32 channels at 1 MS/sec/channel

[faustina]

I'm trying to collect voltage data on 32 channels simultaneously at 1 MS/sec per channel.  I'm using 4 PXI-6133 cards in a PXIe-1065 chassis.  I seem to be only sucessful at 15 channels.  All the channels use the same sampling rate and voltage input range.  They are grouped togather into a single task.  Why am I not achieving the sampling rate desired?  What should I check first, hardware or software?

[crossrulz]

My first thought is to make sure all of the cards are on the same STAR trigger bus.  On the PXI chassis, you will notice verticle lines in with the slot labels.  Those lines show the seperations of the start trigger buses.

I honestly doubt this is your problem, but it doesn't hurt to try.

[faustina]

the cards reside in slots 3-6 so they are on the same PXI segment

[crossrulz]

What controller are you using?  If using a PXIe-PCIe8361, then the max bandwidth is 192MB/s.  So in theory, you should be able to get (192MB/s)/(8bytes/channel)/(1MS/s)=24 channels.  If there is any additional overhead, in the data, that could be cutting into that theoretical number.