Synchronization and Triggering for cDAQ system

[EurekaJX]

Hi, we are tempted to buy a full set of NI DAQ system for our project working on fast sampling rate requirement, i.e. 1kHz. Our project would involve the implementation of 80 channels of strain-gauge type sensors. The plan was that the whole system will be waken up after a sensor was triggered (the analog signal reached certain threshold level). So, we will be using multiple C-series bridge modules (i.e. NI 9237), two units of cDAQ USB-typed chassis (e.g. NI 9179), and a cDAQ controller (i.e. NI 9136).

A simple schematic of our proposed system can be seen in attached figure.

We have some questions to seek for consultation:

[1] Am i right that we do need the synchronization module (NI 9469) for the two chassis? 

[2] Is it right to say that once the two chassis have been synchronized, all modules will also be measured all at the same time? 

[3] How could the triggering be done in our case?

[4] Do I really need to have two separate USB cables interconnecting controller and the two chassis? Is there other method?

Thanks!

[santo_13]

Good choice, here is my point of view,

[1] Am i right that we do need the synchronization module (NI 9469) for the two chassis? 

Yes

[2] Is it right to say that once the two chassis have been synchronized, all modules will also be measured all at the same time? 

Yes, this Sync modules shares the clocks and trigger across chassis

https://knowledge.ni.com/KnowledgeArticleDetails?id=kA00Z000000fz1lSAA&l=en-US

https://www.ni.com/en-us/support/documentation/supplemental/15/synchronization-options-for-multiple-...

Refer for more topology options - https://www.ni.com/pdf/manuals/373337c.pdf

[3] How could the triggering be done in our case?

If the module supports triggering on the bridge measurement, you can configure, if not you can utilize a single trigger input on the chassis

[4] Do I really need to have two separate USB cables interconnecting controller and the two chassis? Is there other method?

As far as I know, you would need USB or Ethernet as these are the typical data transfer methods used by cDAQ (there was an MXI version too), so you must connect them for communication & data transfer from the module to the computer (controller or PC).

Let's hear from more users to be confident.

[EurekaJX]

Hi Santhosh, thanks. It is great to have your comments.

I came to know the following remarks:

[1] Once the NI 9469 has been slotted onto the two respective chassis, the modules across the entire system can be synchronized and real-time measurement (analog input) can be done. Also, the measurements from two chassis (chassis A & B) can be synchronized so long the sampling rate is not too high (say, below 10kHz).

[2] For the triggering part, my current plan was that one of the module in the slot of controller (either from a bridge-typed module or another digital/analog input module) will take in real-time analog measurement when the controller is still active. This measurement will be synchronized within the controller slots. All measurement will be transferred to the pc/ DAQ controller's buffer; the processor/controller will judge whether the data beyond certain threshold. If yes, a triggering signal (digital/analog) will be sent out from the triggering port (BNC/SMB) in DAQ controller (or an extra module on the controller's slot) to the chassis. That trigger will inform all other chassis to start measuring and transferring real-time data to the DAQ controller for logging. Probably the on-board trigger ports allow receiving/sending trigger signal for some particular controller models too?

Is my above thinking correct?

When I read the manual, it's quite hard to confirm whether the trigger mode is digital/analog and how it could be done?