ELECTRICAL MEASUREMENTS (EEE III year II semester) – Backlog management questions
UNIT – I
1.	Explain the construction and working of PMMC instruments.
2.	(a) State the errors of PMMC instrument. b)The coil a 300V moving iron voltmeter has a resistance of 500mho and an inductance of 0.8H.The instrument reads correctly at 50Hz ac supply and takes 100 mA at full scale deflection. What is the percentage error in the instrument reading when it is connected to 200 V DC supply
3.	(a) What are electrostatic instruments? What is the basic principle on which they operate? (b) Discuss the working of a repulsion type electrostatic instrument with a neat sketch.
4.	Explain deflecting system, controlling system and damping system with reference to an electrical indicating instrument.
UNIT – II
1	Draw the equivalent circuit and phasor diagram of a C.T.
2	what is the effect of the following on the characteristics of a potential transformer      (i) Burden (ii) power factor of secondary winding circuit and (iii) frequency
3	Draw the equivalent circuit and phasor diagram of a P.T.
4	Explain with the diagram Kelvin multi cellular voltmeter
UNIT – III
1.	Describe the constructional details and principle of operation of a electrodynamometer type wattmeter.
2.	Two wattmeter connected to measure the input to a balanced three phase circuit  indicate 2000w and 500W respectively find the power factor of a circuit (i).when both the readings are positive and (ii) When the latter reading is obtained after revising the connection to the current coil of first instrument
3	Explain how 3-phase power can be measured with the help of a wattmeter. Explain with a phasor diagram.
4.	In a particular measurement, the wattmeter reading were 5000 and 1000 W Calculate the power and power factor if (i) Both meters reads direct   (ii) one of the meters has to be reversed
UNIT – IV
1.	Derive the expression for deflecting torque in single phase induction type meter. Show that the deflection is maximum when the phase angle between two fluxes is 90 degrees and when the disc is purely non-inductive
2.	Explain the working principle of a trivector meter
3.	Explain in detail working of maximum demand meters.
4	Explain about the Testing of A.C meters by Phantom Loading (phase shifting device in the current circuit
UNIT – V
1	Explain the construction and working principle of polar type potentiometer with a neat sketch?
2	The emf of a stranded cell is measured with a potentiometer which given a reading of 1.01892 V. When in 1MOhm resistor is connected across the stranded cell terminals, the potentiometer reading drop to 1.01874V.calculate the internal resistance of the cell
3	Explain with the help of suitable diagrams, how a D.C. potentiometer can be used for i. Calibration of voltmeter ii. Calibration of ammeter
4	State and explain the essential features of construction of one type of A.C.potentiometer with the help of neat sketch.
UNIT – VI
1.	(a) Draw the circuit of Kelvin’s double bridge used for measurement of low resistance. Derive the condition for balance
2.	(a) Explain the working of a Carey Foster slide wire bridge with a neat circuit diagram. (b) Explain the loss of charge method for the measurement of insulation resistance of the cable. (c) The four arms of a Wheatstone bridge are as follows: AB=100; BC=1000 ; CD=4000; DA=400;.The galvanometer has a resistance  of 10, a sensitivity of 100mm/micro ohm and is connected across AC. A Source of 4V DC is connected across BD. Find the current through the galvanometer  (June-2014)
3.	(a) What are the different factors which affect the precision measurement of medium resistances with Wheatstone bridge? Explain how their effects are minimized or eliminated? (b) In Wheatstone bridge the four arm resistances are as follows: AB = 1000 ; BC = 100 ; AD = 2005 ; DC =200 The battery has an emf of 5V and negligible internal resistance. The galvanometer has a current sensitivity of 10mm/µA and internal resistance of 100. Calculate the deflection of the galvanometer and the sensitivity of the bridge in terms of defection per unit change in resistance
4	A 4 terminal resistor of approximately 100_ resistance was measured by means of a Kelvin's bridge having the following component resistances. Standard resistor = 100.03 µΩ Inner ratio arms = 100.31Ω and 200Ω; Outer ratio arms = 100.24Ω and 200Ω; Resistance of link connecting the standard and the unknown resistance=700 µΩ. Calculate the unknown resistance to the nearest 0.01µΩ
UNIT – VII
1.	Draw the circuit diagram of Desauty bridge and phasor diagram under balance conditions.Derive the equations under balance conditions.
2.	Derive the equations of balance for an Anderson's bridge. Draw the phasor diagram for conditions of under balance.
3	(a) Derive the balance equation and draw the phasor diagram under balance condition for Hay’s Bridge b) The four arms of a Maxwell’s capacitance bridge at balance are: arm ab, an unknown inductance L1 ,having an inherent R1 : arm cd a capacitor of 0.5uf in parallel with a resistance of 1000 Ω; arm da, a resistance of 1000 Ω, find the values of R1and L1 and also draw the phasor diagram
4	With a neat sketch explain the principle of operation of  Schering Bridge
UNIT – VIII
1.	Derive the expression for equation of motion of a ballistic galvanometer
2	Explain working principle of  flux meter
3	Explain in detail determination of B-H Curve of a magnetic material
4.	A Flux meter is connected to a search coil having 500 turn and a mean area of 500mm3. The search coil is placed at the center of a solenoid 1meter long wound with 800 turns. When a current of 5A is reversed, there is a deflection of 25 scale division. calculate the flux linkage per scale division