Static vs dynamic characteristics in instrumentation: Which of the following is classified as a static characteristic of an instrument (i.e., observed under steady or very slowly varying conditions)?

Introduction / Context:
Instrument characteristics are broadly divided into static (evaluated at steady or quasi-steady conditions) and dynamic (observed during rapid changes). Understanding this distinction guides sensor selection, calibration intervals, and expected performance under process transients.

Given Data / Assumptions:

• Static characteristics include accuracy, precision, sensitivity, linearity, hysteresis, repeatability, and drift.
• Dynamic characteristics include time constant, rise time, overshoot, settling time, dynamic error, and time lag.
• We assume ordinary process sensors/transmitters.

Concept / Approach:
Drift is the slow change of an instrument’s output when the measurand remains constant. It reflects long-term stability and is assessed under steady conditions—hence a static characteristic. By contrast, response, time lag, rise time, and dynamic error describe how the instrument behaves when the input changes with time and therefore belong to dynamic characteristics.

Step-by-Step Solution:

Verification / Alternative check:
Instrumentation texts list drift alongside accuracy and linearity in static performance tables, separate from transient response metrics.

Why Other Options Are Wrong:

• Response / rise time / time lag: Time-domain metrics of dynamics.
• Dynamic error: Explicitly a dynamic characteristic describing deviation during transients.

Common Pitfalls:
Confusing “sensitivity” (static) with “response speed” (dynamic); they are not the same. Also, do not equate calibration shift (drift) with noise; drift is systematic over time.

Final Answer:
Drift