DAQmx read.vi; Analog 1D Wfm NChannal N Sample

[huan1445]

Hi 

I am using the Analog 1D Wfm NChannal N Sample mode of the DAQmx Read.vi to collect voltage data. There are 4 physical channels used so I am assuming that there should be 4 wfms as results. However, I wonder why there are 8 sets of data displayed in the waveform chart. 

Take care

Huang

[Gregory]

It might have to do with the task you have wired in: "MyVoltageTask_trial". I would try deleting that and leaving the input empty. Or it might have to do with how you are graphing it.

[Bob_Schor]

A couple of points:

• You persist in posting only a picture of part of the Block Diagram, conveniently "hiding" several DAQmx functions and all of the graphing code (which is, after all, where the problem occurs).
• Attach your VI.  Also, if you are going to use a Task, write a description of the Task.
• Note that the Plot shows 4 channels with names like "Dev1/a04", and four other tasks with names like "Voltage_1".  I'm guessing the latter is from the Task definition, the former from the Channel VI (which you probably shouldn't use, but who can say without seeing the code?).

Bob Schor

[RavensFan]

The task name wired in is almost certainly the problem.

With DAQmx, you can string several Creates together adding channels with each one.  Each create just adds channels to the task that is already coming into it at the top left.  In this specific case, what is coming into that single Create is the task name which probably has 4 channels already defined in it.  So this VI is adding 4 more channels to the 4 already defined in the task.