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Setting up IEPE settings (DAQ MX task) for multiple channels inside a loop instead of having one large Property Node

Error Message

 

I am trying to set IEPE settings for 32 channels, and each channel will have different settings.  I was going to use one task in DAQ MX using the ActiveChans property: http://forums.ni.com/t5/LabVIEW/Configuring-individual-channels-on-the-PXI-4472B/td-p/929764 , but I have so many channels I decided it would be better suited for a loop.  My code right now is for just two channels for simplicity.

 

Question 1: I'm getting an error when trying to setup the channel's IEPE for voltage. It says "You have requested: Voltage" "You can select: Current", but you should be able to select "Voltage" or "Current".

 

Question 2: Is my task going to contain the information for all 32 channels the way I have it in the loop, or just channel 32's information? I can't find much information on "tasks".  Do I have to just do it with one very large Property Node with 32 different ActiveChans properties.

 

 

I'm running LabView 2009 SP1.

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LabViewer35242,

 

Your above image is a little small, but I opened your attached VI and examined it.

 

For Q1: Are you referring to the bottom row of your property node, where it says AI.Excit.VoltageOrCurrent? I am able to manually add a constant here while can be set as Voltage or set as Current. Are you able to do this? Are you just seeing Current as your option here?

 

For Q2: I believe you should get one task to configure multiple channels. I found the below link to be useful to understand working with multiple channels/configurations in a single task.

http://zone.ni.com/devzone/cda/epd/p/id/4524

 

Another example while proves useful for this type of application is below. Here each channel of a task is given a custom change.

http://zone.ni.com/devzone/cda/epd/p/id/6062

 

I hope these help.

 

 

 

 

Regards,

Renée M
Applications Engineer
National Instruments
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Thanks for the reply!

 

The first solution with separate DAQmx create tasks is for each channel is what I was trying to avoid.  The second solution wouldn't necessarily work either because I need to use the Property Nodes, but using shift registers I think will work.

 

Will this loop with shift registers create a task that has all the channels' info?

 

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I am able to change it from Voltage to Current and vice versa, but for some reason I get an error using the Voltage.  I'm wondering if you can't power a voltage measurement with voltage excitation..? Doesn't make sense to me.

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Hi LabViewer35242,

 

What device are you using, and what kind of sensor are you trying to measure?

 

Most of the NI PXI-44xx devices have a built-in current excitation source. They do not support generating voltage excitation. Other devices, such as the NI SCXI-1520, can perform voltage measurements with voltage excitation, but they are designed for different types of sensors (strain gages, load cells, etc.) than the NI 44xx devices (accelerometers, microphones).

 

Brad

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Brad Keryan
NI R&D
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PXI-1042 chassis, PXI-8196 controller, and PXI-4472B modules

 

For this test the sensors will be accelerometers and dynamic pressure transducers.

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For my measurements I only need Current Excitation so I will just take the voltage array out.  I'm guessing Labview doesn't like the Voltage Excitation with the AI_Voltage_VI.

 

The reason I chose the AI_Voltage_VI instead of the AI_Accelerometer_VI was so I could just have one create channel and alter the properties of each channel using a cluster of arrays.

 

How do I make the  AI Voltage VI "AC coupled"?

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Hi LabViewer35242,

 

Voltage excitation is supported with the AI Voltage version of DAQmx Create Channel if you are using a device that supports voltage excitation. The 4472 only supports current excitation.

 

You can enable AC coupling by setting the AI.Coupling channel property to AC.

 

Note that if you put your call to DAQmx Create Channel inside the loop, you can change the parameters you pass for each channel. You just need to make sure you pass the same task every time.

 

Brad

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Brad Keryan
NI R&D
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