Test and Measurement Forum

Sample rate can be reduced?

Post any questions you may have about our current range of oscilloscopes

Sample rate can be reduced?

Postby heng » Mon Jun 11, 2012 7:27 pm

Do the scopes sample at 500 MS/s under all conditions, or can I reduce the sample rate? Specifically, 8 MS storage is plenty for me if I can sample at 30 MS/s (but not at 500MS/s). It's not clear to me that this flexibility exists however.

Perhaps someone could clarify this?

Also, as a prospective customer, I'd like to make my interest for 64-bit linux drivers known.

Cheers,
Henry
heng
Newbie
 
Posts: 0
Joined: Mon Jun 11, 2012 7:08 pm

Re: Sample rate can be reduced?

Postby Hitesh » Tue Jun 12, 2012 4:18 pm

Hi Henry,

You can adjust the sampling rate with our USB PC Oscilloscopes.

With our PicoScope software it is possible to adjust the sampling rate through setting the timebase and number of samples per waveform.

Similarly, with the software development kit, it is possible to set the desired sampling interval and number of samples to capture.

In terms of our current product offering, we do have 64-bit linux drivers available for the original PicoScope 2000 series and the PicoScope 5000 series. Linux drivers are being developed for our other product series, but I am unable to advise on further 64-bit drivers at this moment in time.

I hope this helps.
Hitesh

Technical Specialist
Pico Technology
Hitesh
Site Admin
Site Admin
 
Posts: 2058
Joined: Tue May 31, 2011 3:43 pm
Location: St. Neots, Cambridgeshire

Re: Sample rate can be reduced?

Postby heng » Wed Jun 13, 2012 8:26 am

Thanks! Presumably changing the time base also changes the anti-aliasing filters? The onus is not on me to make sure the signal is band limited? (forgive me if this is obvious wrt to oscilloscopes!)
heng
Newbie
 
Posts: 0
Joined: Mon Jun 11, 2012 7:08 pm

Re: Sample rate can be reduced?

Postby Hitesh » Wed Jun 13, 2012 12:34 pm

Hi Henry,

Changing the timebase should not affect the filtering. I think you just need to make sure that the filter frequency isn't set above the frequency of the signal otherwise you won't see it :D

Regards,
Hitesh

Technical Specialist
Pico Technology
Hitesh
Site Admin
Site Admin
 
Posts: 2058
Joined: Tue May 31, 2011 3:43 pm
Location: St. Neots, Cambridgeshire

Re: Sample rate can be reduced?

Postby heng » Wed Jun 13, 2012 2:48 pm

But there is likely to be crud in my signal that I want to filter out to stop it aliasing.
heng
Newbie
 
Posts: 0
Joined: Mon Jun 11, 2012 7:08 pm

Re: Sample rate can be reduced?

Postby alan » Wed Jun 13, 2012 2:58 pm

Oscilloscopes do not change their bandwidth as sampling rate changes for several reasons. Not least is that its useful to be able to view the envelope of a high frequency signal over a long period of time.

If you have noise in the signal that you want to filter out then most oscilloscopes offer either hardware or software filters. Many of our products have both. Hardware filters tend to be a fixed frequency - eg 20MHz, whilst software ones are programmable.
alan
Site Admin
Site Admin
 
Posts: 171
Joined: Thu May 25, 2006 8:02 am

Re: Sample rate can be reduced?

Postby heng » Wed Jun 13, 2012 7:50 pm

Ok, so now I'm just confused.

Here is my best attempt at an understanding: The scope always sample at 500 MS/s, but then it's possible to down-sample to some other sample rate that is selected through the SDK. An anti-aliasing filter can be imposed in software or hardware prior to the down-sampling. In hardware, this is fixed, in software, it is more flexible.

Is this reasonable?
heng
Newbie
 
Posts: 0
Joined: Mon Jun 11, 2012 7:08 pm

Re: Sample rate can be reduced?

Postby Hitesh » Thu Jun 14, 2012 1:42 pm

Hi Henry,

Looking at your initial post, I presume you are looking at the PicoScope 3204B.

The specifications (http://www.picotech.com/picoscope-specifications.html) show that with 1 channel the maximum sampling rate is 500MS/s, with two channels enabled the sampling rate is 250MS/s due to the hardware implementation.

With PicoScope you specify the timebase per division and the number of samples, and PicoScope will use the driver
to determine the closest sampling interval that can be used.

With the SDK you can select the sampling rate directly and specify the number of samples to collect (the driver will determine whether it is possible to collect that number of samples and return what it can collect).

You may wish to download the PicoScope 6 and run it in Demonstration mode to see it's features - you can download it from:

http://www.picotech.com/software.html

In step 1, select a PicoScope device, then in step 2, select the most recent version of PicoScope, then download the software and install it.

Alternatively, you could download and install the latest Beta version of PicoScope from http://labs.picotech.com/. The following forum post relating to the release of PicoScope 6.7 Beta as well as a Knowledge Base article may be of interest to you:

http://www.picotech.com/support/topic10729.html
http://www.picotech.com/support/kb/kbfiles/PicoScopeUSBStreaming.pdf

There is an improved streaming sampling feature. With streaming mode you are not limited by the buffer memory of the PC Oscilloscope.

In PicoScope, click on the Views -> View Properties menu and observe what happens when you adjust the timebase and number of samples. You can enable up to 4 channels and set different signals of varying frequencies using the in-built signal generator.

I hope this provides suitable clarification.
Hitesh

Technical Specialist
Pico Technology
Hitesh
Site Admin
Site Admin
 
Posts: 2058
Joined: Tue May 31, 2011 3:43 pm
Location: St. Neots, Cambridgeshire

Re: Sample rate can be reduced?

Postby heng » Thu Jun 14, 2012 3:42 pm

I hope this provides suitable clarification.

Not really - I'm still not clear on what filtering is or can be applied, and how changing the sampling rate changes what filtering is being done.

The suggestion to use Picoscope is a little difficult for me as I don't really have ready access to a Windows machine. Also, I'm not sure how it would help with my question.
heng
Newbie
 
Posts: 0
Joined: Mon Jun 11, 2012 7:08 pm

Re: Sample rate can be reduced?

Postby Hitesh » Fri Jun 15, 2012 10:40 am

Hi Henry,

Apologies, I forgot to answer the filtering question.

Filtering (Low-pass) is carried out within the PicoScope software. The PicoScope 6 User Manual (http://www.picotech.com/document/pdf/psw6.en-22.pdf) provides a description of the Lowpass filtering feature on p118 of 204 (section 7.2.1.2).

As described in the manual, filtering is either moving average or FIR. The filtering algorithm that is used is determined by the ratio of the selected cut-off frequency to the sampling rate.

Best wishes,
Hitesh

Technical Specialist
Pico Technology
Hitesh
Site Admin
Site Admin
 
Posts: 2058
Joined: Tue May 31, 2011 3:43 pm
Location: St. Neots, Cambridgeshire

Re: Sample rate can be reduced?

Postby heng » Fri Jun 15, 2012 10:57 am

So crucially, there is no facility to add an anti-aliasing filter prior to down sampling? This means, the onus is on me to make sure my signal is filtered adequately for whatever sampling frequency I wish to capture in. Correct?

To what does the 60MHz bandwidth refer for the 3204A/B models? Is this enforced through a LP filter front end?
heng
Newbie
 
Posts: 0
Joined: Mon Jun 11, 2012 7:08 pm

Re: Sample rate can be reduced?

Postby Hitesh » Fri Jun 15, 2012 11:13 am

That would be correct.

The following article on our website may also be of interest with respect to Bandwidth:

http://www.picotech.com/applications/oscilloscope_tutorial.html

From this article, the bandwidth is the 'frequency at which a sine wave input signal will be attenuated to 71% of its true amplitude (-3 dB point)'. There isn't an LP filter front end.
Hitesh

Technical Specialist
Pico Technology
Hitesh
Site Admin
Site Admin
 
Posts: 2058
Joined: Tue May 31, 2011 3:43 pm
Location: St. Neots, Cambridgeshire

Re: Sample rate can be reduced?

Postby rdohmhardt » Tue Sep 17, 2013 12:28 pm

Hi Hitesh,

I like to buy either an PicoScope 5444B (USB/4Channel/200MHz) or an 3406A/B (USB/4-Channel/200MHz).

With respect to Linux/64bit support, which one (the 3000 or 5000series) do you recommend.
I'm thinking also about supporting the FFT funktion.

Ciao Rüdiger
Hitesh wrote:In terms of our current product offering, we do have 64-bit linux drivers available for the original PicoScope 2000 series and the PicoScope 5000 series. Linux drivers are being developed for our other product series, but I am unable to advise on further 64-bit drivers at this moment in time.

I hope this helps.
rdohmhardt
Newbie
 
Posts: 0
Joined: Tue Sep 17, 2013 12:09 pm

Re: Sample rate can be reduced?

Postby Martyn » Wed Sep 18, 2013 7:21 am

The 3000a drivers are available now http://www.picotech.com/support/topic12745.html the 5000a will follow shortly so the choice is yours.

For FFT you will need to code this yourself, it is not a driver function.
Martyn
Technical Specialist
Martyn
Site Admin
Site Admin
 
Posts: 2348
Joined: Fri Jun 10, 2011 8:15 am
Location: St. Neots


Return to USB PC Oscilloscopes

Who is online

Users browsing this forum: No registered users and 1 guest