Acquire data at multiple frequencies

[PEM@ANU]

I have a M series PCI-6224 DAQ with Ni-DAQmx and LabVIEW. Is it possible to simultaneously acquire data (AI Voltage) at different freqencies? For example I want to acquire data at frequency X on ai0 and at frequency Y on ai1. I tried using two DAQ assistants but gave me errors. Is it possible?

[Salvador_Santolucito]

Hi,

You will not be able to sample different channels at different frequencies. Although your board has many analog input channels, it only has one analog to digital converter and only one set of AI timing circuitry. For this reason, you can only have ONE analog input task running (one DAQ Assistant) at a time. All analog input channels are sampled at the same time (not exactly simultaneous but very close) and are multiplexed through the one ADC.

I would suggest that you set up your analog input acquisition to run at the faster of the two rates. Then in software you can remove the unwanted data points (to look like that channel was sampled slower). However, it may be best to keep all of the data since you need to take it anyway.

-Sal

[gus]

Hello,

For an example that does what Sal is describing, go here.

[PEM@ANU]

Cheers!

[MathMath]

as does a remdier have that, can be used 1 external clock as a sampling rate for my first tension, and the internal clock of the E or M series card for my second tension?

regards

[Brady Trexler]

The following is an excerpt from an NI support
email.

////////
Yes, M series and NI-DAQmx have the ability to scan different channels at different rates. The requirement is that all sampling rates in your task have a common divisor. For example, if your task contains channels 0 and 1. You could sample channel 0 at 300 S/sec and channel 1 at 100 S/sec since they have a common divisor. You would set the sampling rate as 100 S/sec, would place three virtual channels for chan. 0 and one for chan. 1, and then simply interleave the arrays for channel 0 to obtain data sampled at 300 S/sec. This may be more than you were hoping to hear with your first email, so I'll direct you to the following knowledgebase for more
information:

http://digital.ni.com/public.nsf/websearch/96FD2F4685065C7686256F25006EE8DE?OpenDocument

//

Hope this helps,
Brady