Data rate setting in crio 9233

[LyLee]

HI,

I am using crio 9233 to do the measurement.  Since my sample rate is only 4k, I want to set module speed close to that. I use four channels on 9233, so each should be sampling at 4K/S. I use FPGA I/O node in the fpga vi to read the AI input from 9233, at 4k/s interval for each channel.
When I set the Data Rate in Module Configuration (right click the module in project explorer)  to 4.167KS/S, it seems the waveform I acquired is not correct:  The toal data number is only 1/4 of the expected (i.e., 10 seconds of recording, only 2.5 seconds data acquired), and correspondingly the frequency in the acquired waveform seems to be 4 times of what they should be.
When I am sampling at 2k/S interal, the acquired signal seems to have double the frequency.  When I sample at 1k/S, the acquired signal seems to have the correct frequency. 
What's the reason for that?  Is that "Data rate" for individual channel or for all 4 channels?
And, the 9233 manual says the "alias-free bandwidth " is 0.42fs,  so is this "fs" the Data Rate in Module Configuration, or something else?

Thanks!

[JMota]

Hi,

The 9233 is a self-timed module, what that means is that the IO Node for 9233 channels will return data at whatever rate you have configured the module's data rate to. Therefore, you don't need (and should not use) any nodes within the FPGA block diagram to time your acquisition. For example, if you configure the module for 4.167KS/s, the IO Node will block and only return data at that rate. I suggest you look at the examples for the NI 9233 to see how they acquire data. You will notice the acquisition loop is being timed solely by the IO Node.

Regarding your second question, I think you are right that "fs" is the data rate at which you configure the module to run at.

Hope this helps.

JMota

---

@LyLee wrote:
HI,

I am using crio 9233 to do the measurement.  Since my sample rate is only 4k, I want to set module speed close to that. I use four channels on 9233, so each should be sampling at 4K/S. I use FPGA I/O node in the fpga vi to read the AI input from 9233, at 4k/s interval for each channel.
When I set the Data Rate in Module Configuration (right click the module in project explorer)  to 4.167KS/S, it seems the waveform I acquired is not correct:  The toal data number is only 1/4 of the expected (i.e., 10 seconds of recording, only 2.5 seconds data acquired), and correspondingly the frequency in the acquired waveform seems to be 4 times of what they should be.
When I am sampling at 2k/S interal, the acquired signal seems to have double the frequency.  When I sample at 1k/S, the acquired signal seems to have the correct frequency. 
What's the reason for that?  Is that "Data rate" for individual channel or for all 4 channels?
And, the 9233 manual says the "alias-free bandwidth " is 0.42fs,  so is this "fs" the Data Rate in Module Configuration, or something else?

Thanks!

---