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TDMS Defragment (G Dataflow)

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Last Modified: September 23, 2019

Defragments data in a .tdms file.

Use this node to clean up your .tdms data when it becomes cluttered and to increase performance. Data becomes cluttered when you rewrite unnecessary metadata. See TDMS Segments and Metadata on the Details tab for more information.

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file path

Absolute path to the .tdms file on which to perform the operation.

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error in

Error conditions that occur before this node runs.

The node responds to this input according to standard error behavior.

Standard Error Behavior

Many nodes provide an error in input and an error out output so that the node can respond to and communicate errors that occur while code is running. The value of error in specifies whether an error occurred before the node runs. Most nodes respond to values of error in in a standard, predictable way.

error in does not contain an error error in contains an error
If no error occurred before the node runs, the node begins execution normally.

If no error occurs while the node runs, it returns no error. If an error does occur while the node runs, it returns that error information as error out.

If an error occurred before the node runs, the node does not execute. Instead, it returns the error in value as error out.

Default: No error

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error out

Error information.

The node produces this output according to standard error behavior.

Standard Error Behavior

Many nodes provide an error in input and an error out output so that the node can respond to and communicate errors that occur while code is running. The value of error in specifies whether an error occurred before the node runs. Most nodes respond to values of error in in a standard, predictable way.

error in does not contain an error error in contains an error
If no error occurred before the node runs, the node begins execution normally.

If no error occurs while the node runs, it returns no error. If an error does occur while the node runs, it returns that error information as error out.

If an error occurred before the node runs, the node does not execute. Instead, it returns the error in value as error out.

TDMS Segments and Metadata

Every time a node appends data to a .tdms file, the file creates a new segment. A segment consists of the following three parts:

  • Lead in—The segment's basic information, like the tag that identifies the files as .tdms and indicates the length information of the metadata and the raw data.
  • Metadata—The names and properties of all objects in the segment. The metadata can also include index information for objects that include raw data, like channels.
  • Raw data—All of the raw data associated with any of the objects in the segment.

When you set properties on TDMS nodes, you can omit meta information that is identical from one segment to the next, like channel names and properties. This is optional, but omitting redundant meta information significantly speeds up reading the file and reduces the binary footprint.

If you choose to write redundant information, you can later remove it using the TDMS Defragment node.

Where This Node Can Run:

Desktop OS: Windows

FPGA: DAQExpress does not support FPGA devices

Web Server: Not supported in VIs that run in a web application

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