PID control w/ USB DAQ devices

[Brant at VIE]

Does anyone have any opinions on using one of NI's USB DAQ devices for PID control? We have a customer that might need to move from an E-series PCI card to a USB option. I have used PCMCIA cards in the past and have not been happy with the performance, but have never used a USB device before. I'm looking at the USB-6221 in particular, but would like to hear any opinions on CompactDAQ as well. Thanks.

Edit: The PID loop rates are on the order of 5 Hz.

[BobHamburger]

Ideally, for closed-loop control, you want a real-time platform that gives you consistent, deterministic performance, like cRIO or cFP. Having said that, "real-time" is a relative term; 5 Hz is within Window's ability to stay fairly consistent in timing, so pretty much any DAQ product should work OK. Not sure why you haven't had good results with PCMCIA in the past -- there's nothing intrinsically limiting in that platform for a relatively slow application like this.

[Yair]

As mentioned, Windows should have no problem with that rate. I did PID with the USB-6008 or 6009 at around 20 Hz, if I remember correctly.

[Eugen Graf]

I think if your Samples are timestamped, then you can use closed loop controls in Windows too. Is't right?

Eugen

[Yair]

I don't think the USB modules have an internal timer, so the timestamping will come from the OS anyway. As mentioned, it can be used to do this, but it depends on the speed and the determinism (which you can't get in Windows anyway).