Jawaharlal Nehru Technological University Hyderabad B.Tech IV SENSORS AND TRANSDUCERS Previous Question Paper (September - 2022 - R16)

Measurement methods are categorized based on how the measurand is evaluated against a standard. The distinction between direct and indirect methods is as follows:

• Direct Comparison Method: In this method, the physical quantity to be measured is compared directly against a primary or secondary standard. The measurement involves a physical observation of the quantity, such as using a meter scale to measure length or a balance to measure mass. These methods are simple but often lack high sensitivity and are prone to human observational errors.
• Indirect Comparison Method: This method involves converting the physical quantity into an equivalent analog or digital signal, which is then measured. Since direct comparison is not always feasible for quantities like pressure, temperature, or flow, transducers are used to convert these into measurable electrical signals (voltage, current, or resistance).

Measurement errors are deviations from the true value of a quantity. They are classified into three primary categories:

• Gross Errors: These are primarily caused by human mistakes in reading, recording, or calculating data. Examples include misreading an instrument scale, incorrect adjustment of an instrument, or improper application of a device. These errors cannot be treated mathematically and are minimized by taking multiple readings and ensuring careful observation.
• Systematic Errors: These are predictable and repeatable errors that occur due to shortcomings in the instrument or the measurement environment. They are further classified into:
  • Instrumental Errors: Due to inherent defects, friction, or hysteresis in the device.
  • Environmental Errors: Due to external conditions like temperature, pressure, or magnetic fields affecting the sensor.
  • Observational Errors: Such as parallax error while reading a pointer.
  These can be reduced by calibration and applying correction factors.
• Random Errors: These are unpredictable errors that remain after systematic errors have been accounted for. They are caused by unknown, small fluctuations in the experiment, such as electrical noise or minor vibrations. These errors follow statistical laws, and their impact is minimized by calculating the arithmetic mean of a large number of readings and applying statistical analysis like standard deviation.