TDMS Set Properties

Sets the properties of a .tdms file, group, or channel. You must close the reference to the .tdms file or use the TDMS Flush node to flush data to the .tdms file for changes to take effect.

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Inputs/Outputs

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property values

Property values of the .tdms file, group, or channel.

This input accepts the following data types:

  • Signed and unsigned integer
  • Single-precision or double-precision floating-point number
  • Complex single-precision or double-precision floating-point number
  • Extended-precision floating-point number
  • Alphanumeric string that does not contain null characters
  • Timestamp
  • Boolean
  • Variant that contains any of the data types specified above
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property names

Property names of the .tdms file, group, or channel.

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tdms file

A reference to a .tdms file. Use the TDMS Open node to obtain the reference.

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group name

Channel group on which to perform the operation.

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channel name

Channel on which to perform the operation.

If you wire a value to channel name, you must also wire a value to group name.

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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

Default value: No error

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tdms file out

A reference to the .tdms file.

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group name out

Channel group on which you performed the operation.

If you do not specify a group name, this output returns Untitled.

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channel name out

Channel on which you performed the operation.

If you do not specify a channel name, this output returns Untitled.

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error out

Error information.

The node produces this output according to standard error behavior.

Standard Error Behavior

Searching for Properties at the File, Group, or Channel Level

The following table shows the inputs you must wire to search for properties at the file, group, or channel level.

Search level Inputs to Wire Comments
File or root level None Leave group name and channel name empty to search at the file or root level.
Group level group name
Channel level group name and channel name If channel name contains a value, group name must also contain a value.

Setting Multiple Properties

To set multiple properties using the same node, you can wire a 1D array of an acceptable data type to property values. Each value in the array corresponds to a single property. However, a single property cannot hold an array of values.

Properties in a .tdms File

Every TDMS object can have an unlimited number of properties. Each TDMS property consists of a combination of a name (always a string), a data type, and a value. Typical data types for properties include numeric types such as integers or floating-point numbers, time stamps, or strings. TDMS properties do not support arrays. TDMS properties help you organize and document data and later perform searches on that data by adding meta information specific to your data set.

The following table lists all properties you might find in a .tdms file.

Property Name Data Type Access Available in File Format Versions Description
name String Read/write 2.0 Specifies the object name, such as the root name, group name, or channel name, in a .tdms file.
NI_ArrayColumn 32-bit signed integer Read only 1.0 and 2.0 Indicates the index of a column in a 2D array. This property appears in a .tdms file only if you write a 2D array of data to the file.
NI_ChannelLength 64-bit unsigned integer Read only 1.0 and 2.0 Represents the number of values in a channel of a .tdms file.
NI_DataType 16-bit unsigned integer Read only 1.0 and 2.0 Represents the data type of a channel. The value is an integer that corresponds to a type code.
NI_DigitalCompression Boolean Read only 1.0 and 2.0 Indicates whether a digital table is compressed or not. A value of 1 indicates that the digital table is compressed. If the digital table is not compressed, this property does not appear.
NI_DigitalLine 32-bit signed integer Read only 1.0 and 2.0 Indicates the index of a row in a digital table.
NI_DigitalNumberOfLines 32-bit signed integer Read only 1.0 and 2.0 Indicates the number of rows in a digital table.
NI_Number_Of_Scales 32-bit unsigned integer Read/write 2.0 Specifies the number of scales to use when you read data from a .tdms file. For example, if a .tdms file has five scales and you set the value of NI_Number_Of_Scales to 4, only the first four scales are applied to the data when you read the .tdms file.
NI_Scale[n]_config, where n represents the order of the scale and config represents the configuration of the scale. N/A Read/write 2.0 Specifies the scaling information for the data in a .tdms file. You can create more than one scale in a .tdms file.
NI_Scaling_Status String Read/write 2.0 Specifies whether to scale data when reading the data from a .tdms file. If the value is unscaled and the .tdms file contains one or more scales, the node scales the data. If the value is scaled, the node does not scale the data.
unit_string String Read/write 1.0 and 2.0 Specifies the unit of the channel data in a .tdms file.
wf_increment Double Read/write 1.0 and 2.0 Represents the increment between two consecutive samples on the x-axis.
wf_samples 32-bit signed integer Read/write 1.0 and 2.0 Represents the number of samples in the first data chunk of the waveform you write to a .tdms file. The value must be greater than zero.
wf_start_offset Double Read only 1.0 and 2.0 Represents the first value on the x-axis used by frequency-domain data and histogram results.
wf_start_time Timestamp Read only 1.0 and 2.0 Represents the time at which the waveform was acquired or generated. This property can be zero if the time information is relative or the waveform is not in the time domain.
wf_time_pref String Read only 1.0 and 2.0 Indicates whether to interpret the x-axis data in absolute time or relative time.
wf_xname String Read only 1.0 and 2.0 Indicates the name of the x-axis of the waveform.
wf_xunit_string String Read only 1.0 and 2.0 Indicates the unit text of the x-axis.

If the data type of a property is not valid, this node treats the property as a customized property and the property will not function as described in the table.

Additional Properties that Affect .tdms Data and Performance

The following table lists all properties that do not exist in a .tdms file, but which you can use to perform certain actions.

Property Name Data Type Access Available in File Format Versions Description
NI_DiskCacheSize 32-bit unsigned integer Read/write 2.0
  • You can use the NI_DiskCacheSize property to improve the .tdms data writing performance by allocating a specific cache size in memory for the data.
  • .tdms data is written in bytes per file. This property is valid only when the disable buffering input of the TDMS Open node is True. The default value for this property is approximately 2 MB. Wire a different value to the property values input of the TDMS Set Properties node to change the cache size.
  • A greater value for the NI_DiskCacheSize property usually can improve the writing performance; however, a greater value also requires more computer resources.
NI_DiskGapSize 32-bit unsigned integer Read/write 2.0
  • You can use the NI_DiskGapSize property to improve the .tdms data reading performance when reading discontinuous data by indicating how you want the node to read the data.
  • This property is valid only when the disable buffering input of the TDMS Open node is True. The value of the NI_DiskGapSize property is a multiple of the sector size of the local hard disk. The default value for this property is 10.
  • If the data gap in the .tdms file is less than the value of the NI_DiskGapSize property, the TDMS Read node can read all data from the file at one time. If the data gap in the .tdms file is greater than the value of the NI_DiskGapSize property, the TDMS Read node reads each piece of data one at a time until this node finishes reading all data. Wire a value to the property values input of the TDMS Set Properties node to change the gap size.
    Note Obtaining the optimal reading and writing performance is a trial-and-error process. The same configuration might not return the same optimal performance on different computers. You might need to adjust the property values after you deploy an application from one computer to another.
NI_MinimumBufferSize 32-bit unsigned integer Read/write 1.0 and 2.0
  • You can use the NI_MinimumBufferSize property to improve the .tdms data writing performance by writing to a file less often. This property can reduce the size of a .tdms file by controlling the number of times the data is written to disk.
  • The NI_MinimumBufferSize property is valid only if the data layout input of the TDMS Write node is non-interleaved. By default, the value of the NI_MinimumBufferSize property is zero.
  • If you set the value at the group level, this node also sets the value of underlying channels whose value is zero. If you set the value at the file level, this node also sets the value of underlying groups and channels whose value is zero. Use of this property and the NI_DiskCacheSize property affects file buffering with .tdms files.
NI_UpdateChannelName String Write only 1.0 and 2.0
  • You can use the TDMS Set Properties node to rename groups and channels in .tdms files.
  • Wire NI_UpdateGroupName to the property names input if you want to rename a group and wire NI_UpdateChannelName to the property names input if you want to rename a channel. Wire the new group or channel names to the property values input and wire the group or channel names that you want to replace to the group name or channel name input.
  • If the groups or channels you wire to group name or channel name do not exist, new groups or channels are created with the new names.
NI_UpdateGroupName

File Buffering with TDMS Files

When a TDMS node writes data to a .tdms file, the data waits in a buffer until the buffer fills up or until you close the file. Buffering holds more data values in memory and allows you to wait and flush data to disk once, rather than continuously writing data. This both improves performance and causes the .tdms file to have fewer segments and be less fragmented. Files with fewer segments are more compact and take less time to open.

Buffering can occur at the channel layer, in the operating system (OS) file system, or in the TDMS disk cache. The layer at which buffering occurs depends on the property you set using the node. For example, the NI_MinimumBufferSize property determines the number of data samples to buffer at the channel layer. The disable buffering input of TDMS nodes determines whether to disable system buffering, which occurs in the OS. When the disable buffering input is True, this product disables system buffering and buffering occurs in the TDMS disk cache. The NI_DiskCacheSize property determines the amount of cache size in the TDMS disk cache to allocate for data. This property is valid only if the disable buffering input is True.

To write all buffers directly to the TDMS file, use the TDMS Flush node.

Note The NI_MinimumBufferSize property and the NI_DiskCacheSize property do not apply to the Advanced TDMS nodes.

When to Disable Buffering

You may want to disable buffering to speed up data transfers in the following situations:

  • When you want to read or write a large sample size.
  • When you want to read or write a large amount of data from different samples.
  • When you use a Redundant Array of Independent Disks (RAID) to increase processing speed. A RAID is a set of hard disks acting as a single disk that the OS can simultaneously access, taking less time to read or write data. If you access a RAID with buffering enabled, this product can take more time to copy data to the OS than the OS takes to actually write the data to the disk.