Extract Channels > Special Considerations

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Special Considerations

Note the Visible channels only check box at the top of the Save As dialog box. This option must be selected (an X appears in the check box) for the extract channels function to work as described in the Activating Procedure. If this option remains unselected (no X appears in the check box) and the extract channels procedure is completed, all channels in the original file will be extracted rather than just the desired (or visible) ones.


Note also the Output all values when compressed check box. This option must be selected if you would like to output all data values without changing Edit Compression to 1 (i.e., if this box in unselected Edit Compression will change to 1 for all values). See Waveform Compression for details on compressing waveforms.


This function makes extensive use of the Display Format Selection and Variable Waveform Assignments functions. Literally, whatever channels are displayed on the screen (and the order in which they are displayed) at the time the Extract Channels utility is invoked become the channels that are ported to the newly created file. For example, if we assume that a file containing five channels (1-5) is displayed and you want to create a new file consisting of only channels 2,4, and 5 in that order, you would perform the following:


  1. Enable Display Format number 5 (ALT+5). Note that any Display Format capable of displaying 3 or more channels may be used.
  2. Assign channels to windows in the desired order (1=2, 2=4, 3=5).
  3. Disable the display of waveform information in window 4 (4=0).
  4. Invoke the Extract Channels function (in the File menu click on Save As… or Choose File Save As… with ALT, F, A keystrokes).
  5. Select Visible channels only, and supply any valid DOS file name (such as NEWDATA.DAT).


Following execution of the last command above, file NEWDATA.DAT has been created containing three channels of information (NEWDATA.DAT channel 1 is the original file’s channel 2; NEWDATA.DAT channel 2 is the original file’s channel 4; and NEWDATA.DAT channel 3 is the original file’s channel 5).


The above procedures are valid for any display format and any combination of Variable Waveform Assignments. For example, if you wanted to extract just a single channel, you would enable Display Format 1 and assign to display window 1 the channel number to be extracted. Another approach would be to enable a multiple window Display Format and disable all but one window (by assigning them to channel 0), then assigning the waveform channel to be extracted to the remaining window.


Note that since the Variable Waveform Assignments function allows any given channel to be assigned to more than one window (1=2, 2=2, 3=2, etc.) the Extract Channels function can produce multiple copies of the same waveform within the file it creates.


See also Export Special Considerations for more information on file storage format options.