THEORY EXAMINATION (SEM–IV) 2016-17 MEASUREMENT AND METROLOGY

Course: B.Tech (Mechanical Engineering)
Subject Code: EME403
Subject Title: Measurement and Metrology
Exam Type: Theory
Duration: 3 Hours
Maximum Marks: 100

SECTION – A (10 × 2 = 20 Marks)

Short, direct questions to test conceptual clarity

SECTION – B (5 × 10 = 50 Marks)

Conceptual and descriptive questions focusing on measurement principles

(a) Generalized Measuring System

Components:

Primary Sensing Element – detects input (e.g., pressure diaphragm).

Transducer Element – converts signal to electrical form.

Signal Conditioning – amplifies or filters.

Output Device – indicates, records, or controls.

(b) Types of Errors in Measurement

Systematic Errors: calibration, environmental, observational.

Random Errors: unpredictable, due to small uncontrollable factors.

Gross Errors: human mistakes in observation or computation.

(c) Sigma Comparator

Construction: Plunger, mechanical linkage, amplifying lever, and dial indicator.

Working: Converts small linear displacement into amplified pointer movement.

Use: For high-precision comparison of parts within micron range.

(d) AC Laser Interferometer

Principle: Interference of light waves — measures distance, flatness, and straightness.

Working: Laser beam split into two paths; phase difference between reflected beams indicates displacement or misalignment.

Advantage: Extremely high accuracy (up to nanometer level).

(e) Roundness Measurement

V-Block Method: Workpiece rotated in a V-groove; deviations indicate roundness error.

Three-Point Probe: Measures eccentricity and form error more accurately.

Limitation of V-Block: Not suitable for non-circular deviations and large eccentricities.

(f) Pitch Measurement (Threads)

Pitch Measuring Machine: Uses microscope, micrometer heads, and optical systems to measure lead, pitch, and angle of threads.

Applicable for: Internal and external threads.

(g) LVDT (Linear Variable Differential Transformer)

Construction: Primary coil and two secondary coils with movable soft iron core.

Principle: Differential voltage induced in secondary coils corresponds to displacement.

Advantages: High accuracy, frictionless operation, infinite resolution.

(h) Taylor’s Principle of Gauge Design

“A GO gauge should check maximum material condition; a NO-GO gauge should check minimum material condition.”

Types:

Ring Gauge: For external diameter checks.

Plug Gauge: For internal hole measurements.

SECTION – C (2 × 15 = 30 Marks)

Application-based and analytical questions

Q3. (i) Thermocouples

Principle: Seebeck effect — EMF generated between two dissimilar metals when temperature difference exists.

Types: Iron–Constantan, Copper–Constantan, Chromel–Alumel.

Applications: Temperature measurement in furnaces, engines, etc.

(ii) Strain Gauge Torque Meter

Measures torque through strain produced in shaft surface.

Wheatstone bridge detects resistance change in strain gauges → calibrated for torque.

Q4. Pressure Measurement

(i) Piezo-Electric Pressure Transducer

Quartz crystal generates charge proportional to applied pressure.

Advantage: High frequency response, suitable for dynamic pressures.

(ii) Variable Capacitance Transducer

Pressure changes plate spacing or dielectric → capacitance change.

Used for: Low pressure, high-sensitivity measurement.

Q5. Linear & Angular Measurement

(i) Vernier Caliper

Used for internal, external, and depth measurements.

Principle: Difference between main and vernier scale readings gives precision (0.02 mm typical).

(ii) Limitation of Sine Bar

Not suitable for angles >15° due to cosine error, limited roller accuracy, and setup instability.

Summary

This Measurement and Metrology (EME403) paper thoroughly tests:

Principles of precision measurement

Instrument operation (comparators, transducers, interferometers)

Error analysis and tolerance design

Linear, angular, and surface measurement

Modern metrological tools (laser, strain gauge, LVDT)