Export subset data

[mrbiz404]

In SE there is an option to subset and resample data.  Once filtered, can only the data subset be exported to an ascii file?

[Phil_J1]

In the Add Step palette/menu, there is a "Subset and Resample" under Processing >> Analog Signals.

You can then take the result and send it to a "Save to ASCII/LVW" step found under Save/Load Signals >> Analog Signals.

Phil

[mrbiz404]

Thanks. This was very straightforward. However, it also presented another problem.

My problem is now that I am unable to capture the desired subset of data.  My 'Input Signal' screen only displays 400 ms worth of data at a time.  This is probably related to the fact that I recorded data using continuous sampling at 250 kHz with a buffer of 100k. 

When I try capture a subset of data, I only capture a subset of the data that appears only in the 'Input Signal' during the final 400 ms of the experiment.  For example, let's say my experiment last for 2 s. I open the 'Subset & Resampling' Paletter and select my signal of interest.  In the 'Input Signal' window, I see 400 ms of data. On the 'Subset Configuration' tab, I select the 'Extract subset' and 'Relative time' features. If I set the start position at 0 and the subset length at 200 ms and then click run, the Processed Signal window displays the data from 1.6 s to 1.8 s instead of the first 0.2 s of the experiment.  If I set the started position at a value greater than 400 ms, then the Process Signal window is blank.

Any help is appreciated.

[Christophe R]

Hi,

Do you mean that you would like to create a new log from a subset of an existing log? If this is the case, here's what you can do:

- Select the playback mode and point to the log you want to extract the subset from.

- Open the playback tool from the view menu. From this tool, you should be able to specify a start and time time for the playback operation.

- Drop a step that doesn't modify the signal (for example: Scaling with gain of 1, Window with window set to none). Right-click on the output of the step and select "Enable Recording". Run the project.

This will cause SignalExpress to play and re-record your log from the start and end time that you've specified. The end result will be a subset of your original log. This sounds a little complicated, but the next version of SignalExpress will make this operation much easier.

I hope this helps.

Christophe

[mrbiz404]

I tried Christophe's suggestions. However, the subset data starts at the specified time, but then only records for 400 ms. This corresponds to the size of the sample buffer (100k) for my sampling frequency (250 kHz). Any thoughts on how to get SE to record for the specified time range? Should I adjust the settings in the "Playback block configuration" portion of the "Playback options" tab?

Thanks.

[Christophe R]

What start time and end times have you specified in the playback tool? If only one full buffer fits between the start and end time, then only one buffer is going to be played back. By default SignalExpress only plays full buffers but you can uncheck the "ignore last iteration if partial" to play incomplete buffers.

You can also reduce the playback block size to have more buffers fit between you start and end time.

Christophe

[RJJE]

Christophe

I'm trying to do the same thing using SE 2.5. I've got 4 channels of analog data logged for about 2 mins and I need to grab snippets of that data.

I have tried all your instructions but nothing works. Well, it sort of works but not the way I want, The logged data created from the scale step is empty or if not empty it is from a wrong time section of the data. I've toyed with the sample size and adjusted the start/stop times. Sometimes I will get data starting from stop time or ending at the start time.

The common thing is that when ever I try another attempt the end result is different, I've even locked SE up several times.

Is there a written set of instructions on how to perform this task?

Randy

[David L.]

Hi Randy,

Below is a picture of what I believe you are trying to do in LabVIEW SignalExpress, and I do not have any issues with inputs to other functions. I am a bit confused when you say ‘The logged data created from the scale step is empty…’ Can you please post your project and screenshots of your results, as this will allow me to analyze your code as well as try to reproduce what you are seeing. The more information and different screenshots posted, the more I can understand and analyze the issue.

Message Edited by David L. on 10-12-2007 03:47 PM

[RJJE]

Hi David

I don't know how to show screen shots. I've attached my project file, (hopefully).

I'm working on a post acquisition file, the first logged data file to be exact. When the complete log is dragged into Data View, the whit & red traces between the sharp spikes is my target. Here I wanted to drag the data out for further post processing such as average, min & max values.

So I open the file in SE, make the first log as active and then go into Playback mode. Here I go into Playback options and drag the start & stop markers to frame the center portion of the traces. I had a problem setting up  the digital capture, I entered a much too large sample time.

I then set block size so that only 1 iterations is showing. As above, it was mentioned that 1 iteration is used for the start/stop markers.

Then I had add a scaling step with scale set to 1 and then I right click scaled output and enable recording. Hit run and a new data log is created, sometimes it is empty and other times the data snippet window is at a different time. I think it has to do with how I set the block size.

Hope that is clear enough for you. Thanks for your help.

[David L.]

Hi Randy,

I took a look at your project, but unfortunately cannot correlate it to what you wrote in the post as there are no steps in the playback mode, therefore no averaging or saving will be done. There are also no conditioning steps in the record mode – only acquisition steps. I would like to ask that you post screenshots of the ‘blank’ logs, and any ‘lockups’ that you have. There is no need to embed them into the post – simply attaching them is fine. Feel free to attach as many pictures as needed for a detailed explanation of your results and what is wrong. (If you would like to know how to embed pictures as I did above, please see this post) 

Attached is a project that I made, which I believe to be similar to what you are looking for. (Acquire & Log data, and then in the Playback mode – scale it, and do some averaging with  the data). Please try this and post back your results, and if you get any blank logs. Do these blank logs have absolutely no data, bad data, all points are the same data? Please explain in detail.

What DAQ card are you using? I would suggest verifying that your DAQcard is working properly by running test panels in Measurement and Automation Explorer. After this, we can continue with LabVIEW SignalExpress.

Message Edited by David L. on 10-17-2007 10:45 PM