Read From Measurement File

LabVIEW 8.5 Help
August 2007

NI Part Number:
371361D-01

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Reads data from a text-based measurement file (.lvm) or binary measurement file (.tdm or .tdms).

You also can use this VI to read Multisim data if you have Multisim 9.0 or later installed. Use the Write To Measurement File Express VI to write data to a measurement file. You also can use the Storage VIs to read from and write to .tdm files.

Details Examples

Dialog Box Options

Block Diagram Inputs

Block Diagram Outputs

Dialog Box Options

Parameter

Description

File Name

Displays the full path to the file from which you want to read data. The Express VI reads data from the file that this parameter specifies only if the File Name input is unwired. If you wire the File Name input, the VI reads data from the file that this input specifies instead.

File Format

Contains the following options:

Text (LVM)—Sets the file format to text-based measurement file (.lvm) and the file extension in File Name to .lvm.

When you select this file format, you enable the Read generic text files checkbox. Selecting this checkbox allows you to read data from generic text files.
Binary (TDMS)—Sets the file format to binary measurement file (.tdms) and the file extension in File Name to .tdms. If you select this option, the Time Stamps and Generic Text File sections are not available.
Binary with XML Header (TDM)—Sets the file format to binary measurement file (.tdm) and the file extension in File Name to .tdm. If you select this option, the Time Stamps and Generic Text File sections are not available.

When you select this file format, you enable the Lock file for faster access checkbox. Selecting this checkbox makes reading and writing significantly faster (at the expense of the ability to multitask certain activities). It is recommended that you use this option in most cases.
Note When this option is enabled, no two Express VIs can access the same file at the same time when one of them is writing a "series of files."

Action

Contains the following option:

Ask user to choose file—Displays a dialog box that prompts users to select a file.

Segment Size

Contains the following options:

Retrieve segments of original size—Retrieves segments of the signal from the file in the original size.
Retrieve segments of specified size—Retrieves segments of the signal using the size you specify in Samples.
- Samples—Specifies the number of samples you want to include in the segment size read from the file. The default is 100. This option is available only when you select the Retrieve segments of specified size option.

Time Stamps

Contains the following options:

Relative to start of measurement—Displays the numeric object in terms of hours, minutes, and seconds starting from zero. For example, 100 in decimal equals 1:40 in relative time.
Absolute (date and time)—Displays the numeric object in terms of time elapsed since 12:00 a.m., Friday, January 1, 1904, Universal Time.
Note These options are available only when you select the Text (LVM) option from the File Format section.

Generic Text File

Contains the following options:

Start row of numeric data—Indicates the first row of numeric data. The Express VI begins reading data from this row. The default is 1.
First row is channel names—Specifies that the channel names are in the first row of the data file.
First column is time channel—Specifies that the time data for each channel are in the first column of the data file.
Read File Now—Imports the data from the file you specify in File Name into the Sample data table.
Sample data—Displays the data from the file you specify in File Name when you click the Read File Now button.
Note These options are available only when you select the Text (LVM) option from the File Format section.

Delimiter

Contains the following options:

Tab—Uses tabs to delimit fields in the text file.
Comma—Uses commas to delimit fields in the text file.
Note These options are available only when you select the Text (LVM) option from the File Format section.

Decimal Point

Contains the following options:

. (dot)—Uses a period as the decimal separator.
, (comma)—Uses a comma as the decimal separator.
Note These options are available only when you select the Text (LVM) option from the File Format section.

Block Diagram Inputs

Parameter	Description
Enable	Enables or disables the Express VI. The default is ON or TRUE.
File Name	Specifies the name of the file from which you want to read data.
Reopen File	Resets the file position such that the next read starts at the beginning of the file.
error in (no error)	Describes error conditions that occur before this VI or function runs.

Block Diagram Outputs

Parameter	Description
Description	Returns the description in the header of the .lvm or .tdm file.
Comment	Returns the appended comment of each data set in the .lvm or .tdm file.
Signals	Contains the output signal or signals.
File Name Out	Returns the name of the file.
error out	Contains error information. If error in indicates that an error occurred before this VI or function ran, error out contains the same error information. Otherwise, it describes the error status that this VI or function produces.
EOF?	Returns TRUE when the Express VI reaches the end of the file.