Synchronizing acquisition from two PXI chassis / NIDAQmx C calls ?

[FBurton]

I have two identical PXI-1042 chassis connected to one computer, and each chassis has 4 M-series boards (PXI-6225). Synchronization of data acquisition within one chassis is achieved using the technique given in ContinuousAI.c (Synchronization\Multi-Device\Continuous AI), extended from two to four devices, setting the clock source for each device to "PXI_Clk10" and the rate to 10000000.0 Hz (10MHz). (The example cites master and slave tasks, but in this case all device tasks are "slaved" to the 10MHz PXI Clock built into the backplane of the chassis.)

I need to synchronize data acquisition between the two chassis. Presumably this means using a physical cable to connect one (or more) lines between the boxes. What is the recommended method for doing this? Which line(s) should I be using? Would it be straightforward to use one of the digital IO ports, or would PFI0 or ai/SampleClock be more appropriate? And what, if anything, I need to do in my C code to use this connection?

Thanks in advance!

[James_McN]

Hi, The simplest method to do this is to connect the clock sources by the BNC connectors on the back of the chasses. The signal on the Clock input will overwrite the on board 10MHz clock. There will however be some propogation delay on the signal through the BNC cable but this should not be huge. There is an article specific to this although it doesn't offer a lot more information! this is at http://digital.ni.com/public.nsf/allkb/64154143B6B898AA86256C2B006D11CC. Otherwise NI do make some PXI cards purely for this purpose such as the 6652 abd 6653, if you need high precision these will give sub picosecond delay between the clocks. Regards,

[FBurton]

Hi James,

A wonderfully simple and straightforward solution - thank you! It makes perfect sense, given that intra-PXI board synchronization is also achieved using the backplane clock.

Cheers,

Francis