Synchronization and triggering between multiple AI ports.

[Amartansh13]

Hello everyone, 

I have successfully synchronized input and output ports (read and write) of my DAQ device (USB 6356) by sharing clock between AI and AO tasks and by triggering the AI task using AO start trigger. It works perfectly.  

But I was wondering, are two input ports of any DAQ device are already synchronized (because they share the same clock and distance between them is too small for any latency)? I am acquiring signals with 2 AI ports. So is the data acquisition by these two ports already synchronized? Or I have to do something additional like I did for synchronizing AI and AO. 

In short, are 8 AI channels of my device synchronized? 

Thanks in advance! 

[crossrulz]

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@Amartansh13 wrote:

In short, are 8 AI channels of my device synchronized?

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Considering you can only have 1 AI task per device, the answer would have to be yes.  It is also assumed you put all 8 channels in the same task.  In reality, they will be slightly off of each other due to the multiplexer to the ADC.  But for most applications, that delay is small enough that it does not really matter.

[Amartansh13]

Thanks a lot for your prompt reply! 

Yes, I am using one AI task. 

The maximum sampling rate of the device per channel is 1MS/s. I am taking measurements for many hours (around 5 hours). So, a small delay can cumulate over time to become large. So, will the delay between the AI channels over a long period can be comparable to this sampling rate? I mean can delay be the order of few microseconds? Because if that is so, then the phase related calculation between two channels will not be accurate. 

Thank you

[crossrulz]

You are thinking of the wrong time difference.  The task will perform a scan of all the channels in a task at the rate you give.  So if there is any error in the sample clock, all of the channels will have the same delay error over many hours.  The time between each channel being sampled (ie A0 to A1) will be very small (microseconds) and consistent over time.  If you need truly exactly the same time, then you need to look into a synchronous DAQ which have many ADCs on it that can sample at the exact same time.