Features for Logging Waveform Data to Disk

NI VeriStand 2018 Help

Edition Date: May 2018

Part Number: 372846M-01

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You implement embedded logging of AI channel data from DAQ devices through waveform tasks. When a task runs with logging enabled, NI VeriStand streams data directly from the device buffer to the hard disk of the target to which the device is connected. Tasks allow logging to .tdms files only.

Note  The following sections explain concepts involved in configuring logging of waveform acquisitions on Logging configuration pages in the System Explorer.

Allowing Logging versus Enabling Logging

Allowing logging for a task means the task is capable of logging data. When logging is allowed, you can enable and disable logging with the Logging Enabled channel. To improve system performance, do not allow logging if you do not plan to log data from a task.

You allow logging for a task on its Logging configuration page in the System Explorer.

Starting New Log Files

You can configure NI VeriStand to start logging to a new file when one or more of the following conditions are true.

Condition How to Configure this Behavior
A new acquisition begins. Select Create new file in the Action on new acquisition drop-down menu on the Logging configuration page.
The number of samples written to a file reaches a certain limit. Place a checkmark in the Span multiple files checkbox on the Logging configuration page and enter the number of samples at which to start logging in a new file.
The Start New File channel receives a TRUE value. Write a TRUE value to the channel.

Filenames for Acquisitions that Span Multiple Log Files

If you configure a task to create a new log file when the number of samples written to a file reaches a certain limit, NI VeriStand creates a new file with the naming convention of <filename>_####.tdms, where #### starts at 0001 and increments automatically with each new file. For example, if the file specified is C:\data.tdms, the next filename used is C:\data_0001.tdms.

Note  If you also configure the task to timestamp log filenames, NI VeriStand uses the original timestamp in the name of each file the acquisition spans and not the current timestamp when the additional log file(s) are created.

Improving System Performance while Logging

If you do not need to access acquired data in real time, you can choose to stream data directly to a log file without reading the data into a waveform. For example, if you do not need visualize the waveform in a graph as it is acquired, the system does not need to read the acquired values. NI VeriStand can devote more resources to other processes if it does not also read the data from the device.

To enable this behavior, select Log only in the Logging mode drop-down menu.

TDMS File Format

Refer to ni.com/tdms for additional information about the TDMS file format and reading from TDMS files. National Instruments provides a number of mechanisms for reading TDMS files, including software support in LabVIEW, LabWindows/CVI, ANSI C, DIAdem, and Measurement Studio. In addition, National Instruments provides a Microsoft Excel plugin.

Related Links

Setting Up Timing and Logging Properties for Waveform Acquisitions

Overview: Acquiring Waveform Data from DAQ Devices

Waveform Task Channels

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