Transducers Explained

UNIT-1
TRANSDUCER
DEEPA MISHRA ASSISTANT PROFESSOR JIT 1

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.

INTRODUCTION(cont’d)
• 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.
• 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.

MECHANICAL TRANSDUCER
• Mechanical Transducer are simple and rugged in construction, cheaper in cost, accurate
and operate without external power supplies but are not advantageous for many of the
modern scientific experiments and process control instrumentation owing to their poor
frequency response, requirement of large forces to overcome mechanical friction, in
compatibility when remote control or indication is required, and a lot of other
limitations. All these drawbacks have been overcome with the introduction of electrical
transducers.
ELECTRICAL TRANSDUCERS
• Mostly quantities to be measured are non-electrical such as temperature, pressure,
displacement, humidity, fluid flow, speed etc., but these quantities cannot be measured
directly. Hence such quantities are required to be sensed and changed into some other
form for easy measurement.

ELECTRICAL TRANSDUCERS(cont’d)
• Electrical quantities such as current, voltage, resistance. inductance and
capacitance etc. can be conveniently measured, transferred and stored,
and therefore, for measurement of non-electrical quantities these are to
be converted into electrical quantities first and then measured.
• The function of converting non-electrical quantity into electrical one is
accomplished by a device called the electrical transducer. Basically an
electrical transducer is a sensing device by which a physical, mechanical or
optical quantity to be measured is transformed directly, with a suitable
mechanism, into an electrical signal (current, voltage or frequency). The
production of these signals is based upon electrical effects which may be
resistive, inductive, capacitive etc in nature.

BASIC REQUIREMENTS OF A TRANSDUCER
• 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.
No Hysteretic. It should not give any hysteretic during measurement while
input signal is varied from its low value to high value and vice-versa.
Residual Deformation. There should be no deformation on removal of
local after long period of application.

CLASSIFICATION OF TRANSDUCER
• Primary and Secondary Transducers:Transducers, on the basis of methods
of applications, may be classified into primary and secondary transducers.
When the input signal is directly sensed by the transducer and physical
phenomenon is converted into the electrical form directly then such a
transducer is called the primary transducer.
• For example, in case of pressure measurement, bourdon tube is a primary
sensor which converts pressure first into displacement, and then the
displacement is converted into an output voltage by an LVDT. In this case
LVDT is secondary transducer.

ACTIVE AND PASSIVE TRANSDUCERS
• Transducers, on the basis of methods of energy conversion used, may be
classified into active and passive transducers.Self-generating type transducers
i.e. the transducers, which develop their output the form of electrical voltage
or current without any auxiliary source, are called the active transducers. Such
transducers draw energy from the system under measurement. Normal such
transducers give very small output and, therefore, use of amplifier becomes
essential.
• Transducers, in which electrical parameters i.e. resistance, inductance or
capacitance changes with the change in input signal, are called the passive
transducers. These transducers require external power source for energy
conversion. In such transducer electrical parameters i.e. resistance, inductance
or capacitance causes a change in voltages current or frequency of the
external power source. These transducers may draw sour energy from the
system under measurement. Resistive, inductive and capacitive transducer
falls in this category.

ANALOG AND DIGITAL DTANSDUCER
• Transducers, on the basis of nature of output signal, may be classified into
analog and digital transducers. Analog transducer converts input signal
into output signal, which is a continuous function of time such as
thermistor, strain gauge, LVDT, thermo-couple etc. Digital transducer
converts input signal into the output signal of the form of pulse e.g. it
gives discrete output.
• These transducers are becoming more and more popular now-a-days
because of advantages associated with digital measuring instruments and
also due to the effect that digital signals can be transmitted over a long
distance without causing much distortion due to amplitude variation and
phase shift. Sometimes an analog transducer combined with an ADC
(analog-digital convector) is called a digital transducer.

TRANSDUCERS AND INVERSE TRANSDUCERS
• Transducer, as already defined, is a device that converts a non-electrical
quantity into an electrical quantity. Normally a transducer and associated
circuit has a non-electrical input and an electrical output, for example a
thermo-couple, photoconductive cell, pressure gauge, strain gauge etc. An
inverse transducer is a device that converts an electrical quantity into a non-
electrical quantity. It is a precision actuator having an electrical input and a
low-power non-electrical output.
• For examples a piezoelectric crystal and transnational and angular moving-coil
elements can be employed as inverse transducers. Many data-indicating and
recording devices are basically inverse transducers. An ammeter or voltmeter
converts electric current into mechanical movement and the characteristics of
such an instrument placed at the output of a measuring system are important.
A most useful application of inverse transducers is in feedback measuring
systems.

SELECTION OF TRANSDUCERS
• In a measurement system the transducer (or a combination of
transducers) is the input element with the critical function of transforming
some physical quantity to a proportional electrical signal. So selection of
an appropriate transducer is most important for having accurate results.
• In case one or more transducer principles are capable of generating a
satisfactory signal, decision is to be taken whether to employ a
commercially available transducer or build a suitable transducer. If the
transducers are available in the market at a suitable price, the choice will
probably be to purchase one of them, otherwise own transducer will have
to be designed, built and calibrated.

SELECTION OF TRANSDUCERS
• 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.
• 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.
• However the total measurement error in a transducer-activated system
may be reduced to fall within the required accuracy range by adopting the
following techniques.

ERROR(CONTINUED)
 Calibrating the transducer output against some known standards while in
use under actual test conditions. This calibration should be performed
regularly as the measurement proceeds.
 Continuous monitoring of variations in the environmental conditions of the
transducer and correcting the data accordingly.
 Controlling the measurement environment artificially in order to reduce
possible transducer errors. Artificial environmental control includes the
enclosing of the transducer in a temperature-controlled housing and
isolating the device from external shocks and vibrations.

POTENTIOMETER
• A potentiometer, informally a pot, is a three-terminal resistor with a
sliding or rotating contact that forms an adjustable voltage divider If only
two terminals are used, one end and the wiper, it acts as a variable
resistor or rheostat.
• The measuring instrument called a potentiometer is essentially a voltage
divider used for measuring electric potential (voltage); the component is
an implementation of the same principle, hence its name.
• Potentiometers are commonly used to control electrical devices such as
volume controls on audio equipment. Potentiometers operated by a
mechanism can be used as position transducers for example, in a joystick.

POTENTIOMETER DIAGRAM

WORKING PRINCIPLE OF POTENTIOMETER
• The potentiometer can be used as a voltage divider to obtain a manually
adjustable output voltage at the slider (wiper) from a fixed input voltage
applied across the two ends of the potentiometer. This is their most
common use.
• The voltage across RL can be calculated by:
VL =( ( R2.RL)/R1.RL+R2.RL+R1.R2).VS
If RL is large as compared to other resistances then output will be
calculated by simple equation:
VL=((R2)/R1+R2)*VS

APPLICATION OF POTENTIOMETER
• Potentiometers are commonly used to control electrical devices such as
volume controls on audio equipment. Potentiometers operated by a
mechanism can be used as position transducers, for example, in a joystick.
Potentiometers are rarely used to directly control significant power (more
than a watt), since the power dissipated in the potentiometer would be
comparable to the power in the controlled load.
• Potentiometer is widely used in various fields: automotive, medical
equipment, robotics, wood processing machines, molding machines,
injection mold machines.
• How to choose an electronic ruler/potentiometer? Important
parameters include: 1, the required accuracy, linearity 2, the expected
range 3, repeatability / resolution 4, required torque (low) 5, the
environment, vibration, dust, temperature, humidity, 6, 7 electrical stroke,
requiring speed and price expectations and life.

LVDT
• An LVDT is a Linear Position Sensor With a Proportional Analog Output
• An LVDT has 2 Elements, a MovingCore and a Stationary Coil Assembly
Linear Variable Differential Transformer
• Transformer: AC Input / AC Output
• Differential: Natural Null Point in Middle
• Variable: Movable Core, Fixed Coil
• Linear: Measures Linear Position

CONSTRUCTION OF LVDT
LINEAR VARIABLE DIFFERENTIAL TRANSFORMER

Working principle of LVDT

LVDT Characteristics
• LVDT

Summary
• LVDT’s are robust equipment for measuring deflection.
• AC LVDT’s require separate signal conditioning equipment, while DC LVDT’s
include signal conditioning equipment on the device.
• There are three types of LVDT: unguided armature, captive armature, and
spring-extended armature.
• AC LVDT’s cost less than DC, but the entire measurement system must be
considered.
• Thus LVDT plays an important role in transforming energy from one
form to another

Strain Gauge
• If a metal conductor is stretched or compressed,its resistance changes on
account of the fact thatboth diameter and length of conductor
change.Also there is change in the value of resistivityof the conductor
when it is strained and this property is called piezoresistive
effect.Therefore ,resistance strain gauges are also known as piezoresistive
Gauges
Types Of Strain Gauge :
The following are the major types of strain gauges:
• Unbonded Metal Strain Gauges.
• Bonded Metal wire Strain Gauges.
• Bonded Metal foil Strain Gauges.
• Vacuum deposited thin metal film strain Gauges.

(continued)
Bonded Metal wire Strain Gauges.
• The Bonded metal wire strain gauge are used for both stress analysis and
for construction of Transducer.
• For Excellent and Reproducible result,it is desirable that the resistance
wire strain Gauges should have the following characteristics:
1. The Strain Gauge should have a high value of Gauge factor Gf.
2. The Resistance of the strain gauge should be as high as high
as possible

(continued)
• Bonded Metal foil Strain Gauges:
• This class of strain Gauge is only an Extension of the
bonded metal wire strain Gauges.
• Foil type Gauges have a much greater heat dissipation capacity as compared with wire
wound strain gauges on account of their greater
Surface area for the same volume.
Evaporation Deposited Thin Metal Strain Gauges :
Evaporation deposited thin film.

DIAGRAM FOR STRAIN GAUGE

APPLICATION OF STRAIN GAUGE
• strain gauge and method of making same for use in certain medical
applications, such as sensing the occurrence of an apnea event.
• The device is also applicable to monitoring mechanical motion associated with
other medical conditions.
• The strain gauge actually measures the change in direct current resistance
produced by stretching and compression of a number of carbon deposits
coupled in series on a longitudinally extendible substrate.
• This extendibility is produced by suitably die cutting a flexible but inherently
inelastic insulative substrate.
• The easily produced device may be used externally or encapsulated for
implantation.

RESISTANCE THERMOMETER
• An instrument used to measure a change in temperature by its effect on the
electrical resistance of a platinum or other metal wire.
• Resistance thermometers, also called resistance temperature
detectors (RTDs), are sensors used to measure temperature. Many RTD
elements consist of a length of fine wire wrapped around a ceramic or glass
core but other constructions are also used.
• The RTD wire is a pure material, typically platinum, nickel, or copper. The
material has an accurate resistance/temperature relationship which is used to
provide an indication of temperature. As RTD elements are fragile, they are
often housed in protective probes.
• RTDs, which have higher accuracy and repeatability, are slowly
replacing thermocouples in industrial applications below 600 °C.

IMAGES FOR RESISTANCE THERMOMETER

RESISTANCE THERMOMETER

ADVANTAGE AND LIMITATION OF RESISTANCE
THERMOMETER
The advantages of platinum resistance thermometers include:
• High accuracy
• Low drift
• Wide operating range
• Suitability for precision applications.
• Limitations:
• RTDs in industrial applications are rarely used above 660 °C. At
temperatures above 660 °C it becomes increasingly difficult to prevent the
platinum from becoming contaminated by impurities from the metal
temperature changes and have a slower response time. However,
thermistors have a smaller temperature range and stability.

ADVANTAGE AND LIMITATION OF RESISTANCE
THERMOMETER(CONTINUD)
• At very low temperatures, say below −270 °C (3 K), because there are very
few phonons, the resistance of an RTD is mainly determined
by impurities and boundary scattering and thus basically independent of
temperature. As a result, the sensitivity of the RTD is essentially zero and
therefore not useful.
• Compared to thermistors, platinum RTDs are less sensitive to small
temperature changes and have a slower response time.
• However, thermistors have a smaller temperature range and stability.

THERMOCOUPLE
• A thermocouple is an electrical device consisting of two dissisimilar
conductor forming electrical junction at different temperatures.
• A thermocouple produces a temperature-dependent voltage as a result of
the thermoelectric effect, and this voltage can be interpreted to measure
temperature.
• Thermocouples are a widely used type of temperature sensor.
• The main limitation with thermocouples is accuracy; system errors of less than
one degree Celsius (°C) can be difficult to achieve.
• Thermocouples are widely used in science and industry; applications include
temperature measurement for kilns, gas turbine exhaust, diesel engines, and
other industrial processes. Thermocouples are also used in homes, offices and
businesses as the temperature sensors in thermostats, and also as flame
sensors in safety devices for gas-powered major appliances.

THERMOCOUPLE(continued)
• Thermocouples are widely used in science and industry; applications
include temperature measurement for kilns, gas turbine exhaust, diesel
engines, and other industrial processes.
• Thermocouples are also used in homes, offices and businesses as the
temperature sensors in thermostats, and also as flame sensors in safety
devices for gas-powered major appliances.

THERMOCOUPLE(continued)

PRINCIPLE OF OPERATION OF THERMOCOUPLE
• When different metals are joined at the ends and there is a temperature difference
between the joints, a magnetic field is observed. At the time Seebeck referred to this as
thermo-magnetism. The magnetic field he observed was later shown to be due to
thermo-electric current.
• In practical use, the voltage generated at a single junction of two different types of wire
is what is of interest as this can be used to measure temperature at very high and low
temperatures. The magnitude of the voltage depends on the types of wire used
• Generally, the voltage is in the microvolt range and care must be taken to obtain a
usable measurement. Although current flows very little, power can be generated by a
single thermocouple junction.
• Power generation using multiple thermocouples, as in a thermopile, is common.

PRINCIPLE OF OPERATION OF
THERMOCOUPLE(CONTINUED)
• The standard configuration for thermocouple usage is shown in the figure.
Briefly, the desired temperature Tsense is obtained using three inputs—the
characteristic function E(T) of the thermocouple, the measured voltage V,
and the reference junctions' temperature Tref.
• The solution to the equation E(Tsense) = V + E(Tref) yields Tsense. These
details are often hidden from the user since the reference junction block
(with Tref thermometer), voltmeter, and equation solver are combined into
a single product.

APPLICATION USING THERMOCOUPLE

APPLICATION USING THERMOCOUPLE
• Thermocouples are suitable for measuring over a large temperature range,
from −270 up to 3000 °C (for a short time, in inert atmosphere).
• Applications include temperature measurement for kilns gas turbine
exhaust, diesel engines, other industrial processes and fog machines.
• They are less suitable for applications where smaller temperature
differences need to be measured with high accuracy, for example the
range 0–100 °C with 0.1 °C accuracy.
• For such applications thermistors silicon bandgap temperature
sensors and resistance thermometersare more suitable
• Steel industry

RVDT
• A rotary variable differential transformer (RVDT) is a type of electrical transformer
used for measuring angular displacement
• More precisely, a Rotary Variable Differential Transformer (RVDT) is an
electromechanical transducer that provides a variable alternating current (AC)
output voltage that is linearly proportional to the angular displacement of its input
shaft. When energized with a fixed AC source, the output signal is linear within a
specified range over the angular displacement.
• RVDTs use brushless, non-contacting technology to ensure long life and reliable,
repeatable position sensing with infinite resolution. Such reliable and repeatable
performance assures accurate position sensing under the most extreme operating
conditions.
• Most RVDTs consist of a wound, laminated stator and a salient two-pole rotor The
stator, containing four slots, contains both the primary winding and the two
secondary windings. Some secondary windings may also be connected together.

OPERATION OF RVDT
• The two induced voltages of the secondary winding vary linearly to the
mechanical angle of the rotor, θ:
θ =(v1-v2)/(v1+v2)).G
where G is gain sensitivity
• The second voltage can be reverse determined by
V2=V2+-Gθ
• The difference gives a proportional voltage
• Δ v=2.G.θ
and the sum of the voltages is a constant:
• C=∑=2V0

DIAGRAM OF RVDT

ADVANTAGE
• The advantages of the RVDT are:
• low sensitivity to temperature, primary voltage & frequency variations
• Sturdiness
• low cost
• simple control electronics
• small size

UNIT-2
TRANSDUCER-II

CAPACITIVE TRANSDUCER DIAGRAM

CAPACITIVE TRANSDUCER
• A capacitor consists of two conductors (plates) that are electrically
isolated from one another by a nonconductor (dielectric).
• When the two conductors are at different potentials (voltages), the
system is capable of storing an electric charge. The storage capability of a
capacitor is measured in farads.
• The principle of operation of capacitive transducers is based upon the
equation for capacitance of a parallel plate capacitor as shown in fig:
Where, A = Overlapping area of plates; m2,
d = Distance between two plates ;
E = Permittivity (dielectric constant); F/m.

DIAGRAM FOR CAPACITIVE TRANSDUCER

APPLICATION OF CAPACITIVE TRANSDUCER
• Capacitive transducers can be used for measurement of both linear and
angular displacements.
• The capacitive transducers are highly sensitive and can be used for
measurement of extremely small displacements down to the order of
molecular dimensions, i.e., 0.1x10-6 mm.
• On the other hand, they can be used for measurement of large displacements
up to about 30 m as in aeroplane altimeters.
• The change in area method is used for measurement of displacements
ranging from 10 to 100 mm. Capacitive transducers can be used for the
measurement of force and pressure

ADVANTAGE AND DISADVANTAGE OF
CAPACITIVE TRANSDUCER
ADVANTAGE:
• 1. construction is very simple.
• 2. cost of the transducer is low.
• 3. Has very high sensitivity.
DISADVANTAGE:
A disadvantage is that the seeing distance is very short, and
is varied.

PIEZOELECTRIC TRANSDUCERA
• Transducer can be anything which converts one form of energy to another.
Piezoelectric material is one kind of transducers. We squeeze this material
or we apply force or pressure on this material it converts it into electric
voltage and this voltage is function of the force or pressure applied to it.
• The force and pressure to be measured are first converted todisplacement
which causes a change of capacitance. Capacitive transducers can also be
used directly as pressure transducers in all those cases where the
dielectric constant of a medium changes with pressure.
• They can be used for measurement of humidity in gases and moisture
content in soil / food products etc.

PIEZOELECTRIC TRANSDUCER(CONTINUED)
• The material which behaves in such a way is also known as piezoelectric
sensor.The electric voltage produced by piezoelectric transducer can be
easily measured by voltage measuring instruments, which can be used to
measure stresses or forces. The physical quantity like mechanical stress or
force cannot be measured directly. Therefore, piezoelectric transducer can
be used.
• The material which behaves in such a way is also known as piezoelectric
sensor.The electric voltage produced by piezoelectric transducer can be
easily measured by voltage measuring instruments, which can be used to
measure stresses or forces. The physical quantity like mechanical stress or
force cannot be measured directly. Therefore, piezoelectric transducer can
be used.

DIAGRAM FOR PIEZOELECTRIC TRANSDUCER

PIEZOELECTRIC TRANSDUCER
ADVANTAGE:
• They generate a voltage proportional to the velocity the crystal is
deformed so require no local power source.
DISADVANTAGE :
• They are high impedencand can pick up stray voltages in the
connecting wires. The crystal is also prone to cracking if overstressed

APPLICATION
Application of Piezoelectric Materials?
• In microphones, the sound pressure is converted into electric signal and
this signal is ultimately amplified to produce louder sound.
• Automobile seat belts lock in response to a rapid deceleration is also done
by piezoelectric material.
• It is also used in medical diagnostics.
• It is used in electric lighter used in kitchens. Pressure made on
piezoelectric sensor creates an electric signal which ultimately causes flash
to fire up.
• They are used for studying high speed shock waves and blast waves.

HALL EFFECT TRANSDUCER
• The Hall effect is the production of a voltage difference (the Hall voltage)
across a current carrying conductor (in presence of magnetic field),
perpendicular to both current and the magnetic field.
• The Hall effect was discovered in 1879 by Edwin Herbert Hall whileworking
on his doctoral degree at the Johns Hopkins University in Baltimore,
Maryland, USA.
• A static magnetic field has no effect on a charged particle unless it is
moving.
• When charges flow, a mutually perpendicular force (Lorentz force) is
induced on the charge.
• Now electrons and holes are separated by opposite force.

THEORY
• A static magnetic field has no effect on a charged particle unless it is
moving.
• When charges flow, a mutually perpendicular force (Lorentz force) is
induced on the charge.
• Now electrons and holes are separated by opposite force.
• Thus R=Vh/aJH=Vhb/IH
• Vh is Hall Voltage and I is Jab

DIAGRAM FOR HALL EFFECT

WORKING
• When a beam of charged particles passes through a magnetic field, forces
act on the particles and the beam is deflected from a straight path.
• The flow of electrons through a conductor is known as a beam of charged
carriers. When a conductor is placed in a magnetic field perpendicular to
the direction of the electrons, they will be deflected from a straight path.
• As a consequence, one plane of the conductor will become negatively
charged and the opposite side will become positively charged.
• The voltage between these planes is called Hall voltage.

WORKING(CONTINUED)
• When the force on the charged particles from the electric field
balances the force produced by magnetic field, the separation of
them will stop.
• If the current is not changing, then the Hall voltage is a measure of
the magnetic flux density. Basically, there are two kinds of Hall
effect sensors.
• One is linear which means the output of voltage linearly depends
on magnetic flux density; the other is called threshold which means
there will be a sharp decrease of output voltage at each magnetic
flux density.

WORKING DIAGRAM

APPLICATION OF HALL EFFECT
• Position sensing:
• Sensing the presence of magnetic objects (connected with the
position sensing) is the most common industrial application of Hall
effect sensors, especially those operating in the switch mode
(on/off mode).
• The Hall effect sensors are also used in the brushless DC motor to
sense the position of the rotor and to switch the transistors in the
right sequence.
• Smartphones use hall sensors to determine if the Flip Cover
accessory is closed.

APPLICATION OF HALL EFFECT(CONTINUED)
• Direct current (DC) transformers:
Hall effect sensors may be utilized for contactless measurements of DC
current in current transformers. In such a case the Hall effect sensor is
mounted in the gap in magnetic core around the current conductor. As a
result, the DC magnetic flux can be measured, and the DC current in the
conductor can be calculated.
• Automotive fuel level indicator:
The Hall sensor is used in some automotive fuel level indicators. The main
principle of operation of such indicator is position sensing of a floating
element. This can either be done by using a vertical float magnet or a
rotating lever sensor.

ADVANTAGE OF HALL EFFECT TRANSDUCER
• A Hall effect sensor may operate as an electronic switch.
• Such a switch costs less than a mechanical switch and is much more
reliable.
• It can be operated up to 100 kHz.
• It does not suffer from contact bounce because a solid state switch with
hysteresis is used rather than a mechanical contact.
• It will not be affected by environmental contaminants since the sensor is
in a sealed package. Therefore, it can be used under severe conditions.
• In the case of linear sensor (for the magnetic field strength
measurements), a Hall effect sensor:
• can measure a wide range of magnetic fields
• is available that can measure either North or South pole magnetic fields
• can be flat

DISADVANTAGE OF HALL EFFECT
• Hall effect sensors provide much lower measuring accuracy than fluxgate
magnetometers or magnetoresistance-based sensors. Moreover, Hall
effect sensors drift significantly, requiring compensation.
OPTO ELECTRONIC TRANSDUCER
Opto Electronic transducer include photh voltaic cell,semiconcuctor photo
diode and photo diode.
PHOTO VOLTAIC CELL

OPTO-ELECTRONIC TRANSDUCER
PHOTO VOLTAIC CELL :
Photovoltaics (PV) covers the conversion of light
into electricity using semiconducting materials that exhibit the photo
voltaic , a phenomenon studiedin physics photochemistry,and electro-
chemistry .
• A typical photovoltaic system employs solar panels each comprising a
number of solar cells, which generate electrical power.
• Solar PV generates no pollution.
• The direct conversion of sunlight to electricity occurs without any moving
parts.

DIAGRAM FOR PHOTO VOLTAIC CELL

UNIT-3
• GENERAL TELEMETRY SYSTEM
• DATA ACQUISITION SYSTEM

GENERAL TELEMETRY SYSTEM
• Telemetry may be defined as measurement at a distance.
• A general telemetering system consist of following stages:
• 1. Measurand
• 2. Primary Sensing Element
• 3. Telemeter Transmitter
• 4. Telemeter Channel
• 5. Telemeter Receiver
• 6. End Devices

C
• This electrical signal in usable form is indicated or recorded by an end
device,which is graduated in terms of measurand.
Types Of Telemetering System
• There are two types of Telemetering system:
1. Land Line Telemetry
2. R.F. (Radio Frequency) Telemetry
LAND LINE TELEMETRY:
A Land Line Telemetering system requires a telemeter channel which is a
physical link between the telemeter transmitter and Receiver.

APPLICATION OF PHOTO VOLTAIC CELL

ADVANTAGE AND DISADVANTAGE OF PHOTO
VOLTAIC CELL

PHOTO DIODE
PHOTO DIODE :
A photodiode is a semiconductor device that
converts light into current. The current is generated when photons
are absorbed in the photodiode.
• A small amount of current is also produced when no light is
present. Photodiodes may contain optical filters, built-in lenses, and
may have large or small surface areas.
• Photodiodes usually have a slower response time as their surface
area increases. The common, traditional solar cell used to generate
electric solar power is a large area photodiode.

PHOTO DIODE(CONTINUED)
• Photodiodes are similar to regular semiconductor diodes except that they
may be either exposed (to detect vacuum UV or X-rays) or packaged with a
window or optical fiber connection to allow light to reach the sensitive
part of the device.
• A photodiode is a p–n junction or PIN structure. When a photon of
sufficient energy strikes the diode, it creates an electron-hole pair. This
mechanism is also known as the inner photoelectric effect.
• If the absorption occurs in the junction's depletion region, or one
diffusion length away from it, these carriers are swept from the junction
by the built-in electric field of the depletion region.
• Thus holes move toward the anode, and electrons toward the cathode,
and a photocurrent is produced

• If the absorption occurs in the junction's depletion region, or one
diffusion length away from it, these carriers are swept from the
junction by the built-in electric field of the depletion region.
• Thus holes move toward the anode, and electrons toward
the cathode, and a photocurrent is produced.
• The total current through the photodiode is the sum of the dark
current (current that is generated in the absence of light) and the
photocurrent, so the dark current must be minimized to maximize
the sensitivity of the device.

DIAGRAM FOR PHOTO DIODE

PHOTO DIODE
• photo diode donot work for long distance photo diode act as a receiver.
• Advantages compared to photomultipliers.
• Excellent linearity of output current as a function of incident light
• Spectral response from 190 nm to 1100 nm (silicon),
longer wavelengths with other semiconductor materials
• Low noise
• Ruggedized to mechanical stress
• Low cost
• Compact and light weight
• Long lifetime
• High quantum efficiency, typically 60–80%
• No high voltage required

• Small area
• No internal gain (except avalanche photodiodes but their gain is
typically 102–103 compared to 105-108 for the photomultiplier).
• Much lower overall sensitivity.
• Photon counting only possible with specially designed, usually
cooled photodiodes, with special electronic circuits
• Response time for many designs is slower
• latent effect

APPLICATION OF PHOTO DIODE
• P–n photodiodes are used in similar applications to other photodetectors,
such as photoconductors, charge-coupled devices and photomultiplier tubes .
• They may be used to generate an output which is dependent upon the
illumination (analog; for measurement and the like), or to change the state of
circuitry (digital; either for control and switching, or digital sig-
-nal processing.
• Photodiodes are used in consumer electronics devices such as compact
discplayers, smoke detectors, and the receivers for infrared remote control
devices used to control equipment from televisions to air conditioners.
• For many applications either photodiodes or photoconductors may be used.

PHOTO TRANSISTOR
• The sensitivity of a photodiode can be increased by as a large factor 100
by addition of a junction which makes it a N-P-N i.e a photo transistor.
• Illumination of the central region causes the release of electron hole pair
here.This lowers the barrier potential across the both junction,causing an
increase in the flow of electron from left hand region in to the central
region and on the right hand region.
• For a given amount of illumination on a very small area ,the photo
transistor provides a much larger output current than that is available
and therefore photo transistors are much sensitive than a photodiode

DIAGRAM FOR PHOTO TRANSISTOR

APPLICATION OF PHOTO TRANSISTOR
• Phototransistors are photodiode-amplifier combinations integrated
within a single silicon chip. The phototransistor can be viewed as a
photodiode whose output current is fed into the base of a
conventional transistor.
• These photodiode-amplifier combinations are put together to
overcome the major limitation of photodiodes: unity gain.
• The typical gain of a phototransistor can range from 100 to over
1500. Many applications demand a greater output than can be
generated by a photodiode alone.

CIRCUIT SYMBOL

MEASUREMENT OF PRESSURE
BOURDON TUBE:
• Many techniques have been developed for the measurement
of pressure and vacuum. Instruments used to measure and display pressure in
an integral unit are called pressure gauges or vacuum gauges.
• A manometer is a good example as it uses a column of liquid to both
measure and indicate pressure
• Likewise the widely used Bourdon gauge is a mechanical device which both
measures and indicates, and is probably the best known type of gauge.
• A vacuum gauge is an absolute pressure gauge used to measure the pressures
lower than the ambient atmospheric pressure.
• Other methods of pressure measurement involve sensors which can transmit
the pressure reading to a remote indicator or control system

BOURDON TUBE

MEASUREMENT OF TEMPERATURE
• A thermistor is a type of resistor whose resistance is dependent
on temperature, more so than in standard resistors. The word is
a portmanteau of thermal and resistor. Thermistors are widely used
as inrush current limiter, temperature sensors (Negative Temperature
Coefficient or NTC type typically), self-resetting overcurrent protectors,
and self-regulating heating elements (Positive Temperature Coefficient
or PTC type typically).
• Thermistors are of two opposite fundamental types:
• With NTC, resistance decreases as temperature rises to protect against
inrush overvoltage conditions. Commonly installed parallel in a circuit. As
current sink.
• With PTC, resistance increases as temperature rises to protect
against overcurrent conditions. Commonly installed series in a circuit. As
resetteable fuse.

APPLICATION OF THERMISTOR
• As current-limiting devices for circuit protection, as replacements for
fuses. Current through the device causes a small amount of resistive
heating. If the current is large enough to generate more heat than the
device can lose to its surroundings, the device heats up, causing its
resistance to increase. This creates a self-reinforcing effect that drives the
resistance upwards, therefore limiting the current.
• As timers in the degaussing coil circuit of most CRT displays. When the
display unit is initially switched on, current flows through the thermistor
and degaussing coil.
• The coil and thermistor are intentionally sized so that the current flow will
heat the thermistor to the point that the degaussing coil shuts off in under
a second.

APPLICATION OF THERMISTOR(CONTINUED)
• As heater in automotive industry to provide additional heat inside
cabin with diesel engine or to heat diesel in cold climatic conditions
before engine injection.
• In temperature compensated synthesizer voltage controlled
oscillators.
• In lithium battery protection circuits.
• In an electrically actuated Wax motor to provide the heat necessary
to expand the wax.

DIAGRAM FOR THERMISTOR

CHARACTERISTICS OF THERMISTOR

MEASUREMENT OF FLOW
• The third most common flowmeter (behind differential pressure and
positive displacement flow meters) is the magnetic flow meter, also
technically an electromagnetic flow meter or more commonly just called
a mag meter.
• A magnetic field is applied to the metering tube, which results in a
potential difference proportional to the flow velocity perpendicular to the
flux lines.
• The physical principle at work is electromagnetic induction. The magnetic
flow meter requires a conducting fluid, for example, water that contains
ions, and an electrical insulating pipe surface, for example, a rubber-lined
steel tube.

MEASUREMENT OF FLOW(CONTINUED)
• If the magnetic field direction were constant, electrochemical and other
effects at the electrodes would make the potential difference difficult to
distinguish from the fluid flow induced potential difference.
• To mitigate this in modern magnetic flowmeters, the magnetic field is
constantly reversed, cancelling out the electrochemical potential
difference, which does not change direction with the magnetic field.
• This however prevents the use of permanent magnets for magnetic
flowmeters.

DIAGRAM FOR ELECTROMAGNETIC FLOW METER

DIAGRAM FOR MEASUREMENT OF LIQUID LEVEL BY
ULTRASONIC METHOD

ULTRA SONIC METHOD
• ULTRA SONIC METHOD :
• Ultrasonic testing (UT) is a family of non-destructive testing techniques
based on the propagation of ultrasonic waves in the object or material
tested.
• In most common UT applications, very short ultrasonic pulse-waves with
center frequencies ranging from 0.1-15 MHz, and occasionally up to
50 MHz, are transmitted into materials to detect internal flaws or to
characterize materials.
• A common example is ultrasonic thickness measurement, which tests the
thickness of the test object, for example, to monitor pipework corrosion.

• Ultrasonic testing is often performed on steel and other metals and alloys,
though it can also be used on concrete, wood and composites, albeit with
less resolution. It is used in many industries including steel and aluminium
construction, metallurgy, manufacturing, aerospace, automotive and
other transportation sectors.

UNIT-3
• GENERAL TELEMETRY SYSTEM
• DATA ACQUISITION SYSTEM

DATA ACQUISITION SYSTEM
• Telemetry may be defined as measurement at a distance.
• A general telemetering system consist of following stages:
• 1. Measurand
• 2. Primary Sensing Element
• 3. Telemeter Transmitter
• 4. Telemeter Channel
• 5. Telemeter Receiver
• 6. End Devices

DATA ACQUISITION SYSTEM(CONTINUED)
• This electrical signal in usable form is indicated or recorded by an end
device,which is graduated in terms of measurand.
Types Of Telemetering System
• There are two types of Telemetering system:
1. Land Line Telemetry
2. R.F. (Radio Frequency) Telemetry
LAND LINE TELEMETRY:
A Land Line Telemetering system requires a telemeter channel which is a
physical link between the telemeter transmitter and Receiver.

Types Of Telemetering System(continued)
• Telemeter Channel may be any physical link like cable.
• The land line telemetry system can be classified as:
1. Voltage Telemetering System
2.Current Telemetering system
3. Position Telemetering system

Type of Telemetering system(continued)
Voltage Telemetering system:
A voltage telemetering system transmits the measured variable as a function
of an a.c. or d.c. Voltage.
• A Voltage telemetering system is suitable for adding several output
voltages in series.
Current Telemetering system :
A current telemetering system transmits the
measured variable as a function of a.c. or d.c. current.
• Current Telemetering system includes slide wire potentiometer connected
in series with a battery, thereby changing the current in the circuit. This
current is measured with the help of milliammeter whose scale is graduated
in terms of pressure.
• The commonly used current telemetering system are Motion and Force
Balance type which are improved forms of the basic current telemetering
system.

Current Telemetering system(continued)
• In a Motion Balance System the slidewire is replaced by a position
detector like an
LVDT.Capacitive transducer may also be used.
• In Force Balance system , a part of the current output is fedback to
appose the motion of the input variable.
Position Telemetering System:
A Position Telemetering System transmits
and reproduces the measured variable by positioning variable resistor or
other electrical components in a bridge circuit form so as to produce
proportional changes at the transmitter and Receiver end.This is known as
bridge type system.
• Another most commonly used position telemetry system utilizes a synchro
Transmitter and Receiver .

Radio Frequency Telemetering System
• A Technology that enables the user to collect data from several
measurement points at inaccessible or inconvenient locations.
• This requires no physical link between transmitting and receiving stations.
• The link between transmitting station and receiving station is through
radio link.
• R.F Telemetry is suitable if the data is to be transmitted over
distancesgreater than 1 km.
• The Rocket ao unnammed space craft presents more obvious need for a
radio
Link based telemetry.The vehicle in this case is too small to carry even
one person,much lessthe entireteam of engineers and also a computer.

Transmission Channel And Media
• A path between two nodes in a network. It may refer to the physical cable, the signal transmitted
within the cable or to a subchannel within a carrier frequency. In radio and TV, it refers to the
assigned carrier frequency.
• Transmission can be by electrical conductors, radio or optical fibre .
• High-frequency signals can also be propagated without a medium, and are called radio. As
frequency rises further the electromagnetic energy is termed 'light' which can also travel without a
medium, but can also be guided through a suitable medium.
•
• TRANSMISSION MEDIA
• The means through which data is transformed from one place to another is called transmission or
communication media. There are two categories of transmission media used in computer
communications.
• BOUNDED/GUIDED MEDIA
• UNBOUNDED/UNGUIDED MEDIA

TRANSMISSION MEDIA
• BOUNDED MEDIA:
• Bounded media are the physical links through which signals are
confined to narrow path. These are also called guide media.
• Bounded media are made up o a external conductor (Usually
Copper) bounded by jacket material.
• Three common types of bounded media are used of the data
transmission. These are:
• Coaxial Cable
• Twisted Pairs Cable
• Fiber Optics Cable

TRANSMISSION MEDIA(CONTINUED)
• UnBounded/UnGuided Transmission Media
• Unguided or wireless media sends the data through air (or water), which is
available to anyone who has a device capable of receiving them. Types of
unguided/ unbounded media are discussed below :
• Radio Transmission
• MicroWave Transmission
• Radio Transmissioan
• Its frequency is between 10 kHz to 1GHz. It is simple to install and has high
attenuation. These waves are used for multicast communications.

TRANSMISSION MEDIA(CONTINUED)
• Microwave Transmission
• It travels at high frequency than the radio waves. It requires the sender to
be inside of the receiver. It operates in a system with a low gigahertz
range.
• It is mostly used for unicast communication.
• There are 2 types of Microwave Transmission :
• Terrestrial Microwave
• Satellite Microwave

Data Receiver and Transmitter
Receiver
A device, as in a radio or telephone, that converts incoming
radio or microwave signals to a form, such as sound or light the
at can be perceived by humans.
Transmitter:
• a device that sends out radio or television signals
• a person or thing that causes something to be spread
or transmitted to others.

Acquisition System
• An instrumentation system is an aggregation or assembly of device united
by some form of regular interaction of and interdependance.
• Data Acquisition systems are used to measure and record analog signals in
basically two different ways:
1.Signals which originate from direct measurement of electricalAnalog Data
Acquisition system typically consist of some or all of the following
elements:
2.Signals which originate from use oftransducer.
Types Of Instrumentation System
The instrumentation system can be classified in to two distinct categories:
Analog System:
These system deal with information in analog form.

Types Of Instrumentation System(continued)
• Digital System:
A digital quantity may consist of a number of discrete or discontinuous
pulses whose time relationship contains information about the magnitude
and nature of the quantity under measurement of voltage versus time.
Analog Data Acquisition System
An analog data acquisition system typically consists of some or all of
the following elements:
• Transducer:
This is use to convert one form of energy to another and vice-
versa.
• Signal conditioning Equipment:
This includes any equipment that assists in
transforming the output of the transducer to the desired magnitude or form
required by the next stage of the DAS.

Types Of Instrumentation System(continued)
• Multiplexer:
Multiplexing is the process of sharing a single channel with
more than one output.
• Calibrating Equipment:
Before each test there is a pre- calibration , and
often after each calibration there is a post –calibration.
• Integrating Equipment
• Analog Recorder
• Analog Computer
• High Speed Cameras and TV Equipment.

Types Of Multiplexing System
There are two methods of multiplexing:
1.Time Division multiplexing
2. Frequency Division multiplexing
Time Division Multiplexing:
In time division multiplexing the information
fromdifferent measuring points is transmitted serially one after another
on the same communication channel.
Frequency Division Multiplexing:
Several information can be simultaneously
using different carrier frequency and employing
modulation Technique.

Digital Data Acquisition System
An Digital data acquisition system typically consists of some or all of
thefollowing elements:
• Transducer:
This is use to convert one form of energy to another and vice-
versa.
• Signal conditioning Equipment:
This includes any equipment that assists in
transforming the output of the transducer to the desired magnitude or form
required by the next stage of the DAS.

Digital Data Acquisition System(continued)
• Multiplexer:
Multiplexing is the process of sharing a single channel with
more than one output.
• Signal Converter
• A/D Converter
• Auxilliary Equipment
• Digital Recorder

BLOCK DIAGRAM FOR
DDAS

Digital Data Acquisition System(continued)
• Digital Recorder
Functional Operation OF DigitaL
• Handling of Analog Signals.
• Making the measurements.
• Internal programming and control
Uses Of DAS
• Analog DAS are used when wide frequency width is required or when
lower accuracy can be tolerated.

Uses Of DAS(continued)
• Digital DAS are used when physical quantity being monitored has a
narrow bandwidth.
MODERN DIGITAL DAS
The electronics devices that perform the interfacing function between the
analog and digital world.
Besides A/D or D/A, DAS may employ one or more of the following circuit
functions:
• Transducer:
converts energy from one form to another and vice versa.
• Amplifier:
This is use for amplifying signal.
• Filter:
This reduces high frequency signal,unwanted signal from signal.

MODERN DIGITAL DAS(continued)
• Nonlinear analog function:
This performs the non linear operation on the
high levelsignal.
• Analog multiplexer
• Sample Holds
some of the specific application in which data converters are use are
data telemetry system,pulse coded communication,automatic test
system.

UNIT-4
DISPLAY DEVICES AND RECORDERS

DISPLAY DEVICES AND RECORDER
DISPLAY DEVICES:
A display device is an output device for presentation of
information in visual or tactile form (the latter used for example in tactile)
electronic displays for blind people.
When the input information is supplied has an electrical signal,
the display is called an electronic display.
RECORDER:
An apparatus for recording sound, pictures, or data.

DIGITAL STORAGE OSCILLOSCOPE
• The digital storage oscilloscope, or DSO for short, is now the preferred
type for most industrial applications. Instead of storage-type cathode ray
tubes, DSOs use digital memory which can store data as long as required
without degradation.
• A digital storage oscilloscope also allows complex processing of the signal
by high-speed digital signal processing circuits.
• The vertical input is digitized by an analog to digital converter to create a
data set that is stored in the memory of a microprocessor. The data set is
processed and then sent to the display, which in early DSOs was a cathode
ray tube, but is now more likely to be an LCD flat panel. DSOs with color
LCD displays are common.

DIGITAL OSCILLOSCOPE (CONTINUED)
• The data set can be sent over a LAN or a WAN for processing or archiving.
The screen image can be directly recorded on paper by means of an
attached printer or plotter, without the need for an oscilloscope camera.
• The oscilloscope's own signal analysis software can extract many useful
time-domain features (e.g., rise time, pulse width, amplitude), frequency
spectra, histograms and statistics, persistence maps, and a large number
of parameters meaningful to engineers in specialized fields such as
telecommunications, disk drive analysis and power electronics.
• Digital storage also makes possible another type of oscilloscope, the
equivalent-time sample oscilloscope. Instead of taking consecutive
samples after the trigger event, only one sample is taken.

DIGITAL OSCILLOSCOPE (CONTINUED)
• However, the oscilloscope is able to vary its timebase to precisely time its
sample, thus building up the picture of the signal over the subsequent
repeats of the signal.
• This requires that either a clock or repeating pattern be provided. This
type of oscilloscope is frequently used for very high speed communication
because it allows for a very high "sample rate" and low amplitude noise
compared to traditional real-time oscilloscopes.

DIAGRAM FOR DIGITAL OSCILLOSCOPE

ANALOG STORAGE OSCILLOSCOPE
• Trace storage is an extra feature available on some analog oscilloscopes; they used direct-
view storage CRTs. Storage allows the trace pattern that normally decays in a fraction of a
second to remain on the screen for several minutes or longer. An electrical circuit can then be
deliberately activated to store and erase the trace on the screen.
• The storage is accomplished using the principle of secondary emission. When the ordinary
writing electron beam passes a point on the phosphor surface, not only does it momentarily
cause the phosphor to illuminate, but the kinetic energy of the electron beam knocks other
electrons loose from the phosphor surface.
• This can leave a net positive charge. Storage oscilloscopes then provide one or more
secondary electron guns (called the "flood guns") that provide a steady flood of low-energy
electrons traveling towards the phosphor screen.
• Flood guns cover the entire screen, ideally uniformly.

ANALOG STORAGE OSCILLOSCOPE(CONTINUED)
• If the energy of the flood gun electrons is properly balanced, each
impinging flood gun electron knocks out one secondary electron from the
phosphor screen, thus preserving the net positive charge in the
illuminated areas of the phosphor screen.
• In this way, the image originally written by the writing gun can be
maintained for a long time — many seconds to a few minutes.
• Eventually, small imbalances in the secondary emission ratio cause the
entire screen to "fade positive" (light up) or cause the originally written
trace to "fade negative" (extinguish). It is these imbalances that limit the
ultimate storage time possible.

ANALOG STORAGE OSCILLOSCOPE(CONTINUED)
• The electrons from the flood guns are more strongly drawn to the areas of
the phosphor screen where the writing gun has left a net positive charge;
in this way, the electrons from the flood guns re-illuminate the phosphor
in these positively charged areas of the phosphor screen.
• Storage oscilloscopes (and large-screen storage CRT displays) of this type,
with storage at the phosphor, were made by Tektronix.
• Other companies, notably Hughes, earlier made storage oscilloscopes
with a more-elaborate and costly internal storage structure.

DIAGRAM FOR ANALOG STORAGE OSCILLOSCOPE

CATHODE RAY TUBE
• simplest type of oscilloscope consisted of a cathode ray tube a
vertical amplifier, a timebase, a horizontal amplifier and a power supply.
These are now called "analog" oscilloscopes to distinguish them from the
"digital" oscilloscopes that became common in the 1990s and 2000s.
• Before the introduction of the CRO in its current form, the cathode ray
tube had already been in use as a measuring device. The cathode ray tube
is an evacuated glass envelope, similar to that in a black-and-
white television set, with its flat face covered in a fluorescent material
(the phosphor).
• The screen is typically less than 20 cm in diameter, much smaller than the
one in a television set. Older CROs had round screens or faceplates, while
newer CRTs in better CROs have rectangular faceplates.

CATHODE RAY TUBE(CONTINUED)
• However, when G1 becomes less negative with respect to the cathode,
another cylindrical electrode designated G2, which is hundreds of volts
positive referred to the cathode, attracts electrons through the hole. Their
trajectories converge as they pass through the hole, creating quite-small
diameter "pinch" called the crossover. Following electrodes ("grids"),
electrostatic lenses, focus this crossover onto the screen; the spot is an
image of the crossover.
• Typically, the CRT runs at roughly -2 kV or so, and various methods are
used to correspondingly offset the G1 voltage. Proceeding along the
electron gun, the beam passes through the imaging lenses and first anode,
emerging with an energy in electron-volts equal to that of the cathode.
The beam passes through one set of deflection plates , then the other,
where it is deflected as required to the phosphor screen.

CATHODE RAY TUBE(CONTINUED)
• The average voltage of the deflection plates is relatively close to
ground, because they have to be directly connected to the vertical
output stage.
• A small negative grid potential (referred to the cathode) is used to
block electrons from passing through the hole when the electron
beam needs to be turned off, as during sweep retrace or when no
trigger events occur.
• In the neck of the tube is an electron gun, which is a small heated
metal cylinder with a flat end coated with electron-emitting oxides.
Close to it is a much-larger-diameter cylinder carrying a disc at its
cathode end with a round hole in it; it's called a "grid" (G1), by
historic analogy with amplifier vacuum-tube grids.

DIAGRAM FOR CRT

DUAL BEAM OSCILLOSCOPE
• A dual-beam oscilloscope was a type of oscilloscope once used to
compare one signal with another.
• There were two beams produced in a special type of CRT.
• Unlike an ordinary "dual-trace" oscilloscope (which time-shared a single
electron beam, thus losing about 50% of each signal), a dual-beam
oscilloscope simultaneously produced two separate electron beams,
capturing the entirety of both signals.
• One type (Cossor, UK) had a beam-splitter plate in its CRT, and single-
ended vertical deflection following the splitter. (There is more about this
type of oscilloscope near the end of this article.)

DUAL BEAM OSCILLOSCOPE(CONTINUED)
• On some dual-beam oscilloscopes the time base, horizontal plates and
horizontal amplifier were common to both beams (the beam-splitter CRT
worked this way).
• More elaborate oscilloscopes like the Tektronix 556 and 7844 could
employ two independent time bases and two sets of horizontal plates and
horizontal amplifiers.
•
• Thus one could look at a very fast signal on one beam and a slow signal on
another beam.
• Most multichannel oscilloscopes do not have multiple electron beams.
Instead, they display only one trace at a time, but switch the later stages
of the vertical amplifier between one channel and the other either on
alternate sweeps (ALT mode) or many times per sweep (CHOP mode).

DUAL BEAM OSCILLOSCOPE(CONTINUED)
• Very few true dual-beam oscilloscopes were built.
• With the advent of digital signal capture, true dual-beam oscilloscopes
became obsolete, as it was then possible to display two truly simultaneous
signals from memory using either the ALT or CHOP display technique, or
even possibly a raster display mode.
• Other dual-beam oscilloscopes had two complete electron guns, requiring
tight control of axial (rotational) mechanical alignment in manufacturing
the CRT. In the latter type, two independent pairs of vertical plates deflect
the beams.
• Vertical plates for channel A had no effect on channel B's beam. Similarly
for channel B, separate vertical plates existed which

BLOCK DIAGRAM FOR DUAL BEAM OSCILLOSCOPE

SPECTRUM ANALYSER
• A spectrum analyzer measures the magnitude of an input signal versus
frequency within the full frequency range of the instrument.
• The primary use is to measure the power of the spectrum of known and
unknown signals.
• The input signal that a spectrum analyzer measures is electrical;
however, spectral compositions of other signals, such as acoustic pressure
waves and optical light waves, can be considered through the use of an
appropriate transducer.
• A Optical spectrum analyzers also exist, which use direct optical
techniques such as a monochromator to make measurements.

SPECTRUM ANALYSER(CONTINUED)
• The display of a spectrum analyzer has frequency on the horizontal axis and
the amplitude displayed on the vertical axis.
• To the casual observer, a spectrum analyzer looks like an oscilloscope and, in
fact, some lab instruments can function either as an oscilloscope or a
spectrum analyzer.
• spectrum analyzers may seem really technical and scientific to the ears. This is
because spectrum analyzers are often used in factories and in laboratories.
• Spectrum analyzers are instruments that is used to receive and select
frequency levels based on the superheterodyne principle. It is very sensitive,
converting higher frequencies of up to 10s GHZ into something that is
measurable. Received frequencies are first put into a series of pre-selected
values.

SPECTRUM ANALYSER(CONTINUED)
• These are then converted into a frequency that is selected to a DC level
that is measurable. Often the values are converted into the logarithmic
scales. These values are then displayed in the CRT, with the signal strength
in the y-axis and the frequency in the x-axis.
• Signals that are weaker than the noise in the background cannot be
measured by the spectrum analyzer, power levels that are often seen in
microwave receivers.
• This is the reason why spectrum analyzers need the RBW to be able to
determine these measurements. Here, the received signals are measured
in decibels rather than voltage because of the low signal strengths that are
received and the frequency range of the measurements.

SPECTRUM ANALYSER
• Another use is as a microwave tower monitor, where its transmitted
power and receiver power is measured. This is one way to verify the
strength and frequency of the signal.
• Spectrum analyzers are also being used to identify and measure
interference in signals, which are often needed in site operations of
telecom towers, TV stations and the guiding systems of airports
• Spectrum analyzers especially the modern ones have a lot of uses. One of
which is as a device frequency response measurements, which is used
primarily in measuring amplitude response in dBm in comparison to the
frequency of the device. The resulting value is on Hertz.

DIAGRAM FOR SPECTRUM ANALYSER

WORKING OF TRANSDUCER
A strip chart recorder records the variations of a quantity with respect to
time while X-Y recorder is an instrument which gives a graphic record of
the relationship between two variables.
In strip chart recorders, usually self-balancing potentiometers are used.
These self-balancing potentiometers plot the emf as a function of time.
The X-Y recorder, an emf is plotted as a function of another emf.
This is done by having self-balancing potentiometer control the position
of the rolls while another self-balancing potentiometer controls then
position of the recording pen

X-Y RECORDER(CONTINUED)
• In some XY recorder, one self-balancing potentiometer circuit moves a
recording pen in the X direction while another self-balancing
potentiometer circuit moves the recording pen in the Y direction at right
angles to the X directions, while the paper remains stationary
• They are many variations of XY recorders. The emf, for operation of XY
recorders, may not necessarily measure only voltages. The measured emf
may be the output of a transducer that may measure displacement force,
pressure, strain, light intensity or any other physical quantity.
• Thus with the help of XY recorders and appropriate transducers, a
physical quantity may be plotted against another physical quantity.

X-Y RECORDER(CONTINUED)
• Hence an XY recorder consists of a pai of serve system, driving a recording
pen in two axes through a proper sliding pen and moving arm
arrangement, with reference to a stationary paper chart.
• An signal enters each of the two channels. The signal are attenuated to
the inherent full scale range of the recorder, the signal then passes to a
balance circuit where it

DIAGRAM FOR STRIP CHART RECORDER

STRIP CHART RECORDER(CONTINUED)
It records one or more variables with respect to time. It is a X-t recorder. A
strip chart recorder consists of:
A long roll of graph paper moving vertically.
A system for driving a paper at some selected speed. A speed selector
switch is generally provided. Chart speed of 1-100 m/s are usually used.
A stylus driving system which moves the stylus in a near exact replica
It records one or more variables with respect to time.
It is a X-t recorder.

• A range selector switch is used so that input to the recorder drive system is with in
the acceptable level.
• A. Paper drive system:
• The paper system should move the paper at a uniform speed. A spring would may
be used but in most of the recorder a synchronous motor is used for driving the
paper. B. Marking Mechanism: There are many types of mechanism used for
making marks on the paper. The most commonly used ones are:
• 1. Marking with ink filled stylus. The stylus is filled with ink by gravity or capillary
actions. This requires that ihe pointer shall support an ink reservoir and a pen, or
capillary connection between the pen and a pen reservoir.
• In general red ink is used but other colours are available and in instrumentation
display a colour code can be adopted. 2. Marking with headed stylus. Some
recorders use a heated stylus which writes on a special paper. This method
overcomes the difficulties encountered in ink writing systems. 3. Chopper Bar.

• C. Tracing system:
• There are two types of tracing system used for producing graphic representation.
1. Curvilinear system. In the curvilinear system, the stylus is mounted on a central
pivot and moves through an are which allows a full width chart marking.
• If the stylus makes a full range recording, the line drawn across the chart will be
curved and the time intervals will be along the curved segments.
• 2. Rectilinear system.
• It is notices that a line of constant time is perpendicular to the time axis and
therefore this system produces a straight line across the width of the chart. Hence
the stylus is actuated by a drive cord over pulleys to produce the forward and
reverse motion as determined by the drive mechanism

• The stylus may be actuated by a self-balancing potentiometer system, a
photoelectric deflection system, a photoelectric potentiometer system, or
a bridge balAance system.
• This system is usually used with thermal or electric wiring.
• If a chart made from a pressure sensitive paper is used a simple recording
process is possible.
• A V-shaped pointer is passed under a chopper bar which presses the pen
into the paper once per second thus making a series on the special paper.

• In fact this system is not purely continuous and hence is suitable for
recording some varying quantities. 4. Electric stylus marking.
• This method employs a paper with a special coating which a
sensitive to current.
• When current is conducted from the stylus to the paper, a trace
appears on the paper. It is clear that the electric stylus marking
method has a wide range of marking speeds, has low stylus friction
and a long stylus life.
• The disadvantage is that the cost of paper is very high.

MAGNETIC TAPE RECORDER
A recorder is used to produce a permanent record of the signal that is
measured. A record is used to analyse how one variable varies with
respect to another and how the signal saries with time.
The objective of a recording system is to record and preserve information
pertaining to measurement at a particular time and also to get an idea of
the performance of the unit and to provide the results of the steps taken
by the operator.
The basic components of a general recorder are an operating mechanism
to position the pen or writer on the paper and a paper mechanism for
paper movement and a printing mechanism.

• Description of Magnetic Tape Recorders:
• The magnetic tape is made of a thin sheet of tough plastic material; one
side of it is coated with a magnetic material (iron oxide). The plastic base
is usually polyvinyl chloride (PVC) or polyethylene terephthalate
• Recording head, reproducing head and tape transport mechanism are
also present. Operation of Magnetic Tape Recorders:
• 1. The recording head consists of core, coil and a fine air gap of about 10
micrometer. The coil current creates a flux, which passes through the air
gap to the magnetic tape and magnetizes the iron oxide particles as they
pass the air gap. So the actual recording takes place at the trailing edge of
the gap

• The reproducing head is similar to that of a recording head in appearance.
The magnetic tape is passes over a reproducing head, thereby resulting in
an output voltage proportional to the magnetic flux in the tape, across the
coil of the reproducing head.
• Thus the magnetic pattern in the tape is detected and converted back into
original electrical signal.
• 3. The tape transport mechanism moves the tape below the head at
constant speed without any strain, distrortion or wear. The mechanism
much be such as to guide the tape passed by the magnetic heads with
great precision, maintain propoer tension and have sufficient tape to
magnetic head contact.

ADVANTAGE OF MAGNETIC TAPE RECORDER
• 1. Wide frequency range.
• 2. Low distortion.
• 3. Immediate availability of the signal in its initial electrical form as no
time is lost in processing.
• 4. The possibility of erase and reuse of the tape.
• 5. Possibility of playing back or reproducing of the recorded signal as many
times as required without loss if signal.

APPLICATION OF MAGNETIC TAPE RECORDER
• 1. Data recording and analysis on missiles, aircraft and satelites.
• 2. Communications and spying.
• 3. Recording of stress, vibration and analysis of noise.

DIGITAL TAPE RECORDER

PROCESS CONTROL
• Process control is an engineering discipline that deals with architectures,
mechanisms and algorithms for maintaining the output of a
specific process within a desired range. For instance, the temperature of a
chemical reactor may be controlled to maintain a consistent product output.
• Appropriately measuring accuracy has often been debated in the plastics
industry. Regardless of which method is actually used, blender manufacturers
all agree that samples, obtained from a blended mixture, as a percentage,
should be grouped together about the set point of the feeder.
• This grouping is known as dispersion or deviation from the set point
percentage. A producer needs to understand the importance of an accurate
blend system in relation to the feeder set point, so they can observe,
financially, the blender's performance with respect to the amount of resin
being used in a recipe blend.

PROCESS CONTROL(continued)
• Users of inaccurate and unstable gravimetric blend systems are forced to
actually overdose additives to avoid the low percentage variations that
produce an unsatisfactory product. Thus, overdosing costs large sums of
money to the user. Process Control designs electronic and mechanical feed
controls to minimize blend deviations, creating a more stable set point for
blender accuracy.

ELEMENTS OF PROCESS CONTROL
• 1.Controlled variable
• What you want to control (temperature pressure, level flow rat,
dimensions, position, etc.)
• 2. Measured variable
• What you observe in order to determine the actual condition of the
controlled variable
• In most cases, you measure the controlled variable itself. For instance, if
you want to know how fast a car is going, you measure its speed. In other
cases, you measure a different variable to determine the condition of the
controlled variable. For instance, you can determine the level (controlled
variable) of liquid in an open or vented tank by measuring
the pressure (measured variable) at the bottom of the tank.
• 3. Set Point
• The desired value of the controlled variable; for example, 70 room
temperature a window left open, poor insulation, a damaged thermostat.
•

ELEMENTS OF PROCESS CONTROL
• 4. Deviation.
• The difference between the set point and the actual value of the
controlled variable (which is the measured variable). For example, if your
indoor thermometer reads 65 and you would like a room temperature of
70, the deviation is 5
• Note: Deviation is also referred to as difference or error.
• 5. Manipulated variable
• The variable that is adjusted to close the gap (deviation, difference, or
error) between the set point and the controlled variable; for example, the
amount of electricity or gas to the heater.
• 6. Disturbance
•
Anything that affects the process and could cause deviation from the set
point; for example, a window left open, poor insulation, a damaged
thermostat.
•

ELEMENTS OF PROCESS CONTROL(Continued)
• 5. Manipulated variable
• The variable that is adjusted to close the gap (deviation, difference,
or error) between the set point and the controlled variable; for
example, the amount of electricity or gas to the heater.
• 6. Disturbances
Anything that affects the process and could cause deviation from
the set point; for example, a window left open, poor insulation, a
damaged thermostat.

PNEUMATIC CONTROLLER

APPLICATION OF PNEUMATIC CONTROLLER

DIAGRAM FOR ELECTRONIC CONTROLLER

ELECTRONIC CONTROLLER
• A controller is a comparative device that receives an input signal from a
measured process variable, compares this value with that of a
predetermined control point value (set point), and determines the
appropriate amount of output signal required by the final control element
to provide corrective action within a control loop.
• An Electronic Controller uses electrical signals and digital algorithms to
perform its receptive, comparative and corrective functions.
• Principles of Operation An electronic sensor (thermocouple, RTD or
transmitter) installed at the measurement location continuously sends an
input signal to the controller. At set intervals the controller compares this
signal to a predefined set point.

ELECTRONIC CONTROLLER(CONTINUED)
• If the input signal deviates from the set point, the controller sends a
corrective output signal to the control element. This electric signal must
be converted to a pneumatic signal when used with an air operated valve,
such as a Trerice Series 910 or 940 Control Valve.
• The conversion can be made using a Trerice TA901 I/P Transducer, which
converts a 4 to 20 mA electric signal to a 3 to 15 psi air signal.
• . This electric signal must be converted to a pneumatic signal when used
with an air operated valve, such as a Trerice Series 910 or 940 Control
Valve. The conversion can be made using a Trerice TA901 I/P Transducer,
which converts a 4 to 20 mA electric signal to a 3 to 15 psi air signal

ELECTRONIC CONTROLLER(CONTINUED)
• If the input signal deviates from the set point, the controller sends a
corrective output signal to the control element. This electric signal must
be converted to a pneumatic signal when used with an air operated valve,
such as a Trerice Series 910 or 940 Control Valve.
• The conversion can be made using a Trerice TA901 I/P Transducer, which
converts a 4 to 20 mA electric signal to a 3 to 15 psi air signal.

Transducers Explained

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