Sampling

What it does

Sampling helps you to set the total number of samples (single measurement values at regularly spaced intervals) that make up each of your waveforms and the rate at which they are taken.

You can choose whether to prioritise Buffer memory (a fixed number of samples) or Sample rate (a fixed sampling rate) as you increase your timebase (the time over which each waveform is captured).

When you prioritise Buffer memory you can choose from presets giving you a low, normal or a high number of samples or choose a custom target value. Likewise, when you prioritise Sample rate you can choose from presets giving you a slow, normal or fast sampling rate or choose a custom target value.

Sampling lets you choose where to apply Progressive mode, which determines when the waveform is displayed (either after it has been captured in its entirety or as it is captured, bit by bit).

How it can help you

Waveforms can come in all different shapes and sizes. They can change quickly or slowly and last a long time or a very short time. When capturing waveforms, you must make sure you capture them in their entirety and with sufficient detail. That is, both your timebase and sample rate must be sufficiently high.

In theory, every time we capture a waveform we should assess both our timebase and sample rate needs independently, make sure PicoScope is set accordingly and then just let the total number of samples work itself out. However, this can take a bit of mental juggling so, instead, PicoScope’s Sampling mode priority takes some of this mental strain from us:

If you increase your timebase but keep the sample rate fixed, the total number of samples increases. This is the relationship between the settings you would need if you wanted to look at the same, perhaps repeating, waveform type (i.e. where the detail stays the same) over a longer period of time.

Similarly, if you increase your timebase but keep the total number of samples fixed, the sample rate decreases. This is the relationship between the settings you would need if you wanted to look at waveforms with reducing detail as the capture time increased.

It turns out that the Sample rate and Buffer memory sampling modes, respectively prioritise these two relationships. So rather than having to change the sampling rate every time you need to change your timebase you can use the Sampling mode that is most appropriate to your tasks and then just adjust the timebase up and down as required.

It is possible to capture all your waveforms with an excessively high sample rate, whilst leaving the Sampling mode on Sample rate priority. You would certainly not be missing any detail, however, you might end up with a lot of undesirably large files (the total number of samples could be very large) when saving your captures to your local disk.

When your timebase is relatively high and each of your waveforms is captured over a long time period, it can cause problems if you have to wait for the entire waveform to be captured before it is displayed. For example, you might miss an important waveform event that would cause you to complete the test or restart the capture. Or, worse still, you might find out that you are capturing the wrong waveform. By displaying a lengthy waveform as each part of it is captured, Progressive mode gives you a chance, before it is too late, to check your waveforms and act on any important waveform details or events.

How to use it

Click on the Timebase control to open the Timebase panel, then click the Sampling tab to view the Sampling options.

Under Sampling mode priority, choose Buffer memory if, as you increase the timebase, you want to keep the number of samples constant or, alternatively, Sample rate if you want to keep the sample rate constant.

If prioritising Buffer memory, choose a preset (Low, Normal or High) number of samples or adjust the Target number of samples to set a Custom value. If prioritising Sample rate, choose a preset (Slow, Normal or Fast) sample rate or adjust the Target sampling rate to set a Custom value.

Use the Progressive mode control to increase or decrease the timebase value that determines when PicoScope transitions from displaying each waveform once it has been captured in its entirety to displaying it bit by bit as it is captured.