How do I use the Signal Express Recording Start/Stop Conditions?

[Physics Aide]

I am pulling in what is essentially a square wave function from an oscilloscope and I would like to be able to only get data from the peak (here a flat area since it's a square wave).  The wave has a frequency of 1 Hz, each peak is at 5 volts and is 700us long, with troughs of about 45000us long.  I have tried setting a start condtion so that the recording feature starts with a rising slope at 3 volts and a falling slope at three volts hoping that this would capture only the peaks.  However, this particular set of conditions produces no data.  With just the start condition and no stop condition it records the peaks, but also the troughs, and waits approximately 4 seconds before it starts recording anything. 

(Note, this is on a scale of 100us in the Signal Setup horizontal tab.  When the scale is on 100ms, it only records 1 point per peak and all the troughs.  When the scale is on 10us, it records thousands of points from the same peak and never reaches the other peaks.)

I'm sure that I am just misunderstanding some piece of vocabulary, but I have reread the descriptions of the components (like start/stop conditions) in the Help section and do not seem to be getting anywhere. 

Any suggestions?

Thanks,

Physics Aide

[CharlesD]

Hello,

What have you specified as your recording trigger settings.  I was able to record 1 pulse - high level - with settings outlined in the attached images.  Basically specifying a start trigger level of 2.5 V, hysterisis of .1V to ensure the trigger does not re-trigger automatically - ie stop the recording, the start trigger is specified as rising slope, and the stop trigger is defined to stop on the falling slope past 2.5 V.  

Please check the following 3 images to see if this is what you need.  if its not re-post with a little bit more details and I will try to rework the process to make this work for your application. 

Thank you 

[Physics Aide]

The recording you took is what I am trying to obtain.  I followed the directions but when I converted the log to ASCII and tried to open it in Excel there was no data.   I have attached a Word document with printscreens of the settings.  Also, I am using Signal Express Tektronix Edition, so the screens look different from yours.  I hope this helps.

Thank you,

Physics Aide

Message Edited by Physics Aide on 02-25-2009 03:39 PM

[CharlesD]

Does the log file show the proper data but the ASCI file doesn't? Or is there no data in the log file either?  This is important because If we are getting the right data in the log file then it is a problem with the ASCI conversion, if not then we are seeing a problem with the acquisition.  Also how are you converting the log file to an ASCI File?  Giving us these details will us try to replicate this on our end

Thank you 

[Physics Aide]

Charles,

Thank you for taking so much time to help me figure this out.  I have attached a Word document with more printscreens providing the information that you requested.  I wasn't exactly sure what you meant by obtaining the log data that had not been converted to ASCII, so if I did not include that part, please direct me as to how to send it to you. 

Thanks,

Physics Aide

[StevieZ]

What version of Signal Express Tek Edition are you using. You can find this information by going to Help»About.

Regards,

Steven Zittrower

Applications Engineer

National Instruments

http://www.ni.com/support

[Physics Aide]

I'm using version 2.5.1

Physics Aide

[Justin_E]

Hey PhysicsAide,

In the second document that you posted, there is a screenshot that has data in Excel. So it looks like here we are seeing two different behaviors, one without any data in Excel and one with data in Excel. What changes are made between the graphs that you can export in Excel with data (albeit not the exact data that you want), and the graph that you export into Excel without any data?

[Physics Aide]

Justin,

 

The Excel sheet which has the data was created by right-clicking on the image of the pulse in “Data View” (when it is in “Monitor/Record” mode) and exporting the data to Excel.  Since the “Data View” cycles through the different pulses, the data in Excel shows separate peaks and troughs for each pulse.  

 

There are two situations when the Excel sheet does not show data:

 

1) I click on the log that has been created with the start/stop conditions (located in the bottom left corner of the screen), convert the data to ASCII and open it in Excel.  No Data.

 

2) I change the “Data View” mode from “Monitor/Record” to “Playback”, click on the same log and drag it over to the Data View screen.  At this point a graph, which looks exactly like the original pulse (peak and trough) appears. If I then right-click on that graph and “Export the Data to Excel” I get a message that says “No Data to Export”.  (It seems odd that a graph of an entire pulse would appear as a result of dragging the log over to the Data View if there was No Data to Export, and that it instead should just leave an empty screen.)

 

Other than what I have mentioned, there were no changes made (Start/Stop conditions, Setup conditions, etc) while I tried these three different ways to export data.

 

Thanks,

 

Physics Aide

[Justin_E]

So just to clarify, you get some sort of data into Excel when you export while the data is being recorded (and shown in Data View)? It seems like there's definitely a problem with the log file being created, but I'm not really seeing where this error could be occuring. Try removing the start and stop conditions, record some data, and try exporting the log into Excel from there. Let me know what happens when you do this. What I'm trying to do here is see if the issue is with the actual creation of a log file.

A couple more things you can try : Take a look at this KnowledgeBase article : KnowledgeBase 47T8OQ84 : Optimizing LabVIEW SignalExpress for High Speed or High Channel Count Loggi...

There are some steps in here that might streamline the process of logging data, which might fix your issue. Another thing you should try is repairing SignalExpress. You will need whatever installation discs came with SignalExpress to do this. Navigate to the Control Panel (in Windows), and then to Add or Remove Programs. From here, scroll down the list until you see National Instruments Software, and click on Change/Remove. Look for NI LabVIEW SignalExpress 2.5.1 Tektronix Edition, and click on Repair. This should fix any issues with the software itself.