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Multiple channel trigger

Hello,

 

I am trying to make signal aquisition using the board NI-9234, but I am having trouble for set the trigger. I am using different sensors in the input. In the first channel I am reading voltage and the other three channels I have microphones, so I am reading sound pressure. My source to the trigger is the voltage input, and I need to record all four channel simultaneously (with the same rate) after the trigger is actived.

 

I was trying to do that with the Signal Express, but I do not think it is possible, I cannot make both the voltage and the sound pressure signal with the same trigger. Now I am trying with the LabVIEW...

 

Thank you

Frederico

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What is "the trigger"?  Is the 9234 something that plugs into a cDAQ or a cRIO?  Where does the timing come from?  I don't understand using one channel for "voltage" and the other three for "microphones" -- all four channels are A/D (voltage) channels ...

 

Have you tried playing with your device in MAX?  You should be able to set up a multi-channel DAQ Task, including defining the Timing and Triggering.  Once you can do that in MAX, it's generally very simple to do the same thing in DAQmx.

 

Bob Schor

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I have attached my VI. It is slightly different from the one I had mentioned above, but the problem is the same. I can't set properly the trigger. The following error appears:

 

Error -200077 occurred at Property Node DAQmx Trigger (arg 1) in DAQmx Start Trigger (Analog Edge).vi:7160001->Medição de Sinais_LAB1.vi

Possible reason(s):

Requested value is not a supported value for this property. The property value may be invalid because it conflicts with another property.

Property: Start.TrigType
Requested Value: Analog Edge
Possible Values: None

Task Name: _unnamedTask<1B2AE>

 

 

If I 'pass-by' the trigger, the acquisition works fine.

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It looks like "Martelo" is the device whose A/D you are trying to trigger.  I don't know what kind of device this is, so I can't look up whether or not it has the possibility of being triggered by an Analog Edge (the fact that you get an error message suggests not).  I assume you know the Error Wire connected Start Analog Edge to Start Task is missing, right?

 

Oops -- I just noticed that Martelo is not the device, but a designation of the Channel(s) for something (Force IEPE?) -- the Task Input to the first DAQmx VI is unwired!!!  So you are sending commands to no device!  Put a Task Constant in there, right-click it, and see if your Device shows up (it should if you've connected it while MAX is running so that MAX "sees" it).

 

Bob Schor

 

 

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Hi, Bob Schor

 

Thank you for the answer. 

The Task Input of the DAQmx Create Virtual Channel don't need to be specified. If it is not, the LabVIEW creates the task  (http://www.ni.com/product-documentation/2835/en/).

The "Martelo" is a Impact Hammer. The idea is the trigger to activate when I hit with the hammer. Then I can calculate the FRF using also the signal from a accelerometer (both the hammer and the accelerometer are IEPE). But each average from the FRF should be take into account only after the system identify a trigger.

 

I couldn't run the VI again, because I don't have the board A/D with me right now. But as I said before, if I delete the DAQmx Start Trigger, the VI runs fine. For this reason, I believe the problem is occuring in this step. (The error wire was missing so that I could copy the error message). I also tried to remove the while loop, but the error remains.

 

Frederico

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The same error appears with other examples I found in this forum. (Another example is attached)

The only information I found about the triggering with NI 9234 (C series) is that the trigger channel must be the first channel from the board. But still, it does not work...

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