Basic Electronics Electrical Transducers

Basic Electronics
Electrical Transducers
Dr. Nilesh Bhaskarrao Bahadure
https://www.sites.google.com/site/nileshbbahadure/home
July 26, 2021
Dr. Nilesh Bhaskarrao Bahadure () Basic Electronics July 26, 2021 1 / 75

Overview
1 Introduction
2 What is Transducers
3 Selection Criteria of the Transducers
4 Basic Requirements of a Transducers
5 Strain Gauge
6 Inductive Transducer - LVDT
7 Load Cell
8 Temperature Transducers
Resistance Temperature Detector (RTD)
Thermocouple
Thermistor
9 Photoelectric Transducer
10 LDR
11 Photovoltaic Solar Cells
12 Thank You

Introduction
Basically transducer is defined as a device, which converts energy or
information from one form to another. These are widely used in
measurement work because not all quantities that need to be measured
can be displayed as easily as others. A better measurement of a quantity
can usually be made if it may be converted to another form, which is more
conveniently or accurately displayed.
For example, the common mercury thermometer converts variations in
temperature into variations in the length of a column of mercury. Since
the variation in the length of the mercury column is rather simple to
measure, the mercury thermometer becomes a convenient device for
measuring temperature

Introduction...
On the other hand, the actual temperature variation is not as easy to
display directly. Another example is manometer, which detects pressure
and indicates it directly on a scale calibrated in actual units of pressure.

Introduction...
Thus the transducer is a device, which provides a usable output in
response to specific input measured, which may be physical or mechanical
quantity, property or condition. The transducer may be mechanical,
electrical, magnetic, optical, chemical, acoustic, thermal nuclear, or a
combination of any two or more of these.

Introduction...
Example:

What is Transducers

What is Transducers
The transducer is defined as the device which convert the one form of
energy into another form of the energy
Examples:
1 Temperature transducers
2 Thermocouples
3 Resistance-Temperature Detectors (RTD)
4 Thermistors
5 Resistive position transducers
6 Displacement transducers
7 Strain gauge

What is Transducers
The points to be considered in determining a transducer suitable for a
specific measurement are as follows:
1 Operating principle
2 Sensitivity
3 Operating range
4 Accuracy
5 Errors
6 Environmental capability
7 Insensitive to unwanted Signal
8 Stability

Operating principle
Electrical Output Characteristic
The electrical characteristics-the output impedance, the frequency
response, and the response time of the transducer output signal should be
compatible with the recording device and the rest of the measuring system
equipment.

Sensitivity
Sensitivity
The transducer should give a sufficient output signal per unit of measured
input in order to yield meaningful data.

Operating Range
Range
The range of the transducer should be large enough to encompass all the
expected magnitudes of the measured.

Errors
Errors
The errors inherent in the operation of the transducer itself, or those errors
caused by environmental conditions of the measurement, should be small
enough or controllable enough that they allow meaningful data to be taken.

Environmental capability
Physical Environment
The transducer selected should be able to withstand the environmental
conditions to which it is likely to be subjected while carrying out
measurements and tests.
Such parameters are temperature, acceleration, shock and vibration,
moisture, and corrosive chemicals might damage some transducers but not
others

Basic Requirements of a Transducers
The main function of a transducer is to respond only for the measurement
under specified limits for which it is designed. It is, therefore, necessary to
know the relationship between the input and output quantities and it
should be fixed. Transducers should meet the following basic requirements.

Ruggedness
Raggedness
It should be capable of withstanding overload and some safety
arrangement should be provided for overload protection.

Linearity
Linearity
Its input-output characteristics should be linear and it should produce
these characteristics in symmetrical way.

Repeatability
Repeatability
It should reproduce same output signal when the same input signal is
applied again and again under fixed environmental conditions e.g.
temperature, pressure, humidity etc.

High Output Signal Quality
High Output Signal Quality
The quality of output signal should be good i.e. the ratio of the signal to
the noise should be high and the amplitude of the output signal should be
enough.

High Reliability and Stability
High Reliability and Stability
It should give minimum error in measurement for temperature variations,
vibrations and other various changes in surroundings.

Good Dynamic Response
Good Dynamic Response
Its output should be faithful to input when taken as a function of time.
The effect is analyzed as the frequency response.

No Hysteresis
No Hysteresis
It should not give any hysteresis during measurement while input signal is
varied from its low value to high value and vice-versa.

Residual Deformation
Residual Deformation
There should be no deformation on removal of local after long period of
application.

Strain Gauge
Strain Gauge is a passive transducer that converts a mechanical elongation
or displacement produced due to a force into its corresponding change in
resistance R, inductance L, or capacitance C. A strain gauge is basically
used to measure the strain in a work piece. If a metal piece is subjected to
a tensile stress, the metal length will increase and thus will increase the
electrical resistance of the material. Similarly, if the metal is subjected to
compressive stress, the length will decrease, but the breadth will increase.
This will also change the electrical resistance of the conductor. If both
these stresses are limited within its elastic limit (the maximum limit
beyond which the body fails to regain its elasticity), the metal conductor
can be used to measure the amount of force given to produce the stress,
through its change in resistance.
The strain gauge is an example of a passive transducer that uses electric
resistance variation in wires to sense the strain produced by a force on the
wires.

Strain Gauge...
It is a very versatile detector and used for measuring weight, pressure,
mechanical force, or displacement.

Strain Gauge...
It is a very versatile detector and used for measuring weight, pressure,
mechanical force, or displacement.
Figure : Resistive strain gauges: wire construction

Strain Gauge...
The construction of a bonded strain gauge (see figure) shows a fine wire
element looped back and forth on a mounting plate, which is usually
cemented to the member undergoing stress.
When a gauge is subjected to a stress, its length increases while its
cross-sectional area decreases.

Strain Gauge...
From Hooke theory, stress, S, is defined as force/unit area.
S =
F
A
(1)
where,
F= the force in kilograms
A= area in square meters (m2)
The increase in resistance can be seen from the following equation:
R = ρ
L
A
(2)
where,
= the specific resistance of the conductor material in ohm meters
L = length of conductor (meters)
A = area of conductor (m2)

Strain Gauge...
Since the resistance of a conductor is directly proportional to its length
and inversely proportional to its cross-sectional area, the resistance of the
gauge increases with strain.
Strain, G is defined as elongation or compression per unit length, or:
G =
4L
L
(3)
where,
L = the initial length in meters (without strain)
4L = the change in initial length in meters

Strain Gauge...
As consequence of strain, two physical qualities are of particular interest:
1 The change in gauge resistance
2 The change in length
The relationship between these two variables called gauge factor, K, is
expressed mathematically as
K =
4R
R
4L
L
=
4R
R
G
(4)
where,
K = the gauge factor
R = the initial resistance in ohms (without strain)
4R = the change in initial resistance in ohms

Strain Gauge...
The constant of proportionality between stress and strain for a linear
stress-strain curve is known as the modulus of elasticity of material E or
called Youngs modulus. It is written as:
E =
S
G
(5)
where,
E = Young modules in kg/m2
S = the stress in kg/m2
G = the strain (no units)

Linear variable differential transformer (LVDT)
Inductive transducers work on the principle of inductance change due to
any appreciable change in the quantity to be measured i.e. measured. For
example, LVDT, a kind of inductive transducers, measures displacement in
terms of voltage difference between its two secondary voltages. Secondary
voltages are nothing but the result of induction due to the flux change in
the secondary coil with the displacement of the iron bar.
It consists basically of a primary winding and two secondary windings,
wound over a hollow tube and positioned so the primary winding is
between two secondaries. In figure shows the construction of the LVDT.
Main Slide

Linear variable differential transformer (LVDT)..
An iron core slides within the tube and therefore affects the magnet
coupling between the primary and the two secondaries. When the core is
in the centre, voltage induced in the two secondaries is equal. When the
core is moved in one direction from centre, the voltage induced in one
winding is increased and that in the other is decreased. Movement in the
opposite direction reverses this effect
Main Slide

Main Slide

When the core is moved in one direction from the center, the voltage
induced in one winding is increased and that in the others is decreased.
Movement in the opposite direction reverse the effect. Main Slide

Core at the center
e1 = e2
eo = 0
Main Slide

Core moves towards S1
e1>e2
eo increases
Main Slide

Core moves towards S2
e2>e1
eo decreaess
Main Slide

Thus, the amplitude of eo is a function of distance the core has moved. If
the core is attached to a moving object, the LVDT output voltage can be
a measure of the position of the object. The farther the core moves from
the centre, the greater the difference in value between e1 and e2, and
consequently the greater the value of eo.

Advantages of LVDT
1 High Range - The LVDTs have a very high range for measurement
of displacement.they can used for measurement of displacements
ranging from 1.25mm to 250mm
2 No Frictional Losses - As the core moves inside a hollow former so
there is no loss of displacement input as frictional loss so it makes
LVDT as very accurate device.
3 High Input and High Sensitivity - The output of LVDT is so high
that it doesn’t need any amplification.the transducer posseses a high
sensitivity which is typically about 40V/mm.
4 Low Hysteresis - LVDTs show a low hysteresis and hence
repeatability is excellent under all conditions
5 Low Power Consumption - The power is about 1W which is very as
compared to other transducers.
6 Direct Conversion to Electrical Signals - They convert the linear
displacement to electrical voltage which are easy to process
Main Slide

Disadvantages of LVDT
1 LVDT is sensitive to stray magnetic fields so they always require a
setup to protect them from stray magnetic fields.
2 They are affected by vibrations and temperature.
Main Slide

Applications of LVDT
1 They are used in applications where displacements ranging from
fraction of mm to few cm are to be measured. The LVDT acting as a
primary Transducer converts the displacement to electrical signal
directly.
2 They can also acts as the secondary transducers. E.g. the Bourbon
tube which acts as a primary transducer and covert pressure into linear
displacement.then LVDT coverts this displacement into electrical
signal which after calibration gives the ideas of the pressure of fluid.
Main Slide

Load Cell
Load cell is a type of transducer which performs the functionality of
converting force into an electric output which can be measured. You can
find load cell at the heart of any weighing machine or electric scales. This
type of transducer is highly accurate which provides user with required
information that is difficult to obtain by other technology owing to certain
commercial factors. The various load cell types include hydraulic,
pneumatic, and strain gauge.
It is basically a device that measures strain and then converts force into
electric energy which serves as measurement for scientists and workers.
The strain measurement by load cells helps in maintaining integrity of the
unit under pressure and protects people and equipment nearby.

Load Cell...
Uses
The usage of this transducer is not limited to electronic scales. Apart from
this, it is used in industrial scales, load-testing machines, flow-meters, etc.
Functionality
It makes use of different operating principles namely pneumatic, strain
gauge and hydraulic load cells. These load cells are usually attached to
support beam or structural bearing of an application which endures
pressures and stresses often with appropriate adhesive or superglue.

Load Cell...

Load Cell... I
1 Hydraulic load cells are force -balance devices, measuring weight as a
change in pressure of the internal filling fluid. In a rolling diaphragm
type hydraulic load cell, a load or force acting on a loading head is
transferred to a piston that in turn compresses a filling fluid confined
within an elastomeric diaphragm chamber. As force increases, the
pressure of the hydraulic fluid rises. This pressure can be locally
indicated or transmitted for remote indication or control. Output is
linear and relatively unaffected by the amount of the filling fluid or by
its temperature. If the load cells have been properly installed and
calibrated, accuracy can be within 0.25% full scale or better,
acceptable for most process weighing applications. Because this
sensor has no electric components, it is ideal for use in hazardous
areas. Typical hydraulic load cell applications include tank, bin, and
hopper weighing. For maximum accuracy, the weight of the tank

Load Cell... II
should be obtained by locating one load cell at each point of support
and summing their outputs.
2 Pneumatic load cells also operate on the force-balance principle.
These devices use multiple dampener chambers to provide higher
accuracy than can a hydraulic device. In some designs, the first
dampener chamber is used as a tare weight chamber. Pneumatic load
cells are often used to measure relatively small weights in industries
where cleanliness and safety are of prime concern. The advantages of
this type of load cell include their being inherently explosion proof
and insensitive to temperature variations. Additionally, they contain
no fluids that might contaminate the process if the diaphragm
ruptures. Disadvantages include relatively slow speed of response and
the need for clean, dry, regulated air or nitrogen.

Load Cell... III
3 Strain-gage load cells convert the load acting on them into electrical
signals. The gauges themselves are bonded onto a beam or structural
member that deforms when weight is applied. In most cases, four
strain gages are used to obtain maximum sensitivity and temperature
compensation. Two of the gauges are usually in tension, and two in
compression, and are wired with compensation adjustments as shown
in Figure. When weight is applied, the strain changes the electrical
resistance of the gauges in proportion to the load. Other load cells
are fading into obscurity, as strain gage load cells continue to increase
their accuracy and lower their unit costs.

Temperature Transducers
Temperature transducers can be divided into four main categories:
1 Resistance temperature detectors (RTDs)
2 Thermocouples
3 Thermistors
4 Ultrasonic transducer

RTD is a passive device whose resistance changes with temperature. This
condition causes RTD needs an electrical supply to give a voltage output.
RTD commonly employ platinum, nickel or any resistance wire, whose
resistance variation with temperature has high intrinsic accuracy.
They are available in many configurations and size.

Detectors of wire resistance temperature common employ platinum, nickel
or resistance wire elements, whose resistance variation with temperature
has high intrinsic accuracy. They are available in many configurations and
size and as shielded or open units for both immersion and surface
applications.
relationship between temperature and resistance of conductors can be
calculated from the equation:
R = R0(1 + α4T) (6)
where
R = the resistance of the conductor at temperature t (C)
R0 = the resistance at the reference temperature, usually 20C
α = the temperature coefficient of resistance
4T = the difference between the operating and the reference temperature

Advantages of RTD
1 Linearity over a wide operating range
2 Wide operating range
3 Higher temperature operation
4 Better stability at high temperature

Disadvantages of RTD
1 Low sensitivity
2 It can be affected by contact resistance, shock and vibration
3 Requires no point sensing
4 Higher cost than other temperature transducers
5 Requires 3 or 4 wire for its operation and associated instrumentation
to eliminate errors due to lead resistance

Thermocouple
Thermocouple is made up of a pair of different metal wire joined together
at one end.
A temperature difference between two ends of the wires produces a voltage
between the wires.

Thermocouple...
The magnitude of this voltage (emf) depends on the wire materials used
and on the temperature difference between the junctions.
The emf of the thermocouple is given as
E = c(T1 − T2) + k(T2
1 − T2
2 ) (7)
where,
c & k = constants of the thermocouple materials
T1 = the temperature of the ”hot” junction
T2 = the temperature of the ”cold” or ”reference” junction

Thermistor/Thermally Resistor
A thermistor is a thermally sensitive resistor that exhibits change in
electrical resistance with change in temperature.
Thermistor is fabricated from semiconductor material by sintering mixtures
of metallic oxide, such as manganese, nickel, cobalt, copper and uranium
oxides.
Thermistors have Negative Temperature Coefficient (NTC), i.e. resistance
decreases as temperature rises. Thermistor are available with Positive
Temperature Coefficient (PTC), but PTC thermistor are seldom used for
measurement since they have poor sensitivity.

Thermistor/Thermally Resistor...
This figure shows resistance versus temperature for a family thermistor.
The resistance value marked at the bottom end of each curve is a value at
25oC

Advantages of Thermistor
1 Small size and low cost
2 Fast response over narrow temperature range
3 Good sensitivity in the NTC region
4 Cold junction compensation not required due to dependence of
resistance on absolute temperature.
5 Contact and lead resistance problems not encountered due to large
resistance

Limitations of Thermistor
1 Non linearity in resistance vs temperature characteristics
2 Unsuitable for wide temperature range
3 Very low excitation current to avoids self heating
4 Need of shielded power lines, filters, etc due to high resistance

Photoelectric Transducer
What is Photoelectric Effect?
Photoelectric Effect is the emission of electrons from matter upon the
absorption of electromagnetic radiation, such as ultraviolet radiation or
x-rays.-refers to the emission, or ejection, of electrons from the surface of,
generally, a metal in response to incident light.

Photoelectric Transducer...
Photoelectric devices can be categorized as: photoemissive,
photoconductive, or photovoltaic.
No. Types Characteristics
1 Photoemmisive Radiation falling into a cathode
causes electrons to be emitted from
cathode surface.
2 Photoconductive the resistance of a material is changed
when it’s illuminated
3 Photovoltaic Generate an output voltage propor-
tional to radiation intensity

Examples of Photoelectric Transducer
1 The Photomultiplier Tube
2 Photoconductive Cells OR Photocells the electrical resistance of the
materials varies with the amount of light striking.
3 The Photovoltaic Cell or solar cell - produce an electrical current
when connected to the load.

light-dependent resistor
A photoresistor (or light-dependent resistor, LDR, or photo-conductive
cell) is a light-controlled variable resistor. The resistance of a photoresistor
decreases with increasing incident light intensity; in other words, it exhibits
photoconductivity. ... A photoresistor is made of a high resistance
semiconductor.
What are photoresistors?
Photo resistors, also known as light dependent resistors (LDR), are light
sensitive devices most often used to indicate the presence or absence of
light, or to measure the light intensity. In the dark, their resistance is very
high, sometimes up to 1M, but when the LDR sensor is exposed to light,
the resistance drops dramatically, even down to a few ohms, depending on
the light intensity. LDRs have a sensitivity that varies with the wavelength
of the light applied and are nonlinear devices. They are used in many
applications but are sometimes made obsolete by other devices such as
photodiodes and phototransistors. Some countries have banned LDRs
made of lead or cadmium over environmental safety concerns.

How an LDR Works?
It is relatively easy to understand the basics of how an LDR works without
delving into complicated explanations. It is first necessary to understand
that an electrical current consists of the movement of electrons within a
material. Good conductors have a large number of free electrons that can
drift in a given direction under the action of a potential difference.
Insulators with a high resistance have very few free electrons, and therefore
it is hard to make the them move and hence a current to flow.
An LDR or photoresistor is made any semiconductor material with a high
resistance. It has a high resistance because there are very few electrons
that are free and able to move - the vast majority of the electrons are
locked into the crystal lattice and unable to move. Therefore in this state
there is a high LDR resistance.

How an LDR Works?...
As light falls on the semiconductor, the light photons are absorbed by the
semiconductor lattice and some of their energy is transferred to the
electrons. This gives some of them sufficient energy to break free from the
crystal lattice so that they can then conduct electricity. This results in a
lowering of the resistance of the semiconductor and hence the overall LDR
resistance.
The process is progressive, and as more light shines on the LDR
semiconductor, so more electrons are released to conduct electricity and
the resistance falls further.

How an LDR Works?...

Types of LDR
Light dependent resistors, LDRs or photoresistors fall into one of two types
or categories:
Intrinsic photoresistors: Intrinsic photoresistors use un-doped
semiconductor materials including silicon or germanium. Photons fall on
the LDR excite electrons moving them from the valence band to the
conduction band. As a result, these electrons are free to conduct
electricity. The more light that falls on the device, the more electrons are
liberated and the greater the level of conductivity, and this results in a
lower level of resistance.
Extrinsic photoresistors: Extrinsic photoresistors are manufactured from
semiconductor of materials doped with impurities. These impurities or
dopants create a new energy band above the existing valence band. As a
result, electrons need less energy to transfer to the conduction band
because of the smaller energy gap.
Regardless of the type of light dependent resistor or photoresistor, both
types exhibit an increase in conductivity or fall in resistance with increasing
levels of incident light.

Photovoltaic Solar Cells
Can convert about 20% of light power into electricity
Voltage is low (diode drop, 0.6V)

Photovoltaic Solar Cells..
A solar cell is an electronic device that catches sunlight and turns it
directly into electricity. It’s about the size of an adult’s palm, octagonal in
shape, and colored bluish black. Solar cells are often bundled together to
make larger units called solar modules, themselves coupled into even
bigger units known as solar panels.
Just like the cells in a battery, the cells in a solar panel are designed to
generate electricity; but where a battery’s cells make electricity from
chemicals, a solar panel’s cells generate power by capturing sunlight
instead. They are sometimes called photovoltaic (PV) cells because they
use sunlight (”photo” comes from the Greek word for light) to make
electricity (the word ”voltaic” is a reference to Italian electricity pioneer
Alessandro Volta, 17451827).

Photovoltaic Solar Cells..
We can think of light as being made of tiny particles called photons, so a
beam of sunlight is like a bright yellow fire hose shooting trillions upon
trillions of photons our way. Stick a solar cell in its path and it catches
these energetic photons and converts them into a flow of electrons-an
electric current. Each cell generates a few volts of electricity, so a solar
panel’s job is to combine the energy produced by many cells to make a
useful amount of electric current and voltage. Virtually all of today’s solar
cells are made from slices of silicon (one of the most common chemical
elements on Earth, found in sand), although as we’ll see shortly, a variety
of other materials can be used as well (or instead). When sunlight shines
on a solar cell, the energy it carries blasts electrons out of the silicon.
These can be forced to flow around an electric circuit and power anything
that runs on electricity.

How are solar cells made?
Silicon is the stuff from which the transistors (tiny switches) in microchips
are madeand solar cells work in a similar way. Silicon is a type of material
called a semiconductor. Some materials, notably metals, allow electricity
to flow through them very easily; they are called conductors. Other
materials, such as plastics and wood, don’t really let electricity flow
through them at all; they are called insulators. Semiconductors like silicon
are neither conductors nor insulators: they don’t normally conduct
electricity, but under certain circumstances we can make them do so.
A solar cell is a sandwich of two different layers of silicon that have been
specially treated or doped so they will let electricity flow through them in a
particular way. The lower layer is doped so it has slightly too few
electrons. It’s called p-type or positive-type silicon (because electrons are
negatively charged and this layer has too few of them). The upper layer is
doped the opposite way to give it slightly too many electrons. It’s called
n-type or negative-type silicon.

How are solar cells made?..
When we place a layer of n-type silicon on a layer of p-type silicon, a
barrier is created at the junction of the two materials (the all-important
border where the two kinds of silicon meet up). No electrons can cross the
barrier so, even if we connect this silicon sandwich to a flashlight, no
current will flow: the bulb will not light up. But if we shine light onto the
sandwich, something remarkable happens. We can think of the light as a
stream of energetic ”light particles” called photons. As photons enter our
sandwich, they give up their energy to the atoms in the silicon. The
incoming energy knocks electrons out of the lower, p-type layer so they
jump across the barrier to the n-type layer above and flow out around the
circuit. The more light that shines, the more electrons jump up and the
more current flows.
This is what we mean by photovoltaiclight making voltageand it’s one kind
of what scientists call the photoelectric effect.

Application

Thank you
Please send your feedback at nbahadure@gmail.com
For more details and updates kindly visit
https://sites.google.com/site/nileshbbahadure/home
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Basic Electronics Electrical Transducers

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