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MDO3024 long memory record download issue

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estiers
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Joined: June 10th, 2016, 9:31 am
Country: United States

MDO3024 long memory record download issue

Post by estiers » June 10th, 2016, 11:04 am

Hi all-

I have a MDO3024 scope that I am trying to use to collect long sets of data. When I have the scope's record length set to 1M points or less the :CURVE? command returns the same number of samples as what the record length is set to (e.g. record length of 10k results in 10k data points returned), however when I change the record length to 5M or 10M points on the scope the :CURVE? command only returns 2M samples instead of the full dataset.

Here are the commands that I'm sending the scope via ethernet connection and LabView:

Code: Select all

:DATA:SOURCE CH1
:WFMO:ENC BINARY
:WFMO:BYT_N 1
:DATA:SNAP
:CURVE?
With the scope set to a 10M point record length the :CURVE? command returns the following:

Code: Select all

#72000000[followed by 2000000 bytes of scope data]
when I would have expected

Code: Select all

#810000000[followed by 10000000 bytes of scope data]
Is there any way to download the full memory record for 5M and 10M point record lengths?

David N
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Tektronix Applications
Posts: 541
Joined: July 31st, 2008, 8:26 am

Re: MDO3024 long memory record download issue

Post by David N » June 13th, 2016, 9:10 am

The limit may be due to your programs buffer size that you are reading the waveform data into.

estiers
Posts: 3
Joined: June 10th, 2016, 9:31 am
Country: United States

Re: MDO3024 long memory record download issue

Post by estiers » June 14th, 2016, 5:11 am

Thanks for your comments David.

I don't think there is a buffer issue on my program's end because the first few bytes sent back by the :CURVE? command are #72000000, indicating that the scope is only planning on sending me two million datapoints. If we had a buffer problem I'd expect that the scope would say it was going to send 10 million datapoints (#810000000) but then the transmission would get cut off part way.

Does that make sense?

Dave W
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Joined: April 26th, 2010, 12:01 pm
Country: United States

Re: MDO3024 long memory record download issue

Post by Dave W » June 14th, 2016, 9:11 am

Hi estiers. The issue is most likely (based on your code sample) because you have not set your DATA:STOP value. DATA:STOP sets where in the data record to stop sending data from a curve query. DATA:STOP has some default, presumably 2M based on your results. When the record contains a number of data points less than or equal to what DATA:STOP is set to, the whole record is returned. When the record contains more points than what DATA:STOP is set to, you will only receive the data up to the DATA:STOP point. Set DATA:STOP to 10M to get all 10M points from the scope.

Note: There is a DATA:START value as well which defaults to 1. Use this to change where in the record to start the transfer from. Typically you will always leave this set to 1.

estiers
Posts: 3
Joined: June 10th, 2016, 9:31 am
Country: United States

Re: MDO3024 long memory record download issue

Post by estiers » June 17th, 2016, 7:27 am

We got it working, it looks like there were two issues:

1) We did need to specify the DATA:STOP value as Dave W mentioned, I thought DATA:SNAP would set the bounds to include all available points but apparently it actually just snaps the START and STOP values to wherever the cursors are at.

2) After manually specifying the DATA:STOP value we ran into a timing issue - if you send a :CURVE? command with 5M or 10M points and immediately request the data back you only get a partial dataset. If you wait for ~1.5 seconds to start reading data back you get the full dataset back reliably.

Thanks everyone for your helpful comments!

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