Electronic Measurements and Instruments (4331102) - Winter 2022 Solution

Question 1(a) [3 marks]

#

Draw and explain working of Basic Q-Meter.

Answer: Q-meter is an instrument used to measure the quality factor (Q) of an inductor or capacitor.

Diagram:

graph TD
    A[Oscillator] --> B[Amplifier]
    B --> C[Meter Circuit]
    C --> D[Voltage Indicator]
    C --> E[Unknown Component]
    E --> C

• Oscillator: Generates variable frequency signal
• Amplifier: Amplifies the signal to required level
• Resonance Circuit: Contains the component under test
• Voltage Indicator: Measures the voltage across component

Mnemonic: “OARV - Oscillate, Amplify, Resonate, View”

Question 1(b) [4 marks]

#

Explain Spectrum Analyzer in brief.

Answer: A spectrum analyzer measures the magnitude of an input signal versus frequency within the full frequency range of the instrument.

Diagram:

graph LR
    A[Input Signal] --> B[Mixer]
    C[Local Oscillator] --> B
    B --> D[IF Filter]
    D --> E[Detector]
    E --> F[Display]

• Input Signal Processing: Signals enter through attenuator and filters
• Frequency Domain Conversion: Converts time domain to frequency domain
• Display System: Shows amplitude vs. frequency plot
• Applications: Signal analysis, distortion measurement, EMI testing

Mnemonic: “SAME-FD: Signal Analysis Measures Everything in Frequency Domain”

Question 1(c) [7 marks]

#

Explain Wheatstone bridge with circuit diagram. List its advantages and disadvantages.

Answer: Wheatstone bridge is a circuit used to measure unknown resistance with high accuracy.

Diagram:

graph TD
    A((+)) --- R1
    A --- R3
    R1 --- B((G))
    R3 --- B
    R1 --- R2
    R3 --- Rx
    R2 --- C((−))
    Rx --- C

Where:

• R1, R2, R3 are known resistances
• Rx is unknown resistance
• G is galvanometer

Working Principle:

• Bridge is balanced when R1/R2 = R3/Rx
• At balance, no current flows through galvanometer
• Unknown resistance Rx = R3(R2/R1)

Mnemonic: “BARN - Balance Achieved when Ratios are Null”

Question 1(c) OR [7 marks]

#

Define Instrument and explain its characteristics.

Answer: An instrument is a device used for measuring, displaying or recording physical quantities.

Diagram:

graph LR
    A[Input] --> B[Instrument]
    B --> C[Output Reading]
    D[Error Sources] --> B
    E[Environmental Factors] --> B

• Static Characteristics: Properties that don’t vary with time
• Dynamic Characteristics: Properties that vary with time

Mnemonic: “APRS-LRR: Accuracy and Precision, Resolution and Sensitivity, Linearity, Range, Response time”

Question 2(a) [3 marks]

#

Draw the construction diagram of Energy meter.

Answer: Energy meter measures electrical energy consumption in kilowatt-hours.

Diagram:

• Rotating Aluminum Disc: Moves proportional to power
• Current Coil: Creates flux proportional to current
• Voltage Coil: Creates flux proportional to voltage
• Permanent Magnet: Provides braking torque

Mnemonic: “DVCP: Disc Velocity measures Consumed Power”

Question 2(b) [4 marks]

#

Explain working of PMMC in short.

Answer: PMMC (Permanent Magnet Moving Coil) is a basic mechanism used in various meters.

Diagram:

• Deflection Principle: When current flows through coil, it produces torque proportional to current
• Advantages: Linear scale, high accuracy, low power consumption

Mnemonic: “CODA: Current through cOil causes Deflection by Attraction”

Question 2(c) [7 marks]

#

1- A moving coil ammeter reading up to 1 ampere has a resistance of 0.02 ohm. How this instrument could be adopted to read current up to 100 amperes?

2- A moving coil voltmeter reading up to 20 mV has a resistance of 2 ohms. How this instrument can be adopted to read voltage up to 300 volts?

Answer:

1. Ammeter Range Extension:

Diagram:

• Shunt Resistance Calculation: Rs = Rm × Im/(I - Im)
• Given: Rm = 0.02Ω, Im = 1A, I = 100A
• Solution: Rs = 0.02 × 1/(100 - 1) = 0.02/99 = 0.000202Ω

2. Voltmeter Range Extension:

Diagram:

• Series Resistance Calculation: Rs = Rm × (V/Vm - 1)
• Given: Rm = 2Ω, Vm = 20mV, V = 300V
• Solution: Rs = 2 × (300/0.02 - 1) = 2 × (15000 - 1) = 2 × 14999 = 29,998Ω

Mnemonic: “SHIP: Shunt Has Inverse Proportion for current; Series for voltage”

Question 2(a) OR [3 marks]

#

Explain working of electronic multimeter.

Answer: Electronic multimeter measures multiple electrical parameters using electronic components.

Diagram:

graph TD
    A[Input Signal] --> B[Range Selection]
    B --> C[Conversion Circuit]
    C --> D[Display System]

• Range Selection: Selects appropriate measurement range
• Signal Conditioning: Converts input to proportional voltage
• ADC: Converts analog to digital for display
• Digital Display: Shows measured value

Mnemonic: “RSAD: Range Select, Amplify, Digitize”

Question 2(b) OR [4 marks]

#

Explain working of Moving Iron type instruments.

Answer: Moving Iron instruments measure AC/DC current and voltage based on magnetic attraction/repulsion.

Diagram:

• Operating Principle: Current through coil creates magnetic field
• Scale: Non-linear (crowded at lower end)
• Applications: AC and DC measurements, ammeters, voltmeters

Mnemonic: “CADS: Current Activates, Deflection Shows”

Question 2(c) OR [7 marks]

#

Draw the block diagram of Ramp type DVM. Illustrate process of obtaining Multirange DC voltmeter with circuit diagram.

Answer: Ramp type DVM converts voltage to time interval using ramp comparison.

Diagram for Ramp Type DVM:

graph TD
    A[Input Voltage] --> B[Comparator]
    C[Ramp Generator] --> B
    B --> D[Gate Control]
    E[Clock] --> F[Counter]
    D --> F
    F --> G[Display]

• Working Principle: Measures time taken for ramp to equal input voltage
• Comparator: Compares input with ramp voltage
• Counter: Counts clock pulses during comparison
• Display: Shows digital reading

Multirange DC Voltmeter Circuit:

Range Switching Process:

• Each resistor provides different voltage division ratio
• Switch selects appropriate voltage divider network
• Voltage divider reduces input to fit DVM range

Mnemonic: “CRCD: Compare Ramp, Count Duration”

Question 3(a) [3 marks]

#

Describe features of Digital storage oscilloscope (DSO).

Answer: Digital Storage Oscilloscope converts analog signals to digital for storage and analysis.

• Sampling Rate: Typically 1 GS/s or higher
• Memory Depth: Determines maximum capture time

Mnemonic: “SACRED: Storage, Analysis, Connectivity, Resolution, Extended functions, Digital processing”

Question 3(b) [4 marks]

#

Explain frequency measurement method using Lissajous pattern.

Answer: Lissajous patterns are used to compare frequencies of two signals.

Diagram:

Method:

1. Apply unknown frequency to X-input
2. Apply reference frequency to Y-input
3. Observe Lissajous pattern on screen
4. Count tangent points to determine ratio

Formula: fx/fy = Ny/Nx

• Where Nx = horizontal tangent points
• Ny = vertical tangent points

Mnemonic: “XTYN: X-Tangents to Y-tangents gives the Number ratio”

Question 3(c) [7 marks]

#

Explain CRO with help of Block diagram.

Answer: Cathode Ray Oscilloscope (CRO) is used to display and analyze waveforms.

Block Diagram:

graph TD
    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[CRT]
    D --> J
    H --> J

• Electron Gun: Produces electron beam
• Deflection System: Moves beam in X and Y directions
• Screen: Phosphor coating converts electrons to visible light

Mnemonic: “VCTHP: Vertical input, Conditioned signal, Triggered sweep, Horizontal deflection, Phosphor display”

Question 3(a) OR [3 marks]

#

Explain different types of CRO probes.

Answer: CRO probes connect the circuit under test to the oscilloscope input.

Diagram:

• Attenuation Ratio: Typically 1:1 or 10:1
• Compensation: Adjustable to match oscilloscope input

Mnemonic: “PACD: Passive, Active, Current, Differential”

Question 3(b) OR [4 marks]

#

Draw internal structure of CRT. Explain in brief.

Answer: Cathode Ray Tube (CRT) is the display device in an oscilloscope.

Diagram:

• Electron Beam: High-velocity electrons emitted by cathode
• Focusing System: Anodes form electron lens
• Deflection System: X-Y plates move beam position
• Phosphor Screen: Glows where beam hits

Mnemonic: “GAFDS: Gun Aims, Focusing Directs, Screen shows”

Question 3(c) OR [7 marks]

#

Draw and explain block diagram of DSO in detail.

Answer: Digital Storage Oscilloscope (DSO) captures, stores and analyzes signals in digital form.

Block Diagram:

graph LR
    A[Input] --> B[Attenuator/Amplifier]
    B --> C[Anti-aliasing Filter]
    C --> D[ADC]
    D --> E[Memory]
    E --> F[Microprocessor]
    F --> G[Display]
    H[Timebase] --> F
    I[Trigger] --> F
    J[Control Panel] --> F

• Sampling Rate: Number of samples per second
• Resolution: Number of bits in ADC (typically 8-12 bits)
• Memory Depth: Number of samples that can be stored
• Processing: Waveform math, measurements, analysis

Mnemonic: “SAMPLE-D: Signal Acquisition, Memory Processing, Locking trigger, Display”

Question 4(a) [3 marks]

#

Give the comparison of NTC and PTC thermistor.

Answer:

Diagram:

Mnemonic: “IN-DP: Increase Negative, Decrease Positive”

Question 4(b) [4 marks]

#

Explain working principle and construction of Thermocouple.

Answer: Thermocouple is a temperature sensor that works on the principle of Seebeck effect.

Diagram:

Construction:

• Two dissimilar metals joined at one end (measuring junction)
• Other ends connected to measuring circuit (reference junction)
• Protective sheath for industrial applications

Working Principle:

• Temperature difference between junctions creates EMF
• EMF is proportional to temperature difference
• Output voltage typically in millivolts range
• Different metal combinations for different ranges

Mnemonic: “STEM: Seebeck-effect Transforms temperature to EMF in Metals”

Question 4(c) [7 marks]

#

Explain Working of strain Gauge and Load cell. Give advantages and disadvantages of RTD.

Answer:

Strain Gauge Working:

• Principle: Resistance changes with mechanical deformation
• Construction: Thin wire or foil grid mounted on backing material
• Operation: When strained, resistance changes proportionally
• Gauge Factor: Ratio of relative change in resistance to strain

Diagram for Strain Gauge:

Load Cell Working:

• Construction: Strain gauges mounted on metal body (beam/ring)
• Operation: Weight causes deformation measured by strain gauges
• Circuit: Typically Wheatstone bridge configuration
• Output: Usually few millivolts per volt of excitation

Diagram for Load Cell:

RTD (Resistance Temperature Detector):

Mnemonic: “SPANNER: Strain Proportionally Alters Nominal Nominal Electrical Resistance”

Question 4(a) OR [3 marks]

#

Explain Humidity Sensor Hygrometer.

Answer: Humidity sensor hygrometer measures relative humidity in air.

Diagram:

graph TD
    A[Humidity] --> B[Sensing Element]
    B --> C[Signal Conditioning]
    C --> D[Display/Output]

• Relative Humidity: Ratio of actual to maximum water vapor
• Measurement Range: Typically 0-100% RH
• Applications: Weather stations, HVAC systems, industrial processes

Mnemonic: “CRT-H: Capacitance/Resistance/Thermal changes with Humidity”

Question 4(b) OR [4 marks]

#

Draw and explain Piezoelectric transducer.

Answer: Piezoelectric transducer converts mechanical stress to electrical signals and vice versa.

Diagram:

Working Principle:

• Direct Effect: Pressure produces electrical charge
• Inverse Effect: Voltage produces mechanical deformation
• Materials: Quartz, PZT, barium titanate

Applications:

• Pressure sensors
• Accelerometers
• Ultrasonic transducers
• Vibration sensors

Mnemonic: “PEMS: Pressure Ensures Measurable Signal”

Question 4(c) OR [7 marks]

#

Give the classification of transducers in detail.

Answer: Transducers convert one form of energy to another, classified in several ways:

Diagram:

graph TD
    A[Transducers] --> B[Active/Passive]
    A --> C[Primary/Secondary]
    A --> D[Analog/Digital]
    B --> B1[Active: Self-generating]
    B --> B2[Passive: External power]
    C --> C1[Primary: Direct conversion]
    C --> C2[Secondary: Multiple steps]
    D --> D1[Analog: Continuous output]
    D --> D2[Digital: Discrete output]

Mnemonic: “APAD RICE: Active/Passive, Analog/Digital with Resistive, Inductive, Capacitive, Electromagnetic”

Question 5(a) [3 marks]

#

Write short note on various Capacitive transducer.

Answer: Capacitive transducers operate on the principle that capacitance changes with physical parameters.

Diagram:

• Capacitance: C = εA/d (ε: permittivity, A: area, d: distance)
• Advantages: High sensitivity, no physical contact needed
• Limitations: Affected by stray capacitance

Mnemonic: “PALD: Parameter Alters the Leading Dielectric”

Question 5(b) [4 marks]

#

Explain LVDT Transducer.

Answer: LVDT (Linear Variable Differential Transformer) measures linear displacement.

Diagram:

Working Principle:

• Primary coil excited by AC voltage
• Core position determines coupling to secondaries
• Output voltage proportional to core displacement
• Null position when core centered (output = 0)

Characteristics:

• Range: Typically ±0.5mm to ±25cm
• Linearity: Excellent around null position
• Sensitivity: High, typically mV/mm
• Resolution: Nearly infinite (analog device)

Mnemonic: “MDVN: Movement Determines Voltage from Null”

Question 5(c) [7 marks]

#

Draw and explain Harmonics Distortion Analyzer.

Answer: Harmonic Distortion Analyzer measures distortion in audio and electronic signals.

Block Diagram:

graph TD
    A[Input Signal] --> B[Attenuator]
    B --> C[Input Amplifier]
    C --> D[Fundamental Notch Filter]
    D --> E[Residual Amplifier]
    E --> F[RMS Detector]
    F --> G[Display]
    C --> H[Reference Level Detector]
    H --> G

Working Principle:

1. Input signal is conditioned and amplified
2. Fundamental frequency is removed using notch filter
3. Remaining harmonic content is measured
4. Distortion calculated as ratio of harmonics to total signal

Characteristics:

• Measurement Range: Typically 0.001% to 100%
• Frequency Range: 20Hz to 100kHz
• Applications: Audio equipment testing, power quality analysis
• Measurements: THD (Total Harmonic Distortion), THD+N (THD plus Noise)

Calculation: THD = √(V₂² + V₃² + V₄² + …)/(V₁ + V₂ + V₃ + …)

• Where V₁ is fundamental, V₂, V₃, etc. are harmonics

Mnemonic: “FAIR-D: Filter And Isolate Residuals for Distortion”

Question 5(a) OR [3 marks]

#

Explain the working principle of Proximity sensors.

Answer: Proximity sensors detect objects without physical contact.

Diagram:

• Operating Modes: Normally open or normally closed
• Output Types: Digital (on/off) or analog (proportional)
• Applications: Manufacturing, automation, security systems

Mnemonic: “CUPS: Capacitive, Ultrasonic, Photoelectric, Sense”

Question 5(b) OR [4 marks]

#

Explain absolute and incremental type of Optical encoder.

Answer: Optical encoders convert mechanical position to digital signals using light detection.

Diagram of Absolute Encoder:

Diagram of Incremental Encoder:

• A, B, Z Outputs:
  • A and B outputs are 90° out of phase for direction detection
  • Z (index) pulse once per revolution for reference

Mnemonic: “APIR-CD: Absolute Provides Immediate Reading, Counter Determines incremental”

Question 5(c) OR [7 marks]

#

Write short note on Digital IC Tester.

Answer: Digital IC Tester is used to verify functionality and detect faults in digital integrated circuits.

Block Diagram:

graph TD
    A[Test Pattern Generator] --> B[IC Socket]
    C[IC Under Test] --> B
    B --> D[Response Analyzer]
    D --> E[Result Display]
    F[Microcontroller] --> A
    F --> D
    F --> E
    G[User Interface] --> F
    H[Power Supply] --> B

Testing Methods:

1. Functional Testing: Verifies logic functionality
2. Parametric Testing: Measures electrical parameters
3. Fault Detection: Identifies shorts, opens, stuck bits

Types of IC Testers:

• Universal Testers: Test multiple IC families (TTL, CMOS)
• Dedicated Testers: Designed for specific IC types
• In-Circuit Testers: Test ICs while in the circuit

Capabilities:

• IC Identification: Recognizes unknown ICs
• Fault Diagnosis: Identifies specific faults
• Auto Test: Performs comprehensive testing sequence

Mnemonic: “GATES: Generate And Test Every Signal”

Question 5(c) (Additional) [7 marks]

#

Below are the solved solutions for remaining questions present in the question paper:

Explain working of electronic multimeter.

Answer: Electronic multimeter uses electronic components to measure various electrical parameters.

Block Diagram:

graph LR
    A[Input] --> B[Range Selection]
    B --> C[Signal Conditioning]
    C --> D[ADC]
    D --> E[Display]
    F[Power Supply] --> C
    F --> D
    F --> E

• Advantages: High input impedance, auto-ranging, digital accuracy
• Applications: Electronics troubleshooting, circuit testing, device calibration

Mnemonic: “MAAD: Measure, Amplify, Analyze, Display”

Explain working of Moving Iron type instruments.

Answer: Moving Iron instruments operate based on magnetic force between current-carrying coil and iron piece.

Diagram:

Characteristics:

• Scale: Non-linear, compressed at lower end
• Response: Measures both AC and DC (responds to RMS value)
• Accuracy: Lower than PMMC type
• Power Consumption: Relatively high

Mnemonic: “AMIR: Attraction Moves Iron with Reluctance”

Explain Humidity Sensor Hygrometer.

Answer: Humidity sensors measure the amount of water vapor in air or other gases.

Types of Humidity Sensors:

Diagram:

Measurements:

• Relative Humidity (RH): Percentage of actual to maximum moisture
• Dew Point: Temperature at which condensation occurs
• Absolute Humidity: Mass of water vapor per volume

Applications:

• Weather stations
• HVAC systems
• Industrial process control
• Medical equipment

Mnemonic: “CRAP-H: Capacitance or Resistance Alters with Presence of Humidity”

Draw and explain Piezoelectric transducer.

Answer: Piezoelectric transducers convert mechanical force to electrical signal and vice versa.

Diagram:

Working Principle:

• Direct Effect: Pressure generates electric charge
• Reverse Effect: Electric field causes mechanical deformation
• Materials: Quartz, PZT, barium titanate, lithium niobate

Characteristics:

• High Frequency Response: Up to MHz range
• High Output Impedance: Requires charge amplifier
• Self-Generating: No external power for sensing
• Dynamic Response: Not suitable for static measurements

Applications:

• Accelerometers
• Pressure sensors
• Ultrasonic transducers
• Microphones
• Ignition systems

Mnemonic: “PEMS: Pressure Equals Measurable Signal”