Using the Data Logger
Data Loggers can be used to log data over long periods of time, in this case, analog voltage data. This guide explains the use of WaveForms' Data Logger instrument. The Data Logger instrument is also referred to as the Logger in WaveForms.
- A Digilent Test & Measurement Device with Analog Input and Output Channels:
- A Computer with WaveForms Software Installed
1. Opening the Logger
Plug in the Test & Measurement Device, then start WaveForms and make sure the device is connected.
If no device is connected to the host computer when WaveForms launches, the Device Manager will be launched. Make sure that the device is plugged in and turned on, at which point it will appear in the Device Manager's device list (1). Click on the device in the list to select it, then click the Select button (2) to close the Device Manager.
Note: “DEMO” devices are also listed, which allow the user to use WaveForms and create projects without a physical device.
Note: The Device Manager can be opened by clicking on the “Connected Device” button in the bottom right corner of the screen (3), or by selecting “Device Manager” from the “Settings” menu at the top of the screen.
Once the Welcome page loads, in the instrument panel at the left side of the window, click on the Logger button to open the Data Logger instrument.
Once the Data Logger instrument opens, the window contains the data plot on the right side and the default data measurements listed on the left side.
2. Using the Data Logger
This section walks through setting up the Data Logger to capture data from the Oscilloscope Channels.
2.1 Hardware Setup
Connect the Test and Measurement Device's Oscilloscope Channel 1 pin to the device's Wavegen Channel 1 pin.
For devices using MTE cables, the input channel uses an orange wire and the output channel uses a yellow wire.
For devices that use differential input channels, such as the Analog Discovery Studio with MTE cables, make sure to connect the Oscilloscope Channel 1 negative pin to the ground pin associated with Wavegen Channel 1.
Note: The analog input channels can be used with BNC Cables. For more information, see the Using the Oscilloscope guide.
2.2 Software Setup
In WaveForms' Welcome tab, open the Wavegen instrument, then click the Run button () in the control bar near the top of the window to begin outputting a signal. With default settings, a 1V amplitude (2V peak-to-peak) 1kHz sine wave is applied to the Wavegen Channel 1 output pin.
For more detail on how to use the Wavegen instrument, please see the Using the Waveform Generator guide.
Return to the Data Logger instrument by clicking on its tab in the bar at the top of the screen.
2.3 Run the Data Logger
Click the Run button in the control bar near the top of the window to begin capturing data on the Oscilloscope Channels. Captured data will appear in the plot pane as a set of colored lines. Each colored line corresponds to one of the default measurements listed on the left side of the window. For example: the yellow line is the measurement named C1 DC, meaning the DC voltage of the Channel 1 input. Since the signal going into Channel 1 is AC and centered about 0 volts, the data this measurement is collecting should be theoretically zero but will appear as a voltage in the low mV range next to the measurement name.
A variety of different measurements can be seen for each of the device's channels, listed on the left side of the window. Additional channels and custom measurements can be added using the green plus button.
2.4 Plot Plane Axes
By default, measurement 1 (named C1 DC) is selected and therefore the vertical axis will automatically display an appropriate range for viewing that particular logged signal data in the same color associated with that data (yellow for C1 DC).
Selecting a different measurement in the list to the left of the plot plane (for example, measurement 2) will adjust the vertical axis such that the selected measurement will be displayed along with all the other desired measurements with an appropriate range for viewing the logged signal data magnitude and change its color to reflect the currently selected data (light blue for measurement 2).
To manually set the range for a measurement:
- Click the Utilities () icon to the right of the measurement color display box
- Uncheck the Auto box
- Enter desired Top and Bottom values
The bottom axis default is time in seconds with a minute long window where zero seconds is on the right side of the bottom axis and sixty seconds is on the left. The default sampling frequency is one second, which means that the displayed data will update once every second. Increase or decrease this displayed time window using the History drop-down menu, located at the top of the data plot.
Note: Using Multiple Instruments
The Data Logger instrument can be used with other WaveForms instruments. Using multiple instruments at the same time is helpful in a wide variety of situations. One example would be to use the Waveform Generator to stimulate a circuit under test, the Power Supplies to provide power to the circuit, and view the response with the Data Logger, all at the same time. More information on how instruments can be operated together can be found in the Using Cross Triggering guide.
It should be noted that the analog input channels cannot be shared by multiple instruments. When the Voltmeter is enabled, any other instruments using the analog input channels are disabled. Other instruments that use the analog input channels include the Oscilloscope, Voltmeter, Spectrum Analyzer, Network Analyzer, and Impedance Analyzer.
3. Data Logger User Interface Overview
This section walks through the wide variety of controls and features present in the Data Logger instrument.
3.1 Control Buttons
As seen in Section 2, the control bar near the top of the window can be used to stop and start the capturing of data from the analog input pins. In addition to the Run/Stop button, the Single button can be used to start data acquisition and run for the time specified under the History drop-down menu. In the Data Logger window, these buttons both start the data acquisition but a second click on the Single button will simply restart the acquisition whereas the Run button will now display Stop and a second click will stop the data acquisition. These options can also be accessed in the Control drop-down menu located above the control bar.
3.2 Data Export
To export data from the Data Logger tool, click the Export () icon located to the right of the History drop-down menu located on the control bar. This will open a new window with two tabs titled “Data” and “Image”.
The Data tab allows for export of a .csv file containing all of the current data points in the plot plane with comments, headers, and labels as default or an image of the current plot plane. Remove comments, headers, and/or labels by unchecking the corresponding box located in the upper left section of this window.
The Image tab allows for saving of an image of the Data Logger tool interface including the plot plane, measurements list, and the control bar with the option of displaying the device, serial number, and time that the image was taken. To change the background color of the plot for printing, see Plot Utilities in section 3.8.
3.3 Measurement Maximum/Minimum Display
To the left of the Single acquisition button described in section 3.1 is a drop-down menu that says “Show”. Click on this to select whether or not to add columns to display the minimum, maximum, and/or average measurements.
3.4 Measurements Pane
The Measurements Pane, on the left side of the screen, displays a table containing measurements of each of the signals captured on the analog input channels. Each measurement corresponds to a line in the plot pane. The Measurements Pane is used to view a summary of measurements currently being tracked, as well as to define what measurements are to be tracked as data is logged.
3.4.1 Measurements - Add and Edit (Basic)
To edit an existing measurement, click once on the measurement to highlight it, then click on the Edit icon () (to the left of the “Show” drop-down menu on the control bar discussed in section 3.3). This will bring up the same window used to add a measurement but with the selected measurement script, name, and unit description. See section 3.6 (Add Measurements) for further information about using this tool. If no measurement is selected, the edit window will not open.
Alternatively, to add a new measurement, from the control bar, click the green plus button to add a new measurement. A new window will open with two tabs titled “Item” and “Function”, with the Function tab displayed by default.
The Item tab contains commonly used, predefined measurements for each channel: DC voltage, True RMS voltage, and RMS voltage. These are the default measurements that are displayed when opening the Data Logger instrument, but if they were to be deleted they can be quickly added again from here.
The Function tab by default displays the script editor window. It can be used to manually type a mathematical function or click on a one of the desired functions displayed below the Insert checkbox to add them to measurement function. To hide the built in functions, uncheck the Insert box.
(NOTE: all trigonometric functions operate on radian values, not degrees.)
Click the Evaluate Script button () to check that the script functions properly. If so, a value should be displayed to the right of the button. If there is some syntactical error “NaN” will be displayed. Below this button are fields to name custom measurement and declare the unit of measurement. Click “Add” and the custom measurement will be added to the measurements list on the left of the plot plane with a unique color automatically applied to that measurement. Click “Close” to not add a custom measurement and the window will close.
To change the color of the measurements, click the color icon associated with the measurement in the list. This will bring up a color spectrum to choose a new color from. Add, Remove, and Edit measurement are also available by right clicking on the measurements list portion of the Data Logger tool.
3.4.2 Measurements - Add and Edit (Advanced)
Within the Function tab of Add Measurements, there are two drop-down menus above the script editor window. The Script menu gives the option to save the custom script or import a previously saved script to/from a .txt file. The Options menu has two options to select. The Code Completion option is selected by default which allows the script editor to suggest functions based on what is currently being typed in the script editor window. For example: if the Code Completion option is selected and the letter “s” is typed in the script editor, the Code Completion will suggest all built-in functions that start with the letter “s” (i.e. square root, sine, etc.). The Debug option opens a new window only if there is text in the script editor window. The Debug button launches a script debugger, which provides an environment to step through complex scripts to ensure proper functionality, locate where scripts are malfunctioning, or identify syntactical errors.
3.4.3 Measurements - Remove
The far left side of the control bar has a green plus () and a red minus () for adding and removing measurements, respectively. To remove a measurement, click on the measurement to be removed in the list. Then, click the red minus and select remove or simply press the delete key on the keyboard. To remove all measurements at once, click the red minus and select “Clear”. To hide a measurement from the plot plane without deleting from the measurements list, uncheck the Plot box associated with that measurement.
3.5 Sampling Utilities
To the right of the Update drop-down menu on the control bar is a Utilities Icon (). Click on this to show options for how each channel is sampled and displays values in the plot plane. The Samples drop-down menu value is the number of samples per measurement to be displayed in the plot plane from 10 to 86400 samples. Changing this value will also update the time axis since the number of displayed samples is linked to the sampling rate of the Data Logger. Below the Samples drop-down menu are drop-down menus for each channel to configure the DC offset and range of the display for each channel.
Important: This menu also allows for the selection of different attenuation factors, which is highly relevant when using BNC cables.
3.6 Plot Plane Cursors
To add a vertical bar cursor to the plot plane, click the Add Cursor () icon in the lower left corner of the plot plane. This will add a cursor on the far right of the plot plane. To move the cursor, click and hold the cursor and drag horizontally to the time position desired. Adding additional cursors will default to a differential measurement between the first cursor position values and the newly added cursor position values. These differential cursors can be moved by clicking once on the cursor and moving to the desired position. This movement is independent of the reference cursor. If a cursor has a differential cursor referenced to it, moving the reference cursor will also move the differential cursor proportionally. Right click the cursor to display the cursor options menu. The menu provides options to precisely change the time position of the cursor in the field, deallocate a differential cursor to an independent cursor, choose a reference cursor for a given cursor in the reference field, change the differential time from a reference cursor (differential cursors only), or change the color of the cursor by clicking on the color icon to produce a color spectrum to choose a color from. To remove a cursor click the Remove button at the bottom of the cursor options menu.
3.7 Quick Measure Tools
Additional cursor types are available by clicking either the Free () or Vertical () icons located in the top right corner of the plot plane.
Click the Free icon once and the mouse cursor will display the time and magnitude values of the selected measurement as it hovers over the plot plane. Click on the plot plane to place a cursor point at the desired position, then drag the mouse horizontally and/or vertically to place a differential cursor point. Click again to replace the original cursor point and so on. Click the Free icon again to exit this mode.
Click the Vertical icon once and the mouse will display a vertical cursor on the plot plane at the cursor position. Click on the plot plane to place the vertical cursor and display a differential cursor, then click again to place the differential vertical cursor. Click again to replace the original vertical cursor and so on. Click the Vertical icon again to exit this cursor mode.
3.8 Plot Utilities
The Utilities Icon () in the top right corner of the plot plane allows for placement of text labels, clearing of labels, toggling the background btween light and dark (ideal for printing), and changing the thickness of the plot lines. These options can alternately be accessed by right-clicking on the plot plane.
3.9 Other Plot Plane Options
To clear the plot plane of all data without removing measurements, click the Clear icon () located on the control bar to the right of the Sampling Utilities icon. This can be done while the Data Logger is running. To hide the plot plane, click the green arrow () on the far right of the control bar. To redisplay the plot plane, click the green arrow again. This also can be done while the Data Logger is running.
For more guides on how to use the Digilent Test & Measurement Device, return to the device's Resource Center, linked from the Test and Measurement page of this wiki.
If voltage values seen in the Data Logger are significantly different from the expected voltage output of the Supplies, please calibrate the device by following the Calibration Guide.
For more information on WaveForms visit the WaveForms Reference Manual.
For technical support, please visit the Scopes and Instruments section of the Digilent Forums.