Electronic Measurements and Instruments (4331102) - Summer 2023 Solution

Question 1(a) [3 marks]

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Illustrate steps to minimize that all type of systematic error.

Answer:

Steps to minimize systematic errors:

Mnemonic: “CCCTS: Calibrate, Correct, Control, Technique, Select”

Question 1(b) [4 marks]

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Define: Resolution, Precision, Sensitivity and Accuracy.

Answer:

Diagram:

graph LR
    A[Measurement Quality] --> B[Resolution]
    A --> C[Precision]
    A --> D[Sensitivity]
    A --> E[Accuracy]
    B --> F[Smallest detectable change]
    C --> G[Repeatability]
    D --> H[Output/Input ratio]
    E --> I[Closeness to truth]

Mnemonic: “RSPA: Resolve Signals Precisely and Accurately”

Question 1(c) [7 marks]

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Explain a principle of Q Meter and Working of practical Q Meter.

Answer:

Q Meter operates on the resonance principle to measure quality factor (Q) of coils and capacitors.

Principle:

• Based on series resonance where Q = XL/R or XC/R at resonance
• Measures voltage magnification at resonance condition

Working of practical Q meter:

Diagram:

• Q factor calculation: Q = V₂/V₁ where V₂ is voltage across capacitor and V₁ is the applied voltage
• Applications: Testing RF components, coil quality measurement
• Resonance indication: Maximum voltage across capacitor indicates resonance

Mnemonic: “VOCAL: Voltage ratio at resonance Oscillator Creates Amplification to measure coiL quality”

Question 1(c OR) [7 marks]

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Explain Wheatstone bridge and derive equation for balanced condition. State application and limitation of Wheatstone bridge.

Answer:

Wheatstone bridge is a network used to measure unknown resistance with high precision.

Circuit diagram:

Balanced condition equation derivation:

• At balance, no current flows through galvanometer
• Potential at point D = Potential at point B
• Voltage across R₁ = Voltage across Rx
• Voltage across R₂ = Voltage across R₃

Therefore:

• (R₁/R₂) = (Rx/R₃)
• Rx = R₃(R₁/R₂)

Applications:

Limitations:

Mnemonic: “BEAR: Balance Equation at Arms Ratio”

Question 2(a) [3 marks]

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Differentiate between moving iron and moving coil type instruments.

Answer:

Mnemonic: “IRON-COIL: Iron uses Repulsion with Non-uniform scale; COIL uses Current with Organized, Improved, Linear scale”

Question 2(b) [4 marks]

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Draw the construction diagram of clamp on Ammeter and explain in detail.

Answer:

Construction diagram of clamp-on ammeter:

Components and working:

• Core: Split laminated ferromagnetic core that can be opened/closed
• Coil: Secondary winding wrapped around the core
• Conductor: Primary conductor (current to be measured) passes through the core
• Measurement circuit: Processes induced current and displays reading
• Spring mechanism: For easy opening and closing of the jaw

Working principle: Based on transformer principle where conductor acts as single-turn primary winding, creating magnetic flux proportional to current.

Mnemonic: “CLASP: Conductor-Loop Amperes Sensed by Primary-secondary relationship”

Question 2(c) [7 marks]

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Describe working and advantages of Integrating type DVM with suitable diagram.

Answer:

Integrating-type Digital Voltmeter converts analog voltage to digital value using dual-slope integration.

Block diagram:

Working principle:

Advantages:

• Noise rejection: Excellent rejection of power line noise (50/60Hz)
• Accuracy: Highly accurate (0.005% to 0.05%)
• Resolution: High resolution (up to 6½ digits)
• Stability: Less affected by component tolerances
• Common mode rejection: High CMRR

Mnemonic: “RISES: Ramp Integration Samples and Eliminates Spikes”

Question 2(a OR) [3 marks]

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Differentiate between Digital Voltmeter over Analog Voltmeter.

Answer:

Mnemonic: “DAPPER: Digital Accuracy and Precise readings; Parallax Error in Reading analog”

Question 2(b OR) [4 marks]

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Draw the construction diagram of Moving iron type Meter and explain in detail.

Answer:

Construction diagram of moving iron meter:

Working principle and components:

• Coil: Creates magnetic field proportional to current
• Iron vanes: Two soft iron pieces (one fixed, one movable)
• Movement: Magnetic repulsion between similarly magnetized iron pieces
• Control: Spring provides opposing torque
• Damping: Air friction damping mechanism
• Scale: Non-uniform scale due to non-linear magnetic force

Types:

• Attraction type: Works on magnetic attraction principle
• Repulsion type: Works on magnetic repulsion principle

Mnemonic: “MIRROR: Magnetic Interaction Requires Repulsion/attraction Of Related iron pieces”

Question 2(c OR) [7 marks]

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Describe construction diagram of Energy meter and explain in detail.

Answer:

Electronic energy meter measures electrical energy consumption in kilowatt-hours.

Construction diagram:

Components and working:

Working principle:

1. Voltage and current are sensed by respective sensors
2. Signals are multiplied to obtain instantaneous power
3. Power is integrated over time to calculate energy
4. Energy is displayed as kilowatt-hours (kWh)

Mnemonic: “WATTAGE: Work And Time Tracked As Generated Electrical energy”

Question 3(a) [3 marks]

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Apply Lissajous pattern for frequency measurement and Phase angle measurement.

Answer:

Lissajous patterns on oscilloscope screen help measure frequency ratio and phase difference.

Frequency measurement:

• Apply reference signal to X-axis and unknown signal to Y-axis
• Frequency ratio = Number of tangent points on Y-axis / Number of tangent points on X-axis
• Frequency of unknown = Frequency of reference × Frequency ratio

Pattern	Frequency Ratio (Y:X)
	1:1
	2:1
	n:m

Phase angle measurement:

• If both frequencies are equal, phase angle (φ) can be measured
• φ = sin⁻¹(A/B) where A = minor axis and B = major axis of ellipse

Mnemonic: “LIPS: Lissajous Indicates Phase and Signal frequency”

Question 3(b) [4 marks]

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Explain Graticules in CRO also Explain its types.

Answer:

Graticules are reference markings on CRO screen for measurements.

Standard graticule features:

• 10 × 8 divisions typically
• Center lines darker for reference
• Small hash marks for subdivisions
• Percentage markings (rise time)

Diagram:

Mnemonic: “GRID: Graticule References for Intensity and Distance”

Question 3(c) [7 marks]

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

Answer:

Digital Storage Oscilloscope (DSO) converts analog signals to digital for storage and processing.

Block diagram:

Working principle:

1. Signal acquisition: Analog signal is sampled at high speed
2. A/D conversion: Continuous signal converted to discrete digital values
3. Storage: Digital values stored in memory
4. Processing: Microprocessor analyzes stored data
5. Display: Data converted back to analog for display or shown directly on LCD

Advantages of DSO:

Mnemonic: “SAMPLE: Storage And Memory Processes Live Events”

Question 3(a OR) [3 marks]

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Differentiate between CRO and DSO.

Answer:

Mnemonic: “ASPAD: Analog Shows Present; Digital Archives Data”

Question 3(b OR) [4 marks]

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Explain structure of 10:1 Probes in detail.

Answer:

10:1 probe reduces signal amplitude by 10 times to extend oscilloscope range.

Structure:

Components:

Working principle:

• Forms voltage divider with oscilloscope input (9MΩ probe + 1MΩ scope = 10:1 division)
• Compensating capacitor ensures flat frequency response
• Reduces circuit loading effect by increasing effective input impedance

Mnemonic: “TAPER: Ten-to-one Attenuation Preserves and Extends Range”

Question 3(c OR) [7 marks]

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Describe Block diagram, working and application of CRO.

Answer:

CRO (Cathode Ray Oscilloscope) displays and measures electrical signals.

Block diagram:

Working principle:

1. Electron beam generation: CRT produces focused electron beam
2. Vertical deflection: Y-plates deflect beam proportional to input signal
3. Horizontal deflection: X-plates sweep beam across screen
4. Triggering: Synchronizes sweep with input signal
5. Display: Beam strikes phosphor screen creating visible trace

Applications of CRO:

Mnemonic: “VIEW: Voltage Inspection and Electrical Waveform observation”

Question 4(a) [3 marks]

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Differentiate RTD and Thermistor.

Answer:

Mnemonic: “METAL-SEMI: Metal Elements Temperature-Linear vs. SEMIconductor Exponential Measurement Instrument”

Question 4(b) [4 marks]

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Give and explain two example of primary and Secondary transducer.

Answer:

Diagram:

graph TD
    A[Transducers] --> B[Primary]
    A --> C[Secondary]
    B --> D[Direct conversion]
    C --> E[Uses intermediate steps]
    D --> F[Thermocouple: Temperature → Voltage]
    D --> G[Piezoelectric: Force → Charge]
    E --> H[Strain Gauge: Force → Resistance → Voltage]
    E --> I[LVDT: Displacement → Magnetic coupling → Voltage]

Mnemonic: “PIDS: Primary Is Direct; Secondary is Stepwise”

Question 4(c) [7 marks]

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Describe Thermocouple with working principle, types and application.

Answer:

Thermocouple is a temperature sensor based on the Seebeck effect.

Working principle:

• When two dissimilar metals are joined, a voltage is generated proportional to temperature difference
• Seebeck effect: Temperature gradient creates electromotive force

Diagram:

Types of thermocouples:

Applications:

• Industrial temperature measurement
• Furnace and kiln temperature control
• Chemical processing
• Food processing
• Automotive engine sensors
• Medical equipment

Mnemonic: “STEVE: Seebeck Thermoelectric Effect Verifies Elevated temperatures”

Question 4(a OR) [3 marks]

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Demonstrate working and principle Semiconductor Temperature Sensor LM35.

Answer:

LM35 is a precision integrated-circuit temperature sensor that provides output voltage proportional to temperature.

Principle:

• Based on the predictable change in base-emitter voltage (VBE) of a transistor with temperature
• Output voltage linearly proportional to Celsius temperature (10mV/°C)

Circuit diagram:

Working characteristics:

• Linear output: 10mV/°C (0.01V/°C) scale factor
• Range: -55°C to +150°C
• Accuracy: ±0.5°C (typical)
• Low self-heating: 0.08°C in still air
• Low impedance output: 0.1Ω for 1mA load

Mnemonic: “LOTUS: Linear Output Temperature Units from Semiconductor”

Question 4(b OR) [4 marks]

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Describe incremental type of Optical encoder with it’s output waveform.

Answer:

Incremental optical encoder generates pulses as shaft rotates to measure position, speed, and direction.

Construction:

Output waveform:

Working principle:

• Light source (LED) shines through slotted disk
• Photodetectors receive light pulses as disk rotates
• Two output channels (A and B) are 90° out of phase
• Direction determined by which channel leads
• Resolution depends on number of slots on disk

Mnemonic: “PADS: Pulses from A and Determine Speed”

Question 4(c OR) [7 marks]

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Describe construction, operation of LVDT with advantages, disadvantages and application.

Answer:

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

Construction:

Operation:

1. AC excitation applied to primary coil
2. Magnetic flux couples to secondary coils
3. Core position determines differential voltage output
4. Null position: Equal voltage in both secondaries
5. Movement: Voltage increases in one secondary, decreases in other

Advantages:

Disadvantages:

Applications:

• Machine tool positioning
• Hydraulic and pneumatic systems
• Aircraft and missile systems
• Automated manufacturing
• Structural testing

Mnemonic: “MOVE-AC: Magnetic Output Varies with Exact Armature Core position”

Question 5(a) [3 marks]

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Describe working of Pressure measurement using Capacitive transducer.

Answer:

Capacitive pressure transducer uses changes in capacitance to measure pressure.

Working principle:

• Pressure deforms diaphragm, changing distance between capacitor plates
• Capacitance inversely proportional to distance (C = ε₀εₐA/d)
• Change in capacitance is measured and converted to pressure reading

Diagram:

Application: Industrial process monitoring, atmospheric pressure measurement, liquid level sensing

Mnemonic: “CAPS: Capacitance Alters as Pressure Shifts”

Question 5(b) [4 marks]

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Define rise time, fall time, Pulse width and duty cycle.

Answer:

Diagram:

Mnemonic: “RPFD: Rise Pulses, Fall Determines”

Question 5(c) [7 marks]

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Discuss Function generator block diagram.

Answer:

Function generator produces various waveforms over a range of frequencies.

Block diagram:

Function and operation of each block:

Output waveforms:

Mnemonic: “FASTEST: Frequency Amplitude Shaping Together Ensures Signal Types”

Question 5(a OR) [3 marks]

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Discuss Working, construction of strain gauge.

Answer:

Strain gauge converts mechanical deformation to electrical resistance change.

Construction:

Working principle:

• Based on piezoresistive effect: resistance changes with mechanical deformation
• When bonded to object, strain gauge deforms along with it
• Resistance increases with tension (elongation)
• Resistance decreases with compression (shortening)
• Resistance change is measured using bridge circuit

Resistance change relation:

• ΔR/R = GF × ε
• Where: ΔR = resistance change, R = initial resistance
• GF = gauge factor (sensitivity), ε = strain

Materials used:

• Foil: Constantan, Karma, Nichrome alloys
• Semiconductor: Silicon, Germanium for higher sensitivity

Mnemonic: “SERB: Strain Effects Resistance by Bonding”

Question 5(b OR) [4 marks]

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Describe working of Digital IC tester with suitable diagrams.

Answer:

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

Block diagram:

Working principle:

1. IC is inserted into test socket
2. User selects IC type/number using keypad
3. Microcontroller loads appropriate test pattern
4. Test patterns applied to IC inputs
5. Output responses compared with expected values
6. Pass/Fail result displayed

Features of digital IC tester:

• Tests TTL, CMOS, HCMOS logic families
• Can identify unknown ICs by analyzing pin functions
• Performs functional and parametric tests
• Checks for static and dynamic characteristics

Mnemonic: “PIPE: Pattern Input, Pin Examination”

Question 5(c OR) [7 marks]

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Discuss working of Spectrum Analyzer with suitable diagrams.

Answer:

Spectrum analyzer displays signal amplitude versus frequency, showing frequency components.

Block diagram:

Working principle:

1. Superheterodyne conversion: Input signal mixed with local oscillator
2. Frequency sweep: Local oscillator sweeps across frequency range
3. IF filtering: Narrow bandpass filter selects frequency components
4. Detection: Amplitude of each frequency component is measured
5. Display: Amplitude vs. frequency plot shown on screen

Types of spectrum analyzers:

Applications:

• EMI/EMC testing
• Signal purity measurement
• Harmonic distortion analysis
• Communication system testing
• Modulation analysis

Mnemonic: “SHAFT: Sweep, Heterodyne, Analyze Frequency and Time”