USB 4431 DAQ, bad sampling from AI0 with loaded AO0

[JohnDoe23]

Hi, I use a USB 4431 DAQ for continuous input sampling on AI0 while outputting a pulse signal (0V and 3V) an AO0.  While the outputted pulse is in the 0V phase, the input sampling works fine.  But when the output is 3V, during that time the input sampling returns zeros (then it works again when the output is 0V again).

I don't have much experience in this area, I suspect, that the custom made device that is connected to AO0 of the USB 4431 DAQ is pulling too much current and this is the cause of this behaviour.  I find it strange, because AI0 and AO0 should be independent, pulling too much current from AO0 should not cause AI0 to return bad samples, it should signal an error or something.

Would you please enlighten me some more about this?  Thank you.

[Zody]

Hi JohnDoe23,

What do you mean by " While the outputted pulse is in the 0V phase, the input sampling works fine. ". What does it mean that it works fine? That you read 0 Volts?

Please post the section of the code that is doing the generation and the acquisition.

According to the manual at the page 4, you have a dealy on the analog input give by the filter. Therefore, if you have a loopback test where you generate and acquire the same data, you should be able to see the same signal with 39 samples delay.

I am looking forward with great intersts in your reply.

Best regards,

IR

[JohnDoe23]

Hi IonR!

The pulse we generate with the DAQ on AO0 is 3V for 30msec, then 0V for 70msec which is used for triggering purposes.  During this time we read sound pressure data samples from AI0 which is connected to a microphone.  While the DAQ is outputing 3V, the read samples are all 0 (bad values).  While the DAQ is outputting 0V, the read samples are correct.

If I disconnect AO0 then all read samples are correct.

[Zody]

Hi JohnDoe23,

What version of DAQmx are you using?

The behavior sounds like could be a problem either with the HW either with the firmware that runs on it.

I would recommend to upgrade to the news version that you can find on www.ni.com/drivers by searching for DAQmx.

Best regards,

IR