[Total No. of Printed Pages—4 Total No. of Questions—12] -154 S.E. (Electrical) (First Sem.) EXAMINATION, 2010 ELECTRICAL MEASUREMENTS AND INSTRUMENTATION (2008 COURSE) Time : Three Hours N.B. :— Maximum Marks : 100 (i) Answer any three questions from each Section. (ii) Answers to the two Sections should be written in separate answer-books. (iii) Neat diagrams must be drawn wherever necessary. (iv) Figures to the right indicate full marks. (v) Use of logarithmic tables, slide rule, Mollier charts, electronic pocket calculator and steam tables is allowed. (vi) Assume suitable data, if necessary. SECTION I 1. (a) What is meant by static and dynamic characteristics of measuring instruments ? Explain : Accuracy, resolution, drift. (b)  Describe construction and working of PMMC instrument with suitable diagram. Derive its torque equation with usual notations.  Or 2. (a) Give detailed classification of measuring instruments. Elaborate each type in brief.  (b) (i) The inductance of moving iron ammeter with a full scale deflection of 90º at 1.5 amp is given by the expression L = 180 + 40 θ – 4θ2 – θ3 µH, where θ is deflection in radian from zero position. Calculate spring constant.  (ii) With a neat sketch, explain construction and working of moving iron instrument. What are the advantages of this instrument ?  -154 1 P.T.O.
3. (a) Give classification of resistance. Give suitable method of measurement for each category. (b)  What are the different detectors used in a.c. bridges ? Elaborate each type in brief. Derive the general equation for bridge balance. (c)  A length of cable is tested for insulation resistance by loss of charge method. An electrostatic voltmeter of infinite resistance is connected between cable conductor and earth forming a joint capacitance of 750 pF. It is observed that after charging, the voltage falls from 250 volt to 92 volt in 1 minute. Calculate the insulation resistance of cable.  Or 4. (a) Draw circuit diagram of Kelvin’s double bridge. Derive expression for unknown resistance with usual notations. (b)  With a circuit diagram derive the equation for unknown capacitance measurement using Schering bridge. (c)  The arms of Anderson’s bridge are as follows : arm AB : Unknown impedance with R1, L1 in series with variable resistor r1 arm BC : Pure resistance R3 = 100 W arm CD : Pure resistance R4 = 200 W arm DA : Pure resistance R2 = 250 W arm DE : Variable pure resistance r arm EC : A loss free capacitor C = 1 µF arm BE : A detector. a.c. supply is connected between terminal A and C. Calculate resistance and inductance R1, L1, if 229.7 W under balance condition. -154 2 r1 = 43.1 W and r = 
5. (a) State and explain errors in dynamometer type wattmeter. Also state the compensation for each type of error.  (b) Two wattmeter method is used to measure power of three phase star connected lamp bank at balanced load condition. The phase voltage is 200 / 3 volt and line current is 5.5 amp. What will be the reading of each wattmeter ? If now load is connected in delta across same supply, what will be the reading of each wattmeter ?  (c) Draw block diagram of multimeter.  Or 6. (a) With a block diagram explain working of digital frequency meter.  (b) With circuit diagram and phasor diagram explain one wattmeter method for measurement of reactive power in (R + L) load.  (c) Write a short note on LPF type wattmeter.  SECTION II 7. (a) Explain two element energy meter with neat diagram. (b) An energy meter is designed to make 3200 impulses of LED for one unit of energy. Calculate the no. of impulses made by it when connected to a load carrying 20A, 230V, 0.8 p.f. for an hour. If it actually makes 12000 impulses, find the % error.  (c) Define the following terms associated with instrument transformer : (i) Transformation ratio (ii) Turns ratio (iii) Nominal ratio.   Or 8. (a) -154 Explain construction and operation of single phase induction type energy meter with neat diagram. Derive torque equation.  3 P.T.O.
(b) 9. A 230 V, single phase energy meter is connected to a constant load of 6 A, unity power factor for 8 hours. (i) If the impulses made during this are 35328, what is meter constant in imp/kWh. (ii) Calculate the power factor of load if no. of impulses made by LED are 31795 when operating at 230 V, 9A for 6 hours.  (a) What are different selection factors for selecting transducers.  (b) In an experiment, the voltage across 5 kW resistor is applied to C.R.O. The screen shows a sinusoidal signal of total vertical occupancy 4 cm and total horizontal occupancy of 2 cm. The front panel controls volts/div and time/div are on 5 V/div and 5 ms/div respectively. Calculate the maximum, rms values of voltage across resistance and current through resistance. Also find its frequency.  (c) Explain Pirani guage for measurement of low pressure. Also state advantages and disadvantages.  Or 10. 11. (a) What are the advantages of electric transducer ? (b) Explain the following terms associated with CRO : (i) Volts/division (ii) X10 (iii) Invert.   (c) Explain different characteristics of transducer.  (a) Explain ultrasonic flowmeter with neat diagram.  (b) Explain construction and working of LVDT with neat diagram.  Or 12. (a) Explain hydraulic method for measurement of level.  (b) Explain foil strain guage.  -154 4