ANAND INSTITUTE OF HIGHER TECHNOLOGYKAZHIPATTUR

Department of Electronics & Instrumentation Engineering

Staff Name: R.Umashankari,M.Surya Year/Sem : II / IIISub/ Code : Electrical Measurements/EI2202

PART A

Unit I - Measurement of voltage and Current

1. Explain why the PMMC instruments are not used to measure alternating quantities (EI Nov 10)Torque reverses if the current reverses. If the instrument is connected to A.C, the

pointer cannot follow the rapid reversals and the deflection corresponds to mean torque, which is zero. Hence these instruments cannot be used for A.C.2. What is known as shunt? (EI Nov 10)

Coil winding of a basic movement is small and light can carry very small currents since the construction of an accurate instrument with a moving coil to carry currents greater than 100ma is impracticable owing to the bulk and weight of the coil that would be required. When heavy currents are to be measured, the major part of the coil is bypassed through a low resistance called a shunt

3. Bring out the differences between moving coil and moving iron instruments. (EC Nov ’07, EI May ’07, EI may ‘11) Sl.No Moving Coil Moving Iron1. Can be operated only in dc Can be used for both ac and dc

circuits.2. Scale is uniform Scale is non-uniform3. Cost is higher than MI instruments Cheap4. Torque is directly proportional to the current Torque is directly proportional

to the square current

4. Write two applications of PMMC Instruments (EI Nov ’09)

Measurement of dc voltage and currentUsed in dc galvanometer.

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5. What is the basic principle of PMMC instrument (EI May ’06)

The interaction between the induced field and the field produced by the permanent magnet causes a deflecting torque, which results in rotation of the coil. The deflecting torque produced is described below in mathematical form:

Deflecting Torque: If the coil is carrying a current of, the force on a coil side = BildN (newton, N).

Td = GI; G = NB ld

Controlling Torque: The value of control torque depends on the mechanical design of the control device. For spiral springs and strip suspensions, the controlling torque is directly proportional to the angle of deflection of the coil.

..,ie Control torque Tc=Kθ

where, θ = deflection angle in radians and = spring constant K.

Damping Torque: damping torque is produced by movement of aluminium former moving on the magnetic field of permanent magnet.

6. What does systematic errors of instrument mean? (EI May ’06)

These types of errors are divided into three categories such as Instrumental errors, environmental errors and observational errors. Instrumental errors occur due to three main reasons due to inherent shortcomings of the instrument, due to misuse of instruments and due to loading effects of the instruments. Environmental errors are due to conditions external to the measuring device including conditions in the area surrounding the instrument. Observational errors occur due to parallax errors.

7. What is the importance of static characteristics of systems? (EE May ’08)Static characteristics of an instrument are those that must be considered when the

system is used to a condition not vary with time or vary only quite slowly.

8. What is meant by accuracy of an instrument? (EE May ’08)Accuracy means the degree of closeness of measured value to the true value. Thus

accuracy means approaching or confirming truth.

9. Compare and contrast moving iron and electrodynamometer type meters. (EI May ’06)

Sl.No Moving iron Electrodynamometer type 1 The torque is proportional to the

square of current. The torque proportional to the square of voltage.

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2 Hysteresis and Eddy Current losses are present

Free from Hysteresis and Eddy Current losses

3 Cheap Expensive compared to Moving Iron Instruments

4. High Torque/Weight ratio Low Torque/Weight ratio

10. List the errors that occur in induction type instrument (EI Nov ’09)

The errors that occur are incorrect magnitude of fluxes, incorrect phase angles and lack of symmetry in the magnetic circuit.

11. Why the MI meter has non uniform scale? (EI May ’08)

The deflection in a Moving Iron instrument is given by

θ = ½. I2/K. dL/dθThus the angular deflection is proportional to the square of operating current and the instrument has a square law response. The deflection is in terms of RMS values of current or voltage. As the deflection is proportional to the square of operating current, the scale is non-uniform.

12. What is Residual Error? (EI May ’08)

These errors are due to multitude of small factors which change or fluctuate from one measurement to another and are due surely to chance. The quantity being measured is affected by many happenings throughout the universe. The happenings or disturbances about which we are unaware are lumped together and are called Random or Residual. Hence the errors caused by these happenings are called Random or Residual Errors.

13. Define standards (EC Nov ’07)

A standard is a physical representation of unit of measurement. The term “standard” is applied to a piece of equipment having a known measure of physical quantity. They are used for the purposes of obtaining the values of physical properties of other equipments by comparison methods.

14. Define Voltage sensitivity in a galvanometer (EI May ’07)

Voltage sensitivity is the deflection in scale divisions per unit voltage impressed on the galvanometer.

Voltage sensitivity Sv = scale division per unit voltage = d/(i.Rg.106) scale division/µV.

For a galvanometer with scale 1m away scale division of 1 mm,

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Sv = 2000 G/(K. Rg.500) mm/ µV.

15. Bring out the differences between moving coil and moving iron instruments. (EC Nov ’07, EI May ‘07)

Sl.No Moving Coil Moving Iron1. Can be operated only in dc Can be used for both ac

and dc circuits.2. Scale is uniform Scale is non-uniform3. Cost is higher than MI instruments Cheap

16. Define Ballistic sensitivity. (EC Nov ’07)

Ballistic sensitivity is the deflection in scale divisions per unit voltage impressed on the galvanometer.

Ballistic sensitivity Sv = scale division per unit voltage = d/(i.Rg.106) scale division/µV.

For a galvanometer with scale 1m away scale division of 1 mm, Sv = 2000 G/(K. Rg.500) mm/ µV.

17. State the advantages and disadvantages of rectifier type instruments(EI Nov ’07).

Advantages:

a. The frequency range extends from about 20Hz to high audio frequencies.b. Lower operating current for voltmeters.c. Uniform scale for most of the rangesd. Accuracy is about ± 5٪ under normal operating conditions.

Disadvantages

a. Sensitivity is lessb. Loading Effects are high

18. Where does a rectifier type instrument find application? (EI Nov ’06)

Rectifier type instruments finds application in communication circuits and all other light current work circuits, medium sensitivity service type voltage measurements in medium impedance circuits.

19. What is the major advantage of induction type instrument? (EI Nov ’06)

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The major advantages are low friction and higher torque/weight ratio. Induction type meters are inexpensive, accurate and retain their accuracy over a wide range of loads and temperature conditions.

20. Why calibration of instrument is important? (EE May ’08)

The calibration of all instruments is important since it affords the opportunity to check the instrument against a known standard and subsequently to errors in accuracy.

21. Explain the function of measurement system. (nov /dec 2012)

The measurement system consists of a transducing element which converts the quantity to be measured in an analogous form. The analogous signal is then processed by some intermediate means and is then fed to the end device which presents the results of the measurement.22. What are the advantages of moving ion instrument? (nov/dec 2012)

1) Universal use: These instruments can be used for both ac and dc. Although moving ion instruments are responsive to dc. The hysteresis effect causes an appreciable error in measurement.

2) Robustness: The instruments are robust owing to simple construction and also that there are no current carrying moving part.

3) Errors: The instruments are subjected to serious errors due to hysteresis, frequency change and stray magnetic field.

23. Mention the two types of junction capacitances. (april 2013)1). Conduction 2) Diffusion

24. Define thermal runaway. (april 2013) The collector current Ic causes the collector base junction temperature to rise which in turn increase Ic. As a result Ic will increase further , which will further rise the temperature at collector base junction. This process will become cumulative leading to thermal runaway.25. what are the essential features of indicating instruments?(Nov/Dec 2013)a) Device for deflecting the pointer over the scale,b)Device for controlling the movements of the pointer, andc)Device to ensure that the pointer comes to rest quickly at its correct reading positions without excessive oscillation and in short time.26. Give any two advantage and disadvantage of thermal type

instruments?(Nov/Dec2013)Advantage:1)The thermocouple type of instruments accurately indicates the root mean square value of current and voltages irrespective of the waveform. There is a wide varieties of range of thermocouple instruments are available in the market.2) Thermocouple type of instruments give very accurate reading even at high frequency, thus these types of instruments are completely free from frequency errors.

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Disadvantage:Instead of many advantages these type of instruments posses one disadvantage,The over load capacity of thermocouple type of instrument is small, even fuse is not able to the heater wire because heater wire may burn out before the fuse blows out.

Unit II Measurement of Power and Energy

1. Write the advantages of induction type kWh meter. (EI may’11)i)Simple in operationii)High torque/weight ratioiii)Cheap in costiv)Correct registration even at very low power factor

v)Unaffected by temperature variations

2. Why the ordinary wattmeter’s are not suitable for low power factor circuits (EI Nov 10)

a) Deflecting torque on the moving system is small even when the current coil and pressure coils are fully excited;

b) Errors introduced because of inductance of pressure coils tend to be large at low power factor

3. Write down the advantages of electrodynamometer type wattmeter. (EI Nov ’09)

a. As the coil is aircored, these instruments are free from hysteresis and eddy current errors.

b. Precision grade accuracy for frequencies upto 40 to 500 Hz.c. Can be used for both a.c and d.c circuits.d. Provides accurate measurement of rms values of voltage, irrespective of

waveforms.

4. What is the use of brake magnet in an energy meter (EI Nov ’09)

A permanent magnet positioned near the edge of the aluminium disc forms the braking system. The aluminium disc moves on the field of this magnet and thus provides a braking torque. The position of permanent magnet is adjustable and thus

5. Two wattmeters are connected to measure the input of a balance 3 phase circuit, indicates 1000 W(+ve) and 125W (+ve) respectively. Find the powerfactor of the circuit. (EI May ’08)

tanΦ=√3[(P1-P2)/(P1+P2)]

Φ=53.41

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cos Φ = 0.59 –Power factor

6. What is the need for light load compensation in Watthour meter ? (EI May ’08)

Despite every care taken in the design of both the jeweled-pivot bearing, which forms the lower bearing of the spindle, and of the simple sleeve pin-type bearing at the top of the spindle, friction errors are liable to be serious particularly at light loads. In order to ensure accurate registration at low loads, it is therefore necessary to arrange for small torque, practically independent of the load on the meter, which acts in the direction of rotation and which is nearly as possible equal in magnitude to the friction torque.

7. What are the functions of lag adjustment incorporated in the construction of single phase induction type kWH meter ? (EI May ’06)

By providing the below arrangements, shunt magnet flux is brought in quadrature with the applied voltage.

The lag device is adjusted till the motor runs at correct speed. A few turns of thick

wire are placed around the central limb of the shunt magnet and the circuit is closed through a low adjustable resistance. The resistance of the circuit is altered to adjust the lag angles of flux.

Copper shading bands are placed around the central limb of the shunt magnet instead of a lag coil with adjustable resistance. As the shading bands move up they embrace more flux. This results in greater value of induced emf, current and mmf and lag angle increases.

8. An induction type energy meter runs fast. How the speed can be reduced ? (EI May ’07)

The speed of the induction type energy meter can be slowed down by adjusting the position of braking magnet and making it move away from the centre of the disc.

9. List out the special features incorporated in an electrodynamometer type of wattmeter, for low power factor applications. (EI May ’07)

The pressure coil is connected across the rated supply voltage and rated full load current is passed through the current coil at 0.5 pf lagging. The lag device is adjusted till the motor runs at correct speed.

10. List the various types of registering mechanism used in single phase energy meter. (EI Nov ’07)

The various types of registering mechanism are

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Pointer type Register Cyclometer type Register

11. Derive the average deflecting torque equation for electrodynamometer type wattmeter. (EI Nov ’07)

Td=VI cosɸ/Rp* dM/dƟ

12. What is the use of copper shading bands in induction type wattmeter? (EI Nov ’06)

Copper shading bands are provided on the central limb. The position of these bands is adjustable. The function of these bands is to bring the flux produced by the shunt magnet exactly in quadrature with the applied voltage.

13. Write down the deflecting torque equation in dynamometer type wattmeter.

Td α VI CosΦ

14. What are the types of energy meters?

Electrolytic meters Motor meters. Clock meters

15. What is Ampere hour and watt hour? (EE May ’08). Ampere hour

A current flow for one hour measured in amperes (amps). Abbreviated "Ah" and commonly called "amp-hour," it is widely used to rate how long it takes for a battery to discharge. For smaller batteries, a milliampere-hour (mAh) rating is used. For example, a 500 mAh battery means it will release 500 milliamps of current at a specific voltage for one hour before it is discharged.

watt hour: A measure of electrical energy equivalent to a power consumption of one watt for one hour.

16. Define Phantom loading. (EI Nov ’06)

Method by which energizing the pressure coil circuit and current coil circuits separately is called phantom loading.\

17. Name the errors caused in Dynamometer type wattmeter. (EI May ’06)

Error due to pressure coil inductance Error due to pressure coil capacitance Error due to methods of connection

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Error due to stray magnetic fields Error due to eddy current.

18. What is creeping? How it is prevented? (nov/dec 2012) In some meters a slow but some continuous rotation in obtained even when there is no current flowing through the current coil and only pressure coil is energized. This is called creeping.

Prevention: Two diametrically opposite holes are drilled in the disc. The disc will come to rest with one of the hole under the edge of the pole of shunt magnet.

19. What is pressure coil? (nov/dec 2012)

20. Draw one biasing circuit for an enhancement type MOSFET. (april 2013)

21. Give the symbol for SCR, DIAC and TRIAC. (april 2013)

Unit III Potentiometer and Instrument Transformers

1. What is the necessary precaution to be taken in C.T? (EI Nov 10)

2. What is the basic principle used in potentiometer.

A potentiometer is an instrument designed to measure an unknown voltage by comparing it with a known voltage. The known voltage may be supplied by a standard cell or any other known voltage (reference source). Measurement using comparison methods are capable of high degree of accuracy because the result obtained does not depend on the actual deflection of pointer but only upon the accuracy with which the voltage of reference source is known.

3. What are the applications of DC potentiometer? (EI May ’08)

1. Calibration of Voltmeter2. Calibration of Ammeter3. Calibration of Wattmeter4. Measurement of resistance5. Measurement of Power

4. Define Nominal ratio for CT and Turns ratio for PT. (EI May ’08)

Nominal Ratio of the CT is the ratio of rated primary winding current to the rated secondary winding current. Turns ratio of PT is ratio of Number of turns of primary winding to the Number of turns of secondary winding.

5. Draw a phasor diagram of Current Transformer. (EI May ’07)

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6. How the true zero is obtained in a Crompton’s Potentiometer. (EI May ’07)

In the student type potentiometers it is impossible to obtain true zero because the two contacts cannot coincide absolutely. This drawback is eliminated in the simplified circuit. The slide wire BC is provided with a shunt resistor which is tapped to D. This tapping is made zero on the main dial. When the contact is in a position such that r1/r3 = r2/r4 that zero. The slider can travel a little lower that zero position giving a small negative reading. The movement of slider above zero gives positive reading. The range of slide is usually from -0.005 V to +.105 V.

7. Why series type ohmmeter preferred over shunt type ohmmeter? (EI Nov ’07)The battery is in series with an adjustable resistance R1 and the D'Arsonval movement. The

unknown resistance is connected across terminals A andB in parallel with the meter. An on–off switch is to be provided to disconnect the battery from the circuit when not being used. If Rx = 0, the meter current is zero. If Rx = 8, the current finds a path only through the meter. The meter can be made to read full scale by adjusting R. Thus, the meter deflection is proportional to the value of the unknown resistance Rx.This meter is more suitable for measuring low values of resistances, upto 100 kO. This instrument is used in laboratories.

8. Comment on the effect of change of input frequency on the characteristics of a current transformer.(Nov/Dec 2013)

The effect of increase in frequency will result in a proportionate decrease in flux density. Thus, In general the effect of increase in frequency is similar to that produced by decrease in impedance of secondary winding burden.

9. Show the connections of electrodynamometer type instrument when used to measure (a) Voltage (b) Power (EI May ’06)

10. How does DC potentiometer differ from AC potentiometer in working principle? (EI May ’06)

DC potentiometer is accurate and versatile

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11. Mention any two applications of CT. (EI May ’06)

Measurement of current Measurement of Power Over current and under current protection circuits. High Current or High Voltage monitoring circuits.

12. What are the limitations of Gall Tinsley type AC potentiometer? (EI May ’06)

Errors may occur due to slight differences in reading of the reflecting dynamometer instrument on ac as compared with the reading on dc, Inaccuracy of the method of measuring the frequency, the inter-capacitance, earth capacitance and mutual capacitance effects are present in the slide wire coils and the existence of harmonics in the supply waveform.

13. Write down the principle of operation of megger. (EI May ’06)

There are two voltage coils V1 and V2. V1 coil is in a weak magnetic field when the pointer is at α (infinity) position and hence this coil can exert a very little torque. The torque exerted by the voltage coil increases as it moves into a stronger field and this torque is maximum when it is under the pole face and under this condition pointer is at its zero end of the resistance scale. In order to modify the torque in the voltage circuit, another coil V2 is used. This coil is also so located that it moves into stronger field as the pointer moves from α (infinity) position towards the zero position of the scale. The combined action of the two voltage coils V1 and V2 may be considered as though the coils constituted a spring of variable stiffness.

14. What is the basic difference between AC and DC potentiometers? (EI Nov ’06)

The basic difference between AC and DC potentiometers is that, whereas in a DC potentiometer only the magnitudes of unknown emf and potentiometer voltage drop have to be made equal to obtain balance, in the ac instrument both magnitudes and phase has to be made equal to obtain balance.

15. How the phase angle is measured in polar type potentiometers. (EI May ’07)

It is measured from the position of phase shifter.

16. Define standardization of a potentiometer. (EI Nov ’09)

It is the process by which adjusting the current flows through the potentiometer coil to make the voltage across the standard cell is equal.

17. Define ratio error.(EI Nov ’07)

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The ratio of energy component current and secondary current is known as the ratio error.

18. How the phase angle error is created. (EI Nov’09)

It is mainly due to magnetizing component of excitation current.

19. How the CT and PT are connected in the circuits.(Nov/Dec 2013)

CT is connected in series and PT is connected in parallel

20. State the applications of potentiometer. (EI May ’08)

Used for measurement of unknown emf Used for ammeter calibration Used for Voltmeter calibration Used for wattmeter calibration

21. How true zero is obtained in a Crompton’s potentiometer? (nov/dec 2012) In student type potentiometer, it is impossible to obtain true zero, because the two contacts cannot coincide absolutely. This drawback is eliminated in the simplified manner. The slide wire is provided with shunt resistor tapped at D. This tapping is made zero on the main dial. When the contact is in a position such r1/r3=r2/r4=0. The slide can travel a little lower than zero position giving a small negative reading. The movement of slider above zero gives a little positive reading. The range of slide wire is -0.005v to +0.105v.

22. What is volt – ratio box? (nov/dec 2012) General purpose potentiometers cover a maximum voltage range of approximately 0-1.6v in case of American instrument and 0-1.8v in case of British instruments. If higher voltage range have to be measured a precision potential divider called a volt – ratio box is used.

23. How are amplifiers classified based on biasing condition? (april 2013)1) Class A2) Class B3) Class C

24. What is crossover distortion? How it can be minimized? (april 2013) This is caused by non-linearity of the input characteristic of the transistors. Transistors do not turn ON at zero volt applied to the emitter junction but only when the emitter junction is forward biased by the cut in voltage Vr=0.3v for germanium and 0.7 for silicon.

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The sinusoidal base voltage excitation will not result in a sinusoidal o/p current. In the regions of small input currents the o/p is much smaller than it would be if the response were linear. This effect is called crossover distortion. To minimize: The transistors must operate in Class AB mode where a small standby flows at zero excitation.

Unit IV Resistance Measurement

1. What are the depending factors for any earthing system? (Apr 11)1. Shape of the electrodes2. Depth in the soil in which electodes buried into the soil3. Specific resistance of the soil surrounding and in the neighborhood of

electrodes2. Define Bridge Sensitivity. (Apr 11)

Deflections of the the galvanometer per unit fractional changes in unknown resistance.

3. Classify the resistance from the point opf view of measurements (EI Nov 10) Low resistance - Order of 1Ω Medium resistance -1 Ω to 0.1 M Ω High resistance - Order of 0.1M and upwards

4. What are the different difficulties encountered in the measurements of high resistances (EI Nov 10)

a) Insulation resistance of the resistor may be comparable to the actual value, due to that leakage currents are produced,

b) Due to electrostatic effect stray changes can appear in the measuring circuit causing errors

c) charging and absorbing currents take a considerably long time to decayd) change in the atmospheric temperature affect the resistance values

5. Why is a guard ring provided in a megger ? (EI Nov’09) The guard ring intercepts leakage current. Any leakage currents intercepted are shunted to the negative side of the generator. They do not flow through coil a; therefore, they do not affect the meter reading.

6. Define the terms low resistance and high resistance. (EI May ’08) All resistances of the order of 1 ohm and under may be classified as low resistance. Resistances of the order of 0.1M ohm and upwards are classified as high resistances.

7. What is the need of battery in ohmmeters? (EI May ’08)An ohmmeter is an electrical instrument that measures electrical resistance, the opposition to an electric current. Micro-ohmmeters (microhmmeter or microohmmeter) make low resistance measurements. Megohmmeters large values of resistance. The unit of measurement for resistance is ohms (Ω).

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8. List out the factors which affect the precision measurement of medium resistance with whetstone’s bridge (EI Nov ’07)

Resistance of connecting leads Thermoelectric effects Temperature effects Contact resistance

9. Low resistances are provided with four terminals. Why? (EI May ’07)

Special types of construction and techniques have to be used for the measurement of low resistances in order to avoid serious errors occurring due to resistances of leads and contacts. These resistances though small are appreciable in comparison to low resistances.

Low resistances are constructed with four terminals. One pair of terminals called current terminals is used to lead the current IR to and from the resistor. The voltage drop V is measured between other two terminals called the potential terminals. The voltage V is thus IR times the resistance R between potential terminals and does not include any contact resistance drop at the current terminals.

10. What are the possible errors introduced in the low resistance measurement using Kelvin’s bridge. (EI May ’06)

Errors are introduced in case the ratios are not exactly equal thermoelectric emfs.

11. Name the methods used for low resistance measurement. (EI Nov’09)

Ammeter – voltmeter method Potentiometer method Kelvin double bridge method Ohm meter method.

12. Where high resistance m/s is required?(Nov/Dec2013)

Insulation resistance of cables High resistance circuit elements Volume resistivity of a material Surface resistivity.

13. How resistance is measured in loss of charge method. (EI Nov’06) In this method a capacitor is charged and discharged for a specific time period and from this resistance is measured.

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14. Draw the circuit of Kelvin Double bridge? (nov/dec 2012)

15. Classify the resistance from the point of view of measurements. (nov/dec 2012)Electrical resistivity is an intrinsic property that quantifies how strongly a given material opposes the flow of electric current. A low resistivity indicates a material that readily allows the movement of electric charge. Resistivity is commonly represented by the Greek letter ρ (rho). The SI unit of electrical resistivity is the ohm⋅metre (Ω⋅m)[1][2][3] although other units like ohm⋅centimetre (Ω⋅cm) are also in use. As an example, if a 1 m × 1 m × 1 msolid cube of material has sheet contacts on two opposite faces, and the resistance between these contacts is 1 Ω, then the resistivity of the material is 1 Ω⋅m.

16. What type of feedback is used in emitter follower circuit? (april 2013) The feedback used in emitter follower is voltage series feedback circuit.

17. A Wein bridge oscillator has a frequency of 500 kHz. If the value of C is 1000pF, determine the value of R. f=1/2π RC R=1/2π fC= 1/ 2π *500* 103 *1000*10-12

=318.47Ω

Unit V- Impedance Measurement

1. Mention sources and detectors used for AC bridge (Apr 11)sourcesFor Low frequency, power line For High frequency, electronic oscillators DetectorsVibration galvanometerHead phones

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Tuneable Amplifiers

2. List the two advantages of Anderson ‘s bridge (EI Nov 10)a) easier to obtain balance in the case of Anderson ‘s bridge than in maxwell’s

bridge for low q-coilsb) Fixed capacitor can be used instead of a variable capacitor as in the case of

maxwells brigbec) Used for accurate determination of capacitances in terms of inducance

3. Explain the term “tuning” in a vibration galvanometer (EI Nov 10)Adjustment of the natural frequency of the moving system os that it is equal to the frequency of the current passing through the coil.

4. Why it is preferable in bridge circuits to have balance equations independent of frequency? (EI May ’07)

It is preferable in bridge circuits to have balance equations independent of frequency as the exact value of source frequency need not be known. Also if a bridge is balanced for fundamental frequency it should also be balanced for any harmonic and the waveform need not be purely sinusoidal.5. Give the general equation for balance of a. c. bridges.

E1=E2

I1.Z1 = I2. Z2

Z1.Z4 = Z2.Z3

6. Why it is preferable in bridge circuits to have balance equations independent of frequency? (EI May ’07)

It is preferable in bridge circuits to have balance equations independent of frequency as the exact value of source frequency need not be known. Also if a bridge is balanced for fundamental frequency it should also be balanced for any harmonic and the waveform need not be purely sinusoidal.

7. List the disadvantages of Anderson Bridge. (EI May ’07)

a. Anderson’s Bridge is more complex than its prototype Maxwell’s Bridge. The balance equations are not simple and in fact are very much tedious.

An additional junction point increases the difficulty of shielding the bridge.

8. Name any two compensation methods used in AC bridges. (EI May ’06)

Resistance Measuring BridgesCapacitance Measuring Bridges

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9. Give the general equation for balance of a. c. bridges.

E1=E2

I1.Z1 = I2. Z2

Z1.Z4 = Z2.Z3

10. What is the use of Schering Bridge? (EI Nov ’06)

Measurement of relative permittivity Measurement of Mutual Inductance and Self Inductance

11. Sketch the circuit diagram of Kelvin’s double bridge for measurement of low resistance. (EI Nov ’06)

12. Name the bridge circuits used for the measurement of mutual inductance. Write down its relevant equation. (EI May ’08)

The Heaviside Campbell bridge, The Campbell bridge.

13. Which type of detector is used in ac bridges? (EI Nov’09)

Headphones, Vibration galvanometers and Tuneable Amplifier detectors are used.

14. Name the sources of errors in ac bridge measurement. (EI Nov ’07)

Errors due to stray magnetic fields, Leakage errors, Eddy current errors, Residual errors, Frequency and waveform errors.

15. State the advantages and disadvantage of Maxwell-wein Bridge.(Nov/Dec 2013)

The balance equation is independent of frequency and therefore more accurate.This method needs a standard variable capacitor. Variable Capacitor is costliest.

16. Define Q-factor of the coil. (EI May ‘08)

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It is the ratio between power stored in the coil to the power dissipated in the coil.

17. A Maxwell bridge is having bridge constants at balance as C1=0.01 uF, R1=470 K, R2=5.1 K, R3=100 K. find the series equivalent of unknown impedance.

(EE May ’07)

18. What two conditions must be satisfied to make an a.c. bridge balance? (nov/dec 2012)

i)As we saw with DC measurement circuits, the circuit configuration known as a bridge can be a very useful way to measure unknown values of resistance. This is true with AC as well, and we can apply the very same principle to the accurate measurement of unknown impedances.ii)To review, the bridge circuit works as a pair of two-component voltage dividers connected across the same source voltage, with a null-detector meter movement connected between them to indicate a condition of “balance” at zero volts.

19. Define the term null as it applies to bridge measurement. (nov/dec 2012)A Wheatstone bridge is an electrical circuit used to measure an unknown electrical resistance by balancing two legs of a bridge circuit, one leg of which includes the unknown component

20. Draw the circuit of Schmitt Trigger. (april 2013)

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PART B

Unit I - Measurement of voltage and Current

1. Give the construction and principle of operation of a moving coil ammeter. List their advantages and disadvantages. Explain how measuring range is increased in ammeters. (EI May ’06)

2. (i)Explain briefly on the deflecting torque, controlling torque and damping torque in indicating instruments. (EI May ’06)

(ii)With neat figures explain how the range of measurements is extended in ammeters.(12+4)

3. Give the construction and working principle of PMMC type voltmeter. What are its advantages and disadvantages.(12+4) (EI May ’06)

4. (i) With neat figures explain the principle of operation of Moving Iron attraction type of voltmeter. (EI May ’07)

(ii) What are hysteresis error and stray field error effects in these types of instruments?(iii) A 230 volt MI voltmeter with current of 0.25 A connected to 230 V DC supply. The coil has inductance of 20 mH. Determine the reading on the meter when connected to 230 V, 50 Hz a.c. supply. (6+6+4)

5. With neat figures explain the construction, principle of a PMMC type ammeter. What is the importance of torque in functioning of indicating instruments? (10 + 6) ( EI May ’07)

6. (i) Explain the working principle of induction type meter with suitable sketches. (8)(EI Nov ’07)

(ii) A moving coil instrument has a resistance of 5 Ω between terminals and full scale deflection is obtained with a current of 15 mA. This instrument is to be used with a manganin shunt to measure 100 A at full scale. Calculate the error caused by a 10"C rise in temperature:

(1) When the internal resistance of 5 Q is due to copper only?(2) When a 4Ω manganin swamping resistance is used in series with a copper coil of 1Ω resistance.

The resistance temperature coefficients of copper and manganin are 0.4 %/0 C and 0.0157 %/0 C rise respectively. (8)

7. (i) Describe in detail about the constructional features of PMMC instrument. (8)(EI Nov ’07)

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(ii) A resistance of 50 Ω is connected in series with a rectifying device, a moving coil ammeter and a hot wire ammeter. The circuit is then connected across a sinusoidal a.c supply of 100 V. The resistance of rectifying device is 50 Ω in one direction, and 250 Ω in the opposite direction. Calculate: (8)

(1) The readings on two ammeters,(2) Power supplied from mains,(3) Power dissipated in the rectifying device.

8. Discuss the constructional features of D’Arsonval galvanometer and find an expression for steady deflection when a current flows through it. (EI Nov ’09)

9. Discuss the principle of operation and construction of PMMC instrument with a neat diagram. What are the sources of errors in such a meter? (EI Nov ’09)

10. (i). Describe the constructional details and principle of operation of D’Arsanoval Galvanometer. (8) (EI May ’06)

(ii). A permanent magnet moving coil voltmeter has a resistance of 10 Ω and full scale deflection is reached when the potential difference of 150 mV is applied across the terminals. The area of moving coil is 6 x 10-4 and there are 40 turns on it. The torque provided by the spring is 0.4 gm cm at the full scale deflection. Calculate the flux density in the air gap. (8)

11. (i) Briefly discuss the extension of AC and DC current and voltage measuring instruments using suitable accessories. (8) (EI May ’06)

(ii) In a ballistic galvanometer a discharge of 0.001 Columb produces a first swing of 60 degrees. Find the quantity of electricity to produce (8) (EI May ’06)

a. A swing of 90 degrees in the instrument andb. A spot deflection of 10 mm on a scale of 1m away.

12. (i). Mention the different types of errors that occur in ammeters and voltmeters. Explain how they can be compensated. (8) (EI Nov ’06)

(ii) A moving coil instrument gives a full scale deflection of 10 mA when the potential difference across the terminals is 100 mV. Calculate (1) Shunt resistance for a full scale deflection corresponding to 100 A. (2) Series resistance for a full scale deflection reading with 1000 V. Calculate the power dissipation in each case. (8)

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13. (i) Derive the deflecting torque equation of a Moving Iron instrument. (10)(EI Nov ’06)

(ii) The inductance of a Moving Iron Ammeter with full scale deflection of 90 degrees at 1.5 A is given by the expression L=(200+40.θ-4θ2-θ3)µH where θ is the deflection in radians from the zero position. Estimate the angular deflection of the pointer for current 0f 0.1A. (6)

14. (i) Describe the constructional details and working of electrodynamometer type instrument. (8) (EI May ’07)

(ii).The inductance of a certain moving iron ammeter is 8+4θ-1/2 θ2 µH where θ is the deflection in radians from the zero position. The control spring torque is 12 x 10-6

N-m/rad. Calculate the scale positions in radian for current 1, 2, 3 and 4 A and discuss the scale shape obtained. (8)

15. (i). Define the operational constants of a D’Arsonval galvanometer. Express the equation of motion of D’Arsonval galvanometer in terms of operational constants. (8)

(ii) When a current of 0.001 A is passed through a ballistic galvanometer it gives a steady deflection of 50 scale divisions. When a capacitor charge to a potential of 100 V d.c is discharged through the galvanometer it gives a maximum throw of 220 scale divisions. The periodic time of swing is 4 sec.. find the value of capacitance. The value of logarithmic decrement is 0.2. (8) (EI May ’07)

16. (i). Write the merits and demerits of PMMC and PMMI instruments. (8) (EI May’08)

(ii). Explain in detail about the working principle of D’Arsonval Galvanometer. (8)

17. (i) A moving coil ammeter has a fixed shunt of 0.02 Ω with a coil resistance of R=1000Ω and a potential difference of 500 mV across it. Full scale deflection is obtained.

(10) (EI May’08)(1) To what shunt current does this current corespond to?(2) Calculate the value of R to give full scale deflection when shunted current I is

10A(case 1) and 75 A(case 2) and(3) With what value of R is 40% deflection obtained with current I=100 A.

(ii) Write short notes on thermoelectric instruments with an example. (6)

18. a) Explain the working of moving iron meter with neat diagram. Derive the torque equation for moving iron instruments. (8+8)Or(b) How can the range of d.c ammeter and d.c voltmeter be extended? Derive the expressions to calculate shunt resistance and multiplier resistance. (nov / dec 2012)

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19. a) i) The reverse saturation current of a silicon PN junction diode is 10µA. Calculate the diode current for the forward bias voltage of 0.6V at 25o C. (8) ii) Discuss the construction and applications of Schottky Diode. (8)Or(b) i) Draw the collector –to- base bias circuit for a transistor amplifier and obtain its stability factor. (8)

ii) Derive the transistor equation IC=βIB+(1 + β)ICBO (8) (may / june 2013)

Unit II -Measurement of Power and Energy

1.Give the construction with deriving the deflection torque equation for a dynamometer type Watt meter with neat figures. (EI May ’07)

2.A 230 V, 15 A dynamometer type wattmeter has current coil resistance of 0.6 Ω and potential coil resistance of 15,000 Ω. Find the percentage error due to each of the two methods of connection when unity p.f. loads at 230 V of (i) 5 A (ii) 20 A. Neglect the error due to inductance of pressure coil. (8+8) (EI May ’07)

3.(i) Derive the expressions for the capacitance connected across the resistor in the pressure coil circuit so as to neutralize the effect of inductance of pressure coil circuit.(8)

(ii) A watt hour meter is calibrated to measure energy on a 250 V supply. On test a steady current of 15 A is passed through it 5 hours at unity power factor. If the meter readings before and after the test are 8234.21 kWh and 8253.13 kwh respectively, calculate the percentage error. If the spindle turns through 290 revolution during 5 minutes when a current of 20 A is passing through the meter at 250 V and 0.8 power factor, calculate the meter constant. (8) (EI May ’07), (EI Nov ’07)

4.(i) What is phantom loading? Explain with an example how is it more advantageous than testing with direct loading? (8) (EI May ’07, EI Nov ‘07)

(ii) If the current in the pressure coil of a wattmeter lags 20 behind the voltage and instrument is accurate when cosΦ=1, find the percentage error when cosΦ=0.8,0.6 and 0.4 respectively. (8)

5.(i) Describe the working of a dynamometer wattmeter with the help of a neat diagram. (10) (EI Nov ’07)

(ii) A 250 V, 10 A dynamometer wattmeter has a resistance of current and voltage coils of 0.5 Ω and 12500 Ω respectively. Find the percentage error due to each of the two methods of connection when unity power factor loads at 250 V are: (1) 4A and (2) 12 A. Neglect error due to inductance of pressure coils. (6)

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7. Explain the principle of operation and construction of electrodynamometer type wattmeter, with a neat sketch. Discuss the errors. (EI Nov ’09)

8.Explain with a neat circuit diagram, a method of testing an energy meter using Phantom loading. What are the advantages in this method? (EI Nov ’09)

9.(i) With a neat circuit diagram explain the calibration of induction type energy meter.(8) (EI May ’06)

(ii). Derive the torque equation for an electrodynamometer type wattmeter. Explain the special features incorporated in it so that it can be used for low power factor application. (8)

10.(i) Describe the adjustments that are necessary to make the single phase energy meter to read correctly so that errors are within the allowable limits. (8) (EI Nov ’06)

(ii). An energy meter is designed to make 100 revolutions of disc for one unit of energy. Calculate the number of revolutions made by it when connected to a load carrying 40A at 230 V and 0.4 power factor for an hour. If it actually makes 360 revolutions, find the percentage error. (8)

11.(i) Enumerate the features to be incorporated in electrodynamometer wattmeter so that it can be used for measurement of power in low power factor circuits. (8)

(ii) A wattmeter has a current coil of 0.1 Ω resistance and a pressure coil of 6500 Ω resistance. Calculate the percentage error due to resistance only (1) when the pressure coil is connected on supply side and (2) when the pressure coil is connected on load side.

(8) (EI Nov ’06)

12. (i) What are the errors in electrodynamometer type wattmeter and discuss its compensation methods. (8) (EI May ’08)

(ii) A wattmeter has a current coil of 0.03 Ω resistances and a pressure coil of 6000 Ω resistance. Calculate the percentage of error if the wattmeter is so connected that

(1) The current coil is on the load side(2) The pressure coil is on the load side.

a. If the load takes 20 A at a voltage of 220 V and 0.6 power factor in each case?

b. What load current would give equal error with two connections? (8)

13. Explain the construction and theory of operation of single phase induction type energy meter. (16) (EI May ’08)

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14. a)Explain how power can be measured in a 3 phase circuit with the help of two watt meters. (16)Or (b) Explain the various adjustments available in single phase energy meter to get the accurate reading. (16) ( nov / dec 2012)

15. a) i) Define the parameters trans conductance gm , drain resistance rd , and amplification factor µ of a JFET and establish a relation between them. (8) ii) Describe the construction and characteristics of n-channel D-MOSFET. (8)Or (b) i) Draw and explain the static emitter characteristics of UJT. (8) ii) Explain the operation and characteristics of SCR. (april 2013)

Unit III Potentiometer and Instrument Transformers

1. Explain how potentiometers are used to calibrate ammeters and resistances. Give the principle of operation of a typical a.c. potentiometer with a neat figure. (16) (EI May’06)

2. (i) Distinguish between operating conditions of a current transformer and potential transformer with regard to materials used, windings, operation and application.

(ii) A PT rated 33 kV/220 V and a CT of 100/5 A are used to measure the voltage and current in a transmission line. If the voltmeter shows 200 V and the ammeter shows 4 A, determine the voltage and current in the line. (12 + 4)

3. (i). Describe the principle of operation of current transformer. (10) (EI May’06)

(ii) A current transformer has 3 primary turns and 300 secondary turns. The total impedance is 0.583+j0.25 Ω. The secondary current is 8 A. The ampere turns required to supply excitation and iron losses are 10 and 5 per volt induced in the secondary. (6)

4. Give reasons why are instrument transformers desirable to current shunts or voltage multipliers? Explain the working principle of potential transformer.(6+10) (EI May ’07)

5. Write briefly on any TWO of the following: (8+8) (EI May ’07)

(i) Polar type AC potentiometer(ii) Ratio and phase Angle error in instrument transformer(iii) Student type potentiometer.

6. (i) Describe the construction and working of a co-ordinate type ac potentiometer. How is it standardized? Explain how an unknown voltage can be measured it. (10)

(EI Nov ’07)

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(ii) The emf of a standard cell is measured with a potentiometer which gives a reading of 1.01892 V. When in 1 MΩ resistor is connected across the standard cell terminals, the potentiometer reading drops to 1.01874 V. Calculate the internal resistance of the cell. (6)

7. (i) Discuss the major sources of errors in current transformer' Describe the design and constructional features used in current transformers to reduce the errors. (8)

(ii) A 500/100 v potential transformer has the following constants:

Primary winding resistance = 47.25 Ω, secondary winding resistance = 0.43 Ω, Primary winding reactance = 33.1 Ω. Secondary winding reactance is negligible; no load primary current = 0.1 A at 0.6 p.f. Calculate (1) the no load angle between primary winding and reversed secondary winding voltages.(2) the value of secondary winding current at unity power factor when the phase angle is zero. (8) (EI Nov’07)

8. Draw the circuit diagram of a Crompton’s potentiometer and explain its working. Describe the steps used when measuring an unknown resistance. (EI Nov ’09)

9. (i) Explain the use of instrument transformers for the measurement of power with a neat diagram. (12) (EI Nov ’09)

(ii) Explain the term ratio correction factor with respect to instrument transformer. (4)

10. With neat figure explain the working principle of (8+8) (EI May ’06)(i) Drydscale potentiometer.(ii) Co-ordinate Potentiometer

11. (i) Describe the construction and procedure of standardization of a polar type AC potentiometer. (8) (EI May ’06)

(ii) A 1000/100 volt potential transformer has the following constants,

Primary winding resistance = 94.5 Ω, Secondary winding resistance = 0.86 Ω, Primary winding reactance = 66.2 Ω.Total equivalent Reactance=110 ΩMagnetizing current = 0.02 A at 0.4 power factor

Calculate the phase angle error at no load and the load in VA at unity power factor. (8)

12. (i) Explain with necessary circuit diagram how the calibration of an ammeter using DC potentiometer is carried out. (8) (EI May ’06)

(ii) An AC potentiometer is used for the calculation of impedance of a coil and the following results are obtained. The voltage across a 1 ohm resistor in series with the coil

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is 0.245-0.092j V. The voltage across a 10:1 potential divider used with the coil is 0.3021+ j 0.246 V. Calculate resistances and reactance of the coil. (8)

13.(i) Describe with a suitable diagram, how a dc potentiometer can be used for (1) Calibration of voltmeter (2) Calibration of ammeter (8) (EI May ’07)

(ii) A slide wire potentiometer is used to measure the voltage between two points of a certain dc circuit. The potentiometer reading is 1V across the same two points when a 10,000 Ω/V voltmeter is connected; the indicated reading on the voltmeter is 0.5V on its 5V range. Calculate the input resistance between two points. (8)

14 (i) Describe the design and constructional features used in potential transformers for the reduction of ratio and phase angle errors. (8) (EI May ’07)

(ii) A 1000/5, 50 Hz current transformer has a secondary burden comprising a non inductive impedance of 1.6 Ω. The primary winding has one turn. Calculate the flux in the core and ratio error at full load. Neglect leakage reactance and assume iron loss in the core to be 1.5W at full load. The magnetizing MMF is 100 A. (6)

15. Explain the operation of Drydscale phase shifting transformer. How it is used in polar type AC potentiometer to measure the unknown emf? (EI May’08)

16. Derive the expression for ratio error and phase angle error of CT. (EI May’08)17. a) Describe the construction and working of a.c. potentiometer. How it is standardized? (16)Or (b)Draw neat diagram for measuring high voltage and high current with the help of PT and CT. What purpose do they serve (16) (nov / dec 2012)

18. a) i) Draw the h-parameter model of a CE transistor and define the h-parameters. (8) ii) For the CE amplifier shown in the figure, calculate the mid frequency voltage gain and lower 3 dB point. The transistor has h-parameters life=400 and h ie=10kΩ. The circuit details are RL=5kΩ, RS=600Ω, RE= 1kΩ , VCC=12V, R1=15kΩ, R2= 2.2 kΩ and CE=50µF. (8)Or

(b) i) In a class A amplifier, VCE(max)=15V, VCE(min)=1V. find the overall ed\fficiency for (1) series –fed load, (4) (2) transformer coupled load. (4) ii) Derive the conversion efficiency and the relation between maximum power output and maximum power dissipation for class B push-pull power amplifier. (8) (may/june 2013)

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Unit IV Resistance Measurement

1. Describe Price’s guard wire method of finding a high resistance and state the precautions. (16)(EI May ’06)

2. (i) A 4–terminal resistance of approximately 50 mW is measured by using a Kelvin double bridge with the component resistances as given below: (EI May ’06)Standard resistor = 100.03 mWInner ratio arms = 100.31 W and 200 WOuter ratio arms = 100.24 W and 200 WValue of low resistance link = 700 mWFind the unknown resistance to the nearest of 0.01 W.

(ii) Give the constructional details and state the working of a Megger. (4 + 12)

3. Write briefly with neat figures the construction of (i) Megger (ii) Repulsion type Moving Iron Instruments.(8+8)4. Explain the resistance measurement using the Kelvin double bridge and explain the need for compensation circuit. (10 + 6)

(EI May ’07)

5. Write briefly on any TWO of following (EI May ’07)(i) Megger(ii) Price's Guard wire method(iii) Measure of earth resistance.

6. (i). What is the importance of the value of Earth's resistance? What are the factors which influence its value? Describe the fall of potential method for measurement of earth resistance.(12) (EI Nov ’07, EI May’08)

(ii) Calculate insulation resistance of a cable in which the voltage falls from 100 to 80 V in 20s. The capacitance is 300 pF. (4)

7. (i) Draw the circuit of Kelvin double bridge used for measurement of low resistance. Derive the condition for balance. (8) (EI Nov ’07)

(ii) A short circuit fault is located by Varley loop test. The ratio arms are set at P = 5 Ω and Q = 10 Ω and the values of variable resistance S are 16 Ω for position 1 of switch K and 7 Ω for position 2. The sound and faulty cables are identical and have a resistance of 0.4 Ω /km. Determine the length of each cable and the distance of fault from the test end.

(8)

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8. Explain the principle of working of a Kelvin’s double bridge. Also obtain the balance conditions for this type of bridge. (EI Nov ’09)

9. Write short notes on: (EI Nov ’09, EI May ’08)(i) Megger. (8)(ii) Measurement of Earth resistance. (8)

10. (i) Describe the measurement of insulation resistance of a length of cable using Price Guard wire method.(8) (EI May ’06)

(ii). How can the low resistance be measured using Kelvin’s double bridge method? What are its merits and demerits? (8) (EI May’08)

11.(i) Describe the procedure for measurement of earth resistance. (8) (EI May ’06)

(ii). A cable of length 1000 m is tested for insulation resistance by the loss of charge method. An electrostatic voltmeter of infinite resistance is connected between the cable conductor and earth forming a joint capacitance of 8 x 10 -4µF. It is observed that after charging, voltage falls from 400 to 200 V in 50 seconds. Calculate the insulation resistance of the cable of length 500 m.(8)

12.(i) Describe the working of Megger.(8) (EI May ’07)

(ii) Draw the circuit of a Wheatstone’s Bridge and derive the conditions of balance. (8)

13.(i) Explain the loss of charge method for measurement of insulation resistance of cables.(10) (EI May ’07)(ii) Write short notes on ohmmeter.(6)

14.(i) Design a series type ohmmeter. The movement to be used required 0.5 mA for full scale deflection has an internal resistance of 50 Ω. The internal battery has a voltage of 3V. the desired half scale resistance is 3000 Ω. Calculate

(1) The values of series (R1) and parallel resistance(R2).(2) The range of values of R2 if the battery voltage may vary from 2.7V to 3.1V. Use

the value of R1 calculated in (1). (10) (EI May’08)

15. a) Illustrate the operation of the Wheatstone bridge. Compare the measuring accuracy of a Wheatstone bridge with the accuracyof an ordinary ohmmeter. (16)Or(b) What are the various difficulties encountered in the measurement of high resistance? Explain how these difficulties are overcome. (16) (nov/dec 2012)

16. a) i) An amplifier has a voltage gain of 400, f1=50 Hz, f2=200kHz and a distortion of 10% without feedback. Determine the amplifier gain, f1f , f 2f , Df when a negative feedback is applied with a feedback ratio of 0.01. (8)

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ii) Draw the circuit of a CE amplifier with voltage- shunt feedback and explain. (8)Or(b) i) Derive the expression for frequency of oscillation of RC phase shift oscillator. (10) ii) Draw the circuit of a crystal oscillator and explain its operation. (6). (may/june 2013)

Unit V Impedance Measurement

1. (i) With neat figures explain the bridge balance condition for (a) Maxwell bridge (b) Schering Bridge.(5+5)

(ii) Find the equivalent parallel resistance and capacitance that causes Wien’s bridge to null with the following components. R1=2.7 K, C1=5uF, R2=270 K, R4=100 K. operating frequency is 2.2 KHz. (6)(EI May ’06)

2. (i)Derive the expression for the value of capacitance for a Schering bridge.(EI May ’07)

(ii) If a capacitor bridge has an arm AB as 500 pF, arm CD with non inductive resistance of 600 ohms, arm AD with resistance in parallel to capacitive with 75 ohm and .04 pf respectively. The supply voltage is 50 Hz. calculate the capacitance and dielectric loss angle '5' at arm BC. (8 + 8)

3. (i) With neat figure derive the bridge balance equation for an Anderson Bridge. (EI May ’07)(ii) Give the principle of a vibration galvanometer. (8+8)

4. (i) Describe the working of a Schering’s bridge and obtain the equation at balance. (8)

(ii) A dielectric sheet of thickness 1mm is tested at 50 Hz between two electrodes of 10 cm diameter. The Schering’s bridge employed has the following constants at balance: a standard capacitor of 100 pF, a pure resistor of 320 ohms in parallel with 0.5 µF and a non-inductive resistor of 280 ohms. Calculate the power factor and permittivity of the sheet. (8)(EI May ’06)

5. (i) Mention the significance of screening and earthing in AC bridge circuits and explain the Wagner earth connection. (8)(EI May ’06)

(ii) The four arms of an AC bridge contain the following elements: PQ, a coil of unknown impedance; QR, a non inductive resistor of 1000 Ω; RS, a non inductive resistor of 85 Ω in series with a standard capacitor of 0.35 µF; SP, a pure resistor of 16,500 Ω. The supply frequency is connected to points P and R, and a detector to points Q and S. Determine the inductance and resistance of the coil. (8)

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6. (i) Describe the working of Wien’s Bridge for measurement of frequency with the help of a neat circuit diagram. (10)(EI Nov ’06)

(ii) The four arms of a Wien’s supplied with AC voltage have the following values:

AB-Resistance of 200 Ω in parallel with a capacitance of 1 µF.BC- Resistance of 400 Ω , CD- Resistance of 1000 ΩDA- Resistance of R2 in series with 2 µF capacitance. Determine the value of R2 and the frequency at which the bridge will balance. (6)

7. (i) Explain how the inductance can be measured using Maxwell’s bridge with the aid of neat circuit diagram and phasor diagrams. Obtain the equation at balance.(10)

(ii) A Maxwell’s bridge is used to measure an unknown inductance in comparison with capacitance. The various values at balance

R2=400 Ω , R3=600Ω, R4=1000Ω and C4=0.5 µF

8. Calculate the values of R1 and L1. Calculate also the value of Q factor of coil if frequency is 1000 Hz. (6) (EI Nov ’06)

9. What are the different sources of errors in ac bridges? Explain the precautions taken and techniques used for elimination/ minimization of these errors. (EI May ’07)

10. (i) Describe the working of Maxwell Bridge and obtain the equation at balance.(8)

(ii) The four arms of a bridge network are made up as follows: AB, a resistor of 50Ω in parallel with an inductor of 0.1H; BC, a resistor of 100 Ω; CD an unknown resistor R in parallel with an unknown capacitor C. DA, a resistor of 1000 Ω. A 50 Hz voltage supply is applied across AC is undeflected. Find R and C when a vibration galvanometer connected across BD is undeflected. (8) (EI May ’07)

11. (i). Derive the expression for unknown inductance in Anderson’s bridge and also draw its vector diagram.(12) (EI May ’08)

(ii) What are the advantages and disadvantages of Hay’s Bridge ? (4)

12. (i)Explain the construction and working principle of vibration galvanometer. (10

(ii)Explain with a neat sketch about located a short circuit fault in a cable by Murray test.(6)(EI May ’08)

13. (i) Describe the sources and the null detectors that are used for a.c bridges. (8)(EI Nov ’07)

(ii) A four branch bridge network ABCD balanced at 1000 Hz has branches AB and BC of pure resistance of 1000 Ω and 1250 Q respectively. Unknown impedance forms the

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arm CD and the branch DA consists of a standard capacitor of 0.1 pF capacity and negligible resistance, connected in series with a non-inductive resistance of 10 Ω to give balance. The supply voltage is 15 V and the supply is given at the points B and D. Find the components of unknown impedance and draw the necessary phasor diagram. (8)

14. (i). A capacitor busing forms arm AB of a Schering bridge and a standard capacitor of 500 pF capacitance and negligible loss, forms arm AD. Arm BC consists of a non-inductive resistance of 300 Ω. When the bridge is balanced arm cd has a resistance of 72.6 Ω in parallel with a capacitance of 0.148 uF. The supply frequency is 50 Hz. Calculate the capacitance and dielectric loss angle of capacitor. Derive the equations for balance and draw the phasor diagram under the conditions of balance. (8)

(EI Nov ’07)

(ii) Explain why Maxwell's inductance – capacitance bridge is useful for the measurement of inductance of coils having storage factor between 1 and 10 (8)

15. (i) Explain the working of a Schering bridge. (10) (EI Nov ’09)

(ii) Draw its phasor diagram under balance condition. (6)

16. Explain the working of a vibration galvanometer. Also derive an expression for the deflection of vibration galvanometer. (EI Nov ’09)

17. (i) Explain the Maxwell’s bridge method for finding an unknown inductance.(8) (EI May ’07)

(ii) Derive the balance condition of a Schering bridge. (8 + 8)

18. Write briefly on any TWO of the following:

(i) Compensation methods in watt meters (ii) Bridge configuration to measure mutual inductance (iii) Measurement of high resistance by loss of charge method. (8 + 8)

19. a) Explain why Maxwell’s bridge is useful for measurement of inductance of coils having storage factor between 1 and 10. (16)

(b) What are the different sources of errors in ac bridges? Explain the precautions takenAnd the techniques used for elimination of these errors. (16) (Nov / Dec 2012)20. a) i) Draw the circuit of biased positive clipper and explain with suitable waveforms.

(8)ii) With suitable waveforms, describe the working of a bridge rectifier. (8)

(b) i) Classify multivibrators and mention their applications. (8) ii) Discuss the design of a zener diode voltage regulator. (8) (May/June 2013)

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