Spectrum view displays the amplitudes of all the underlying frequencies that occur within your waveforms. The feature processes your waveforms using a Fast Fourier Transform (FFT) and displays their amplitudes on the vertical axis against frequency on the horizontal axis. The FFT is repeatedly applied to successive parts of your waveforms so that you can see how the amplitudes against frequency change with time.
Every waveform you ever look at is made up of one or more parts (sine waves) oscillating at a given frequency with a given amplitude and phase (time offset). Sometimes we want to know more about these parts than we do the overall waveform pattern. In these cases, we can use Spectrum to split up your waveform into its parts using an FFT and then display their amplitudes against their frequency as the waveform is captured.
Spectrum view is especially useful for Noise, Vibration and Harshness (NVH) analysis when we want to lock on to or identify specific frequencies of noise or vibration. A related example is finding the vibration frequency of an auxiliary drive belt, which we can use to calculate the belt tension (see the Belt tension guided test in PicoScope 7 Automotive).
It is possible to have both Scope and Spectrum views open in PS7 so you can see the overall waveform pattern (in the time domain) and how its parts are behaving (in the frequency domain).
Click the More… icon to open the More... panel then, within that, click on the Instruments icon to open the Instruments panel.
Click on the Spectrum icon to change the view from a time-based instrument (Scope) to a frequency-based instrument (Spectrum).
Alternatively, click on the Views icon to open the Views panel and then click Scope or Spectrum within that to add additional views of either.
When a Spectrum view is enabled the Timebase control changes to a Spectrum control containing all the relevant settings and options. The timebase of any active Scope views are automatically adjusted depending on the options selected in the Spectrum control.