Waveform averaging

In PicoScope, waveform averaging is a mathematical function that computes the average of a sequence of waveforms. This is useful for removing noise from a repetitive signal. The result of averaging is a cleaner picture with the same frequency resolution as the original capture but with increased vertical resolution.

PicoScope can display the current waveform (without any averaging) alongside the averaged waveform. This allows you to see the effect averaging is having on the signal.

Figure 1: Unstable filtered square wave viewed with PicoScope

The signal source used in this example was the PicoScope 3206B’s own arbitrary waveform generator. The oscilloscope timebase was adjusted so that one cycle almost filled the scope view. In this real-time view, we can see that the pulse heights vary but there is no way to measure the variability.

Figure 2: The Buffer Navigator displays thumbnail pictures of the 32 stored waveforms

PicoScope automatically stores the selected number of waveforms (by default, 32) in the waveform buffer. We can now click the Buffer Navigator button to explore the contents of the buffer:

Figure 3: Color persistence mode shows the variation between waveforms

The Navigator view can be scrolled to review the stored waveforms. Any waveform can be transferred to the main scope view by clicking its thumbnail picture in the Navigator. This method allows us to make detailed measurements on any waveform we like, but we are still limited to viewing one waveform at a time.

Another way to view multiple waveforms is to enable Color Persistence mode. This is switched on by clicking the Persistence Mode button:

PicoScope now displays new data superimposed on old data, with the more stable parts of the waveform in brighter colors. This gives an indication of the relative frequency of occurrence of the unstable pulses. We can now see that most pulses have clean exponential rising and falling edges (shown in red) but some of them are truncated (as shown in blue). This mode gives a qualitative view of the variability of the waveform, but average pulse height and width can only be estimated.

Figure 4: The math channels wizard

To obtain quantitative results, we can use the averaging function provided by the Math Channels feature. This is done by simply clicking the Create button in the Math Channels dialog, then the x (average) button and the channel A button:

Figure 5: Live waveform (top), averaged waveform (bottom)

All other settings can be left at their defaults. The result is a new, averaged waveform added to the display (we also used the Auto Arrange Axes context menu command to separate the two traces):

Figure 6: Averaged waveform with measurements table

With this averaged waveform we can now click the Add Measurement button to measure parameters such as amplitude, pulse width and rise time:

Rapid Trigger mode

PicoScope acquires the specified number of waveforms directly into the scope’s buffer memory before displaying the data the screen. This mode can achieve very short delays between waveforms: as little as 1 µs on fast timebases. The averaging function works on these waveforms too.