SIDDHARTH GROUP OF INSTITUTIONS :: PUTTUR (AUTONOMOUS) Siddharth Nagar, Narayanavanam Road 517583 QUESTION BANK (DESCRIPTIVE) Suject : Electrical & Electronic Measurements(16EE224) Year & Sem: III-B.Tech & II-Sem Course & Branch: B.Tech & EEE Regulation: R16 UNIT I MEASURING INSTRUMENTS 1 a Define the terms indicating instruments, recording instruments and integrating instruments. Give examples of each case. Design an Aryton shunt to provide an ammeter with the current ranges 1 A, 5A, 10 A. A asic meter resistance is 50 ohm and full scale deflection current is 1 ma. 2 a Explain the construction &working of an electrodynamic type moving coil ammeter derive torque equation. A 10 A electrodynamometer is controlled y a spring having a torsion constant of 0.1x10-6 Nm/degree. The full scale deflection is 110 o. Determine the inductance of the instrument when measuring a current of 10A. The mutual inductance at 0 o deflection is 2μH and the change in mutual inductance is linear as the deflection. 3 Explain the construction & working of PMMC type of instrument. Derive torque Equation. Enlist advantages and disadvantages of PMMC metres 4 a How the electrical measuring instruments are classified Discuss aout errors and compensations of measuring instruments 5 a Explain principle of MI instruments. Derive an expression for the Deflecting torque in MI type instruments List the advantages & disadvantages of MI type instruments 6 a Descrie the construction and working of attraction type MI instrument? ELECTRICAL TECHNOLOGY Page 1
The inductance of a moving iron ammeter with a full scale deflection of 90 o at 1.5A is given y : L= 180+40θ-4θ 2 θ 3. wh ere, θ is the deflection in radians from the zero position, calculate (i) spring constant. (ii) The angular deflection of the pointer for a current of 10A. 7 How do you extend the range of an Ammeter? Explain Aryton Shunt with diagram 8 a Explain the principle of Electrostatic Instruments and derive force and torque equations of Electrostatic voltmeters An electrostatic voltmeter has full scale deflection of 90 o.the control constant of spring is 8x10-6 Nm/rad. When reading is zero, the capacitance is 12pF. What is the capacitance,when the instrument reads 1500V and deflection is 90. 9 a Descrie the construction of a quadrant type of electrostatic voltmeter. Descrie the construction of attracted disc type kelvin asolute electrometer An asolute electrometer uses a circular plate 70mm in diameter. During a voltage measurement, the distance etween the plates is 3.2mm and the force of attraction is 0.003N. The medium is air. Find voltage V. 10 a Classify instruments. Define Eddy current Damping c Write difference etween Ammeter &Voltmeter d Define (i) Measurand (ii) Measurement e Define Galvanometer UNIT-II DC AND AC BRIDGES 1 a Explain riefly how a Wheatstone Bridge is used for measurement of resistance [9M] What are the sources of measurement errors in Wheatstone ridge What are the limitations of a Wheatstone Bridge 2 a Explain how insulation resistance of a cale can e measured with a help of [3M] Loss of charge method The value of high resistance is measured y loss of charge method. A capacitor ELECTRICAL TECHNOLOGY Page 2
having a capacitance of 2.5 μf is charged to a potential of 500V D.C and is discharged through the high resistance. An electrostatic voltmeter, kept across the high resistance, reads the voltage as 300V at the end of 60 seconds. calculate high value of resistance. 3 Explain the procedure of measuring a low resistance with the help of Kelvins doule Bridge.Derive the relation for finding unknown resistance 4 a Draw the general form of an A.C ridge and derive the general equation for its Balance. Explain riefly how inductance can e measured y Maxwell Bridge in terms of a capacitor 5 6 a Descrie Anderson ridge and deduce self inductance. List Advantages & Disadvantages Explain how Wien s ridge can e used for experimental determination of frequency Determine the equivalent parallel resistance and capacitance that causes a Wien ridge to null with the following component values : R 1 = 3.1kΩ ; C 1 = 5.2μF ; R 2 =25kΩ; R 4 =100KΩ ; f=2.5khz 7 a Explain the Desauty s Bridge with a neat sketch List the advantages and disadvantages of Maxwell s Bridge ELECTRICAL TECHNOLOGY Page 3
8 a With the help of circuit diagram explain how capacitance can e measured y the 9 a use of Schering ridge The Schering ridge has the following constants: Arm AB.Capacitor of 0.5μF in parallel with 1kΩ resistance Arm BC resistance of 3kΩ Arm CD.Unknown resistance C x and R x in series Arm DA 1kHz Determine the following: (a) Unknown resistance and capacitance () Dissipation factor. In a kelvin doule ridge, there is error due to mismatch etween the ratios of outer And inner arm resistances.in ridge, standard resistance = 100.03μΩ; Inner ratio Arms =100.31Ω and 200Ω; Outer ratio arms = 100.24Ω and 200Ω; the resistance of Connecting leads from standard to unknown resistor is 680 μω. Calculate unkown Resistance. An ac ridge circuit working at 1Khz have its arms as follows: Arm AB : 0.2 µf capacitance Arm BC : 500 ohm resistor Arm CD : unknown impedance Arm DA : 300 ohm resistor in parallel with 0.1µf capacitor Find R and L or C constants of the Arm CD considering it as a series circuit 10 a What is a ridge? Write short notes on sustitution method. c Write short notes on Ammeter- Voltmeter method. d What are detectors used in ridge. ELECTRICAL TECHNOLOGY Page 4
e Write ridge alance equations of AC & DC. UNIT III MEASUREMENT OF POWER AND ENERGY 1 Descrie the construction and working of a single phase dynamometer type Wattmeter.Derive the expression for deflection for a.c operation if the instrument is spring controlled. 2 a Explain the special features of a wattmeter suitale for working on low power Factor circuits? A wattmeter has a current coil of 0.03Ω resistance and a pressure coil of 6000Ω Resistance.Calculate the percentage error if the wattmeter is so connected that: (i) The current coil is on the load side; (ii) The pressure coil is on the load side. (a) If the load takes 20A at a voltage of 220V and 0.6 p.f in each case; () What load current would give equal errors with the two connections? 3 a Explain the construction of Two element dynamometer wattmeter? A dynamometer wattmeter is used to measure the power factor of a 20µF Capacitor.The pressure coil of the wattmeter having a resistance 1000Ω and An inductive reactance of 15Ω is connected across a 50Hz supply. The current coil of the wattmeter, a variale resistor R and the capacitor are connected In series across the same supply.the wattmeter deflection is made zero y Adjusting the value of R to 1.65Ω.If the current coil resistance is 0.1Ω and its Inductance negligile, determine the power factor of the capacitor. 4 Discuss errors and its compensations in the dynamometer type wattmeters 5 a Explain the measurement of LPF and UPF In a dynamometer wattmeter the moving coil has 500 turns of mean diameter 30mm. Estimate the torque if the axes of the field and moving coils are at (a)60⁰ ()90⁰ when the density in the field coils is 15x10-3 W/m 2,the current in moving Coil is 0.05A and the power factor is 0.866. ELECTRICAL TECHNOLOGY Page 5
6 Descrie the construction and working of a single phase induction type energy Meter.Show that the numer of revolutions made y its disc during a particular Is proportional to the energy consumed. 7 a Explain driving, raking and moving system in a single phase induction type Energy meter Explain the advantages and disadvantages of single phase Induction type Energy meter? 8 a Explain the working of 2 element energy meter with a neat diagram [9M] A 5A, 230 V meter on full load UPF test makes 60 revolutions in 360 seconds. [3M] If the normal disc speed is 520 revolutions per Kwh, find the percentage Error 9 a Discuss the errors and compensations in Energy meters [9M] The name plate of a meter reads 1kWh=15000revolutions.In a check up, [3M] The meter completed 150 revolutions during 45 seconds.calculate the power in the circuit. 10 a Define Wattmeter Draw the circuit of dynamometer type wattmeter c Define (i) Energy (ii) Energy meter d What are sources of errors in induction type energy meters e Classify types of wattmeters and Energy meters UNIT-IV INSTRUMENT TRANSFORMERS & POTENTIOMETERS 1 a Give the comparison etween Current and Potential transformer List out the advantages and disadvantages of instrument transformers 2 Explain the construction, operation& characteristics of current transformer 3 Explain the construction, operation & characteristics of potential transformer 4 Explain the construction and working of Crompton s DC potentiometer and How it is standardized? 5 a Explain how potentiometer can e used for measurement of unknown ELECTRICAL TECHNOLOGY Page 6
Resistance and current? A Crompton s potentiometer consists of a resistance dial having 15 steps Of 10Ω each and a series connected slide wire of 10Ω which is divided into 100divisions.If the working current of the potentiometer is 10mA and each Division of slide wire can e read accurately upto 1/5 of its span,calculate The resolution of the potentiometer in volts. 6 a Descrie the construction and working of a polar type potentiometer. Explain The method for standardizing it. The following readings were otained during the measurement of power y a Polar potentiometer: Voltage across a 0.2Ω standard resistance in series with the load =1.46 32⁰ Voltage across a 200:1 potential divider across the line =1.37 56⁰ Determine the current, voltage,power and power factor of the load 7 a Explain the construction & working of coordinate type potentiometer and how it is standardized? The current taken y a small iron core choke coil is measured y a rectangular Coordinate potentiometer. A 1Ω non inductive resistance is connected in series With the choke coil. The voltages measured across the resistance and the coil are (0.8-j0.75)V and (1.2+j0.3)V respectively.determine the iron loss in the coil (Assume voltage and current to e sinusoidal). 8 a Discuss riefly the applications of A.C.Potentiometer The following readings were otained during the measurement of inductance Of a coil on an A.C.Potentiometer: Voltage drop across 0.1Ω standard resistor connected in series with the coil =0.613 12.6⁰6 V.Voltage across the test coil through a 100:1 volt ratio ox =0.781 50⁰48 V; Frequency= 50Hz.Determine the value of Inductance. 9 a Discuss Advantages & Disadvantages of A.C. Potentiometer Discusss advantages of D.C.Potentiometers and its uses 10 a Define Instrument transformers Draw wiring diagram of C.T & P.T c What is Actual transformation ratio & Ratio correction factor. ELECTRICAL TECHNOLOGY Page 7
d Define Potentiometer e What is standardisation? UNIT-V MAGNETIC MEASUREMENTS &DIGITAL METERS 1 a Descrie the construction & working of a Ballistic galvanometer Derive equation of motion of Ballistic galvanometer 2 a Prove that is a Ballistic galvanometer, the charge is proportional to first swing of the moving coil. A allistic galvanometer has a free period of 10 seconds and gives a steady Deflection of 200 divisions with a steady current of 0.1mA.A charge of 121µC Is instantaneously discharged through the galvanometer giving rise to a first First maximum deflection of 100divisions.Calculate the decrement of the Resulting oscillations 3 a Explain construction & working of flux meter with neat sketch Compare flux meter with allistic galvanometer 4 a Draw the lock diagram of CRO and explain the working of it Explain the functioning of a time ase generator in a CRO 5 a With the help of neat diagram explain riefly the main parts of CRT Descrie in detail aout the vertical amplifier used in CRO 6 Descrie riefly how the following measurements can e made with the Use of CRO.(i)Frequency (ii) Phase Angle (iii) Voltage 7 Discuss aout Lissajous patterns and how frequency is measured y it 8 a Explain riefly the principle on which digital meters work How does a digital system differ from an analog system 9 a Explain uilding locks and Characteristics of Digital meters Discuss aout applications of the digital meters 10 a Define CRO &CRT What is the function of Horizontal amplifier. ELECTRICAL TECHNOLOGY Page 8
c Write applications of CRO d Define digital instrument e What is Resolution in digital meters Prepared y: P.Chandra Sekhar ELECTRICAL TECHNOLOGY Page 9