USB cDAQ for fast point-to-point processing ?

[VdG]

Hi,

i've written a application with LabVIEW that do fast point-to-point processing  (i.e. read one analog samples, do some processing and send the result on a analog output). On internal PCI or PCI-express card, i can reach around 1000 samples/s. Switching to a cDAQ USB system, i hardly reach 100 samples/s with many tweaks on the daqmx property nodes...Furthermore, the application become very processor consumming and sensitive to UI activites. Is this a real caveat with the USB bus (too many interruptions ?) or is there some means to have a high rate point-to-point USB transfert ?

All the best,

[ThibaultP]

Hello Vincent,

What kind of PCI card did you used and what are the C series modules in you cDAQ chassis ?

Best Regards,

Thibault P

National Instruments

[crossrulz]

For what you are doing, you might want to consider using an FPGA to do the processing and output directly on the module.  You can do this with a 9147 chassis.  You could then use an Ethernet connection to send data back and forth for your GUI.

[VdG]

Thanks for the 2 answers.

I know the ultimate solution would be a FPGA based system (i already use some for other purposes), but i was just wondering about the possibility of using one of our cDAQ. I'm not aiming a truely real-time processing, just a moderately fast and reliable one, as the one i got with a internal PCI card.

About the C-modules i used, it's 9215 for input and a 9263 for output. I'm far from the max. rate specifications of theses modules, but i guess the highest rate is only reachable with N samples bloc transfert. Unfortunatly, this isn't the way i have to go.

Have a great day,

[Dennis_Knutson]

I haven't read the specs. Doors it support hardware timed single point acquisition. If it doesn't, then you are using software timed acquisition and you'll never achieve high rates.

[VdG]

Hi Dennis,

yes i'm using software timed acquisition (single sample AI read and AO write in a timed loop), but as i said i don't want to achieve really high rates, but just try to understand why i can't get with the cDAQ approximatively the same rate i get with the PCI card. For now it's 10 times slower....