JNTU B.Tech III ELECTRICAL AND ELECTRONICS INSTRUMENTATION Previous Question Paper (August - 2022 - R16)

Calibration is the process of comparing an instrument's output against a known standard to ensure its accuracy. It is categorized into static and dynamic types based on the nature of the input signal.

Static Calibration involves applying known constant (DC) inputs to the instrument and recording the corresponding outputs. This process determines the static performance characteristics, such as sensitivity, linearity, and hysteresis, by comparing the instrument's reading to a standard reference under steady-state conditions.

Dynamic Calibration involves applying time-varying inputs, such as sinusoidal, step, or ramp functions, to the instrument. This evaluates how the instrument responds to changing signals, identifying characteristics like frequency response, phase shift, and settling time, which are critical for instruments used in real-time monitoring.

The static characteristics of an instrument describe its performance when measuring a constant input. Key characteristics include:

• Accuracy: The closeness with which an instrument reading approaches the true value of the variable being measured.
• Precision: The measure of the reproducibility of measurements given a fixed value of a variable.
• Sensitivity: The ratio of the change in output to the change in input, defined as the slope of the calibration curve.
• Resolution: The smallest change in the input value that produces a detectable change in the instrument output.
• Linearity: The ability of an instrument to produce an output that is directly proportional to the input over its operating range.
• Hysteresis: The difference in output readings for the same input value when approached from increasing versus decreasing directions.
• Threshold: The minimum input value required to produce a detectable output change from zero.
• Drift: A gradual shift in the instrument's output over time while the input remains constant, often caused by environmental changes or component aging.

Standard test signals are used to analyze the dynamic response and stability of control systems. These signals provide a known input to a system, allowing engineers to observe the output and determine characteristics such as speed of response, accuracy, and stability.

The primary standard test signals are:

1. Step Signal: Represents a sudden change in the input value at a specific time. It is defined as r(t) = A for t ≥ 0 and 0 for t < 0. It is used to test the transient response and steady-state error of a system.
2. Ramp Signal: Represents a signal that increases linearly with time. It is defined as r(t) = At for t ≥ 0 and 0 for t < 0. It is used to determine the system's ability to track a changing input, often used to evaluate velocity error constants.
3. Parabolic Signal: Represents a signal that increases quadratically with time. It is defined as r(t) = At²/2 for t ≥ 0 and 0 for t < 0. It is used to test the system's response to acceleration inputs.
4. Impulse Signal: Represents a signal of very high magnitude applied for an infinitesimally small duration. It is defined as the derivative of the step signal, where the area under the pulse is unity. It is primarily used to determine the impulse response of a system, which characterizes the system's transfer function.
5. Sinusoidal Signal: Represents a signal that varies periodically with time, defined as r(t) = A sin(ωt). It is used to analyze the frequency response of a system, providing information about bandwidth, gain margin, and phase margin.