A word derived from the Latin oscillum, meaning to swing back and forth, and the Greek word skopien, meaning to observe or examime.

Voltmeters sample electrical current and display the results as numbers on a screen (digital) or as a needle sweeping across a scale (analogue).

Mains electricity traced on an oscilloscopeOscilloscopes sample the electrical circuit much more frequently, and display the results as a moving dot, which leaves a trace on a screen with a graph and graticules as a background.

The oscilloscope has two voltage probes, one of which we connect to the signal we want to observe, and the other which we connect to ground. The oscilloscope then reports in the difference in potential between the two probes.

Many oscilloscopes have a separate ground connection which helps protect both the instrument and the operator. You should always connect this and the probe earth before probing other circuits.

NOTE: Oscilloscopes can only measure voltage, they CANNOT measure current. What oscilloscopes can do is to make use of an inductive current clamp around a current carrying conductor.

As we know, electrical current always has an associated magnetic field, and the oscilloscope can use this magnetic field to measure the corresponding current flow. The oscilloscope can then display a value for the current flow.

» Course Glossary

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