Why did Fetch waveform Vi generates strange 1D array data(all elements are -5.2)?

Question

I just made some changes on the Getting Startted vi of tkds30xx scope driver to catch the start process of a power supply output(2Vdc). I use Initiate Acquisition vi followed by Fetch waveform vi to get the waveform on scope. I use a logical signal controlled by the Agilent 34903A switch to trigue the waveform acquisition. Then I get the 1D array output from Fetch waveform vi for calculation by another subvi. The waveform sample points are 10E+3 points(default). When running the program, the waveforms on the scope screen are right what I expect, but the 1D array data values are all -5.2V.

Answer 1

Without seeing your code it would be hard to give specifics, but does -5.2V appear anywhere else in the system? One possibility is that you aren't looking at the channel you think you are.
How much delay is there between when you tell the scope to begin acquisition and the read occurs? Could the read be getting its data before the scope actually triggers?
What happens when you run the "Fetch Waveform" vi by itself? In other words, if you setup the system and generate the trigger manually such that the proper waveform is on the scope, does Fetch Waveform run by itself return the proper result?
If this is not correcct there is something basically wrong with the function for reading the waveform. Again, giving specifics are hard, but open the VI and go
through it statement by statement making sure that the settings and commands make sense for your application. Many vendors make excellent instrumentation, but I have yet to see one that could write a good driver.
Also, could you describe what the proper waveform looks like?
Mike...
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