Afternoon all,

Question 1.

This post http://www.autonerdz.com/cgi/yabb2/YaBB.pl?num=1265231719is the seed of this question.

Picoscope 6.3.43.0 running in demo mode.

In the attached .gif,No of samples is given as 109(2242).

What does this mean?What's my No of samples?

Question 2.

I have recently come across a reference to aliasing.

Can anyone explain what this is,how would I recognise it and what it means if it happens?

Thanks in advance,
Paul Galvin.

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I believe one is requested samples and the the other is actual number of samples collected.  The requested sample on pico units is adjustable.
I am not sure if it will help, I did a video clip on you tube showing the difference in requested sample rate changes.  Being in demo mode without a previously recorded file those numbers may not be accurate.

http://www.youtube.com/watch?v=YJEbhELLJQY

Sam

Hi Paul,

I try to address these questions as briefly as I can.

First of all, demo mode really does not show you how the real thing will perform.  


Quote:

What's my No of samples?

That is how many samples you are actually collecting, per active channel, per screen.

The important number is the sample rate.  This is the real time sample rate for each active channel based on your current settings.



Quote:

I have recently come across a reference to aliasing. Can anyone explain what this is,how would I recognize it and what it means if it happens?

Aliasing occurs when your scope sample rate is <2x signal frequency.  Aliasing renders the scope capture useless, displaying things that are not real.  This is an operator error issue that occurs when you push the scope beyond its limits.  

One of the best ways to conceptualize this is to play with the tools on this page:

http://www.autonerdz.com/java/SampleRateCalculator.html

Ever noticed how the wagon wheel on an old western movie sometimes turns backwards?  That's aliasing.  The wagon wheel is not really turning backwards.  The camera is taking samples of the scene at a fixed sample rate.  When the wheel gets too fast, aliasing occurs.

A PicoScope is very resistant to aliasing because of its sample rate capabiliy.  You can deliberately adjust the settings to make it alias though.

Here is a graphic description of aliasing...

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Jarvis,Tom and Joe,
thanks for the replies.

Joe,your graphic makes it very clear,thanks again.