Data File


By default, opening and closing of data files (aka event files) is controlled via MWClient. By including a data file device in your experiment, you can transfer responsibility for data-file management to the experiment itself.

If an experiment includes a data file device, a data file will be opened automatically when the experiment starts running. If a data file with the specified filename is already open (e.g. because this is the second run of a protocol), then the existing file remains open. If a data file with a different name is open, that file is closed before the new file is created. If a data file with the specified filename already exists and is not currently open, the existing file will not be overwritten. If opening the data file fails for this or any other reason, the experiment will not start.

While an experiment with a data file device is loaded, data files cannot be opened or closed via MWClient. However, the client will still display the name of the current data file.

Note: An experiment can include only one data file device. Also, Start IO Device, Stop IO Device, and autostart have no effect on this device.



Required Parameters



Filesystem path and name for the data file, excluding the file extension (.mwk2), which is appended automatically.

If the filename is a relative path (i.e. it does not begin with /), then the standard data-file directory is prepended to it before the file is created. Absolute paths are not modified.

Typically, the filename will make use of variable and/or expression interpolation to ensure that each experimental session produces a unique data file. The interpolated components of the filename are re-evaluated each time the experiment starts, so changes to variable values and expression results between runs in a given session will result in different filenames for each run.

Optional Parameters




If YES, the device will start I/O automatically (as if by an implicit Start IO Device action) when the experiment starts running.

Note: Device I/O will always stop automatically when the experiment stops running, irrespective of this setting.


Alternative device to use if this one fails to initialize (e.g. because the required hardware is not available). If #allowAltFailover is set to 0 or false, this parameter is ignored.


Allowed at top level:


Allowed parent: