Does the ppk2 average the high sampling rate when using its low sampling rate?

RE: Does the ppk2 average the high sampling rate when using its low sampling rate?

Simonr — Thu, 13 Apr 2023 12:04:42 GMT

Sorry, I guess that wasn't very clear. Can you provide the .ppk files (they can be exported from the app and uploaded in a .zip file to DevZone) of your application starting up at I.E. 1 sample/sec and 1000 samples per sec. for example where it should be easy to see the difference in timing.

Best regards,

Simon

UPDATE: More exactly what our developer wants you to do. Repeat the experiment with both sampling frequencies and also at higher or even full frequency and use the same window selected (also use SHIFT+LEFT CLICK and DRAG as shown in the UI) in order to correlate the different measurements might help us decide if this is in fact a bug or just a fluke.

RE: Does the ppk2 average the high sampling rate when using its low sampling rate?

douglas.malnati — Wed, 12 Apr 2023 12:50:53 GMT

Hi, thanks for the update!

[quote userid="75734" url="~/f/nordic-q-a/98079/does-the-ppk2-average-the-high-sampling-rate-when-using-its-low-sampling-rate/419949"]Do you think you can upload the same data set under different sampling conditions in the same time window and provide some calculations so we can be sure that we're seeing this on the same measurements?[/quote]

I'm not sure what you mean by that.

In the images above, I showed two different sampling rates for the event of a device turning on. My questions were around how the "average" values were calculated given the timeframes and sampling rates stated.

What are you looking for?

Thanks.

Doug

RE: Does the ppk2 average the high sampling rate when using its low sampling rate?

Simonr — Wed, 12 Apr 2023 12:27:54 GMT

So I got a hold of a person involved in writing the averaging algorithm, and here's what they have to say (paraphrasing):

It is a simple rolling average that does not use buffers.

We have tested the averaging extensively so that it provides the same average value below the chart for a given selected window for the same datasets within a reasonable error margin.

Do you think you can upload the same data set under different sampling conditions in the same time window and provide some calculations so we can be sure that we're seeing this on the same measurements?

Best regards,

Simon

RE: Does the ppk2 average the high sampling rate when using its low sampling rate?

Simonr — Wed, 12 Apr 2023 09:19:05 GMT

Just wanted to give you an update. We're struggling to find the right person to answer this correctly. I'll let you know when I find a good answer to this.

Again, thank you for your patience!

Simon

RE: Does the ppk2 average the high sampling rate when using its low sampling rate?

douglas.malnati — Thu, 06 Apr 2023 12:50:22 GMT

Ok thanks, happy holidays!

RE: Does the ppk2 average the high sampling rate when using its low sampling rate?

Simonr — Mon, 03 Apr 2023 07:12:36 GMT

Hi Doug

Just wanted to let you know that I've forwarded this question internally as well, but we're now in the Easter holiday here in Norway, so we're short on staff and delayed replies must be expected. I can't guarantee any updates on this before Tuesday April 11th. Thank you for your patience!

Best regards,

Simon

RE: Does the ppk2 average the high sampling rate when using its low sampling rate?

douglas.malnati — Thu, 30 Mar 2023 13:02:53 GMT

Hi Simon, thanks for looking into that!

Not sure I understand how the described approach leads to the first graph I showed though.

Here, at 1 sample per second, I see it takes more than 3 seconds for my current measurement to rise from ~8mA to ~25mA.

However, I know, from a high-speed measurement, that the rise time is less than 1 second.

So that means, in the 1-sample-per-second graph:

the first plotted rise point used some of the rise in its average
the second plotted rise point used some of the rise in its average
the third plotted rise point used some of the rise in its average

How can that be?

If each point takes into consideration 100,000 samples, and the device takes 100,000 samples per second, then each of the plotted points couldn't have seen the rise in their window.

Or do the 1-sample-per-second plot points use overlapping data from one another?

And did you find out about how the rolling window is centered?

Thanks.

Doug

RE: Does the ppk2 average the high sampling rate when using its low sampling rate?

Simonr — Thu, 30 Mar 2023 05:41:44 GMT

Sorry about the late reply, I got an update from the devs on this yesterday, and we're using Simple Moving Average to calculate the samples on the fly in the Power Profiler: https://github.com/NordicSemiconductor/pc-nrfconnect-ppk/blob/7d175d9da2a43582de82ce370e75b65ea4236d6b/src/actions/deviceActions.ts#L274-L291

For 1 sample/sec for example, we use Simple Moving Average on 100 000 samples before returning the averaged values, for 10 samples/sec we do it on 10 000 samples, and so on. So the difference could indeed be quite big.

Best regards,

Simon

RE: Does the ppk2 average the high sampling rate when using its low sampling rate?

douglas.malnati — Fri, 24 Mar 2023 13:58:22 GMT

Thank you Simonr.

I had seen the advanced settings, and did increase the size. Very useful.

My primary concern is not the duration of capture, though, but to understand how the averaging works (all my questions above, really). Please let me know when you find out!

Thanks!

RE: Does the ppk2 average the high sampling rate when using its low sampling rate?

Simonr — Fri, 24 Mar 2023 13:55:11 GMT

The Power profiler app does indeed average the 100 000 samples per second into the resolution of your choosing. I've asked the developers for details on how exactly the averaging is done, and I'll get back to you when I hear from them.

An alternative to get larger logs at higher sample rates is to open the advanced settings with SHIFT+Ctrl+Alt+A when you've opened the PPK2 and increase the sampling buffer size to get higher sampling rates for longer times.

Best regards,

Simon

RE: Does the ppk2 average the high sampling rate when using its low sampling rate?

douglas.malnati — Fri, 24 Mar 2023 01:30:53 GMT

Ah I also wanted to understand how the "average" and "max" values were calculated, once I understand the windowing.

Based on some toying around, the "max" appears to be the max of the actual plotted values. The average I'm less clear on. Would it be the average of all the values in the rolling window?