signl-2ppt.ppt

7/28/2019 signl-2ppt.ppt

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MT-II

EEE CYCLE


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TRANSDUCERS 2L

SIGNAL CONDITIONING 2L

DISPLAY DEVICES - 2L


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Radiant Electrical Mechanical Thermal Chemical Magnetic

Radiant Filter Photodiode

Electrical LED transistor ReversePiezo-Electricity

peltier Electro -plating

coil

Mechanical DirectPiezo-Electricity,Piezo-resistance

Gear box

Thermal seebeck Heatexchanger

Chemical pH Chemicalreaction

Magnetic Hall effect Magnetic

ckt

Devices used to convert one form of energy toanother.


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Instrument Transducers are devices which

for the purpose of measurement convert

physical input quantities into an electrical

output signal.


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Why Conversion to Electrical Signal? ?

Easy to modify

Easy to process

Easy to Transmit

Easy to Display

No mass-inertia effects


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Transducer Classification:

Energy Converter

(Called Self Generating or Active)

Thermocouple, Solar Cell

Energy Controller

(Called Passive or Modulating)

LDR, RTD


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Transduction principle

Resistive, Capacitive, Inductive Primary Input quantity

Flow, temperature, motion, pressure

Material and technology

SMT (Silicon Micro technology), MEMS, Fiber

Optic

Application: Environmental, Biomedical


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Factors influencing choice of transducers

Size

Weight

Shape

Sensitivity to desired, modifying and

interfering inputs

Accuracy

Operating range

Transient and Frequency response

Static characteristics


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Ruggedness (shock surround)

Reliability (MTBF, MTTR)

Availability and Delivery

Stability ( characteristics not changing with

time)

Environmental compatibility

Cost

Electrical aspects ( Impedance, length and

type of cable)


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Major types of Resistive transducers Potentiometers

Strain Gauges

Resistance temperature detector (RTD)

Thermistors

Light Dependent Resistor (LDR)

RESISTIVE TRANSDUCERS


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Preset(open style)

Presets(closed style)

Multiturnpreset

Variable pot


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RESISTIVITE POTENTIOMETERS

A resistance element provided with a movablecontact.

The contact motion can be

translation

rotation

combination of the two such as helical


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Loading Effect Of Potent iom eters


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K1mK1K

R||RRR

R||R

e

e

xmxp

xm

ex

0

m

p

t

i

p

x

R

Rm&x

x

R

R

K=

Rm= detector is of infinite impedance i.e. m = 0

Ke

e

ex

0


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Error = output voltage at loaded condition -

output voltage under no load

K1mK1K.eex

m

1K1K

K1Ke2

ex

At K = 0 and K = 1, error = 0. At all other points

error is (ve)


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For good linearity, for a meter of a given

resistance Rm, choose a potentiometer ofsufficiently low resistance relative to Rm

Max eex = pPR

Low value of Rp

allows only a small eex

and therefore a small sensitivity


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A variable pot has a total resistance of 2.2 K ohm and

is fed from 10 V DC supply. The output is connected

to a load resistance of 5.1 K ohm. Tabulate errors for

wiper positions from 0.1 to 1.0 in increments of 0.1.

pm

ex

R

R

KK

KKE

1

1Error

2

K 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Error 0 -0.0037 -0.0013 -0.025 -0.037 -0.048 -0.0573 -0.058 -0.052 -0.036 0


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Problem : we have two resistors of 10 ohm and

330 both having power rating of 0.25W. Can we

connect both resistors to 6V battery?

Solution :

power dissipated by 330 ohm resistor is

W

R

V109.0

330

662

power dissipated by 10 ohm resistors is

WR

V6.3

10

662


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10 ohm resistor will burn, since power

dissipated by it exceeds its rated

capacity.


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Inductive transducers are those in which

SELF INDUCTANCE of a coil or the

MUTUAL INDUCTANCE of a pair of coil

is altered due to variation in the

measurand.

Change in inductance L is measured.

INDUCTIVE TRANSDUCERS


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The self inductance of a coil refers to

the flux linkage within the coil due to

current in the same coil.

Mutual inductance refers to the flux

linkages in a coil due to current in

adjacent coil.


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Fig2.3e

SELF INDUCTANCE TRANSDUCER


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MUTUAL INDUCTANCE TRANSDUCER


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In the magnetic circuits, reluctance is equivalent

to resistance and depends on :

Number of turns

Area of cross section of wire

Permeability of the medium

Air has much lower permeability than a

ferromagnetic material.

Introducing air gap is like introducing high

resistance.


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Air Cored Coils

Can be operated at higher frequencies because

there are no eddy current losses in air core.

Iron cored coils

Inductance depends on the value of current.

At high frequencies eddy current losses arehigh.

Size much smaller than air cored.


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VARIABLE RELUCTANCE TRANSDUCERS


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PROBLEM:

A variable reluctance type tachometer has 60 rotor

teeth. The counter records 3600 counts per second.

Determine the speed in rpm.

Soln:

Speed (rps) = pulses per second / number of teeth

rpmrps 360060

3600


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A disk has 20 holes, the light detector is

connected to frequency meter for shaft

speed measurement. If the frequency

meter reading is 720 Hz. Calculate theshaft speed.

What is the minimum speed that can be

detected?


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20 holes => 20 pulses /rev

720 Hz => 720 pulses/sec

Speed (rps) = pulses per second / number of holes

= 720 / 20 = 36 rps = 2160 rpm

Minimum speed corresponds to 1 Hz

1 Hz corresponds to 2160 / 720 = 3 rpm


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Linear Variable Differential Transformer

(LVDT)


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There is one primary winding connected to

an ac source (50 Hz 20 kHz), excitation

3 15 Vrms.

Core is made of high permeability softiron or nickel iron. Two secondary

windings are connected in series

opposition


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G t i t f il t i ll d


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Geometric centre of coil arrangement is called

the NULL position. The output voltage at the null

position is ideally zero.

However it is small but nonzero (null voltage).

Why?

1. Harmonics in the excitation voltage and stray

capacitance coupling between the primary

and the secondary

2. Manufacturing defects.


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A typical signal conditioning provides


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A typical signal conditioning provides

1. Power supply

2. Frequency generator to drive LVDT

3. Phase sensitive Demodulator and

Low Pass Filter to convert ac to dc

4. DC amplifier to amplify the final

output signal


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Ad t


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Advantages

Wide range of displacement from m to cm.

Frictionless and electrical isolation.

High output.

High sensitivity [sensitivity is expressed in mV

(output voltage)/ mm (input core displacement)].


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Disadvantages

Sensitive to stray magnetic fields.

Affected by vibrations.

Dynamic response is limited mechanically by

the mass of core and electrically by frequency

of excitation voltage.

CAPACITIVE TRANSDUCERS


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A capacitor is an electrical component which

essentially consists of two plates separated

by an insulator.

The property of a capacitor to store anelectric charge when its plates are at different

potential is referred to as capacitance.

CAPACITIVE TRANSDUCERS

Q


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V

Q

d

AC r0

Capacitance C =

.

If the capacitance is large, more charge is

needed to establish a given voltage difference.

The capacitance between two parallel metallic

plates of area

m

F120 1085.8


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A capacitor is made of N parallel plates each of


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A capacitor is made of N parallel plates each of

area A and spaced a distance d apart. A second

set of N identical plates is positioned midway

between the first set, as shown below. What is

the total capacitance of the whole system?

To see what's happening, let's take N = 2:


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pp g,

h th 2 l t i h t th b


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when there are 2 plates in each set, the number

of capacitors, i.e., sheets of positive and

negative charges separated by a distance d/2, is

3, i.e., (2N - 1). Therefore, if there are N plates

in each set, there are (2N - 1) capacitors in

parallel, so the total capacitance is:

(2N - 1) [oA/(d/2)] = 2(2N - 1) [oA/d]


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PLATE DISTANCE CHANGE

PLATE AREA CHANGE


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d)xL(wC r0

PLATE AREA CHANGE


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For area variation, the capacitance is maximum


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when the overlap area is maximum and is givenby

dAC maxr0max

2

rA

2

max

(if plates are semi-circular in shape)

.CC max

d2

rC

2

r0

SENSITIVITY= K

d2

rC 2r0


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DIELECTRIC CHANGE

Capacitive Sensors


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Capacitive Sensors

Other Configurations

c. Differential Mode

b. Variable Dielectric Mode

a. Variable Area Mode

LINEARIZATION TECHNIQUES


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Displacement-capacitance relationship is

non linear

Nonlinearity corrupt the performance of a

simple parallel plate sensor

LINEARIZATION TECHNIQUES


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Different ial Capacito r

2ECE 1EC


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21

21

CCE

21

12

CC

ECE

For x=0,21 CC

2

EEE 21

E

d2

xdE1

E

d2

xdE2

xd

AC

xd

AC

upmovesX

21


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12 EEE

E

d

xE

S = Sensitivity Gd

E

X

E

PIEZOELECTRIC


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ANDHALL EFFECT TRANSDUCERS

WHO DISCOVERED PIEZOELECTRICITY?

The first experimental demonstrationof piezoelectric was published in

1880 by brothers Pierre and JacquesCurie when they were 21 & 24 yearsold.

Piezoelectricity


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Piezoelectricity

Phenomenon of generating an electric

charge in a material when subjecting it to a

mechanical stress (direct effect).

and

Generating a mechanical strain inresponse to an applied electric field

(converse effect)


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Pi l t i t i l A i t i


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Piezoelectric materials are Anisot rop ic

Electrical and mechanical properties differalong different directions

TYPES OF PIEZOELECTRIC


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MATERIALS

Natural: Tourmaline; Quartz; Topaz;Rochelle salt (sodium potassium

tartrate tetrahydrate).

Synthetic: Barium Titanate (BaTiO3);Lead Zirconate (PbZio3); PolymerFilms (Polyvinylidene fluoride (PVDF), (-CH2-

CF2-)n).


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There are two families of constants: g constantsand d constants. In the constants the firstsubscript refers to the direction of electrical effectand the second to that of the mechanical effect

according to the axis systems.


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i

33

f

Q

3directioninappliedforce

3directioningeneratedeargchd

)wl/(f

t/e

3directioninappliedstress

3directioninproducedfield

gi

0

33

g = 12 * 10-3 (V/m) / (N/m2) for barium Titanate


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g 0 ( / ) / ( / ) o ba u ta ate

g= 50 * 10-3 (V/m) / (N/m2) for quartz.

A quartz crystal 0.1 inch thick would have a

sensitivity of 0.88 V/psi

psi

m

NPa 4

21045.111


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33

ii

0

i

0

33

d

f

Q

f

C.e

/f

t/e

stress

fieldg

d33 = 33g.

ptge

p.t

e

f.t

A.e

/f

t/eg

330

0

i

0

i

033

Piezoelectric Transducers are used for


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Piezoelectric Transducers are used for

measurement and recording of dynamic

changes in mechanical variables such as

pressure, force and acceleration.

Gas LightersGeneration of sonar wavesQuartz clocksLoudspeaker

LOW FREQUENCY DEVICES


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(Force, Position, Acceleration, Spark generator)

AUDIO DEVICES

(Microphone Heads, Stereophonic pickups, Loud

Speaker)

RF DEVICES

(Ultrasonic generators/receiver/Scanner)


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HALL EFFECT SENSORS


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WHO

INVENTED

HALL EFEFCT ?


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Edwin Herbert Hall discovered the "HallEffect" in 1879 while working on his

doctoral thesis in physics in university ofJohn Hopkins in Baltimore


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Commercially available Hall generators

made of

Bulk Indium Arsenide (InAs)

Thin Film InAs

Gallium Arsenide (GaAs)

Indium Antimonide (InSb).

VH = KHOC ICB sin I B


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kGmA

mVisKofunit HOC

Ic x B

IC is the control current in mA ( ac or dc),

B is the magnitude of flux density inkilogauss (kG) [1 Tesla = 10,000 Gauss)

is the angle in degrees of the incidentmagnetic field from a line drawn parallel

to the Hall plate.

silicon Hall effect transducers can be


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silicon Hall effect transducers can befabricated on standard bipolar and

CMOS integrated circuit processes.

Sensitivities of semiconductor Halltransducers are still very low, fallingin the 10mV to 100mV/Gauss,

additional signal conditioning isusually required for any practicalapplication.


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Preamplifier and a threshold detector areintegral to Hall effect sensor ICs.

Significant amounts of signal processingcircuitry can be incorporated on the

same die as the transducer.

Typical Hall IC has three pins. Supply,

Ground and Output.

Hall ICs cost from $ 0.2 to $ 1.5.


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PHOTOELECTRIC

TRANSDUCERS

The basic principle behind the working of


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The basic principle behind the working of

the Photoelectric Transducers is the

Photoelectric effect.

The photoelectric effect was explained

mathematically by Albert Einstein

Einstein won the Noble award for the

discovery of photoelectric effect in 1921.


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For a given surface, there is a

minimum frequency of radiation atwhich emissions occur

Incident radiation with a lowerfrequency( Energy) than the

threshold, does not cause electronsto be emitted, regardless of intensity.
http://encyclopedia.thefreedictionary.com/frequencyhttp://encyclopedia.thefreedictionary.com/frequency


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What is

Emission Spectrum?

Spectral Response?

A graph of energy output of source


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g p gy p

plotted versus frequency or wavelength

is Emiss ion Spectrum of source.Source Characteristics

Graph of device current, voltage or

resistance versus radiation frequency

is Spectral Response.

Dev ice Characterist ics

EMISSION SPECTRUM


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EMISSION SPECTRUM

SPECTRAL RESPONSE


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Photo emissive cell


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The photoelectric current produced

I = S


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Cathode is photo emissive light release


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Cathode is photo emissive, light release

electrons ,which are attracted towards anodeproducing a electric current .

The cathode and anode are enclosed in glass

or quartz envelope which is either evacuated

or filled with a inert gas.


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Photoelectric tube response to different

wavelength of light is influence by

Transmission characteristics ofglass tube envelope

The photo emissive characteristics ofthe cathode material


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.

If the p-n junction is operated in the thirdquadrant, the product of a negative current


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quadrant, the product of a negative currentand a positive voltage will yield a negative

power.

Negative power corresponds to a source

of power.

A p-n junction operated in the third

quadrant can be used as a source ofpower : the principle behind the solar cell.

Photodiodes


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Photodiode (pn junction) operated in reverse bias

In a reverse biased p-n junction a Reverse

Saturation Current flows due to minority carriers

which are thermally generated.Increasing the reverse bias does not increases the

reverse current significantly. Increasing what

parameter will increase reverse current?

TEMPERATURE and ILLUMINATION increases

number of minority carriers (reverse) current.


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Small current converted to appreciable voltageBy passing through resistor (I V converter)


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Es = VR1 -VD


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To cause a change in resistance photonsincident on these materials must have energy,


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gy,

Eg is the band gap in electron volts (eV), h isPlancks constant (4.14 x 10-15 eV.s), is the

frequency of the light.

gEhv

In the dark, the resistance is very high-mega ohm

range.When illuminated, the resistance may drop to a

few hundred ohms.

Bulk resistivity decreases with increasingillumination, allowing more photocurrent to flow.


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, g p

Bulk effect photoconductors are referred asphotoconductive cells or simply photocells.

Photocells are thin film devices made by

depositing a layer of a photoconductive materialon ceramic substrate


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Cannot be practically used for high


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Cannot be practically used for highspeed switching. WHY ?

Exhibit "memory effect

Require on the order of a secondfor the resistance to rise to its dark

resistance.


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Count no. of people going/coming in aroom

Count no. of objects moving on a

conveyer belt Find the complexion of your face

Automatic Headlight Dimmer


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Night Light Control

Street Light Control

Absence / Presence (beam breaker)

Position Sensor

Can handle many watts, so a relay can


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be directly operated using an LDR.

LDRs are used as switching devices todetect presence or absence of light.

Counters, twilight switches, camera

control systems


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Photovoltaic Cells


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A device that turns light into electricenergy.

Where were they developed ??

For What application ??


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The photovoltaic cells were developed atBell Labs in 1950

primarily for space applications

The Hubbell telescope utilizes solar


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panels for its energy requirements.

Space satellites

Rural health clinics for Lighting,Refrigeration,

Water pumps for irrigation

Small scale power generation.

thin layer of crystalline


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semiconductor (Se, Si, Cu2O, )

sandwiched between two differentmetal electrodes

No Bias but irradiation causesformation of electron hole-pair

formation

Photovoltaic cells generate a voltagewhich is proportional to EM radiation


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which is proportional to EM radiation

intensity.

Called photovoltaic cells because of

their voltage generatingcharacteristics.

Active transducers i.e., they do notneed an external source to power

them


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The power from a cell is afunction of cell area andpower density of light.


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Short-circuit current (I )


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Short-circuit current (ISC)current produced when the positive and negative

terminals of the cell are short-circuited,voltage between the terminals is zero(load resistance of zero)

Open-circuit voltage (VOC)

voltage across the positive and negative terminalsunder open-circuit conditions,current is zero (an infinite load)

Fill factormeasures the "squareness" ofthe I-V curve


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It describes the degree to which the voltageat the maximum power point (Vmax) matchesVoc

andthe current at the maximum power point(Imax) matches Isc

ocscVI

VI

FF maxmax

Consider a solar cell driving a load of 3.Thi ll h f 3 3 d i


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This cell has an area of 3cm 3cm and is

illuminated with light of intensity 700 W/m2

.Voltage and current for maximum power pointwith load of 3 ohm are 0.475 V and 157 mArespectively.

Find (i) Power delivered to the load,

(ii) Efficiency of the solar cell in this circuit,

(iii) Fill factor of the solar cell. Given :

Isc = 178 mA Voc = 0 58 V


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The power delivered to the load : Pout = I*V = (15710

-3)(0.475 V)

= 0.0746 W or 74.6 mW

The input power of sunlight :

Pin

= (Light intensity) (Surface area)

= (700 W /m2) (0.03m)2 = 0.63 W

07460 WP


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%8.11

63.0

0746.0100100(%)

W

Wxx

P

PEfficiency

in

out

%72722.0

)58.0)(178(

)475.0)(157(maxmax

or

VmA

VmA

VI

VIFF

ocsc

1.7x1023 kW Sun Emits8.5 x1013 kW reaches the earth


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6x1013 kW penetrates earths atmosphere.

With sun directly overhead on a clear day,

power density of sunlight is

100 mW/cm2

1 SUN = 1kW/m2 =100 mW / cm2

On a cloudy day, power density of


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sunlight might be 0.3 SUN or 30

mW/cm2.

Energy Density (Langley )product of power density and time.

1 Langley = 11 62 W hr/m2

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