Reading waveform from Agilent 54855a

[Penny]

Hi Everyone,

I am reading a waveform from an Agilent 54855a oscilloscope

with a GPIB card.  The waveform looks great on my LabView

chart.  However, I keep noticing that there are too many total

data points in the plot, considering the sampling frequency of

the scope.

When I grab the waveform with my LabView code, am I taking

the exact data points acquired by the scope, or is there some

interpolation happening to create more data points in between

the real ones?  Thanks for any thoughts on this.

Regards,

Penny

[NathanT]

Hello Penny,
          You can acquire more points from the scope than what is displayed on the scope's front panel.  Are you using one of the LabVIEW Plug and Play drivers that is available for your instrument?  If so, it seems like you should use Conf Measurement Acquisition to set the number of  points that you would like to acquire.  If you are just  running the example VIs that come with the driver I don't think that there is a way to specify the number of points that you would like to acquire.

Cheers,

NathanT

[Penny]

Hi NathanT,

Thanks for the reply.  Yes, I have started by using the Plug-and-Play drivers for the Agilent 54855a.  At the moment I am looking at Utility Read Binary Data Block.vi (attached).  What I don't seem to understand is where I tell LabView how many bytes to grab.  From the looks of this piece of code, I should be grabbing 2 bytes of data.  However, I seem to end up with 20005 data points by the time this utility is finished.  Not only is that more than 2 bytes of data, it is more points than the scope could have sampled in that time (based on my external function generator and the sampling frequency of the scope).  Eek.

Thanks,

Penny

[Penny]

Hi NathanT,

Well, I took a closer look at that utility vi, and then looked at the oscilloscope set-up, and there WAS some interpolation happening, creating extra data points.  Once I switched that option off (under the scope's Setup/Acquisition menu), I started seeing the expected number of data points on my LabView chart.  Hooray!  (For now).  Thanks again.

-Penny

[NathanT]

Hello Penny,
     I am glad that with further investigation, you found out what the cause of the issue was.

Cheers,

NathanT