JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD
JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech II Year TRANSDUCERS AND INSTRUMENTATION Previous Question Paper (July/August - 2021 - R13)
Answer any Five Questions. All Questions Carry Equal Marks.
Main
What are the important performance features of the gyroscope, which lend themselves for application for measurement of angular displacement and torque?
Answer
A gyroscope is a device based on the principle of conservation of angular momentum, consisting of a rotor spinning at high speed about an axis. Its performance features that make it suitable for measuring angular displacement and torque include:
- Gyroscopic Inertia (Rigidity in Space): A spinning rotor maintains its orientation in inertial space regardless of the motion of its support frame. This property allows it to serve as a stable reference for measuring angular displacement relative to an initial orientation.
- Precession: When an external torque is applied to the spinning rotor about an axis perpendicular to the spin axis, the gyroscope responds by rotating about a third axis, known as the precession axis. The angular velocity of this precession is directly proportional to the applied torque, which is the fundamental principle used in gyroscopic torque sensors.
- Sensitivity to Angular Motion: Gyroscopes exhibit high sensitivity to small angular changes. By measuring the precession rate or the displacement of the gimbal assembly, one can precisely quantify angular velocity or displacement.
- Dynamic Response: Gyroscopes provide a rapid response to changes in orientation or applied torque, making them ideal for real-time measurement systems in navigation and control.
For angular displacement measurement, the gyroscope is typically configured as a directional gyro where the orientation of the spin axis is tracked relative to a fixed frame. For torque measurement, the device acts as a rate gyro where the magnitude of the precession torque or the precession angle is measured against a calibrated spring or transducer, providing a direct reading of the input torque.
Explain principle, operation of piezo electric transducers.
Answer
The piezoelectric effect is the phenomenon where certain crystalline materials, such as quartz, Rochelle salt, or polarized ceramics like barium titanate, generate an electric charge when subjected to mechanical stress. Conversely, they undergo mechanical deformation when an electric field is applied.
The operation is based on the displacement of internal charges within the crystal lattice. When a mechanical force is applied along the sensitive axis, the internal dipoles are displaced, resulting in a net charge accumulation on the crystal surfaces. The magnitude of the generated charge Q is directly proportional to the applied force F:
where d is the piezoelectric charge constant (C/N). The voltage V generated across the crystal is given by:
where g is the voltage sensitivity constant, t is the thickness of the crystal, and P is the applied pressure. These transducers are primarily used for dynamic measurements, such as vibration, pressure pulses, and acceleration, because the charge leaks away under static conditions due to finite insulation resistance.
Describe any one velocity sensor.
Answer
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Explain the working of strain gauge type of torque transducers. Explain its advantages and disadvantages.
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Describe the operating principles of bonded strain guage.
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Explain any one force measuring device functionality.
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How is the current range of a PMMC instrument extended with the help of shunt? Describe a method of reducing errors due to temperature changes in the shunt connected instruments.
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Explain why Maxwell’s inductance-capacitance bridge is useful for measurement of inductance of coil having storage factor between 1 and 10.
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What is the working principal of electrolytic-type hygrometer.
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Explain the different modes of operations of frequency synthesizer.
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Describe the different types of channels used for telemetry. Explain its advantages and disadvantages.
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