JNTU
JNTU B.Tech III INSTRUMENTATION AND PROCESS CONTROL Previous Question Paper (May - 2018 - R15)
Note: This question paper contains two parts A and B. Part A is compulsory which carries 25 marks. Answer all questions in Part A. Part B consists of 5 Units. Answer any one full question from each unit.
Part A
What is time constant for a first order type instrument?
Answer
The time constant of a first-order instrument is defined as the time required for the output to reach approximately 63.2% of its total change following a step input. It is a measure of the speed of response of the instrument and is represented by the symbol τ (tau). Mathematically, for a first-order system with transfer function G(s) = K / (τs + 1), it represents the ratio of the system's capacitance to its resistance.
Define reproducibility and sensitivity of an instrument.
Answer
Reproducibility is the degree of closeness between a number of measurements of the same input value made under the same operating conditions over a period of time. It indicates the ability of an instrument to repeatedly provide the same output for a given input.
Sensitivity is defined as the ratio of the change in output of the instrument to the corresponding change in the input being measured. It is expressed as:
A higher sensitivity indicates that the instrument produces a larger output change for a small input variation, making it more responsive to changes in the measured variable.
What is thermocouple? Mention its uses.
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Write about the working principle and applications of emission spectrometer.
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What are the types of liquid column manometers?
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Write notes about hydrometer specific gravity meter.
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What is servomechanism-type problem?
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Define transportation lag. Write the transfer function for a process containing transportation lag.
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What are Bode diagrams? Mention its uses.
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For a process the transfer function is given by G(s) = 1/(20s+1). Find the amplitude ratio and phase angle.
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Part B
Explain the classification of instruments according to their: source of power and method of arrangement.
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Discuss the dynamic response of first order type instrument to a linear change.
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With a neat sketch, explain the construction and mechanical operations of industrial pressure – spring thermometer.
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Write the working principle of bimetallic thermometer.
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Discuss the characteristics and useful range of: Iron – Constantan thermocouple and Chromel – Alumel thermocouple.
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Explain the protection of thermocouple materials by thermal wells.
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What are the mechanical properties which must be considered in the selection of a thermal well?
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With a schematic diagram, explain the analysis of hydrocarbons and gases from petroleum refining industries by Infra – red absorption spectrometers.
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Explain the relationship between: (i) gauge pressure, absolute pressure and atmospheric pressure and (ii) liquid head and pressure.
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Discuss the mechanism of the following indicating elements for pressure gauges: pressure tight bearing shaft system and Inductance coil system.
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Discuss the measurement of fluid velocity by pitot tube with neat sketch.
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Explain the liquid flow measurement using rectangular – notch weir.
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A thermometer having a time constant of 0.1 min is at a steady-state temperature of 90°F. At time t = 0, the thermometer is placed in a temperature bath maintained at 100°F. Determine the time needed for the thermometer to read 98°F.
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For the Step response of a second-order system, explain the nature of roots and description of response if the damping ratio (ζ) is having the following values: ζ < 1, ζ = 1 and ζ > 1.
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Draw the block diagram of a simple control system and explain the functions of components present in it.
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Explain the response of a Proportional – Integral (PI) controller to a unit-step change in error.
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For the multi loop control system, determine the transfer function (C/R) for the system and reduce the multi block diagram into a single block diagram.
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What is root locus diagram? Explain its applications.
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Describe the stability criteria of a control system using gain margin and phase margin.
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Define Bode stability criterion. Mention its significance.
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