ELEC 243 Lab

Background

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, Fluke DMM has a specified accuracy of $\pm0.3\%$ for DC voltage measurements, 1.5% for DC current, 2% for AC voltage and current, and 0.5% for resistance. Tables of these accuracies are usually published in operating manuals (see the Instruction Manuals page).

Resolution is the smallest measurable change that can be detected. The DMM has a resolution of one least significant digit. The resolution of the oscilloscope depends on how good your eyesight is. Something on the order of 0.5% would be typical. 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.