Saving and Loading Data

Overview

In this section we discuss how to save and record measurement data with the SHFQA Instrument using the LabOne user interface. In the LabOne user interface, there are 3 ways to save data:

  • Saving the data that is currently displayed in a plot

  • Continuously recording data in the background

  • Saving trace data in the History sub-tab

Furthermore, the History sub-tab supports loading data. In the following, we will explain these methods.

Saving Data from Plots

A quick way of save data from any plot is to click on the Save CSV icon btn uielements savecsv at the bottom of the plot to store the currently displayed curves as a comma-separated value (CSV) file to the download folder of your web browser. Clicking on btn uielements savecsv will save a graphics file instead.

Recording Data

The recording functionality allows you to store measurement data continuously, as well as to track instrument settings over time. The Config Tab gives you access to the main settings for this function. The Format selector defines which format is used: HDF5, CSV, or MATLAB. The CSV delimiter character can be changed in the User Preferences section. The default option is Semicolon.

The node tree display of the Record Data section allows you to browse through the different measurement data and instrument settings, and to select the ones you would like to record. For instance, the demodulator 1 measurement data is accessible under the path of the form Device 0000/Demodulators/Demod 1/Sample. An example for an instrument setting would be the filter time constant, accessible under the path Device 0000/Demodulators/Demod 1/Filter Time Constant.

The default storage location is the LabOne Data folder which can for instance be accessed by the Open Folder button btn uielements openfolder um. The exact path is displayed in the Folder field whenever a file has been written. Clicking on the Record checkbox will initiate the recording to the hard drive.

FileManagerTab General
Figure 1. Browsing and inspecting files in the LabOne File Manager tab

In case HDF5 or MATLAB is selected as the file format, LabOne creates a single file containing the data for all selected nodes. For the CSV format, at least one file for each of the selected nodes is created from the start. At a configurable time interval, new data files are created, but the maximum size is capped at about 1 GB for easier data handling. The storage location is indicated in the Folder field of the Record Data section.

The File Manager Tab is a good place to inspect CSV data files. The file browser on the left of the tab allows you to navigate to the location of the data files and offers functionalities for managing files in the LabOne Data folder structure. In addition, you can conveniently transfer files between the folder structure and your preferred location using the Upload/Download buttons. The file viewer on the right side of the tab displays the contents of text files up to a certain size limit. An example of the Files tab after recording Demodulator Sample and Filter Time Constant for a few seconds can be found below. The file viewer shows the contents of the demodulator data file.

The structure of files containing instrument settings and of those containing streamed data is the same. Streaming data files contain one line per sampling period, whereas in the case of instrument settings, the file usually only contains a few lines, one for each change in the settings. More information on the file structure can be found in the LabOne Programming Manual.

History List

Tabs with a history list such as Sweeper, Monitor Scope, support feature saving, autosaving, and loading functionality. By default, the plot area in those tools displays the last 100 measurements (i.e., depending on the tool, sweep traces, scope shots, DAQ data sets, or spectra), and each measurement is represented in as a list entry in the History sub-tab. The button to the left of each list entry controls the visibility of the corresponding trace in the plot; the button to the right controls the color of the trace. [1]Double-clicking on a list entry allows you to rename it. All measurements in the history list can be saved with btn uielements saveall um.

Figure 2 illustrates the data loading feature.

functional history
Figure 2. History sub-tab features. The entries "My measurement 1" etc. were renamed by the user. Measurement 1, 2, 3, 4 are currently displayed in the plot because their respective the left-hand-side button is enabled. Clicking on Save Sel would save "My measurement 3" and "My measurement 4" to a file, because these entries were selected (gray overlay) by a Control key + mouse click action.

Which quantities are saved depends on which signals have been added to the Vertical Axis Groups section in the Control sub-tab. Only data from demodulators with enabled Data Transfer in the Lock-in tab can be included in the files.

The history sub-tab supports an autosave functionality to store measurement results continuously while the tool is running. Autosave directories are differentiated from normal saved directories by the text "autosave" in the name, e.g. sweep_autosave_000. When running a tool continuously (btn uielements runstop um button) with Autosave activated, after the current measurement (history entry) is complete, all measurements in the history are saved. The same file is overwritten each time, which means that old measurements will be lost once the limit defined by the history Length setting has been reached. When performing single measurements btn uielements single um button) with Autosave activated, after each measurement, the elements in the history list are saved in a new directory with an incrementing count, e.g. sweep_autosave_001, sweep_autosave_002.

Data which was saved in HDF5 file format can be loaded back into the history list. Loaded traces are marked by a prefix "loaded " that is added to the history entry name in the user interface. The createdtimestamp information in the header data marks the time at which the data were measured.

  • Only files created by the Save button in the History sub-tab can be loaded.

  • Loading a file will add all history items saved in the file to the history list. Previous entries are kept in the list.

  • Data from the file is only displayed in the plot if it matches the current settings in the Vertical Axis Group section the tool. Loading e.g. PID data in the Sweeper will not be shown, unless it is selected in the Control sub-tab.

  • Files can only be loaded if the devices saving and loading data are of the same product family. The data path will be set according to the device ID loading the data.

The history data loading feature is illustrated below.

functional history loading
Figure 3. History data loading feature. Here, the file sweep_00000.h5 is loaded by drag-and-drop. The loaded data are added to the measurements in the history list.

Supported File Formats

HDF5

Hierarchical Data File 5 (HDF5) is a widespread memory-efficient, structured, binary, open file format. Data in this format can be inspected using the dedicated viewer HDFview. HDF5 libraries or import tools are available for Python, MATLAB, LabVIEW, C, R, Octave, Origin, Igor Pro, and others. The following example illustrates how to access demodulator data from a sweep using the h5py library in Python:

import h5py
filename = 'sweep_00000.h5'
f = h5py.File(filename, 'r')
x = f['000/dev3025/demods/0/sample/frequency']

The data loading feature of LabOne supports HDF5 files, while it is unavailable for other formats.

MATLAB

The MATLAB File Format (.mat) is a proprietary file format from MathWorks based on the open HDF5 file format. It has thus similar properties as the HDF5 format, but the support for importing .mat files into third-party software other than MATLAB is usually less good than that for importing HDF5 files.

SXM

SXM is a proprietary file format by Nanonis used for SPM measurements.


1. Among the mentioned tools, the Scope is exceptional: it displays the most recent acquisition, and its display color is fixed. However, the Persistence feature represents a more specialized functionality for multi-trace display.