Waveform Buffer Index problem

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Joined: Wed Aug 26, 2020 2:23 pm

Waveform Buffer Index problem

Post by Juanmaloria »

Hi !!

I am having trouble seeing the waveform in the spectrum (FFT) of the signals while measuring.

I am using Picoscope 4424 with software
(Fig. 1 attached)

In the file while measuring, it shows the number of signal processed in the "Capture Count" (0,1,2,3,4 ...)
(Fig. 2 attached)

But in the "Waveform Buffer Index" it only reaches number 3 and does not show the others.
(Fig. 3 attached)

I do not understand what the problem is, and if a patch that solves it?
Thanks in advance!!

Posts: 900
Joined: Mon Aug 11, 2014 11:14 am

Re: Waveform Buffer Index problem

Post by Gerry »

Hi Juan,

These are 2 completely independent counters.

The Waveform Buffer Index (your figure 3) tells you how many waveforms have been captured and are currently being held in Memory, while the Capture Count (your figure 2) tells you how many of the waveforms captured during the current Multiwaveform Capture are being used for the Statistical Values in the Measurement Bar (e.g. for Max, Average etc). So, during a Multiwaveform capture, the available waveform buffers (3 in your case) can be filled. Once that has happened any new waveforms that are captured, will overwrite the already captured waveforms, and this cycle repeats until you stop the capture. As you have only 3 Waveform buffers available, if you were able to stop the capture at the statistical Capture count of 10, you would have the last 3 of the captured waveforms in the waveform buffers, but the statistical value for Average (of the Amplitudes at Peak) would be the Average of all 10 waveforms that were captured, including the 7 that were overwritten (because you didn't have enough Waveform Buffers to capture all 10).

You may have set the maximum waveforms to be stored in the Wavefom Buffer specifically, but in case you haven't, and are wondering why you only have 3, I'll explain how that can happen now.

The Buffer Memory in the hardware PicoScope is split up to capture multiple triggered Waveforms, when you select a trigger Mode other than 'Single'. There will be a maximum number of split waveform buffers available for any capture, and this maximum defaults to 32 (if you haven't changed any settings). The maximum number of waveforms that will actually be stored for any capture will depend upon a number of things including the length of the capture period (selected as the 'Time-Base') along with the size of the Buffer Memory in your Hardware PicoScope. As you increase the length of the capture period, you will reach a point where there isn't enough memory left in the hardware PicoScope to store the maximum number of waveforms with each one using the capture period that you have selected. So at this point, the number of waveforms to be captured is reduced from the maximum value so that you will have fewer waveforms, but they will all have the capture time that you have selected.

However, you can also intentionally reduce the Maximum number yourself (if you haven't already done so) or increase it up to an absolute maximum of 10,000 waveforms by going to the menu options 'Tools->Preferences' and then setting the value you want.

The Maximum number of captures that will be used for statistics can also be changed (increased to a Maximum of 1,000) on the same preferences Tab.

I hope this clarifies things for you,


Technical Specialist

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