ELEC 243 Lab

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Accuracy, Precision, and Resolution of Measurement Instruments

Accuracy

There is no such thing as an absolutely accurate or a perfect measurement. A measurement's accuracy represents how closely it represents the actual value. Instruments themselves obey physical laws and usually interact with the phenomenon being measured, limiting measurement accuracy. Using a Digital Multimeter (DMM) as an example, accuracy is often stated as some percentage of the actual measurement, or as a percentage of the full scale measurement. For example, the Hewlett-Packard DMM has a specified accuracy of \({\pm}0.3\%\) for DC voltage measurements, \(1%\) for DC current, \(2%\) for AC voltage and current, and \(0.7%\) for resistance. Tables of these accuracies are usually published in operating manuals.

Resolution

The smallest measurable change that can be detected is resolution. The DMM has a resolution of one least significant digit. The resolution of the scope and function generator depends on how good your eyesight is. Something on the order of \(0.5%\) would be typical.

Precision

Precision specifies an instrument's ability to repeat a given measurement. If you measure a resistance using the ohmmeter mode on the DMM and then come back a few minutes later, you should record the same value for the resistance. However, instruments can drift and the stability of the measured phenomenon may be in question.