1. FUNDEMANTELS OF MEASUREMENTS (EE 3003)

 These are short notes for revision purpose. please refer you Reference book & College study materials for complete study.

For Further Notes Join 📍

• WhatsApp Group - https://chat.whatsapp.com/DWpN7vYqSutBNXY9R5Q2Te
• Telegram Channel - https://t.me/BTER_Electrical_Branch

1. FUNDAMENTALS OF MEASUREMENTS

1.1 Measurements: Significance, Units, Fundamental Quantities, and Standards

• Measurement refers to the process of determining the value of a physical quantity using appropriate instruments.
• Significance: Accurate measurement is essential in engineering for designing, controlling, and testing electrical and electronic systems.
• Units: Standard units are critical for consistency. The International System of Units (SI) is used globally. Some common units in electrical measurements include:
  • Length: Meter (m)
  • Time: Second (s)
  • Mass: Kilogram (kg)
  • Current: Ampere (A)
  • Voltage: Volt (V)
  • Resistance: Ohm (Ω)
• Fundamental Quantities: The seven base quantities in SI units are:
  • Length (meter)
  • Mass (kilogram)
  • Time (second)
  • Electric current (ampere)
  • Thermodynamic temperature (kelvin)
  • Amount of substance (mole)
  • Luminous intensity (candela)
• Standards: A standard is a reference against which measurements are compared. Some standards are:
  • Primary standards: These are established by national and international bodies and are highly accurate.
  • Secondary standards: Derived from primary standards, these are used for practical measurements.

1.2 Classification of Instrument Systems

1.2.1 Null and Deflection Type Instruments

• Null Instruments: These instruments measure a physical quantity by nullifying or balancing the effect of the measured quantity. Examples include a Wheatstone bridge.
  • Pros: High accuracy
  • Cons: Requires manual adjustments and a steady environment.
• Deflection Type Instruments: These instruments indicate the measured quantity by the deflection of a pointer or a display. Examples include analog voltmeters and ammeters.
  • Pros: Simple and easy to use.
  • Cons: Less accurate than null instruments.

1.2.2 Absolute and Secondary Instruments

• Absolute Instruments: These provide a direct reading of the quantity to be measured. Examples are the galvanometer and digital voltmeter.
  • Pros: They give the exact value of the quantity.
  • Cons: Expensive and complex.
• Secondary Instruments: These require calibration against primary standards to give accurate readings. Examples are analog voltmeters, ammeters.
  • Pros: Cheaper and easier to use.
  • Cons: Not as accurate as absolute instruments.

1.2.3 Analog and Digital Instruments

• Analog Instruments: These provide continuous readings on a scale (e.g., a needle on a dial). Example: Analog voltmeter.
  • Pros: Can show a continuous range of values.
  • Cons: Less precise and may suffer from parallax error.
• Digital Instruments: These provide readings in numerical form on a display. Example: Digital multimeter.
  • Pros: More accurate, easy to read, and no parallax error.
  • Cons: May require a power supply and can have resolution limits.

1.3 Types of Errors

Errors in measurement are unavoidable and can be classified into:

• Systematic Errors: These errors are consistent and repeatable, often caused by the calibration or design flaws of the instrument. Examples: zero error, temperature drift.
  • Can be corrected by proper calibration or recalibration of the instrument.
• Random Errors: These errors occur due to unpredictable factors like environmental conditions and observer interpretation.
  • Can be minimized by repeated measurements and averaging the results.
• Gross Errors: These errors occur due to human mistakes like misreading the instrument or wrong setup.
  • Can be minimized by careful observation and correct handling.

1.4 Calibration: Need and Procedure

• Need for Calibration: Calibration ensures that the instrument provides accurate and reliable measurements. Without proper calibration, measurements can be erroneous.
• Procedure:
  1. Select a known standard (e.g., a standard voltage source or reference).
  2. Adjust the instrument to match the standard value.
  3. Verify that the instrument produces the correct output for a range of values.
  4. Document any calibration certificates or records.

1.5 Classification of Measuring Instruments

1.5.1 Indicating Instruments

• Indicating Instruments display the value of the quantity being measured directly, typically using a pointer or digital display. Examples include voltmeters and ammeters.
• These instruments do not record data over time, only showing the instantaneous value.

1.5.2 Recording Instruments

• Recording Instruments continuously record the measured value over time. These include devices like oscillographs, strip chart recorders, and data loggers.
• Useful in applications where monitoring of trends over time is necessary, such as in temperature or current monitoring.