JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD
JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech III MECHANICAL MEASUREMENTS AND CONTROL SYSTEMS Previous Question Paper (August - 2022 - R18)
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Main
Explain the static and dynamic performance characteristics of measuring instruments.
Answer
Performance characteristics of measuring instruments are categorized into static and dynamic characteristics based on whether the input signal is time-invariant or time-varying.
Static Characteristics describe the performance of an instrument when measuring a constant input. Key parameters include:
- Accuracy: The closeness of the measured value to the true value.
- Precision: The ability of an instrument to reproduce a certain reading with a given degree of consistency.
- Sensitivity: The ratio of the change in output to the change in input, defined as d(Output)/d(Input).
- Linearity: The ability of the instrument to produce an output that is directly proportional to the input.
- Hysteresis: The difference in output readings for the same input when approached from increasing versus decreasing directions.
- Resolution: The smallest change in input that can be detected by the instrument.
- Threshold: The minimum input value required to produce a detectable change in output.
- Drift: A gradual change in the output over time while the input remains constant.
Dynamic Characteristics describe the performance of an instrument when the input varies rapidly with time. These are defined by the instrument's response to standard inputs like step, ramp, or sinusoidal signals:
- Fidelity: The ability of the system to reproduce the input signal faithfully without distortion.
- Speed of Response: How quickly an instrument reacts to changes in the measured variable.
- Dynamic Error: The difference between the true value of the time-varying input and the measured value at any instant.
- Lag: The time delay between the application of an input and the corresponding change in the output.
Instruments are mathematically modeled as differential equations (typically first or second order) to determine their dynamic behavior, focusing on parameters like time constant, natural frequency, and damping ratio.
Discuss the following transducers with respect to their construction, working and characteristics:
Piezo-electric
Answer
A Piezo-electric transducer operates on the principle of the piezo-electric effect, where certain crystalline materials, such as quartz, Rochelle salt, or barium titanate, generate an electric potential when subjected to mechanical stress. The construction consists of a thin slice of piezoelectric material sandwiched between two metal electrodes. When a force is applied to the crystal, the internal crystalline structure deforms, causing a displacement of charges and creating a potential difference across the electrodes proportional to the applied force.
Key characteristics include:
- Excellent high-frequency response, making them ideal for dynamic measurements like vibration and pressure transients.
- High sensitivity and high output impedance, requiring high-impedance amplifiers (charge amplifiers) for signal conditioning.
- They are self-generating (active transducers) and do not require an external power source.
- They are unsuitable for static measurements because the generated charge leaks away over time.
Capacitance
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Explain the principle, construction working of ultrasonic flow meter with neat sketch.
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Describe the construction of
Bubbler level indicator
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Ultrasonic level indicator
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Explain the construction, working and applications of vibrometer.
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Explain the construction and working principle of A.C tachometer with a neat diagram. State its advantages and limitations.
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Classify the dynamometers. Explain with a neat diagram, the working of a prony brake for estimating power.
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Explain the various elements of control system in detail.
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Enumerate the role of control system in engineering applications.
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