Signal Conditioning

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SCXI-1520 excition measurement

After setting the excition voltages of the SCXI-1520 either with MAX or the AI Parameter.vi, I can read back the value for a given channel with AI Parameter.vi's "Get" function or with the SCXI channel strings "ob0!sc1!md1!p_posX" & "ob0!sc1!md1!p_negX" (where X is the channel number).

The values reported are slightly different than the commanded value. Which of these is the most accurate value of the actual voltage?

Rich
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Greetings Rich,

Using the SCXI channel strings will actually read back the excitation voltages using the A/D of the DAQ device cabled to the SCXI chassis. Using the AI Paramenter VI to get the excitation value will just read the NI-DAQ configuration file and return what you set the excitation value to within MAX or LabVIEW. So the AI Parameter VI should just be used to ensure that the excitation was set (this isn't actually reading the excitation voltages using the A/D of the DAQ device).

So, reading with the SCXI channel strings will allow you to confirm the voltage levels of excitation. Using the AI Parameter VI will ensure that the setting for excitation has taken affect.

I hope this helps. Let me know if you have additional questions. Have a great day.


Regards,

Todd D.
NI Applications Engineer
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