Why the AI (voltage) is always 4.9987 for PCI 6036E using Ni-Daq low-level functions, such as ScanSingleBufAsync.c?

[paulliu]

Hi,
I am not very experienced in the field of DAQ.

So I cannot solve the following problem:
Why the AI (voltage) is always 4.9987 for PCI 6036E using Ni-Daq low-level functions, such as ScanSingleBufAsync.c?

This problem can be overcomed using Labview.
But my C++ code worked before at previous
workplace. Now it can also handle noise signal,
but not the real one.

Any help is really appreciated.

[Salvador_Santolucito]

Hi Paulliu,

What voltages are you trying to read? Are all of them above 5 volts?

If you can properly read voltages below 5 volts, but it rails on voltages above 5, you have an incorrect gain setting. You will need to insert an AI_Configure function to set up the proper range. Check out the following KB's:

http://digital.ni.com/public.nsf/websearch/D4211BD64091F8C486256D980006DA8D?OpenDocument

http://digital.ni.com/public.nsf/websearch/8D621EE9861552DB86256EA8007C3C45?OpenDocument

[paulliu]

Thanks. I later found out that the voltage do change
when the signal changes significantly.

The default setting can handle a voltage upto 10 V.
My worry resulted from the different behaviours of
these low-level function from Labview program which
always outputs non-constant voltage, even the
real signal does not change.