Synchronisation of different modules in the same Chassis

[Archimedes92]

Hi,

I have some very basic questions regarding the synchronisation of modules (2 x NI9231 and NI9231) in the same cDAQ chassis (NI cDAQ-9188):

1. Should I have one task per module in LabView? I think the answer is yes, since I have tried one task and it did not work.

2. For the 2 NI9231 modules one task is enough, isn't it? I have tried it and I can chose different channels and it seems to work. 

3. If I have now 2 tasks, how can I synchronise those? Just using the same sample clock?

4. Does the acquisition rate for the 2 tasks has to be the same? 

What my goal is: I have 16 microphones connected to the 2 NI9231 and I want to record synchroneously a trigger signal from a camera using the NI9215 module.

Cheers,

Arch

[PhillipDBrooks]

Found a similar question by searching the forum for "9231 sync"

https://forums.ni.com/t5/Multifunction-DAQ/Synchronizing-Multiple-NI-9231-Modules-with-cDAQ-9171-Cha...

[Archimedes92]

Thank you, I also found that before, however this is about a PPS signal, so it does not answer my specific questions. 

[cordm]

If you use the same sampling rate for all modules, I think you could use a single task.

If you need multiple sampling rates, use two tasks and have at look at this article:

Signal-based Synchronization of Analog Input C Series Modules with NI-DAQmx in LabVIEW - Multirate Synchronization

https://www.ni.com/en/support/documentation/supplemental/21/signal-based-synchronization-of-analog-i...

It's complicated when mixing DSA (9231) and SAR (9215) modules and personally I never managed to compensate for DSA delay.

[mcduff]

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@cordm wrote:

If you use the same sampling rate for all modules, I think you could use a single task.

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This is true. You can use "Channel Expansion" for all the channels in the task, including ones from different modules.

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It's complicated when mixing DSA (9231) and SAR (9215) modules and personally I never managed to compensate for DSA delay.

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You will have to post process your data to remove the DSA delay. 

What exactly is the 9215 recording? Are you using it as a trigger signal or do you want to record the trigger? Is your trigger a digital signal? You could use the PFI input on your chassis to digitally trigger both modules.

[Archimedes92]

Thank you so much.

What is the order of magnitude of the time delay between DSA and SAR? 

What exactly do you mean by channel expansion? I just can select the channels I need of the three modules.

What exactly is the 9215 recording? Are you using it as a trigger signal or do you want to record the trigger? Is your trigger a digital signal? You could use the PFI input on your chassis to digitally trigger both modules.

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The 9215 is recording a trigger signal for the camera, so I can link the data from the 9231 to the camera frames. 

[mcduff]

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What exactly do you mean by channel expansion? I just can select the channels I need of the three modules.

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Channel Expansion is what NI calls "adding all the channels together into a SINGLE task". Channel Expansion handles all of the synchronization for you.

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What is the order of magnitude of the time delay between DSA and SAR? 

The delay depends on the sample rate. You can look in the 9231 manual for the formula or you can use the DAQmx property AFTER setting your timing specifications to programmatically query the filter delay. The property is below. You need to set it a relevant channel, that is, one of the 9231 channels that you are using. The 9215 has no filter delay.