EX-604-A Electronic Instrumentation - May 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
   aDraw a block diagram of general purpose CRO and explain the function of each block. Write at least four applications of CRO.
   How to answer

   • Block diagram: CRT, vertical amplifier, delay line, time base, horizontal amplifier, trigger circuit, power supply
   • Function of each block
   • Applications: voltage, frequency, phase measurement, waveform display
2. 7 Marks
   bElaborate the principle and working of dual beam and dual trace oscilloscope with neat sketch.
   How to answer

   • Dual beam: two electron guns, independent deflection
   • Dual trace: single beam, electronic switch, alternate and chop modes
   • Block diagrams of both
   • Comparison
3. 7 Marks
   aDraw a circuit diagram for Maxwell's inductance-capacitance bridge. Derive the expression for measurement of unknown parameters. Also discuss its merits and demerits.
   How to answer

   • Circuit with unknown $L_1, R_1$, standard $C_4 \parallel R_4$, resistances $R_2, R_3$
   • Balance: $(R_1 + j\omega L_1)\frac{R_4}{1 + j\omega C_4 R_4} = R_2 R_3$
   • Separate real and imaginary parts
   • Merits: frequency independent, Q up to 10; demerits: unsuited for high Q, variable standard capacitor
4. 7 Marks
   bA capacitor is tested by a Schering Bridge which forms one arm AB of the bridge. The other arms are AD - a non-inductive resistance of $100\,\Omega$, DC a non-reactive resistance of $300\,\Omega$ in parallel with a capacitor of $0.5\,\mu F$, BC - a standard loss free capacitor of $100\,pF$, the supply frequency is 50 Hz. The bridge is balanced. Calculate the capacitor value and power factor of the capacitor under test.
   How to answer

   • Schering bridge balance equations
   • $C_1 = C_2 R_4 / R_3 = 300\,pF$
   • $r_1 = R_3 C_4 / C_2$
   • Dissipation factor $\omega C_1 r_1$, power factor
5. 7 Marks
   aDefine strain gauge. Compare the gauge factor and temperature sensitivity of metal and semiconductor resistance strain gauge.
   How to answer

   • Definition and principle $GF = \frac{\Delta R / R}{\epsilon}$
   • Metal: GF about 2, low temperature sensitivity, linear
   • Semiconductor: GF 100-200, high temperature sensitivity, nonlinear
   • Comparison table
6. 7 Marks
   bA resistance strain gauge with a gauge factor of 2 is cemented to a steel member, which is subjected to a strain of $1 \times 10^{-6}$. If the original resistance value of the gauge is $130\,\Omega$, calculate % change in resistance.
   How to answer

   • $\Delta R/R = 2 \times 10^{-6}$
   • Percentage change $2 \times 10^{-4}\%$
   • $\Delta R = 2.6 \times 10^{-4}\,\Omega$
7. OR Choice

   7 Marks
   bA piezo quartz crystal has the dimensions $2\,mm \times 2\,mm \times 1\,mm$. Quartz has the following properties: charge sensitivity = 21 C/N, Young's modulus = $86 \times 10^{10}\,N/m^2$, Permittivity = $40.6 \times 10^{-12}\,F/m$. Calculate the value of force, charge and voltage if the crystal is subjected to a strain of $10 \times 10^{-6}$ m/m.
   How to answer

   • Stress = E x strain; force = stress x area (2 mm x 2 mm)
   • Charge = charge sensitivity x force
   • Voltage = Q t / (epsilon A) with t = 1 mm
   • State units
8. 7 Marks
   aWhat is signal generator? Draw the block diagram of a function generator and explain the method of producing sine wave.
   How to answer

   • Definition and types of signal generators
   • Function generator block diagram: constant current sources, integrator, comparator, resistance-diode shaping network
   • Sine from triangle by diode shaping
9. 7 Marks
   bWhat do you mean by spectrum analysis? Draw the block diagram of spectrum analyser.
   How to answer

   • Frequency domain representation of a signal
   • Swept-tuned superheterodyne spectrum analyser block diagram
   • Explanation of sweep, mixer, IF filter, detector, display
10. 7 Marks
    aState the advantages of a DVM. With the help of diagram explain the operating principle of ramp type DVM.
    How to answer

    • Advantages: accuracy, resolution, no parallax, output for data logging
    • Ramp DVM block diagram: ramp generator, input and ground comparators, gate, counter, clock
    • Timing diagram and counting principle
11. 7 Marks
    bA 3½ digit voltmeter is used for voltage measurement.

    1. i)Find its resolution
    2. ii)How would 11.52 V be displayed on the 10 V range?
    3. iii)How would 0.5234 V be displayed on 1 V and 10 V ranges?
    How to answer

    • Resolution = 1/1000 = 0.001
    • 10 V range: max 19.99 V so 11.52 displayed as 11.52
    • 1 V range: 0.523; 10 V range: 0.52
12. 3 Marks
    aDescribe the different types of graticules used in CRO.
    How to answer

    • External, internal and projected graticules
    • Parallax error with external graticule
    • Typical 8 x 10 division grid
13. 4 Marks
    bA Lissajous pattern on an oscilloscope is stationary and has 5 horizontal tangencies and 2 vertical tangencies. The frequency of horizontal input is 1000 Hz. Find the frequency of vertical input.
    How to answer

    • $f_v = f_h \times 5/2 = 2500$ Hz
14. 7 Marks
    cList the applications of sampling oscilloscope and what precautions must be taken when using a sampling oscilloscope?
    How to answer

    • Applications: very high frequency repetitive signals, GHz range, pulse rise-time
    • Precautions: signal must be repetitive, input amplitude limits, triggering, avoid aliasing
15. 7 Marks
    aExplain the construction and working of LVDT with the help of a neat diagram. Draw the input-output characteristics of LVDT. Mention its advantages and limitations.
    How to answer

    • Construction: primary, two secondaries in series opposition, movable core
    • Working and null position
    • Output vs displacement characteristic with residual voltage
    • Advantages and limitations
16. 7 Marks
    bList the various types of temperature transducers and describe the applications based on measurement range.
    How to answer

    • RTD, thermistor, thermocouple, semiconductor sensor, radiation pyrometer
    • Range and typical application of each
    • Selection table
17. 7 Marks
    aBriefly discuss the use of LED and LCD as display devices in instrumentation. Comment on their relative merits and demerits.
    How to answer

    • LED: emissive, seven segment, high brightness, higher power
    • LCD: non-emissive, low power, needs backlight, slower at low temperature
    • Merits and demerits table
18. 7 Marks
    bWhat do you understand by digital meter? Explain the working principle and operation of a digital frequency meter.
    How to answer

    • Digital meter: numeric readout via counting
    • Frequency meter: input amplifier/Schmitt trigger, gate opened for known time by time base, counter, display
    • Counting principle and accuracy