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Data Acquisition with Fast Frame

DPO70000SX, DPO/MSO70000, DPO7000 Series, DPO/MSO5000 Series
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Xiaowei
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Joined: February 11th, 2018, 7:00 am
Country: United States

Data Acquisition with Fast Frame

Post by Xiaowei » January 9th, 2019, 10:00 pm

I'm acquiring data using Fast Frame mode with DPO7354C. Our trigger rate is 1 KHz, and the oscilloscope can successfully capture 10000 frames in 10 seconds. The Oscilloscope monitor shows the info "Captured frames/Total frames on demand" in real time. So we know that the oscilloscope indeed spent about 10 s to capture 10000 frames. However, it spent another ~8 s waiting there after that, then started to transfer data back to PC. I wonder why it needs the extra 8 s. It seems the data is not available until some kind of post processing procedure is done. But all I need is the raw data, is there any way to return the raw data back to PC as soon as the trigger is over (10 s for 10000 samples with 1 KHz trigger)?

Carl M
Tektronix Applications
Tektronix Applications
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Joined: July 30th, 2008, 4:45 pm
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Re: Data Acquisition with Fast Frame

Post by Carl M » January 11th, 2019, 12:30 pm

FastFrame mode decreases the trigger rearm time significantly by using all available record to buffer multiple small acquisitions. This also defers post acquisition tasks while still maintaining precision timing between trigger events. It is a great boon in laser diode research where pulses are short and infrequent.

Independent of FastFrame, the DPO7304C will still need to transfer sample data to the application software, perform DSP corrections, raster the waveform for display, and perform any additional analysis tasks. The resulting throughput of any digital storage oscilloscope is highly depend on the settings and it is hard to predict. Regardless, here are some things you can try,
  • in the vertical settings, set all channels to Analog Only (disables DSP)
  • in the display pull-down menu, set Waveform Display off (disables rasterization/plotting, analysis can still be performed)
  • in the trigger settings, disable Trigger Position enhancement
  • in the acquisition settings, disable ENOB enhancement
I generally do not recommend disabling these features because they will have an unknown effect on acquisition accuracy (i.e. not calibrated or guaranteed).

Fundamentally, a large record is going to take some time to analyze and the oscilloscope application effectively handles a fastframe acquisition as a single large record.
Tektronix Application Engineer

Xiaowei
Posts: 5
Joined: February 11th, 2018, 7:00 am
Country: United States

Re: Data Acquisition with Fast Frame

Post by Xiaowei » January 12th, 2019, 12:53 am

Thanks, Carl. I turned off the trigger channel (channel 2) via the "CH2" button on the front panel. And the post process time is reduced down to ~3 s for 10K frames acquisition. Turning off the CH1 display can further reduce the time by ~0.4 seconds, and DSP disabling can improve the process by another ~0.4 seconds. So the best I got for now is 2.2 seconds delay.

Another thing I don't understand is that how the oscilloscope is triggered when I turn the trigger channel (CH2) off. When CH2 is on, the highest sample rate for both CH1 and CH2 is 20Gs/s. When CH2 is off, the sample rate of CH1 can be set to 40Gs/s, which seems to indicate that the oscilloscope is not samping CH2 at all. However, the oscilloscope is still triggered by CH2 signal. The trigger signal for CH2 is from a photodiode detecting femtosecond laser pulses, and its rising time is as short as 130 --second. I don't know if trigger time is accurate or not in this case.

Best Regards,
Xiaowei Wang

Carl M
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Tektronix Applications
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Joined: July 30th, 2008, 4:45 pm
Country: United States

Re: Data Acquisition with Fast Frame

Post by Carl M » January 14th, 2019, 1:52 pm

For the DPO7354C, the trigger system is analog and asynchronous to the acquisition system allowing you to trigger on a channel without actually sampling it (and reducing the acquisition burden). In FastFrame mode, time accuracy between frames is maintained with a high resolution counter, not the individual trigger events. Trigger events are susceptible to small amounts of delay and uncertainty, especially if you disable Trigger Position enhancement.
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