DAQmx Acquisition Sample Timing

[jrdwight]

Let's say I start a DAQmx acquisition task using with the DAQmx Timing VI set to Sample Mode = Continuous Samples, and Rate = 1000 S/s. If my DAQmx Read VI only reads 1 sample every 100 ms, the data it reads from the buffer was still acquired at the specified 1000 S/s, right? (Obviously this would quickly lead to a buffer overflow, but I'm just trying to understand whether the timing of the acquired data is at all dependent on when/where my DAQmx Read VI occurs.)

If so, is it also correct to say the data was acquired using hardware timing rather than software timing?

[santo_13 · Accepted solution]

Your hardware will continue to read AI at the configured sampling rate (coerced to hardware capability) and will push data to the driver's buffer. The DAQmx read just fetches the samples from the driver's buffer once available. There is a little more intelligence in DAQmx driver to detect whether the buffer is full or waiting for samples.

[jrdwight]

You say "at the configured sampling rate (coerced to hardware capability)". How would I know what the true sampling rate is? Would I have to use something like a waveform output instead of double output, so that it tells me dt?

[santo_13 · Accepted solution]

After configuring sample timing, you can read back the actual sampling rate using the property node.

This is done in all shipping examples.

[jrdwight]

I'd never noticed that! Thank you for your help!