Resistors, Current and Voltage measurements, Ohm s law, Kirchhoff s first and second law. Kirchhoff s first Objectives:

Transcription

1 EE -050 Ciruit L Experiment # esistors, Current nd Voltge mesurements, Ohm s lw, Kirhhoff s first nd seond lw. Kirhhoff s first Ojetives: Slmn in Adul Aziz University Eletril Engineering Deprtment. Fmiliriztion with the l poliy, eletri iruit omponents, sfety rules, nd min equipment (multi-meters, meters, power supplies, dede resistne ox).. Verifition of Ohm s low. Verifition of KV nd KC lws 4. Verifition of voltge nd urrent division rules. Equipments: DC power supply. Three olor ode resistors, Three dedes resistne ox, Pek Teh digitl multimeters 470 Ω, KΩ,.5KΩ,. K Ω, 4.7KΩ, nd 0 KΩ esistors. 0 (two), Ω Note: Plese reord ny dmge, if exists ny while performing the experiment. You n lso write the diffiulties you re onfronted with when using the equipment, nd your suggestions nd ritis relted with the equipment you used. Bkground:. esistors There re mny different types of esistors ville nd they n e used in oth eletril nd eletroni iruits to ontrol the flow of urrent or voltge in mny different wys. But in order to do this the tul esistor needs to hve some form of "resistive" or "esistne" vlue, nd resistors re ville le in rnge of different resistne vlues from frtions of n Ohm (Ω) to millions of Ohms. Oviously, it would e imprtil to hve ville resistors of every possile vlue for exmple, Ω, Ωs, Ωs, 4Ωs et euse literlly hundreds of thousnds, if not millions of resistors would need to exist. nsted, resistors re mnuftured in preferred vlues with their "esistne" rting printed onto their ody in olored ink. Experiment # Pge

2 The resistne vlue, tolerne, nd wtt rting of the resistor re generlly printed onto the ody of the resistor s numers or letters when the resistor is ig enough to red the print, suh s lrge power resistors. When resistors re smll suh s /4W Cron nd Film types, these speifitions must e shown in some other mnner s the print would e too smll to red. So to overome this, smll resistors use olored pinted nds to indite oth their resistive vlue nd their tolerne with the physil size of the resistor inditing its wttge rting. These olored pinted nds re generlly known s esistors Color Code.. esistors Color Code An nterntionl resistor olor ode sheme ws developed mny yers go s simple nd quik wy of identifying resistors vlue. t onsists of olored rings (in spetrl order) whose menings re illustrted elow in Fig.. nd Tle. Blk Brown ed Ornge Yellow Green Blue Violet Gry White Fig.. esistor olor ode Experiment # Pge

3 Tle. esistor Colour Code Colour Digit Multiplier Tolerne Blk 0 Brown 0 ± % ed 00 ± % Ornge K Yellow 4 0K Green 5 00K ± 0.5% Blue 6 M ± 0.5% Violet 7 0M ± 0.% Grey 8 White 9 Gold 0. ± 5% Silver 0.0 ± 0% None ± 0%. Clulting esistor Vlues The esistor Color Code system is ll well nd good ut we need to understnd how to pply it in order to get the orret vlue of the resistor. The "left-hnd" or the most signifint olored nd is the nd whih is nerest to onneting led with the olor oded nds eing red from left-to-right s follows; Digit, Digit, Multiplier Color, Color x 0 olor in Ohm's (Ω's) For exmple, esistor hs the following olored mrkings; Yellow Violet ed x Ω or 4k7. The fourth nd, if used, determines the perentge tolerne of the resistor nd is given s; Brown %, ed %, Gold 5%, Silver 0 % f resistor hs no fourth tolerne nd then the defult tolerne would e t 0%.. The British Stndrd (BS 85) Code Generlly on lrger power resistors, the resistne vlue, tolerne, nd even the power (wttge) rting re printed onto the tul ody of the resistor insted of using the resistor olour ode system. Beuse it is very esy to "misred" the position of deiml point or omm espeilly when the omponent is Experiment # Pge

4 dirty, n esier system for writing nd printing the resistne vlues of the individul resistne ws developed. This system onforms to the British Stndrd BS 85 Stndrd oding method where the deiml point position is repled y the suffix letters "K" for thousnds or kilohms, the letter "M" for millions or megohms oth of whih denotes the multiplier vlue with the letter "" used where the multiplier is equl to, or less thn, with ny numer oming fter these letters mening it's equivlent to deiml point, s illustrted in Tle. Tle. BS 85 Codes for esistor Vlues 0.47Ω 47 or 047.0Ω 0 4.7Ω 47 47Ω Ω 470 or 0K47.0KΩ K0 4.7KΩ 4K7 47KΩ 47K 470KΩ 470K or 0M47 MΩ M0 Sometimes depending upon the mnufturer, fter the written resistne vlue there is n dditionl letter whih represents the resistors tolerne vlue suh s 4k7 J nd these suffix letters re given s in Tle. Tle. Tolerne Letter Coding for esistors (±). B 0.% C 0.5% D 0.5% F % G % J 5% K 0% M 0% Experiment # Pge 4

5 Also, when reding these written odes, e reful not to onfuse the resistne letter k for kilohms with the tolerne letter K for 0% tolerne or the resistne letter M for megohms with the tolerne letter M for 0% tolerne.. Voltge Division ule Voltge divider referened to ground is reted y onneting two eletril impednes in series, s shown in Figure. The input voltge is pplied ross the series impednes Z nd Z nd the output is the voltge ross Z. Both of Z nd Z my e omposed of ny omintion of elements suh s resistors, indutors nd pitors. Fig.. Voltge divider rule using impednes Applying Ohm's Lw, the reltionship etween the input voltge, V in, nd the outputt voltge, V out, n e found: V out V in Z Z Z The trnsfer funtion (lso known s the divider's voltge rtio) of this iruit is simply: H V V out in Z Z Z. esistive divider A resistive divider is speil se where oth impednes, Z nd Z, re purely resistive s shown in Fig.. Sustituting Z nd Z into the previous expression gives: V out V in Experiment # Pge 5

6 Fig.. Voltge divider rule using pure resistnes. Current Division ule The formul desriing urrent divider is similr in form to tht for the voltge divider. eferring to Fig. 4, generl formul for the urrent in resistor tht is in prllel with nother resistor is: in Fig. 4. Current Divider 4. Delt ( ) nd Wye (Y) Connetion: There re ertin iruit onfigurtions in whih the resistors do not pper to e in series or in prllel. Under these onditions, it is neessry to onvert the iruit under investigtionn from one form to nother. Delt ( ) nd Wye (Y) Connetions re the most ommon onnetions tht exist in eletri iruits s shown in Fig. 5. -onnetion is lso known s Pi / (n)-onnetion nd Y-onnetion is lso known s str or Te (T)-onnetion. The trnsformtion is used to estlish equivlene for networks with terminls. Where three elements terminte t ommon node nd none re soures, the node is eliminted y trnsforming the impednes. For equivlene, the impedne etween ny pir of terminls must e the sme for oth networks. The equtions given here re vlid for rel s well s omplex impednes. Experiment # Pge 6

7 Experiment # Fig. 5 Delt nd Wye onnetions 4. Wye to Delt Trnsformtion The generl ide is to ompute the impedne '' to djent nodes in the iruit y where re ll impednes in the 4. Delt to Wye Trnsformtion Fig. 5 Delt nd Wye onnetions The generl ide is to ompute the impedne y t terminl node of the Y iruit with impednes iruit y " ' y re ll impednes in the iruit. This yields the speifi formule Pge 7 t terminl node of the Y iruit with impednes ',

8 Proedure :- esistne mesurement: - Given three olor oded resistors found on your experiment enh, determine the vlue of eh, first y lultion using the olor ode, nd seond y mesurement with n ohmmeter. eord your redings elow in tle 4. esistor # # # Tle 4: esistne mesurement y olor ode nd ohmmeter Vlue y Vlue y Colors Clultion Ohmmeter Comment: - Using n ohmmeter, mesure the ssigned different resistnes from the dede resistne ox s shown in tle 5, reord your redings. Also lulte the tolerne s shown on the dede resistne ox nd the errors of your redings. Tle 5: esistne mesurement nd lultion of tolerne nd errors. eding Dede Box nge Assigned esistne Ohmmeter eding % Tolerne % Error. 4 Ω Ω Ω 4. KΩ 5 KΩ 5. 0 KΩ 0 KΩ Experiment # Pge 8

9 () Perentge Tolerne: Using the perentge tolerne errors, indited on the ox rnges, lulte the eptle rnges of eh resistor vlue, nd reord your result in tle ove. Exmple: nge hs % tolerne of 0.5%, then the resistne vlue of 4 Ω hs tolerne of 4 (0.5/00) ± 0. 0Ω nd the rel resistne vlue is loted within 4 ± 0. 0Ω i.e..98ω to 4.0Ω. () Perentge Error: 4.Clulte the % error of your redings (mesurements) for eh meter ording to the following: Aul meter reding stndrd (dede ox) reding % error 00 stndrd (dede ox) reding Proedure :- Verifition of Ohm's lw. Assemle the iruit s shown in Fig. 6 using resistor 00Ω. Mke sure tht the polrity of the voltge soure nd the multi-meters is orret, nd tht the orret mesurement rnge hs een seleted. U E 00Ω Fig.6 Current nd voltge mesurement for one resistne Beginning with 0 volts, inrese the input voltge to 0 V y steps of volt. Mesure the urrent t eh step. Do not hnge the mesurement rnge setting of the multi-meter. eord the results in tle 6. U Determine the quotients for the vlues reorded in tle 4 nd enter them in the olumn provided for tht purpose in the sme tle. Experiment # Pge 9

10 Tle 6: Mesurement results U ( V ) (ma) 00Ω 0 Ω KΩ U ( V A) (ma) U ( V A) (ma) U ( V A) Plot the vlues mesured on the grph (ma) Current-Voltge hrteristis of different resistors U (V) Experiment # Pge 0

11 Wht reltionship n e seen etween urrent nd voltge? Proedure Voltge Divider rule nd Kirhhoff s seond low Assemle the iruit s shown in Fig. 7. Mke sure tht the polrity of the voltge soure nd the multi-meters is orret, nd tht the orret mesurement rnge hs een seleted. 00Ω 00 Ω ΚΩ U E Set the input voltge g. (ma) Fig.7. Mesuring voltge drop ross resistors onneted in series U E to 0 V, then mesure nd reord the totl urrent g. Mesure & Clulte the voltge U ross resistor nd reord it in tle 7 Mesure & Clulte the voltge U ross resistor nd reord it in tle 7 Mesure & Clulte the voltge U ross resistor nd reord it in tle 7 Tle 7: Mesured nd Clulted voltges U (V) mesured U (V) lulted 00 Ω 50 Ω 000 Ω Experiment # Pge

12 eltion etween resistne vlue nd voltge drop s well s Kirhhoff's Seond lw. Add up the omponent voltges mesured nd ompre this sum with the input voltge Wht is your omment on this omprison? At whih resistor is omponent voltge drop the gretest? At whih resistor is it lest? Wht rule n e dedued from this? Proedure V Current Divider rule nd Kirhhoff s first low Assemle iruit s shown in Fig. 8. Mke sure tht the polrity of the voltge soure nd the mesuring instruments re orret, nd tht the orret mesurement rnge hs een seleted. U E U E 00Ω ΚΩ Fig.8. Mesuring the totl urrent with two resistors onneted in prllel Set the input voltge U E t 0 V, then mesure nd reord the totl urrent g in tle 8. Mesure nd Clulte the urrent in the rnh with resistor Mesure nd Clulte the urrent in the rnh with resistor 00Ω nd reord this in tle 8. KΩ nd reord this in tle 8. Experiment # Pge

13 Tle 8: Mesured nd Clulted urrents Mesured Clulted g Add up the omponent urrents mesured nd ompre this sum with the input urrent g Wht is your omment on this omprison? Compre the rtio of the omponent urrents with the rtio of the omponent resistors At whih resistor is omponent urrent the gretest? At whih resistor is it lest? Wht rule n e dedued from this? Experiment # Pge

14 U E 5V 470Ω 0ΚΩ 0Ω ΚΩ 0Ω Fig. 9. Simple iruit for - Y trnsformtion Mesure the urrent nd ompre it with the vlue lulted previously Clulted. mesured Comment:. Clulte the equivlent Wye (Y) for the tul Delt ( ) shown in Fig. 9 nd reord the vlues of the resistors,, nd eonstrut the iruit of Fig. 9 using Y equivlents nd lulte the urrent using - Y trnsformtion. Clulted.. Mesure the urrent nd ompre it with the lulted vlue Clulted. mesured.. Comment: Experiment # Pge 4