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Experiment-1: Wheatstone’s bridge
Date :__________
1. Aim: To study and perform an experiment to measure the unknown
Resistance by Wheatstone’s bridge.
2 . Requirements :
L igh t Spot DC Galvanomete r, Various Med ium Res is to rs ,
Mult imete r, Po rtab le Wheats tone b ridge
3 . Pre -Experiment Exerc ise :
Brie f Theory
A bridge c i rcu i t in i ts simples t fo rm cons is ts o f network o f fou r
res is tance arms fo rming a c losed c i rcu i t , wi th a dc source o f cu rren t
app l ied to two opposi te junc tions and a cu rren t de tec to r connec ted to the
o ther two junc t ions .
Wheats tone‟s b ridge is used fo r accurate measuremen t o f res is tance .
The c ircu i t d iagram of a typ ical Wheat s tone‟s b ridge is given in fig . 1 .1
F ig 1 .1 Wheats tone Bridge
2
When SW 1 is c losed , cu rren t flows and d ivides in to the two arms at po in t
A, i .e . I 1 and I2 . T he b ridge is balanced when the re is no cu rren t th rough
the galvanomete r, o r when the po ten t ial d i ffe rence at po in ts C and D i s
equal , i .e . the po ten t ial ac ross the galvanomete r is ze ro .
To ob tain the b ridge balance equat ion , we have from the fig . 1 .1 ,
I1 R 1 = I2 R 2 ( 1 .1 )
Fo r the galvanomete r cu rren t to be ze ro, the fo l lowing cond i t ions shou ld
be sat is fied .
I1 = I3 = E/( R 1 + R 3)
I2 = I4 = E/( R 2 + R 4)
Subs t i tu t ing in Eq . (1 .1 )
(E*R 1 )/ (R 1+R 3) = (E *R 2)/ (R 2+R 4)
R 4 = (R 2 *R 3) / R 1
This is the equat ion fo r b ridge to be balanced .
Circui t Diagram:
R 1 = 1 K R 3 =10 K
R 2
M
-
0 -12V
D C SUP P LY
Rs =1 K
R X
A
10E
B
100
E
C
1 K
D
1 0 K
E
1 0 0 K
F
5 0 0 K
F ig 1 .2 : Wh ea tston e‘s B rid g e
3
4 . Laboratory Exercise :
Procedure
1) T ake The T rainer ki t . Measure res is to rs A, B , C , D , E , F , R1 and the
variab le po t R 3 by ad jus t ing “ADJ R 3” . No te down the values o f each
res is to rs .
2 ) Now inse rt i t s mains co rd in mains 230 V supp ly p lug and switch i t
'ON‟. Measure the DC supp ly vo l t age . ( It shou ld be 12V DC )
3 ) Selec t the unknown res is to r and measure i ts res is tance Rx and no te i t
down .
4 ) Connec t the res isto r to the te rminal ( Rx ), and connec t the power
supp ly in to the c i rcu i t . Connec t the galvanomete r to M of the b ridge
with the he lp o f jumper.
5 ) Connec t the S 1 te rminal to any res is to r A, B , C , D, E , F . Ad jus t po t
„R 3‟ to ge t a nu l l read ing on the galvanomete r.
6 ) Once the „Nu ll , read ing is found , remove al l the jumpers and measure
the value o f R 3 . Pu t the value o f R 3 in the fo rmula given be low and
calcu late Rx p rac t ical ly.
Rx=R 2*R3 /R 1 (R 2=A or B or C….. or F)
7) Match the p rac t ical „Rx‟ with that o f the Rx d irect ly measured on
mult imete r.
8 ) T ake four to five reading to find the unknown res is tance i .e . Rx with
d iffe ren t res is to rs .
No te : Use unknown resis to rs o f values be tween 10 Ω to 10 KΩ fo r the
be t te r sens i t ivi ty.
Res is tor R 2 Rx Range which can be measured
A-10 Ω 10 Ω to 100 Ω
B-100 Ω 100 Ω to 1 KΩ
C-1 KΩ 1 KΩ to 10 KΩ
D-10 KΩ 10 KΩ to 100 KΩ
E-100 KΩ 100 KΩ to 500 KΩ
F-500 KΩ 500 KΩ to 1 MΩ
Conc lus ion:
4
Experiment-2: Maxwell’s Bridge
Date : __________
1. Aim: To study and perform an experiment to measure the unknown inductance and
capacitance by Maxwell’s Bridge.
2 . Requirements :
Head Phone (p rovided) , L .C. Mete r , Digi tal Mult imete r , Few
co i ls and capac i to rs o f s tandard values , T rainer ki t , Patch Cords
3 . Pre -Experiment Exerc ise :
Brie f Theory
Maxwell‟s b ridge which is shown in fig . 2 .1 , measur es an unknown
induc tance in te rms o f a known capac i to r. The use o f s tandard arm o ffe rs
the advantage o f compac tness and easy sh ield ing. The capac i to r is almost
a loss -less componen t . One arm has a res is tance R 1 in paral le l wi th C 1 , and
hence it i s eas ie r t o wri te the balance equat ion us ing the admit tance o f
arm 1 ins tead o f the impedance .
The general equat ion fo r b ridge balance is ,
Z 1 Z X = Z 2 Z 3
i .e . Z x = Z 2 Z 3 / Z 1 = Z 2 Z 3 Y1 ( 2 .1 )
where Z 1 = R 1 in paral le l wi th C 1
Y 1 = 1 /R 1 + jωC 1
Y1 = 1 /R 1 + jωC 1
Z 2 = R 2
Z 3 = R 3
Z x = R x in se ries with L x = R x + jωL x
From Eq . 2 .1 we have
R x + jωL x = R 2 R 3 ( 1 /R 1 + jωC 1 )
R x + jωL x = R 2 R 3 /R 1 + jωC 1 R 2 R 3
5
Fig . 2 .1 Maxwell’s Bridge
Equating real te rms and imaginary te rms we have
R x = R 2 R 3 / R 1
L x = C 1 R 2 R 3
Q = ωL x / R x = ω C 1 R 1
The Maxwell‟s Bridge us ing a fixed capac i to r has th e d isadvan tage
that the re is in te rac t ion be tween the res is tance and reac tance balances .
This can be avo ided by varying the capac i tances , ins tead o f R 2 and R 3 , to
ob tain a reac tance balance .
C 1
R 1
R 2
Rx
R 3
Lx
De tecto r
6
Circui t Diagram:
H e a d P h on e
R C 1=10 Ώ
R C 3 =1 k R C 2 = 1 0 0 Ώ
Fig. 2 .2 Maxwell‟s Bridge
4 . Laboratory Exercise :
Procedure
1 ) T ake the t raine r ki t and inse rt i t s mains co rd in main s supp ly
p lug, switch i t 'ON ' .
2 ) Observe the ou tpu t o f bui l t in osc i l lato r on CRO . Measure th e
frequency band o f the osc i l lato r.
3 ) For find ing induc tance value , connect a s tanda rd 1 mic ro -fa rad
capac i to r at C 1 , sho rt Rx, and selec t R C 1 , wi th the patch co rd and
induc to r at Lx.
4 ) Connec t headphone to the Headphone socke t . App ly the Aud io
Signal to the b ridge inpu t shown by do t ted l ine . Listen to the
aud io ou tpu t o f the Headphone , and ad jus t R A t i l l you do no t hear
R x
L x
R A= 1 0 K
(T en tu rn )
R 1 =1 K
C 1
A UD I O
S I G N AL G E N E R A T O R
7
any aud io sound . If aud io sound cont inues fo r al l the pos i t ion o f
R A , t ry with R C 2 and R C 3 , in p lace o f R C 1 .
5 ) The b ridge is balanced when you don 't ge t any sound from the
headphone with the ad jus tmen t o f R A .
6 ) Note the value o f R A & R C a fte r separat ing them from the b ridge
us ing Digi tal Mult imete r . Remove al l the connec t ions o f
Headphone , Aud io Signal & R C wh i le measuring the values .
7 ) Apply the fo rmula o f equat ion given be low fo r find ing Lx.
Lx = R A X R C X C 1
8 ) Note the value o f inducto r and veri fy your resul t wi th the value
measured by LC mete r.
NOTE: T he componen ts , values o f the ki t are des igned to measure the
induc tance value from 1 mH to 100 mH.
Experimenta l procedure for measuring the va lue o f unknown
capac itor:
1 ) For find ing unknown capac i to r value , connec t a 10 mH standard
induc to r at Lx. Short Rx, se lect R C , and Connec t unknown capac i to r at
C 1 and headphone at the ou tpu t .
2 ) Adjus t R A fo r ge t t ing nu l l cond i t ion as pe rfo rmed in p revious
p rocedure o f inductance measuremen t .
3 ) Apply the fo rmula o f equat ion given be low fo r find ing C 1 .
C 1= Lx / R A*R C
4 ) Verify your resu l t by measuring the value on capac i tance mete r.
Experimenta l procedure for measuring the va lue o f unknown
res is tance :
1) Short Lx, remove C 1 , se lec t R C and connec t the unknown res isto r at Rx.
2 ) Adjus t R A fo r nul l po in t and app ly the fo rmula o f Wheats tone b ridge .
3 ) Verify your resu l t wi th the value observed from the ohmmeter.
Conc lus ion:
8
Experiment 3: Wien Bridge Date : ______
1. Aim: To study and perform an experiment to measure the frequency by Wien’ s
bridge.
2 . Requirements : S ine wave genera to r, CRO, d igi tal mult imete r ,CRO probes .
3 . Pre -Experiment Exerc ise :
Brief Theory
The Wien Bridge , shown in fig . , has a se ries RC combinat ion in one arm
and a paral lel combinat ion in the ad jo ining arm. Wien Bridge in i ts bas ic fo rm
is des igned to measure frequency. It can also be used fo r the measuremen t o f
unknown capac i to r with great accuracy.
The impedance o f one arm is
Z 1 = R 1 – j /ωC 1 .
The admit tance o f the paral le l arm is
Y3 = (1 /R 3) + j ωC 3 .
Us ing the Bridge balance equat ion ,
We have
Z 1Z 4 = Z 2Z 3 .
There fo re
Z 1Z 4 = Z 2 /Y3 , i .e .Z 2 = Z 1Z 4Y 3
R 2 = R 4 (R 1 – j / ωC 1 ) [(1 /R 3) + j ωC 3) ]
R 2 = (R 1R 4 /R 3) – j R 4 /ω (C 1R 3) + j ω C 3 R 1 R 4 + C 3 R 4 / C 1
R 2 = (R 1R 4 /R 3) + (C 3 R 4 / C 1 ) – j [(R 4 /ω (C 1R 3)) – (ω C 3 R 1 R 4 ) ]
Equating the real and imaginary terms we have
R2 = (R1R4/R3) + (C3 R4/ C1) and (R4/ω (C1R3)) – (ω C3 R1 R4) = 0
9
(R2/R4) = (R1/R3) + (C3 / C1)
Therefore
(R2/R4) = (R1/R3) + (C3 / C1)
and 1/ωC1R3 = ω C3R1
ω2 = 1/ (C1R1C3R3)
ω = 1/ (C1R1C3R3)1/2
ω= 2 ∏ f
f = 1/ 2∏ (C1R1C3R3) 1/2
The Bridge is u sed fo r measuring frequency in the aud io range . Res is tance
R1 and R3 can be ganged together to have iden tical values . Capac i to rs C1 & C3
are no rmally o f fixed values .
The aud io range is no rmally d ivided in to 20 – 200 – 2K – 20KHz ranges .
In th is case , the res is tance can be used fo r range changing and capaci to r C1 &
C3 fo r fine frequency con tro l wi th in the range . The Bridge can also be used
measuring capac i tances . In that case , the frequency o f operat ion must be known.
An accuracy o f 0 .5% - 1% can be read i ly ob tained us ing th is b ridge .
Because it i s frequency sens i t ive , i t i s d i fficu l t to balance un less the wavefo rm
o f app l ied vo l tage is pu re ly s inuso idal .
4 . Laboratory Exercise :
Procedure
1) Make connec t ions as shown in Fig.3 .1
2 ) Connec t unknown s ine wave frequency (1 kHz) ac ross the inpu t
te rminal marked as „inpu t‟ variab le frequency.
3 ) Connec t capaci to r C 1 and C 3 as ind icated by do ted l ine th rough
patch co rds . No te that C 1 and C 3 shou ld be o f equal value .
4 ) Now connec t res is to r R 2 and R 4 so that (R 4 /R 2) = 2 .
5 ) Now ad jus t R con tro l so that ind icato r shows nu l l .
6 ) Afte r balance cond i t ion d isconnec t the connec t ion o f a rm A - D o f
A-B and measure the value o f po rt R by mult imete r.
7 ) With the he lp o f fo rmula given . Find ou t ou tpu t frequency.
8 ) Repeat the above p rocedure fo r o the r values o f capac i to r.
FORMULA:
ω = 2 ∏ f
f = 1 / [2∏ (C 1R 1 C 3 R 3 )1 / 2
]
10
F igure 3 .1 Wien Bridge
B . Observation Table
Conc lus ion:
Sr. No . Value o f
capac i to r
„c ‟
Measured
Frequency „ f‟
1 .
2 .
N U L L D E T E C T O R
0 . 1 M F
0 . 0 0 1 M F
0 . 0 1 M F
R 2
R 1
0 . 1 M F
0 . 0 1 M F
D
0 . 0 0 1 M F
2 K
2 0 K
2 0 0 k
1 K
1 0 K
1 0 0 K
C 2
C 1
R 4 R 3
A.C
IN P UT
11
Experiment 4: Lissajous Patterns Date :-__________
1 . Aim: To study and perform an experiment to measure unknown
frequency us ing Lissa jous method.
2 . Requirements :
C.R.O,Func t ion generato rs , Patch co rds , C RO probes e tc .
3 . Pre -Experiment Exerc ise :
Brie f Theory
The osc i llo scope is a sens i t ive ind icato r fo r frequency and phase
measuremen ts . The techn iques used are s imple and dependab le , and
measuremen t may be made at any frequency in the response range o f the
osc il lo scope .
One o f the qu ickes t methods o f de te rmining frequency is by us ing
Lissajous pat te rns p roduced on a sc reen . Th is part icu lar pat te rn resu l ts when
s ine waves are app lied s imultaneous ly to bo th pair o f the de flec t ion p lats . If one
frequency is an in tegral mult ip le o f the o ther, the pat te rn wil l be s tat ionary, and
is cal led a Lissajous figu re .
In method o f measuremen t a s tandard frequency is app l ied to one se t o f
de flec t ion p lates o f the CRT tube while the unknown frequency is
s imultaneous ly app l ied to o the r se t o f p lates wh ich is shown in the figu re 4 .1 .
However the unknown frequency is p resen ted to ve rt ical p lates and the known
frequency to the ho rizon tal p lates . The resu lt ing pat te rns depend on the in tegr al
and phase re lat ionsh ip be tween the two frequenc ies . (The horiz on tal s ignal is
des ignated as f h and the ve rt ical s ignal as f v).
12
4 . Laboratory exerc ise
F ig 4 .1 Se t- up fo r frequency measuremen t by L issajous method .
A. Procedure :
1 ) Connec t two Func tion Generat o rs to the channel 1 and 2 as shown
in Fig 4 .1 .
2 ) Cons ider channe l -1 as unknown frequency channe l and channe l -2
as known frequency channel .
3 ) P ress XY mode switch o f C .R.O, s o that channe l -1 s ignal is
connected to the ve rt ical p late and channel -1 s ignal is connec ted
to ho rizon tal plate .
4 ) Se t the frequency as given in obse rvat ion table and very the
unknown freq as given pat te rn .
FORMULA
(Fv/ F h) = No . o f ho rizon tal tangen t ices
No. of vertical tangentices
Where F v = Unknown Frequency
Fh = Known frequency
CH 1 CH 2 FG1
Fv
FG2
Fh
C.R.O.
Screen
13
B . Observation table : -
Known
Frequency
I f
Pattern Unknown Frequency
Fv
100 Hz
100 Hz
100 Hz
100 Hz
100 Hz
100 Hz
Conc lus ion:
14
Experiment-5: Strain Gauge Date : ______
1 . Aim: To s tudy and perform an experiment on s tra in gauge
amplifier and s tra in gauge transducer.
2 . Requirements :
Digi tal Mult imete r, Patch Cords , Diffe ren t Weigh ts (From 100gm.to 1
Kg.) , St rain Gauge Kit
3 . Pre -Experiment Exerc ise :
Brie f Theory
The s t rain gauge is an example o f a pass ive t ransducer that uses the
variat ion in e lectrical res is tance in wires to sense the s t rain p roduced by a
fo rce on the wires . General ly , d isp lacemen t is though o f in te rms o f a
motion o f a few mil l imete rs (mm)or le ss . The measuremen t o f
d isp lacemen t is made frequen t ly to re late to some o ther measured , and
hence d isp lacemen t t ransducers are fundamental componen ts o f any
ins t rumen tat ion sys tem. Disp lacemen t is c lose ly assoc iated with mo tion ,
i .e . from one po in t to ano ther, and pos i t ion , i .e . a change from one
pos i t ion to the next . Disp lacemen t can be measured by bo th mechan ical
and e lec trical methods , but only e lec trical methods which are common in
indus tries .
Res is tance Strain Gaug e :
Strain gauge is a pos i t ive type res is tance t ransducer wh ich converts a
mechan ical d isp lacemen t in to a change o f res is tance . It i s the most
commonly used t ransducer fo r the measurement o f d isp lacemen t . The
res is tance gauge is e ssen t ial ly a fine wire wh ich ch anges i ts res is tance ,
when mechan ical ly s t rained , due to phys ical e ffec ts . Its length and c ross
sec t ional area vary and a change o f e lec trical res is t ivi ty also occurs . The
s t rain gauge is moun ted to the measured su rface so that i t e longates o r
con trac ts wi th that su rface . Th is de fo rmation o f the sens ing mate rial
causes i t to undergo a change in resis tance . The res is tance change o f the
s t rain gauge is usual ly converted in to vo l tage by connec t ing one , two , o r
fou r s imilar gauges as arms o f a Wheats tone b ridge (known as s t rain
gauge b ridge) and app lying exc i tat ion to the b ridge . The b ridge ou tpu t
vo l tage is then a measure o f the s t rain , sensed by each s t rain gauge .
15
Circuit Diagram:
Fig.5.1 Set Up for Strain Gauge Amplifier and Transducer
4 . Laboratory Exercise :
Procedure
1 . Connec t the t raine r Kit to the mains supp ly and Switch i t ON.
2 . Connec t the Strain Gauge T ransducers to the inpu t Socke t o f the Kit .
16
3 . Connec t the ou tpu t o f in s t rumentat ion Ampl ifie r to the Digi tal
ind icato r.
4 . Now ad jus t the ' Zero Adj . ' Po ten t iomete r to ge t Zero read ing on the
ind icato r.
5 . Now p lace the Weight o f 100 -gm at the cen tre o r near the bo rder o f the
pan fi t ted on the s t rain Gauge Can t ilever ar rangement .
6 . Observe and no te down the read ing.
7 . Place the Weigh ts from 100 -gm to 500 -gm (l Kg. Maximum) in such a
way that maximum s tress is app l ied at the can t i lever ar rangement . Pu t the
Weigh ts near the bo rder o f the Pan . No te the read ing o f Ampli fie r ou tpu t
fo r each inc remen t o f 100 -gm.
8 . Draw the graph o f Weigh t V /S. Ou tput in mic ro vo l ts .
Conc lus ion:
17
Experiment 5: Linear Variable Differential Transducer (L.V.D.T)
Date: _______
1. Aim: To study and perform an experiment on Linear Variable Differential
Transducer (L.V.D.T)
2. Requirements:
Dual Trace CRO, Patch cords, L.V.D.T. Trainer Kit, Digital Multimeter.
3. Pre-Experimental Exercise:
Brief Theory
The differential transformer is a passive inductive transformer. The transformer
consists of a single primary winding P1 and two secondary windings S1 and S2 would on a
hollow cylindrical former. The secondary windings have an equal number of turns and are
identically placed on either side of the primary windings. The primary winding is connected
to an AC source. A movable soft iron core slides within the hollow former and therefore
affects the magnetic coupling between the primary and two secondaries. The displacement to
be measured is applied to an arm attached to the soft iron core. In order to convert the output
from S1 to S2 into a single voltage signal, the two secondaries S1 and S2 are connected in
series oppositions. Hence the output voltage of the transducer is the difference of the two
voltages. Therefore the differential output voltage E0 = Es1-Es2. The output voltage of an
LVDT is a linear function of the core displacement.
4. Laboratory Exercise:
A. Procedure
1) Connect the Trainer Kit to the mains supply and switch it „ON‟.
2) Now observe the output of the sine wave of approx.4-kHz with adjustable
output of 10-volt Peak to Peak.
3) Set the amplitude of the 4-khz oscillator to get maximum output.
4) Connect the output signal to the input of the LVDT Transducer Primary.
5) Short the secondary terminals of LVDT shown by dotted lines.
6) Refer to Figure 6.1 & observe the output of LVDT on the second channel of the
CRO (Between A & C) You should observe the same signal with 180 degree
out of phase. Note the amplitude of this output signal.
This is the output observe when LVDT shaft is not displaced.
18
7) Now slowly shift the position of LVDT shaft as per the observation table and
record the output for all the position. Observe Null Point and 180degree phase
shift of the input signal between A & C terminals.
Fig- 6.1 L.V.D.T. Detector Circuit
8) Now connect the output of LVDT point A, B and C at the LVDT Detector
circuit with the help of patch cords. Refer to Fig. 6.1 calibrate the output of
LVDT to 10 mm by adjusting the output potentiometer of the displacement
indicator digital meter.
9) Connect the output of LVDT detector circuit to the displacement indicator
digital meter.
10) Observe and record the output of LVDT and plot the graph of displacement
in mm v/s output in D.C millivolts verify the linearity of the LVDT.
B. Observation Table
Sr. No. Input displacement in
mm
Meter reading in
mv
1.
2.
3.
4.
O /P .Adj .
P RIMARY
S EC 1
S EC 2
IN 4007
IN 4007
1 k
1 k
1 k
1 k
A
B
C
+
-
0 .45µ F
19
Note:
In right side direction consider displacement reading as +ve.
In left side direction consider displacement reading as –ve.
Conclusion:
5
20
Experiment-6: RTD as a Transducer Date : ______
1 . Aim: To s tudy and perform an experiment on the princ iple and working
o f a temperature Contro l ling RTD as a transducer.
2 . Requirements :
T raine r Kit , PT - 100 Sensor , Wate r Heate r, Patch co rds , Thermomete r,
Digi tal Multimete r
1 . Pre-Experiment Exerc ise
Brie f Theory
The circu i t o f the RT D Temperatu re Ind icato r & Con tro l le r is
bas ical ly an ON-OFF type temperatu re contro l le r wi th wate r heate r as
p rocess . We can con tro l the temperatu re o f wate r kep t in a Wate r Heate r.
The RTD sensor (PT -100) is kep t in wate r heate r. The Heate r ge ts i t s
mains supp ly from the contro l le r c i rcui t . Suppose the se t po int o f the
wate r is kep t at 70° C, then the temperatu re ind icato r c i rcu i t wi ll p roduce
approx. 70 mV at the A 2 ou tput . The comparato r A 3 compress the 70 mV
process value and the 70 mV re fe rence value . As soon as the temperatu re
c rosses 70° C , the Op amp A3 i .e . comparato r switches o f re lay hence no
supp ly to the wate r hea te r.
Res is tance temperatu re detec to rs are the rmal ly sens i t ive res is t ive
e lemen ts that exh ib i t an inc rease in res is tance as that temperatu re o f the ir
environment inc reases . Thus , these devices have a pos i t ive temperatu re
coeffic ien t , and they cons truc ted o f p latinum, n icke l , copper, tungs ten , o r
n icke l -i ron . Since the RTD wil l inc rease i ts res is tance when the
temperatu re o f i ts environment inc reases , i t s res is tance is a func t ion o f
temperatu re and i t 's u sual ly de te rmined at O‟C. Thus a 100 -Q RTD wil l
exh ib i t 100 -Q o f res is tance when i ts temperatu re is 0 " C, o r 32° F. As i ts
temperatu re inc reases , l ike -wise i ts res istance inc reases . To de te rmine the
res is tance o f an RTD at any temperatu re with in i ts range , the RTD's
temperatu re coeffic ien t mus t be used . The p os i t ive temperatu re coeffic ien t
o f res is tance is s tated as 'a lpha ' and rep resen ts the pe rcen t o f change in
res is tance fo r each -Ce ls ius change in temperatu re .
21
Fig. 7.1 Circuit of temperature indicator using R.T.D. and Thermistor
22
4 . Laboratory Exercise :
Procedure
(A) To s tudy ind icato r ac t ion
1 . Connec t the given temperatu re senso r (PT 100) to the socke t
p rovided fo r senso r.
2 . Observe the ou tput o f b ridge on Voltmete r.
3 . Adjus t the Ten Turns po ten t iomete r o f b ridge to the room
temperatu re , i .e . the vo ltage read ing in mil l ivol ts . Suppose the
room temperatu re is 30° ad jus t the po ten t iomete r to ge t 30 .0 on
mete r in 200 mil l ivol t s range .
4 . Now connect the d igi tal indicato r at the final amplifie r ou tpu t &
cal ib rate the sys tem by the po t ent iomete r p rovided in the
amplifie r c i rcu i t . The sys tem can be cal ib rated at 100‟ C by
bo i l ing the wate r in wate r heate r.
5 . Now switch o ff the wate r heate r and remove the rmomete r and
sensor from the wate r. In se rt the senso r in no rmal wate r to coo l
i t at ro om temperatu re .
6 . Now p lace the senso r near the ki t and observe the read ing on
d igi tal pane l mete r. Th is is the room temperatu re . Verify i t wi th
the reading on the rmomete r.
(B) T o s tudy con tro lle r ac t ion
7 . Now connec t the heate r at "Connec t Heate r" socket o f the Kit .
8 . Connec t Ref. Inpu t (se t po in t ) to the con trol le r c i rcu i t & A 2 to
the inpu t o f con tro lle r c i rcu it .
9 . Set the Value o f re fe rence be tween 40° to 80°C.
10 . Verify that comparato r makes the heate r ON & OFF when the
wate r temperatu re reaches above the s e t o r be low the se t po in t .
No te : T emperatu re o f Wate r can be set by p ress ing the Se t Poin t
switch . The Ind icato r now showed the set value .
23
Conc lus ion:
24
Experiment-8: CRO Demonstrator
Date : ______
1 . Aim: To s tudy and perform an experiment on CRO demonstrator.
2 . Requirements :
C .R.O Demonstrato r t raine r, Patch co rds, Mult imete r, Func t ion generato r,
Connec to rs
3 . Pre -Experiment Exerc ise :
Brie f Theory
The Cathode Ray Osc i l loscope (CRO) is p robably the most ve rsat i le
too l fo r the deve lopment o f e lectron ic ci rcu its and sys tems. It al lows the
ampli tude o f e lec tron ic s ignals , whe ther they are vo l tage , cu rrent o r
power to be d isp layed as a func t ion o f t ime . The depends on the
movement o f an e lec tron beam , wh ich is bombarded on a sc reen coated
with a fluo rescen t mate rial , to p roduce a vis ib le spo t , If the e lec tron beam
is de flec ted on bo th the convent ional axes , i .e . X-axis and Y-axis , a two
d imens ional pat te rn is p roduced .
Block Diagram of CRO :
The b lock d iagram of CRO is shown in fig 8 .1 . It con tains fo l lowing
majo r b locks .
1 . Signal inpu t (panel p1 )
2 . Beam switch & XY amplifie r (pane l p2 )
3 . T race & T rigger con tro l (pane l p3 )
4 . Time base (pane l p4 )
5 . CRT & Beam con tro l (pane l p5 )
6 . Power supp ly (pane l p6 )
7 . Fau l t generat ion t roub le shoo t ing pane l (pane l p7 )
25
F ig 8 .1 Block Diagram of CRO
26
The func t ions o f th e various b locks are as fo l lows:
1 . Signal inpu t ( pane l -p1 )
F ig 8 .2 shows the b lock d iagram of s ignal inpu t . It con tains
at tenuato r and p re -amplifie r and componen t tes te r c i rcu i t .
At tenuato r is the main b lock which at tenuates the s ignal to a
spec ified leve l . The p re -amplifie r generates a d iffe ren tial outpu t
from s ingle ended inpu t .
Componen t tes te r mode d isab les regular working by d isab ling
sweep and con tro ls the c i rcu i t th rough CT x and CT y fo r obse rving
the pat te rns o f any componen t .
2 . Beam switch and X-Y ampli fie r (pane l -p2)
F ig 8 .3 shows the b lock d iagram of beam switch and X -Y amplifie r.
The d iffe ren t ial s ignal ob tain ing from pre -amplifie r s tage is
supp l ied to the inpu t stage o f Y final amplifie r. T h is amplifie r
cons is ts o f several d i ffe ren t ial pairs fo r ob tain ing h igh gain at
the final s tage . Th is h igh gain ou tpu t is d i rec t ly fed to Y p lates o f
tube .
A sweep s ignal and X-Pos i t ion con tro l is appl ied as an
inpu t to the X final amplifie r which also inc ludes several
d i ffe ren t ial amplifie rs fo r p roper shapi ng and h igh gain at final
s tage . Th is amplified signal is d i rec t ly fed to X deflec t ion p lates o f
cathode ray tube .
In XY mode o f operat ion , the sweep generato r is
d isconnec ted and CH-2 is connec ted to ho rizon tal amplifie r.
Since bo th the p re -amplifie rs a re iden tical and have a same de lay
t ime , accurate X-Y measuremen t can be made .
3 . T race and T rigger con tro l (pane l -p3)
Fig 8 .4 shows the b lock d iagram of t race and t rigger con tro l
c i rcu i t . The t rigger c i rcui t i s ac t ivated by s ignals o f varie ty o f
shapes and ampli tudes , wh ich are converted to t rigger pulses o f
un ifo rm ampli tude fo r the p rec is ion sweep operat ion .
The t rigger comparato r is used to t rigger the shortest s ignal
jus t by se t t ing p roper t rigger leve l to one inpu t and the s ignal is
app l ied to the ano ther inpu t .
4 . Time base (pane l -p4)
F ig 8 .5 shows the b lock d iagram of t ime base pane l . It i s used
to de lay the s ignal fo r some t ime in the ve rt ical sec t ions . It i s u sed
to generate the saw too th vo l tage requ ired to de flec t the beam i n the
ho rizon tal sec t ion .
27
5 . CRT & Beam con tro l (pane l -p5)
The osc i l loscope is bas ical ly an e lec tron beam vo l tmete r. It i s
more ve rsat i le too l fo r the deve lopment o f e lectron ic ci rcu i ts and
sys tems. The heart o f the osc i l lo scope is the Cathode Ray Tube
which makes the app l ied vo l tage vis ib le by the de flec t ion o f a th in
beam of e lec trons . The e lec tron beam fai th fu l ly fo l lows rap id
variat ions in s ignal vol tage and t races a vis ib le path on the CRT
sc reen .
Since it is e lectron ic in natu re , the osc i lloscope can rep roduce
HF waves which are too fas t fo r e lec tro mechan ical devices to
fo l low.
The e lec tron gun is the source o f e lec trons wh ich fi res
e lec trons s t rikes on the flat wal l o f tube which is chemical ly coated
to fo rm a fluo rescent sc reen generates a spo t on the sc reen . The
con tro l grid in CRT is cyl ind rical , wi th a smal l apertu re in l ine with
the cathode . The e lec trons emit ted from the cathode emerge from
th is apertu re as a s l igh tly d ive rgen t beam. The negat ive b ias vo ltage
is app l ied to grid , contro ls the be am curren t . The in tens i ty o f
phosphorescen t spot depends on the beam curren t . Hence this
con tro l b ias is cal led as in tens i ty.
The d ivergent beam of e lectron is converged and focused on
the sc reen by 2 acce le rat ing anodes , which fo rms an e lec tron ic lens .
The combinat ion o f the fi rs t anode cyl inder and the wider second
anode cyl inder operated at h igher pos it ive po ten t ials p roduces an
e lec tric fie ld that focuses the e lectron beam on the sc reen . The
e lec tron ic lens ac t ion is con tro l by the focus con tro l .
6 . Power supp ly (pane l -p6)
There are two power suppl ies , a –ve High Voltage (HV)
supp ly and a +ve Low Voltage (LV) supp ly. T wo vo ltages are
generated in the CRO. The +ve vo l tage supp ly is from+300 to
400V. The –ve h igh vo l t supp ly is –1000 to –1500 V. Th is vo l tage
i s passed th rough a b leeder res isto r at a few mA.
The in te rmed iate vo ltages are ob tained from the b leeder res is to r
fo r in tens i ty, focus and pos i t ioning con tro ls .
28
Fig. 8 .2 Signal Input Pane l - p1
29
F ig. 8 .3 Beam switch and X -Y amplifie r - p2
30
Fig. 8 .4 T race and T rigger Con tro l -p3
31
Fig. 8 .5 T ime Base Panel - p4
32
Fig. 8 .6 CRT and Beam con tro l -p5
33
Fig. 8 .7 Power Supp ly- p6
34
Fig. 8 .8 Fau lt generat ion t roub le shoo t ing pane l - p7
35
4 . Laboratory Exercise :
T o s tudy al l the b locks o f CRO Demonstrato r ki t .
Conc lus ion:
36
Experiment 9: Digital Multimeter Demonstrator
Date : _______
1 . Aim: To s tudy and perform an experiment on Dig ita l Multimeter
Demonstrator.
2 . Requirements :
Digi tal mult imete r demonstrato r, patch co rds .
3 . Pre -experimenata l Exerc ise :
Brie f-Theory
The heart o f measuremen t o f DMM traine r is a 3 ½ d igi t digi tal panel
mete r (DPM) with a sens i t ivity o f 199.9 mV D.C. The DPM is des igned on
in te rs i l 7107 h igh perfo rmance , low power 3 ½ d igit A/D converte r con tain ing
al l the necessary ac t ive devices on a s ingle CMOS i .e . inc luded in this IC are
seven segmen t decoder, d isp lay d rive rs , re fe rences source and a c lock. This IC
7107 can d irec t ly d rive seven se gmen t d iode (LED) d isp lays . Th is DPM based
on 7107 IC can read D.C. vo l tages from 0 to 199 .9 mV with an accuracy o f 1%.
For measuremen t o f h igher vo l tage , the inpu t vo l tage has to be d ivided by us ing
vo l tage d ivider ne twork.
The four dec imal po in ts co rresp ond ing to fou r LED d isp lays are p rovided on
fron t pane l . The decimal po in ts are to be manual ly se lec ted depend ing upon the
range o f input vo l tage o r cu rren t to be measured .
The DPM works on bu i l t in s tab i l ized vol tage o f 5 V D.C.
4 . Laboratory Exercise :
Any vo l tage which is h igher than 199 .9 m V, we have to use vo ltage
d ivider ne twork.
Fo l lowing FSD ranges are p rovided
a) 200 m V
b ) 2V.
c ) 20 V.
d ) 200 V.
A. Procedure :
1 ) Connec t 199 .9 mV. D.C. to inpu t o f DPM T rainer marked as INPUT 199 .9
V DC. Observe the d isp lay read ing .Reverse the po lari ty o f inpu t supp ly
the d isp lay wil l show same read ing bu t with negat ive po lari ty. Se lec t the
p roper dec imal po in t by short ing common with co rrespond ing DP te rminal
as shown by dashed l ines .
2 ) Now increase the vo l tage more than 200 m V and observe the d isp lay. It
wi l l no t show proper read ing.
37
3 ) Now connec t inpu t to vo l tage d ivider ne twork, se lec t 2V.D.C. range .
Connec t ou tpu t o f vo l tage divider network to inpu t o f DPM. Se lec t
co rrespond ing dec imal poin t . Now you can read Voltages co rrec t ly up to
2V, fo r h igher ranges say 20V and 200 V D.C. se lec t the p roper vo ltage
d ivider range .
D.C.Current Measurement :
The inpu t d .c . cu rren ts are connec ted to a res is tance ne twork. The ou tput
wh ich is in mV is connec ted to inpu t o f DPM. The ne twork can measure cu rren t
fo r 2mA FSD to 200mA in the fo l lowing th ree ranges .
a) 2 mA.
b ) 20 mA.
c ) 200 mA.
Procedure :
1) Connec t 2mA (DC) cu rren t to inpu t o f res is tance network. Connec t ou tpu t
o f ne twork to inpu t o f DPM. Short the co rrespond ing (2mA) te rmina l with
inpu t . Se lec t the p roper DP po in t on d isplay (1 .999mA).
2 ) Change the po lari ty o f input cu rren t obse rve the ( -ve ) ind icat ion on
d isp lay.
3 ) For h igher cu rren ts up to 200mA se lec t the p roper ne twork in the pane l .
Resis tance Measurement:
For resis tance me asuremen t a cons tan t cu rren t o f 10 Micro Amps is passed
th rough unknown res istance . The vol tage deve loped ac ross the res is tance is then
connected to inpu t o f DPM.
Maximum res is tance to be measured = 10 × 10-6
× 20 × 103 .
= 200 mil l i 1 /Ω.
= 20K Ω.
So any res istance up to 20K Ω can be measured .
Procedure :
1) Connec t any unknown res is tance up to 20KΩ. Across the te rminals make R
(dashed) connect ou tpu t te rminal to inpu t o f DPM. Se lec t p roper dec imal
po in t (19 .99KΩ). T he d isp lay wil l d i rectly read res istance in Kilo ohms.
38
AC Voltage Measurement:
The complete c i rcu i t diagram of AC/DC converte r is engraved on fron t
with an inpu t o f 200mV A.C. the ou tpu t wil l be 200mV d .c fo r h igher A.C
vo l tage measuremen t use vo l tage d ivided ne two rk.
Procedure:
1) Connec t the inpu t o f 200 mV (1kHz) to AC/DC converte r. Connect
ou tpu t o f A.C / D.C converte r the DPM. Se lec t the p roper po in t
(199 .9 ).
2 ) For measuremen t o f h igher A.C vo l tage , connect the inpu t to vol tage
d ivider ne twork. The ou tput o f vo l ta ge d ivided ne twork shou ld be
connected to AC/ DC converte r. The ou tpu t o f AC/DC converte r
shou ld be connec ted to inpu t te rminal o f DPM. Use the vo l tage
d ivider ne twork, fo r measuremen t o f h igher A.C. vo l tage .
Conclus ion:
39
Experiment: 10 Function Generator Demonstrator Date: _________
1 . Aim: To study and perform an experiment on the operation o f
function generator us ing IC 8038 .
2 . Requirements:
Func t ion generato r t raine r ki t , CRO, Digi tal Mil l imete r, CRO
p robes .
3 . Pre -Experimenta l Exercise :
Brie f Theory
The func t ion generato r t raine r ki t demonstrated is based on the generato r
IC 8038 . The ICL 8038 wavefo rm generato r is a mono l i th ic in tegrated c i rcu i t
capable o f p roducing h igh accuracy s ine, square , t ria ngular, saw too th and pu lse
wavefo rms with min imum of exte rnal componen ts . The frequency can be
se lec ted exte rnal ly from 0 .001 Hz to more than 300 kHz us ing e ithe r res is to r o f
capac i to rs and frequency modu lat ion and sweep ing can be accomplished with an
exte rnal vo l tage . These devices may be in te rfaced with phase locked loop
c ircu i t ry to reduce temperatu re d ri ft to le ss than 250ppm/°C.
The various ou tpu t o f the generato r can be made avai lab le at the same
t ime . For example , the generato r can p rovide a square wave to tes t the l ineari ty
o f an amplifie r and s imultaneous ly p rovide a saw too th to d rive the ho rizon tal
de flec t ion amplifie r o f the CRO to p rovide a visual d isplay.
40
Figure 10 .1 Block d iagram of func t ion generato r
4 . Laboratory Exercise :
A. Procedure:
1) Connec t the requ ired supp ly and switch ON the un i t . See that the
supp ly ind icato r glows .
2 ) Connec t the CRO at the te rminal marked ou tpu t and observe the
wave fo rm.
3 ) Keep the func t ion switch ON s ine wave and frequency switch on
10Hz and ampli tude contro l po t maximum.
4 ) Vary the fine frequency po t from min imum to maximum and no te
the min imum and maximum frequency and ampli tude .
5 ) Repeat the above p roced ure fo r each frequency range se lec ted .
6 ) Repeat the above p rocedure fo r d i ffe ren t wav efo rms se lected by
the func t ion switch .
7 ) Observe the wavefo rm at va rious stages in the c i rcu i t .
B. Observation:
Draw the observed wavefo rms.
Conclus ion:
Upper
cons t .
Curren t
source
Lower const .
cu rren t
source
Freq
con tro l
N/W
with
exte rnal
con tro l
Res is tanc
e
Diode
shap ing
ckt
Vltg
comparat
o r
m/v
o /p
amp#1
o /p
amp#2
I n t e g r a t o r
C
