Measurements with the Oscilloscope

The oscilloscope is the instrument of choice for observing how a voltage changes over time. It plots voltage on the vertical axis against time on the horizontal axis, drawing a graph of the waveform that lets an engineer read its amplitude, period, frequency, rise time and shape directly. By comparing two channels it can also measure the time delay or phase difference between signals, making it indispensable for understanding the dynamic behaviour of a circuit rather than just a single value.

A steady display depends on triggering. The trigger circuit starts each horizontal sweep at the same point on the waveform, for example each time the signal crosses a chosen level going upward, so that successive traces overlay and the picture appears to stand still. Without proper triggering a repetitive waveform drifts across the screen and cannot be read. Multi-channel scopes display several signals at once using chop or alternate modes to share the single display between channels.

Signals usually reach the scope through a probe. A common passive probe contains a 10X attenuator that divides the signal by ten; this raises the effective input impedance and reduces the loading the scope places on the circuit, at the cost of a smaller displayed signal that the scope scales back. Modern instruments are digital storage oscilloscopes, which sample the input, store it in memory and process it numerically, allowing single events to be captured and frozen. Feeding two signals to the vertical and horizontal inputs produces Lissajous figures whose shape reveals their frequency ratio and phase relationship.

Frequently asked questions

Why does an oscilloscope need triggering?

Triggering starts each sweep at the same point on a repetitive waveform so successive traces overlap and the display stands still, making it readable instead of drifting.

What does a 10X probe do?

A 10X passive probe attenuates the signal tenfold, which raises input impedance and reduces circuit loading. The oscilloscope scales the reading back to show the true value.

What is a digital storage oscilloscope?

It samples the input signal, stores the samples in memory and processes them digitally, which allows it to capture and freeze single, non-repeating events for later analysis.