Static and dynamic performance parameters

Static characteristics describe an instrument's performance when the input is constant or changes very slowly. Dynamic characteristics describe its response when the input changes with time.

Static parameters

• Accuracy: closeness of the measured value to the true value.
• Precision: closeness of repeated readings to each other (reproducibility).
• Resolution: smallest change in input that gives a detectable change in output.
• Sensitivity: change in output per unit change in input (Δo/Δi).
• Linearity: how closely the calibration curve is a straight line; expressed as a percentage of full scale.
• Threshold: minimum input needed to start any output change from zero.
• Hysteresis: different outputs for the same input depending on direction of change.
• Drift: change in output with no change in input (zero drift, span drift).
• Range and span: limits of input the instrument can measure; span = max − min.
• Dead zone / dead band: range of input where there is no output change.
• Repeatability and reproducibility, stability, tolerance.

Dynamic parameters

• Speed of response: how quickly the instrument responds to a change in input.
• Measuring lag: delay in response; retardation type (immediate but slow response) and time-delay type (response starts after a dead time).
• Fidelity: ability to reproduce the input waveform without distortion.
• Dynamic error: difference between the true value and the indicated value when the input changes with time.
• Bandwidth and frequency response: range of input frequencies for which the amplitude ratio stays within limits.
• Time constant, rise time, settling time, overshoot for first- and second-order systems.
• Damping ratio and natural frequency for second-order systems.