CompactDAQ speed

[nuflare]

I am investigating replicating  a function now running on PCIe And PXIe on C-series devices.

The function consists of two synchronous waveforms running at maximum speed of 250 k samples.

This is a raster scan with X Y channels and ADC input.

I have been testing a C-series setup:

9184 chassis

9264 DAC

9205 ADC

For continuous running waveforms I have some speed issues.

I know the 9264 is not fast enough so I will upgrade to a 9262.

I just learned the CompactDAQ chassis support only one DAC channel in regenerative mode so all scan waveforms must be memory based.

My question:

With the latency for the CompactDAQ chassis interface how fast will this run continuously?  

John

[Kevin_Price]

If you switch to the 9264, your cDAQ system should be able to handle 250 kHz sampling pretty much indefinitely.  I don't know any reason why not.

Granted, the code has to be at least decent, so plan on the following:

1. Keep the DAQ loop lean, and send the data via Queue, Programmable Event, or Channel Wire to a parallel loop for any further work.  Further work includes analysis, chart displays, writing to file, pretty much *any* data handling.

2. You can write your AO waveforms in their entirety to your task before starting it and then entering your DAQ reading loop.   DAQmx manages the dirty work behind the scenes of moving the data from your task buffer to the actual device.

-Kevin P

[nuflare]

Kevin,

 Thank you for your reply.

You said : “If you switch to the DAC 9264, your cDAQ system should be able to handle 250 kHz”

Did you mean the DAC 9262 (1MS/s)      The 9264 (25kS/s) seems to be my bottleneck.

I was also concerned the 9205 ADC (250kS/s) may be a bottleneck at 250 k max speed.

Another question:

I am testing now with  a cDAQ 9184 chassis I had.

I plan to replace this with a chassis with more slots.

Will the cDAQ 9179 USB3 chassis have reduced latency compared to the Ethernet versions?

Thanks again,

John

[Kevin_Price]

Oops, yes, I meant the 9262, not the 9264.

Also, I never looked into the specs for the 9205 since you hadn't raised it as a concern.  I see that it has a max rate of 250 kHz aggregate.  So 1 channel at 250 kHz, 2 at 250/2 kHz, N at 250/N kHz.

   If you only need to acquire 1 AI channel, I'd expect it to be ok.  The limitation is related to the A/D converter circuitry, not the bandwidth for delivering data from cDAQ to PC.

I'm not highly experienced with a range of cDAQ chassis and modules, so I really can't speak to differences in bandwidth or latency.

What's the reason for asking about latency  rather than bandwidth?  Buffered, hw-clocked tasks are always going to have some noticeable latency and if you have an app where latency really matters a lot, you probably shouldn't be using USB or Ethernet based DAQ.

-Kevin P