SRI SUKHMANI INSTITUTE OF ENGINEERING & TECHNOLOGY DERA
BASSI
DEPARTMENT:
ELECTRONICS & COMM.
LAB: EMI
LABORATORY MANUAL
SUBJECT CODE:
SEMESTER: 4th
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.
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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
1.
2.
3
For Kelvin Double Bridge
Calculated Value
[1 + 0.001x0] x 100 = 100
[0 + 96 x 0.001] x 100 = 9.6
[0.9 + 49 x 0.001] x 100 = 94.9
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From Multimeter
Theoretical Value(Ω)
100.2
10.7
95.4
%
Tolerance
0.199
10.2
0.52
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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SRI SUKHMANI INSTITUTE OF ENGINEERING & TECHNOLOGY DERA
BASSI
DEPARTMENT:
ELECTRONICS & COMM.
LAB: EMI
LABORATORY MANUAL
SUBJECT CODE:
BTEC 407
SEMESTER: 4th
EXPERIMENT NO-2
AIM:-Measurement of Inductance by Maxwell’s Bridge
APPARATUS:1.
2.
3.
4.
5.
P-Three decade resistance dial having value(10x100,10x10,10x1)
R-Single decade resistance dial having value(10x100)
L1-Fixed standard inductance having value 20mH.
L2-Unknown inductance(10 MH)
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
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i.
ii.
Head Phones
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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SRI SUKHMANI INSTITUTE OF ENGINEERING & TECHNOLOGY DERA
BASSI
DEPARTMENT:
ELECTRONICS & COMM.
LAB: EMI
LABORATORY MANUAL
SUBJECT CODE:
BTEC 407
SEMESTER: 4th
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.
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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
2002
2004
2006
2008
200B
200D
200F
2012
2014
2016
2019
201B
201D
2020
3E 80
D3 03
3E FA
D3 00
CD 30 20
3E F6
D3 00
CD 30 20
3E F5
3D 00
CD 30 20
3E F9
D3 00
CD 30 20
C3 04 20
MVI
OUT
START: MVI
OUT
CALL
MVI
OUT
CALL
MVI
OUT
CALL
MVI
OUT
CA
JMP
A,80
initialize all ports as out ports
03
A,FA
00
Output code for step 0.
DELAY
Delay b/w two steps.
A,F6
00
Output code for step 1.
DELAY
Delay between two steps.
A,F5
00
Output code for step 2.
DELAY
Delay b/w two steps.
A,F9
00
Output code for step 3.
DELAY
Delay b/w two steps.
START
Start.
Delay Routine:2030
2033
2036
11 55 55
CD BC 03
C9
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DELAY: LXI
CALL
RET
D,5555
DELAY
Genetate a delay
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
SSIET/ EMI LABORATORY
SRI SUKHMANI INSTITUTE OF ENGINEERING & TECHNOLOGY DERA
BASSI
DEPARTMENT:
ELECTRONICS & COMM.
LAB: EMI
LABORATORY MANUAL
SUBJECT CODE:
BTEC 407
SEMESTER: 4th
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%.
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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
Least step(ohms)
resistance(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
R4
Unknown
(X100)
(X1000)
Resistance
1.
2.
3.
4.
RESULT:-Wheat stone bridge is balanced and value of unknown
measured.
PRECAUTIONS:1) Connections of Unknown resistance should be tight.
2) Wheat stone bridge should be balanced properly.
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resistance is
SRI SUKHMANI INSTITUTE OF ENGINEERING & TECHNOLOGY DERA
BASSI
DEPARTMENT:
ELECTRONICS & COMM.
LAB: EMI
LABORATORY MANUAL
SUBJECT CODE:
BTEC 407
SEMESTER: 4th
EXPERIMENT NO-5
AIM-
To Study Transmitter- Receiver Characteristic of a Synchronic set to use the
set as Control Component.
APPARATUSAc synchronous transmitter-receiver, multimetre, connecting leads.
CIRCUIT DIAGRAM:-
THEROYThe 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
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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 electri cal
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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