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1. Fall time 350mS Peak spectral 610nm response _ PROCEDURE 1 Connect the circuit as shown in diag 2 a The socket C of Wire Wound pot to 12V b The socket A of Wire Wound pot to OV c The socket B of wirewound pot to input of Power Amplifier 20 d The output of Power Amplifier to input of Lamp Filament e The other input of filament lamp to ve input of Moving Coil Meter f The ve input of Moving Coil Meter to OV g Connect C Socket of Slide Potentiometer to 5V h Output of Photoconductive Cell to B input of Slide Potentiometer i Connect a Digital Multimeter as voltmeter on 20V DC range to measure the Photoconductive cell output voltage between output of photoconductive cell and OV 2 Set the 10KQ Slide Potentiometer setting to 3 so that the photoconductive cell load resistance is approximately 3KQ can be verified with DMM 3 Place the opaque box over the plastic enclosure to exclude all ambient light 4 Switch ON the power supply amp set the wire wound pot to minimum for zero output voltage from Power Amplifier 5 Take readings of Photoconductive cell short circuit output current as indicated as Digital Multimeter as lamp voltage is increased in 1V steps Record results in table 1 6 Switch OFF the power supply 7 Plot the graphs of photoconductive cell short circuit current amp open circuit voltage against Lamp Filament voltage It should resemble the one given graph OBSERVAT2. 6 incidence above which the total internal reflection occurs When light traveling in a dense medium hits a boundary at a steep angle larger than the critical angle for the boundary the light will be completely reflected This effect is used in optical fibers to confine light in the core Light travels along the fiber bouncing back and forth off of the boundary Because the light must strike the boundary with an angle greater than the critical angle only light that enters the fiber within a certain range of angles can travel down the fiber without leaking out This range of angles is called the acceptance cone of the fiber The size of this acceptance cone is a function of the refractive index difference between the fiber s core and cladding In simpler terms there is a maximum angle from the fiber axis at which light may enter the fiber so that it will propagate or travel in the core of the fiber The sine of this maximum angle is the numerical aperture NA of the fiber Fiber with a larger NA requires less precision to splice and work with than fiber with a smaller NA Single mode fiber has a small NA From Computer Desktop Encyclopedia 1999 The Computer Language Co Inc Black polyurethane outer jacket Strength members Buffer Jacket Silicone coating Cladding silica Core silica Optical fiber Fig1 Cross Section of Optical Fiber 7 Special purpose fiber Some special purpose optical fiber is
3. DC amplifier 2 Place the opaque box over the plastic enclosure to exclude all ambient light 3 Switch ON the power supply amp set the 10KQ wire wound pot to minimum for zero output voltage from Power Amplifier 4 Adjust OFFSET control of DC Amplifier to read zero in DMM Meter for zero input at DC Amplifier 5 Take readings of Amplifier output voltage on the Digital Multimeter as lamp voltage is increased in 1V steps Record results in table 1 6 Switch OFF the power supply 7 Change the Current Amplifier to Buffer to measure output of PIN photodiode Take readings of PIN photodiode output voltage as the lamp voltage is increased in 1V step record the result in table Remember to adjust the offset of DC amplifier is giving zero output for zero input 8 Plot the graph between PIN photodiode current amplifier output voltage buffer amplifier output voltage amp Lamp Filament voltage It should resemble the one given below 25 OBSERVATION Lamp Filament voltage V PIN Photodiode DC amplifier y eP PPEPEP A PIN Photodiode Buffer output voltage V GRAPH PIN Photodiode Output Voltage cv Lamp Filament Voltage volts CONCLUSION 26 Experiment No 6 Characteristics of Phototransistors AIM To study characteristics of phototransistors APPARATUS Optical Transducers Trainer kit ST 2301 SCIENTECH THEORY A phototransistor is a normal transistor in which the envelope enclosi
4. Holographic media 4 Principle of working and related theory 5 Various features 6 Applications 31 Experiment No 8 Case study of Turbidity Meter Aim To study the Turbidity Meter Theory The case study is evidence of study the turbidity meter practically Mainly the focus given to the technical and design aspects of turbidity meter Available turbidity meters should be refered but sufficient technical information is not covered with the user manual hence student have to search related on the refrence books and internet search Following point should be described in the case study 1 Concept of turbidity 2 Working principle 3 Constructional features 4 Sample requirement 5 Factors affecting measurement 6 Advantages and disadvantages discussion 7 Application area discussion 8 Sample experimentation possible on the meter 9 Cost and manufacturer 32 Experiment No 9 An Assignment on Optical Devices Aim To study the Optical Devices Apparatus LED LCD and there required circuit Theory The assignment would be the evidence of detailed study of the devices like LED LCD As these devices are widely used in optical instrumentation and communication This study should be followed following points 1 Working principle 2 Material used 3 Sectional views schematics Blocks diagram 4 Mounting 5 Circuit 6 Working 7 Features 8 Application Color illustration given along with will be en
5. aaa ea min 7 ga me Ba TE x Ot Fi An stimulated emission Fig 3 Absorbtion Spontaneous emission and stimulated emission mechanism POPULATION INVERSION Atomic energy states are much more complex than indicated by the description above There are many more energy levels and each one has its own time constants for decay The four level energy diagram shown in figure 4 is representative of some real lasers The electron is pumped excited into an upper level E4 by some mechanism for example a collision with another atom or absorption of high energy radiation It then decays to E3 then to E2 and finally to the ground state E1 Let us assume that the time it takes to decay from E2 to E1 is much longer than the time it takes to decay from E2 to E1 In a large population of such atoms at equilibrium and with a continuous pumping process a population inversion will occur between the E3 and E2 energy states and a photon entering the population will be 14 amplified coherently ne 3 on 10 orn eA A IN eo AA ee 1 soles sa ii A nVn y ji eB A i V gt m N on A r gt why A 3 f JAMAN e J gt 4 if j gt 441 VN We NI gt AAN T V N V A f A pe 1 Wie 7 P ale A V Y V A l 4 prg tim gt st Re Ulate n sy i a One Zs I excited decayed via decayed via spontaneous emission stimulated emission Fig 4 Amplification by stimulated emission Ad
6. circuit output voltage 5 Switch ON the power supply and take the readings adding results to table1 6 Switch OFF the power supply 7 Plot the graphs of photovoltaic cell short circuit current amp open circuit voltage against Lamp Filament voltage It should resemble the one given graph OBSERVATION PARAMETER CONDITIONS MIN j Surfacearea T Tani mm Open circuit ambient 1 6 V voltage Short circuit ambient 3 uA arm ee Lamp Filament fae eae 3 4 15 7 lage ON PREETI Short Circuit output current A KENEN KAN Open Circuit output ea voltage V Ft Et iy GRAPH Open Circuit Photovoltaic Cell Photovoltaic Cell Open Circuit Short Circuit Output Voltage Output Current volts pA Graph 2 Lamp Filament Voltage volts CONCLUSION 18 Experiment No 4 Characteristics of Photoconductive Cell AIM To study characteristics of Photoconductive Cell APPARATUS Optical Transducers Trainer kit ST 2301 SCIENTECH THEORY Electrical conduction in semiconductor materials occurs when free charge carriers e g electrons are available in the material when an electric field is applied In certain semiconductors Photoconductive cell are elements whose conductivity is a function of incident electromagnetic radiation Since resistance of these materials decrease with increase in incident light therefore these materials are also called Light Dependent Resistor or LDR Commercial
7. element analysis 4 Miscellaneous analysis 35
8. optical fiber by total internal reflection This causes the fiber to act as a waveguide Fibers which support many propagation paths or transverse modes are called multi mode fibers MMF while those which can only support a single mode are called single mode fibers SMF Multi mode fibers generally have a larger core diameter and are used for short distance communication links and for applications where high power must be transmitted Single mode fibers are used for most communication links longer than 550 meters 1 800 ft Principle of operation An optical fiber is a cylindrical dielectric waveguide non conducting waveguide that transmits light along its axis by the process of total internal reflection The fiber consists of a core surrounded by a cladding layer both of which are made of dielectric materials To confine the optical signal in the core the refractive index of the core must be greater than that of the cladding The boundary between the core and cladding may either be abrupt in step index fiber or gradual in graded index fiber Total internal reflection Total internal reflection is an optical phenomenon that occurs when a ray of light strikes a medium boundary at an angle larger than a particular critical angle with respect to the normal to the surface If the refractive index is lower on the other side of the boundary no light can pass through and all of the light is reflected The critical angle is the angle of
9. should be done during the next lab session The immediate arrangements for printouts related to submission on the day of practical assignments 2 Students should be taught for taking the printouts under the observation of lab teacher 3 The promptness of submission should be encouraged by way of marking and evaluation patterns that will benefit the sincere students 8 9 INDEX To study Optical fiber To study Sources of light for Optical fiber To study characteristics of Photovoltaic cell To study characteristics of Photoconductive Cell To study characteristics of PIN Photodiode To study characteristics of phototransistors To study the Holography To study the Turbidity Meter To study the Optical Devices 10 Study of Flame Photometer Experiment No 1 Study of Optical Fiber Aim To study Optical fiber Apparatus Optical fiber Cutter light source etc Theory An optical fiber or fiber is a glass or plastic fiber that carries light along its length Fiber optics is the overlap of applied science and engineering concerned with the design and application of optical fibers Optical fibers are widely used in fiber optic communications which permits transmission over longer distances and at higher bandwidths data rates than other forms of communications Specially designed fibers are used for a variety of other applications including sensors and fiber lasers Light is kept in the core of the
10. ION ze PPE EET voltage V Picci ed Photo conductive ami TT r m kak GRAPH 21 Phogoconductive Cell Output Voltage Cy 4 oO 10 Lamp Filament Voltage volts CONCLUSION 22 Graph Experiment No 5 Characteristics of PIN Photodiode AIM To study characteristics of PIN Photodiode APPARATUS Optical Transducers Trainer kit ST 2301 SCIENTECH THEORY One of the problems with P N junction photodevices is the electric field which forms across the junction This manifests itself as a capacitance of typically 100pF which limits the rise and fall time of the photocurrent To minimize this effect a third layer of intrinsic or very lightly doped silicon can be incorporated This separates the charged regions and greatly reduces the capacitance to typically 15pF A PIN photodiode can be operated in two ways The tiny photocurrent can be amplified by a high gain current voltage converter whose output can then be converted to a voltage A suitable circuit with a gain of 10 000 is provided on the 2301 and the output will rise linearly with increasing illumination Alternatively the device can be connected via a buffer to a high gain voltage amplifier the utput from this will rise lograthmically with increasing with increasing irradiance oug 23 window light e a k 4 BPX65 Fig 5 The Photodiode is reverse biased The reverse bias saturation current is dependent upon the intens
11. Jawaharlal Nehru Engineering College Laboratory Manual OPTICAL INSTRUMENTATION For Final Year Students Author JNEC INSTRU DEPT Aurangabad 1 This manual is intended for the final year students of instrumentation in the subject Optical Instrumentation Manual typically contains practical Lab Sessions related Measurement System fundamentals covering various aspects related the subject to enhanced understanding Students are advised to thoroughly go though this manual rather than only topics mentioned in the syllabus as practical aspects are the key to understanding and conceptual visualization of theoretical aspects covered in the books Good Luck for your enjoyable laboratory sessions DOs and DON T DOs in Laborary 1 Do not handle any equipment before reading the instructions Instruction manuals 2 Read carefully the power ratings of the equipment before it is switched on whether ratings 230 V 50 Hz or 115V 60 Hz For Indian equipments the power ratings are normally 230V 50Hz If you have equipment with 115 60 Hz ratings do not insert power plug as our normal supply is 230V 50 Hz which will damage the equipment 3 Observe type of sockets of equipment power to avoid mechanical damage 4 Do not forcefully place connectors to avoid the damage 5 Strictly observe the instructions given by the teacher Lab Instructor Instruction for Laboratory Teachers 1 Submission related to whatever lab work has been completed
12. able in different colours 5 Linearity is more and compatible with integrated circuits 11 Disadvantages of LED 1 Output power gets affected by the temperature variation 2 Quantum efficiency is low 3 Gets damaged because of overvoltage and over current HAMAR AG Fig 2 Different types of LED 2 LASER Light Amplification by Stimulated Emission of Radiation A laser Light Amplification by Stimulated Emission of Radiation is a device that emits light electromagnetic radiation through a process called stimulated emission Laser light is usually spatially coherent which means that the light either is emitted in a narrow low divergence beam or can be converted into one with the help of optical components such as lenses More generally coherent light typically means the source produces light waves that are in step They have the same frequencies and identical phase ABSORPTION SPONTANEOUS AND STIMULATED EMISSION 12 In general when an electron is in an excited energy state it must eventually decay to a lower level giving off a photon of radiation This event is called spontaneous emission and the photon is emitted in a random direction and a random phase The average time it takes for the electron to decay is called the time constant for spontaneous emission and is represented by t On the other hand if an electron is in energy state E2 and its decay path is to E1 but before it has a chance to spontaneous
13. constructed with a non cylindrical core and or cladding layer usually with an elliptical or rectangular cross section These include polarization maintaining fiber and fiber designed to suppress whispering gallery mode propagation Photonic crystal fiber is made with a regular pattern of index variation often in the form of cylindrical holes that run along the length of the fiber Such fiber uses diffraction effects instead of or in addition to total internal reflection to confine light to the fiber s core The properties of the fiber can be tailored to a wide variety of applications Materials Glass optical fibers are almost always made from silica but some other materials such as fluorozirconate fluoroaluminate and chalcogenide glasses are used for longer wavelength infrared applications Like other glasses these glasses have a refractive index of about 1 5 Typically the difference between core and cladding is less than one percent Properties of Optical Fiber 1 Numerical Aperture of any type of fiber is defined as NA 4 n ni where n1 is the refractive index along the central axis of the fiber core n 2 refractive index of cladding 2 Attenuation 3 Dispersion 3 Fiber strength 4 Band width parameters 5 Rise Time Applications and Advantages 1 Optical fiber can be used as a medium for telecommunication and networking because it is flexible and can be bundled as cables 2 It is especially adva
14. couraged The objective is to provoke the student for extra learning and detail approach of the knowledge 33 EKPERIMENT NO 10 Study of flame photometer AIM To study flame photometer APPARATUS flame photo meter kit THEORY Flame photometry is based on the measurement of light emitted or photons emitted when a metal is introduced into a flame The colour of wavelength a intensity gives the constituents of the element Flame Photometry Photo Detector Callimating mirror Amplifier Meter PUEL Ee Oxygen a Sample The above figure shows the schematic diagram of simple modified flame photometer As shown in above figure it consist of a burner of total combustion type a collimating mirror a monochromator a prism and detector system consist of a photo detector followed by amplifier and readout system Working An atomizer operated by one of the flame producing gases sucks the sample solution The sample is aspirated into the flame in form of a fine spray Spectral emission 34 comes form the excited atoms formed during the process of combustion This emitted radiation is collected by collimating concave mirror from the flame and is allowed to pass through prism and slit The radiation of appropriate wavelength strikes on photo detector and the magnitude of electrical signals are read on meter APPLICATIONS 1 Qualitative analysis 2 Quantitative analysis 3 Simultaneous multi
15. f phototransistor output voltage against Lamp Filament voltage It should resemble the one given below OBSERVATION romeo PT PP EP PPP PY voltage V aseen 1 TdT TITI output voltage V GRAPH Phototransistor Output Voltage Y yv N e A 0O TO Lamp Filament Voltage volts CONCLUSION 30 Experiment No 7 An Assignment on Holography Aim To study the Holography Theory Holography is the recording of visible object in terms of light wave phenomena Unlike the photographic recording the recorded object seems to be as it was originally In photographic only two dimensions of object can be preserved which losses various important details of it Holography overcome the difficulty by recording the same in terms of wave parameter i e amplitude and phase shift This information once recorded remain unaltered It can be brought on the holographic medium as a pattern of interference of two phase viz refrenece beam and reflected beam This words was introduced by the Greek letters holus whole and graphy writing The entire holography can be divided into two part 1 Holographic recording 2 Image reconstruction LASER is required for the same by virtue of its good coherence monochromacity and directionality student are suppose to study holography indepth and have to be written in there own words on the basis of the following points 1 Need and history of holography 2 The light source 3
16. ident _ Light Output Light Lens CHARACTERISTICS 28 ristics are as under The device used on ST2301 is MEL11 its characte PARAMETER The Phototransistor is already connected as under O P a oV PROCEDURE 1 Connect the circuit as shown in diag a The socket C of Wire Wound pot to 12V b The socket A of Wire Wound pot to OV c The socket B of wirewound pot to input of Power Amplifier d The output of Power Amplifier to input of Lamp Filament e The other input of filament lamp to ve input of Moving Coil Meter f The ve input of Moving Coil Meter to OV g Connect 5V to C input of slide potentiometer h Connect B input of the slide potentiometer to Output of Phototransister i Connect a Digital Multimeter as voltmeter between output of phototransister amp ground on 20V DC range to measure the phototransistor output voltage 2 Set the 10KQ slide potentiometer control to minimum setting 1 so that the phototransistor load resistance is approximately 1KQ protection resistor only 3 Fit an opaque box over the clear plastic enclosure to exclude all ambient light 4 Switch ON the power supply amp set the 10KQ wire wound pot to minimum for zero output voltage from Power Amplifier 5 Take readings of phototransistors output voltage as indicated on the Digital Multimeter as lamp voltage is increased in 1V steps Record results in table 1 6 Switch OFF the power supply 7 Plot the graph o
17. ity of incident light The Photocurrent Vs light relationship is linear over a wide range In order to maintain linearily the bias voltage should be kept constant The output resistance of photodiode is very high of the order of tens of megaohms The DC resistance is the diode leakage resistance and that too is very high This DC resistance depends upon the light intensity The frequency response of a Photodiode is largely dependent upon the intrinsic capacity which reduces junction capacitance CHARACTERISTICS The device used on ST2301 is BPX65 its characteristics are given below PARAMETER Dark curent id Light current OOOO O bme Peak spectral 850nm I R response Capacitance SSS RL 5kQ Response time 24 PROCEDURE 1 Connect the circuit as shown in diag a The socket C of Wire Wound pot to 12V b The socket A of Wire Wound pot to OV c The socket B of wirewound pot to input of Power Amplifier d The output of Power Amplifier to input of Lamp Filament e The other input of filament lamp to ve input of Moving Coil Meter f The ve input of Moving Coil Meter to OV g Output of PIN photodiode to input of Current Amplifier which is used to measure the current output of the PIN Photodiode h Output of current amplifier to input of DC amplifier i Connect a Digital Multimeter as voltmeter on 20V DC range between output of DC Amplifier and OV to measure the output voltage of
18. ly available photoconductive cell materials are cadmium sulphide CdS and cadmium selenoid CdSe with band gap of 2 42 eV amp 1 74 eV respectively On account of the large energy bands both the materials have a very high resistivity at ambient temperature which gives a very high value of resistance for practical purposes The photoconductive cells use a special type of construction which minimises resistance while providing maximum surface Photoconductive cells are made by chemically sintering the required powder into tablets of the protective envelope of glass or plastic Electrons are deposited on the 19 tablet surface and are made of materials which give an ohmic contact but with low resistance compared with that of the photoconductor The electrodes are usually in the form of interlocked fingers as shown cadmium sulphide disk contact contact g gold contact fingers When using photoconductive cell for a particular application it 1s Important to select the proper dark resistance as well as suitable sensitivity The sensitivity is defined as S AR Q Wm AH Where AR Change in resistance Q AH Change in irradiation W m CHARACTERISTICS The device used on ST2301 is ORP12 Its characteristics are given below CONDITIONS MIN TYP MAN oa o lux 24KO O O typical ambient ambient 5000 75mS PARAMETER Cell resistance Dark resistance Rise time
19. ly decay a photon happens to pass by whose energy is approximately E24E1 there is a probability that the passing photon will cause the electron to decay in such a manner that a photon is emitted at exactly the same wavelength in exactly the same direction and with exactly the same phase as the passing photon This process is called stimulated emission Absorption spontaneous emission and stimulated emission are illustrated in figure Now consider the group of atoms shown in figure below All begin in exactly the same excited state and most are effectively within the stimulation range of a passing photon We also will assume that t is very long and that the probability for stimulated emission is 100 percent The incoming stimulating photon interacts with the first atom causing stimulated emission of a coherent photon these two photons then interact with the next two atoms in line and the result is four coherent photons on down the line At the end of the process we will have eleven coherent photons all with identical phases and all traveling in the same direction In other words the initial photon has been amplified by a factor of eleven Note that the energy to put these atoms in excited states is provided externally by some energy source which is usually referred to as the pump source 13 h z wei mai absorption Paty S asi See are kasian O E E gt Ort E E2 5 spontaneous emission
20. ng the junction in transparent or the light reaches the base through the entitles which has a wide band gap so it is transparent to the wavelengths detected Alternatively it can be said that it is a transistor in which light generates by transistor action making the device very sensitive The phototransistor has three layers of silicon containing tiny amounts of impurities These layers are termed as emitter base amp collector When a positive voltage is applied between collector amp emitter a tiny reverse saturation current flows This _ current is due to electrons and holes created by warmth The geometry ofa phototransistor allows light to shine on the collector base junction and this creates additional current carriers This current is amplified by transistor action The device used is MEL11 it is a high gain phototransistor in which the collector current is proportional to the incident light 27 IRA base connection o c this cut flows out via the base emitter junction and is amplified resistor Ry when light falls on the base region the leakage current increases with the Si by normal transistor action to give a large change in collector leakage current With N increased current flowing in load resistor Rq output voltage reduces and is dependent upon falling light Vour V lcro R where V Supply volt lego Collector leakage current Rr Load resistance E E C Incident Inc
21. ntageous for long distance communications because light propagates through the fiber with little attenuation compared to electrical cables This allows long distances to be spanned with few repeaters 3 Additionally the per channel light signals propagating in the fiber can be modulated at rates as high as 111 gigabits per second although 10 or 40 Gb s is typical in deployed systems 4 Each fiber can carry many independent channels each using a different wavelength of light wavelength division multiplexing WDM 5 The net data rate data rate without overhead bytes per fiber is the per channel data rate reduced by the FEC overhead multiplied by the number of channels usually up to eighty in commercial dense WDM systems as of 2008 The current laboratory fiber optic data rate record is multiplexing 155 channels each carrying 100 Gbps over a 7000 km fiber Conclusion Hence Optical fiber is studied in detail Experiment No 2 Sources of light for Optical fiber Aim To study Sources of light for Optical fiber Theory Optical source is often considered to be the active component of an OFC system lts function is to convert electrical energy in the form of current into optical energy in efficient manner into the fiber Three main types of optical fibers sources are 1 Wideband continous spectra sources incandescent lamps 2 Monochromatic incoherent sources Light Emitting Diodes 3 Monochromatic coherent sources Lase
22. rs For optical Fiber communications LED s and LASERS are preferred sources 1 Light Emitting Diodes Construction and working principle The LED consists of an encapsulated chip of semiconductor diode with a suitable lens The length of Anode terminal is greater than cathode terminal LEDs are based on the semiconductor diode When the diode is forward biased switched on electrons are able to recombine with holes and energy is released in the form of light This effect is called electroluminescence and the color of the light is determined by the energy gap of the semiconductor The LED is usually small in area less than 1 mm with integrated optical components to shape its radiation pattern and assist in reflection 10 electron conduction band eee ee Fee Tawa band gap iforbr dden band valence band Fig 1 Working Principle of LED Material for LED In case of LED different materials are used to get the radiation in infrared region and in the visible region To get radiation in infrared region Ga As material is used Sometimes the combination Ga As with indium and aluminium is used It gives the wavelength as follows In Ga As 8500 Angstrom Al Ga as 9000 Angstrom Advantages of LED 1 They are small in size and light in weight 2 They are mechanically rugged and have low operating temperature 3 No complex driving circuitry is required 4 Have high switching speed and are avail
23. vantages of LASER over other Light Sources 1 LASER light has narrow spectral bandwidth 2 Light is coherent and monochromatic 3 LASER light has good directionality 4 More percentage of the LASER light is in the visible range as compared to conventional lamps 5 LASER has high quantum efficiency and high modulation rate 6 LASERS are point source of light 7 LASER has excellent stability 8 LASER light can be modulated externally or it has ability of direct modulation 15 Types of LASERs According to the type of material used for the formation of LASER beam the LASERs are classified as the solid state laser gaseous laser power lasers and semiconductor LASERs A Solid State LASERS 1 Ruby Laser 2 Nd YAG Laser B Semiconductor LASER C Gas LASERs 1 Helium Neon Lasers 2 Carbon Dioxide Laser Conclusion Thus sources of light are studied in detail 16 Experiment No 3 Characteristics of Photovoltaic Cell AIM To study characteristics of Photovoltaic cell APPARATUS Optical Transducers Trainer kit ST 2301 SCIENTECH THEORY The photovoltaic cell is a two layer device It generates a voltage by electron hole pair production when the junction is exposed to light These diffuse across the junction to set up voltage A Current will flow if a resistance is placed across the terminals Devices optimized for energy production are often called solar cells This is an important class of photodetectors The
24. y generate a voltage which is proportional to EM radiation intensity They are called photovoltaic cell because of their voltage generating characteristics when light falls on them They infact convert the EM energy into electrical energy They are active transducers 1 c they do not need an external source to power them instead they penerate voltage The photovoltaic cell is shown in Fig 2 Symbol PROCEDURE 1 Connect the circuit as shown in diag 2 a The socket C of Wire Wound pot to 12V The socket A of Wire Wound pot to OV The socket B of wirewound pot to input of Power Amplifier a0 FD The output of Power Amplifier to input of Lamp Filament The other input of filament lamp to ve input of Moving Coil Meter The ve input of Moving Coil Meter to OV Output of Photovoltaic Cell to OV through a Digital Multimeter connected as an Ammeter at 2mA range to measure short circuit current of photovoltaic cell gt 0 Q 17 2 Switch ON the power supply amp set the 10KQ wire wound pot to minimum for zero output voltage from Power Amplifier 3 Place the opaque box over the plastic enclosure to exclude all ambient light Take readings of Photovoltaic cell short circuit output current as indicated as Digital Multimeter as lamp voltage is increased in 1V steps Record results in table 1 4 Switch OFF the power supply amp set the Digital multimeter as a voltmeter at 2 20 V DC range to read the open
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