ME-402 Instrumentation and Control - Dec 2024 Question Paper

Under each question, How to answer lists the points an answer should cover, outlined by CampusPrep from the syllabus. Check the details against your textbook.

1. 7 Marks
   aWhat do you mean by uncertainties? Explain.
   How to answer

   • Define uncertainty as doubt about validity of measurement result
   • Distinguish from error; sources: random and systematic effects
   • Types: Type A (statistical) and Type B (non-statistical) evaluation
   • Expression of uncertainty, confidence interval concept
2. 7 Marks
   bWhat is error? Discuss the various types of error during measurement.
   How to answer

   • Define error as difference between measured and true value
   • Classify: systematic, random and gross errors
   • Discuss sources and examples of each type
   • Methods to minimize / eliminate errors
3. 7 Marks
   aThe accuracy of pressure gauge of range $1000\text{ kN/m}^2$ is stated to be $\pm 1\%$ of full scale deflection. What would be the possible readings if the pressure is $100\text{ kN/m}^2$. How these results would get modified if the error is specified as $\pm 1\%$ of true value.
   How to answer

   • Full-scale error = 7% of 1000 kN/m8 = 70 kN/m8
   • Possible readings at 100 kN/m8 = 90 to 110 kN/m8
   • For 7% of true value error = 7 kN/m8, readings 99 to 101 kN/m8
   • Explain why % full-scale gives large relative error at low readings
4. 7 Marks
   bExplain the need and standard procedure for calibration.
   How to answer

   • Define calibration and its need: accuracy, traceability, reliability
   • Standard procedure: comparison with standard, ascending/descending cycles
   • Calibration curve, corrections, frequency and documentation
   • Example of pressure/temperature instrument calibration
5. 7 Marks
   aExplain various elements of a measurement system.
   How to answer

   • Block diagram of measurement system
   • Elements: primary sensor, transducer, signal conditioner, display/recorder
   • Function of each element with example
   • Active vs passive elements concept
6. 7 Marks
   bExplain static performance characteristics with diagrams.
   How to answer

   • Define static characteristics: accuracy, precision, sensitivity, linearity, hysteresis etc.
   • Explain each with input-output diagrams
   • Diagrams for linearity, hysteresis, threshold, dead zone
   • Importance in instrument selection
7. 7 Marks
   aExplain briefly about harmonic signal and non harmonic signal system?
   How to answer

   • Define harmonic signal: sinusoidal, single frequency
   • Define non-harmonic/complex signal: superposition, Fourier concept
   • Examples and waveforms for each
   • Relevance to measurement system analysis
8. 7 Marks
   bDescribe briefly about first and second order in measurement system with suitable examples.
   How to answer

   • First-order system: governing equation, time constant, thermometer example
   • Second-order system: mass-spring-damper equation, natural frequency, damping ratio
   • Step response characteristics of each
   • Suitable measurement examples
9. 7 Marks
   aWhat do you mean by manometer? Discuss the construction, working and application of U-tube manometer.
   How to answer

   • Define manometer for pressure measurement
   • U-tube construction: U-tube, manometric fluid, scale
   • Working: hydrostatic balance $p = \rho g h$, diagram
   • Applications: differential, vacuum, low pressure measurement
10. 7 Marks
    bDiscuss on the following:

    1. i)Thermistor
    2. ii)Bi-metallic strip
    How to answer

    • Thermistor: semiconductor principle, resistance-temperature relation, types and uses
    • Bi-metallic strip: differential expansion principle, bending action
    • Construction diagrams for both
    • Temperature measurement and control applications
11. 7 Marks
    aWhat does a venturimeter measure? Discuss the working principle of venturimeter with neat diagram.
    How to answer

    • Venturimeter measures flow rate / discharge
    • Principle: Bernoulli + continuity, pressure drop at throat
    • Construction diagram: convergent, throat, divergent sections with manometer
    • Discharge formula and applications
12. 7 Marks
    bDefine Orifice meter. Discuss the working principle of Orifice meter with neat diagram.
    How to answer

    • Define orifice meter as obstruction-type flow meter
    • Principle: pressure difference across orifice plate
    • Neat diagram: pipe, orifice plate, pressure taps, manometer
    • Formula, advantages, limitations vs venturimeter
13. 7 Marks
    aList the procedure to mount a strain gauge with paper backing on the surface under study.
    How to answer

    • Surface preparation: cleaning, smoothing, degreasing
    • Steps: marking, adhesive application, gauge placement, curing, wiring
    • Precautions for bonding paper-backed gauge
    • Curing and protection of installation
14. 7 Marks
    bExplain the method of usage of resistance strain gauge for bending compressive and tensile strains.
    How to answer

    • Resistance strain gauge principle: $\Delta R/R = G_f \epsilon$
    • Bridge arrangement for bending: gauges on top and bottom for tensile/compressive strain
    • Separation of bending and axial effects
    • Temperature compensation concept
15. 7 Marks
    aA $150\text{ Ohm}$ strain gauge is bonded to a steel bar which is subjected to a tensile load. Cross-sectional area of the bar is $0.5 \times 10^{-4} \text{m}^2$ and Young's modulus for the bar material is $200\text{ GN/m}^2$. If a load of $60\text{ kN}$ produces a change of $1.5\text{ Ohm}$ in the gauge resistance, determine the gauge factor of the gauge.
    How to answer

    • Stress $\sigma = P/A$, strain $\epsilon = \sigma/E$
    • Strain $\epsilon = 60000/(0.5\times10^{-4}\times200\times10^9)=0.006$
    • Gauge factor $G_f = (\Delta R/R)/\epsilon = (1.5/150)/0.006$
    • Result $G_f \approx 1.67$
16. 7 Marks
    bExplain the open loop and closed loop control system with suitable diagram.
    How to answer

    • Define open-loop: no feedback, e.g., washing machine; block diagram
    • Define closed-loop: feedback, error detector, e.g., temperature control
    • Block diagrams for both systems
    • Comparison: accuracy, stability, cost, complexity