SRI SUKHMANI INSTITUTE OF ENGINEERING & TECHNOLOGY DERA BASSI DEPARTMENT: ELECTRONICS & COMM. LABORATORY MANUAL LAB: EMI SUBJECT CODE: SEMESTER: 4th

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1 SRI SUKHMANI INSTITUTE OF ENGINEERING & TECHNOLOGY DERA BASSI DEPARTMENT: ELECTRONICS & COMM. LABORATORY MANUAL LAB: EMI 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.

2 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. [ x0] x 100 = [ x 0.001] x 100 = [ x 0.001] x 100 =

3 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.

4 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. 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 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

5 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: Z 1 Z 4 = Z 2 Z 3 L 1 R 3 = R 4 L 2 R 3 (R 2 +jwl 1 ) = R 4 (jwl 2 ) R 2 R 3 +jwl 1 R = jwr 4 L 2 L 2 =L 1 (R 3 /R 4 ) = L 1 (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 L 2 on the front panel. 3. Connect the headphone or CRO across the detector sockets. 4. Adjust the R to 100 ohm value.

6 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 L 2 =L 1 R 3 /R 4 8. Adjust R 3 to another value and repeat observation. PRECAUTIONS:- 1. Connections should be tight. RESULT:- Unknown Induction is calculated with the help of Maxwell bridge

7 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: % 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.

8 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 and 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

9 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: E 80 MVI A,80 initialize all ports as out ports 2002 D3 03 OUT E FA START: MVI A,FA 2006 D3 00 OUT 00 Output code for step CD CALL DELAY Delay b/w two steps. 200B 3E F6 MVI A,F6 200D D3 00 OUT 00 Output code for step F CD CALL DELAY Delay between two steps E F5 MVI A,F D 00 OUT 00 Output code for step CD CALL DELAY Delay b/w two steps E F9 MVI A,F9 201B D3 00 OUT 00 Output code for step D CD CA DELAY Delay b/w two steps C JMP START Start. Delay Routine: DELAY: LXI D,5555 Genetate a delay 2033 CD BC 03 CALL DELAY 2036 C9 RET

10 To move the motor in reverse direction, change the contents at the addresses as mentioned below: Address Forward Reverse 2005 FA F9 200C F6 F 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

11 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 ohms to M ohms. Accuracy: 0.5% to 1%.

12 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 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) M 1000

13 Unknown resistance = decade resistance reading * dial readings. OBSERVATION AND CALCULATION:- S.NO. R 1 R 2 R 3 R 4 Unknown (X1) (X10) (X100) (X1000) Resistance 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.

14 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. 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

15 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.

16 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.

17 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

Electronic Measurements & Instrumentation. 1. Draw the Maxwell s Bridge Circuit and derives the expression for the unknown element at balance?

Electronic Measurements & Instrumentation. 1. Draw the Maxwell s Bridge Circuit and derives the expression for the unknown element at balance? UNIT -6 1. Draw the Maxwell s Bridge Circuit and derives the expression for the unknown element at balance? Ans: Maxwell's bridge, shown in Fig. 1.1, measures an unknown inductance in of standard arm offers