Are the signals in channels sincronized?

[Wilfried_71]

Your card is a M-serie and not a S-serie, so the inputs are multiplexed and not perfectly synchronous. So, it can be right that you have some phase shift between channel. If you want to know how is exactly this time, I think it must be written in the product manual ... we can search if you won't find it ...

[Asier_gast]

Thanks,
I found the manual online but it doesn´t appear to say anything about the delay. They say whta you told me,that for simultaneous adquisitions th S series are the ones that work better. Anyway, Do you think it´s possible to assume a constant shift between channels for all the measurements? I mean if I meassure the shift with the analog oscilloscope and then meassure it with labview, will this shift remain constant in the former measurements?

[Dennis_Knutson]

Instead of trying to guess, convert the assistant to DAQmx code and then you can use the property node to return the actual inter-channel delay if you need the value in your program. However, it should remain the same as long as you don't change the sample rate or number of channels. You can also set the inter-channel delay with a property node.

[Ima U]

Hi Asier,

From my understanding, you are using LabVIEW, DAQmx and a PCI 6220 to acquire an analog input  from your pressure  transducer and an AC sine wave.   From my understanding you are concerned with a 700us delay between the two analog input channels. 

There is expected to be some sort of delay because of the architecture of the M-Series DAQ card that you are using.  Please take a look at this Knowledge Base and this Developer Zone document to get further understanding of this delay.  I believe the “Software Makes All Timed Hardware Simultaneous” section of this Developer Zone document will be useful to you in solving this.  It mentions the align and resample express VI available to you In LabVIEW.

I would like to know how you are measuring the 700us delay.  You mentioned that you are using an oscilloscope.  Did you connect it to the pins going into the M-Series device?  I did not see this delay being calculated in your LabVIEW program.

[Asier_gast]

I get the real signal by connecting the oscilloscope directly to the transducer and the function generator. Then i compare them to the signal appearing on the computer, that´s how i calculate the delay. I set the adquisition rate at a much higher speed and now the delay seems to have been reduced. I will take notice of your advice. Anyway, i was using the DAQ assistant, not the DAQmx even if most people recommend me to do that.
Thanks,
Asier

[Ima U]

Hi Asier,

I am glad to hear the delay has now been reduced to an amount tolerable for your application.