JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD
JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech III Year MEASUREMENTS AND INSTRUMENTATION Previous Question Paper (January/February - 2023 - R18)
Note: i) Question paper consists of Part A, Part B. ii) Part A is compulsory, which carries 25 marks. In Part A, Answer all questions. iii) In Part B, Answer any one question from each unit. Each question carries 10 marks and may have a, b as sub questions.
Part A
Define controlling torque and deflecting torque.
Answer
Deflecting torque is the force produced by the electrical quantity being measured that causes the moving system of an instrument to deflect from its zero position. Controlling torque is the opposing force produced by a spring or gravity that acts in the opposite direction to the deflecting torque, ensuring the pointer comes to rest at a position where the two torques are equal and proportional to the measured quantity.
Draw sketches for range extension of ammeter and voltmeter.
Answer
The range of an ammeter is extended by connecting a low resistance, known as a shunt resistor (Rsh), in parallel with the meter movement. This allows the majority of the current to bypass the meter, protecting it while measuring higher total currents.
where Rm is the internal resistance of the meter and m is the multiplying factor (total current / full-scale current).
The range of a voltmeter is extended by connecting a high resistance, known as a multiplier resistor (Rs), in series with the meter movement. This limits the current through the meter to its full-scale deflection value even when measuring higher voltages.
where m is the multiplying factor (total voltage / full-scale voltage).
What are instrument transformers? What are their uses?
Answer
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Define ratio error and phase angle error in potential transformer.
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What is tri-vector meter? What are its applications?
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Define driving and braking torques of induction type energy meter.
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State the conditions for AC bridge balancing.
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Draw the circuit diagram for H. V. Schering Bridge and write its uses.
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What are true RMS meters and what are their applications?
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Write the working principle of strain gauge and define its gauge factor.
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Part B
Explain the principle and working of PMMC type instruments and derive the expressions for its deflecting and controlling torque.
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Explain with a neat sketch the working of attracting disc type electrostatic volt meter and describe the range extension of E.S. Volt meter.
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Explain the principle and working of electrometer type volt meter and describe their range extension.
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A deflecting electrostatic voltmeter gives full scale deflection of 40 degrees with 9V applied to its terminals. Its capacitance is 10pF at zero deflection and 30 pF at 30 degrees and varies uniformly with deflection. The moment of inertia of moving vanes is 0.02×10-6 kg/m2. Calculate the undamped period of instrument.
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Describe the principle and operation of D. C. Crompton’s potentiometer with a neat diagram and explain how unknown resistance and voltage is measured using it.
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Derive the expressions for the phase angle errors of a current transformer with a neat phasor diagram.
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Explain the principle and working of A.C. Potentiometer with a neat diagram and describe its standardization.
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Explain the construction, principle and working of current transformer. Explain the Wilson compensation method for reduction of errors in current transformers.
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Explain the construction, principle and operation of single phase three element electro dynamometer type watt meter and derive its torque equation.
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If the reactance of the pressure coil circuit of a watt meter is 1 percent of its resistance, calculate the percentage error due to this cause at power factors of 0.8, 0.5 and 0.1 respectively.
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Explain with neat sketches the measurement of active and reactive powers in balanced and unbalanced systems.
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Explain the extension of ranges of watt meters using instrument transformers with help of neat diagrams.
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Draw the neat sketch of Kelvin’s double bridge for measurement of low resistance and describe it’s working.
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Explain with a neat circuit the working of Wein’s bridge for measurement of capacitance and frequency of the supply voltage and derive the expression for unknown capacitance and frequency.
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Describe the working of Maxwell’s inductance capacitance bridge for measurement of unknown inductance and derive the expression for its balance condition. Draw its phasor diagram.
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Explain with neat diagram for measurement of capacitance and loss angle using Desauty’s Bridge.
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Explain the classification of transducers with examples and discuss the general characteristics of transducers.
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Describe with a neat sketch the principle and working of piezoelectric accelerometer and derive the expression for its output.
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Explain the construction, working principle and applications of capacitive transducers.
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Explain the methods of measurement of torque on rotating shafts using strain gauges with help of neat sketches.
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