Introduction to benchtop equipment and data acquisition  (Page 4/6)

2.8 accessing oscilloscope data on the pc

To facilitate saving files to the hard drive of the lab computers, each of the oscilloscopes has a networkinterface card installed.

• Open Internet Explorer.
• Under Favorites, click the link titled o-scope. This should bring up a window that has a screen shot of the LCD display of theoscilloscope.
• Click on the tab labeled DATA.
• In this window, data from the input, math and reference channels can be saved to the computer.
• For example, using the options under Waveform transfer from the instrument, choose the Source as CH1, and the Format asSPREADSHEET.
• Click Get. A dialog box opens for the data to be saved.
• Make sure to add the correct file extension when saving the data. (.xls for Excel.)

Part 3: data acquisition

For some applications, it is not practical to use an oscilloscope to analyze a signal.

• Some applications generate signals that operate on timescales of hours or weeks.
• Some signals require statistical analysis
• Some data are processed by complicated algorithms.
• Some signals are used to control electromechanical systems.

For any of these applications, you would need a data acquisition (DAQ) system that measures a signal and thenwrites the data to a file for later analysis, or communicates with another system for real-time use.

In the next section of this lab, you will connect your signal (the function generator) to your signalconditioning equipment (the National Instruments SCXI) and data acquisition equipment (the PCI data acquisition card). You will useLabVIEW, a graphical programming language, to generate a simple Virtual Instrument (VI) to acquire data, chart the data on yourmonitor, and write the data to a file.

3.1 introduction to data acquisition hardware

The SCXI is used to condition a signal. The SCXIs in this lab are equipped with modules that prepare the inputsignal by:

• Applying a gain (magnification) to the input signal
• Filtering out high frequency characteristics
• Balancing a strain bridge

Once the signals are conditioned, they are multiplexed into a single signal. This signal is then passed by aserial cable to the data acquisition card in the PCI slot of the PC. The data acquisition card uses an analog to digital converter(ADC) to record the magnitude of an analog signal as a digitalvalue. As a digital value, these data can be interpreted by a computer.

3.2 configuring hardware and opening a new program

Connect the function generator output to the BNC connector on Channel 0 (the first input) of the SCXI-1520module on the SCXI chassis.

1. Use the function generator to produce a 200 Hz sinusoidal wave.

2. Open LabVIEW 8.0.

3. Click Blank VI. Your new VI will open with two windows: the Front Panel (the user interface) and the BlockDiagram (which is where you develop your graphical code). These two windows are linked, and as you develop your VI, you will see thatsome objects that you place in one of the windows will appear simultaneously in the other window.

4. On either the front panel or the block diagram, click File>>Save As. Save your VI to the folder (on the desktop) that corresponds to your lab section. (Saving eitherwindow will save the content from both the front panel and block diagram windows.)