NI 9225 Data Acq Rate

[TESTniques]

Hello,

I have a NI 9225 in a cDAQ-9174 chassis.  I have software to set a 1000Hz sample clock timing, then to trigger a callback once 1000 samples are acquired.  Acquisition mode is continuous.  The callback fires after 620 mSec. No error codes are shown.  Callback should trigger at 1000 mSec intervals.  Any suggestions?  My application depends on the callback firing evey 1000mSec.

The same software when used with other devices such as NI 9215, USB-6008, or USB-6215 works fine, the callback fires at regular 1000mSec intervals.

CVI 8.1.1 and DAQmx 9.2.2

[Seth_B.]

Hello TESTniques,

The NI 9225 has a minimum sampling rate of 1.613 kHz.  As a result, if you set a 1000 Hz sampling rate, the rate will be coerced to 1613 Hz, which is why your call back is firing faster than you expect.  This is detailed on page 17 of the User Guide and Specifications.

You can either use 1613 samples to trigger your callback or read the NI-DAQmx Timing property "Rate" to determine what rate the module will actually be sampling at.

The other devices you mentions don't have a minimum sample rate (well, they do but that's limit of the rollover of the on board clock, so it's on the order of minutes per sample).

[TESTniques · Accepted solution]

Thank you for the answer.  Tried it out today.  Works well with 2000 Hz aacq rate and 2000 sample between callbacks.  Callback fires at 1000 mSec interval.

[hgfghgf]

Hello. 

I'm a beginer and I'm doing an high speed acquisition from  3 NI 9225 modules with maximum sampling rate simultaneously. Please tell me how to write data to FIFO (in FPGA VI), and how to read data from FIFO (in RT Host VI) in order not to loss any data. I write to FIFO at a rate of 800ticks, and read from FIFO at a rate of 2ms, but overflow occures. Thank you beforehand!!

[Jake_H]

Hello,

Since this answer is marked as "Solved", I would recommend starting a new thread so that users have a chance to examine your post. Although you are using the same C Series module, the DAQmx and FPGA/RT programming environments are very different so this question would be more appropriate in the LabVIEW FPGA or the Real Time Measurement and Control thread.

[hgfghgf]

Thank you very much for your help!!

[昭]

hello:

i do not know how to figure out the sampling rate of NI9225. there is a fomular of Date rates which is Fs=(Fm/256)/n, but how to find out the value of n? anyone knows?

[昭]

Hi Sir:

My NI 9225 is installed in compactRIO 9022. and signal source is nomal three phase imput.

[lis@jiang]

Hello 昭,

As mentioned in the other forum you started:

Since your 9225 module is used with a cRIO, your coding is going to be different from the DAQmx code you may have previously seen.  Setting sampling rate is done by a property node "AI Sampling Rate," not by setting the value of n in that formula.  Please take a look at the shipping example found in Help >> Find Examples.  Then navigate to Hardware Input and Output, CompactRIO, Basic IO, and Analog Input - cRIO.lvproj.

Thanks,

Lisa