Electronic Measurements & Instruments (4331102) - Winter 2024 Solution

Question 1(a) [3 marks]

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Define following term: (1) Accuracy (2) Resolution (3) Error

Answer:

Mnemonic: “ARE precise: Accuracy shows Reality, Error shows deviation, Resolution shows detail.”

Question 1(b) [4 marks]

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Explain construction of unbounded strain gauge transducer with necessary diagram in detail. Also list application of it.

Answer:

An unbounded strain gauge consists of a fine wire wound in a grid pattern attached to a backing material.

graph TD
    A[Backing Material] --- B[Fine Wire Grid]
    B --- C[Lead Wires]
    C --- D[Electrical Connections]
    style B fill:#f9f,stroke:#333,stroke-width:2px

• Construction elements: Fine resistance wire is looped back and forth on an insulating base material
• Working principle: Changes resistance when subjected to strain
• Applications: Weight measurement, pressure sensors, force sensors, structural health monitoring

Mnemonic: “WIRE Flexes: Wire grids Indicate Resistance changes from External stress.”

Question 1(c) [7 marks]

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Explain working of Schering Bridge with circuit diagram for balance condition. List its advantages, disadvantages and applications.

Answer:

Schering Bridge is an AC bridge used to measure unknown capacitance and its dissipation factor.

graph TD
    A[R1] --- B[R2]
    B --- C[C2]
    C --- D[Cx]
    D --- A
    E[AC Source] --- A
    E --- C
    F[Detector] --- B
    F --- D
    style Cx fill:#f9f,stroke:#333,stroke-width:2px

Balance condition:

Advantages:

• High accuracy
• Direct reading of capacitance
• Wide measurement range

Disadvantages:

• Requires careful shielding
• Frequency dependent errors
• Complex to balance

Applications:

• Capacitor testing
• Insulation testing
• Dielectric material evaluation

Mnemonic: “SCUBA dive: Schering Calculates Unknown capacitance By Advanced circuit Designs In Various Equipment.”

Question 1(c OR) [7 marks]

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Explain working of Maxwell’s bridge with circuit diagram for balance condition. List its advantages, disadvantages, and applications.

Answer:

Maxwell’s bridge is used to measure unknown inductance in terms of known capacitance.

graph TD
    A[R1] --- B[R2]
    B --- C[R3]
    C --- D[Lx + Rx]
    D --- A
    E[AC Source] --- A
    E --- C
    F[Detector] --- B
    F --- D
    G[C4] --- B
    G --- C
    style G fill:#f9f,stroke:#333,stroke-width:2px
    style D fill:#bbf,stroke:#333,stroke-width:2px

Balance condition:

Advantages:

• Independent of frequency
• High accuracy for medium Q coils
• Easy to balance

Disadvantages:

• Not suitable for low Q coils
• Requires standard capacitor
• Limited range

Applications:

• Measuring inductors
• Audio frequency measurements
• Transformer testing

Mnemonic: “MAGIC bridge: Maxwell Analyses Great Inductors by Comparing bridge Elements.”

Question 2(a) [3 marks]

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Explain working of electronic multimeter with necessary diagram.

Answer:

Electronic multimeter converts various electrical parameters into proportional DC voltage for measurement.

graph LR
    A[Input Selection] --> B[Attenuator/Range Selector]
    B --> C[Converter Circuit]
    C --> D[Amplifier]
    D --> E[ADC]
    E --> F[Display]
    style E fill:#f9f,stroke:#333,stroke-width:2px

• Circuit elements: Input selector → Attenuator → Converter → Amplifier → ADC → Display
• Measurement types: DC voltage, AC voltage, Current, Resistance
• Power source: Battery powered for portability and safety

Mnemonic: “SACRED device: Signal Attenuated, Converted And Rectified for Electronic Display.”

Question 2(b) [4 marks]

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Differentiate between Digital Voltmeter over Analog Voltmeter.

Answer:

Mnemonic: “PARIOS: Parallax-free, Accurate, Resolution high, Impedance high, Observation digital, Sampling rate.”

Question 2(c) [7 marks]

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Describe construction diagram of Energy meter and explain in detail.

Answer:

Energy meter measures electrical energy consumption over time in kilowatt-hours (kWh).

graph TD
    A[Voltage Coil] --> B[Current Coil]
    B --> C[Aluminum Disc]
    C --> D[Mechanical Counter]
    E[Permanent Magnet] --> C
    F[Braking System] --> C
    G[Load Terminals] --> B
    style C fill:#f9f,stroke:#333,stroke-width:2px

Components:

• Voltage coil: Creates flux proportional to voltage
• Current coil: Creates flux proportional to current
• Aluminum disc: Rotates due to eddy currents
• Counting mechanism: Registers disc rotations
• Permanent magnet: Acts as brake to control disc speed
• Adjustment systems: For calibration and accuracy

Working principle: Disc rotation speed is proportional to power consumption (V×I×cosΦ)

Mnemonic: “VADCR meter: Voltage And current Drive Counter through Rotations.”

Question 2(a OR) [3 marks]

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Explain working of clamp on Ammeter with necessary diagram.

Answer:

Clamp-on ammeter measures current without breaking the circuit by using electromagnetic induction.

• Construction: Split ferrite core with sensing coil
• Working principle: Current-carrying wire creates magnetic field → induces voltage in sensing coil
• Advantages: Non-contact measurement, quick, safe

Mnemonic: “CICS: Clamping Induces Current Signal.”

Question 2(b OR) [4 marks]

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Differentiate between PMMC type Meter over Moving iron type Meter.

Answer:

Mnemonic: “PMMC is DAUPHIN: DC only, Accurate, Uniform scale, Power efficient, High sensitivity, Independent of frequency, Needs polarity.”

Question 2(c OR) [7 marks]

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Draw the block diagram and Explain working of Integrating type DVM with necessary diagram and waveform.

Answer:

Integrating type DVM converts input voltage to time through integration for high accuracy measurements.

graph LR
    A[Input Buffer] --> B[Integrator]
    B --> C[Comparator]
    C --> D[Control Logic]
    D --> E[Clock]
    D --> F[Counter]
    F --> G[Display]
    D -->|Reset| B
    style B fill:#f9f,stroke:#333,stroke-width:2px

Working principle:

• Input voltage is integrated for fixed time period
• Integrator output ramps up proportionally to input
• Reference voltage with opposite polarity discharges integrator
• Time taken for discharge is measured by counting clock pulses
• Count is proportional to input voltage

Waveforms:

Advantages:

• High noise rejection
• Good accuracy
• Excellent resolution
• Rejects common-mode noise

Mnemonic: “DIRT meter: Direct Integration Relates Time to measure voltage.”

Question 3(a) [3 marks]

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Differentiate between CRO over DSO.

Answer:

Mnemonic: “PASSED: Processing-Analog/digital, Storage-none/yes, Signal-raw/processed, Easy-basic/advanced, Display-phosphor/digital.”

Question 3(b) [4 marks]

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Explain CRO Screen.

Answer:

CRO screen displays electrical signals and consists of several important elements.

Components:

• Phosphor coating: Emits light when struck by electrons
• Graticule: Grid lines for measurement reference
• Scales: Calibrated markings for voltage/time
• Center reference point: (0,0) coordinate
• Intensity control: Adjusts brightness of display

Mnemonic: “PGSCR: Phosphor Glows when Struck, Creating Representation.”

Question 3(c) [7 marks]

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Explain Block diagram, working and advantage of CRO with necessary diagram.

Answer:

CRO (Cathode Ray Oscilloscope) visualizes electrical signals as waveforms.

graph LR
    A[Vertical Input] --> B[Vertical Attenuator]
    B --> C[Vertical Amplifier]
    C --> D[Vertical Deflection Plates]
    E[Trigger Circuit] --> F[Time Base Generator]
    F --> G[Horizontal Amplifier]
    G --> H[Horizontal Deflection Plates]
    I[Power Supply] --> J[Electron Gun]
    J --> K[CRT]
    D --> K
    H --> K
    I --> B
    I --> C
    I --> E
    I --> F
    I --> G
    style K fill:#f9f,stroke:#333,stroke-width:2px

Working principle:

• Electron gun: Generates electron beam
• Vertical system: Controls Y-axis deflection proportional to input signal
• Horizontal system: Sweeps beam across screen at constant rate
• Trigger circuit: Synchronizes horizontal sweep with input signal
• CRT: Displays electron beam movement on phosphor screen

Advantages:

• Real-time signal display
• Wide bandwidth
• High input impedance
• Versatile triggering options
• Multiple signal analysis

Mnemonic: “EARTH view: Electron beam Amplification Reveals Time-based Horizontal view.”

Question 3(a OR) [3 marks]

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Apply Lissajous pattern for frequency measurement and Phase angle measurement.

Answer:

Lissajous patterns are created when two sine waves are applied to X and Y inputs of CRO.

Pattern Type	Example	Measurement Formula
Frequency Measurement		fx/fy = ny/nx
Phase Angle Measurement		sin(φ) = A/B

• Frequency ratio: Count vertical tangent points / horizontal tangent points
• Phase measurement: sin(φ) = sin/sinmax where sin is pattern height at zero crossing
• Applications: Signal comparison, frequency calibration

Mnemonic: “LIPS patterns: Lissajous Indicates Phase and Sine frequency.”

Question 3(b OR) [4 marks]

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Explain Graticules in CRO. Also Explain its types.

Answer:

Graticules are reference grids on a CRO screen that help in measurement of waveform parameters.

Types of graticules:

Mnemonic: “GRIT: Graticules Render Important Time-voltage measurements.”

Question 3(c OR) [7 marks]

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Describe Block diagram, working and advantage of Digital storage oscilloscope (DSO).

Answer:

Digital Storage Oscilloscope (DSO) digitizes signals for storage, processing, and display.

graph LR
    A[Input Signal] --> B[Attenuator/Amplifier]
    B --> C[ADC]
    C --> D[Memory]
    D --> E[Processor]
    E --> F[DAC]
    F --> G[Display]
    H[Time Base] --> E
    I[Trigger System] --> E
    J[Control Panel] --> E
    style D fill:#f9f,stroke:#333,stroke-width:2px

Working principle:

• Acquisition: Signal is sampled at high rate by ADC
• Storage: Digital values stored in memory
• Processing: Digital signal processing enhances analysis
• Display: Reconstructed signal shown on screen
• Triggering: Advanced digital triggering options

Advantages:

• Signal storage capability
• Pre-trigger viewing
• One-shot signal capture
• Advanced measurements
• Deep memory for long captures
• Digital filtering and analysis
• Network connectivity

Mnemonic: “SAMPLE: Storage And Memory Preserves Long-term Events.”

Question 4(a) [3 marks]

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Differentiate RTD and Thermistor.

Answer:

Mnemonic: “RTD is PLAINS: Platinum, Linear, Accurate, Industrial range, Narrow sensitivity, Stable.”

Question 4(b) [4 marks]

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Explain Optical encoder with its output waveform.

Answer:

Optical encoder converts mechanical motion to digital pulses using light interruption through a coded disc.

Output waveforms:

• Components: Light source, coded disc, photodetector
• Types: Incremental (pulses) or absolute (unique position code)
• Applications: Position measurement, speed detection, motion control

Mnemonic: “DROPS: Disc Rotation Outputs Pulse Signals.”

Question 4(c) [7 marks]

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Describe Thermocouple with working principle, types and application.

Answer:

Thermocouple is a temperature sensor that operates on the Seebeck effect, generating voltage proportional to temperature difference.

graph LR
    A[Hot Junction] --- B[Metal A]
    A --- C[Metal B]
    B --- D[Cold Junction]
    C --- D
    D --- E[Measuring Instrument]
    style A fill:#f9f,stroke:#333,stroke-width:2px

Working principle:

• Two dissimilar metals joined at one end (hot junction)
• Temperature difference between hot and cold junctions generates voltage
• Voltage is proportional to temperature difference

Types of thermocouples:

Applications: Industrial furnaces, engines, chemical processing, food processing, research

Mnemonic: “SHOVE theory: Seebeck Hot-cold Output Voltage Equals Temperature.”

Question 4(a OR) [3 marks]

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Differentiate active and passive transducers.

Answer:

Mnemonic: “SIMPLE difference: Self-powered Is Main Principle of Leading Energy transducers.”

Question 4(b OR) [4 marks]

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Explain Capacitive Transducer with necessary diagram in detail. Also list application of it.

Answer:

Capacitive transducer works on the principle of change in capacitance due to physical displacement.

graph TD
    A[Fixed Plate] --- B[Dielectric]
    B --- C[Movable Plate]
    C --- D[Physical Parameter]
    E[Capacitance Measuring Circuit] --- A
    E --- C
    style B fill:#f9f,stroke:#333,stroke-width:2px

Working principle:

• Capacitance C = ε₀εᵣA/d
• Varies with change in: area (A), distance (d), or dielectric constant (εᵣ)
• Displacement changes the capacitance
• Measured using bridge circuit or oscillator

Applications:

• Pressure measurement
• Liquid level sensing
• Humidity sensors
• Displacement measurement
• Accelerometers

Mnemonic: “CADAP: Capacitance Alters with Distance, Area, or Permittivity.”

Question 4(c OR) [7 marks]

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Explain LVDT Transducer operation, construction with necessary diagram in detail. Also list advantage, disadvantage and application of LVDT.

Answer:

LVDT (Linear Variable Differential Transformer) is an electromechanical transducer that converts linear displacement into electrical output.

graph TD
    A[Primary Coil] --- B[Secondary Coil 1]
    A --- C[Secondary Coil 2]
    D[AC Excitation] --- A
    E[Ferromagnetic Core] --- F[Core Rod]
    B --- G[Output Voltage]
    C --- G
    style E fill:#f9f,stroke:#333,stroke-width:2px

Construction:

• Primary coil in center
• Two secondary coils wound symmetrically
• Movable ferromagnetic core
• Signal conditioning circuitry

Operation:

• AC excitation energizes primary coil
• Core position determines magnetic coupling to secondaries
• Differential voltage output proportional to displacement
• Phase indicates direction of displacement

Advantages:

• Non-contact operation
• Infinite resolution
• High linearity
• Robust construction
• Long operational life
• Immunity to harsh environments

Disadvantages:

• Requires AC excitation
• Bulky compared to other sensors
• Affected by external magnetic fields
• Limited dynamic response

Applications:

• Precision measurement
• Hydraulic systems
• Aircraft controls
• Power plant controls
• Automated manufacturing

Mnemonic: “CDPOS sensor: Core Displacement Produces Output Signal.”

Question 5(a) [3 marks]

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Demonstrate working and principle of Semiconductor Temperature Sensor LM35.

Answer:

LM35 is an integrated circuit temperature sensor that outputs voltage linearly proportional to temperature in Celsius.

Working principle:

• Integrated circuit with built-in temperature-sensing element
• Linear output voltage: +10mV/°C
• Calibrated directly in Celsius
• Operating range: -55°C to +150°C

Circuit:

• Requires only power supply connection
• Output directly readable with voltmeter
• No external calibration needed

Mnemonic: “TEN mV TRICK: Temperature Escalation Noted in milliVolts: Ten Rise Indicates Celsius Kelvin.”

Question 5(b) [4 marks]

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Describe working of Harmonic distortion analyzer with necessary diagram.

Answer:

Harmonic distortion analyzer measures the harmonic content in signals to determine signal quality.

graph LR
    A[Input Signal] --> B[Attenuator]
    B --> C[Notch Filter]
    C --> D[Amplifier]
    D --> E[RMS Detector]
    A --> F[Reference RMS]
    E --> G[Calculator]
    F --> G
    G --> H[Display]
    style C fill:#f9f,stroke:#333,stroke-width:2px

Working principle:

• Fundamental frequency is filtered out using notch filter
• Remaining harmonics are measured
• THD = (VRMS of harmonics)/(VRMS of fundamental)
• Expressed as percentage or dB

Operation steps:

1. Measure total signal RMS
2. Filter out fundamental
3. Measure remaining harmonics
4. Calculate THD ratio

Mnemonic: “FRONT analysis: Filter Removes Original Note Totally for Analyzing Leftover Signals.”

Question 5(c) [7 marks]

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Describe working of Spectrum Analyzer with necessary diagram in detail.

Answer:

Spectrum Analyzer displays signal amplitude versus frequency, showing the spectral composition of signals.

graph LR
    A[RF Input] --> B[Attenuator]
    B --> C[Mixer]
    D[Local Oscillator] --> C
    C --> E[IF Filter]
    E --> F[Detector]
    F --> G[Display]
    H[Sweep Generator] --> D
    H --> G
    style E fill:#f9f,stroke:#333,stroke-width:2px

Working principle:

• Superheterodyne principle: Input signal mixed with local oscillator
• Sweep technique: LO frequency swept across range of interest
• Resolution bandwidth: Controlled by IF filter bandwidth
• Detection: Converts IF signal to amplitude information
• Display: Shows frequency domain representation

Types:

• Swept-tuned spectrum analyzer
• FFT-based spectrum analyzer
• Real-time spectrum analyzer

Applications:

• Signal analysis
• EMI/EMC testing
• Communication systems testing
• Harmonic analysis
• Modulation analysis

Mnemonic: “SAFER view: Sweep Analyzes Frequencies for Examining RF.”

Question 5(a OR) [3 marks]

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Explain analog transducer and digital transducer. Also explain primary transducer and secondary transducer.

Answer:

Mnemonic: “PADS: Primary And Digital/analog Secondary.”

Question 5(b OR) [4 marks]

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Explain working of Digital IC tester with necessary diagram in detail.

Answer:

Digital IC tester verifies functionality of integrated circuits by applying test patterns and analyzing responses.

graph TD
    A[Microcontroller] --> B[Test Pattern Generator]
    A --> C[Result Analyzer]
    B --> D[Test Socket]
    D --> C
    A --> E[Display/Interface]
    F[Power Supply] --> D
    style D fill:#f9f,stroke:#333,stroke-width:2px

Working principle:

• IC inserted in ZIF (Zero Insertion Force) socket
• Test parameters selected for IC type
• Pattern generator applies specific input signals
• Outputs compared with expected results
• Pass/fail indication displayed

Features:

• Tests TTL, CMOS, memory ICs
• Identifies unknown ICs
• Detects open/short circuits
• Function verification

Mnemonic: “TRIG test: Test, Run patterns, Identify faults, Generate report.”

Question 5(c OR) [7 marks]

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Explain working of function generator with necessary diagram in detail.

Answer:

Function generator produces various waveforms at different frequencies for testing electronic circuits.

graph LR
    A[Frequency Control] --> B[Oscillator]
    C[Waveform Selector] --> D[Waveform Shaper]
    B --> D
    D --> E[Amplitude Control]
    E --> F[Output Amplifier]
    F --> G[Output]
    H[DC Offset] --> F
    style B fill:#f9f,stroke:#333,stroke-width:2px

Working principle:

• Oscillator: Generates basic waveform (usually triangle)
• Waveform shaper: Converts to sine, square, triangle, ramp
• Frequency control: Sets oscillation rate
• Amplitude control: Adjusts output voltage level
• DC offset: Adds bias to output signal
• Output amplifier: Provides low impedance output

Output waveforms:

Applications:

• Testing amplifiers
• Filter characterization
• Signal analysis
• Educational demonstrations
• Calibration reference

Mnemonic: “SWATOR: Sine Wave And Triangle OSCillator Renders signals.”