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EXPERIMENT NO-1

Aim:- Low Resistance Using Kelvin Double Bridge

We aim to measure the resistance of a given resistor using Kelvin Double Bridge and

determine its tolerance. Kelvin Double Bridge is nothing but a modification of

Wheatstone bridge. It is used for measuring of low resistance to a good precision. It

compares two ratio arms P,Q and p,q and hence is called 'double bridge'.

P, Q, p, q are the resistances in the ratio arms. G is a galvanometer of D'Arsonal type,

used as a null detector. S is a small standard resistor, R is a resistance under

measurement. Usually low resistance consists of four leads. Two of them are called as

voltage leads and remaining as current leads. "r" is the resistance of connecting lead

between R and S.

SRI SUKHMANI INSTITUTE OF ENGINEERING & TECHNOLOGY DERA

BASSI

DEPARTMENT: ELECTRONICS & COMM.

LABORATORY MANUAL

LAB: EMI

SUBJECT CODE:

SEMESTER: 4th

SSIET/ EMI LABORATORY

Under balanced conditions,

From the above equation, it is clear that the resistance of connecting leads "r" has no

effect on the measurement if the two sets of ratio arms have equal ratios ie, P/Q = p/q.

The effect of thermo-electric Emf can be eliminated by making other measurement with

battery terminals reversed and taking the average of the two readings can eliminate the

effect of thermo-electric Emfs.

Procedure for the measurement of low resistance R using Kelvin Double Bridge

1. Move the Galvanometer switch to increase position. This connects the built-in

galvanometer to the circuit. If an external more sensitive galvanometer is

available, connect it to the terminals marked "extgalv" and put the galvanometer

switch in "EXT" position.

2. Four terminals are provided for connecting unknown resistance of the bridge

circuit. They are labeled by "+C, +P, -C, -P". Here +C and -C constitute the

current terminals. If the given unknown resistance is of four leads then connect

the two potential leads to +P & -P and current leads to +C & -C with correct

current polarity. If the unknown resistance has two terminals then the leads from

+C and +P are connected to other terminals of unknown resistance.

3. Now, press the button on the panel and obtain the balance by varying the dials.

4. Under balanced conditions, the sum of two dials multiplied by multiplier sitting

gives the value of unknown resistance.

5. Find the tolerance of the resistance and tabulate the results. The example results

are as given in the tabular form below:

S.No For Kelvin Double Bridge

Calculated Value

From Multimeter

Theoretical Value(Ω)

%

Tolerance

1. [1 + 0.001x0] x 100 = 100 100.2 0.199

2. [0 + 96 x 0.001] x 100 = 9.6 10.7 10.2

3 [0.9 + 49 x 0.001] x 100 = 94.9 95.4 0.52

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Precautions

Press the push button immediately during the course of balance.

A variable high resistance should be connected in series with galvanometer for

initial adjustments in order to protect it from high currents. Once the balance

point is reached, the resistance should be cut-off to increase the sensitivity.

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EXPERIMENT NO-2

AIM:-Measurement of Inductance by Maxwell’s Bridge

APPARATUS:- 1. P-Three decade resistance dial having value(10x100,10x10,10x1)

2. R-Single decade resistance dial having value(10x100)

3. L1-Fixed standard inductance having value 20mH.

4. L2-Unknown inductance(10 MH)

5. R1-Continuously variable resistance 0-100 ohm for impedance matching in d.c

arm.

6. Terminal are provided for external connections to connect unknown inductance,

AC supply and headphone.

THEORY: AC bridge method are of outstanding importance for measurement of electrical

quantities. Measurement of inductance, capacitance, storage factor, loss factor may

be made conveniently and accurately by employing AC bridge network. The AC

bridge is a natural outgrowth of the Wheatstone bridge. An AC bridge, in its basic

form, consists of four arms, a source of excitation, and a balanced detector. The

usefulness of AC bridge circuits is not restricted to the measurement of unknown

impedance and associative parameter like inductance, capacitance, storage factor,

dissipation factor etc. For higher frequency electronic oscillator are universally used

as bridge source supplies. These oscillators have the advantage that the frequency is

constant, easily adjustable, and determinable with accuracy, The waveform is very

close to sine wave, and their power output is sufficient for most bridge

measurement. A typical oscillator has a frequency range of 40Hz-125Hz with a

power output of 7W. The detectors commonly used for AC bridges are

SRI SUKHMANI INSTITUTE OF ENGINEERING & TECHNOLOGY DERA

BASSI

DEPARTMENT: ELECTRONICS & COMM.

LABORATORY MANUAL

LAB: EMI

SUBJECT CODE:

BTEC 407 SEMESTER: 4th

SSIET/ EMI LABORATORY

i. Head Phones

ii. CRO

Head phones are widely used as detectors at frequency of 250Hz and over upto 3 or

4KHz. They are most sensitive detector for this frequency range.

MAXWELL INDUCTANCE BRIDGE:- This bridge is an AC bridge used to measure the inductance. THIs bridge circuit

measures an inductance by comparison with the variable standard self inductance.

At balance:

Z1Z4 = Z2Z3

R3(R2+jwL1) = R4(jwL2)

R2R3+jwL1R = jwR4L2

L1R3 = R4L2

L2=L1(R3/R4) = L1(R/P)

PROCEDURE:- 1. Connect the output of audio frequency function generator across terminals

marked audio oscillator, 1KHz, 20v peak to peak amplitude.

2. Connect the unknown inductance across terminals marked L2 on the front panel.

3. Connect the headphone or CRO across the detector sockets.

4. Adjust the ‘R’ to 100 ohm value.

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5. Switch ON the audio frequency generator and put on headphone. There will be

noise in the Head phone. Or, switch ON the CRO. There will be waveform

equivalent to sine wave.

6. Vary the resistance P to balance the bridge till the noise is reduced to minimum

or complete silence on Head phone or DC line on the CRO.

7. Calculate the value of inductance ‘L’ by using formula

L2=L1R3/R4

8. Adjust ‘R3” to another value and repeat observation.

PRECAUTIONS:-

1. Connections should be tight.

RESULT:- Unknown Induction is calculated with the help of Maxwell bridge

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EXPERIMENT NO-3

AIM:-To study a stepper motor and control its direction speed and number of steps

with help of Microprocessor.

APPARATUS:- Permanent magnet D>C stepping motor two phase bifilar wound

Step angle:1.80 +-5% non-cumulative.

Step/Revolutions:200

THEORY:- The sleeping action is caused by sequential switching of supply to the two phases of the

motor as described in switching diagram. All stepping motor are of bifilar type with six

leads. Watch of the two phases of motor has double winding with a centre tap switching

the supply from one side another of a phase causes reversal of magnetic polar w/o

actually reversing the polarity of supply. For step input sequence give 0.90(half) step

function.

The above switching sequence ill move shaft in one direction. To change

direction of rotation read the sequence upward. The specified torque of any stepping

motor is the torque at stand still (holding torque) . This torque is directly proportional to

the current in the winding. As the switching sequence starts the inductive reactance of

the winding which increases with frequency of switching opposes the rise of current to

desired level within the tie given for one step depending upon the speed of stepping.

This is mainly due to L/R time constant of winding. The drop in current level causes

drop in torque as the speed increases. In order to improve torque at high speed it is

necessary to maintain current. This can be done by following method:

By using a constant current source with w/o a chopper instead of using a constant

voltage source which will give even better performance.

SRI SUKHMANI INSTITUTE OF ENGINEERING & TECHNOLOGY DERA

BASSI

DEPARTMENT: ELECTRONICS & COMM.

LABORATORY MANUAL

LAB: EMI

SUBJECT CODE:

BTEC 407 SEMESTER: 4th

SSIET/ EMI LABORATORY

STARTING AND STOPPING UNDER LOAD:-

There is a limit for every type of stepping motor as regards the speed at which it

will start and stop without loosing step. The limit is due to load torque as well as load

intertie. To overcome this acceleration and declaration techniques have to be employed.

Acceleration means stepping rate on switching should be very low and should increase to

desired level gradually depending on inertia to be encountered. Acceleration/deceleration

may be as high as 1000 to 3000 steps/sec.

SPEED CONTROL OF STEPPER MOTOR:-

The program initializes the 8255(P1) in order to make port. A as output port. The PA0

to PA3 is connected through buffer and driving circuit to the winding of the sleeper motor.

The codes for clockwise movement of stepper motor are FA,F6,F5 and F9. These codes are

to be output in the sequence they are written. The daily routine is called to generate the delay

b/w the steps.

The speed for steps can be varied by changing the content at 2031-2032 and 2037-2038.

These values are taken by register pair DE and a corresponding delay is generated. The

individual delay can be calculated by X basic machine cycle, N#O.

PROCEDURE:-

1. Switch ON 8085 kit.

2. Connect 26 pin FRC cable from 8255-I connector of kit to 26 pin connector of SMC

card at CN1 connector.

3. Connect stepper motor cable to given stepper motor card at CN4 connector.

4. Connect stepper motor power supply connector from external

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supply source at CN2 connector of SMC module.

5. Enter the given program from 2000 address and execute from 2000 address.

6. See the speed of motor as defined delay.

PROGRAM:-

2000 3E 80 MVI A,80 initialize all ports as out ports

2002 D3 03 OUT 03

2004 3E FA START: MVI A,FA

2006 D3 00 OUT 00 Output code for step 0.

2008 CD 30 20 CALL DELAY Delay b/w two steps.

200B 3E F6 MVI A,F6

200D D3 00 OUT 00 Output code for step 1.

200F CD 30 20 CALL DELAY Delay between two steps.

2012 3E F5 MVI A,F5

2014 3D 00 OUT 00 Output code for step 2.

2016 CD 30 20 CALL DELAY Delay b/w two steps.

2019 3E F9 MVI A,F9

201B D3 00 OUT 00 Output code for step 3.

201D CD 30 20 CA DELAY Delay b/w two steps.

2020 C3 04 20 JMP START Start.

Delay Routine:-

2030 11 55 55 DELAY: LXI D,5555 Genetate a delay

2033 CD BC 03 CALL DELAY

2036 C9 RET

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To move the motor in reverse direction, change the contents at the addresses as

mentioned below:

Address Forward Reverse

2005 FA F9

200C F6 F5

2013 F5 F6

201A F9 FA

PRECAUTIONS:-

1. Programming should be error free.

RESULT:-

1. Speed and direction are controlled made as per instructions in programs

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EXPERIMENT NO-4

AIM: Measurement of unknown resistance using wheat stone bridge.

APPARATUS: Wheatstone bridge kit, unknown resistance.

DIAGRAM:-

THEORY: Portable wheat stone bridge has been designed for an accurate

measurement of medium value resistances. This is entirely self contained with a dry

battery 9V and a galvanometer.

Range of measurement: The range of measurement is 0.001 ohms to 11.11 M ohms.

Accuracy: 0.5% to 1%.

SRI SUKHMANI INSTITUTE OF ENGINEERING & TECHNOLOGY DERA

BASSI

DEPARTMENT: ELECTRONICS & COMM.

LABORATORY MANUAL

LAB: EMI

SUBJECT CODE:

BTEC 407 SEMESTER: 4th

SSIET/ EMI LABORATORY

Series arms: Consists of four decades resistance dials having equal steps of 1, 10, 100

and 1000 ohms respectively and can be used as a resistance box ranging from 10 ohm to

10K ohms.

Ratio arm: The ratio can be selected are 0.001, 0.01, 0.1, 1, 10, 100 and 1000.

PROCEDURE:-

1. Connect the unknown resistance to be measured across the terminal marked

unknown.

2. Select a proper multiplication factor from multiply by dial, depending upon the

range of resistance measurement.

3. Set the direct / shunted switch to shunted position and press both the press key and

adjust the four decade resistance dials until the galvanometer pointer reads zero and

then set the direct / shunted switch to direct/ shunted position and adjust the dials for

final balance point.

4. Note the readings of the four decade dials and the multiplier dial. Then the unknown

resistance can be calculated as follows:

Ratio(multiply by) Total

resistance(ohms)

Least step(ohms)

0.001 0-11.110 0.001

0.01 0-111.1 0.01

0.1 0 -1111 0.1

1 0 -11110 1

10 0 - 111100 10

100 0 - 1111000 100

1000 0 - 11.11M 1000

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Unknown resistance = decade resistance reading * dial readings.

OBSERVATION AND CALCULATION:-

S.NO. R1

(X1)

R2

(X10)

R3

(X100)

R4

(X1000)

Unknown

Resistance

1.

2.

3.

4.

RESULT:-Wheat stone bridge is balanced and value of unknown resistance is

measured.

PRECAUTIONS:-

1) Connections of Unknown resistance should be tight.

2) Wheat stone bridge should be balanced properly.

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EXPERIMENT NO-5

AIM- To Study Transmitter- Receiver Characteristic of a Synchronic set to use the

set as Control Component.

APPARATUS- Ac synchronous transmitter-receiver, multimetre, connecting leads.

CIRCUIT DIAGRAM:-

THEROY-

The rotor of synchro transmitter is a silent pole clumbill shaked of the transmitter

voltage is applied through ship rings and brushes mounted on the rotor. The rotor

has three secondary coils namely s1, s2, s3 wound on its skewed slots distributed

around its periphery 120 apart. One end of each s1, s2, s3 is slotted to make star

connection is not brought act as fig. Despite the fact that winding are shown 120

apart fact that resembling achromatic diagram of a three phase machine , only single

SRI SUKHMANI INSTITUTE OF ENGINEERING & TECHNOLOGY DERA

BASSI

DEPARTMENT: ELECTRONICS & COMM.

LABORATORY MANUAL

LAB: EMI

SUBJECT CODE:

BTEC 407 SEMESTER: 4th

SSIET/ EMI LABORATORY

phase voltage appears across any of these winding . The flux lines each of these

coils depending upon angular position of the rotor. In the position shown in the fig.

That main voltage appears across coil s2 and neutral and s1 to neutral. If the shift

the transmitter is rotated the voltage from s2 to natural decreases and is zero when is

at 90 degree from the origin position the magnitude of s1 to N and s2 to N voltage

across also vary as the cosine of rotor. The neutral is not brought out, therefore only

voltage can be measure are the voltage appearing across s1, s2, s3 at the electrical

zero v3 become maximum at 90 degree at this position. Since for small angles sin is

equal to the angle itself.

SYNCHRO AS TORQUE TRANSMITTER:-

In instrumentation system synchros are normally used in the torque transmission

mode. In this mode, the synchros transmitter and receiver are connected. Initially

winding s2 of the stator of transmitter is positioned for maximum coupled with rotor

winding suppose its voltage is V. The coupling between s1 and s2 of the stator and

primary winding are proportional to cos60 degree or they are v/2 each so as long as

the rotor of the transmitter and receiver remains in this position, no current flow

between the winding because of voltage balance when the rotor of the transmitter is

moved through to a new position the voltage balance is distributed. Assume that the

transmitter is moved through 30 degree. The stator winding voltage of the

transmitter will be changes to 0, √3 ∕2V. This there is voltage balance between the

winding producing a torque that tends to rotor of the receiver to position where the

voltage balance is again restored.

PROCEDURE:-

1. Connect patch card to s1 of the transmitter to s1 of receiver, s2 of transmitter

to s2 of the receiver and s2 of transmitter to s3 of receiver.

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2. Connect R1 of both transmitter and receiver to R1 of power I/P R1 and R2 of

both transmitter to receiver to R1 of power.

3. Connect power supply to kit 230V, 1 phase AC.

4. Now voltage of transmitter between s1s2, s2s3, s3s1 of receiver between s1s2,

s2s3, s3s1.

5. Repeat each two steps for various position of transmitter positional in step of

30.i.e.30, 60, 90.

PRECAUTION:-

1. Connection should be tight.

2. Reading should be taken carefully.

RESULT:-

We studied transmitter receiver characteristic synchro as a control component.

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EXPERIMENT NO-6

AIM: Study characteristics of Light transducer like Photovoltaic cell,

Phototransistor and Pin Photodiode with implementation of small project using signal conditioning circuit. APPARATUS REQUIRED: Light Trainer Kit, Connecting Leads, Multimeter

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