Photoelectric cell-Biosensors and Transducers

Photoelectric cell-Biosensors and Transducers

1. PHOTOELECTRICCELL
-
MUKESH SUNDARARAJAN

2. PHOTOELECTRICCELL
➢Adeviceusedtoconvertlightenergyintoelectricalenergyiscalledphotoelectric
cell.
➢Photocellisbasedonthephenomenonofphoto-electriceffect.
➢Einsteinin1905proposedthattheincidentlightconsistedofindividualquanta
calledphotonsthatinteractedwithelectronsinmetallikediscreteparticlesrather
thancontinuouswaves.
➢AlbertEinsteinwas honouredwiththenobelprizeinphysicsin1921for
successfullyexplainingthephotoelectriceffect.
Typesof photoelectriccell
➢Photo-emissivecell
➢photo-voltaiccell
➢Photo-conductivecell

3. PHOTOEMISSIVECELL
➢Therearetwotypesof photo-emissivecells;vacuumtype orgas
filled.
➢Consistsoftwoelecrodes:-cathode&anode.
➢Cathode:-coatedwithphotosensitivemateriallikesodium,
potassiumor cesium.
➢Anode:-straightwiremadeofnickelorplatinum
➢Evacuatedglassorquartzbulb
➢Photo-electronsflowfromcatode
toanode,gas ionizethegas
filledandhencecurrentgets
modified.

4. Drawbacksof gasfilledcell
Photo-electriccurrentdoesnotvarylinearlywithintensityof
light.
Application
Thereisno time lag betweentheincidentlightandtheflow
of electronsandhence current,thereforesuchcellis
usedin
Television
Photometry
Fire-alarm

5. PHOTO-VOLTAICCELL
➢Based ofprincipleofinnerphotoelectriccell.
➢This is called true cell because it generates e.m.f without the
applicationof anyexternalofany externalpotentialdifference.
➢Itconsistsof semiconductorlayerformedon thesurfaceof metal
plateby eitherheattreatmentor cathodesputtering.
➢Afilmofsemitransparentmetaliscoatedoverthesemiconductor.

6. ??????I
➢Currentispropostionaltotheintensityofincidentlight.
ADVANTAGES:-
Itrequiresnoexternalvoltageforitsoperation.
APPLICATION:-
Photographic exposures meters,photometersandilluminatiometers.

7. PHOTO-CONDUCTIVECELL
➢Basedoninnerphotoelectriceffect.
➢Itconsistsofthinfilmofsemiconductorlike seleniumor
thalliumsulphide
placedbelowathinfilmof semitransparentmetal.
➢Theironbaseandthetransparentmetalfilmis
connetcedthroughbetteryand resistance.
➢Whenlightfallsonthecellitsresistancedecreasesand
hencethecurrentstarts
flowingintheexternalcircuit.

8. ➢Inversesquarelaw:-
whereE:-electriclummincance, d: distance
I:-luminousintensityofanelectriclamp
θ :-deflectionshownbythemicroammeter

9. ➢characteristics
➢Application:-
Makingstreetlights turnonandoffautomaticallyaccordingtothelevel
ofdaylight.
Insecuritydevicessuchasmotionsensinglightsandcameras.
Inalarmsystems.
Aslightmetersinphotographicapplications.

10. THANK YOU