Basic AC Waveform

transformer     wave

This page shows a simple example of the oscilloscope in use.

The picture on the far left is a typical AC mains transformer in a power supply and the waveform shows the AC waveform from it.

The voltage changes smoothly and rises to a value above the central (zero volts) line by the same amount as it falls below the line.

The oscilloscope timebase is set to 10 mS/Div and the trace takes two divisions to complete one cycle (ie: from one positive peak to the next) which is 20 mSeconds. So, there are 1000 / 20 = 50 cycles per second. The frequency is 50Hz.

The oscilloscope's vertical (Y) amplifier is set to 5 volts/Div and there are just under three divisions from peak to peak - roughly 14 volts. The stated 10 volts output from the transformer is known as its rms value - the waveform's true peak to peak value is 1.4 times this, ie: 14 volts.