JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech III ELECTRONIC MEASUREMENTS AND INSTRUMENTATION Previous Question Paper (August - 2022 - R16)

A generalized measuring system consists of three primary stages: the primary sensing element, the variable conversion element, and the data presentation element. The block diagram follows a sequential flow: Input Quantity → Primary Sensing Element → Variable Conversion Element → Variable Manipulation Element → Data Transmission Element → Data Presentation Element.

1. Primary Sensing Element: Receives the physical quantity (measurand) and produces an output proportional to the input, such as a transducer converting pressure to displacement.
2. Variable Conversion Element: Converts the output of the sensor into a more suitable variable, such as electrical voltage or current, without changing the information content.
3. Variable Manipulation Element: Modifies the signal to a form suitable for the next stage, typically involving amplification, filtering, or attenuation.
4. Data Transmission Element: Transmits the signal from one location to another, often over long distances, using cables, telemetry, or wireless links.
5. Data Presentation Element: The final stage that provides the information in a human-readable format, such as a digital display, recorder, or computer interface.

Static characteristics describe the performance of an instrument when the measurand is constant or varies very slowly over time. Key static characteristics include:

• Accuracy: The closeness of the measured value to the true value of the quantity.
• Precision: The ability of an instrument to reproduce the same reading consistently under identical conditions.
• Sensitivity: The ratio of the change in output to the change in input, defined as
  S = d(output) / d(input)
  .
• Resolution: The smallest change in the input that can be detected by the instrument.
• Linearity: The ability of the instrument to maintain a linear relationship between input and output over its operating range.
• Hysteresis: The difference in output readings for the same input when approached from increasing versus decreasing directions.
• Drift: A gradual change in the output over time while the input remains constant, often due to environmental factors like temperature.