JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech IV ELECTRONIC MEASURING INSTRUMENTS Previous Question Paper (December - 2020 - R16)

Accuracy is the measure of how close a measured value is to the true or accepted value of the quantity being measured. It indicates the degree of correctness of the measurement and is typically expressed in terms of error, such as absolute error or percentage error. High accuracy ensures that the instrument provides a reading that represents the actual physical state of the parameter.

Precision is a measure of the reproducibility or consistency of a series of measurements. It describes the ability of an instrument to yield the same reading when the same input is applied repeatedly under identical conditions, regardless of whether that reading is close to the true value. Precision is characterized by the spread or dispersion of the measured values.

The necessity of these terms is fundamental to instrumentation for the following reasons:

• Accuracy is necessary to ensure that the data obtained is reliable and reflects the actual physical reality. In industrial control systems, inaccurate measurements can lead to improper process adjustments, resulting in safety hazards or product failure.
• Precision is necessary for repeatability and reliability in experimental and manufacturing processes. An instrument may be precise but inaccurate (e.g., due to a constant calibration offset), but high precision allows for the application of calibration corrections to achieve accuracy.
• Together, they define the performance specifications of an instrument. A high-quality instrument must be both accurate (to represent the truth) and precise (to maintain consistency over time and varying conditions).

Electronic and electrical measuring instruments are defined by their reliance on active components such as vacuum tubes, transistors, and integrated circuits to manipulate signals. Their performance is characterized by the following key attributes:

1. Sensitivity: These instruments exhibit high sensitivity, allowing for the measurement of extremely low-level signals (microvolts or picoamperes) that would be undetectable by purely mechanical instruments. This is achieved through internal amplification stages.
2. Input Impedance: Electronic instruments typically offer very high input impedance, particularly in voltage measurement. This minimizes the loading effect on the circuit under test, ensuring that the measurement does not alter the operating conditions of the source.
3. Frequency Response: Unlike mechanical instruments limited by inertia, electronic instruments possess an exceptionally wide bandwidth. They can accurately measure signals ranging from DC to several gigahertz, making them essential for high-frequency communication systems.
4. Speed of Response: Because they lack moving parts with significant mass, electronic instruments provide near-instantaneous readings. This allows for the monitoring of rapidly changing or transient signals.
5. Accuracy and Precision: These instruments offer superior accuracy due to stable electronic components and the ability to incorporate feedback loops. Digital versions further improve precision by eliminating reading errors associated with parallax or scale interpolation.
6. Signal Processing and Versatility: Electronic instruments can perform complex operations such as filtering, rectification, integration, and differentiation. They often include digital interfaces, allowing for data storage, remote control, and automated logging via computer systems.
7. Power Consumption: While the measurement circuitry requires a power supply, the actual power drawn from the measured source is negligible, which is a critical advantage in sensitive electronic circuit analysis.