Frequency drop outs.

Ask any questions about using PicoScope Automotive software here.

Frequency drop outs.

Postby Fat Freddy » Mon May 08, 2017 3:40 am

Has there been any comment from the Pico team anywhere about the frequency graphing drop outs as mentioned here:
topic16831-10.html
that I have missed.

It's a reasonable common thing. Apply Freq(A) to the file located here viewtopic.php?f=48&t=16871&view=unread#unread the results are hit and miss.

Cheers
FF
User avatar
Fat Freddy
TwoWaves
TwoWaves
 
Posts: 311
Joined: Fri May 04, 2012 6:52 am

Re: Frequency drop outs.

Postby Martyn » Mon May 08, 2017 12:39 pm

If you activate low pass filtering in the channel options, I left it at 1kHz, and apply a maths channel for freq(A), the trace becomes stable across all buffers.

When using frequency based maths it is often useful to filter out some of the noise as this can be interpreted as crossing points for the frequency calculations, causing misleading values. Remember the software has the same base code as the test and measurement version, which is designed for very high frequencies compared to those found in the automotive world.
Martyn
Technical Support Manager
Martyn
Pico Staff Member
Pico Staff Member
 
Posts: 219
Joined: Thu Aug 11, 2011 9:43 am
Location: Cambridgeshire

Re: Frequency drop outs.

Postby Fat Freddy » Mon May 08, 2017 2:52 pm

Thanks Martyn. I had not tried that. A handy tip to know. :D

But I could not get it to work on the other example here. topic16831-10.html
So what am I missing?
User avatar
Fat Freddy
TwoWaves
TwoWaves
 
Posts: 311
Joined: Fri May 04, 2012 6:52 am

Re: Frequency drop outs.

Postby Martyn » Mon May 08, 2017 3:41 pm

The issue with those traces are the signal levels are very low, the traces are set at x3 to make them more visible in the display, and there are glitches of noise present. This make it difficult to calculate the mid level crossing points, with the necessary boundary settings, to be able to determine the frequency. Where you see jumps in the frequency trace, zoom in on the live channel data and you will often see a spike.

I had suggested AC coupling this signal to centre it around the zero line and allow for a fuller scale signal trace, but even this has a certain amount of ripple which is throwing out the calculations. If you zoom in on the frequency jumps you can usually see something different happening in the live trace.
Martyn
Technical Support Manager
Martyn
Pico Staff Member
Pico Staff Member
 
Posts: 219
Joined: Thu Aug 11, 2011 9:43 am
Location: Cambridgeshire

Re: Frequency drop outs.

Postby Fat Freddy » Tue May 09, 2017 10:55 am

Thanks for the info there Martyn. Good to know. :)
User avatar
Fat Freddy
TwoWaves
TwoWaves
 
Posts: 311
Joined: Fri May 04, 2012 6:52 am


Return to PicoScope 6 Automotive software

Who is online

Users browsing this forum: No registered users and 0 guests