(SEM V) THEORY EXAMINATION 2023-24 ELECTRONIC INSTRUMENTATION AND MEASUREMENTS

Course: B.Tech (Semester V)

Subject Code: KEC057

Subject Name: Electronic Instrumentation and Measurements

Exam Duration: 3 Hours

Maximum Marks: 100

Paper ID: 310409

Date: 19 January 2024

Total Sections: A, B, C

Instruction:
“Attempt all sections. If required, choose missing data suitably.

Paper Pattern Overview

 SECTION A — Short Questions (10 × 2 = 20 Marks)

Each question tests your concept understanding and recall.

Differentiate accuracy and precision:

Accuracy = closeness to true value.

Precision = repeatability or consistency of results.

Absolute error:

∣10.25−10.22∣=0.03Ω|10.25 - 10.22| = 0.03 \Omega∣10.25−10.22∣=0.03Ω

Advantages of digital voltmeter:

No parallax error, high resolution, automatic range, data storage.

Calibration:

Comparison of a measurement instrument with a known standard (e.g., thermometer calibration).

Kelvin Double Bridge importance:

Eliminates errors due to lead resistance; ideal for measuring low resistances (<1 Ω).

Two bridges for capacitance measurement:

Schering Bridge and De Sauty Bridge.

Deflection plates in CRO:

Vertical = amplitude; Horizontal = time sweep.

Difference between CRO and DSO:

CRO = analog, real-time; DSO = digital, stores and analyzes waveforms.

Temperature range:

Thermistor: –100°C to 300°C; Thermocouple: up to 1800°C; RTD: –200°C to 600°C.

Devices to measure flow:

Venturi meter, Orifice meter.

Tip: Write concise 2–3 line answers with correct units and examples.

SECTION B — Descriptive Questions (Any 3 × 10 = 30 Marks)

These are diagram + explanation-based questions.

PMMC Instrument (Principle & Control Torque):

Works on D’Arsonval principle — torque on a coil in magnetic field proportional to current.

Spring provides control torque, air friction provides damping.

Transistor Voltmeter:

Uses transistor amplifier for voltage measurement.

Features: high input impedance, low loading effect.

Kelvin Double Bridge:

Used for low resistance measurement; includes two sets of ratio arms (main and auxiliary).

Q-Meter:

Measures quality factor (Q) of coils and capacitors using resonance principle.

Equation:

• Q=VCV=1RLCQ = \frac{V_C}{V} = \frac{1}{R}\sqrt{\frac{L}{C}}Q=VVC​​=R1​CL​​

Thermocouple:

Works on Seebeck effect; emf generated by temperature difference between two junctions.

Draw labeled diagram showing hot and cold junctions.

SECTION C — Analytical / Long Answer (Any 1 Part from Each = 50 Marks)

Q3 (a)

Explain advantages of DC Ammeter and Voltmeter, working of DC Voltmeter with neat diagram.

Q3 (b)

Numerical:
Given parameters —
l=d=2.5 cm,B=100 mT,L=2.5 m,k=5×10−6 Nm/radl = d = 2.5 \text{ cm}, B = 100 \text{ mT}, L = 2.5 \text{ m}, k = 5 \times 10^{-6} \text{ Nm/rad}l=d=2.5 cm,B=100 mT,L=2.5 m,k=5×10−6 Nm/rad.
Calculate number of turns for 100 mm/µA current sensitivity with on-scale deflection 300 mm.

Q4 (a)

Discuss Digital Voltmeter (DVM):

Converts analog voltage into digital form.

Includes: attenuator, ADC, reference voltage, and digital display.
 

Q4 (b)

Define probes and explain current measurement using electronic instruments — Hall-effect sensors or current transformers.
 

Q5 (a)

Maxwell Bridge:
Used for measuring unknown inductance.
Balance condition:

Lx=R2R3C4L_x = R_2 R_3 C_4Lx​=R2​R3​C4​
 

Q5 (b)

Wheatstone Bridge:
For measuring unknown resistance.
Balance condition:

R1R2=R3Rx\frac{R_1}{R_2} = \frac{R_3}{R_x}R2​R1​​=Rx​R3​​ 
 

Q6 (a)

Digital Storage Oscilloscope (DSO):

Captures, digitizes, and stores signals.

Advantage over CRO: better accuracy, waveform storage, FFT analysis, and triggering capabilities.
 

Q6 (b)

Wave Analyzer & Digital Counter:

Wave Analyzer: separates and measures frequency components.

Digital Counter: counts pulses or measures time/frequency using logic circuits.
 

Q7 (a)

LVDT (Linear Variable Differential Transformer):

Converts linear displacement into voltage signal.

Used with Bourdon Tube to measure pressure.
 

Q7 (b)

Strain Gauge:

Measures mechanical strain through resistance change.

Derivation:

• ΔRR=G⋅ε\frac{\Delta R}{R} = G \cdot \varepsilonRΔR​=G⋅ε

where GGG = Gauge Factor, ε\varepsilonε = Strain.
 

Key Topics to Revise Before Exam
 

Measurement errors — absolute, relative, percentage.

PMMC, Moving Iron, and Electrodynamic Instruments.

Bridge Measurements — Wheatstone, Kelvin, Maxwell, Schering.

Q-Meter & Transistor Voltmeter.

Thermocouple, RTD, and Thermistor.

Digital Voltmeter (DVM), DSO, and frequency counters.

LVDT, Strain Gauge, and pressure sensors.

Conclusion
 

The Electronic Instrumentation and Measurements (KEC057) paper tests both conceptual clarity and analytical ability.

To score high:
 

Write crisp definitions in Section A.

Include neat, labeled diagrams in Sections B and C.
 

Derivations and formulas should be accurate and complete.
 

Mastering this subject provides practical knowledge essential for careers in testing labs, industrial automation, sensor design, and calibration engineering.