Comparing Signals from Different Sources in SignalExpress
Primary Software: LabVIEW Signal Express>>Development System
Primary Software Version: 1.0
Primary Software Fixed Version: N/A
Secondary Software: N/A
Problem: I need to acquire and compare two signals from different sources, such as different hardware devices or files. Is there any way I can readily do this in SignalExpress?
Solution: To compare two signals in SignalExpress simply drag the two signals onto the same graph in the data view window. However, depending on the amplitude and/or timing of the two signals they may not immediately align on the graph in a useful way for comparing them. One quick method for improving the alignment of the two signals on the graph is to right click on the graph and select the appropriate Time Stamp option for your signals: Ignore, Absolute, or Relative. These three options are explained below:
- If you select Ignore, all the plots on the graph start at zero independently of the actual time stamp of the plotted signals. Select this option to display multiple plots with unrelated time stamps, such as displaying an acquisition result and a simulation signal loaded from a file.
- If you select Absolute, all the plots on the graph display signals that show the actual time stamp of each waveform. Use this option if you want to display a waveform acquired using a triggered digitizer where the time stamp reference (zero) is linked to the trigger point.
- If you select Relative, you can choose which reference signal to use as the relative reference in the associated pull-down menu. The graph displays the reference signal starting at zero and displays the other plots starting at a time relative to the reference time stamp. For example, if you plot two waveforms time stamped at 15 and 13, and select the first waveform as the reference, the two plots start at 0 and –2. Use this option if you want to display multiple channels acquired by a multiplexed MIO board and want to display the timing relationship between the different channels (correct for the inter-channel delays).
Alternatively, you can also use the Interactive Alignment step for a more "interactive" comparison of two input signals. The interactive alignment step also provides some additional measurement capabilities and a precise output signal illustrating the exact difference between the two signals. See the SignalExpress help file for more details on the Interactive Alignment step.
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Report Date: 05/11/2005
Last Updated: 05/11/2005
Document ID: 3LA8G2L2
