magnetic etc.,)
when exposed to a physical phenomenon (pressure,
temperature, displacement , force etc.,).

3. Transducer
Transducer are devices which converts an input of one
form of energyin to an output of another form of
energy.

4. Performance terminology
•Static characteristics
–Static characteristics of an instrument are the
parameters which are more or less constant or varying
very slowly with time.
•Dynamic characteristics
–Sensors and actuators respond to inputs that change
with time. Dynamic characteristics of an instrument are
the parameters which are varying with time.

5. Classification of sensor and transducer
ACTIVE SENSOR:
Power required to produce the output is provided by the
sensed physical phenomenon
It is other wise called as SELF GENERATING
TRANSDUSER
PASSIVE SENSOR:
It required external power source
Strain gauge, Resistance Thermo meters.
ANALOG SENSOR:
It produces Continuous signal
It requires Analog to Digital conversion for Output

6. DIGITAL SENSOR:
Digital sensors are the other hand to produce digital outputs
directly interfaces with the digital controller.
OTHER WAY OF CLASSIFYING SENSOR:
PRIMARY SENSOR (ACTIVE SENSORS)
Produce output which is directly measure from the input
SECONDARY SENSOR (PASSIVE SENSOR)
The Output which is not direct representation of physical
phenomenon

7. Static characteristics
Range–Every sensor design to work for a specific
range
e.g.: a thermocouple may have a range of -100 to
1260°C
Span: Life time of a component. Inaccuracy
maximum value of input –minimum value of input
Error: measured value –true input value
Accuracy: A very important characteristics of a
sensor which really means inaccuracy.
High accurate sensors produces low errors.

8. Static characteristics
Sensitivity:itisdefinedasthechangeinoutputper
changeininput.
Hysteresis:Itisdefinedasthemaximumdifferenceinoutput
foragiveninputwhenthisvalueisapproachedfromthe
oppositedirection.
Linearity:itisrefertotheoutputthatisdirectlyproportional
toinputoveritsentirerange.

9. Static characteristics
•Repeatability:itisdefinedastheabilityofthesensorto
givesameoutputreadingwhenthesameinputvalueis
appliedrepeatedlyunderthesameoperatingconditions.
•Reproducibility:itisdefinedasthedegreeofcloseness
amongtherepeatedmeasurementsoftheoutputforthe
samevalueofinputunderthesameoperatingconditionsat
differenttimes.

10. Static characteristics
Stability: it means the ability of the sensor to indicate the
same output over a period of time for a constant input.
Dead time: it is the time taken by the sensor from the
application of input to begin its response and change.
Resolution: it is defined as the smallest change that can be
detected by a sensor
Non-Liearity: From the input to the output, error takes
place

11. Static characteristics
Precision: Precision is the estimate which signifies the decimal
points to the property.
Selectivity: Sensor ability to measure a single component in the
presence of others. Light sensor does not measure sound etc,.
Output impedence:out put result of the sensor.

12. Dynamic characteristics
Response time(True output when subjected to input)
Time constant(constant time output cant varies)
Rise time( Length of time taken for the output to reach
90%)
Setting time(Close range to steady state value)
Frequency response
Dynamic error

13. Displacement sensor
Potentiometer sensor
Strain gauge sensor
Capacitive sensor
Inductive sensors (LVDT)

14. Potentiometer Displacement sensor
Linear potentiometer

15. Potentiometer Displacement sensor
Rotary potentiometer

16. Potentiometer Displacement sensor
Potentiometer with voltage divider

17. Strain gauge Displacement sensor
Strain gauge with Wheatstone bridge circuit

18. Mechanical dispalcement changes in resistance,
Wrafer like devices are attached to the variety of
materials are with suitable adhesive.
Increase in resistivity of the gauge which produces an
electric signal propotional to the deformation

20. Capacitive displacement sensor
Different form of capacitive sensor

21. Push –pull capacitive sensor
Capacitive proximity sensor

22. The sensors can directly measure varietyofthings such
as motion , displacement, small displacements
accurately.
Capacitor is connected central conductor coaxial cable
Other is formed by a target.
APPLICATIONS
MEASURING POSITION
DISPLACEMENT GAUGING
ADVANTAGES
Excellent linearitywhen dynamic stituations
High sensitivity
High speed , good stability
Etc.,

23. Linear variable Differential Transformer (LVDT)

24. It is passive type sensor.
It is electro mechanical device to produce AC voltage to
displacement.
Movable core to three windings in the static transformer.
Primary coil is excited then the two coils is excited
1 Khz voltage is passing through primary coil then AC
voltage is induced in secondary coils
When the core is in center position output voltages are
equal
When the positions changes there is electro magnetic
imbalance occurs


25. Linear variable Differential Transformer (LVDT) output

26. Rotary variable Differential Transformer (RVDT)
•It is used to measure rotational angles under same principles of
LVDT
•RVDT uses Rotary ferromagnetic core

27. Position sensors
potentiometer
Capacitive sensor
Inductive sensor
Hall effect sensors
Photoelectric sensor
Optical encoder

28. Hall effect sensors
Principle of Hall effect

29. A hall effect sensor is a transducer
Output changes with changes in magnetic field.
“When a conductor or semiconductor flowing in one
direction was introduced perpendicular to magnetic field a
voltage could be measured at right angles to the current
path”
Whenperpendicular magnetic field is present
Force is exerted
Force disturbes the current distribution results potential
difference.

30. Hall effect Sensor

31. Hall effect sensor used to measure FUEL LEVEL in FUEL
TANK.
The gap between magnet and hall sensor will changed.
The result changing the output.
The springs allow the float vertically.

32. Fluid level Hall effect Sensor

33. APPLICATIONS:
Proximity switching, positioning, speed detection
Timing wheels shafts for internal combustion engine
They are used brushless DC electric motor for permanat
magnet positioning
ADVANTAGES:
Low cost
High frequency operation
Robust and working in all environment

34. EDDY CURRENT SENSOR
It detects the presence of targets by sensing the
magnetic fields
Sensor detects Ferrous and non ferrous materials
It measures position or displacements
The magnetic field is produced ,At the time
Sense the reference coil creates the output signal

36. Applications
POSITION MEASUREMENT:
It represents the size of the distance between
Transducer and conductor
Monitoring or sensing the precise location in machine
tool
VIBRATION MOTION MEASURENENT:
It is suitable for finding alternate positionsin vibrating
conductor
For non contact eddy current transducer is highly
recommended.

37. ADVANTAGES
Compact In size
Cost is low
Reliability is high
High frequency response
DISADVANTAGE
Gap between transducer and conductor is small
Non conductive material is not finding the position

38. Temperature sensors
Bimetallic strips
Resistance temperature detectors (RTDs)
Thermistors
Thermocouples
Thermodiodes and transistors

39. Bimetallic strips

40. These are widely used in industry for temperature
control
They usedbecause robustness, simplicity, range etc
Two dissimilar metals are bonded together and
fixed at one end
It converts the temperature in to mechanical
displacement
Working:
One strip is bend at the time of temperature
changes
Mostly used bimatallicstrips are expansion
alloys such as steel and invar and copper

41. Advantages:
Power source not required
Cost is low
Robust construction
It used up to 500 c
DISADVANTAGES:
less accuruate
limited applications such as house hold
thermometer
Suitable for very low temperature areas

42. Resistance temperature
detectors (RTDs)

43. Metal wire is heated at the time resistance increases
RTD’s is similar to electrical transducers
Changes the temperature to voltage by the measurement
resistance
RTD’s is normally of platinum, copper, nickel iron alloy
CONSTRUCTION:
RTD s is spring like wires are surrounded by insulator
Insulator is PROCELIAN INSULATOR
When it is placed in liquid or gas medium incoelquickel
reaches the medium.

44. ADV:
Measuring high temperatures
High accuracy
Good stability and repeatibility
Dis Adv:
Size is more than a thermocouple
Power supply is required
Resistance element is more expensive

45. THERMISTERS
Thermister= thermal + resistor
Thermisterare non linear device
With increase in temperature decrease in resistance
faster than RTD’s
Thermisteris small and made up of metal oxides such
as chromium, nickel ,manganese ,cobalt.
WORKING:
metals are oxides through a chemical reaction
then compressed and subjected to very high heat.

46. Thermistors
Bead typehave platinum wire sintered in to a ceramic body
(bead)
Metalized surfacecontact thermistors are called chips or
flakes

47. Resistance with increase in temperature is called
positive temperature coefficient
Resistance with decrease in temperature is called
negative temperature coefficient
ADV:
MORE ACCURUATE
Manufacture almost any shape and size
Good stabiltyand repetability
DISADV:
Limited measuring range
Self heating is occur
Power supply required

48. Thermocouple

49. It is the device which converts thermal energy in to
electrical energy
Works on seeback effect.
Two dissimilar metals A and B are used, close loop with
two different temperatures T1 and T2 , emf is
produced.
CONSTRUCTION:
Thermocouple in rigid matal sheath
Measuring junction is normally bottomof the
thermocouple
Magnesium oxide prevents vibration in wires and
enhance measuring
Heating junction voltage is always higher than the
reference junction

50. THERMODIODES AND TRANSISTORS
THERMODIODES:
Temperature measuring instrument
Mobility of semiconductor diode will change in
temperature changes
In temperature changes voltage and current changes.

51. THERMO TRANSISTOR
TEMPERATURE SENSES Base to emitter voltage drop of
transister.
Transistercan be used as temperature sensor
Temperature range as -50 to 150 degree celcius
ADVANTAGES:
LINEAR OUTPUT
IN EXPENSIVE
HIGHEST OUTPUT
COMPACT IN SIZE.
DISADVANTAGES:
SLOW OUTPUT, SELF HEATING.

52. LIGHT SENSORS
Light sensor converts radiant power.
Light absorbs they changes in resistance, current or
voltage
Digitalization takes place (analog to digital)

53. Light sensors
Photo resistors
Photodiode
phototransistors

54. PHOTODIODE
Rate of generation of electrons,
Absorbtion of electrons results in free charge
Electrical conductivity also increased
P-N junction fabricated the semi conductor material
From the diagram bottom Doped with N-type silicon
Upper side doped with P-type silicon
P-N junction region created
Radiation passed ELECTRON HOLE Pair is generated
then neutrailized

55. Photodiode

56. PHOTO TRANSISTERS
Light sensitivity collector based P-N junction diode
When the light rays passes to the circuit.
The light can be converted in to current
Current can be converted in to voltage
It is the reverse process of light from voltage

57. Phototransistors
Phototransistor light detector circuit

58. PHOTORESISTER
It consists of semi conductor material faces of
electrodes.
Cadmium Sulphate used as a detector
Other photo conductive material Lead sulphite,
mercury cadmium tellurite.
It increase in light sensitivity Photo resistor
decrease the output.
It decrease in light sensitivity Photo resistor
increase the output.

60. Photoelectric sensor
It is a device used to detect the Distance, absence or
presence of object
Using light transmitter, often INFRARED or LED
All the objects are sensed by these sensor like small,
large, transparent, shiny, static, motion
Distance = few mm to 100 m
Light is detected by a receiver

61. Photoelectric sensor
Through beam method
Retro reflective method

62. Selection of sensors
Accuracy required
Precision
Sensitivity
Operating range
Resolution
Speed range
Reliability
Calibration
The nature of output
Linearity
Environmental
conditions
Interfacing
Size and weight