Magnetic concept Sensor & Transducer

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BANGLADESH UNIVERSITY OF TEXTILES
TEJGAON, DHAKA-1208
B.Sc. in Textile Engineering
Electrical and Electronic Engineering
EEE-6
 Magnetic Concept
 Sensor and transducer
Md. Asaduz-Zaman
Assistant Professor (Electrical)
Bangladesh University of Textiles
Tejgaon, Dhaka-1208
Date: 01/03/2017

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Magnetic Concept
1.6 Properties of Ferromagnetic Materials
Those materials which when placed in a magnetic field are strongly magnetized in the direction of the applied
field are called ferromagnetic material. Example: iron, nickel, cobalt etc. Ferromagnetism is the property of a
material to be strongly attracted to a magnetic field and to become a powerful magnet. Ferromagnetic materials
have following properties:
1. A ferromagnetic material is strongly attracted by a magnet.
2. In ferromagnetic materials, the magnetic lines of forces due to the applied magnetic field are strongly
attracted towards the material.
3. When a rod of ferromagnetic substance is suspended freely in a uniform magnetic field, it quickly
aligns itself in the direction of the applied field.
4. When a ferromagnetic substance is placed in a non-uniform magnetic field, it movers from weaker to
stronger regions of magnetic field.
5. All ferromagnetic materials become paramagnetic above a temperature called Curie temperature.
6. The relative permeability (µr) is greater than 1(one).
7. Magnetic susceptibility is large and positive.
8. Magnetic susceptibility decreases with the rise in temperature according to Curie-Weiss law.
9. The source of ferromagnetism is the spin of the electrons.
10. Ferromagnetic materials like Fe, Co, Ni have incomplete inner shells. These shells can be completed
by using Hund’s rule.
11. When the specimen of a ferromagnetic material is magnetized by gradually increasing the
magnetizing fields, then the change of magnetic flux through the material is not continuous but in
small discrete steps. Along the steep portion of the M-H magnetization curve, the discontinuous
rotation of the magnetic domains give rise to Barkhauszen effect.
2.6 Domain Theory of Magnetism
Within each atom, the orbiting electrons are also spinning as they revolve around the nucleus. The atom, due to
its spinning electrons, has a magnetic field associated with it. In nonmagnetic materials, the net magnetic field is
effectively zero since the magnetic fields due to the atoms of the material oppose each other. In magnetic
materials such as iron and steel, however, the magnetic fields of groups of atoms numbering in the order of 1012
are aligned, forming very small bar magnets. This group of magnetically aligned atoms is called a domain. Each
domain is a separate entity; that is, each domain is independent of the surrounding domains. For an
unmagnetized sample of magnetic material, these domains appear in a random manner, such as shown in Fig.(a).
The net magnetic field in any one direction is zero.

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Fig.: Demonstrating the domain theory of magnetism.
When an external magnetizing force is applied, the domains that are nearly aligned with the applied field will
grow at the expense of the less favorably oriented domains, such as shown in Fig.(b). Eventually, if a
sufficiently strong field is applied, all of the domains will have the orientation of the applied magnetizing force,
and any further increase in external field will not increase the strength of the magnetic flux through the core that
is a condition referred to as saturation. The elasticity of the above is evidenced by the fact that when the
magnetizing force is removed, the alignment will be lost to some measure, and the flux density will drop to BR
(residual flux density). In other words, the removal of the magnetizing force will result in the return of a number
of misaligned domains within the core. The continued alignment of a number of the domains, however, accounts
for our ability to create permanent magnets.
At a point just before saturation, the opposing unaligned domains are reduced to small cylinders of various
shapes referred to as bubbles. These bubbles can be moved within the magnetic sample through the application
of a controlling magnetic field. These magnetic bubbles form the basis of the recently designed bubble memory
system for computers.
3.6 Write short note on: Flux Density, Permeability, Reluctance, Magnetomotive Force, Magnetizing Force
Flux Density: The number of flux lines per unit area is called the flux density ( B).
A
B


B=Teslas(T), Ф =Webers(Wb), A=Square meters (m2
) and 1T=1Wb/m2
Fig. Flux density
Permeability: The permeability (μ) of a material is a measure of the ease with which magnetic flux lines can
be established in the material. Materials in which flux lines can readily be set up are said to be magnetic and to
have high permeability. The permeability of free space (vacuum) is, μ0=4πx10-7
(Wb/Am)
Practically speaking, the permeability of all nonmagnetic materials, such as copper, aluminum, wood, glass,
and air, is the same as that for free space. Materials that have permeabilities slightly less than that of free space
are said to be diamagnetic, and those with permeabilities slightly greater than that of free space are said to be

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paramagnetic. Magnetic materials, such as iron, nickel, steel, cobalt, and alloys of these metals, have
permeabilities hundreds and even thousands of times that of free space. Materials with these very high
permeabilities are referred to as ferromagnetic.
The ratio of the permeability of a material to that of free space is called its relative permeability (μr)
μr=μ/μ0
In general, for ferromagnetic materials, μr ≥ 100, and for nonmagnetic materials, μr= 1. Since μr is a variable,
dependent on other quantities of the magnetic circuit, values of μr are not tabulated.
Reluctance: The opposition to the setting up of magnetic flux lines in the material is the reluctance (R). The
reluctance is inversely proportional to the permeability. The larger the permeability the smaller the reluctance.
The materials with high permeability, such as the ferromagnetics, have very small reluctances and will result in
an increased measure of flux through the core.
Magnetomotive Force (mmf): It is the external force or pressure required to set up the magnetic flux lines
within the magnetic material. The magnetomotive force,
F=NI
The unit is At(Ampere-turn).
Fig: Defining the components of a magnetomotive force.
Magnetizing Force: The magnetomotive force (F) per unit length is called the magnetizing force (H).
)/( mAt
L
F
H 
Fig: Defining the magnetizing force of a magnetic circuit

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4.6 Magnetic Core and Core Loss
A magnetic core is a piece of magnetic material with a high permeability used to confine and guide magnetic
fields in electrical, electromechanical and magnetic devices such as electromagnets, transformers, electric
motors, generators, inductors, magnetic recording heads, and magnetic assemblies. It is made of ferromagnetic
metal such as iron, or ferrimagnetic compounds such as ferrites.
When the core is subjected to a changing magnetic field, as it is in devices that use AC current such as
transformers, inductors, and AC motors and alternators, some of the power that would ideally be transferred
through the device is lost in the core, dissipated as heat and sometimes noise. This is due primarily to two
processes:
(i) Eddy Currents: If the core is electrically conductive, the changing magnetic field induces circulating loops
of current in it, called eddy currents, due to electromagnetic induction. The loops flow perpendicular to the
magnetic field axis. The energy of the currents is dissipated as heat in the resistance of the core material.
Fig(1): Defining the eddy current losses of a ferromagnetic core.
To describe eddy current losses in greater detail, we will consider the effects of an alternating current passing
through a coil wrapped around a ferromagnetic core. As the alternating current passes through the coil, it will
develop a changing magnetic flux Ф linking both the coil and the core that will develop an induced voltage
within the core as determined by Faraday’s law. This induced voltage and the geometric resistance of the core
RC =(ρL/A) cause currents to be developed within the core, icore =(eind /RC), called eddy currents. The currents
flow in circular paths, as shown in figure, changing direction with the applied ac potential.
The eddy current losses are determined by, Peddy= i2
eddyRcore . The magnitude of these losses is determined
primarily by the type of core used. If the core is nonferromagnetic and has a high resistivity like wood or air the
eddy current losses can be neglected. In terms of the frequency of the applied signal and the magnetic field
strength produced, the eddy current loss is proportional to the square of the frequency times the square of the
magnetic field strength: Peddy ∞ f2
B2
Eddy Current Reduction: Eddy current losses can be reduced if the core is constructed of thin,laminated
sheets of ferromagnetic material insulated from one another and aligned parallel to the magnetic flux. Such
construction reduces the magnitude of the eddy currents by placing more resistance in their path.
(ii) Hysteresis: When the magnetic field through the core changes, the magnetization of the core material
changes by expansion and contraction of the tiny magnetic domains it is composed of, due to movement of the

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domain walls. This process causes losses, because the domain walls get "snagged" on defects in the crystal
structure and then "snap" past them, dissipating energy as heat. This is called hysteresis loss. It can be seen in
the graph of the B field versus the H field for the material, which has the form of a closed loop. The amount of
energy lost in the material in one cycle of the applied field is proportional to the area inside the hysteresis loop.
Since the energy lost in each cycle is constant, hysteresis power losses increase proportionally with frequency.
Hysteresis losses in terms of the frequency of the applied signal and the magnetic field strength produced, the
hysteresis loss is proportional to the frequency to the 1st power times the magnetic field strength to the nth
power: Phys ∞ f1
Bn
where n can vary from 1.4 to 2.6, depending on the material under consideration.
Hysteresis Loss Reduction: Hysteresis losses can be effectively reduced by the injection of small amounts of
silicon into the magnetic core, constituting some 2% or 3% of the total composition of the core. This must be
done carefully, however, because too much silicon makes the core brittle and difficult to machine into the shape
desired.
5.6 B-H curve
A curve of the flux density B versus the magnetizing force H of a material is called B-H curve.
Fig(1): Series magnetic circuit used to define the hysteresis curve.
Fig(2): B-H curve

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A typical B-H curve for a ferromagnetic material such as steel can be derived using the setup of Fig.(1). The
core is initially unmagnetized and the current I=0. If the current I is increased to some value above zero, the
magnetizing force H (=NI/l) will increase. The flux Ф and the flux density B (=Ф/A) will also increase with the
current I (or H). If the material has no residual magnetism, and the magnetizing force H is increased from zero
to some value Ha, the B-H curve will follow the path shown in Fig.(2) between o and a. If the path is shown in
Fig.2 between o and a. If the magnetizing force H is increased until saturation (Hs) occurs, the curve will
continue as shown in the Fig.2 to point b. When saturation occurs, the flux density has, for all practical
purposes, reached its maximum value Bmax. Any further increase in current through the coil increasing H =NI/l
will result in a very small increase in flux density B. If the magnetizing force is reduced to zero by letting I
decrease to zero, the curve will follow the path of the curve between b and c. The flux density BR, which
remains when the magnetizing force is zero, is called the residual flux density. It is this residual flux density that
makes it possible to create permanent magnets. If the coil is now removed from the core of Fig.1, the core will
still have the magnetic properties determined by the residual flux density, a measure of its retentivity. If the
current I is reversed, developing a magnetizing force, -H, the flux density B will decrease with an increase in I.
Eventually, the flux density will be zero when -Hd (the portion of curve from c to d) is reached. The magnetizing
force -Hd required to “coerce” the flux density to reduce its level to zero is called the coercive force, a measure
of the coercivity of the magnetic sample. As the force -H is increased until saturation again occurs and is then
reversed and brought back to zero, the path def will result. If the magnetizing force is increased in the positive
direction (+H), the curve will trace the path shown from f to b. The entire curve represented by bcdefb is called
the hysteresis curve for the ferromagnetic material, from the Greek hysterein, meaning “to lag behind.” The flux
density B lagged behind the magnetizing force H during the entire plotting of the curve. When H was zero at c,
B was not zero but had only begun to decline. Long after H had passed through zero and had become equal to -
Hd did the flux density B finally become equal to zero.
6.6 Faraday’s Laws of Electromagnetic Induction
First Law: Whenever the magnetic flux linked with a circuit changes, an e.m.f. is always induced in it. Or
Whenever a conductor cuts magnetic flux, an e.m.f. is induced in that conductor.
Second Law: The magnitude of the induced e.m.f. is equal to the rate of change of flux linkages.
Explanation: Suppose a coil has N turns and flux through it changes from an initial value of Φ1 webers to the
final value of Φ2 webers in time t seconds. Then, remembering that by flux-linkages mean the product of
number of turns and the flux linked with the coil.
Initial flux linkages = NΦ1
Final flux linkages = NΦ2
Induced e.m.f., e=(NΦ1- NΦ2)/t=N(Φ1- Φ2)/t
Putting the above expression in its differential form, we get
e=N(dΦ/dt)
Usually, a minus sign is given to the right-hand side expression to signify the fact that the induced e.m.f. sets up
current in such a direction that magnetic effect produced by it opposes the very cause producing it.
e=-N(dΦ/dt)

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7.6 A circuit has 1000 turns enclosing a magnetic circuit 20cm2
in section. With 4A, the flux density is
1.0Wb/m2
and with 9A, it is 1.4Wb/m2
. Find the mean value of the inductance between these current
limits and the induced e.m.f. if the current falls from 9A to 4A in 0.05 seconds.
Solution: The mean value of inductance,
H
dI
dB
NA
dI
BAd
N
dI
d
NL
16.0
)49(
)14.1(
10201000
)(
4









The induced e.m.f.
V
dt
dI
LeL
16
05.0
)49(
16.0




8.6 Magnetic Field Strength of a Long Solenoid
Fig.1: Magnetic field around a coil carrying electric current Fig.2
Let the magnetic field strength along the axis of the solenoid be H. Let us assume that (i) the value of H
remains constant throughout the length l of the solenoid and (ii) the volume of H outside the solenoid is
negligible. Suppose, a unit N-pole is placed at point A outside the solenoid and is taken once round the
completed path (shown dotted in Fig.2) in a direction opposite to that of H. Remembering that the force of H
newtons acts on the N-pole only over the length l (it being negligible elsewhere), the work done in one round is
= H × l joules = Amperes
The ‘ampere-turns’ linked with this path are NI where N is the number of turns of the solenoid and I the
current in amperes passing through it. According to Work Law, H×l=NI or H = NI/l A/m. Also, B =µNI/l
Wb/m2
.

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9.6 Alternating Voltage and Current Generation
Alternating voltage may be generated by rotating a coil in a magnetic field as shown in Fig. (a) or by rotating a
magnetic field within a stationary coil as shown in Fig. (b).
The value of the voltage generated depends, in each case, upon the number of turns in the coil, strength of the
field and the speed at which the coil or magnetic field rotates. Alternating voltage may be generated in either of
the two ways shown above, but rotating field method is the one which is mostly used in practice.
10.6 Equations of the Alternating Voltages and Current
Consider a rectangular coil, having N turns and rotating in a uniform magnetic field, with an angular velocity of
ω radian/second, as shown in Fig.(a).
Fig.(a)
Let time be measured from the X-axis. Maximum flux Φm is linked with the coil, when its plane coincides
with the X-axis. In time t seconds, this coil rotates through an angle θ=ωt. In this deflected position, the
component of the flux which is perpendicular to the plane of the coil, is Φ = ΦmCosωt. Hence, flux linkages of
the coil at any time are, NΦ = NΦmCosωt. According to Faraday’s Laws of Electromagnetic Induction, the
e.m.f. induced in the coil is given by the rate of change of flux-linkages of the coil. Hence, the value of the
induced e.m.f. at this instant (i.e. when θ=ωt) or the instantaneous value of the induced e.m.f. is

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When the coil has turned through 90º i.e. when θ = 90º, then sin θ = 1, hence e has maximum value, say Em.
Therefore, from Eq. (i) we get
Em=ωNΦm=ωNBmA=2πfNBmA …………………………....(ii)
Where, Bm = maximum flux density in Wb/m2
, A = area of the coil in m2
, f = frequency of rotation of the coil
in rev/second, Substituting this value of Em in Eq. (i), we get
e(t)=Em Sinθ=EmSinωt …………………..............................(iii)
Similarly, the equation of induced alternating current is i(t)=ImSinωt ………….(iv)
provided the coil circuit has been closed through a resistive load.
Fig.(b)
It is seen that the induced e.m.f. varies as sine function of the time angle ω t and when e.m.f. is plotted against
time, a curve similar to the one shown in Fig.(b) is obtained. This curve is known as sine curve and the e.m.f.
which varies in this manner is known as sinusoidal e.m.f.
)......(..........................................................................................
)sin(
)(
)()(
iSinN
tSinN
tN
tCos
dt
d
N
N
dt
d
te
m
m
m
m










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11.6 Magnetic Force on a Current Carrying Conductor
When an electrical wire is exposed to a magnet, the current in that wire will be affected by a magnetic field.
The effect comes in the form of a force. The expression for magnetic force on current can be found by summing
the magnetic force on each of the many individual charges that comprise the current. Since they all run in the
same direction, the forces can be added.
The force (F) of a magnetic field (B) exerts on an individual charge (q) traveling at drift velocity vd is:
F=NqvdBSinθ
Given that N=nV, where n is the number of charge carriers per unit volume and V is volume of the wire, and
that this volume is calculated as the product of the circular cross-sectional area (A) and length (L) yields the
equation:
F=nVqvdB Sinθ
F=nALqvdB Sinθ
F=(nqAvd)LB Sinθ
The terms in parentheses are equal to current (I= nqAvd), and thus the equation can be rewritten as:
F=ILB Sinθ
In vector form, F=L I×B
θ
B
F
I
L
directed into the paper

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12.6 Thyristor or Silicon Controlled Rectifier (SCR)
A thyristor is a four-layer semiconductor device of p-n-p-n structure with three p-n junctions. It has three
terminals: anode(A), cathode(C) and a gate(G). Figure (1) shows the thyristor symbol and the sectional view of
the three p-n junctions.
Fig(1): Thyristor symbol and three pn-junctions
Fig.2: Thyristor circuit and V-I characteristics
When the anode voltage made positive with respect to the cathode, junctions J1 and J3 are forward biased and
junction J2 is reverse biased. The thyristor said to be in the forward blocking or off-state condition. A small
leakage current flows from anode to cathode and is called the off state current. If the anode voltage VAK is
increased to a sufficiently large value, the reverse biased junction J2 would breakdown. This is known as
avalanche breakdown and the corresponding voltage is called the forward breakdown voltage VBO. Since the
other two junctions J1 and J3 are already forward biased, there will be free movement of carriers across all three
junctions. This results in a large forward current. The device now said to be in a conducting or on state. The

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voltage drop across the device in the on-state is due to the ohmic drop in the four layers and it is very (typically
1 V). In the on state the anode current is limited by an external impedance or resistance as shown in figure (2-a).
Latching Current (IL): This is the minimum anode current required to maintain the thyristor in the on-state
immediately after a thyristor has been turned on and the gate signal has been removed. If a gate current, greater
than the threshold gate current is applied until the anode current is greater than the latching current IL then the
thyristor will be turned on or triggered.
Holding Current (IH) : This is the minimum anode current required to maintain the thyristor in the on state. To
turn off a thyristor, the forward anode current must be reduced below its holding current for a sufficient time for
mobile charge carriers to vacate the junction. If the anode current is not maintained below IH for long enough,
the thyristor will not have returned to the fully blocking state by the time the anode-to-cathode voltage rises
again. It might then return to the conducting state without an externally applied gate current.
Reverse Current (IR): When the cathode voltage is positive with respect to the anode, the junction J2 is
forward biased but junctions J1 and J3 are reverse biased. The thyristor is said to be in the reverse blocking state
and a reverse leakage current known as reverse current IR will flow through the device.
Forward Break-over Voltage VBO : If the forward voltage VAK is increased beyond VBO, the thyristor can be
turned on. However, such a turn-on could be destructive. In practice, the forward voltage is maintained below
VBO and the thyristor is turned on by applying a positive gate signal between gate and cathode.
Once the thyristor is turned on by a gate signal and its anode current is greater than the holding current, the
device continues to conduct due to positive feedback even if the gate signal is removed. This is because the
thyristor is a latching device and it has been latched to the on state.
Thyristor Applications: Thyristors, or silicon controlled rectifiers, SCRs are used in many areas of electronics
where they find uses in a variety of different applications. Some of the more common applications for them are
outlined below:
(i) AC power control (including lights, motors etc).
(ii) Overvoltage protection crowbar for power supply.
(iii) Thyristors are able to switch high voltages and withstand reverse voltages making them ideal
for switching applications, especially within AC scenarios.
(iv) Control elements in phase angle triggered controllers.
(v) Within photographic flash lights where they act as the switch to discharge a stored voltage
through the flash lamp, and then cut it off at the required time.

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13.6 Cathode Ray Oscilloscope (CRO)
The cathode ray oscilloscope is an extremely useful and versatile laboratory instrument used for studying
wave shapes of alternating currents and voltages as well as for measurement of voltage, current, power and
frequency, in fact, almost any quantity that involves amplitude and waveform. It allows the user to see the
amplitude of electrical signals as a function of time on the screen. It is widely used for trouble shooting radio
and TV receivers as well as laboratory work involving research and design. It can also be employed for studying
the wave shape of a signal with respect to amplitude distortion and deviation from the normal. In true sense the
cathode ray oscilloscope has been one of the most important tools in the design and development of modern
electronic circuits.
Fig: CRO block diagram
A basic block diagram of a general purpose oscilloscope is shown in figure. The instrument employs a cathode
ray tube (CRT), which is the heart of the oscilloscope. It generates the electron beam, accelerates the beam to a
high velocity, deflects the beam to create the image, and contains a phosphor screen where the electron beam
eventually becomes visible. For accomplishing these tasks various electrical signals and voltages are required,
which are provided by the power supply circuit of the oscilloscope. Low voltage supply is required for the
heater of the electron gun for generation of electron beam and high voltage, of the order of few thousand volts,
is required for cathode ray tube to accelerate the beam. Normal voltage supply, say a few hundred volts, is
required for other control circuits of the oscilloscope.
Horizontal and vertical deflection plates are fitted between electron gun and screen to deflect the beam
according to input signal. Electron beam strikes the screen and creates a visible spot. This spot is deflected on
the screen in horizontal direction (X-axis) with constant time dependent rate. This is accomplished by a time
base circuit provided in the oscilloscope. The signal to be viewed is supplied to the vertical deflection plates
through the vertical amplifier, which raises the potential of the input signal to a level that will provide usable
deflection of the electron beam. Now electron beam deflects in two directions, horizontal on X-axis and vertical
on Y-axis. A triggering circuit is provided for synchronizing two types of deflections so that horizontal
deflection starts at the same point of the input vertical signal each time it sweeps.

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Sensor and Transducer
14.6 Sensor and Transducer
Sensor is a device used to generate an equivalent electrical signal, either in the form of voltage or current, if
a non-electrical physical quantity is applied to it. Example: A light dependent resistor (LDR) is a sensor in
which the resistance changes if the intensity of light is changed. If the LDR is connected with a voltage source,
the current will also change (Fig.1). The change of current will be in accordance with the change of light
intensity.
Fig.1 Sensor Fig.2 Transducer
Usually the electrical signal extracted by a sensor is too weak to be used further. In such cases an amplifier
is used at the first step, to make the signal strong, so that it can be now connected to other circuit. A transducer
is a device which include a sensor and other circuits if necessary, to produce a suitable electrical signal, which
can be connected directly to other circuits, for control or further processing (Fig.2).
In the broadest sense, a transducer is any device that receives energy from one system and retransmits it,
usually in another form, to a system. The word sensor is more restrictive, it refers to that part of a transducer that
responds to the quantity being measured.
15.6 Non-electrical Quantity
 Position and displacement
 Rotation
 Pressure
 Temperature
 Light intensity
 Fluid flow
VCC
LDR
A
at
Incident
light LDR
VCC
Amplifier
Control
Circuit
Load
Incident
light

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16.6 Application of Sensor Technology in Textiles
Normally a sensor is a converter that measures a physical quantity and converts it into a signal which can be
read by an observer or by an (today mostly electronic) instrument. In this modern technology era sensor is
widely used in all branch of the textile industry, at all of the departments. Without applying of sensor
technology efficiency of the machine will be decrease, wastage will be increase and overall cost will be
increase. Besides, accident can be occurred without using sensor in textile machine. Without machinery, textile
sensor systems are capable of capturing comprehensive physiologic data from the body and are designed to be
seamlessly integrated into everyday garments. Wearable monitoring provides a comfortable and user-friendly
way to obtain body data measurements to assist consumers in managing their top wellness concerns of weight
loss, physical health and energy level. Textronics sells sensor components and markets its own line of clothes
for personal monitoring under the brand name NuMetrex™. Now a days, sensor is widely used in smart textile.
So, we must have to know about the Sensor technology and it’s operating and working procedure to become a
good textile engineer.
Sensor in textile
It is seen in textile industry so far that, the sensor problems and sensor technology related issues are being
observed and fixed by the computer engineers. But, as the textile engineers knows everything about textile
except sensor, it is the time to learn about the sensor technology to have an all-round performance in textile
engineering. life.
The offered range of textile machine sensors is developed by trusted vendors, who ensure to made it utilizing
high grade raw material and innovative technology. Along with this, the offered range of textile machine sensors
is ideally utilized in different sectors such as textile industry foe sensing applications.
In Textile, two types of Sensor are used. One is Capacitive Sensor; another is Optical Sensor. Again, Optical
Sensor is divided into two types: 1. One Dimensional Optical Sensor, 2. Two Dimensional Optical Sensor.
Capacitive Sensor: Capacitive Sensor is used for determination of mass variation. In textile spinning industry,
the Capacitive sensor is widely used in order to determine the production parameters. By taking the calculation
result from the capacitive sensor, some of the spinning machines are to be set up.
Optical Sensor: Optical sensor is used for determination of diameter variation. It has advantages with regard to
visual appearance of the yarn. One dimensional sensor comes to very close to observation of human eye;
whereas, two dimensional Optical sensor offers advantages for the determination of the roundness and the
density of the Yarn.

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The other major sensors are: Proximity Sensors, Inductive Sensor, Namur Sensors, Field Plate/Hall Sensors,
Photo Electric Sensors, Sensors & Electronic module for textile - Indigenous /Imported Machines, Connector &
cable assembly and Peripheral & Relay Units, Certified Zener Barriers, Field Programmable smart Sensors for
which WIPO patent is pending.
Sensor is used in all kind of textile machineries but widely used in machines such as Air Jet Loom, Auto
Coner 138, 238 / Auto Coro, Carding, Drawing Frame, Pre Winder, Rapier Loom, Projectile Loom, Staubli
Dobby 2605, P 7100, PU 85, PU 153, GTM Loom, Omni Loom, Ring Frame etc.
17.6 Features of Textile Sensors
 Longer functional life
 High performance
 Easy maintenance
 Reliable operations
18.6 Light Dependent Resistor
A photoresistor or light dependent resistor (LDR) is a resistor whose resistance decreases with increasing
incident light intensity. The resistance of LDR is of the order of mega ohms (MΩ) in the absence of light and
reduces to a few ohms (Ω) in presence of light. A photoresistor is made of a high resistance semiconductor. If
light falling on the device is of high enough frequency, photons absorbed by the semiconductor give bound
electrons enough energy to jump into the conduction band. The resulting free electron (and its hole partner)
conduct electricity, thereby lowering resistance.
Application of LDR
Photoresistors come in many types. Inexpensive cadmium sulphide cells can be found in many consumer
items such as camera light meters, street lights, clock radios, alarm devices, outdoor clocks, solar street lamps
and solar road studs, etc. They are also used in some dynamic compressors together with a small incandescent
lamp or light emitting diode to control gain reduction and are also used in bed lamps, etc.
Cadmium sulfide or
Cadmium selenide
Incident
light

18. Page18of23(AZ)
19.6 Piezoelectric Effect
There are some special type of materials in which an electric potential appears across certain surfaces of
some crystals if the dimensions of the crystal are changed by application of an oscillatory mechanical force. The
effect is reversible, that is, if a varying potential is applied, the dimension will change. The effect is known as
piezoelectric effect. Some piezoelectric materials are, rochelle salt, lithium sulphate, dipotassium tartarate etc. A
piezoelectric sensor is a device that uses the piezoelectric effect.
Fig.2 Piezoelectric effect
Application of Piezoelectric Effect:
 Microphones, Touchscreen
 Detection and generation of sonar waves
 Energy harvesting
 Power monitoring in high power applications (e.g. Medical treatment, sono-chemistry and industrial
processing).
 Piezoelectric micro-balances are used as very sensitive chemical and biological sensors.
Lower electrode
Force
Piezoelectric
Material
Upper electrode
material

19. Page19of23(AZ)
20.6 Energy Harvesting
The process by which energy is derived from external sources, captured, and stored for different purposes is
called Energy harvesting. Harvesting and storing electrical energy is an essential issue for the different parts of
world to fulfill the electrical energy demands of consumers.
Piezoelectric Fabrics for Energy Harvesting:
Fig.1 Piezofiber composite structure
It represents the conversion of electrical energy from mechanical energy by developing textile fabrics which
are able of performing the mentioned act (i.e. piezoelectric effect). The mechanical energy is achievable from
wind (environmental resource) or from the motion of the user of the textile fabric. For example, piezoelectric
fabrics could be used in the design of clothing capable of collecting some of the mechanical energy associated
with walking or running. The harvested Energy could be used to recharge battery or to directly power a device
(wireless sensor networks, wearable instruments, and LED).
21.6 Strain Gauge
Any external force applied to a stationary object produces stress and strain. The object's internal resisting
forces are referred to as stress while the displacement and deformation that occur is termed as strain. Strain can
be either compressive or tensile and is usually measured by strain gauges. A strain gage is a device whose
electrical resistance varies in proportion to the compression and tension forces it is experiencing. It is used to
measure displacement, force, load, pressure, torque or weight etc.
The strain gauge is connected into a wheatstone bridge circuit as shown in the diagram. The complete
wheatstone bridge is excited with power supply and with additional conditioning electronics, can be zeroed at
the null point of measurement. Typically, the rheostat arm R2 of the bridge is set at a value equal to the strain
gauge resistance with no force applied. The two ratio arms of the bridge (R1 and R3) are set equal to each other.
Thus, with no force applied to the strain gauge, the bridge will be symmetrically balanced and the voltmeter will
indicate zero volts, representing zero force on the strain gauge. As the strain gauge is either compressed or
tensed, its resistance will decrease or increase, respectively, thus unbalancing the bridge and producing an
indication at the voltmeter.

20. Page20of23(AZ)
22.6 Speed Measurement Using DC Tachometer Generator
The DC tachometer generator can be used for speed measurement. The armature of the tachometer is kept in
the permanent magnetic field. The armature is coupled to the machine whose speed is to be measured. When the
shaft of the machine revolves, the armature of the tachometer revolves in the magnetic field producing EMF
which is proportional to the product of the flux and speed to be measured. Now as the field of the permanent
field is fixed, the EMF generated is proportional to the speed directly. The EMF induced is measured using
moving coil voltmeter with uniform scale calibrated in speed directly. The series resistance is used to limit the
current under output short circuit condition. The polarity of output voltage indicates the direction of rotation.
The commutator collects current from armature conductors and converts internally induced AC EMF into DC
EMF while the brushes are used to collect current from commutator and make it available to external circuitry
of DC tachometer generator.
Advantages
1. The output voltage is small enough to measure it with conventional d.c voltmeters.
2. The polarity of output voltage directly indicates the direction of rotation.
Disadvantages
1. Because of variations in contact resistance, considerable error is introduced in the output voltage. Hence
periodic maintenance of the commutator and brushes is required.
2. Non-linearity in the output of the d.c tachogenerator occurs because of distortions in the permanent magnetic
field due to large armature currents. Hence input resistance of meter should be very high as compared to the
output resistance of the generator.

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23.6 Resistance Temperature Detector
Resistance thermometers or resistance temperature detectors (RTDs), are sensors used to measure
temperature by correlating the resistance of the RTD element with temperature. Most RTD elements consist of a
length of fine coiled wire wrapped around a ceramic or glass core. The RTD element is made from a pure
material, platinum, nickel or copper. The material has a predictable change in resistance as the temperature
changes; it is this predictable change that is used to determine temperature.
Fig.1 Resistance temperature detector
Resistance at to
C, Rt = Rref (1+ t)
Rref= Resistance at reference temperature
t=Difference between operating and reference temperature
=Temperature co-efficient
Application of RTD
 Textile production
 Air conditioning and refrigeration servicing
 Food Processing
 Stoves and grills
 Plastics processing
 Petrochemical processing
 Micro electronics
 Air, gas and liquid temperature measurement
 Exhaust gas temperature measurement
24.6 Temperature Measurement Using Thermistor
Initially, thermistor is placed in the environment whose temperature is to be measured. Then, thermistor is
connected in a series simple circuit consisting of battery and micro-ammeter as shown below. Any change in
temperature causes a change in resistance of thermistor. Hence, corresponding change in circuit current. By
directly calibrating micro-ammeter in terms of temperature, we can measure temperature.

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25.6 Uninterruptible Power Supply
Uninterruptible Power Supply (UPS) is an AC battery supported power supply device intended to provide a
backup source of AC power without power interruption to the connected load.
A UPS is typically used to protect computers, data centers, telecommunication equipment or other electrical
equipment where an unexpected power disruption could cause injuries, fatalities, serious business disruption or
data loss.
Types of UPS system:
1. Offline UPS or Standby UPS
2. Line-interactive
3. Online / Double-conversion
Operation of a Standby UPS: In this type of UPS, the primary power source is line power from the utility, and
the secondary power source is the battery. It is called a standby UPS because the battery and inverter are
normally not supplying power to the equipment.
Fig.1 Block schematic of a standby UPS
During normal operation, the input AC power from the line is supplied to the load via the UPS switch. The
additional devices like surge suppressor and filter may be incorporated to protect against line noise and other
problems that would not cause a switch to battery power. In this time battery is charged through the charger. The
battery charger is a rectifier circuit which converts AC voltage into DC voltage. The battery and inverter are
waiting on standby until they are needed.
When the AC input supply voltage is out of UPS preset tolerances or AC power is goes out, the transfer
switch changes his position and it is connected with the battery power line. Now inverter is activated and
converts DC voltage to AC voltage from the battery which is fed to the load. When line power is restored, the
UPS switches back.
AC Power
Supply
Transfer
Switch
Battery
Charger
Surge
Suppressor
Battery Inverter
Filter
Load

23. Page23of23(AZ)
26.6 Difference Between UPS and IPS System
SI Instant Power Supply (IPS) Uninterruptible Power Supply (UPS)
1. Use a large number of electronic equipment Use a small number of electronic equipment
2. Provide large time backup Provide short time backup
3. Require a minimum switching time of 1
second or more and causes user's devices to
reset or restart. This power drop and sudden
power up may harm electronic devices.
Will not allow any power drop while switching to
battery in a very little fraction of second (0.1 or
less) so that the user's computer or any devices
connected with will not reset or restarts, that
means no interruption.
4. Can be operate more than one electronic
equipment.
Can be operate only one equipment.
5. Must be use big size battery Small size battery
6. Backup system is so high Backup system is low