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Logging Data to Multiple Files in LabVIEW SignalExpress



Primary Software:
Primary Software Version: N/A
Primary Software Fixed Version: N/A
Secondary Software: N/A

Problem:
I am recording data for a long period of time in LabVIEW SignalExpress. I want to protect against all my data being lost in the case of a power failure or a system crash. Is there a way to log my data continuously, but have it be saved in a series of files?

Solution:
There are two ways to do this with LabVIEW SignalExpress.  You can do it by manipulating your recording options, or by having a step that saves the data for you.  Manipulating the recording options gives you the ability to save the data as a TDMS file and is the best solution for recording larger amounts of data.

When the following steps are followed with Signal Express, data is collected, recorded, paused while the next file is opened, and then the reading and recording of data continues.  Some data will be lost during the pause and while the next file is opened.  This cannot be avoided with Signal Express, only optimized so that the data lost is limited. KnowledgeBase 47T8OQ84: Optimizing LabVIEW SignalExpress for High Speed or High Channel Count Logging explains how to optimize data recordings and reduce data loss.  To record truly continuous data in multiple files, the best alternative is to use LabVIEW and DAQmx 9.3.  Discussion Forum: DAQmx Logging New Features - Split files, non-buffered logging, and pause/resume explains how to accomplish this task.

  1. Click on the Recording Options tab.  If it is not visible go to the View menu and select it.
  2. Click on the Stop Conditions category.
  3. Select the Condition source as Duration.
  4. Under the Duration(s) setting input the time you want to have each file record.
  5. Click on the Start Conditions category.
  6. Go to the Restart Behavior section in Start Conditions.
  7. Change Restart start/stop cycle in to new log.
  8. Change Repeat start/stop cycle to either a number of times to run or until a certain date and time.

Figure 1: Set Stop conditions

Figure 2: Set Start conditions

The other option is to have a LabVIEW SignalExpress project that includes the Save to ASCII/LVM step.  This step is called every iteration of the program and can be used to write a new file every time through.  The main challenge with this solution is storing an ASCII file, which takes up much more space per data point than a TDMS file. Figure 2 shows the Save to ASCII step.

Figure 3: Save to ASCII Step



Related Links:
KnowledgeBase 47T8OQ84: Optimizing LabVIEW SignalExpress for High Speed or High Channel Count Logging
Discussion Forum: DAQmx Logging New Features - Split files, non-buffered logging, and pause/resume

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Report Date: 02/28/2007
Last Updated: 10/26/2011
Document ID: 46RIGRT7

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