Trigger Multiple Scopes with one pulse

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BenC
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Trigger Multiple Scopes with one pulse

Post by BenC » Thu Dec 13, 2018 9:08 pm

I'm running 3 Picoscope 2204 scopes connected to one computer in block mode. I'd like them to trigger all at once from a signal supplied on one of the scopes. Everything I see in the manual won't let me assign a different scope as the trigger, so I'm limited to one trigger channel and one data channel per scope. Is there any way around this? I was thinking of trying to run in streaming mode and try capture the data from the other two scopes, but I'm not sure it would be quick enough or simple to do without some moving buffers (maybe that's not too hard, but I'm relatively new to programming this type of data acquisition).

Anyone have experience doing this sort of thing could point me in the right direction?

Thanks a lot

Gerry
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Re: Trigger Multiple Scopes with one pulse

Post by Gerry » Fri Dec 14, 2018 12:27 pm

Hi BenC,

You can't assign a PicoScope as the trigger for capturing data, without using the hardware trigger in each PicoScope to start the capture, but you can use the Software to start the capture instead of a trigger (by disabling the trigger for the PicoScopes and just calling the command to start the capture, e.g. ps2000RunBlock() or ps2000RunStreaming() ). However, when capturing data from 3 PicoScopes at the same time, and issuing commands to start the captures, all 3 PicoScopes could start their capture more than one sample interval out-of-sync, unless you're using a Sample Interval that is 10ms or longer (depending upon computer CPU overhead, and USB bus availability). This is because you would have to send the command that will start the capture to the PicoScopes via USB, which can delay the reception of the command by the Hardware PicoScope by any where up to around 10ms .

If you want to trigger three 2204A PicoScopes simultaneously (for faster than 10ms sample intervals, or 100Hz sample rates) with a pulse from one of the PicoScopes, then your only option would be to connect the Signal Generator of one PicoScope to the input of each PicoScope. Clearly, this form of capture start synchronisation is not very productive, because you would be using all 3 PicoScopes to gain just one extra channel. Worse than that, you would only be synchronising the start of the capture, so the samples being captured by the PicoScopes can drift apart during the capture period (because the sample clocks will not be running at exactly the same frequencies).

Regards,

Gerry
Gerry
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barab
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Re: Trigger Multiple Scopes with one pulse

Post by barab » Wed Jan 15, 2020 9:35 am

Hi, I'm new here and couldn't start a new post. Just found this one similar to the problem I need to solve. I want to synchronise 2 Picos, one 5444D and one 5444D MSO. Need to have all 8 channels synchronised.
How can I do this best? Using Function Generator in one unit and Ext. Trigger in the other one? What about time drift after being synchronised? Thanks!

Gerry
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Re: Trigger Multiple Scopes with one pulse

Post by Gerry » Thu Jan 16, 2020 1:05 pm

Hi barab,

You can synchronize the the start of a capture by triggering one channel on each PicoScope with the same trigger source, but we currently have no means to prevent or correct the difference between the sample clocks that will cause a drift between the samples. Note that on PicoScopes the Ext Trigger is typically not as responsive as the Trigger on an internal channel, so using it will mean that the start of synchronization would not be as tightly synchronized.

Regards,

Gerry
Gerry
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barab
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Re: Trigger Multiple Scopes with one pulse

Post by barab » Fri Jan 17, 2020 12:25 pm

Hi Gerry,

thanks for the input. Concerning drift, do you have some figures on how much the internal clocks could differ from each other? Based on that I may adapt sampling rates and capture time in order to be less impacted by timing discrepancies. Thanks!

Regards,
Barab

Gerry
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Re: Trigger Multiple Scopes with one pulse

Post by Gerry » Mon Jan 20, 2020 10:36 am

Hi Barab,

You'll find the Timebase accuracy quoted as ±2 ppm (0.0002%) here: https://www.picotech.com/oscilloscope/5000/picoscope-5000-specifications under the 'Horizontal' section of our specs, which means that, in the worst case scenario, your 2 PicoScope 5444D's could be as much as 4 ppm (0.0004%) apart. However you also need to consider the TimeBase drift if it has been some time since the scopes were last calibrated, which adds an additional worst case of 2 ppm (0.0002%) between the scopes, per year (for average operating conditions, and storage).

Regards,

Gerry
Gerry
Technical Specialist

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