Python continuously log DAQmx IEPE vibration data

[Liwenhu]

I am trying to use Python API to continuously access/log the tri-channel IEPE vibration data. I was following this example code:

https://forums.ni.com/t5/Example-Code/Vibration-Continuous-Acquisition-with-Triggering-in-Python-wit...

However, such an example code is only for a single channel plus the IEPE sensor needs internal excitation source settings.

Does anyone know how to set the excitation for the IEPE sensors? Any example code would be appreciated.

[Liwenhu]

By the way, I am using NI-9234 on NI-9185 if it matters.

[ZYOng · Accepted solution]

From the example you found:

Line 2: 

from nidaqmx.constants import AcquisitionType, ExcitationSource

Line 18:

acceltask = task.ai_channels.add_ai_accel_chan(channel_name, units = units_g)

acceltask.ai_excit_src=ExcitationSource.INTERNAL

To add more channels, call add_ai_accel_chan a few more times (Easily Synchronize and Trigger NI-DAQmx with Channel Expansion), or use NI-DAQmx Syntax for Specifying Physical Channel Strings to add multiple channels.

[Liwenhu]

Thank you for the reply. Do you know what's the default excitation current? And how do we change that value?

[santo_13]

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@Liwenhu wrote:

Thank you for the reply. Do you know what's the default excitation current? And how do we change that value?

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You can find the default and supported excitation current from your instrument datasheet.

9234 supports only 2mA excitation current and you can ON/OFF from software

[Liwenhu]

Thanks for the reply, but I don't think the default is 2mA, from the datasheet, it says a minimum of 2mA and there should be a way to adjust this value through python API rather than just on/off.

I used Labview to log the data, and it can be set as 4mA. I think there should be a way to adjust it.

[santo_13]

I can guarantee that the 9234 support only 2mA and if you try to set it to any other value from the DAQmx API, you will get an error.

There are other DSA modules that support 2mA or 4mA but your 9234 supports only 2mA. And yes, you can set the excitation current using DAQmx API.

For example, PXIe-4464 supports 4mA,10mA and 20mA as listed in the datasheet.

Some related articles,

https://knowledge.ni.com/KnowledgeArticleDetails?id=kA03q000000YIWmCAO&l=en-US

https://forums.ni.com/t5/Multifunction-DAQ/Toggling-IEPE-on-off-for-9234-voltage/td-p/892349

https://knowledge.ni.com/KnowledgeArticleDetails?id=kA00Z000000P8uwSAC&l=en-US

[Liwenhu]

Thanks, I think it works.

[Liwenhu]

Hi, I tried to use the code to record and compare with the LabView recorded data, I found the python recorded some how is much smaller than LabVIEW data.

I guess even python did not give me any error but it did not really initiated the excitation. Any idea how to identify which step is wrong?