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Scrollbars for time axis

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Scrollbars for time axis

Postby adynis » Mon Mar 23, 2009 12:30 am

Hello,
I'm interested in buying an usb pc oscilloscope (I would like the 2204 model) but I'm not understending somtehing related to the PicoScope software. I have installed PicoScope 6 and tested it with the demo version of the 2204 scope. The question:
How can I see a single shot signal that is longer than the width of the screen ? I expected to something simple like: chosing the time base and then scrolling a scrollbar in the last X ms or us or whatever in the buffer...
If I change the time base to view the entire signal, i understend that it would not be so detalied if I use zoom utility, as in a time base more appropriate...
For example: How can i view a signal (single shot type) of about 500ms at about 40kHz frequency with enough details (from a A/C remote controll)

Sorry for my english,
Thank you.
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Postby Robin » Mon Mar 23, 2009 10:20 am

Hi

You can use the horizontal zoom and scroll controls.

To the left of the time base control is the horizontal zoom control. By default, it will be set to x1.

Hope this helps

Robin
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Postby adynis » Mon Mar 23, 2009 3:27 pm

thank you,
Is true that i did not see that option :oops:
but...:
Testing the 2204 with a Square signal at 80KHz (1V) i can present my problem:
If the signal has about 200ms long and it is a non-peridocaly (continuous repeating) signal I would like to view the Entire signal and also to view exactcly one of it's square form.
I made this test with the demo:
In the first screenshot (FastPrintScreen 12) It's the entire section of 200ms
In the second one (FastPrintScreen 13 ) I tried to see if, when I zoom in, I can see all the details of one period; The situation isn't very happy.
In the third screenshot I tried to change the time base to see which is the limit for seeing clearly the signal ... I chose 5ms, it looks very clear now, but ... this way I can see only 5ms of the entire signal (not 200).

Is there any way to resolve this example ?

I don't understand exactly what the 32 buffers ar for. If they memorize the las 32 screens (X ms shown to the screen) how can I combine all that the buffers saved in one single image? (for example I select 5ms time base and than I combine all of the 32 segments (from buffer) of 5 ms each and this way I could see exactcly the entire 200ms signal, and also very fine detiles like in FastPrintScreen 14; I saw that I can see each of the 32 buffers .. but ... can I combine their information into one)

Sorry for my complicated language;

Thank you.
Attachments
FastPrintScreen 14.png
Square, 80Khz, 1MS, Total Time: 5ms, Horizontal Zoom: x132
(95.21 KiB) Downloaded 55 times
FastPrintScreen 13.png
Square, 80Khz, 1MS, Total Time: 200ms, Horizontal Zoom: x132
(111.32 KiB) Downloaded 48 times
FastPrintScreen 12.png
Square, 80KHz, 1MS, Total Time: 200ms, Hoizontal Zoom: x1
(75.12 KiB) Downloaded 46 times
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Postby Robin » Mon Mar 23, 2009 3:44 pm

This is a sample rate issue. When using long timebases, the sampling rate has to be decreased (due to the finite memory of the scope). Your sample rate is too low to capture your waveform accurately. Click on the "properties" tab on the right hand side of the trace to see the sample rate.

The waveform buffer stores the most recent x waveforms. The value of x depends on the scope memory and the number of samples per waveform. Each waveform includes a trigger event. There is a gap between the waveforms, which is why you cannot combine them in to one long waveform.

I hope this is clear!

Let me know if you have any more questions

Robin
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Postby Robin » Mon Mar 23, 2009 3:52 pm

Having said that, you should be able to capture a 80 kHz square wave with a 200 ms timebase. With this timebase, data is streamed continually via the USB. The maximum sampling rate for fast streaming is 1 MS/s. It looks like fast streaming is not implemented in the demo.

See the attached image, which was created using a 2203 and sig gen.

Robin
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80k square.png
(88.38 KiB) Downloaded 59 times
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Postby adynis » Mon Mar 23, 2009 8:03 pm

Ohh yess :P
I understand that with the real 2203 (or 2204) (not the demo) my situation from above will look like in your screenshot <80k square.png> which is a very attractive image :d Indeed in the demo , timebase: 200ms , 80KHz, square, I see in the properties a Sample Rate : 24.41 kS/s which it's nowhere near 1 MS/s :D

The discusion has gone a little bit offtopic (or my first title isn't the best one) but, for me , it was very helpfull.
One more little question: In what real case theese buffers are helpfull ? [If those buffers ware a single long buffer i could see their utility, but in this case .. i don't imagine exactly how their are usefull]

Another <Thank you> for all your answers !
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Postby Robin » Tue Mar 24, 2009 9:22 am

If you have a waveform with a large number of samples (long timebase/high sample rate), the scope will need to use the whole buffer for one waveform.

If you look at the image I posted, you can see that it says "1 of 1".

If you have a short waveform, the buffer can store up to 1000 waveforms. Each one will include a trigger event.

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Postby adynis » Thu Mar 26, 2009 11:13 pm

I have a new Picoscope 2204 :D :D and I'm very happy :p

But I cannot reproduce, for testing, the 80k square.png example.

I used the signal generator for a 80KHz signal; In 200ms/div the sample rate is to slow ... i think .. comparing to the other example. And .. in the screenshot you can see that the frequency that is shown is not 80Khz... What am I missing here ?

Thankyou, sorry for my offtopic post;
Attachments
FastPrintScreen 16.png
(103.65 KiB) Downloaded 47 times
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Postby Robin » Fri Mar 27, 2009 9:14 am

Hi

Look under tools->preferences->sampling and check the slow sampling transition time. Make sure this is set to 100 ms/div.

Also, check the software version you have (help->about). The most recent version is 6.2.2.12. www.picotech.com/software

Let me know how you get on.

Robin
Last edited by Robin on Fri Mar 27, 2009 9:45 am, edited 1 time in total.
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Postby adynis » Fri Mar 27, 2009 9:40 am

wow ... That was the difference !!
It was set at 200ms/div ... I change it to 100ms/div and now the sample rate is 1MS/s in my desired example ! And the signal from my remoe control looks GREAT !! :D
Thank you !

Lateredit:
I see now what big differences are in SampleRate if chosing, for example: 200ms/div for time/div -> sample rate: 1MS/s
100ms/div for time/div -> sample rate 6KS/s

I think the 200ms/s is best in ... ms :)
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Postby Robin » Fri Mar 27, 2009 10:07 am

The reason for this is that the scope operates in either streaming or block mode. In streaming mode, data is continually streamed over the USB link. In block mode, data is stored in the scope's memory and then transferred to the PC. This allows higher sampling rates, but you have to use short time bases to get the high sampling rates (because the scope has a finite memory). The 2204 can sample at 100 MS/s.

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