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PicoScope 6 Sampling Rate Adjustment

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PicoScope 6 Sampling Rate Adjustment

Postby Hitesh » Thu Feb 04, 2016 10:56 am

Hi,

When changing the timebase in the PicoScope 6 software, you may wonder why the sampling rate shown in the Properties view also changes. This post aims to demonstrate why.

A PicoScope 5244A was used to create the screenshots below, with the signal generator output (5 Hz sine wave) connected to Channel A, but this will apply to our other products that are supported by the software.

The figure below shows a waveform trace captured in streaming mode (timebase is set to 200ms/div i.e. 2 seconds across the screen) with 1 MS requested from the device.

Collection_200ms_per_div.png
Timebase at 200ms/div

Note the change in sample interval when the timebase is changed to 100ms/div (here the PicoScope switches to a block mode capture due to the PicoScope 6 settings). The collection time has changed (1 second across the screen) but the number of samples is FIXED.

Collection_100ms_per_div.png
Timebase at 100ms/div

When the timebase is changed again to 50ms/div, we are still requesting 1 MS from the device but note that the collection time is now 500 ms. The software finds the fastest possible sampling interval and will collect the number of samples based on the sampling interval and the collection time selected.

Collection_50ms_per_div.png
Timebase at 50ms/div

To summarise, the sample rate will be set according to the collection time and the maximum number of samples that the device can collect (based on the number of samples requested).

Regards,
Last edited by Hitesh on Mon Oct 03, 2016 11:36 am, edited 1 time in total.
Reason: Corrections to text
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Re: PicoScope 6 Sampling Rate Adjustment

Postby powersupplyguy » Thu Aug 04, 2016 8:50 pm

Greetings,

I was going to ask you to tell me the slowest sampling rate. Maybe that is not what I really need to know.

I have to record 17 hours of data. I think 12bits of resolution would be best. I would like to be able to do 4 channels at a 10kHz sample rate. Then number of samples would be 4(channels) * 10K(samples) * 60(seconds) * 60(minutes) * 17(hours) = 2448 Megasamples.

I cannot seem to adjust the software parameters to get there. Am I barking up the wrong tree? Should I be looking at a data logger?

Thank you
Bob
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Re: PicoScope 6 Sampling Rate Adjustment

Postby Hitesh » Fri Aug 05, 2016 9:25 am

Hi Bob,

When collecting data in streaming mode using one of the PicoScope oscilloscopes with the PicoScope 6 software, there is a limit of a 100 MS record length shared between all channels, and the maximum length of time would be just under 14 hours.

The only way to collect continuously over 17 hours at 10 kS/s would be to use an oscilloscope and write your own application using the Software Development Kit.

With the quantity of data to be collected, it might be better to split the data collection into smaller files if you are writing to file.

Regards,
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Re: PicoScope 6 Sampling Rate Adjustment

Postby francois » Fri Sep 30, 2016 1:36 pm

Hi,
Reading your explanations I tried the following:
Time base = 100ms/div
Number of sample = 2GS
Which resulted in an automatic setting at 312.5 MS/s, 312 M samples record with my 6403C
With my application 109MS/s is enough and I need 2 to 3 sec recording.
Thus I set Time base = 200ms/div
Number of sample = 2GS
Which resulted in an automatic setting at 9.766 MS/s, 19 M samples record ...
This is unexpected for me. My expectation was a 156.25 MS/s, 624 M record samples
This is really a shame because I need that sampling frequency and time window for solving my issues. I'm debugging RF transactions. Acquisitions are post processed by a software decoder on a PC and must be fully captured.
Could you tell me what I missed?
Best regards,
François
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Re: PicoScope 6 Sampling Rate Adjustment

Postby Martyn » Sat Oct 01, 2016 3:00 pm

Go to Tools->Properties->Sampling and change the Slow Sampling transition time to 1s/div and this will ensure you are running in block mode not streaming at 200ms/div , then repeat the test.
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Re: PicoScope 6 Sampling Rate Adjustment

Postby francois » Mon Oct 03, 2016 9:09 am

Thank you Martin,
However this doesn't solve my issue. In order to avoid already solved issues, before applying your recommendation, I decided to upgrade Picoscope 6.
Firstly, since I installed the latest revision, with 100ms/div and 2GS range settings I see that the scope gets 156M samples at 156.3MSp/s sampling rate. Before with the same hardware it was 312M samples at 312MS/s. That's a bad surprise to me but not a show stopper unlike the initial memory usage problem.
Secondly, I have been into Tools > Preferences > Sampling and set 1s/div before going into slow sampling. This doesn't change anything to my problem.
Going further, looking to the effect of the number of samples I saw that asking 2GS is the same as asking 200MS (Millions of samples). Thus all samples available above the 200MS have no effect!
Now, I'm still stuck with the time window acquired and I wonder why the update has decreased the performances.
Help required please !
Best regards,
François
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Re: PicoScope 6 Sampling Rate Adjustment

Postby Martyn » Mon Oct 03, 2016 12:19 pm

If you let me know which scope model you have, and which software version you are using, Help->About gives the information, I can then advise how to set the scope up.
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Re: PicoScope 6 Sampling Rate Adjustment

Postby francois » Mon Oct 03, 2016 12:48 pm

Hello Martyn,
Here is the info:
>> PicoScope® 6 - PC Oscilloscope software version: 6.11.12.1692
>> Copyright © 1995-2016, Pico Technology Ltd.
>> Model: PicoScope 6403C
>> Serial Number: CO808/001
>> USB Version: 3,0
>> Calibration Date: mardi 3 novembre 2015
>> Hardware Version: 1 1
>> Driver Version: 1.4.6.3
>> Firmware Version: 1.4.0.0 / 1.1.39.0
Also I have found that the memory amount of my scope is probably 512MS. I thought it was 2GS because the software was offering 2GS. But it may be a software issue.
Best regards,
François
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Re: PicoScope 6 Sampling Rate Adjustment

Postby Martyn » Mon Oct 03, 2016 1:04 pm

Yes the 6403C only has 512MS

It is always worth opening the properties window, right click on the display and select View Properties, to show the actual settings.

The way PicoScope works is to set the time to display across the screen, the hard fixed parameter, then select how many samples you would like per screen, the soft fixed parameter, the software will then select a sample interval to get as close to the number of samples as possible, the calculated parameter. If you want the max number of samples possible then over specify the number of samples you require by setting 2GS as you have done.

Remember that all active channels share the available memory and, unless you select Single Trigger, the available memory will be halved so that the scope can capture to a new buffer whilst preserving the previous one.
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Re: PicoScope 6 Sampling Rate Adjustment

Postby francois » Tue Oct 04, 2016 8:10 am

Hello Martyn,
Thank you. With your help I better understand how it works.
1/ Firsty, only the time scale is respected. The number of sample selected is a wish and software is going to select the highest possible which can be very different from the request for many reasons. It can be scope real memory available and other unknown constraints for me.
2/ Secondly, In order to reach the maximum sampling rate with the maximum time window the slow sampling mode must not be activated. This option is available in menu Tools > Preference > Sampling. We must take care that transition time scale is higher than the one intended to be used.
3/ The single trigger mode has to be activated otherwise the memory available is half what is possible.

With my initial settings (100ms/div, 2GS, Single trig) I reached 312.5Me/s, 312.5 MS.
With your settings (200ms/div, 2GS, Single trig) I'm able to reach 156Me/s, 312.5MS. That is great because it doubles the time window with a sampling frequency better than enough for my application.

Now if I want to record a wider time window how is it possible? Is it possible to upgrade the scope internal memory? Is there a way to set 108.5Me/s? Is there a way to use the 512MS available on my scope?

Thanks,
Best regards,
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Re: PicoScope 6 Sampling Rate Adjustment

Postby Martyn » Mon Oct 10, 2016 12:13 pm

To reach 108.5Me/s you would need a 400ms/div screen setting which is not available, the next being 500ms/div Unfortunately upgrading the memory is not possible either. The only current option would be to use the SDK to develop an application to collect exactly the number of samples required at the requested rate, with no restrictions on having to meet a specified screen display time.

We are looking at alternative approaches for PicoScope when setting up the software, and displaying the data, so I will add your request to the list.
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