This document discusses different types of sensors and transducers. It begins with an introduction to sensors, defining them as devices that convert non-electrical quantities into electrical signals. It then covers various classifications of sensors including primary/secondary, active/passive, and analog/digital. Specific types of sensors are described in more detail, including resistive sensors such as potentiometers, temperature dependent resistors, and strain gauges. Capacitive and inductive sensors are also briefly mentioned. The document provides examples and equations to explain the functioning and properties of different sensors.
PLC Ladder Diagram basics, with two solved examples
For more information go to
http://shrutizpresentations.blogspot.in/2014/04/plc-ladder-diagram-basics.html
One of the welding processes that used in Engineering field is the metal inert gas welding. There are several types of welding processes similar to this, but MIG welding has its unique features.
Thanks for the colleagues who give this slides to publish.
One of the welding processes that used in Engineering field is the TIG welding. There are several types of welding processes similar to this, but tig welding has its unique features.
Thanks for the colleagues who give this slides to publish.
Gas Metal Arc Welding or MIG welding .
Gas metal arc welding (GMAW), sometimes referred to by its subtypes metal inert gas (MIG) welding or metal active gas (MAG) welding, is a welding process in which an electric arc forms between a consumable wire electrode and the workpiece metal(s), which heats the workpiece metal(s), causing them to melt and join
pulsed spray
globular spray
PLC Ladder Diagram basics, with two solved examples
For more information go to
http://shrutizpresentations.blogspot.in/2014/04/plc-ladder-diagram-basics.html
One of the welding processes that used in Engineering field is the metal inert gas welding. There are several types of welding processes similar to this, but MIG welding has its unique features.
Thanks for the colleagues who give this slides to publish.
One of the welding processes that used in Engineering field is the TIG welding. There are several types of welding processes similar to this, but tig welding has its unique features.
Thanks for the colleagues who give this slides to publish.
Gas Metal Arc Welding or MIG welding .
Gas metal arc welding (GMAW), sometimes referred to by its subtypes metal inert gas (MIG) welding or metal active gas (MAG) welding, is a welding process in which an electric arc forms between a consumable wire electrode and the workpiece metal(s), which heats the workpiece metal(s), causing them to melt and join
pulsed spray
globular spray
MIG Welding. Gas metal arc welding (GMAW), also known as MIG (metal inert gas) welding or MAG (metal active gas) welding, is a process in which an electric arc forms between an electrode and a metal workpiece, heating the metals and causing them to melt, and be joined.
In electrical engineering, a switch is an electrical component that can "make" or "break" an electrical circuit, interrupting the currentor diverting it from one conductor to another.The mechanism of a switch removes or restores the conducting path in a circuit
when it is operated. It may be operated manually, for example, a light switch or a keyboard button, may be operated by a moving
object such as a door, or may be operated by some sensing element for pressure, temperature or flow. A switch will have one or more
sets of contacts, which may operate simultaneously, sequentially, or alternately. Switches in high-powered circuits must operate
rapidly to prevent destructive arcing, and may include special features to assist in rapidly interrupting a heavy current. Multiple forms
of actuators are used for operation by hand or to sense position, level, temperature or flow.Special types are used, for example, for control of machinery, to reverse electric motors, or to sense liquid level. Many specialized forms exist. A common use is control of
lighting, where multiple switches may be wired into one circuit to allow convenient control of light fixtures.
By analogy with the devices that select one or more possible paths for electric currents, devices that route information in a computer
network are also called "switches" - these are usually more complicated than simple electromechanical toggles or pushbutton devices, and operate without direct human interaction.
This ppt covers MIG welding process using 100% CO2 gas .Here the development,equipments used,mechanism,troubleshooting and safety for MIG welding is shown
One of the welding processes that used in Engineering field is the resistance projection welding. There are several types of welding processes similar to this, but resistance projection welding has its unique features.
Thanks for the colleagues who give this slides to publish.
MIG Welding. Gas metal arc welding (GMAW), also known as MIG (metal inert gas) welding or MAG (metal active gas) welding, is a process in which an electric arc forms between an electrode and a metal workpiece, heating the metals and causing them to melt, and be joined.
In electrical engineering, a switch is an electrical component that can "make" or "break" an electrical circuit, interrupting the currentor diverting it from one conductor to another.The mechanism of a switch removes or restores the conducting path in a circuit
when it is operated. It may be operated manually, for example, a light switch or a keyboard button, may be operated by a moving
object such as a door, or may be operated by some sensing element for pressure, temperature or flow. A switch will have one or more
sets of contacts, which may operate simultaneously, sequentially, or alternately. Switches in high-powered circuits must operate
rapidly to prevent destructive arcing, and may include special features to assist in rapidly interrupting a heavy current. Multiple forms
of actuators are used for operation by hand or to sense position, level, temperature or flow.Special types are used, for example, for control of machinery, to reverse electric motors, or to sense liquid level. Many specialized forms exist. A common use is control of
lighting, where multiple switches may be wired into one circuit to allow convenient control of light fixtures.
By analogy with the devices that select one or more possible paths for electric currents, devices that route information in a computer
network are also called "switches" - these are usually more complicated than simple electromechanical toggles or pushbutton devices, and operate without direct human interaction.
This ppt covers MIG welding process using 100% CO2 gas .Here the development,equipments used,mechanism,troubleshooting and safety for MIG welding is shown
One of the welding processes that used in Engineering field is the resistance projection welding. There are several types of welding processes similar to this, but resistance projection welding has its unique features.
Thanks for the colleagues who give this slides to publish.
This article provides an introduction to the fundamental of Sensors and Transducers. It illustrates the different classifications of sensors and transducers. Explains capacitive, resistive and inductive transducers in brief. Also shows the examples under these types of transducers.
Sachpazis:Terzaghi Bearing Capacity Estimation in simple terms with Calculati...Dr.Costas Sachpazis
Terzaghi's soil bearing capacity theory, developed by Karl Terzaghi, is a fundamental principle in geotechnical engineering used to determine the bearing capacity of shallow foundations. This theory provides a method to calculate the ultimate bearing capacity of soil, which is the maximum load per unit area that the soil can support without undergoing shear failure. The Calculation HTML Code included.
Using recycled concrete aggregates (RCA) for pavements is crucial to achieving sustainability. Implementing RCA for new pavement can minimize carbon footprint, conserve natural resources, reduce harmful emissions, and lower life cycle costs. Compared to natural aggregate (NA), RCA pavement has fewer comprehensive studies and sustainability assessments.
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Hierarchical Digital Twin of a Naval Power SystemKerry Sado
A hierarchical digital twin of a Naval DC power system has been developed and experimentally verified. Similar to other state-of-the-art digital twins, this technology creates a digital replica of the physical system executed in real-time or faster, which can modify hardware controls. However, its advantage stems from distributing computational efforts by utilizing a hierarchical structure composed of lower-level digital twin blocks and a higher-level system digital twin. Each digital twin block is associated with a physical subsystem of the hardware and communicates with a singular system digital twin, which creates a system-level response. By extracting information from each level of the hierarchy, power system controls of the hardware were reconfigured autonomously. This hierarchical digital twin development offers several advantages over other digital twins, particularly in the field of naval power systems. The hierarchical structure allows for greater computational efficiency and scalability while the ability to autonomously reconfigure hardware controls offers increased flexibility and responsiveness. The hierarchical decomposition and models utilized were well aligned with the physical twin, as indicated by the maximum deviations between the developed digital twin hierarchy and the hardware.
Overview of the fundamental roles in Hydropower generation and the components involved in wider Electrical Engineering.
This paper presents the design and construction of hydroelectric dams from the hydrologist’s survey of the valley before construction, all aspects and involved disciplines, fluid dynamics, structural engineering, generation and mains frequency regulation to the very transmission of power through the network in the United Kingdom.
Author: Robbie Edward Sayers
Collaborators and co editors: Charlie Sims and Connor Healey.
(C) 2024 Robbie E. Sayers
NUMERICAL SIMULATIONS OF HEAT AND MASS TRANSFER IN CONDENSING HEAT EXCHANGERS...ssuser7dcef0
Power plants release a large amount of water vapor into the
atmosphere through the stack. The flue gas can be a potential
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Additionally, harmful acids released from the stack can be
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Condensation of vapors in flue gas is a complicated
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condenser depends on the knowledge and understanding of the
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numerical simulations of water (H2O) and sulfuric acid (H2SO4)
condensation in a flue gas condensing heat exchanger was
developed using MATLAB. Governing equations based on
mass and energy balances for the system were derived to
predict variables such as flue gas exit temperature, cooling
water outlet temperature, mole fraction and condensation rates
of water and sulfuric acid vapors. The equations were solved
using an iterative solution technique with calculations of heat
and mass transfer coefficients and physical properties.
Cosmetic shop management system project report.pdfKamal Acharya
Buying new cosmetic products is difficult. It can even be scary for those who have sensitive skin and are prone to skin trouble. The information needed to alleviate this problem is on the back of each product, but it's thought to interpret those ingredient lists unless you have a background in chemistry.
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Saudi Arabia stands as a titan in the global energy landscape, renowned for its abundant oil and gas resources. It's the largest exporter of petroleum and holds some of the world's most significant reserves. Let's delve into the top 10 oil and gas projects shaping Saudi Arabia's energy future in 2024.
6. 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
7. Overview
• Introduction
• Classification of sensors
• Passive sensors
• Active sensors
7Instrum. & Control Eng. for Energy Systems - Ch. 4 Sensors and Transducers
8. 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
9. 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
10. 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
11. 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
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 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
15. 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
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 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
18. 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
19. 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
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
• 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
32. 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
33. 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
34. 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
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 – 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
36Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
37. Capacitive Transducers – Pressure Sensor
• Components: Fixed plate, diaphragm, displaying device,
dielectric material (air)
• When the diaphragm deflects, there is change in the gap
between the two plates which in turn deflects the meter
d
C
1
α
37
• Capacitance C of the
capacitor is inversely
proportional to distance d
between the plates, i.e.,
Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
38. Capacitive Transducers - Linear Displacement
• Variable area capacitance displacement transducer
38Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
39. Overview
• Introduction
• Classification of sensors
• Passive sensors
• Resistive sensors
• Capacitive sensors
• Inductive sensors
• Active sensors
39Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
40. 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
40
R
n
l
n
AL
22
== µ
Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
41. • 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
41Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
42. LVDT - Output Characteristics
Output characteristics of an LVDT
42Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
43. 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..
43Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
44. 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
44Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
45. • When pressure is applied via the hole,
the bellow expands a distance d
• This displacement can be calibrated in
terms of pressure
• Where:
• d: distance moved by the bellows in m,
• A is cross sectional area of the bellow in m2
• λ is the stiffness of the below in N.m-1
LVDT – Bellows
• The bellow is held inside a protective casing
• Differential pressure sensor
• Used to measure low pressure
45
λ
A
d
Punknown =
Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
46. LVDT and Bellow Combination
• Bellows produce small displacement
• Amplified by LVDT and potentiometer
46Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
47. Overview
• Introduction
• Classification of sensors
• Passive sensors
• Active sensors
• Thermoelectric transducers
• Photoelectric transducers
• Piezoelectric transducers
• Hall-effect transudes
• Tachometric generators
47Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
48. 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
48
)(....)()( 21
2
2
2
121 TTTTTTEemfInduced −≈+−+−== αβα
Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
49. 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
49
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
50. 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
50Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
51. 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
51Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
52. 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
53. 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
53
Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
54. 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
54Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
56. Overview
• Introduction
• Classification of sensors
• Passive sensors
• Active sensors
• Thermoelectric transducers
• Photoelectric transducers
• Piezoelectric transducers
• Hall-effect transudes
• Tachometric generators
56Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
57. 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
57Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
58. 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
58Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
59. 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
59Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
60. Piezoelelectric Transducers ….
• Piezoelelectric sensors have good frequency response
• Example: Accelerometer
60
Piezoelectric accelerometer
Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
61. 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
61Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
62. Overview
• Introduction
• Classification of sensors
• Passive sensors
• Active sensors
• Thermoelectric transducers
• Photoelectric transducers
• Piezoelectric transducers
• Hall-effect transudes
• Tachometric generators
62Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
63. 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
63
t
I
KV C
HH
β
=
Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
64. 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
64Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
65. 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
65Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
66. Overview
• Introduction
• Classification of sensors
• Passive sensors
• Active sensors
• Thermoelectric transducers
• Photoelectric transducers
• Piezoelectric transducers
• Hall-effect transudes
• Tachometric generators
66Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
67. 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.
67Introduction to Instrumntaion Eng‘g - Ch. 4 Sensors and Transducers
68. Tachometric Generators
• Voltage generated is proportional to rotation of the shaft
68
D.C. tachometric generator A.C. tachometric generator