Static Characteristics of Measuring Instruments:

The Static Characteristics of Measuring Instruments are, in general, considered for instruments which are used to measure an unvarying process condition.

All the static performance characteristics are obtained by one form or another of a process called calibration. There are a number of related definitions (or characteristics), which are described below, such as accuracy, precision, repeatability, resolution, errors, sensitivity, etc.

1. Instrument:

A device or mechanism used to determine the present value of the quantity under measurement.

2. Measurement:

The process of determining the amount, degree, or capacity by comparison (direct or indirect) with the accepted standards of the system units being used.

3. Accuracy:

The degree of exactness (closeness) of a measurement compared to the expected (desired) value.


The smallest change in a measured variable to which an instrument will respond.

5. Precision:

A measure of the consistency or repeatability of measurements, i.e. successive reading do not differ. (Precision is the consistency of the instrument output for a given value of input).

6. Expected value:

The design value, i.e. the most probable value that calculations indicate one should expect to measure. .

7. Error:

The deviation of the true value from the desired value.

8. Sensitivity:

The ratio of the change in output (response) of the instrument to a change of input or measured variable.

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