Performance Characteristics of Measuring Instruments

Static Characteristics

Sensitivity: For the smallest changes in the measured variable, the instrument responds.

Static Error: The difference between true value of the quantity to the value shown by the instrument not changing with the time.

Repeatability: When the Instrument is calibrated at different times, has to show the same at different times.

Accuracy: Closeness of instrument reading to the true value of the measured variable.

Reproducibility: The degree of closeness with which a given value is repeatedly measured. The instrument has to the show same value over long periods of time under the same operating conditions.

Drift: Slow shift in the calibration of the instrument. This may be due to the variation of metallic properties, due to chemical changes. For example coating formation on RTD elements, Thermocouple. Due to continuous exposure. Atomic structure changes occur in metals of RTDs, Thermocouples.

Dead Zone: For the largest changes in the measured variable, the instrument does not respond.

Precision: Degree of exactness for which the instrument is designed.

For example exact figure is 1,592,154 ohms   It should not be rounded to show is 15 ohms.

Dynamic Characteristics

Dynamic Error: The difference between the true value of the quantity to the value shown by the instrument (changing with time).

Speed of response: Rapidity with which instrument responds to the changes in the measured variable.

Fidelity: The degree to with which instrument responds to the changes in a measured variable without dynamic error.

Lag: Delay in the response of the instrument to the measured variable.