misgina Mengesha, profile picture
Uploaded bymisgina Mengesha
PPT, PDF4,063 views

Cn3 sensors and transducers-12

This document discusses different types of sensors and transducers. It begins by classifying sensors as either primary or secondary, active or passive, and analog or digital based on their method of application, energy conversion, and output signal characteristics. It then describes various passive resistive, capacitive, and inductive sensors including potentiometers, temperature dependent resistors, strain gauges, photoconductors, capacitive displacement and pressure sensors, and inductive proximity switches. Active sensors that generate their own output signal like thermocouples and photovoltaic cells are also introduced. Key applications and operating principles of different sensors are outlined.

Embed presentation

Downloaded 346 times
Chapter 3: Sensors and/or Transducers 1 Introduction to Different Types of Sensors
Application of sensor 2
Application off sensor Grey code encoder reflection sensor 3
Application of sensor Infrared reflection sensor 4
Application of sensors Instrum. & Control Eng. for Energy Systems - Ch. 4 Sensors and Transducers 5
Goals of the Chapter • Define classification of sensors and some terminologies • Introduce various types of sensors for measurement purpose and their applications • Example: Displacement, motion, level, pressure, temperature, … 6Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
Overview • Introduction • Classification of sensors • Passive sensors • Active sensors 7Instrum. & Control Eng. for Energy Systems - Ch. 4 Sensors and Transducers
Introduction • Sensors • Elements which generate variation of electrical quantities (EQ) in response to variation of non-electrical quantities (NEQ) • Examples of EQ • Temperature, displacement, humidity, fluid flow, speed, pressure,… • Sensor are sometimes called transducers 8 Sensing element Signal conditioning element Signal conversion/ processing element Output presentation Non-electrical quantity Electrical signal Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
Introduction … • Advantages of using sensors include 1. Mechanical effects such as friction is reduced to the minimum possibility 2. Very small power is required for controlling the electrical system 3. The electrical output can be amplified to any desired level 4. The electrical output can be detected and recorded remotely at a distance from the sensing medium and use modern digital computers 5. etc … 9Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
Introduction - Use of Sensors 1. Information gathering: Provide data for display purpose • This gives an understanding of the current status of the system parameters • Example: Car speed sensor and speedometer, which records the speed of a car against time 1. System control: Signal from the sensor is an input to a controller 10 Controller System under control Output signalDesires signal Sensor Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
Introduction – Sensor Requirements • The main function of a sensor is to respond only for the measurement under specified limits for which it is designed • Sensors should meet the following basic requirements 1. Ruggedness: Capable of withstanding overload • Some safety arrangements should be provided for overload protection 1. Linearity: Its input-output characteristics must be linear 2. Repeatability: It should reproduce the same output signal when the same input is applied again and again 3. High output signal quality 4. High reliability and stability 5. Good dynamic response 6. No hysteresis, … 11Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
Overview • Introduction • Classification of sensors • Passive sensors • Active sensors 12Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
Classification of Sensors • Sensors can be divided on the basis of • Method of applications • Method of energy conversion used • Nature of output signals • Electrical principle • In general, the classification of sensors is given by • Primary and secondary sensors • Active and passive sensors • Analog and Digital sensors 13Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
Primary and Secondary Sensors • Classification is based on the method of application • Primary sensor • The input NEQ is directly sensed by the sensor • The physical phenomenon is converted into another NEQ • Secondary sensor • The output of the primary sensor is fed to another (secondary) sensor that converts the NEQ to EQ 14 Load cell Strain- gauge NEQ Secondary sensor Weight (Force ∆F) Primary sensor NEQ EQ Displacement ∆d Resistance ∆R Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
Active and Passive Sensor • Classification based on the basis of energy conversion • Active sensor • Generates voltage/current in response to NEQ variation • Are also called self-generating sensors • Normally, the output of active sensors is in µV or mV • Examples • Thermocouples: A change in temperature produces output voltage • Photovoltaic cell: Change solar energy into voltage • Hall-effect sensors, … 15 Active sensors NEQ Ex. Temperature EQ Voltage or current Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
Active and Passive …. • Passive sensors • Sensors that does not generate voltage or current, but produce element variation in R, L, or C • Need an additional circuit to produce voltage or current variation • Examples • Thermistor: Change in temperature leads to change in resistance • Photo resistor: Change in light leads to change in resistance • Straingauge: Change in length or position into change in resistance) • LVDT, Mic 16 Passive sensors NEQ ∆R, ∆L, ∆C Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
Analog and Digital Sensors • Classification based on the nature of the output signal • Analog sensor • Gives an output that varies continuously as the input changes • Output can have infinite number of values within the sensor’s range • Digital sensor • Has an output that varies in discrete steps or pulses or sampled form and so can have a finite number of values • E.g., Revolution counter: A cam, attached to a revolving body whose motion is being measured, opens and closes a switch • The switching operations are counted by an electronic counter 17Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
Sensor Classification • Sensors can also be classified according to the application • Example • Measurement of displacement, motion, temperature, intensity, sensors 18Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
Overview • Introduction • Classification of sensors • Passive sensors • Resistive sensors • Potentiometers, temperature dependent resistors, strain gauge, photoconductors (photoresistors), Piezoresistive • Capacitive sensors • Inductive sensors • Active sensors 19Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
Resistive Sensors - Potentiometer • Examples: Displacement, liquid level (in petrol-tank level indicator) using potentiometer or rheostat • Convert s linear (translatory) or angular (rotary) displacement into a change of resistance in the resistive element provided with a movable contact 20 • Petrol-tank level indicator • Change in petrol level moves a potentiometer arm • Output signal is proportion to the external voltage source applied across the potentiometer • The energy in the output signal comes from the external power source Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
Resistive Sensors – Potentiometer … • A linear or rotary movement of a moving contact on a slide wire indicates the magnitude of the variable as a change in resistance which can easily be converted by a proper electrical circuit into measurements of volt or current 21Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
Resistive Sensors – Temperature Dependent Resistors • Two classes of thermal resistors are • Metallic element • Semiconductor • For most metals, the resistance increases with increase in temperature • Where α is the temperature coefficient of resistance and given as • Example: Platinum • Has a linear temperature-resistance characteristics • Reproducible over a wide range of temperature • Platinum Thermometers are used for temperature measurement 22 ]1[...]1[)(R 0 2 210 TRTTRT ααα +≈+++= 0 1 R R T ∆ ∆ =α Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
Resistive Sensors – Temperature Dependent… • Semiconductor based resistance thermometers elements • The resistance of such elements decreases with increasing temperature • Example: Thermistor • The resistance-temperature relationship is non-linear and governed by • Where R0 is the resistance at absolute temp (in Kelvin) and β is material constant expressed in degree Kelvin • Most semiconductor materials used for thermometry possess high resistivity and high negative temperature coefficients 23 KTeRT TT 0 0 ) 11 ( 0 300;)(R 0 == −β Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
Resistive Sensors – Temperature Dependent… • The temperature coefficient of resistance is • β is typically 4000 k and for T = 300k, 24 2 0 1 TR R T β α −= ∆ ∆ = 044.0 300 4000 22 −=−=−= T β α Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
Resistive Sensors – Strain Gauges • Is a secondary transducer that senses tensile or compressive strain in a particular direction at a point on the surface of a body or structure • Used to measure force, pressure, displacement • Where e=∆l/l is the strain • The resistance of an unstrained conductor is given as • Under strained condition, resistance of conductor changes by ∆R because of ∆l, ∆A, and/or ∆ρ 25 )(R eR= A l ρ=R Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
Resistive Sensors – Strain Gauges … • To find the change in resistance ∆R, • Dividing both sides by R, we get the fractional change as • Let us define eL = ∆l/l as the longitudinal stain and eT as the transversal strain • Also assume that eT = -νeL ,where ν is the Poisson’s Ratio 26 ρ ρρ ρ ρ ∆+∆−∆= ∆ ∂ ∂ +∆ ∂ ∂ +∆ ∂ ∂ =∆ A l A A l l A R A A R l l R 2 R ρ ρ∆ + ∆ − ∆ = ∆ A A l l R R Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
Resistive Sensors – Strain Gauges … • Then, Gauge Factor, G is defined as • G is also known as Strain-Sensitivity factor; rearranging terms, we get • Where is the Piezoresistive term • For most metals, the Piezoresistive term is about 0.4 and 0.2 < ν < 0.5 • Thus, Gauge factor for metallic stain gauges is in the range 2.0–2.5 (not sensitive) 27 Le G ρρ υ / )21( ∆ ++= Le ρρ/∆ Lell G R/R / R/R ∆ = ∆ ∆ = Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
Resistive Sensors – Strain Gauges … • Sensitive measurements require very high Gauge factors in the range of 100-300 • Such factor can be obtained from semiconductor strain gauges • Due to the significant contribution from the Piezoresistive term 28Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
Piezoresistive Pressure Sensor • Piezoresistivity is a strain dependent resistivity in a single crystal semiconductor • When pressure is applied to the diaphragm, it causes a strain in the resistor • Resistance change is proportional to this strain, and hence change in pressure 29Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
Resistive Sensors – Photoconductor • Are light sensitive resistors with non-linear negative temperature coefficient • Are resistive optical radiation transducers • Photoconductors have resistance variation that depends on illumination • The resistance illumination characteristics is given by • Where RD is Dark Resistance and E is illumination level in Lux • Photoconductors are used in • Cameras, light sensors in spectrophotometer • Counting systems where an object interrupts a light beam hitting the photoconductor, etc. 30 E DeR α− =R Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
Photoconductive Transducers • A voltage is impressed on the semiconductor material • When light strikes the semiconductor material, there is a decrease in the resistance resulting in an increase in the current indicated by the meter • They enjoy a wide range of applications and are useful for measurement of radiation at all levels • The schematic diagram of this device is shown below 31Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
Photovoltaic Cells • When light strikes the barrier between the transparent metal layer and the semiconductor material, a voltage is generated • The output of the device is strongly dependent on the load resistance R • The most widely used applications is the light exposure meter in photographic work Schematic of a photovoltaic cell. 32Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
Overview • Introduction • Classification of sensors • Passive sensors • Resistive sensors • Capacitive sensors • Inductive sensors • Active sensors 33Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
Capacitive Transducers • The parallel plate capacitance is given by • d= distance between plates • A=overlapping area • ε0 = 8.85x10-12 F/m is the absolute permittivity, εr =dielectric constant (εr =1 for air and εr =3 for plastics) d A C rεε0= • Displacement measurement can be achieved by varying d, overlapping area A and the dielectric constant Schematic of a capacitive transducer. 34Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
Capacitive Transducers – Liquid Level Measurement • A simple application of such a transducer is for liquid measurement • The dielectric constant changes between the electrodes as long as there is a change in the level of the liquid Capacitive transducer for liquid level measurement. 35Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
Capacitive Transducers – Liquid Level Measurement • A simple application of such a transducer is for liquid measurement • The dielectric constant changes between the electrodes as long as there is a change in the level of the liquid Capacitive transducer for liquid level measurement. 36Introduction to Instrumntaion Eng‘g - Ch. 3 Sensors and Transducers
Capacitive sensors – Pressure Sensor • Use electrical property of a capacitor to measure the displacement • Diaphragm: elastic pressure senor displaced in proportion to change in pressure • Acts as a plate of a capacitor 37Introduction to Instrumntaion Eng‘g - Ch. 3 Sensors and Transducers
Capacitive Sensor – Proximity Switch • A capacitive sensor functions like a typical capacitor. • The metal plate in the end of the sensor electrically connects to the oscillator, and the object to be sensed acts as the second plate. • When this sensor receives power, the oscillator detects the external capacitance between the target and the internal sensor plate. Instrum. & Control Eng. for Energy Systems - Ch. 3 Sensors and Transducers 38
Capacitive Sensor – Proximity Switch 39Introduction to Instrumntaion Eng‘g - Ch. 3 Sensors and Transducers • This arrangement completes the circuit and provides the necessary feedback path for the output circuit to evaluate. • Capacitance increases as any object (P) gets closer because additional capacitance paths C2 & C3 are added and increase in value as the separation reduces. C1 is always present. C1 C3 C2 P
Capacitive Sensor – Proximity Switch Instrum. & Control Eng. for Energy Systems - Ch. 3 Sensors and Transducers 40
Capacitive Transducers - Linear Displacement • Variable area capacitance displacement transducer Where: • ra=inner cylinder radius • rb=outer cylinder radius • L=length of the cylinder 41Introduction to Instrumntaion Eng‘g - Ch. 3 Sensors and Transducers
Capacitive sensors • Application of capacitive sensors Instrum. & Control Eng. for Energy Systems - Ch. 4 Sensors and Transducers 42
Overview • Introduction • Classification of sensors • Passive sensors • Resistive sensors • Capacitive sensors • Inductive sensors • Active sensors 43Introduction to Instrumntaion Eng‘g - Ch. 3Sensors and Transducers
Inductive Sensors • For a coil of n turns, the inductance L is given by • Where • n: Number of turns of the coil • l: Mean length of the magnetic path • A: Area of the magnetic path • µ: Permeability of the magnetic material • R: Magnetic reluctance of the circuit • Application of inductive sensors • Force, displacement, pressure, … • Inductance variation can be in the form of • Self inductance or • Mutual inductance: e.g., differential transformer 44 R n l n AL 22 == µ Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
• Input voltage (alternating current): One primary coil • There will be a magnetic coupling between the core and the coils • Output voltage: Two secondary coils connected in series • Operates using the principle of variation of mutual inductance Linear Variable Differential Transformer (LVDT) Schematic diagram of a differential transformer • The output voltage is a function of the core’s displacement • Widely used for translating linear motion into an electrical signal 45Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
LVDT - Output Characteristics Output characteristics of an LVDT 46Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
LVDT – Applications • Measure linear mechanical displacement • Provides resolution about 0.05mm, operating range from ± 0.1mm to ± 300 mm, accuracy of ± 0.5% of full-scale reading • The input ac excitation of LVDT can range in frequency from 50 Hz to 20kHz • Used to measure position in control systems and precision manufacturing • Can also be used to measure force, pressure, acceleration, etc.. 47Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
Inductive Sensors –proximity switch • Coil inductance increases as iron / steel object (S ) gets closer, because lines of magnetic flux can flow through the iron, making the effective path shorter. Inductive proximity sensor Instrum. & Control Eng. for Energy Systems - Ch. 3 Sensors and Transducers 48 S
Inductive sensor-proximity switch • An inductive proximity sensor has four components; • The coil, oscillator, detection circuit and output circuit. • The oscillator generates a fluctuating magnetic field the shape of a doughnut around the winding of the coil that locates in the device’s sensing face. • When a metal object moves into the inductive proximity sensor’s field of detection, Eddy circuits build up in the metallic object, magnetically push back, and finally reduce the Inductive sensor’s own oscillation field. Instrum. & Control Eng. for Energy Systems - Ch. 3 Sensors and Transducers 49
LVDT – Bourdon Tube Pressure Gauge • LVDT can be combined with a Bourdon tube • LVDT converts displacement into an electrical signal • The signal can be displayed on an electrical device calibrated in terms of pressure 50Introduction to Instrumntaion Eng‘g - Ch. 3 Sensors and Transducers
LVDT and Bellow Combination • Bellows produce small displacement • Amplified by LVDT and potentiometer 51Introduction to Instrumntaion Eng‘g - Ch. 3 Sensors and Transducers
Overview • Introduction • Classification of sensors • Passive sensors • Active sensors • Thermoelectric transducers • Photoelectric transducers • Piezoelectric transducers • Hall-effect transudes • Tachometric generators 52Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
Active Sensors - Thermocouple • Thermoelectric transducers provide electrical signal in response to change in temperature • Example: Thermocouple • Thermocouple: Converts thermal energy into electrical energy • Application: To measure temperature • Contains a pair of dissimilar metal wires joined together at one end (sensing or hot junction) and terminated at the other end (reference or cold junction) • When a temperature difference exists b/n the sensing junction and the reference, an emf is produced 53 )(....)()( 21 2 2 2 121 TTTTTTEemfInduced −≈+−+−== αβα Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
Active Sensors – Thermocouple … • Typical material combinations used as thermocouples • To get higher output emf • Connect two or more Thermocouples in series • For measurement of average temperature • Connect Thermocouples in parallel 54 Type Materials Temp. Range Output voltage (mV) T Copper-Constantan -2000 C to 3500 C -5.6 to 17.82 J Iron-Constantan 0 to 7500 C 0 to 42.28 E Chromel-Constantan -200 to 9000 C -8.82 to 68.78 K Chromel-Alumel -200 to 12500 C -5.97 to 50.63 R Platinum = 13% Rhodium = 87% 0 to 14500 C 0 to 16.74 Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
Active Sensors – Thermocouple … • Applications • Temperature measurement • Voltage measurement • Rectifier based rms indications are waveform dependent • They are normally designed for sinusoidal signals • Hence, error for non-sinusoidal signals • Use thermocouple based voltmeters • Here, temperature of a hot junction is proportional to the true rms value of the current 55Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
Active Sensors – Thermocouple Meter • The measured a.c. voltage signal is applied to a heater element • A thermocouple senses the temperature of the heater due to heat generated ( ) • The d.c. voltage generated in the thermocouple is applied to a moving-coil meter • The thermocouple will be calibrated to read current (Irms) • AC with frequencies up to 100 MHz may be measured with thermocouple meters • One may also measure high frequency current by first rectifying the signal to DC and then measuring the DC Schematic of a thermocouple meter. 2 rmsI 56Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
Overview • Introduction • Classification of sensors • Passive sensors • Active sensors • Thermoelectric transducers • Photoelectric transducers • Piezoelectric transducers • Hall-effect transudes • Tachometric generators 57Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
Photoelectric Transducers • Versatile tools for detecting radiant energy or light • Are extensively used in instrumentation • Most known photosensitive devices include 1.Photovoltaic cells • Semiconductor junction devices used to convert radiation energy into electrical energy 58 Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
Photoelectric Transducers … 2. Photo diode • A diode that is normally reverse-biased=> Current is very low • When a photon is absorbed, electrons are freed so current starts to flow, i.e., the diode is forward biased • Has an opening in its case containing a lens which focuses incident light on the PN junction 3. Photo transistor • Also operate in reverse-biased • Responds to light intensity on its lens instead of base current 59Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
Photo transistor Instrum. & Control Eng. for Energy Systems - Ch. 4 Sensors and Transducers 60
Overview • Introduction • Classification of sensors • Passive sensors • Active sensors • Thermoelectric sensors • Photoelectric sensors • Piezoelectric sensors • Hall-effect sensors • Tachometric sensors 61Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
Piezoelelectric Transducers • Convert mechanical energy into electrical energy • If any crystal is subject to an external force F, there will be an atomic displacement, x • The displacement is related to the applied force in exactly the same way as elastic sensor such as spring • Asymmetric crystalline material such as Quartz, Rochelle Salt and Barium Tantalite produce an emf when they are placed under stress • An externally force, entering the sensor through its pressure port, applies pressure to the top of a crystal • This produces an emf across the crystal proportional to the magnitude of the applied pressure 62Introduction to Instrumntaion Eng‘g - Ch. 3 Sensors and Transducers
Piezoelelectric Transducers • A piezoelectric crystal is placed between two plate electrodes • Application of force on such a plate will develop a stress and a corresponding deformation The piezoelectric effect • With certain crystals, this deformation will produce a potential difference at the surface of the crystal • This effect is called piezoelectric effect 63Introduction to Instrumntaion Eng‘g - Ch. 3 Sensors and Transducers
Piezoelelectric Transducers … • Induced charge is proportional to the impressed force Q = d F • d= charge sensitivity (C/m2 )/(N/m2 ) = proportionality constant • Output voltage E= g t P • t= crystal thickness • P = impressed pressure • g=voltage sensitivity (V/m)/(N/m2 ) • Shear stress can also produce piezoelectric effect • Widely used as inexpensive pressure transducers for dynamic measurements 64Introduction to Instrumntaion Eng‘g - Ch. 3 Sensors and Transducers
Piezoelelectric Transducers …. • Piezoelelectric sensors have good frequency response • Example: Accelerometer 65 Piezoelectric accelerometer Introduction to Instrumntaion Eng‘g - Ch. 3 Sensors and Transducers
Piezoelelectric Transducers … • Example: Pressure Sensors • Detect pressure changes by the displacement of a thin metal or semiconductor diaphragm • A pressure applied on the diaphragm causes a strain on the piezoelectric crystal • The crystal generates voltage at the output • This voltage is proportional to the applied pressure 66Introduction to Instrumntaion Eng‘g - Ch. 3 Sensors and Transducers
Overview • Introduction • Classification of sensors • Passive sensors • Active sensors • Thermoelectric transducers • Photoelectric transducers • Piezoelectric transducers • Hall-effect transudes • Tachometric generators 67Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
Hall-effect Transducers • Hall voltage is produced when a material is • Kept perpendicular to the magnetic field and • A direct current is passed through it • The Hall-voltage is expressed as • Where • Ic: Control current flowing through the Hall-effect sensor, in Amps • β: Flux density of the magnetic field applied, in Wb/m2 • t: Thickness of the Hall-effect sensor, in meters • KH : Hall-effect coefficient • Hall-effect sensors are used to measure flux density • Can detect very week magnetic fields or small change in magnetic flux density 68 t I KV C HH β = Introduction to Instrumntaion Eng‘g - Ch. 3 Sensors and Transducers
Hall-effect Transducers … • Like active sensors, it generates voltage VH • It also need an external control current IC like passive sensors • The sensor can be used for measurement of • Magnetic quantities (B, φ) • Mobility of carriers • Very small amount of power 69Introduction to Instrumntaion Eng‘g - Ch. 3 Sensors and Transducers
Hall-effect Transducers … • Magnetic field forces electrons to concentrate on one side of the conductor (mainly uses semiconductor) • This accumulation creates emf, which is proportional to the magnetic field strength • Used in proximity sensors 70Introduction to Instrumntaion Eng‘g - Ch. 3 Sensors and Transducers
Overview • Introduction • Classification of sensors • Passive sensors • Active sensors • Thermoelectric transducers • Photoelectric transducers • Piezoelectric transducers • Hall-effect transudes • Tachometric generators 71Introduction to Instrumntaion Eng‘g - Ch. 3 Sensors and Transducers
Tachometric Generators • Tachometer – any device used to measure shaft’s rotation • Tachometric generator • A machine, when driven by a rotating mechanical force, produces an electric output proportional to the speed of rotation • Essentially a small generators • Tachometric generators connect to the rotating shaft, whose displacement is to be measured, by, e.g., • Direct coupling or • Means of belts or gears • They produce an output which primarily relates to speed • Displacement can be obtained by integrating speed • Types of Tachometric generators: Generally a.c. or d.c. 72Introduction to Instrumntaion Eng‘g - Ch. 3 Sensors and Transducers
Tachometric Generators • Voltage generated is proportional to rotation of the shaft 73 D.C. tachometric generator A.C. tachometric generator

More Related Content

PPTX
Radiation pyrometer
byVivek5103
 
PPTX
Linear Variable Differential Transducer(LVDT)
byEpuri Chiranjeevi
 
PPT
Recorders.ppt
byANURUPAa
 
PPTX
Static characteristics - Mechanical Measurements
byAmeya Nijasure
 
PPTX
INTRODUCTION TO LVDT,RVDT and Potentiometer
bySACHINNikam39
 
DOCX
Data Acquisition System
byPriyanka Goswami
 
PDF
Basics of Sensors & Transducers
byBurdwan University
 
PPTX
OPTICAL PYROMETER
byAnkit Mistry
 
Radiation pyrometer
byVivek5103
 
Linear Variable Differential Transducer(LVDT)
byEpuri Chiranjeevi
 
Recorders.ppt
byANURUPAa
 
Static characteristics - Mechanical Measurements
byAmeya Nijasure
 
INTRODUCTION TO LVDT,RVDT and Potentiometer
bySACHINNikam39
 
Data Acquisition System
byPriyanka Goswami
 
Basics of Sensors & Transducers
byBurdwan University
 
OPTICAL PYROMETER
byAnkit Mistry
 

What's hot

PPTX
Classification of transducer
byLingalaSowjanya
 
PPTX
Measuring instruments
bySayyed Raza
 
PPTX
Displacement measurement
bywasim shah
 
PPTX
PYROMETER
byGulfam Hussain
 
PPT
Sensor and transducers lect 1
byprashant tripathi
 
PPTX
Photoelectric sensors
byDarshil Shah
 
PPT
Static and Dynamic characteristics of Measuring Instrument
byArchana Vijayakumar
 
PPTX
Capacitive transducers
bykaroline Enoch
 
PPT
Transducers
byNaveen Sihag
 
PPTX
Temperature Transducers
byAsim Raza
 
PPTX
Electronic Measurement and Instrumentation
byManipal University Jaipur
 
PPTX
Sensors and its types
byNutronicsIndia
 
PPTX
Piezoelectric transducer
byArchi Jain
 
PPTX
Functional elements of an instrument
bySanthosh Kumar
 
PPTX
Mm ppt
bymahesh kumar
 
PPTX
Electronics measurement and instrumentation ppt
byImranAhmad225
 
PPTX
bimetallic strip
byarunkumar6836
 
PPTX
SENSORS A DISCUSSION
byPraveen Kumar
 
PPTX
Classification of transducers
byManash Deka
 
PPTX
Measurement
byMohamed EL Fattah
 
Classification of transducer
byLingalaSowjanya
 
Measuring instruments
bySayyed Raza
 
Displacement measurement
bywasim shah
 
PYROMETER
byGulfam Hussain
 
Sensor and transducers lect 1
byprashant tripathi
 
Photoelectric sensors
byDarshil Shah
 
Static and Dynamic characteristics of Measuring Instrument
byArchana Vijayakumar
 
Capacitive transducers
bykaroline Enoch
 
Transducers
byNaveen Sihag
 
Temperature Transducers
byAsim Raza
 
Electronic Measurement and Instrumentation
byManipal University Jaipur
 
Sensors and its types
byNutronicsIndia
 
Piezoelectric transducer
byArchi Jain
 
Functional elements of an instrument
bySanthosh Kumar
 
Mm ppt
bymahesh kumar
 
Electronics measurement and instrumentation ppt
byImranAhmad225
 
bimetallic strip
byarunkumar6836
 
SENSORS A DISCUSSION
byPraveen Kumar
 
Classification of transducers
byManash Deka
 
Measurement
byMohamed EL Fattah
 

Viewers also liked

PDF
25633083 sensors-and-transducers
byIndranil bhattacharyya
 
PPTX
Introduction to sensors & transducers by Bapi Kumar Das
byB.k. Das
 
PPT
Introduction to sensors
byMIGUEL ANGEL CONTRERAS DOMINGUEZ
 
PPTX
Sensors and transducers
byAnish Das
 
PPT
Pe 4030 ch 2 sensors and transducers part 1 final sept 20 2016
byCharlton Inao
 
PPTX
Transducers
byAmrit Aggarwal
 
25633083 sensors-and-transducers
byIndranil bhattacharyya
 
Introduction to sensors & transducers by Bapi Kumar Das
byB.k. Das
 
Introduction to sensors
byMIGUEL ANGEL CONTRERAS DOMINGUEZ
 
Sensors and transducers
byAnish Das
 
Pe 4030 ch 2 sensors and transducers part 1 final sept 20 2016
byCharlton Inao
 
Transducers
byAmrit Aggarwal
 

Similar to Cn3 sensors and transducers-12

PPT
cn3-Sensors and Transducers-12.ppt
byMathsmaster,Potostudy
 
PPTX
sensors and transducers Module 1 n 2
byAnchal bassi
 
PDF
Chapter Three instrumentation studing.pdf
byyohannestafete
 
PPTX
TRANSDUCERS OWN.pptx
byModernVickypedia
 
PPTX
Chapter-3 Transducer.pptxygggghhhhhhhhhhh
byteddiyfentaw
 
PPT
EMI-tansducers
byÐîgëñ Tàìlør
 
PPT
TRANSDUCERS (2).ppt
byVigneshwariMahamuni1
 
PPT
Chapter 6 TRANSDUCERS.ppt
byprakash65044
 
PPTX
Instrumentation Sensors Transducers_Lecture Part 2 Sept -2024.pptx
byrajeeb21ug
 
PPTX
Transducer
byAshok Mannava
 
PPTX
Unit 1 SA.pptx
bySwatiMemane1
 
PDF
classification of Sensor & Transducer...
bybhowmikdip555
 
PDF
CH-3 Transduser.pdfvnjjnnnfsssvnnnngfddgnnn
byTemesgenErena
 
PPTX
Sensor presentation, INSTRUMENTATION & MEASUREMENT
byRamanKhanal2
 
PPTX
Presentation123456789009876543212345.pptx
byarghya0001
 
PPT
BMI-1.3.ppt
byYadav Raj
 
PPTX
Transducers (1)
byLingalaSowjanya
 
PPT
9343197.ppt
byVikrantKadam12
 
PPT
Transducers_sensors.ppt
byvlkumashankardeekshi th
 
PDF
Transducers: a CLIL lesson
byschool
 
cn3-Sensors and Transducers-12.ppt
byMathsmaster,Potostudy
 
sensors and transducers Module 1 n 2
byAnchal bassi
 
Chapter Three instrumentation studing.pdf
byyohannestafete
 
TRANSDUCERS OWN.pptx
byModernVickypedia
 
Chapter-3 Transducer.pptxygggghhhhhhhhhhh
byteddiyfentaw
 
EMI-tansducers
byÐîgëñ Tàìlør
 
TRANSDUCERS (2).ppt
byVigneshwariMahamuni1
 
Chapter 6 TRANSDUCERS.ppt
byprakash65044
 
Instrumentation Sensors Transducers_Lecture Part 2 Sept -2024.pptx
byrajeeb21ug
 
Transducer
byAshok Mannava
 
Unit 1 SA.pptx
bySwatiMemane1
 
classification of Sensor & Transducer...
bybhowmikdip555
 
CH-3 Transduser.pdfvnjjnnnfsssvnnnngfddgnnn
byTemesgenErena
 
Sensor presentation, INSTRUMENTATION & MEASUREMENT
byRamanKhanal2
 
Presentation123456789009876543212345.pptx
byarghya0001
 
BMI-1.3.ppt
byYadav Raj
 
Transducers (1)
byLingalaSowjanya
 
9343197.ppt
byVikrantKadam12
 
Transducers_sensors.ppt
byvlkumashankardeekshi th
 
Transducers: a CLIL lesson
byschool
 

More from misgina Mengesha

PPTX
Lecture9
bymisgina Mengesha
 
PPTX
Lecture8
bymisgina Mengesha
 
PDF
Lecture6
bymisgina Mengesha
 
PDF
Lecture5
bymisgina Mengesha
 
PDF
Lecture5(1)
bymisgina Mengesha
 
PPTX
Lecture4
bymisgina Mengesha
 
PPTX
Lecture3
bymisgina Mengesha
 
PPTX
Lecture2
bymisgina Mengesha
 
PPTX
Lecture1
bymisgina Mengesha
 
PDF
Sprabq8
bymisgina Mengesha
 
PPT
Sensors2006
bymisgina Mengesha
 
PPT
Sensors31
bymisgina Mengesha
 
PPT
Sensing for robotics and control s set13
bymisgina Mengesha
 
PPT
Introduction to sensors
bymisgina Mengesha
 
PPT
Cn3 sensors and transducers-1
bymisgina Mengesha
 
PPT
480 sensors
bymisgina Mengesha
 
PPTX
Wwwwww
bymisgina Mengesha
 
Lecture9
bymisgina Mengesha
 
Lecture8
bymisgina Mengesha
 
Lecture6
bymisgina Mengesha
 
Lecture5
bymisgina Mengesha
 
Lecture5(1)
bymisgina Mengesha
 
Lecture4
bymisgina Mengesha
 
Lecture3
bymisgina Mengesha
 
Lecture2
bymisgina Mengesha
 
Lecture1
bymisgina Mengesha
 
Sprabq8
bymisgina Mengesha
 
Sensors2006
bymisgina Mengesha
 
Sensors31
bymisgina Mengesha
 
Sensing for robotics and control s set13
bymisgina Mengesha
 
Introduction to sensors
bymisgina Mengesha
 
Cn3 sensors and transducers-1
bymisgina Mengesha
 
480 sensors
bymisgina Mengesha
 
Wwwwww
bymisgina Mengesha
 

Recently uploaded

PPTX
How Does LNG Regasification Work | INOXCVA
byINOXCVA
 
PDF
engineering management chapter 5 ppt presentation
byericaangelatoledo06
 
PDF
Rajesh Prasad- Brief Profile with educational, professional highlights
byRajesh Prasad
 
PDF
Module 4 python programming-1BPLCK105B-2025 by Dr.SV.pdf
bySURESHA V
 
PPTX
Presentation-WPS Office.pptx afgouvhyhgfccf
byEndaleTimerga
 
PPTX
Basic Volume Mass Relationship and unit weight as function of volumetric wate...
byMahmoodKhalid11
 
PDF
Model QP 2025 scheme Q &A- Module 1 and 2.pdf
bySURESHA V
 
PPTX
Batch-1(End Semester) Student Of Shree Durga Tech. PPT.pptx
byrashesw1122s
 
PPTX
What Green Hydrogen Is Definition: Hydrogen produced via electrolysis of wate...
byThit57
 
PPTX
Introduction to AI and Applications Module-4.pptx
byKalaiselviSubramania2
 
PPTX
operating_systems.pptx m,nm,nm,n,nm,n,nm,nikl
bykirthigaaiml
 
PPT
Ceramic Matrix Composites Slide from Composite Materials
byUsman635773
 
PDF
Ericsson 6230 Training Module Document.pdf
byMd Bellal Hossain
 
PPTX
ISO 13485.2016 Awareness's Training material
byPrakashSivan
 
PDF
Computer Network Lab Manual ssit -kavya r.pdf or Computer Network Lab Manual ...
bykavya R
 
PDF
Decision-Support-Systems-and-Decision-Making-Processes.pdf
byPatankarNikhil
 
PDF
Basics of Electronics Task by Vivaan Jo Varghese.pdf
byVivaan Jo Varghese
 
PPTX
Value engineering and cost analysis with case study
byhp9879098082
 
PDF
PROBLEM SLOVING AND PYTHON PROGRAMMING UNIT 3.pdf
byA R SIVANESH M.E., QIP-PG (Cyber Security)., (Ph.D)
 
PDF
Soil Compressibility (Elastic Settlement).pdf
byMahmoodKhalid11
 
How Does LNG Regasification Work | INOXCVA
byINOXCVA
 
engineering management chapter 5 ppt presentation
byericaangelatoledo06
 
Rajesh Prasad- Brief Profile with educational, professional highlights
byRajesh Prasad
 
Module 4 python programming-1BPLCK105B-2025 by Dr.SV.pdf
bySURESHA V
 
Presentation-WPS Office.pptx afgouvhyhgfccf
byEndaleTimerga
 
Basic Volume Mass Relationship and unit weight as function of volumetric wate...
byMahmoodKhalid11
 
Model QP 2025 scheme Q &A- Module 1 and 2.pdf
bySURESHA V
 
Batch-1(End Semester) Student Of Shree Durga Tech. PPT.pptx
byrashesw1122s
 
What Green Hydrogen Is Definition: Hydrogen produced via electrolysis of wate...
byThit57
 
Introduction to AI and Applications Module-4.pptx
byKalaiselviSubramania2
 
operating_systems.pptx m,nm,nm,n,nm,n,nm,nikl
bykirthigaaiml
 
Ceramic Matrix Composites Slide from Composite Materials
byUsman635773
 
Ericsson 6230 Training Module Document.pdf
byMd Bellal Hossain
 
ISO 13485.2016 Awareness's Training material
byPrakashSivan
 
Computer Network Lab Manual ssit -kavya r.pdf or Computer Network Lab Manual ...
bykavya R
 
Decision-Support-Systems-and-Decision-Making-Processes.pdf
byPatankarNikhil
 
Basics of Electronics Task by Vivaan Jo Varghese.pdf
byVivaan Jo Varghese
 
Value engineering and cost analysis with case study
byhp9879098082
 
PROBLEM SLOVING AND PYTHON PROGRAMMING UNIT 3.pdf
byA R SIVANESH M.E., QIP-PG (Cyber Security)., (Ph.D)
 
Soil Compressibility (Elastic Settlement).pdf
byMahmoodKhalid11
 

Cn3 sensors and transducers-12

  • 1.
    Chapter 3: Sensorsand/or Transducers 1 Introduction to Different Types of Sensors
  • 2.
  • 3.
    Application off sensor Greycode encoder reflection sensor 3
  • 4.
    Application of sensor Infraredreflection sensor 4
  • 5.
    Application of sensors Instrum.& Control Eng. for Energy Systems - Ch. 4 Sensors and Transducers 5
  • 6.
    Goals of theChapter • Define classification of sensors and some terminologies • Introduce various types of sensors for measurement purpose and their applications • Example: Displacement, motion, level, pressure, temperature, … 6Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
  • 7.
    Overview • Introduction • Classificationof sensors • Passive sensors • Active sensors 7Instrum. & Control Eng. for Energy Systems - Ch. 4 Sensors and Transducers
  • 8.
    Introduction • Sensors • Elementswhich generate variation of electrical quantities (EQ) in response to variation of non-electrical quantities (NEQ) • Examples of EQ • Temperature, displacement, humidity, fluid flow, speed, pressure,… • Sensor are sometimes called transducers 8 Sensing element Signal conditioning element Signal conversion/ processing element Output presentation Non-electrical quantity Electrical signal Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
  • 9.
    Introduction … • Advantagesof using sensors include 1. Mechanical effects such as friction is reduced to the minimum possibility 2. Very small power is required for controlling the electrical system 3. The electrical output can be amplified to any desired level 4. The electrical output can be detected and recorded remotely at a distance from the sensing medium and use modern digital computers 5. etc … 9Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
  • 10.
    Introduction - Useof Sensors 1. Information gathering: Provide data for display purpose • This gives an understanding of the current status of the system parameters • Example: Car speed sensor and speedometer, which records the speed of a car against time 1. System control: Signal from the sensor is an input to a controller 10 Controller System under control Output signalDesires signal Sensor Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
  • 11.
    Introduction – SensorRequirements • The main function of a sensor is to respond only for the measurement under specified limits for which it is designed • Sensors should meet the following basic requirements 1. Ruggedness: Capable of withstanding overload • Some safety arrangements should be provided for overload protection 1. Linearity: Its input-output characteristics must be linear 2. Repeatability: It should reproduce the same output signal when the same input is applied again and again 3. High output signal quality 4. High reliability and stability 5. Good dynamic response 6. No hysteresis, … 11Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
  • 12.
    Overview • Introduction • Classificationof sensors • Passive sensors • Active sensors 12Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
  • 13.
    Classification of Sensors •Sensors can be divided on the basis of • Method of applications • Method of energy conversion used • Nature of output signals • Electrical principle • In general, the classification of sensors is given by • Primary and secondary sensors • Active and passive sensors • Analog and Digital sensors 13Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
  • 14.
    Primary and SecondarySensors • Classification is based on the method of application • Primary sensor • The input NEQ is directly sensed by the sensor • The physical phenomenon is converted into another NEQ • Secondary sensor • The output of the primary sensor is fed to another (secondary) sensor that converts the NEQ to EQ 14 Load cell Strain- gauge NEQ Secondary sensor Weight (Force ∆F) Primary sensor NEQ EQ Displacement ∆d Resistance ∆R Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
  • 15.
    Active and PassiveSensor • Classification based on the basis of energy conversion • Active sensor • Generates voltage/current in response to NEQ variation • Are also called self-generating sensors • Normally, the output of active sensors is in µV or mV • Examples • Thermocouples: A change in temperature produces output voltage • Photovoltaic cell: Change solar energy into voltage • Hall-effect sensors, … 15 Active sensors NEQ Ex. Temperature EQ Voltage or current Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
  • 16.
    Active and Passive…. • Passive sensors • Sensors that does not generate voltage or current, but produce element variation in R, L, or C • Need an additional circuit to produce voltage or current variation • Examples • Thermistor: Change in temperature leads to change in resistance • Photo resistor: Change in light leads to change in resistance • Straingauge: Change in length or position into change in resistance) • LVDT, Mic 16 Passive sensors NEQ ∆R, ∆L, ∆C Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
  • 17.
    Analog and DigitalSensors • Classification based on the nature of the output signal • Analog sensor • Gives an output that varies continuously as the input changes • Output can have infinite number of values within the sensor’s range • Digital sensor • Has an output that varies in discrete steps or pulses or sampled form and so can have a finite number of values • E.g., Revolution counter: A cam, attached to a revolving body whose motion is being measured, opens and closes a switch • The switching operations are counted by an electronic counter 17Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
  • 18.
    Sensor Classification • Sensorscan also be classified according to the application • Example • Measurement of displacement, motion, temperature, intensity, sensors 18Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
  • 19.
    Overview • Introduction • Classificationof sensors • Passive sensors • Resistive sensors • Potentiometers, temperature dependent resistors, strain gauge, photoconductors (photoresistors), Piezoresistive • Capacitive sensors • Inductive sensors • Active sensors 19Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
  • 20.
    Resistive Sensors -Potentiometer • Examples: Displacement, liquid level (in petrol-tank level indicator) using potentiometer or rheostat • Convert s linear (translatory) or angular (rotary) displacement into a change of resistance in the resistive element provided with a movable contact 20 • Petrol-tank level indicator • Change in petrol level moves a potentiometer arm • Output signal is proportion to the external voltage source applied across the potentiometer • The energy in the output signal comes from the external power source Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
  • 21.
    Resistive Sensors –Potentiometer … • A linear or rotary movement of a moving contact on a slide wire indicates the magnitude of the variable as a change in resistance which can easily be converted by a proper electrical circuit into measurements of volt or current 21Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
  • 22.
    Resistive Sensors –Temperature Dependent Resistors • Two classes of thermal resistors are • Metallic element • Semiconductor • For most metals, the resistance increases with increase in temperature • Where α is the temperature coefficient of resistance and given as • Example: Platinum • Has a linear temperature-resistance characteristics • Reproducible over a wide range of temperature • Platinum Thermometers are used for temperature measurement 22 ]1[...]1[)(R 0 2 210 TRTTRT ααα +≈+++= 0 1 R R T ∆ ∆ =α Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
  • 23.
    Resistive Sensors –Temperature Dependent… • Semiconductor based resistance thermometers elements • The resistance of such elements decreases with increasing temperature • Example: Thermistor • The resistance-temperature relationship is non-linear and governed by • Where R0 is the resistance at absolute temp (in Kelvin) and β is material constant expressed in degree Kelvin • Most semiconductor materials used for thermometry possess high resistivity and high negative temperature coefficients 23 KTeRT TT 0 0 ) 11 ( 0 300;)(R 0 == −β Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
  • 24.
    Resistive Sensors –Temperature Dependent… • The temperature coefficient of resistance is • β is typically 4000 k and for T = 300k, 24 2 0 1 TR R T β α −= ∆ ∆ = 044.0 300 4000 22 −=−=−= T β α Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
  • 25.
    Resistive Sensors –Strain Gauges • Is a secondary transducer that senses tensile or compressive strain in a particular direction at a point on the surface of a body or structure • Used to measure force, pressure, displacement • Where e=∆l/l is the strain • The resistance of an unstrained conductor is given as • Under strained condition, resistance of conductor changes by ∆R because of ∆l, ∆A, and/or ∆ρ 25 )(R eR= A l ρ=R Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
  • 26.
    Resistive Sensors –Strain Gauges … • To find the change in resistance ∆R, • Dividing both sides by R, we get the fractional change as • Let us define eL = ∆l/l as the longitudinal stain and eT as the transversal strain • Also assume that eT = -νeL ,where ν is the Poisson’s Ratio 26 ρ ρρ ρ ρ ∆+∆−∆= ∆ ∂ ∂ +∆ ∂ ∂ +∆ ∂ ∂ =∆ A l A A l l A R A A R l l R 2 R ρ ρ∆ + ∆ − ∆ = ∆ A A l l R R Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
  • 27.
    Resistive Sensors –Strain Gauges … • Then, Gauge Factor, G is defined as • G is also known as Strain-Sensitivity factor; rearranging terms, we get • Where is the Piezoresistive term • For most metals, the Piezoresistive term is about 0.4 and 0.2 < ν < 0.5 • Thus, Gauge factor for metallic stain gauges is in the range 2.0–2.5 (not sensitive) 27 Le G ρρ υ / )21( ∆ ++= Le ρρ/∆ Lell G R/R / R/R ∆ = ∆ ∆ = Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
  • 28.
    Resistive Sensors –Strain Gauges … • Sensitive measurements require very high Gauge factors in the range of 100-300 • Such factor can be obtained from semiconductor strain gauges • Due to the significant contribution from the Piezoresistive term 28Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
  • 29.
    Piezoresistive Pressure Sensor •Piezoresistivity is a strain dependent resistivity in a single crystal semiconductor • When pressure is applied to the diaphragm, it causes a strain in the resistor • Resistance change is proportional to this strain, and hence change in pressure 29Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
  • 30.
    Resistive Sensors –Photoconductor • Are light sensitive resistors with non-linear negative temperature coefficient • Are resistive optical radiation transducers • Photoconductors have resistance variation that depends on illumination • The resistance illumination characteristics is given by • Where RD is Dark Resistance and E is illumination level in Lux • Photoconductors are used in • Cameras, light sensors in spectrophotometer • Counting systems where an object interrupts a light beam hitting the photoconductor, etc. 30 E DeR α− =R Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
  • 31.
    Photoconductive Transducers • Avoltage is impressed on the semiconductor material • When light strikes the semiconductor material, there is a decrease in the resistance resulting in an increase in the current indicated by the meter • They enjoy a wide range of applications and are useful for measurement of radiation at all levels • The schematic diagram of this device is shown below 31Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
  • 32.
    Photovoltaic Cells • Whenlight strikes the barrier between the transparent metal layer and the semiconductor material, a voltage is generated • The output of the device is strongly dependent on the load resistance R • The most widely used applications is the light exposure meter in photographic work Schematic of a photovoltaic cell. 32Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
  • 33.
    Overview • Introduction • Classificationof sensors • Passive sensors • Resistive sensors • Capacitive sensors • Inductive sensors • Active sensors 33Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
  • 34.
    Capacitive Transducers • Theparallel plate capacitance is given by • d= distance between plates • A=overlapping area • ε0 = 8.85x10-12 F/m is the absolute permittivity, εr =dielectric constant (εr =1 for air and εr =3 for plastics) d A C rεε0= • Displacement measurement can be achieved by varying d, overlapping area A and the dielectric constant Schematic of a capacitive transducer. 34Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
  • 35.
    Capacitive Transducers –Liquid Level Measurement • A simple application of such a transducer is for liquid measurement • The dielectric constant changes between the electrodes as long as there is a change in the level of the liquid Capacitive transducer for liquid level measurement. 35Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
  • 36.
    Capacitive Transducers –Liquid Level Measurement • A simple application of such a transducer is for liquid measurement • The dielectric constant changes between the electrodes as long as there is a change in the level of the liquid Capacitive transducer for liquid level measurement. 36Introduction to Instrumntaion Eng‘g - Ch. 3 Sensors and Transducers
  • 37.
    Capacitive sensors –Pressure Sensor • Use electrical property of a capacitor to measure the displacement • Diaphragm: elastic pressure senor displaced in proportion to change in pressure • Acts as a plate of a capacitor 37Introduction to Instrumntaion Eng‘g - Ch. 3 Sensors and Transducers
  • 38.
    Capacitive Sensor –Proximity Switch • A capacitive sensor functions like a typical capacitor. • The metal plate in the end of the sensor electrically connects to the oscillator, and the object to be sensed acts as the second plate. • When this sensor receives power, the oscillator detects the external capacitance between the target and the internal sensor plate. Instrum. & Control Eng. for Energy Systems - Ch. 3 Sensors and Transducers 38
  • 39.
    Capacitive Sensor –Proximity Switch 39Introduction to Instrumntaion Eng‘g - Ch. 3 Sensors and Transducers • This arrangement completes the circuit and provides the necessary feedback path for the output circuit to evaluate. • Capacitance increases as any object (P) gets closer because additional capacitance paths C2 & C3 are added and increase in value as the separation reduces. C1 is always present. C1 C3 C2 P
  • 40.
    Capacitive Sensor –Proximity Switch Instrum. & Control Eng. for Energy Systems - Ch. 3 Sensors and Transducers 40
  • 41.
    Capacitive Transducers -Linear Displacement • Variable area capacitance displacement transducer Where: • ra=inner cylinder radius • rb=outer cylinder radius • L=length of the cylinder 41Introduction to Instrumntaion Eng‘g - Ch. 3 Sensors and Transducers
  • 42.
    Capacitive sensors • Applicationof capacitive sensors Instrum. & Control Eng. for Energy Systems - Ch. 4 Sensors and Transducers 42
  • 43.
    Overview • Introduction • Classificationof sensors • Passive sensors • Resistive sensors • Capacitive sensors • Inductive sensors • Active sensors 43Introduction to Instrumntaion Eng‘g - Ch. 3Sensors and Transducers
  • 44.
    Inductive Sensors • Fora coil of n turns, the inductance L is given by • Where • n: Number of turns of the coil • l: Mean length of the magnetic path • A: Area of the magnetic path • µ: Permeability of the magnetic material • R: Magnetic reluctance of the circuit • Application of inductive sensors • Force, displacement, pressure, … • Inductance variation can be in the form of • Self inductance or • Mutual inductance: e.g., differential transformer 44 R n l n AL 22 == µ Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
  • 45.
    • Input voltage(alternating current): One primary coil • There will be a magnetic coupling between the core and the coils • Output voltage: Two secondary coils connected in series • Operates using the principle of variation of mutual inductance Linear Variable Differential Transformer (LVDT) Schematic diagram of a differential transformer • The output voltage is a function of the core’s displacement • Widely used for translating linear motion into an electrical signal 45Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
  • 46.
    LVDT - OutputCharacteristics Output characteristics of an LVDT 46Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
  • 47.
    LVDT – Applications •Measure linear mechanical displacement • Provides resolution about 0.05mm, operating range from ± 0.1mm to ± 300 mm, accuracy of ± 0.5% of full-scale reading • The input ac excitation of LVDT can range in frequency from 50 Hz to 20kHz • Used to measure position in control systems and precision manufacturing • Can also be used to measure force, pressure, acceleration, etc.. 47Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
  • 48.
    Inductive Sensors –proximityswitch • Coil inductance increases as iron / steel object (S ) gets closer, because lines of magnetic flux can flow through the iron, making the effective path shorter. Inductive proximity sensor Instrum. & Control Eng. for Energy Systems - Ch. 3 Sensors and Transducers 48 S
  • 49.
    Inductive sensor-proximity switch •An inductive proximity sensor has four components; • The coil, oscillator, detection circuit and output circuit. • The oscillator generates a fluctuating magnetic field the shape of a doughnut around the winding of the coil that locates in the device’s sensing face. • When a metal object moves into the inductive proximity sensor’s field of detection, Eddy circuits build up in the metallic object, magnetically push back, and finally reduce the Inductive sensor’s own oscillation field. Instrum. & Control Eng. for Energy Systems - Ch. 3 Sensors and Transducers 49
  • 50.
    LVDT – BourdonTube Pressure Gauge • LVDT can be combined with a Bourdon tube • LVDT converts displacement into an electrical signal • The signal can be displayed on an electrical device calibrated in terms of pressure 50Introduction to Instrumntaion Eng‘g - Ch. 3 Sensors and Transducers
  • 51.
    LVDT and BellowCombination • Bellows produce small displacement • Amplified by LVDT and potentiometer 51Introduction to Instrumntaion Eng‘g - Ch. 3 Sensors and Transducers
  • 52.
    Overview • Introduction • Classificationof sensors • Passive sensors • Active sensors • Thermoelectric transducers • Photoelectric transducers • Piezoelectric transducers • Hall-effect transudes • Tachometric generators 52Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
  • 53.
    Active Sensors -Thermocouple • Thermoelectric transducers provide electrical signal in response to change in temperature • Example: Thermocouple • Thermocouple: Converts thermal energy into electrical energy • Application: To measure temperature • Contains a pair of dissimilar metal wires joined together at one end (sensing or hot junction) and terminated at the other end (reference or cold junction) • When a temperature difference exists b/n the sensing junction and the reference, an emf is produced 53 )(....)()( 21 2 2 2 121 TTTTTTEemfInduced −≈+−+−== αβα Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
  • 54.
    Active Sensors –Thermocouple … • Typical material combinations used as thermocouples • To get higher output emf • Connect two or more Thermocouples in series • For measurement of average temperature • Connect Thermocouples in parallel 54 Type Materials Temp. Range Output voltage (mV) T Copper-Constantan -2000 C to 3500 C -5.6 to 17.82 J Iron-Constantan 0 to 7500 C 0 to 42.28 E Chromel-Constantan -200 to 9000 C -8.82 to 68.78 K Chromel-Alumel -200 to 12500 C -5.97 to 50.63 R Platinum = 13% Rhodium = 87% 0 to 14500 C 0 to 16.74 Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
  • 55.
    Active Sensors –Thermocouple … • Applications • Temperature measurement • Voltage measurement • Rectifier based rms indications are waveform dependent • They are normally designed for sinusoidal signals • Hence, error for non-sinusoidal signals • Use thermocouple based voltmeters • Here, temperature of a hot junction is proportional to the true rms value of the current 55Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
  • 56.
    Active Sensors –Thermocouple Meter • The measured a.c. voltage signal is applied to a heater element • A thermocouple senses the temperature of the heater due to heat generated ( ) • The d.c. voltage generated in the thermocouple is applied to a moving-coil meter • The thermocouple will be calibrated to read current (Irms) • AC with frequencies up to 100 MHz may be measured with thermocouple meters • One may also measure high frequency current by first rectifying the signal to DC and then measuring the DC Schematic of a thermocouple meter. 2 rmsI 56Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
  • 57.
    Overview • Introduction • Classificationof sensors • Passive sensors • Active sensors • Thermoelectric transducers • Photoelectric transducers • Piezoelectric transducers • Hall-effect transudes • Tachometric generators 57Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
  • 58.
    Photoelectric Transducers • Versatiletools for detecting radiant energy or light • Are extensively used in instrumentation • Most known photosensitive devices include 1.Photovoltaic cells • Semiconductor junction devices used to convert radiation energy into electrical energy 58 Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
  • 59.
    Photoelectric Transducers … 2.Photo diode • A diode that is normally reverse-biased=> Current is very low • When a photon is absorbed, electrons are freed so current starts to flow, i.e., the diode is forward biased • Has an opening in its case containing a lens which focuses incident light on the PN junction 3. Photo transistor • Also operate in reverse-biased • Responds to light intensity on its lens instead of base current 59Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
  • 60.
    Photo transistor Instrum. &Control Eng. for Energy Systems - Ch. 4 Sensors and Transducers 60
  • 61.
    Overview • Introduction • Classificationof sensors • Passive sensors • Active sensors • Thermoelectric sensors • Photoelectric sensors • Piezoelectric sensors • Hall-effect sensors • Tachometric sensors 61Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
  • 62.
    Piezoelelectric Transducers • Convertmechanical energy into electrical energy • If any crystal is subject to an external force F, there will be an atomic displacement, x • The displacement is related to the applied force in exactly the same way as elastic sensor such as spring • Asymmetric crystalline material such as Quartz, Rochelle Salt and Barium Tantalite produce an emf when they are placed under stress • An externally force, entering the sensor through its pressure port, applies pressure to the top of a crystal • This produces an emf across the crystal proportional to the magnitude of the applied pressure 62Introduction to Instrumntaion Eng‘g - Ch. 3 Sensors and Transducers
  • 63.
    Piezoelelectric Transducers • Apiezoelectric crystal is placed between two plate electrodes • Application of force on such a plate will develop a stress and a corresponding deformation The piezoelectric effect • With certain crystals, this deformation will produce a potential difference at the surface of the crystal • This effect is called piezoelectric effect 63Introduction to Instrumntaion Eng‘g - Ch. 3 Sensors and Transducers
  • 64.
    Piezoelelectric Transducers … •Induced charge is proportional to the impressed force Q = d F • d= charge sensitivity (C/m2 )/(N/m2 ) = proportionality constant • Output voltage E= g t P • t= crystal thickness • P = impressed pressure • g=voltage sensitivity (V/m)/(N/m2 ) • Shear stress can also produce piezoelectric effect • Widely used as inexpensive pressure transducers for dynamic measurements 64Introduction to Instrumntaion Eng‘g - Ch. 3 Sensors and Transducers
  • 65.
    Piezoelelectric Transducers …. •Piezoelelectric sensors have good frequency response • Example: Accelerometer 65 Piezoelectric accelerometer Introduction to Instrumntaion Eng‘g - Ch. 3 Sensors and Transducers
  • 66.
    Piezoelelectric Transducers … •Example: Pressure Sensors • Detect pressure changes by the displacement of a thin metal or semiconductor diaphragm • A pressure applied on the diaphragm causes a strain on the piezoelectric crystal • The crystal generates voltage at the output • This voltage is proportional to the applied pressure 66Introduction to Instrumntaion Eng‘g - Ch. 3 Sensors and Transducers
  • 67.
    Overview • Introduction • Classificationof sensors • Passive sensors • Active sensors • Thermoelectric transducers • Photoelectric transducers • Piezoelectric transducers • Hall-effect transudes • Tachometric generators 67Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
  • 68.
    Hall-effect Transducers • Hallvoltage is produced when a material is • Kept perpendicular to the magnetic field and • A direct current is passed through it • The Hall-voltage is expressed as • Where • Ic: Control current flowing through the Hall-effect sensor, in Amps • β: Flux density of the magnetic field applied, in Wb/m2 • t: Thickness of the Hall-effect sensor, in meters • KH : Hall-effect coefficient • Hall-effect sensors are used to measure flux density • Can detect very week magnetic fields or small change in magnetic flux density 68 t I KV C HH β = Introduction to Instrumntaion Eng‘g - Ch. 3 Sensors and Transducers
  • 69.
    Hall-effect Transducers … •Like active sensors, it generates voltage VH • It also need an external control current IC like passive sensors • The sensor can be used for measurement of • Magnetic quantities (B, φ) • Mobility of carriers • Very small amount of power 69Introduction to Instrumntaion Eng‘g - Ch. 3 Sensors and Transducers
  • 70.
    Hall-effect Transducers … •Magnetic field forces electrons to concentrate on one side of the conductor (mainly uses semiconductor) • This accumulation creates emf, which is proportional to the magnetic field strength • Used in proximity sensors 70Introduction to Instrumntaion Eng‘g - Ch. 3 Sensors and Transducers
  • 71.
    Overview • Introduction • Classificationof sensors • Passive sensors • Active sensors • Thermoelectric transducers • Photoelectric transducers • Piezoelectric transducers • Hall-effect transudes • Tachometric generators 71Introduction to Instrumntaion Eng‘g - Ch. 3 Sensors and Transducers
  • 72.
    Tachometric Generators • Tachometer– any device used to measure shaft’s rotation • Tachometric generator • A machine, when driven by a rotating mechanical force, produces an electric output proportional to the speed of rotation • Essentially a small generators • Tachometric generators connect to the rotating shaft, whose displacement is to be measured, by, e.g., • Direct coupling or • Means of belts or gears • They produce an output which primarily relates to speed • Displacement can be obtained by integrating speed • Types of Tachometric generators: Generally a.c. or d.c. 72Introduction to Instrumntaion Eng‘g - Ch. 3 Sensors and Transducers
  • 73.
    Tachometric Generators • Voltagegenerated is proportional to rotation of the shaft 73 D.C. tachometric generator A.C. tachometric generator