OMR353_SENSORS_UNIT-4.pptx-Need for Signal Conditioning

Need for Signal Conditioning
Resistive, Inductive and Capacitive Bridges for Measurement
DC and AC Signal Conditioning - Voltage, Current, Power and Instrumentation Amplifiers
Filter and Isolation Circuits
Fundamentals of Data Acquisition System

1. OMR353 SENSORS

2. COURSE OUTCOMES Upon successful completion of the course, students should be able to: 1. Understand various sensor effects, sensor characteristics , signal types, calibration methods and obtain transfer function and empirical relation of sensors. They can also analyze the sensor response . 2. Analyze and select suitable sensor for displacement , proximity, and range measurement. 3. Analyze and select suitable sensor for force, magnetic field, speed, position, and direction measurement . 4. Analyze and select suitable sensors for light detection , pressure, and temperature measurement and familiar with other miniaturized smart sensors. 5. Select and design suitable signal conditioning circuit with proper compensation and linearizing element based on sensor output signal.

3. OPTICAL, PRESSURE, TEMPERATURE AND OTHER SENSORS Unit – IV Photo Conductive Cell, Photo Voltaic, Photo Resistive, LDR Fiber Optic Sensors Pressure –Diaphragm – Bellows - Piezoelectric - Piezo -resistive - Acoustic Temperature – IC, Thermistor, RTD, Thermocouple – Non Contact Sensor - Chemical Sensors - MEMS Sensors - Smart Sensors.

4. Photo Conductive Cell Photoconductive effect Photovoltaic effect Photoelectric effect Photo resistive effect

5. Photo Conductive Cell Effect Definition Key Feature Examples / Devices Photoconductive Effect Increase in electrical conductivity under light Conductivity ↑ with light Photoconductors, photodiodes Photovoltaic Effect Generation of voltage/current under light (no external bias) Voltage generated directly Solar cells , Photoelectric Effect Emission of electrons from a material surface when light energy > work function Electron emission in vacuum/metal Phototubes Photoresistive Effect Change in resistance when exposed to light Resistance ↓ with light LDRs (Light Dependent Resistors )

6. Photo Conductive Cell Photoconductive → Light increases conductivity. Photovoltaic → Light generates voltage. Photoelectric → Light ejects electrons. Photo-resistive → Light decreases resistance.

7. Photo Conductive Cell(PCC)- Design-Construction & Working Cadmium sulfide ( CdS ) and cadmium selenide ( CdSe ) Both respond rather slowly to changes in light intensity. For cadmium selenide , the response time ( t res ) is around 10 ms, while for cadmium sulfide it may be as long as 100 ms. This is known as the  dark resistance( 100 kΩ . ) Dark → High Resistance Bright Light → Low Resistance

8. Advantages and Disadvantages of PCC ✅ Advantages Low Cost – Very cheap and economical light sensor. Simple Design – Easy to construct and integrate in circuits. Wide Range of Resistance Change – High resistance in dark, very low in bright light. Good Sensitivity – Sensitive to a wide range of light intensities. Low Power Consumption – Requires very little power to operate. Compact & Reliable – Small in size and long operating life. ❌ Disadvantages Slow Response Time – Cannot respond quickly to fast-changing light signals. Temperature Dependence – Performance affected by ambient temperature. Limited Spectral Response – Sensitive only to specific wavelength ranges (e.g., CdS responds mostly to visible light). Non-linear Characteristics – Resistance vs. light intensity curve is non-linear. Not Suitable for Precision Applications – Accuracy is lower compared to photodiodes or phototransistors.

9. Photo Conductive Cell-Applications Application Example Device / Use Automatic street lighting Street lamps that turn ON at night and OFF in the morning Light intensity measurement Lux meters, camera exposure meters Camera light control Automatic exposure control in cameras Solar tracking systems Sun-following solar panels Security / Alarm systems Burglar alarms using light beam interruption Smoke & fire detection Smoke detectors, fire alarms Object counting systems Industrial conveyor belt counters Brightness control Automatic brightness adjustment in TVs, smart phones Optical communication Light sensor in optical receivers

10. Photo Voltaic Cell(PVC)- Design, Construction, Working and Application Solar Cell Arsenide, Indium, Cadmium, Silicon, Selenium and Gallium The output voltage and current obtained from the single unit of the cell is very less.  The magnitude of the output voltage is 0.6v, and that of the current is 0.8v.

11. Photo Voltaic Cell(PVC)- Design, Construction, Working and Application

12. Photo Voltaic Cell(PVC)- Design, Construction, Working and Application

13. Photo Voltaic Cell(PVC)- Design, Construction, Working and Application Series Combination of PV Cells Parallel Combination of PV cells Series-Parallel Combination of PV cells

14. Photo Voltaic Cell(PVC)- Design, Construction, Working and Application

15. LDR An LDR is a passive electronic component whose resistance changes with the intensity of incident light. Made of semiconductor materials such as cadmium sulfide ( CdS ) or cadmium selenide ( CdSe ).

16. LDR Voltage Divider

17. FIBER OPTIC SENSORS

18. Non-electric ( immune to electromagnetic and radio-frequency interference ) Withstand high temperature and harsh environments ( corrosion ) High shock survivability. (explosion or extreme vibration ) High Accuracy and Sensitivity. Light Weight and Small Size. High Capacity and Signal Purity. Multiplexing capacity and Can be easily interfaced with data communication systems Why optical sensors?

19. Temperature Pressure Strain Displacement Acceleration Flow rate Vibration Chemical concentrations Electrical and Magnetic Fields Rotation rate What can they measure?

20. FIBER OPTIC SENSOR Light beam changes by the phenomena that is being measured. Light may change in its five optical properties., i.e. Intensity, Phase, Polarization, Wavelength and spectral distribution. E P (t) cos [ ω p t+θ (t)] Intensity based sensor – E P ( t) Frequency varying sensors - ω P (t) Phase modulating sensors- θ(t)

21. FIBER OPTIC SENSOR  A fiber optic sensor is a sensor that uses optical fiber as the sensing element. The basic components are simple. Light is taken to modulation region using a fiber and modulated there by physical or chemical phenomena and modulated light is transmitted back to a receiver; detected and demodulated The fiber optic sensor

22. Fundamental Components Optical fiber (SI,GI) Light sources (LASER,LED) Beam conditioning optics (Lenses, couplers) Modulators Detectors (PIN,APD..)

23. EXTRINSIC FIBER OPTIC SENSOR Extrinsic fiber sensors are the ones where the light signal modulation occurs outside the optical fiber and are delivered by optical fiber, the light transmission depends on the alignment of the fiber cores i.e. input fiber core and the output fiber core. The light is detected by a light detector, any deviation of fiber pair from perfect alignment is sensed immediately by the detector. The extrinsic fiber optic sensor

24. INTRINSIC FIBER OPTIC SENSOR In intrinsic sensors the physical parameter changes some characteristic of the propagating light beam that is sensed . Here the optical fiber itself works as transducer only a simple source and a detector is used.

25. Comparison Extrinsic sensors Intrinsic sensors APPLICATIONS- TEMPERATURE, PRESSURE,LIQUID LEVEL AND FLOW. APPLICATIONS- ROTATION, ACCELERATION, STRAIN, ACOUSTIC PRESSURE AND VIBRATION LESS SENSITIVE MORE SENSITIVE EASILY MULTIPLEXED TOUGHER TO MULTIPLEX INGRESS/ EGRESS CONNECTION PROBLEMS REDUCES CONNECTION PROBLEMS EASIER TO USE MORE ELABORATE SIGNAL DEMODULATION LESS EXPENSIVE MORE EXPENSIVE

26. IMPORTANT FIBER SENSORS The Two important types of fiber sensors are :- Mach-Zehnder Interferometric Sensor & Fiber Optic Gyroscope

27. Mach-Zehnder Interferometric Sensor Mach-Zehnder interferometer is the most sensitive arrangements for a optic sensor used when extreme sensitivity is required. A collimated beam is passed through a fiber optic coupler which splits the beam in two equal amplitudes. The two beams are then passed to second mirror, through two arms the output from the second mirror enter the two detectors where they are sense and detected. The Mach-Zehnder interferometric sensor

28. Fiber Optic Gyroscope The principle of operation of fiber optic gyroscope is based on sagnac effect . It senses the orientation, performing the function of a mechanical gyroscope. Due to sagnac effect, the beam travelling against the rotation experiences a slightly shorter path delay than the other beam, the time taken by the beams are different . This difference in phase shift results in change of intensity which is measured through interferometer.

29. Advantages Fiber optic sensors are less costly and perform like real distributed sensors, implementation is very simple, the possibility of being multiplexed, etc. These sensors have unique benefits like small size, high sensitivity, resistance to electromagnetic interference & radio frequency interference, robustness, lightweight, flexibility & the ability to provide distributed or multiplexed sensing. The inherent benefits of fiber optic sensors include small size, low attenuation, passive, wide bandwidth, etc. Easily integrated into a wide range of structures. Not capable of conducting electric current. Strong and more resistant to harsh environments. Remote sensing capacity. They have multifunctional sensing capacities like pressure, strain, corrosion, acoustic signals & temperature.

30. Disadvantages It is expensive. Detection systems are complex. It is different for the user and thus it needs fundamental training before they use it. It needs exact installation procedures/methods. It is difficult to develop measurement systems with fiber optic sensors. Once we face any difficulty with the fiber optic sensor we need special test equipment. Fiber optic communication is expensive compared to other broadband connection costs. In rural areas, the usage of these sensors is very less.

31. Applications Used to transmit light for accurate marking and cutting. Applied in tunnels, railways, bridges, waste-disposal systems, and industrial ovens. Utilized in environmental and industrial sensing applications. Employed in communications networks. Measure physical properties like temperature, displacement, pressure, strain, velocity, and acceleration. Enable real-time monitoring of structural strength. Used in tunnels, bridges, buildings, and heritage structures. Applied in oil wells for temperature and pressure measurement. Monitor performance of civil infrastructures such as bridges, buildings, pavements, pipelines, dams, piles, and tunnels.

32. Pressure Sensors

33. Pressure Sensors Diaphragm & Bellows Sensors – which work by mechanical deformation Piezoelectric Sensor – which generate a voltage when stressed Piezo resistive Sensor – where resistance changes with pressure Acoustic Sensor -which convert sound or vibrations into electrical signals.

34. Diaphragm Pressure Sensors A diaphragm pressure sensor uses a flexible , thin membrane that deflects proportionally to the pressure of a gas or liquid.

35. Diaphragm Pressure Sensors This mechanical deflection is then converted into an electrical signal , which can be measured and processed. 

36. Diaphragm Pressure Sensors Working Principle When pressure is applied to the diaphragm: It deflects or deforms slightly. This deformation is detected by a sensing element such as: Strain gauges Capacitive plates Piezoelectric materials Optical fibers The change (in resistance, capacitance, or voltage) is then converted into an electrical signal proportional to the applied pressure. Sensing Element Uses Strain Gauge Measure strain (deformation) in a material when it is subjected to stress. The strain gauge converts the mechanical deformation into a change in electrical resistance , which can be measured. Capacitive Plates Detect displacement, pressure, or deformation by measuring the change in capacitance between two plates as the distance or overlapping area changes. Piezoelectric Material Generate an electric charge when subjected to mechanical stress or deformation (and vice versa). Optical Fiber Detect deformation or strain by measuring changes in light properties (intensity, phase, wavelength, or polarization) transmitted through the fiber.

37. Diaphragm Pressure Sensors Construction A typical diaphragm pressure sensor consists of: Diaphragm: A thin metal, silicon, or ceramic membrane that flexes under pressure. Pressure cavity: Holds the reference or process fluid. Sensing element: Converts diaphragm deflection into an electrical signal. Housing: Protects the diaphragm and electronics.

38. Diaphragm Pressure Sensors Types of Diaphragm Pressure Sensors Strain Gauge Type : Uses bonded strain gauges on the diaphragm; resistance changes with strain. → Suitable for static and dynamic measurements. Capacitive Type: Pressure changes the distance between two capacitor plates (one fixed, one diaphragm). → High sensitivity and good for low-pressure applications. Piezoelectric Type: Uses piezoelectric materials that generate a voltage when stressed. → Best for dynamic or fast-changing pressures. Optical Type: Measures diaphragm deflection via light interference or reflection. → Immune to electromagnetic interference.

39. Diaphragm Pressure Sensors Types of Diaphragm Pressure Sensors Strain Gauge Type: Uses bonded strain gauges on the diaphragm; resistance changes with strain. → Suitable for static and dynamic measurements. Capacitive Type : Pressure changes the distance between two capacitor plates (one fixed, one diaphragm). → High sensitivity and good for low-pressure applications. Piezoelectric Type: Uses piezoelectric materials that generate a voltage when stressed. → Best for dynamic or fast-changing pressures. Optical Type: Measures diaphragm deflection via light interference or reflection. → Immune to electromagnetic interference.

40. Diaphragm Pressure Sensors Types of Diaphragm Pressure Sensors Strain Gauge Type: Uses bonded strain gauges on the diaphragm; resistance changes with strain. → Suitable for static and dynamic measurements. Capacitive Type: Pressure changes the distance between two capacitor plates (one fixed, one diaphragm). → High sensitivity and good for low-pressure applications. Piezoelectric Type : Uses piezoelectric materials that generate a voltage when stressed. → Best for dynamic or fast-changing pressures. Optical Type: Measures diaphragm deflection via light interference or reflection. → Immune to electromagnetic interference.

41. Diaphragm Pressure Sensors Types of Diaphragm Pressure Sensors Strain Gauge Type: Uses bonded strain gauges on the diaphragm; resistance changes with strain. → Suitable for static and dynamic measurements. Capacitive Type: Pressure changes the distance between two capacitor plates (one fixed, one diaphragm). → High sensitivity and good for low-pressure applications. Piezoelectric Type: Uses piezoelectric materials that generate a voltage when stressed. → Best for dynamic or fast-changing pressures. Optical Type : Measures diaphragm deflection via light interference or reflection. → Immune to electromagnetic interference.

42. Diaphragm Pressure Sensors Advantages High accuracy and sensitivity Compact and robust design Suitable for harsh or corrosive environments (with proper material) Wide pressure range Good repeatability and linearity

43. Diaphragm Pressure Sensors Applications Industrial process control Automotive (engine pressure, fuel injection) Biomedical (blood pressure monitoring) Aerospace (cabin and hydraulic pressure) HVAC and environmental monitoring

44. Bellows Pressure Sensors A bellows pressure sensor is a type of mechanical pressure sensor that uses a flexible, accordion-like metallic element (called a bellows ) to measure pressure changes. The bellows expand or contract in response to applied pressure, and this displacement is converted into an electrical signal or a mechanical reading.

45. Bellows Pressure Sensors 🔹 Working Principle When pressure is applied: The bellows expand or compress depending on the pressure difference. This mechanical motion is either: Directly measured using a pointer and scale (in mechanical gauges), or Converted into an electrical signal using transducers such as strain gauges, LVDTs (Linear Variable Differential Transformers), or potentiometers. The amount of displacement is proportional to the applied pressure.

46. Bellows Pressure Sensors 🔹 Construction A typical bellows pressure sensor consists of: Bellows element: Corrugated thin-walled metallic tube (brass, bronze, stainless steel). Sealed and open ends: One end fixed, the other moves with pressure changes. Spring or linkage: Maintains mechanical balance or transmits motion. Sensing/ transducing element: Converts motion to electrical signal (in electronic sensors). Housing: Provides protection and mounting support.

47. Bellows Pressure Sensors 🔹 Types Single bellows type: Measures gauge pressure (pressure vs. atmosphere). Double bellows type: Measures differential pressure between two sources. Electrical output bellows sensors: Integrated with LVDT or strain gauges for signal conversion.

48. Bellows Pressure Sensors 🔹 Advantages Simple and reliable construction Good for low and medium pressure ranges Can directly indicate pressure without external power (mechanical type) Suitable for static and slowly varying pressures

49. Bellows Pressure Sensors 🔹 Disadvantages Limited range compared to diaphragm sensors Not suitable for very high pressures Mechanical friction and hysteresis can affect accuracy

50. Bellows Pressure Sensors 🔹 Applications HVAC systems (air pressure monitoring) Pneumatic and hydraulic control systems Barometers and altimeters Process industries (for moderate pressures) Pressure balancing or differential measurement setups

51. Piezoelectric Sensor Piezoelectric Sensor – which generate a voltage when stressed

52. Piezo resistive Sensor Piezo resistive Sensor – where resistance changes with pressure

53. Acoustic Sensor Acoustic Sensor -which convert sound or vibrations into electrical signals. Acoustic sensors detect variations in air pressure (sound) or mechanical vibrations in solids/liquids and convert them into corresponding electrical outputs. They are widely used in applications such as: Microphones (for audio recording and speech recognition) Ultrasonic sensors (for distance measurement and object detection) Structural health monitoring (detecting cracks or stress through vibration analysis)

54. Type of Sensor Working Principle Output Type Measured Quantity Material/Element Used Applications Diaphragm & Bellows Sensor Operate by mechanical deformation due to applied pressure or force. The displacement is proportional to pressure. Mechanical (displacement) or converted to electrical (via transducer) Pressure, Force Metal diaphragm, bellows (brass, stainless steel) Pressure gauges, barometers, HVAC systems Piezoelectric Sensor Generate an electric voltage when subjected to mechanical stress or vibration (piezoelectric effect). Electrical (voltage) Pressure, Vibration, Acceleration Piezoelectric crystals (Quartz, PZT) Vibration measurement, microphones, accelerometers Piezoresistive Sensor Electrical resistance changes with applied pressure or strain. Electrical (resistance change → voltage via bridge circuit) Pressure, Force, Strain Semiconductor materials (Silicon) Pressure transducers, MEMS sensors, automotive sensors Acoustic Sensor Convert sound waves or vibrations into electrical signals. Electrical (voltage or current) Sound pressure, Vibration Piezoelectric or MEMS elements Microphones, sonar, structural health monitoring, ultrasonic detectors

55. Temperature Sensors Temperature – IC, Thermistor , RTD, Thermocouple

56. Temperature Sensors Detects and measures coldness and hotness in an object and convert it into electrical signal . In our daily lives, be it in the form of thermometers, domestic water heaters, microwaves, or refrigerators . 

57. Temperature Sensors Usually, temperature sensors have a wide range of applications, the geotechnical monitoring field , being one of them. Temperature sensors are designed to keep a regular check on concrete structures, bridges, railway tracks, soil, etc.

58. Temperature Sensors What are the temperature sensors? A temperature sensor is a device, typically, a thermocouple or resistance temperature detector, that provides temperature measurement in a readable form through an electrical signal. A thermometer is the most basic form of a temperature meter that is used to measure the degree of hotness and coolness. Temperature meters are used in the geotechnical field to monitor concrete, structures, soil, water, bridges, etc. for structural changes in due to seasonal variations. A thermocouple (T/C) is made from two dissimilar metals that generate an electrical voltage in direct proportion to the change in temperature. An RTD (Resistance Temperature Detector) is a variable resistor that changes its electrical resistance in direct proportion to the change in the temperature in a precise, repeatable, and nearly linear manner.

59. Temperature Sensors What do temperature sensors do? A temperature sensor is a device that is designed to measure the degree of hotness or coolness in an object. The working of a temperature meter depends upon the voltage across the diode. The temperature change is directly proportional to the diode’s resistance. The cooler the temperature, the lesser will be the resistance, and vice-versa. The resistance across the diode is measured and converted into readable units of temperature (Fahrenheit, Celsius, Centigrade, etc.) and, displayed in numeric form over readout units. In the geotechnical monitoring field, these temperature sensors are used to measure the internal temperature of structures like bridges, dams, buildings, power plants, etc.

60. Temperature Sensors How does a temperature sensor work? The basic principle of working the temperature sensors is the voltage across the diode terminals. If the voltage increases, the temperature also rises, followed by a voltage drop between the transistor terminals of the base and emitter in a diode.

61. Temperature – IC A temperature IC is a silicon integrated circuit that acts as a temperature sensor, producing a signal proportional to the temperature it measures.  These ICs can have  analog outputs  (voltage or current) or  digital outputs  (which may include an  analog-to-digital converter  or a  serial interface  like  I2C ).  They integrate signal processing circuitry into a single package, making them easy to use in microchip-based systems for applications such as monitoring and controlling device and ambient temperatures in electronics, computers, and industrial equipment.   I2C High Accuracy Temperature Sensor(MCP9808)

62. Temperature – IC How They Work Sensor Principle:   Temperature sensor ICs often rely on the principle that a diode's  forward voltage ( Vf )  is directly proportional to temperature, allowing the IC to measure temperature by sensing this change in voltage.  Analog Outputs:   Some ICs provide a direct analog output, typically a voltage or current that scales with temperature. For example, the  LM35  outputs 10mV for every 1°C.  Digital Outputs:   Others integrate an analog-to-digital converter (ADC) to provide a digital output that can be read directly by a microcontroller. Some may also feature an I2C interface for digital communication.  Advanced Features:   Some digital temperature sensor ICs include features like alert functions using voltage comparators, control registers, and integrated cold junction compensation for thermocouples.  -55˚ to +120˚C -55⁰C to +125⁰C 

63. Temperature – IC Key Characteristics Operating Range:   Temperatures sensor ICs operate over various temperature ranges, with common grades including commercial (0°C to 70°C), industrial (−40°C to 85°C), and military (−55°C to 125°C).  Integration:   Unlike other temperature sensing methods, ICs incorporate processing and signal conditioning circuitry, simplifying their integration into a final design.  Applications:   They are used in diverse applications, including:  Computer Systems:  For monitoring CPU and board temperatures.  Consumer Electronics:  For temperature control in mobile phones and appliances.  Industrial Applications:  For general temperature monitoring and control. 

64. Temperature – IC Examples of Types Ambient Temperature Sensors :  Measure the surrounding air temperature.  On-Board Temperature Sensors :  Designed to be mounted on circuit boards to monitor the temperature of other components.  Thermocouple ICs :  Designed to work with external thermocouples, providing an IC solution for thermocouple measurements. 

65. Temperature Sensors What are the different types of temperature sensors? Temperature sensors are available in various types, shapes, and sizes. The two main types of temperature sensors are: Contact Type Temperature Sensors:   There are a few temperature meters that measure the degree of hotness or coolness in an object by being in direct contact with it. Such temperature sensors fall under the category of contact type. They can be used to detect solids, liquids, or gases over a wide range of temperatures. Non-Contact Type Temperature Sensors:  These types of temperature meters are not in direct contact with the object rather, they measure the degree of hotness or coolness through the radiation emitted by the heat source. Thermistor RTD Thermocouple

66. Thermistor Thermistors or thermally sensitive resistors are the ones that change their physical appearance when subjected to a change in temperature. The thermistors are made up of ceramic material such as oxides of nickel, manganese, or cobalt coated in glass which allows them to deform easily. Most of the thermistors have a negative temperature coefficient (NTC) which means their resistance decreases with an increase in the temperature. But, there are a few thermistors that have a positive temperature coefficient (PTC), and, their resistance increases with a rise in the temperature.

67. Thermistor

68. Resistive Temperature Detectors (RTD)

69. Resistive Temperature Detectors (RTD)

70. Resistive Temperature Detectors (RTD)

71. Resistive Temperature Detectors (RTD)

72. Thermocouple One of the most common temperature sensors includes thermocouples because of their wide temperature operating range, reliability, accuracy, simplicity, and sensitivity. A thermocouple usually consists of two junctions of dissimilar metals, such as copper and constantan that are welded or crimped together. One of these junctions, known as the Cold junction, is kept at a specific temperature while the other one is the measuring junction, known as the Hot junction. On being subjected to temperature, a voltage drop is developed across the junction.

73. Thermocouple Working Principle The   thermocouple working principle mainly depends on the three effects namely Seebeck , Peltier and Thompson. 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.   The Seebeck effect is the phenomenon where a temperature difference between two dissimilar conductors or semiconductors generates an electric voltage.  This conversion of thermal energy into electrical energy is the principle behind  thermocouples , which act as temperature sensors and are used in applications like thermoelectric generators, spacecraft power systems, and  automotive thermoelectric generators .  

74. Thermocouple Working Principle The   thermocouple working principle mainly depends on the three effects namely Seebeck , Peltier and Thompson. 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.   The Seebeck effect is the phenomenon where a temperature difference between two dissimilar conductors or semiconductors generates an electric voltage.  This conversion of thermal energy into electrical energy is the principle behind  thermocouples , which act as temperature sensors and are used in applications like thermoelectric generators, spacecraft power systems, and  automotive thermoelectric generators .  

75. Thermocouple   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. The Peltier effect is a thermoelectric phenomenon where an electric current passing through a junction of two different conductive materials causes heat to be absorbed or released at that junction, creating a hot and a cold side.  This reversible effect is utilized in  Peltier devices , which are used as  thermoelectric coolers  (TECs) for cooling electronic devices, small refrigerators, and other applications. 

76. Thermocouple 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. The "Thomson effect" can refer to two distinct phenomena: the  Joule-Thomson effect , a thermodynamic process where a gas's temperature changes during expansion through a restriction, and the  thermoelectric Thomson effect , where an electric current passing through a conductor with a temperature gradient causes reversible heat absorption or evolution.  

77. Thermocouple Types of Thermocouple Thermocouples  are available in different combinations of calibrations. The four most common types of calibrations are J, K, T, and E. Each calibration has a different temperature environment and range. Although the maximum temperature depends upon the diameter of the wire used in the thermocouple. Calibration Temperature Range J 0° to 750°C (32° to 1382°F) K 200° to 1250°C (-328° to 2282°F) E 200° to 900°C (-328° to 1652°F) T 250° to 350°C (-418° to 662°F)

78. Thermocouple Advantages of Thermocouple High accuracy Low Cost Wide operating temperature range Thermocouple calibration services Industrial thermocouples Disadvantages of Thermocouple Non-linearity Low voltage Recalibration is difficult Thermocouple Applications Industries where an accurate and huge range of temperatures required. Thermostats in offices, homes, and businesses.

79. Sensor type Pt 100 Range -20o to 80o C Accuracy ± 0.5 % fs standard; ± 0.1 % fs optional Dimension ( Φ  x L) 34 x 168 mm Specifications of ETT-10V Vibrating Wire Temperature Meter Negative Temperature Coefficient (NTC) Thermistor Model ETT-10TH Resistance Thermistor Probe Model ETT-10PT RTD Temperature Probe

80. Parameter RTD Thermocouple Thermistor Temperature Range -260 to 850°C (-436 to 1562°F) -270 to 1800°C (-454 to 3272°F) -80 to 150°C (-112 to 302°F) (typical) Sensor Cost Moderate Low Low System Cost Moderate High Moderate Stability Best Low Moderate Sensitivity Moderate Low Best Linearity Best Moderate Poor Specify For - General purpose sensing- Highest accuracy- Temperature averaging - Highest temperatures - Best sensitivity- Narrow ranges (e.g. medical)- Point sensing

81. Unit-IV Non Contact Sensor Chemical Sensors MEMS Sensors Smart Sensors

82. Classification of Sensors Based on Physical Property Contact Sensors : Require physical contact with the object they are measuring. Example : Tactile sensors, used in touch screens. Non-contact Sensors : Measure without physical contact with the object being measured. Example : Proximity sensors, used in automatic doors. Sensor Type Contact Type Description Examples Contact Sensors Physical Contact Require direct contact with the object or medium being measured. Tactile Sensors (Touch Screens), Thermistors , Strain Gauges Non-contact Sensors No Physical Contact Detect the target parameter remotely using electromagnetic, optical, or ultrasonic means. Proximity Sensors, IR Sensors, Ultrasonic Sensors, Radar Sensors

83. 1. Contact Sensor (Left Image) Description : A sensor that requires physical contact with an object to detect a change. Example Shown : Likely a vibration or pressure sensor with a metal push-button or piezo element. Working Principle : Detects mechanical contact, pressure, force, or vibration when physically touched or pressed. Applications : Limit switches in automation Touch or vibration detection Safety interlock 2. Non-Contact Sensor (Right Image) Description : A sensor that can detect an object without any physical contact . Example Shown : Inductive or capacitive proximity sensor Working Principle : Inductive sensors detect metal objects using electromagnetic fields. Capacitive sensors detect any material (metal or non-metal) based on dielectric properties. Applications : Object detection in conveyors Must be in direct contact with the object to work.

84. Contact and noncontact sensors Contact Sensors – Require direct physical interaction with the target to measure changes. Non-Contact Sensors – Operate without direct contact, using technologies such as infrared, ultrasonic, or electromagnetic fields to detect changes. Type Principle Typical Frequency / Wavelength Range Infrared (IR) Detects thermal radiation (heat energy) or light in the IR spectrum 700 nm – 1 mm Ultrasonic Uses high-frequency sound waves (> 20 kHz) to detect distance or motion 20 kHz – 10 MHz Electromagnetic Field (EMF) Uses variations in magnetic/electric fields to detect metal or movement DC – GHz (depending on sensor type)

85. Contact and noncontact sensors Contact sensor: a sensor that requires physical contact with the stimulus. Examples: strain gauges, most temperature sensors Non-contact sensor: requires no physical contact. Examples: most optical and magnetic sensors, infrared thermometers, etc.

86. Noncontact Sensors In contrast to contact sensors,  non-contact sensors  function without requiring direct physical interaction with the object being measured. These sensors rely on technologies such as infrared radiation, ultrasonic waves, or electromagnetic fields to detect and monitor conditions remotely. For example, instead of using an oral thermometer , which must be placed inside a patient’s mouth to make contact with body heat, a nurse or physician may use an infrared thermometer . This type of non-contact sensor detects infrared radiation emitted by the body to determine temperature, eliminating the need for direct physical contact.

87. Noncontact Sensors Non-contact sensors, therefore, generally rely on technologies that are based on electrical, magnetic, optical, sonic, or other principles , rather than depending on physical contact or mechanical movement to obtain readings. The sensors often emit a form of energy such as radiation that can be used to detect a condition without needing physical contact. The object being sensed or detected is usually referred to as the target.

88. Noncontact Sensors

89. Non Contact Sensors Proximity Sensors A Proximity Sensor is a non-contact type sensor that detects the presence of an object. Proximity Sensors can be implemented using different techniques like Optical (like Infrared or Laser), Sound (Ultrasonic), Magnetic (Hall Effect), Capacitive, etc.

90. Non-Contact Sensors Infrared Sensor (IR Sensor) IR Sensors or Infrared Sensor are light based sensor that are used in various applications like Proximity and Object Detection. IR Sensors are used as proximity sensors in almost all mobile phones.

91. Non-Contact Sensors Light Sensor Sometimes also known as Photo Sensors, Light Sensors are one of the important sensors. A simple Light Sensor available today is the Light Dependent Resistor or LDR. The property of LDR is that its resistance is inversely proportional to the intensity of the ambient light i.e., when the intensity of light increases, its resistance decreases and vise-versa.

92. Non-Contact Sensors Smoke and Gas Sensors One of the very useful sensors in safety related applications are Smoke and Gas Sensors. Almost all offices and industries are equipped with several smoke detectors, which detect any smoke (due to fire) and sound an alarm.

93. Non-Contact Sensors Alcohol Sensor As the name suggests, an Alcohol Sensor detects alcohol. Usually, alcohol sensors are used in breathalyzer devices, which determine whether a person is drunk or not. Law enforcement personnel uses breathalyzers to catch drunk-and-drive culprits.

94. 95 Pyrometers This kind of thermometers is used for distant (noncontact) measurements of temperature. It is based on the analysis of thermal radiation emitted by the objects. Monochromatic pyrometers are used as standard thermometers from the freezing temp. of silver (961,78 C). Classification of pyrometers: TOtal Radiation Pyrometers ( wide bandwidth) Monochromatic Pyrometers TWO-COLOR Pyrometers Multicolor Pyrometers Basic Laws of Thermal Radiation Planck’s law Radiation flux density, i.e. power of radiation per unit of area and unit of wavelength (Wm -2 µ m -1 ) is equal: λ - wavelength, c 1 ,c 2 – radiation constants ε λ –monochromatic emissivity of a source (for a blackbody equal 1)

95. 🔹 Advantages No physical wear and tear Works with moving or hazardous targets High speed and long service life Can operate in harsh environments (dust, oil, vibration)

96. 🔹 Limitations Limited sensing range (compared to contact sensors) Sensitivity may depend on material or surface properties Can be affected by temperature or electromagnetic interference

97. Chemical Sensors – Overview and Working Principle A chemical sensor is a device that detects and measures the concentration of chemical substances in gases or liquids. It converts a chemical interaction between the analyte (the substance being measured) and the sensor’s sensitive layer into an electrical signal that can be measured and processed.

98. 🔹 Basic Working Principle The operation of a chemical sensor involves three main steps : Recognition (Sensing Element): The analyte (gas, ion, or molecule) interacts with a sensitive or selective layer (such as a metal oxide, polymer, enzyme, or electrode surface). This interaction may cause a change in properties like electrical conductivity, potential, mass, or light absorption. Transduction: The physical or chemical change is converted into an electrical signal by the transducer. For example, a change in voltage, current, or resistance is measured. Signal Processing: The signal is amplified, filtered, and processed to display or transmit the analyte concentration.

99. Type Transduction Mechanism Typical Example Measured Quantity Electrochemical Sensors Change in electrical properties (voltage, current, resistance) due to redox reactions pH electrode, oxygen sensor, glucose biosensor Ion concentration, gas concentration Conductometric Sensors Change in conductivity of sensing layer upon analyte interaction Metal oxide gas sensors ( SnO ₂, ZnO ) Gas concentration Potentiometric Sensors Measure potential difference between reference and sensing electrodes pH meter Hydrogen ion concentration Amperometric Sensors Measure current from oxidation/reduction reactions Glucose sensors, oxygen sensors Analyte concentration Optical Sensors Change in light absorption, fluorescence, or refractive index Fiber optic gas sensor, colorimetric sensors Gas/vapor concentration Mass-sensitive Sensors Detect change in mass due to adsorption on a piezoelectric surface Quartz Crystal Microbalance (QCM) Thin film deposition, gas adsorption Thermal Sensors Detect heat changes due to chemical reactions Catalytic bead sensor Combustible gas detection

100. Sensor Type Sensed Chemical Working Mechanism Oxygen Sensor ( Lambda Sensor) O₂ Measures voltage difference due to oxygen ion flow across a zirconia electrolyte Glucose Sensor Glucose Enzymatic oxidation (glucose oxidase ) produces an electrical current proportional to glucose concentration Carbon Monoxide (CO) Sensor CO CO oxidizes on metal oxide surface ( SnO ₂), changing resistance pH Sensor H⁺ ions Glass electrode develops a potential proportional to hydrogen ion concentration