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Timestamps of capture

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Timestamps of capture

Postby kiekerjan » Fri Jun 12, 2015 7:31 am

Hi,

I'm having trouble relating my captured data to the system time. I have a PicoScope 5204 available, which I'm using to measure a pulse using a trigger. I use an alarm to save the captured data. So far so good.
The device that produces the pulse is time synchronized with the laptop that is connected to the PicoScope. What I want to accomplish is to compare the production time of the pulse (produced by the device, measured with the scope, so time stamped with the laptop) with the event (logged within the device, so time stamped by the device) that triggered the pulse. I hope I'm making sense here :oops:
When I open the datafile, a capture time stamp is shown. I'm a little confused about relating the timestamps of the captured samples to the capture time stamp. The trigger time seems to be at t=0, but how is the trigger time related to the capture time stamp?
I have looked at the manual, but could not find the details I'm looking for. It seems to be the same as the timestamp of the file itself, so a property of the file system. Could that be the case?
Also, when I export the data to Matlab, the capture time stamp does not seem to be part of the exported data. How do I obtain the capture time stamp in that case?
Your help in enlightening me is much appreciated.

kind regards
Jan
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Re: Timestamps of capture

Postby Hitesh » Thu Jun 18, 2015 12:38 pm

Hi Jan,

The Capture Time refers to the time in HH:MM:SS when the capture of the waveform began, so it will be the first time value on the horizontal axis that will correspond to this time, bearing in mind that the time value could be less than 1 second.

The trigger point has a time of t = 0 as by adjusting the horizontal position of the trigger marker, this scales the proportion of pre- and post-trigger samples, thus resulting in negative time values for pre-trigger samples.

The export to MATLAB file does not include this information. It includes a Tstart variable for the first time value, and then the number of samples (Length) so this can be used to calculate the time on the horizontal axis, so unfortunately there is no correlation with the capture time.

There is an existing feature request for our Development Team so I will update it with your enquiry.

Regards,
Hitesh

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Re: Timestamps of capture

Postby kiekerjan » Thu Jun 18, 2015 8:02 pm

Hello Hitesh,

Thank you for your answer. Just one question to verify that I understand you correctly. In the picture below, the capture time is 13:40:46 (HH:MM:SS). The capture starts at -5.0 ms. Am I correct in understanding that this would mean that the trigger time in this case is 13:40:46.005 (HH:MM:SS.mmm)?

Image
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Re: Timestamps of capture

Postby Hitesh » Fri Jun 19, 2015 8:34 am

Hi Jan,

The accuracy of the time stamp is to one second as system time is used so the actual start time could be anywhere in the second interval. Depending on the timebase selected subsequent buffers could have the same timestamp.

A higher resolution is possible but it won't be very accurate.

Regards,
Hitesh

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