Unit I - Mechatronics.pptx presentation

Mechatronics

1. ME8791 MECHATRONICS

2. 2 Objective To impart knowledge about the elements and techniques involved in Mechatronics systems which are very much essential to understand the emerging field of automation.

3. 3 Course Outcomes Cos Course Outcome CO 1 Integrate mechanical, electronics, control and computer engineering in the design of mechatronics system. CO 2 Select and apply various sensor for mechatronics system based on the requirements CO 3 Illustrate the different types of microprocessor instructions with suitable programs CO 4 Demonstrate the interfacing of various peripheral devices with the microprocessor CO 5 Design, build, interface and actuate various systems using programmable logic controller. CO 6 Construct and analyze mechatronics systems with suitable actuators.

4. 4 Syllabus Introduction to Mechatronics – Systems – Concepts of Mechatronics approach – Need for Mechatronics – Emerging areas of Mechatronics – Classification of Mechatronics. Sensors and Transducers: Static and dynamic Characteristics of Sensor, Potentiometers – LVDT – Capacitance sensors – Strain gauges – Eddy current sensor – Hall effect sensor – Temperature sensors – Light sensors Unit I - INTRODUCTION 9 Introduction – Architecture of 8085 – Pin Configuration – Addressing Modes –Instruction set - Timing diagram of 8085 – Concepts of 8051 microcontroller – Block diagram Unit II - MICROPROCESSOR AND MICROCONTROLLER 9

5. 5 Syllabus Introduction – Architecture of 8255, Keyboard interfacing, LED display –interfacing, ADC and DAC interface, Temperature Control – Stepper Motor Control – Traffic Control interface. Unit III - PROGRAMMABLE PERIPHERAL INTERFACE 9 Introduction – Basic structure – Input and output processing – Programming – Mnemonics – Timers, counters and internal relays – Data handling – Selection of PLC. Unit IV - PROGRAMMABLE LOGIC CONTROLLER 9

6. 6 Syllabus Types of Stepper and Servo motors – Construction – Working Principle – Advantages and Disadvantages. Design process-stages of design process – Traditional and Mechatronics design concepts – Case studies of Mechatronics systems – Pick and place Robot – Engine Management system – Automatic car park barrier. Unit V - ACTUATORS AND MECHATRONIC SYSTEM DESIGN 9

7. 7 Text books & References Bolton, “Mechatronics”, Prentice Hall, 2008 Ramesh S Gaonkar , “Microprocessor Architecture, Programming, and Applications with the 8085”, 5th Edition, Prentice Hall, 2008. TEXT BOOKS Bradley D.A, Dawson D, Buru N.C and Loader A.J, “Mechatronics”, Chapman and Hall, 1993. Clarence W, de Silva, "Mechatronics" CRC Press, First Indian Re-print, 2013 Devadas Shetty and Richard A. Kolk, “Mechatronics Systems Design”, PWS publishing company, 2007. Krishna Kant, “Microprocessors & Microcontrollers”, Prentice Hall of India, 2007. Michael B.Histand and Davis G.Alciatore , “Introduction to Mechatronics and Measurement systems”, McGraw Hill International edition, 2007. REFERENCES

8. 8 What is Mechatronics? It is a Japanese Concept in 1970’s It can be defined as the application of electronics and computer technology to control the motions of mechanical systems Mecha nisms Elec tronics Mechatronics It is a multidisciplinary approach to product and manufacturing system design

9. 9 Definition Synergistic integration of mechanical engineering, electronics and intelligent computer control in design and manufacture of products and processes

10. 10 Applications of Mechatronics Consumer products – Home appliances, Consumer electronics Manufacturing – CNC machines, Flexible Manufacturing system, etc. Material handling – Conveyors, AGVs, RGVs, etc. Automotive – All automobiles Aerospace – Aircraft and space crafts Medical – Pharmaceutical Industry, X-ray, Scans, Pace maker etc. Defence system – Radars, defence vehicles, etc. Robotics – Material handling robots, welding robots etc. Now a day in all places around us Mechatronics systems are present

11. 11 Consumer products Refrigerator Washing machine Microwave Oven Mobile Phones Laptops Cameras Projectors Coffee Makers Watches

12. 12 Manufacturing Hand Power tools Gear House Machining CNC Machine

13. 13 Manufacturing Desktop sized Factory Build small parts with a small factory Greatly reduces space, energy, and materials Micro Factory Micro Factory Drilling Unit

14. 14 Material handling Conveyors AGV RGV

15. 15 Automotive Speedometers Automated Car Manufacturing Industries Engine Management System

16. 16 Automotive Typical Applications Brake-By-Wire system Steer-By-Wire Integrated vehicle dynamics Camless engines Integrated starter alternator Advantages Reliability Reduced weight Fuel economy Manufacturing flexibility Design freedom Advanced safety features Cost

17. 17 High Speed Trains Train Position and Velocity constantly monitored from main command center. Error margin in scheduling no more than 30 seconds Fastest trains use magnetic levitation JR-Maglev Top Speed: 574 km/h (357 mph) Country: Japan Transrapid Top Speed: 550 km/h (340 mph) Country: German Magnetic Levitation

18. 18 Aerospace Space Craft, space station, satellites Unmanned Vehicles Surveillance Aircraft Passenger or Cargo Planes Advanced technology is making our soldiers safer. Some planes can now be flown remotely.

19. 19 Space Exploration System Can Collect specimens Has automated onboard lab for testing specimens Advantages Robot that can travel to other planets and take measurements automatically . Phoenix Mars Lander's

20. 20 Medical X-ray Computerized tomography (CT) scan Pace maker Used by patients with slow or erratic heart rates. The pacemaker will set a normal heart rate when it sees an irregular heart rhythm. Monitors the heart. If heart fibrillates or stops completely it will shock the heart at high voltage to restore a normal heart rhythm.

21. 21 Medical Prosthetics Arms, Legs, and other body parts can be replaced with electromechanical ones.

22. 22 Defence system Unmanned Defence system Radar defence communication Stealth Bomber

23. 23 Robotics Industrial robots Medical robots

24. 24 Robotics System Can Carry 340 lb Run 4 mph Climb, run, and walk Move over rough terrain BigDog Advantages Robot with rough-terrain mobility that could carry equipment to remote location.

25. 25 Robotics Robots can vacuum floors and clean gutters so you don't have to. Cleans Gutter Vacuum Floors

26. 26 Sanitation Applications System Uses Proximity sensors Control circuitry Electromechanical valves Independent power source Advantages Reduces spread of germs by making device hands free Reduces wasted water by automatically turning off when not in use

27. 27 Sanitation Applications Advantages Reduces spread of germs by making device hands free Reduces wasted materials by controlling how much is dispensed Systems Uses Motion sensors Control circuitry Electromechanical actuators Independent power source Soap Dispenser Paper Towel Dispenser

28. 28 Sanitation Applications Advantages Reduces spread of germs by making device hands free Reduces wasted materials by controlling how much is dispensed Systems Uses Motion sensors Control circuitry Electromechanical actuators Independent power source Soap Dispenser Paper Towel Dispenser

29. 29 Sports Applications Advantages Automatically changes cushioning in shoe for different running styles and conditions for improved comfort Running Shoes

30. 30 Systems Brings together areas of technology Sensors and measurement systems Drive and actuation systems Analysis of behavior of systems Control systems Microprocessor systems Involves systems A system is a group of interacting or interrelated entities that form a unified whole. System Input Output

31. 31 Measurement Systems Three elements Sensor : responds to quantity being measured by giving as its o/p a signal related to the quantity Signal conditioner : Takes signal and manipulates to make it suitable for display or for control Display : maybe a pointer moving across a scale or digital readout

32. 32 Measurement System Example Example: Digital Thermometer Sensor: Semiconductor diode, Potential difference across is a measure of temperature (@ constant current) Signal Conditioner : Amplifier Sensor & Output amplifier maybe incorporated on same silicon chip

33. 33 Measurement System Example Pressure gauge

34. 34 Control System Example: Body Temperature control system – sweat & shiver Room temperature control system Feedback control: comparing the feedback actual o/p with what is required and the o/p is adjusted accordingly

35. 35 Open & Closed loop system Open-loop: Output has no effect on input signal Closed-loop: Output modifies input to maintain an output

36. 36 Open loop vs Closed loop system Advantages: Simplicity and stability : they are simpler in their layout and hence are economical and stable too due to their simplicity. Construction : Since these are having a simple layout so are easier to construct. Advantages: Accuracy : They are more accurate than open loop system due to their complex construction. They are equally accurate and are not disturbed in the presence of non-linearities. Noise reduction ability : Since they are composed of a feedback mechanism, so they clear out the errors between input and output signals, and hence remain unaffected to the external noise sources.

37. 37 Open loop vs Closed loop system Disadvantages: Accuracy and Reliability: since these systems do not have a feedback mechanism, so they are very inaccurate in terms of result output and hence they are unreliable too. Due to the absence of a feedback mechanism, they are unable to remove the disturbances occurring from external sources. Disadvantages: Construction: They are relatively more complex in construction and hence it adds up to the cost making it costlier than open loop system. Since it consists of feedback loop, it may create oscillatory response of the system and it also reduces the overall gain of the system. Stability: It is less stable than open loop system but this disadvantage can be strike off since we can make the sensitivity of the system very small so as to make the system as stable as possible.

38. 38 Basic elements of closed-loop systems Comparison element Control element Correction element Process element Measurement element

39. 39 Basic elements of closed-loop systems Comparison element: Error signal = reference value signal - measured value signal Negative FB: signal feedback subtracts from input value Positive FB: occurs when signal feedback adds to input signal Control element: Decides what action to take when it receives an error. Ex.: operate a switch or open a valve Hard-wired control plan: Control plan is permanently fixed by way of elements connected together Programmable Control plan: stored within a memory unit and altered by reprogramming

40. 40 Correction element: Produces change in process to correct/change; switch on a heater or open a valve; actuator-provides power to carry out control action Process element: What is being controlled, room (temp) or tank (water level) Measurement element: Produces signal related to variable condition of process being controlled; thermocouple gives an emf related to temp Basic elements of closed-loop systems

41. 41 Closed-loop systems (Example) Room heating system

42. 42 Automatic control of water level Closed-loop systems (Example)

43. 43 Closed-loop systems (Example) Shaft speed control

44. 44 Key elements of Mechatronics system

45. 45 Sequential controllers Control actions are strictly ordered in a time or event driven sequence In electrical circuit sets of relays or cam-operated switches are wired up to give the required sequence Hard-wired circuits are replaced by Microprocessor ( μ p) controlled system ; sequencing by programming. Domestic washing machine: Pre-wash cycle: cloth in drum are given wash in cold water Main wash cycle: washed in hot water Rinse cycle: cloths rinsed with cold water many times Spinning: removes water Pre-wash - opening a valve to fill water in drum to required level -> closing valve -> switching on drum motor to rotate drum for specific time -> operate pump to empty water This operating sequence is called ‘program’; contains predefined instructions built into the controller

46. 46 Sequential controllers Automatic Washing Machine Cam operated switch

47. 47 Microprocessor- based controllers Essentially a collection of logic gates and memory elements , not wired up as individual components, whose logical functions are implemented by software rapidly replacing mechanical cam operated controllers and used generally to carry out control functions Greater variety of programs are feasible Most simple systems has embedded microcontroller µp with memory integrated on one chip Specifically programmed for task concerned A more adaptable form is PLC Readily programmed for different tasks µP based controller using programmable memory to store instructions and implement functions like logic, sequence, timing count, arithmetic to control events

48. 48 Automatic camera Program: each step is a simple decision Decision: logic decision with i /p & o/p signals either being low or high to give on-off states Shutter control mode & Aperture control mode Program form Begin if battery check input OK Then continue otherwise stop Loop Read input from range sensor Calculate lens movement Output signals to lens position drive Input data from lens position encoder Compare calculated output with actual output …

49. 49 Engine management system EMS: responsible for ignition and fuel requirements Power and speed controlled by ignition timing and AF mix

50. 50 Emerging/Emerged Areas of Mechatronics Automatic Engineering Engine Management System Anti-lock Braking Systems Automatic Control Lock System, etc. Consumer products. Automated washing machine Digital Camera Air-conditioning System Medical Mechatronics Pacemaker Endoscopy Medical Imaging Implantable devices Robotic Surgical Devices. Aerospace Industries Advanced Manufacturing System. CNC Machines Tool Monitoring System Flexible Manufacturing System (FMS). Industrial Robots. Automatic Packaging System. Machine Vision Automation and Robotics Sensing and control systems

51. 51 Classification of Mechatronics Conventional Mechatronic Systems Micro Electro Mechanical Systems (MEMS) Nano Electro Mechanical Systems (NEMS) Conventional Mechatronics System Bulky Mechanical System is replaced by compact, adjustable, easily controllable system to do the same process with more efficiency . Eg . Domestic washing machine uses cam operated switches in order to control the washing cycle. Such switches are replaced by microprocessors. The microprocessor controlled washing machine may be called as conventional Mechatronics system. Mechanical system has been integrated with electronic controls.

52. 52 Classification of Mechatronics Micro – Electro Mechanical Systems (MEMS) It’s a process technology used to created integrated devices or systems that combine mechanical and electrical components. Fabricated using integrated Circuit (IC) batch processing techniques. It can range in size from micro meter to millimeter. This device has ability to sense, control and actuate in micro scale, and generate effects on the macroscale . MEMS consist of micro sensors, mechanical microstructures, micro actuators and micro electronics, all integrated onto the same silicon chip.

53. 53 Classification of Mechatronics Micro – Electro Mechanical Systems (MEMS) Example Sensors to measure IOP (Intraocular Pressure) to monitor glaucoma disease, which may lead to permanent blindness. A normal eye maintains a positive IOP in the range of 10-22 mmHg. Abnormal elevation (> 22 mmHg) and fluctuation of IOP are considered the main risk factors for glaucoma. MEMS IOP sensor It consists of a disposable contact lens with a MEMS strain-gage pressure sensor element , an embedded loop antenna (golden rings), and an Application Specific Integrated Chip (ASIC) microprocessor (2mmx2mm chip). The MEMS sensor includes a circular active outer ring and passive strain gages to measure corneal curvature changes in response to IOP. The loop antenna in the lens receives power from the external monitoring system and sends information back to the system

54. 54 Classification of Mechatronics Nano – Electro Mechanical Systems (NEMS) Electro Mechanical devices that have critical dimensions from hundreds to few nanometers. NEMS presents interesting and unique characteristics, which deviate from its predecessor MEMS. Fabricated by Micro Machining Process. NEMS based devices have fundamental frequencies in microwave range (~100 GHz) Mechanical Quality factors in the tens of thousands. Low energy dissipation. Active mass in the femtogram range. Force sensitivity at the attonewton range. Mass sensitivity in the range of attogram and sub attogram level. Power consumption in the order of 10 attowatts . Extremely high integration level, approaching 1012 elements/ square centimeter. These unique properties of NEMS devices pave the way to application such as force sensors, chemical sensors, biological sensors and ultra high-frequency resonators.

55. 55 Classification of Mechatronics Nano – Electro Mechanical Systems (NEMS)

56. 56 Sensors and Transducers

57. 57 Static Characteristics of the Sensors The static characteristics are the term used to define the performance of transducers. Static characteristics are the values given when steady – state condition occurs. (i.e.) Output given for steady input. Range Span Error Accuracy Precision Sensitivity Hysteresis error Nonlinearity error Repeatability/reproducibility Stability Dead band/time Drift Resolution Output impedance

58. 58 Static Characteristics of the Sensors Range: It is the minimum and maximum value of physical variable that the sensor can sense or measure. For example, a Resistance Temperature Detector (RTD) for the measurement of temperature has a range of -200 to 800 o C. 2. Span: It is the difference between the maximum and minimum values of input. In above example, the span of RTD is 800 – (-200) = 1000 o C

59. 59 Static Characteristics of the Sensors 3. Error It is defined as the difference between measured value and true value. It is defined in terms of % of full scale or % of reading.

60. 60 Static Characteristics of the Sensors 4. Accuracy: It extent to which value indicated is close to measured value of a standard or known value. Example: The accuracy to which transducer has been calibrated was ±2 o C 5. Precision: Refers to Closeness of two or more reading per measurements.

61. 61 Static Characteristics of the Sensors 6. Sensitivity: It indicates how much output is attained per unit input. It is the ratio of change in output to change in input. Example: resistance thermometer: 0.5Ω/ ℃ Also indicates sensitivity to input other than being measured Ex: pressure sensor with temperature sensitivity of ± 0.1% of the reading per ℃

62. 62 Static Characteristics of the Sensors 7. Hysteresis: It is the difference in output when input is varied in two ways- increasing and decreasing.

63. 63 Static Characteristics of the Sensors 8. Nonlinearity error: Generally linear relation is assumed bet i /p & o/p, over working range; max difference from straight line and the actual value is known as normality error. Methods to determine nonlinearity error. End angle values Best straight line for all values Best straight line from zero point Eg. Transducer for the measurement of temperature might be quoted as having a non – linearity error of 0.25% of the full range

64. 64 Static Characteristics of the Sensors 9. Repeatability/reproducibility: Ability to give same output for repeated applications of same input values = {[max-min value]/full range} x 100 Angular velocity transducer ±0.001% of full range at particular angular velocity 10. Stability: Ability to give same output while measuring constant input over a period of time Drift: change in o/p that occurs over time Expressed as % of full range o/p Zero drift: change in o/p when there is no i /p

65. 65 Static Characteristics of the Sensors 11. Dead band/time: Range of input values for which there is no output Bearing friction in flow meter using rotor: no output until velocity threshold Pyrometer in a furnace gives no output until the input has reached a particular temperature. 12. Drift : Change in output that occurs over time. It is expressed in percentage of the full range output.

66. 66 Static Characteristics of the Sensors 13. Resolution: Smallest change in the input value that produces an observable change in the output. Ex: wire-wound potentiometer, 0.5° or % of full range output Digital output: smallest change is 1 bit. For data word of N bits i.e. a total of 2N bits, resolution is 1/2N 14. Output impedance: Needed for sensors giving electrical output interfaced with electronic circuit; series or parallel. Impedance is resistance offered in the AC circuit.

67. 67 Dynamic Characteristics of the Sensors 1. Response time: Time elapsed, after step i /p is applied, upto a point at which the transducers gives an output corresponding to some specified percentage.

68. 68 Dynamic Characteristics of the Sensors 2. Time constant: Measure of Inertia of the sensor; how fast it will react to the changes in output. 63.2% of response time; bigger TC slower the reaction of the sensor. 3. Rise time: Time taken for output to rise to some specified % of steady-state output; often refers to time taken to rise from 10% to 90 or 95% of the steady-state value 4 . Settling time: Time taken for output to settle to steady-state value

69. 69 Displacement, Position & Proximity sensor Displacement sensors Measurement of the distance moved by the object Position sensors Determination of position of the object with respect to some reference point Proximity sensors Form of position sensor and used to determine when an object moves with in a particular distance of the sensor Factors to be considered for the selection of these sensors: Size of the displacement Displacement is linear or angular The resolution required Accuracy required Object material (Ferrous or Non-ferrous) Cost

70. 70 Displacement, Position & Proximity sensor Displacement and Position sensors Non-contact type Contact type Proximity sensor Non-contact type Have physical mechanical contact It consist of a sensing shaft The displacement of the shaft is monitored by the sensor Shaft movement converted into voltage, resistance, capacitance or mutual inductance Involves in the presence of vicinity of the measured object It causes change in pressure or electrical capacitance or inductance

71. 71 List of sensors and transducers (Given in syllabus) Potentiometers Linear Rotary LVDT - Linear Variable Differential Transformer Capacitance sensors Strain gauges Eddy current sensor Hall effect sensor Temperature sensors Light sensors

72. 72 Potentiometers A potentiometer consist of resistance element with a sliding contact which can moved over the length of the element. Used for linear and rotary displacement It converts displacement into potential difference Linear Potentiometer Rotary Potentiometer

73. 73 Potentiometers Input voltage ( V S )→ Between terminal 1&3 Output voltage ( V out )→ Between terminal 2&3 V out is the fraction of V S Fraction depends on the resistance between terminal 2 & 3   If resistance track has constant resistance per unit length then output is proportional to the linear displacement If resistance track has constant resistance per unit angle then output is proportional to the angular displacement

74. 74 Potentiometers If resistance track is made up of conductive plastic Ideally infinite resolution Non-linearity error: 0.05% Resistance: 500 Ω to 80 kΩ If potentiometer has N turns, Resolution = 100/N . This is limited by the wire diameter: 1.5 to 0.5 mm Track resistance range: 20 Ω to 200 k Ω Non-linearity error: < 0.15 to 1% If load resistance is infinite, V L α V out R L and xR P are parallel to each other  

75. 75 Potentiometers R P (1- x ) and combined resistance (R L & x R P ) are in series Total resistance across the source voltage V S Total resistance = If the load is of infinite resistance V L = x V S Error = x V S – V L = x V S - Error =  

76. 76 Potentiometers Advantages They are cheap. It is easy to use. It gives sufficient output that does not require further amplification. Potentiometer efficiency is high. They are useful for the measurement of large displacement. The resolution is infinite in cermet and metal film potentiometers. Disadvantages The major disadvantage is that it requires a large force to move their sliding contacts. There is wear and tear due to movement of the wiper. It reduces the life of this transducer. Applications of Potentiometer It is used in many applications such as Linear displacement measurement Liquid level measurements using floats Rotary displacement measurement Volume control

77. 77 LVDT (Linear Variable Differential Transformer) This is an inductive type position sensor works on the same principle as the AC transformer used to measure movement It is a very accurate device for measuring linear displacement output is proportional to the position of its moveable core .

78. Dr. M. Madhan, M.E., Ph.D., Asst. Prof., Mechanical Engineering 78 LVDT (Linear Variable Differential Transformer) Consists of 3 coils (1 primary & 2 secondary) spaced symmetrically placed along insulated tube; Identical secondary coils are connected in series . Therefore their output oppose each other Magnetic core moved through central tube AC voltage input to primary → equal alternating EMF is induced in secondary coils → net result zero output When core is displaced from central position → greater amount of magnetic core in one coil → greater EMF → results in net o/p

79. Dr. M. Madhan, M.E., Ph.D., Asst. Prof., Mechanical Engineering 79 LVDT (Linear Variable Differential Transformer) EMF is induced in the secondary coil by changing the input current ( i ) in the primary coil M = mutual inductance M depends and number of turns in the coil and ferromagnetic core For a sinusoidal current Output voltage in Secondary coil 1, Secondary coil 2, , and depends on coupling between primary and secondary coil based on core position is the phase difference between primary and secondary alternating voltage Output voltage = - Output voltage =  

80. Dr. M. Madhan, M.E., Ph.D., Asst. Prof., Mechanical Engineering 80 LVDT (Linear Variable Differential Transformer) When core is at the middle , Output voltage V = 0 When core is more in secondary coil 1 than in coil 2 , Output voltage V = When core is more in secondary coil 2 than in coil 1 , Output voltage V =   LVDT Output

81. Dr. M. Madhan, M.E., Ph.D., Asst. Prof., Mechanical Engineering 81 LVDT (Linear Variable Differential Transformer) LVDT DC Output Phase sensitive demodulator with low-pass filter to convert AC output voltage into a DC voltage giving unique value Typical range: ±2 mm to ±400 mm Non-linearity errors: ±0.25 % Used as: Primary transducer: monitor displacement; spring loaded or threaded for mechanical contact Secondary transducer: measure force, weight & pressure by transforming them to displacement

82. Dr. M. Madhan, M.E., Ph.D., Asst. Prof., Mechanical Engineering 82 LVDT (Linear Variable Differential Transformer) Advantages high measurement range which is from 1.25 mm to 250 mm. low power consumption which is less than about 1 Watt. frictionless device. high resolution which is greater than 10 mm. Higher sensitivity of greater than 40 V/mm can be achieved. smaller in size. less in weight. lower hysteresis. solid and robust in construction. Hence it is tolerant to shocks and vibrations. excellent repeatability. very low output impedance.

83. Dr. M. Madhan, M.E., Ph.D., Asst. Prof., Mechanical Engineering 83 LVDT (Linear Variable Differential Transformer) Disadvantages Large displacement is needed for small output. It is affected due to external magnetic field and hence the entire LVDT circuit need to be shielded to achieve desired accuracy. Vibrations due to displacement can affect the performance of the LVDT device. The performance of LVDT is affected due to increase in temperature. In order to get DC output, external demodulator is required. It has limited dynamic response.

84. Dr. M. Madhan, M.E., Ph.D., Asst. Prof., Mechanical Engineering 84 RVDT (Rotary Variable Differential Transformer)

85. Dr. M. Madhan, M.E., Ph.D., Asst. Prof., Mechanical Engineering 85 Capacitive element Capacitance the ability of a system to store an electric charge . the ratio of the change in an electric charge in a system to the corresponding change in its electric potential. Capacitance C of a parallel plate capacitor ε r : Relative permittivity of dielectric ε : Permittivity of free space A : Area of overlap bet two plates d : Plate separation  

86. Dr. M. Madhan, M.E., Ph.D., Asst. Prof., Mechanical Engineering 86 Capacitive element Three forms of capacitance sensor to measure displacement displacement of one plate with respect to other, so the plate separation changes displacement causes change in overlap are a displacement causes change in position of dielectric medium For displacement causes the increase in plate separation distance from d to (d + x ) Non-linearity between and the displacement x. It is rectified by push-pull sensor .  

87. Dr. M. Madhan, M.E., Ph.D., Asst. Prof., Mechanical Engineering 87 Capacitive element (Push-pull sensor)     Consist of 3 plates Upper and lower plates are fixed Displacement moves the center plate It forms 2 capacitance element 2 capacitance act as 2 arms of AC bridge Initially, the 2 arms are balanced When there is a displacement in center plate, it result in out-of-balance voltage Out-of-balance voltage is proportional to displacement, x

88. Dr. M. Madhan, M.E., Ph.D., Asst. Prof., Mechanical Engineering 88 Capacitive element Capacitive proximity sensor Used for monitoring from few mm to few hundreds of mm; Non-linearity & hysteresis are about ±0.01% of full range Capacitance proximity sensor Consist of single plate capacitance element Another plate formed by the surface of the object When object approaches the probe, plate separation varies Capacitance changes and the presence of object is observed Used to detect only metallic or earthed material .

89. Dr. M. Madhan, M.E., Ph.D., Asst. Prof., Mechanical Engineering 89 Capacitive element Advantages Used to detect non-metallic targets. simple in construction and adjustable. detect dense targets and liquids. lower in cost. higher sensitivity and can be operational with small magnitude of force. used for the measurement of force, pressure and humidity etc. very good resolution (as low as 0.003 mm) and frequency response. Disadvantages It is very much sensitive to changes in environmental conditions such as temperature, humidity etc. This will affect the performance. The measurement of capacitance is hard compare to measurement of resistance. Capacitive proximity sensor are not so accurate compare to inductive sensor type.

90. Dr. M. Madhan, M.E., Ph.D., Asst. Prof., Mechanical Engineering 90 Strain gauges Electrical resistance strain gauge is wafer-like strip (a) metal wire (b) metal foil (c) semiconductor material stuck on surfaces like postage stamp When subjected to strain, resistance in the strain element changes Change in resistance is proportional to strain G = Proportionality constant = Gauge factor  

91. Dr. M. Madhan, M.E., Ph.D., Asst. Prof., Mechanical Engineering 91 Strain gauges G = 2 for metal and metal foil G = +100 for p-type semiconductor G = -100 for n-type semiconductor Gauge factor is usually supplied by the manufacturer resistance changes not only with strain but also temperature Semiconductor SG have greater sensitivity to temperature Problem An electrical strain gauge with 100 ohm resistance has a gauge factor of 2.0. What is the change in resistance when subjected to strain of 0.001? ΔR = Gε x R ΔR = 2x0.001x100 Δ R= 0.2 ohm

92. Dr. M. Madhan, M.E., Ph.D., Asst. Prof., Mechanical Engineering 92 Strain gauges Forms: cantilever, rings or U-shaped flexible elements Used for displacements of 1-30 mm and have non-linearity error of ±1% of full range Cantilever Rings U-shaped

93. Dr. M. Madhan, M.E., Ph.D., Asst. Prof., Mechanical Engineering 93 Strain gauges Advantages of metal strain gauges Inexpensive Small Temperature dependence is less Very sensitive For vibrational sensing and load sensing Disadvantages of metal strain gauges Susceptible to creep error. Since they are highly sensitive and directly bonded to the specimen, over time due to wear of the adhesive will reduce its accuracy. Disadvantages of Semiconductor Strain gauges Temperature sensitive (Semiconductors are highly sensitive to small variation in temperatures) Non linear output. Advantages of semiconductor strain gauges Most sensitive Very cheap Strong output signal (high GF) No creep (no bonding) High pressure range

94. Dr. M. Madhan, M.E., Ph.D., Asst. Prof., Mechanical Engineering 94 Eddy current sensor A coil supplied with AC, alternating magnetic field is produced Eddy current is induced in a metal object in close proximity to this field This eddy current produces a magnetic field which distorts the magnetic field responsible for their production impedance of coil changes and so the amplitude of AC which is used to trigger a switch Used for the detection of non-magnetic but conductive materials Adv: relatively inexpensive, small in size, high reliability and high sensitivity

95. Dr. M. Madhan, M.E., Ph.D., Asst. Prof., Mechanical Engineering 95 Hall effect sensor When a beam of charged particles passes through a magnetic field, forces acts on the particle and the beam is deflected from its straight line path Current flowing in a conductor is a beam of charged particles It can be deflected by the magnetic field This effect is called Hall effect Discovered by E.R.Hall in 1879

96. Dr. M. Madhan, M.E., Ph.D., Asst. Prof., Mechanical Engineering 96 Hall effect sensor Consider electron moving in a conductive plate A magnetic field is applied at right angles to the flow of electrons. Due to hall effect, the electrons are deflected to the one side of the plate and that side become negatively charged and the other side become positively charged This charge separation produces the electric field in the material The charge separation continues until the force due to charge separation electric field balances the force produced by the magnetic field. It results in transverse potential difference  

97. Dr. M. Madhan, M.E., Ph.D., Asst. Prof., Mechanical Engineering 97 Hall effect sensor K H - constant called Hall coefficient B - Magnetic flux density I - Current t - Plate thickness Hall effect sensors are supplied as integrated chips along with signal processing circuitry Two basic forms: Linear: Output vary linearly with Magnetic flux density Threshold: Output shows sharp drop at particular magnetic flux density HES 634SS2 : liner output; range -40 to + 40 mT @ 10 mV/ mT with supply voltage 5 V Allegro UGN3132U : 0-145 mV @ 3 mT (milli Tesla) Linear Threshold

98. Dr. M. Madhan, M.E., Ph.D., Asst. Prof., Mechanical Engineering 98 Hall effect sensor Advantages Operate as switches at 100 kHz Cost less than electromechanical switches No contact bounce Immune to environmental contaminants, so used in severe service conditions Used as displacement, position and proximity sensors when object is fixed with a small permanent magnet Applications Water level sensor Brushless DC motor: alignment of windings with permanent magnet rotor Fluid level indicator

99. Dr. M. Madhan, M.E., Ph.D., Asst. Prof., Mechanical Engineering 99 Temperature sensors Temperature sensors measures and monitors the temperature changes that is generated by object or system. Temperature will be sensed and displayed as analog or digital output . Temperature is sensed either by Expansion or contraction of solids, liquids or gas Changes in electrical resistance of the conductors and semiconductors Thermoelectric emf The commonly used temperature sensors listed below Bimetallic strips Resistance temperature detectors Thermistors Thermo diodes Thermo transistors Thermocouples

100. Dr. M. Madhan, M.E., Ph.D., Asst. Prof., Mechanical Engineering 100 Bimetallic strips Mechanical element that senses temperature and convert it into mechanical displacement. This mechanism can be used to actuate a switching mechanism in order to get electronic output. Bimetallic strip measures temperature and gives output as mechanical displacement of electrical output. It is made by joining two different metals that have different coefficient of thermal expansion . The techniques used to bind two layers of different metals are riveting, bolting and fastening.

101. Dr. M. Madhan, M.E., Ph.D., Asst. Prof., Mechanical Engineering 101 Bimetallic strips Working Principle It works on two principle. When change in temperature takes place, Expansion or contraction occurs in metals. The rate of expansion or contraction depends on temperature, coefficient of expansion of the metal. Temp coefficient different for different metals. Difference in thermal expansion rates is used to produce defections and these deflections are proportional to temperature changes.

102. Dr. M. Madhan, M.E., Ph.D., Asst. Prof., Mechanical Engineering 102 Bimetallic strips Bimetallic strip thermostat Two dissimilar metals behave in a different manner when exposed to temperature variations due to different thermal expansion rates. One layer of the metal expands/ contracts more than the other metal layer, due to which bending or curvature change in strip occurs. This deformation may be used a temperature controlled switch. Eg. Simple thermostat, commonly used for domestic heating system In this magnet is used for hysteresis, to close and open the witch at different temperatures.

103. Dr. M. Madhan, M.E., Ph.D., Asst. Prof., Mechanical Engineering 103 Bimetallic strips Types of bimetallic strips Cantilever type Spiral Helix U shape Features of Bimetallic Thermometer. It works best at higher temperatures. Their sensitivity and accuracy is less at low temperatures. Various forms of bimetallic strips are available. Bimetallic strips are usually coiled to make them compact. Bimetallic strips can be scaled up or down.

104. Dr. M. Madhan, M.E., Ph.D., Asst. Prof., Mechanical Engineering 104 Bimetallic strips Types of bimetallic strips

105. Dr. M. Madhan, M.E., Ph.D., Asst. Prof., Mechanical Engineering 105 Bimetallic strips Applications: Used in house hold applications such as ovens. Thermostat switches. Circuit breakers for electrical devices. Used to control system based on temperature. Advantages: Power source not required. Robust, easy to use and cheap. Disadvantages Not very accurate. Limited to applications where manual reading is acceptable. Not suitable to low temperatures, since expansion of metals tend to be too small, device becomes rather insensitive.

106. Dr. M. Madhan, M.E., Ph.D., Asst. Prof., Mechanical Engineering 106 Resistance Temperature Detectors (RTDs) It is temperature sensors that contain a resistor that changes resistance value as its temperature changes. Used for applications for accuracy, repeatability and stability. Principle Electrical resistance of metal changes in linear and repeatable manner with changes in temperature. RTD have a positive temperature coefficient. Resistance increases with temperature. Resistance of the element at base temperature is proportional to length of element and inverse to cross sectional area.  

107. Dr. M. Madhan, M.E., Ph.D., Asst. Prof., Mechanical Engineering 107 Resistance Temperature Detectors (RTDs) RTDs actually measures the change in resistance of the RTD, which is then used to calculate the change in temperature. The Resistance of the RTD increases with increasing temperature. (similar as resistance of strain gauge increases with increasing strain). The circuit diagram for RTDs is shown in Figure. It consist of three known resistance and an unknown resistance (RTD), A source of voltage and a sensitive Volt meter or Ammeter. Resistor R1, R2 are known resistance of the bridge.

108. Dr. M. Madhan, M.E., Ph.D., Asst. Prof., Mechanical Engineering 108 Resistance Temperature Detectors (RTDs) They ratio the two variable resistance for current flow through Voltmeter/ammeter. R3 is variable resistor, known as the standard arm that is adjusted to meet the unknown resistor. The sensing ammeter / voltmeter visually displays the current that is flowing through bridge circuit. R3 adjusted to make the ammeter reading to zero current. The relation ship between two arms of the bridge can be expressed as below. The resistance of most metal increases, over a limited temperature range. There is a linear relationship between temperature and resistance. R t = R o (1 + t)   R t = Resistance corresponding to temperature t c . R o = Resistance corresponding to temperature 0 c.  = Temperature coefficient of resistance.

109. Dr. M. Madhan, M.E., Ph.D., Asst. Prof., Mechanical Engineering 109 Resistance Temperature Detectors (RTDs) Types Wire wound Thin film Wire-wound RTD Thin platinum wire is wound around an insulator bobbin (cylinder). The wire ends are spot welded or high-temperature soldered to the lead wires. A non-conductive protection coat with good thermal transfer properties covers the whole RTD element assembly. Thin-film RTD Sensing element is formed by depositing a thin layer of platinum onto a ceramic substrate and attaching the leads to the connecting pads. A glass coat encapsulates the element.

110. Dr. M. Madhan, M.E., Ph.D., Asst. Prof., Mechanical Engineering 110 Resistance Temperature Detectors (RTDs) Metals used for RTDs are Platinum Nickel Copper Nickel – copper alloys

111. Dr. M. Madhan, M.E., Ph.D., Asst. Prof., Mechanical Engineering 111 Resistance Temperature Detectors (RTDs) Advantages Due to no fluid present absolute temperature is recorded. It is highly sensitive and gives accurate results. It has a good range of temperature measurement. It can thus measure from very low to very high temperature. Due to electrical output (resistance change) it can be used with PLCs and complete automation can be achieved. Disadvantages Low Sensitivity Higher cost than thermocouples. Affected by shock and vibration. No point sensing. Applications It is widely used in furnaces for automatic temperature measurement. Due to its compactness, it replaces conventional thermometers as well as thermocouples thus eliminating the use of lots of wires. Used in medical and chemical laboratories to detect very low temperatures Due to electrical output it is used wherever feedback system is required and corrective action is thus taken in an automated system.

112. Dr. M. Madhan, M.E., Ph.D., Asst. Prof., Mechanical Engineering 112 Thermistors A thermistor is a resistance thermometer , or a resistor whose resistance is dependent on temperature. The term is a combination of “thermal” and “resistor”. It contains sintered mixture of metallic oxides such manganese, nickel, cobalt, copper, iron and uranium. its resistance decreases with increase in temperature in a very non linear manner. This change in resistance according to their temperature means that thermistors can be used as temperature sensors For example, they can be used to warn drivers when the car engine is overheating. Most thermistors have a useful working range of –90 °C to 200 °C

113. Dr. M. Madhan, M.E., Ph.D., Asst. Prof., Mechanical Engineering 113 Two types of thermistors Negative temperature coefficient thermistor Resistance decreases with increase in temperature Positive temperature coefficient thermistor Resistance increases with increase in temperature It may be in the form of Beads Probes Rods Discs Symbol Thermistors

114. Dr. M. Madhan, M.E., Ph.D., Asst. Prof., Mechanical Engineering 114 Thermistors The relationship governing the characteristics of a thermistor R 1  = resistance of the thermistor at absolute temperature T 1 [ o K ] R 2  = resistance of the thermistor at temperature T 2  [ o K ] β = constant depending upon the material of the transducer Advantages The thermistor has fast response over narrow temperature range. It is small in size. Contact and lead resistance problem not occurred due to large resistance. It has good sensitivity in NTC region. Cost is low.   Disadvantages The thermistor need of shielding power lines. The excitation current should be low to avoid self heating. It is not suitable for large temperature range. The resistance temperature characteristics are non linear.

115. Dr. M. Madhan, M.E., Ph.D., Asst. Prof., Mechanical Engineering 115 Thermo diodes It is usually used as temperature sensor in microprocessors. The term "thermal diode" is sometimes used for a (possibly non-electrical) device which allows heat to flow preferentially in one direction . The term may be used to describe an electrical (semiconductor) diode  in reference to a thermal effect or the term may be used to describe both situations, where an electrical diode is used as a heat-pump or thermoelectric cooler. when the thermal diode's first terminal is hotter than the second , heat will flow easily from the first to the second, but when the second terminal is hotter than the first , little heat will flow from the second to the first . Such an effect was first observed in a  copper–cuprous-oxide  interface in 1930. Later in 2015, a working thermal diode was built.

116. Dr. M. Madhan, M.E., Ph.D., Asst. Prof., Mechanical Engineering 116 Thermo diodes Electrical diode thermal effect or function A sensor device embedded on microprocessors used to monitor the temperature of the processor's die is also known as a "thermal diode". This application of thermal diode is based on the property of electrical diodes to change voltage across it linearly according to temperature. As the temperature increases, diodes' forward voltage decreases . Microprocessors encounter high thermal loads. Thermal diode are usually placed in that part of the processor core where highest temperature is encountered. Voltage developed across it varies with the temperature of the diode. All modern Intel CPUs have on-chip thermal diodes . As they are right there in the middle it provides most relevant CPU temperature readings. Thus we can determine the junction temperature by passing a current through the diode and then measuring voltage developed across it. In addition to processors, the same technology is widely used in dedicated temperature sensor IC's.

117. Dr. M. Madhan, M.E., Ph.D., Asst. Prof., Mechanical Engineering 117 Thermo diodes Advantages Very small compact sensor It gives linear function of temperature. Disadvantages Produces very minimum output potential difference. Hence a signal conditioning circuit is required.

118. Dr. M. Madhan, M.E., Ph.D., Asst. Prof., Mechanical Engineering 118 Thermo transistors Effective heat control device, which can act as heat switch as well as heat modulator. The voltage across the base emitter junction depends on the temperature . It is used to measure the temperature change. Two transistors with different collector currents are used and the difference in base emitter voltages between them is found. This difference is directly proportional to temperature on the kelvin scale. Advantages More Accurate Compact, Small in size. Detect minute temperature variations. Disadvantages Voltage difference produced by sensor is very low. It requires a signal conditioning circuit.

119. Dr. M. Madhan, M.E., Ph.D., Asst. Prof., Mechanical Engineering 119 Thermocouple A Thermocouple is a type of temperature sensor which is used to measure temperature. It consists of two different types of metals that are joined together to form two junctions . One junction is connected to the body whose temperature is to be measured. The other junction is connected to a body of known temperature which is at a lower temperature. The temperature difference causes the development of a voltage that is approximately proportional to the difference between the temperatures of the two junctions.

120. Dr. M. Madhan, M.E., Ph.D., Asst. Prof., Mechanical Engineering 120 Thermocouple Working Principle The thermocouple working principle mainly depends on the three effects Seebeck effect When two different metals are joined together at two junctions, an electromotive force (emf) is generated at the two junctions. The amount of emf generated depends on the combinations of the metals. Peltier effect When two, unlike metals are joined together to form two junctions, emf is generated within the circuit due to the different temperatures of the two junctions of the circuit. Thomson effect When two, dissimilar metals, are joined together, the potential exists within the circuit due to temperature gradient along the entire length of the conductors within the circuit.

121. Dr. M. Madhan, M.E., Ph.D., Asst. Prof., Mechanical Engineering 121 Thermocouple

122. Dr. M. Madhan, M.E., Ph.D., Asst. Prof., Mechanical Engineering 122 Thermocouple Types of Thermocouples based on construction 1. Base wire 2. Insulated Junction 3. Grounded Junction

123. Dr. M. Madhan, M.E., Ph.D., Asst. Prof., Mechanical Engineering 123 Thermocouple Laws of Thermocouples Law of homogeneous circuits If two thermocouple junctions are at T 1 and T 2 , then the thermal emf generated is independent and unaffected by any temperature distribution along the wires. In above Figure, a thermocouple is shown with junction temperatures at T 1 and T 2 .  Along the thermocouple wires, the temperature is T 3 and T 4 . The thermocouple emf is, however, still a function of only the temperature gradient T 2 – T 1

124. Dr. M. Madhan, M.E., Ph.D., Asst. Prof., Mechanical Engineering 124 Thermocouple Laws of Thermocouples Law of intermediate metals The law of intermediate metals states that a third metal may be inserted into a thermocouple system without affecting the emf generated, if, and only if, the junctions with the third metal are kept at the same temperature. When thermocouples are used, it is usually necessary to introduce additional metals into the circuit (soldered or welded) It would seem that the introduction of other metals would modify the emf developed by the thermocouple and destroy its calibration. However, the law of intermediate metals states that the introduction of a third metal into the circuit will have no effect upon the emf generated so long as the junctions of the third metal are at the same temperature

125. Dr. M. Madhan, M.E., Ph.D., Asst. Prof., Mechanical Engineering 125 Thermocouple Laws of Thermocouples Law of intermediate temperatures The law of intermediate temperatures states that the sum of the emf developed by a thermocouple with its junctions at temperatures T 1 and T 2 , and with its junctions at temperatures T 2 and T 3 , will be the same as the emf developed if the thermocouple junctions are at temperatures T 1 and T 3 . This law, illustrated in above Figure, is useful in practice because it helps in giving a suitable correction in case a reference junction temperature other than 0 °C is employed. For example, if a thermocouple is calibrated for a reference junction temperature of 0 °C and used with a junction temperature of 20 °C, then the correction required for the observation would be the emf produced by the thermocouple between 0 °C and 20 °C.

126. Dr. M. Madhan, M.E., Ph.D., Asst. Prof., Mechanical Engineering 126 Thermocouple Thermocouples in series Thermocouples in parallel

127. Dr. M. Madhan, M.E., Ph.D., Asst. Prof., Mechanical Engineering 127 Thermocouple Advantages Rugged devices Cheaper than RTDs. Work for wide range of temperature Work even for long distance transmission. No need of any bridge circuit for measurement. Good speed of response and reproducibility. Disadvantages Lower accuracy Non-linear characteristics. Need amplifier and signal conditioning, since thermocouple output is in millivolt range. Cold junction or isothermal block compensation is necessary.

128. Dr. M. Madhan, M.E., Ph.D., Asst. Prof., Mechanical Engineering 128 Light sensors Photodiodes: semiconductor junction diodes connected to a circuit in reverse bias => very high resistance When light falls on the diode resistance drops and current raises Has fast response to light Current in absence of light with reverse bias of 3 V might be 25 µA, illuminated by 25000 lumens/m 2 current raises to 375 µA Resistance with no light 3/(25x10 -6 ) = 120 k Ω and with light 3/(375x10 -6 ) = 8 k Ω

129. Dr. M. Madhan, M.E., Ph.D., Asst. Prof., Mechanical Engineering 129 Light sensors Phototransistor: light sensitive collector-base pn junction No light: very small collector to emitter current With light: base current proportional to light intensity leads to collector current which is a measure Symbol L14GI Phototransistor

130. Dr. M. Madhan, M.E., Ph.D., Asst. Prof., Mechanical Engineering 130 Light sensors Photoresistor: Resistance depends on the intensity of light linearly Cadmium Sulphide : most responsive to light of wavelength shorter than 515 nm Cadmium Selinide : wavelength less than 700 nm Array of light sensors are required to determine variations of light intensity across the space. Ex: automatic camera Symbol GL5528 Photoresistor

131. Dr. M. Madhan, M.E., Ph.D., Asst. Prof., Mechanical Engineering 131 Selection of sensors Nature of measurement required, eg. Variable to be measured, its nominal value, range, accuracy, required speed of measurement, reliability and environmental conditions Nature of output from sensor; to determine signal conditioning requirements to give suitable output signals from measurement Other conditions like ruggedness, availability, cost, life, power supply requirements Selection cannot be taken in isolation from consideration of the form of output required from the system after signal conditioning and it needs a suitable marriage between sensor and signal conditioner