Question 1(a) [3 marks]

Define Accuracy, Precision, and Sensitivity.

Answer:

Accuracy: The closeness of a measured value to the actual or true value of a quantity.
Precision: The ability of an instrument to reproduce the same output reading when the same input is applied repeatedly under the same conditions.
Sensitivity: The ratio of change in output of an instrument to the change in input, indicating how much output changes for a small change in input.

Table: Differences between Accuracy and Precision

Parameter	Accuracy	Precision
Definition	Closeness to true value	Repeatability of measurement
Focus on	Correctness	Consistency
Representation	Bulls-eye center hits	Clustered hits

Mnemonic: "APS - Accuracy Pinpoints truth, Precision Shows repeatability, Sensitivity Signals small changes"

Question 1(b) [4 marks]

Describe the working and limitations of the Wheatstone bridge with circuit diagram.

Answer:

Working: The Wheatstone bridge measures unknown resistance by balancing two legs of a bridge circuit.

Circuit Diagram:

graph LR
    A[Battery] --> B[Point A]
    A --> C[Point C]
    B --> D[Point B]
    B --> E[Point D]
    C --> E
    C --> F[Point C]
    D --- G[Galvanometer]
    F --- G
    B -- R1 --- D
    D -- R2 --- C
    B -- R3 --- F
    F -- Rx --- C

When bridge is balanced: R1/R2 = R3/Rx, so Rx = R3×(R2/R1)

Limitations:

Limited range: Not suitable for very low or very high resistances
Temperature effects: Resistance changes with temperature
Battery errors: Output voltage must remain stable
Galvanometer sensitivity: Limited by detector sensitivity

Mnemonic: "BALR - Balance is key, Adjust until null, Low/high resistances problematic, Range is limited"

Question 1(c) [7 marks]

Explain various transducers used for temperature measurement. Explain the construction and working of the following in detail: (i) Thermocouple (ii) Thermistor.

Answer:

Temperature Transducers Types:

Type	Working Principle	Range	Advantages	Disadvantages
Thermocouple	Seebeck effect	-270°C to 2300°C	Wide range, robust	Nonlinear, reference needed
Thermistor	Resistance change	-50°C to 300°C	High sensitivity	Nonlinear, limited range
RTD	Resistance change	-200°C to 850°C	High accuracy, linear	Expensive, self-heating
IC Sensors	Semiconductor	-55°C to 150°C	Linear output, easy interface	Limited range

(i) Thermocouple:

Construction: Two dissimilar metal wires (like copper-constantan or iron-constantan) joined at one end to form measuring junction and other ends connected to measuring instrument.

graph LR
    A[Metal A] --- B[Measuring Junction]
    C[Metal B] --- B
    A --- D[Reference Junction]
    C --- D
    D --- E[Measuring Instrument]

Working: When junctions are at different temperatures, a small voltage proportional to temperature difference is generated (Seebeck effect).

Key Points:

Seebeck effect: Temperature difference creates voltage
Cold junction compensation: Required for accuracy
Types: J, K, T, E based on metal combinations

(ii) Thermistor:

Construction: A semiconductor material (metal oxides like manganese, nickel, cobalt) shaped into a bead, disk, or rod with two lead wires.

  Lead Wire        Lead Wire
      |               |
      v               v
    +-----------------+
    |   Ceramic or    |
    | Semiconductor   |
    |     Body        |
    +-----------------+

Working: Resistance decreases as temperature increases (NTC type) or increases with temperature (PTC type).

Key Points:

NTC (Negative Temperature Coefficient): Most common type
High sensitivity: Large resistance change for small temperature change
Nonlinear response: Requires linearization circuits
Self-heating: Current passing through it causes heating

Mnemonic: "TRIP - Thermocouples React to junction differences, Thermistors Intensely change resistance, Point sensors at what you measure"

Question 1(c) OR [7 marks]

Explain the working principles of the following sensors: Temperature sensor, Gas sensor, Humidity sensor and Proximity sensor.

Answer:

Comparison of Sensors:

Sensor Type	Working Principle	Output	Applications
Temperature	Resistance/voltage change	Analog/Digital	HVAC, Medical devices
Gas	Chemical reaction	Resistance change	Safety systems, Air quality
Humidity	Capacitance/resistance change	Analog	Weather stations, HVAC
Proximity	Electromagnetic field disruption	Digital	Automation, Security

1. Temperature Sensor (LM35):

Principle: Semiconductor junction voltage varies with temperature
Working: Integrated circuit provides output voltage proportional to temperature (10mV/°C)
Features: Linear output, no external calibration needed

2. Gas Sensor (MQ-2):

Principle: Chemical reaction between gas and sensing material
Working: Gas molecules interact with metal oxide semiconductor, changing its resistance
Detection: When gas concentration exceeds threshold, output voltage changes

graph LR
    A[Gas molecules] --> B[Sensing layer]
    B --> C[Resistance changes]
    C --> D[Voltage output changes]
    D --> E[Comparator circuit]
    E --> F[Alarm/Output signal]

3. Humidity Sensor (Hygrometer):

Principle: Capacitance or resistance varies with moisture absorption
Working: Dielectric material absorbs moisture, changing electrical properties
Types: Capacitive (more accurate) and resistive (simpler)

4. Proximity Sensor:

Principle: Detects objects without physical contact
Working: Emits electromagnetic field/beam; detects changes when object enters field
Types: Inductive (metals), capacitive (any material), ultrasonic (distance)

Mnemonic: "TGHP - Temperature Generates voltage, Gas Hits semiconductors, Humidity Holds moisture, Proximity Perceives objects"

Question 2(a) [3 marks]

List types of DVM and mention one advantage of each.

Answer:

Types of Digital Voltmeters (DVM):

DVM Type	Working Principle	Advantage
Ramp Type	Compares input with reference ramp	Simple design, low cost
Integrating Type	Measures average over time	Good noise rejection
Successive Approximation	Binary search algorithm	Fast conversion speed
Dual Slope	Integration with fixed time	Excellent noise rejection

Key Points:

Ramp type: Simple but affected by noise
Integrating type: Reduces effect of periodic noise
Successive approximation: Quick readings, good for changing signals
Dual slope: Best accuracy, immune to most noise

Mnemonic: "RISD - Ramp Is Simple Design, Integrating Ignores noise, Successive Secures speed, Dual Deals with interference"

Question 2(b) [4 marks]

Draw and explain Maxwells's bridge.

Answer:

Maxwell's Bridge is used to measure unknown inductance by comparing it with a standard capacitance.

Circuit Diagram:

graph LR
    A[Supply] --> B[Point B]
    A --> C[Point D]
    B --> D[Point A]
    B --> E[Point C]
    C --> E
    C --> F[Point D]
    D --- G[Detector]
    F --- G
    B -- R1 --- D
    D -- R2 --- C
    B -- R3 --- F
    F -- L,R4 --- C

Balance Equations:

Unknown inductance L = R2 × R3 × C
Resistance R4 = R1 × (R3/R2)

Working:

Bridge contains four arms with R1, R2, R3, and L,R4
When bridge is balanced, no current flows through detector
Values of L and R4 calculated using balance equations

Advantages:

High accuracy: Good for medium value inductors
Independent balance: Resistance and inductance balanced separately

Mnemonic: "MILL - Maxwell's Inductance is Like L = R2R3C, when the detector shows Lowered current"

Question 2(c) [7 marks]

Draw the block diagram of a Successive Approximation type Digital Voltmeter (DVM) and explain its working.

Answer:

Successive Approximation DVM converts analog input to digital output using binary search algorithm.

Block Diagram:

graph LR
    A[Analog Input] --> B[Signal Conditioning]
    B --> C[Sample & Hold]
    C --> D[Comparator]
    E[Clock] --> F[Successive Approximation Register]
    F --> G[D/A Converter]
    G --> D
    D --> F
    F --> H[Digital Display]
    I[Reference Voltage] --> G

Working:

Signal conditioning: Scales input voltage to measurement range
Sample & Hold: Captures instantaneous input value
SAR (Successive Approximation Register): Performs binary search
DAC (Digital-to-Analog Converter): Converts digital value to analog
Comparator: Compares input with DAC output
Digital Display: Shows final digital value

Example Conversion Process:

For 4-bit conversion of 9V (range 0-15V):
- Try 8V (1000) → Input > 8V → Keep 1
- Try 12V (1100) → Input < 12V → Change to 0
- Try 10V (1010) → Input < 10V → Change to 0
- Try 9V (1001) → Input = 9V → Keep 1
- Result: 1001 (9V)

Advantages:

Fast conversion: Fixed conversion time regardless of input
Good accuracy: Suitable for most applications
Medium complexity: Balance of performance and cost

Mnemonic: "SHARP - Sample, Hold, Approximate, Register stores, Present result"

Question 2(a) OR [3 marks]

State and explain the working principle of PMMC instruments.

Answer:

PMMC (Permanent Magnet Moving Coil) instruments operate based on electromagnetic principles.

Working Principle: When current flows through a coil placed in a magnetic field, a torque is produced causing the coil to rotate proportionally to the current.

Key Components:

Permanent magnet: Creates strong magnetic field
Moving coil: Wound on aluminum frame
Control springs: Provide restoring torque
Pointer: Indicates reading on scale

Diagram:

                  N
    Spring       | |      Spring
      ↓          | |        ↓
    +=================+
    |      |=====|    |
    |      | Coil|    |
    |      |=====|    |
    |               .-|-.
    |              /     \
    |              |     |  Pointer
    |              \     /
    |               `-|-'
    +=================+
                  | |
                  S

Mnemonic: "PMMC - Permanent Magnet Makes Coil turn when Current flows"

Question 2(b) OR [4 marks]

Draw and explain Schering bridge.

Answer:

Schering Bridge is used to measure capacitance and dissipation factor of a capacitor.

Circuit Diagram:

graph LR
    A[AC Supply] --> B[Point A]
    A --> C[Point C]
    B --> D[Point B]
    B --> E[Point D]
    C --> E
    C --> F[Point C]
    D --- G[Detector]
    F --- G
    B -- R1 --- D
    D -- C2 --- C
    B -- C4,R4 --- F
    F -- Cx,Rx --- C

Balance Equations:

Unknown capacitance Cx = C2 × (R1/R4)
Unknown resistance Rx = R4 × (C4/C2)
Dissipation factor D = ωCxRx = ωC4R4

Working:

Contains four arms with R1, C2, Cx-Rx, and C4-R4
When bridge is balanced, no current flows through detector
Values of Cx and Rx calculated using balance equations

Applications:

Capacitor testing: Measures capacitance and losses
Insulation testing: Evaluates dielectric properties

Mnemonic: "SCAN - Schering Capacitance And taN delta measured together"

Question 2(c) OR [7 marks]

Draw and explain Dual slope integrating type DVM.

Answer:

Dual Slope Integrating DVM is a type of digital voltmeter that converts analog input to digital form using integration method.

Block Diagram:

graph LR
    A[Analog Input] --> B[Input Buffer]
    B --> C[Integrator]
    D[Reference Voltage] --> E[Polarity Switch]
    E --> C
    C --> F[Comparator]
    G[Zero Reference] --> F
    F --> H[Control Logic]
    I[Clock] --> H
    H --> E
    H --> J[Counter]
    J --> K[Digital Display]
    H --> J

Working Principle:

First phase (Fixed time T1):
- Input voltage integrated for fixed time T1
- Output of integrator = -(1/RC)∫V(in)dt
- Counter counts clock pulses
Second phase (Variable time T2):
- Reference voltage of opposite polarity applied
- Integrator output returns to zero
- Time T2 proportional to input voltage
- T2 = T1 × (Vin/Vref)

Advantages:

Excellent noise rejection: Especially power line frequency (50/60 Hz)
High accuracy: Depends only on reference voltage and clock stability
Automatic zero correction: Self-calibrating feature

Key Points:

Integration time: Usually multiple of power line period (20ms or 16.67ms)
Resolution: Determined by clock frequency and counter capacity

Mnemonic: "FIRE - First Integrate input, then Integrate Reference, until Equal to zero"

Question 3(a) [3 marks]

What is the importance of delay line and trigger circuit in a CRO?

Answer:

Delay Line Importance:

Purpose: Delays the signal to display events that trigger the sweep
Function: Allows viewing of leading edge of signal that caused trigger
Implementation: Artificial transmission line with LC network or microstrip

Trigger Circuit Importance:

Purpose: Initiates sweep at specific point on input signal
Function: Ensures stable, stationary display of repetitive waveforms
Controls: Level, slope, source, and coupling

Table: Delay Line vs Trigger Circuit:

Component	Purpose	Benefit
Delay Line	Delays signal path	Shows complete waveform including trigger point
Trigger Circuit	Initiates sweep	Creates stable display with synchronized timing

Mnemonic: "DT-SS - Delay To See Signal, Trigger Stops Screen drift"

Question 3(b) [4 marks]

Explain the internal structure and working of a Cathode Ray Tube (CRT) with a neat diagram.

Answer:

Cathode Ray Tube (CRT) is the heart of an oscilloscope that converts electrical signals into visual display.

Structure Diagram:

       Electron Gun                Deflection System               Screen
      |------------|            |----------------|              |-------|
 +----|------------|------------|----------------|--------------|-------|----+
 |    |            |            |                |              |       |    |
 |    V            V            V                V              V       |    |
 |  +----+      +---+        +----+          +----+          +----+     |    |
 |  |Cath|      |   |        |    |          |    |          |    |     |    |
 |  |ode |----->| F |------->| VA |--------->| H  |--------->| P  |     |    |
 |  |    |      |   |        |    |    |     |Def.|    |     |Scr.|     |    |
 |  +----+      +---+        +----+    |     +----+    |     +----+     |    |
 |                                     |               |                |    |
 |                                   +----+         +----+              |    |
 |                                   |    |         |    |              |    |
 |                                   | V  |         |Flu.|              |    |
 |                                   |Def.|-------->|Scr.|              |    |
 |                                   |    |         |    |              |    |
 |                                   +----+         +----+              |    |
 |                                                                      |    |
 +----------------------------------------------------------------------+    |
      |                                                                      |
    Glass                                                               Vacuum
   Envelope

Key Components:

Electron Gun:
- Cathode: Heated filament that emits electrons
- Control Grid: Regulates electron beam intensity
- Focusing Anodes: Concentrate electrons into beam
- Accelerating Anodes: Increase electron velocity
Deflection System:
- Horizontal Deflection Plates: Control X-axis movement
- Vertical Deflection Plates: Control Y-axis movement
Screen:
- Phosphor Coating: Glows when struck by electrons
- Glass Envelope: Maintains vacuum and provides structure

Working:

Heated cathode emits electrons
Control grid regulates beam intensity (brightness)
Focusing anodes form narrow beam
Accelerating anodes speed up electrons
Deflection plates bend beam horizontally and vertically
Electron beam strikes phosphor screen, creating visible spot

Mnemonic: "EFADS - Electrons Fly, Anodes Direct, Screen shows signals"

Question 3(c) [7 marks]

Explain the working of a Cathode Ray Oscilloscope (CRO) with the help of a block diagram and describe the function of each block.

Answer:

Cathode Ray Oscilloscope (CRO) is an electronic instrument used to visualize and analyze electrical signals.

Block Diagram:

graph LR
    A[Vertical Input] --> B[Vertical Attenuator]
    B --> C[Vertical Amplifier]
    C --> D[Delay Line]
    D --> E[Vertical Deflection Plates]
    F[Trigger Circuit] --> G[Time Base Generator]
    G --> H[Horizontal Amplifier]
    H --> I[Horizontal Deflection Plates]
    J[External Trigger Input] --> F
    C --> F
    G --> K[Blanking Circuit]
    K --> L[CRT]
    E --> L
    I --> L
    M[Power Supply] --> L
    M --> All

Functions of Each Block:

Block	Function
Vertical Attenuator	Scales input signal to suitable level
Vertical Amplifier	Amplifies signal for deflection plates
Delay Line	Delays signal to see triggering event
Trigger Circuit	Initiates sweep at specific point
Time Base Generator	Creates sawtooth wave for horizontal sweep
Horizontal Amplifier	Amplifies sweep signal
Blanking Circuit	Cuts beam during retrace
CRT	Converts electrical signals to visual display
Power Supply	Provides various DC voltages

Working Process:

Signal Input: Connected to vertical attenuator
Vertical Processing: Signal scaled, amplified, delayed
Triggering: Trigger circuit starts time base at specific point
Horizontal Sweep: Time base creates horizontal movement
Display: Electron beam traces signal on screen
Retrace: Beam returns quickly (blanked) for next sweep

Controls:

Vertical: Volts/div, position, coupling
Horizontal: Time/div, position
Trigger: Level, slope, source, mode

Mnemonic: "VATH-CDS - Vertical Attenuates Then amplifies, Horizontal Creates Deflection Sweep"

Question 3(a) OR [3 marks]

Give the differences between Cathode Ray Oscilloscope (CRO) and Digital Storage Oscilloscope (DSO).

Answer:

Comparison between CRO and DSO:

Parameter	Cathode Ray Oscilloscope (CRO)	Digital Storage Oscilloscope (DSO)
Signal Processing	Analog	Digital (ADC conversion)
Storage Capability	None (real-time only)	Can store waveforms in memory
Bandwidth	Limited by CRT technology	Higher bandwidth possible
Display	Phosphor screen	LCD/LED screen
Additional Features	Basic measurements	Advanced analysis, FFT, math functions

Key Differences:

Waveform Storage: DSO can save waveforms, CRO cannot
Signal Processing: DSO converts analog to digital, CRO is purely analog
Pre-trigger Display: DSO can show events before trigger
Analysis Features: DSO offers measurements, math functions, FFT

Mnemonic: "DSO-MAPS - Digital Storage Oscilloscope Measures, Analyzes, Processes, Stores signals"

Question 3(b) OR [4 marks]

Explain how frequency and phase angle can be determined with the help of CRO.

Answer:

Frequency Measurement on CRO:

Method:

Display signal on screen
Measure time period (T) using horizontal time/div setting
Calculate frequency: f = 1/T

Example Calculation:

If 3 cycles span 6 divisions at 0.5ms/div
Time for 3 cycles = 6 div × 0.5ms/div = 3ms
Time for 1 cycle (T) = 3ms ÷ 3 = 1ms
Frequency (f) = 1/T = 1/1ms = 1kHz

Phase Angle Measurement:

Method:

Display both signals on dual channel
Measure time difference (Δt) between corresponding points
Measure time period (T) of complete cycle
Calculate phase difference: φ = (Δt/T) × 360°

Diagram:

    Voltage
       ^
       |
       |    Signal 1      Signal 2
       |       /\           /\
       |      /  \         /  \
       |     /    \       /    \
       |----/------\-----/------\-----> Time
       |   /        \   /        \
       |  /          \ /          \
       | /            V            \
       |/                           \
       +----------------------------->
           |<--Δt-->|
           |<-------T-------->|

Calculation:

If Δt = 1 div at 0.2ms/div, and T = 5 div at 0.2ms/div
Δt = 0.2ms and T = 1ms
Phase difference: φ = (0.2ms/1ms) × 360° = 72°

Mnemonic: "FPL - Frequency = Period's Length reciprocal, Phase = (Lag/Period) × 360"

Question 3(c) OR [7 marks]

Draw the block diagram of a Digital Storage Oscilloscope (DSO) and explain the function of each block.

Answer:

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

Block Diagram:

graph LR
    A[Analog Input] --> B[Attenuator/Amplifier]
    B --> C[Anti-aliasing Filter]
    C --> D[Analog-to-Digital Converter]
    D --> E[Acquisition Memory]
    E --> F[Digital Signal Processor]
    F --> G[Display Memory]
    G --> H[Display Controller]
    H --> I[LCD Display]
    J[Trigger System] --> D
    K[Microprocessor] --> F
    K --> J
    K --> H
    L[Control Panel] --> K
    M[Clock Generator] --> D
    M --> K

Functions of Each Block:

Block	Function
Attenuator/Amplifier	Conditions input signal to ADC range
Anti-aliasing Filter	Removes high frequencies to prevent aliasing
ADC	Converts analog signal to digital samples
Acquisition Memory	Stores digitized waveform data
Digital Signal Processor	Performs mathematical operations on signals
Display Memory	Stores processed data for display
Display Controller	Controls screen update and format
Microprocessor	Controls overall operation and user interface
Trigger System	Determines when to start data acquisition
Clock Generator	Provides timing for sampling and processing

Advantages of DSO:

Single-shot capture: Can capture transient events
Pre-trigger viewing: Shows signal before trigger point
Waveform storage: Saves signals for later analysis
Advanced measurements: Automated amplitude, timing, etc.
Mathematical functions: Addition, FFT, integration, etc.

Working Process:

Input signal conditioned by attenuator/amplifier
Signal filtered to prevent aliasing
ADC samples signal at regular intervals
Digital data stored in acquisition memory
Processor analyzes and prepares data for display
Display shows waveform and measurements

Mnemonic: "AADPD - Attenuate Analog, Digitize, Process, Display the signal"

Question 4(a) [3 marks]

Give the classification of different types of transducers.

Answer:

Classification of Transducers:

Classification Basis	Types
Principle of Operation	Mechanical, Electrical, Thermal, Optical, Chemical
Input/Output Relationship	Primary, Secondary
Signal Generation	Active, Passive
Electrical Parameters	Resistive, Capacitive, Inductive
Transduction	Photoelectric, Electrochemical, Thermoelectric

Primary Classification:

Based on Energy Conversion:
- Active Transducers: Generate electrical output without external power (e.g., thermocouple)
- Passive Transducers: Require external power (e.g., thermistor)
Based on Principle of Operation:
- Primary Transducers: Convert physical change directly to electrical signal
- Secondary Transducers: Require intermediate conversion

Mnemonic: "APRCI - Active/Passive, Resistive/Capacitive/Inductive are key categories"

Question 4(b) [4 marks]

Explain the construction and working of a strain gauge.

Answer:

Strain Gauge converts mechanical strain (deformation) into electrical resistance change.

Construction:

Grid Pattern: Thin foil or wire in zigzag pattern
Backing Material: Polyimide or epoxy carrier
Lead Wires: Connected to measurement circuit
Adhesive: Bonds gauge to test surface

Diagram:

   Lead Wire                Lead Wire
      |                        |
      v                        v
    +----------------------------+
    |                            |  Backing
    |   +--------------------+   |  Material
    |   | /\/\/\/\/\/\/\/\/\ |   |
    |   | \                / |   |
    |   |  \    Grid     /   |   |
    |   |   \   Pattern /    |   |
    |   |    \/\/\/\/\/      |   |
    |   +--------------------+   |
    |                            |
    +----------------------------+

Working Principle:

Based on piezoresistive effect
When object deforms, gauge deforms
Deformation changes resistance per formula:
- ΔR/R = GF × ε
- Where GF = Gauge Factor, ε = Strain

Measurement Circuit:

Usually connected in Wheatstone bridge
Converts small resistance change to voltage
Output voltage proportional to strain

Applications:

Load cells, pressure sensors
Structural testing
Mechanical stress analysis

Mnemonic: "GRID - Gauge Resistance Increases with Deformation"

Question 4(c) [7 marks]

Explain the Linear Variable Differential Transducer (LVDT) with its construction, working, advantages, and applications.

Answer:

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

Construction:

Primary Coil: Central winding excited by AC source
Secondary Coils: Two identical coils on either side
Core: Ferromagnetic material that moves with displacement
Housing: Cylindrical shell with terminals

Diagram:

graph LR
    A[AC Source] --> B[Primary Coil]
    C[Core] --- B
    B --- D[Secondary Coil 1]
    B --- E[Secondary Coil 2]
    D --> F[Signal Conditioning]
    E --> F
    F --> G[Output]
    H[Movement] --> C

Working Principle:

AC voltage applied to primary coil
Magnetic flux couples to secondary coils
Core position determines coupling efficiency
Voltage differential between secondaries ∝ displacement
At null position (center), secondary voltages are equal and opposite

Characteristic Curve:

     Output
       ^
       |                Secondary Voltages
       |                     /
       |                    /
       |                   /
       |                  /
       |                 /
       |----------------/-----------------> Displacement
       |               /
       |              /
       |             /
     --|------------/----
       |           /
  Null Position

Advantages:

Frictionless operation: No mechanical contact
Infinite resolution: Analog output
High linearity: Direct proportional output
Ruggedness: Resistant to shock and vibration
Long life: No wearing parts

Applications:

Industrial: Automated machine tools, robotics
Aerospace: Flight control systems
Civil Engineering: Structural testing
Metrology: Precision measurement instruments

Mnemonic: "LVDT-MAPS - Linear Variable Differential Transformer Measures Accurately Position by Secondary voltage differences"

Question 4(a) OR [3 marks]

State any three uses of PH sensors.

Answer:

Uses of PH Sensors:

Application	Purpose	Importance
Water Treatment	Monitor and control water quality	Ensures safe drinking water
Agriculture	Soil monitoring for optimal plant growth	Increases crop yield
Medical Diagnostics	Measuring body fluid acidity	Critical for patient health

Additional Applications:

Food Processing: Quality control during production
Aquaculture: Maintaining optimal water conditions
Chemical Manufacturing: Process control

Mnemonic: "WAM - Water quality control, Agriculture soil testing, Medical diagnostics are key PH sensor applications"

Question 4(b) OR [4 marks]

Explain the construction and working of a capacitive transducer.

Answer:

Capacitive Transducer converts physical change into capacitance variation which is measured electrically.

Construction:

Parallel Plates: Two conductive plates
Dielectric Medium: Air, ceramic, or other material
Housing: Protective enclosure
Terminals: Electrical connections

Diagram:

    Terminal A             Terminal B
        |                     |
        v                     v
    +----------+         +----------+
    |          |         |          |
    |  Plate A |         |  Plate B |
    |          |<------->|          |
    |          |    d    |          |
    +----------+         +----------+
           |                 |
           |    Dielectric   |
           |     Material    |
           |                 |
    +--------------------------+
    |        Housing           |
    +--------------------------+

Working Principle:

Capacitance C = ε₀εᵣA/d
- ε₀ = Permittivity of free space
- εᵣ = Relative permittivity of dielectric
- A = Area of plates
- d = Distance between plates

Types of Variation:

Area variation: Changing overlap of plates
Distance variation: Changing separation between plates
Dielectric variation: Changing dielectric material

Applications:

Pressure sensors: Diaphragm changes plate distance
Level sensors: Dielectric changes with fluid level
Humidity sensors: Dielectric changes with moisture
Proximity sensors: Distance changes with object presence

Mnemonic: "CAD - Capacitance changes with Area, Distance, or Dielectric variations"

Question 4(c) OR [7 marks]

Describe absolute optical encoder and its A, B, C waveform outputs with proper illustration.

Answer:

Absolute Optical Encoder directly measures angular position by generating a unique digital code for each position.

Construction:

Code Disc: Contains concentric tracks with transparent/opaque sectors
Light Source: LED array illuminating the disc
Photo Detectors: Sensors detecting light through disc patterns
Signal Conditioning: Converts photodetector signals to digital outputs

Diagram:

graph LR
    A[LED Light Source] --> B[Code Disc]
    B --> C[Photodetectors]
    C --> D[Signal Conditioning Circuit]
    D --> E[Digital Output]
    F[Rotating Shaft] --> B

Code Disc Pattern:

          Track C (Index)
            |
     -------|-----------------
            |
          --+--  --+--  --+--
           Track B
     -------|-----------------
            |
          -++--  -++--  -++--
           Track A
     -------|-----------------
            |
          -+++- -+++- -+++- -
     -------|-----------------
            |
            V
          Rotation

Waveform Outputs:

Signal	Purpose	Characteristics
A Signal	Position information	Square wave, 50% duty cycle
B Signal	Direction information	90° phase shifted from A
C Signal	Reference/index	Single pulse per revolution

Output Waveforms:

    A Signal  _____|‾‾‾‾‾|_____|‾‾‾‾‾|_____|‾‾‾‾‾|_____|‾‾‾‾‾|_____
    
    B Signal  __|‾‾‾‾‾|_____|‾‾‾‾‾|_____|‾‾‾‾‾|_____|‾‾‾‾‾|_____|‾‾
    
    C Signal  _____|‾|_________________________________________________
              
              0°    90°   180°   270°   360°   450°   540°   630°   720°

Working principle:

A & B output provides quadrature signals (90° out of phase)
Direction determined by which signal leads:
- If A leads B: Clockwise rotation
- If B leads A: Counter-clockwise rotation
Position determined by counting pulses
C signal provides reference/home position

Applications:

CNC machines: Precise position control
Robotics: Joint angle measurement
Camera systems: Lens positioning
Industrial automation: Motor control

Mnemonic: "ABC-PDP - Absolute encoder tracks A, B, C Provide Direction, Position, and reference pulse"

Question 5(a) [3 marks]

Describe the working principle of a basic frequency counter.

Answer:

Frequency Counter measures frequency of an input signal by counting events over a precise time interval.

Working Principle:

Count number of cycles/pulses of input signal
Divide by the precise gate time
Display resulting frequency

Basic Blocks:

Input Conditioning: Shapes signal to digital levels
Gate Control: Opens gate for precise time
Counter: Counts pulses during gate open time
Time Base: Generates precise gate timing
Display: Shows frequency value

Simplified Diagram:

graph LR
    A[Input Signal] --> B[Input Conditioning]
    B --> C[AND Gate]
    D[Time Base] --> E[Gate Control]
    E --> C
    C --> F[Counter]
    F --> G[Display]

Mnemonic: "CTPG - Count The Pulses, Gate the time"

Question 5(b) [4 marks]

Draw the diagram of an energy meter and explain its working principle.

Answer:

Electronic Energy Meter measures electrical energy consumption in kilowatt-hours (kWh).

Block Diagram:

graph LR
    A[Voltage Sensor] --> C[Analog Multiplier]
    B[Current Sensor] --> C
    C --> D[Voltage-to-Frequency Converter]
    D --> E[Pulse Counter]
    E --> F[Microcontroller]
    F --> G[LCD Display]
    H[Crystal Oscillator] --> F
    F --> I[LED Indicator]
    F --> J[Communication Interface]

Working Principle:

Energy = Power × Time
Power = Voltage × Current
Voltage and current sensed separately
Multiplied to get instantaneous power
Integrated over time to get energy
Pulses generated proportional to energy
Each pulse represents fixed energy unit
Counter accumulates pulses
Display shows accumulated energy

Features:

Tamper detection: Prevents electricity theft
Multiple tariffs: Different rates for different times
Communication: Remote reading capability

Mnemonic: "VCPI - Voltage and Current are multiplied, Pulses Indicate energy used"

Question 5(c) [7 marks]

Briefly explain the working principle and functions of a function generator. Describe its front panel controls and explain how it is used to test electronic circuits with suitable examples.

Answer:

Function Generator is an electronic test instrument that generates different waveforms with adjustable frequency and amplitude.

Working Principle:

Generates base signal using oscillator circuit
Shapes waveform using wave-shaping circuits
Adjusts amplitude, frequency, and offset parameters
Outputs waveform through buffer amplifier

Block Diagram:

graph LR
    A[Oscillator] --> B[Wave Shaper]
    B --> C[Output Amplifier]
    D[Frequency Control] --> A
    E[Waveform Selector] --> B
    F[Amplitude Control] --> C
    G[DC Offset Control] --> C
    C --> H[Output]
    I[Modulation Input] --> A

Front Panel Controls:

Control	Function	Typical Range
Frequency	Sets signal frequency	0.1 Hz - 20 MHz
Amplitude	Sets signal amplitude	0 - 20 Vpp
DC Offset	Adds DC voltage	±10V
Waveform Select	Chooses waveform type	Sine, Triangle, Square, Pulse
Duty Cycle	Adjusts pulse width	10% - 90%
Modulation	AM/FM modulation	Internal/External

Output Waveforms:

    Sine      /\      /\      /\
             /  \    /  \    /  \
    _______ /    \__/    \__/    \__
    
    Square   ______      ______
            |      |    |      |
    ________|      |____|      |____
    
    Triangle  /\      /\      /\
             /  \    /  \    /  \
    ________/    \__/    \__/    \__
    
    Pulse     __        __        __
             |  |      |  |      |  |
    _________|  |______|  |______|  |_

Circuit Testing Applications:

Application	Waveform Used	Purpose
Amplifier Testing	Sine wave	Gain, frequency response
Digital Circuit Testing	Square wave	Logic timing, thresholds
Filter Testing	Sine sweep	Cutoff frequency, response
Triggering Circuits	Pulse	Threshold testing

Example: Testing Amplifier

Connect function generator to amplifier input
Set sine wave of appropriate amplitude
Vary frequency to test frequency response
Monitor output on oscilloscope
Calculate gain = Output amplitude / Input amplitude

Mnemonic: "FAWOD - Frequency, Amplitude, Waveform, Offset, Duty cycle are key controls"

Question 5(a) OR [3 marks]

Describe the working of a spectrum analyzer.

Answer:

Spectrum Analyzer measures signal amplitude versus frequency, showing frequency components of signals.

Working Principle:

Converts time-domain signals to frequency-domain
Shows spectral components and their amplitudes
Uses superheterodyne receiver architecture
Sweeps local oscillator to analyze frequency range

Block Diagram:

graph LR
    A[Input Signal] --> B[Attenuator/Amplifier]
    B --> C[Mixer]
    D[Local Oscillator] --> C
    C --> E[IF Filter]
    E --> F[Detector]
    F --> G[Display]
    H[Sweep Generator] --> D
    H --> G

Applications:

Signal analysis: Measuring harmonics, distortion
EMI testing: Finding interference sources
Communications: Channel analysis, modulation quality

Mnemonic: "SAME - Spectrum Analyzer Maps signal Energy across frequencies"

Question 5(b) OR [4 marks]

Draw a neat diagram of a clamp-on meter and explain its working.

Answer:

Clamp-on Meter (Current Clamp) is a non-contact device for measuring AC/DC current.

Construction Diagram:

         Display
         .------.
        /        \
       /  120.5A  \    Function
      /            \    Selector
     |   O |--|     |  .----.
     |     |  |     |  |    |
     |     |  |     |--'    |
     |     |  |     |       |
     |     |  |     |       |
     |     '--'     |       |
      \   Trigger   /       |
       \           /        |
        |         |        /
        |         |       /
        |         |      /
        `---------´     /
             |         /
           Clamp      /
             |       /
            /       /
           /       /
          /       /
         `-______´
         Test Leads

Working Principle:

Based on electromagnetic induction (Faraday's Law)
Current-carrying conductor creates magnetic field
Clamp's ferromagnetic core concentrates field
Secondary coil in the clamp induces proportional voltage
Circuit converts induced voltage to current reading

Advantages:

Non-contact: No need to disconnect circuit
Safety: Isolation from high voltages
Convenience: Easy to use in confined spaces

Applications:

Electrical maintenance: Motor current, load testing
Power quality: Measuring power factor, harmonics
Troubleshooting: Finding unbalanced loads

Mnemonic: "CLIP - Clamp measures current, Lets magnetic Induction Produce voltage"

Question 5(c) OR [7 marks]

Explain the working principle of a digital IC tester. Describe its block diagram and explain how it is used to test the functionality of digital ICs with a suitable example.

Answer:

Digital IC Tester verifies functionality of digital integrated circuits by applying test patterns and comparing responses.

Working Principle:

Applies predefined test vectors to IC pins
Compares actual outputs with expected outputs
Identifies faulty ICs or incorrect functions
Tests multiple IC types using stored test patterns

Block Diagram:

graph LR
    A[Microcontroller] --> B[ROM/Test Pattern Memory]
    A --> C[Input Pattern Generator]
    C --> D[ZIF Socket/IC Under Test]
    D --> E[Output Response Analyzer]
    E --> A
    A --> F[Display]
    G[Keypad/Control Panel] --> A
    H[Power Supply] --> D
    H --> A

Major Components:

ZIF Socket: Zero Insertion Force socket for easy IC placement
Test Pattern Memory: Stores test vectors for various ICs
Output Response Analyzer: Compares actual vs. expected outputs
Microcontroller: Controls testing sequence and evaluation
Display: Shows test results and status

Testing Method:

Step	Action	Purpose
1	Select IC type	Load correct test parameters
2	Insert IC in ZIF socket	Prepare for testing
3	Start test	Begin test sequence
4	Apply test vectors	Exercise IC functions
5	Compare responses	Identify errors
6	Display results	Show pass/fail status

Example: Testing 7400 NAND Gate IC:

Select "7400" from IC list
Insert IC in ZIF socket
Tester applies all input combinations:
- Input 1A=0, 1B=0 → Expected output 1Y=1
- Input 1A=0, 1B=1 → Expected output 1Y=1
- Input 1A=1, 1B=0 → Expected output 1Y=1
- Input 1A=1, 1B=1 → Expected output 1Y=0
Repeat for all gates in package (7400 has 4 NAND gates)
Compare actual outputs to expected truth table
Display "PASS" if all tests succeed, or error code if failure

Features of Modern IC Testers:

Auto-identification: Detects unknown ICs
Learning mode: Creates test patterns for new ICs
Functional testing: Tests in-circuit operation
Parameter testing: Checks timing, voltage margins

Mnemonic: "TEST - Test patterns Exercise all States, Then verify outputs"

  Lead Wire        Lead Wire
      |               |
      v               v
    +-----------------+
    |   Ceramic or    |
    | Semiconductor   |
    |     Body        |
    +-----------------+

Working: Resistance decreases as temperature increases (NTC type) or increases with temperature (PTC type).

Key Points:

NTC (Negative Temperature Coefficient): Most common type
High sensitivity: Large resistance change for small temperature change
Nonlinear response: Requires linearization circuits
Self-heating: Current passing through it causes heating

Mnemonic: "TRIP - Thermocouples React to junction differences, Thermistors Intensely change resistance, Point sensors at what you measure"