USB 6218, Anybody have one yet?

[Vr6Fidelity]

Im going to be purchasing one of these today. Anyone used one yet? Thoughts? impressions?

I searched but this is the first 6218 post ever.

It states that it is 250K/s sec for one channel (aggregate)

What does this yield im im using 15 diff channels??

How does this compare with another one of my systems using dual 6221 M series cards?

[Salvador_Santolucito]

Hi,

The USB-6218 has an aggregate sampling rate of 250 kS/s.  This means that you can achieve this sampling rate if you have only one analog input channel in your task.  If you are using multiple channels, the 250 kS/s maximum will be divided by the number of channels in your task.

For example:  250 kS/s divided by 15 channels will yield a maximum sample clock rate of 16.666 kS/s. 

Using a moderately fast computer with USB 2.0, you should be able to sustain the maximum rate for analog input without any problems. 

Thanks,

Sal

[Vr6Fidelity]

how does that compare to dual 6221's?

im unsure if they are aggregate and how the actual computer deals with 2 pci devices.

Thanks.

[Salvador_Santolucito]

Hi,

The PCI-6221 device also has a maximum aggregate sampling rate of 250 kS/s.  This means that the 250 kS/s sampling rate is divided by the number of channels in the task.

I'm assuming that you needed two PCI-6221's because you have only 8 differential channels on a 6221.  So you can have 8 differential channels on one 6221 and 7 channels on the other.  250 kS/s divided by 8 channels yields a maximum rate of 31.25 kS/s. 

So, using two devices with an aggregate sampling rate of 250 kS/s will yield a higher maximum rate (for 15 channels) than only using one device with a maximum aggregate rate of 250 kS/s.

The computer treats each PCI-6221 as a separate data aquisition device.  Each device has its own maximum rate and runs independently of the other.  In fact, each of the two PCI-6221 devices must run in a separate NI-DAQmx task.

Thanks,

Sal

[Vr6Fidelity]

Thank you.

New question, what about EMI shielding? I will be placing the USB device right next to a very powerfull permanent magnet generator so it may be influenced by magnetic fields and strong currents nearby, not electrically, but physical location.

Is the plastic case an effective shield?

[Salvador_Santolucito]

Hi,

The USB-621x devices are housed in a plastic enclosure.  They are certified as a Class A device for electromagnetic radiation immunity.  More information about the electromagnetic compliance of the device can be found in the specifications.

The USB-6218 is designed to not be susceptible to noise in a typical office or lab environment.  Although I haven't used one in the presence of a high electromagnetic field, I wouldn't be surprised if you did see noise on your measurements because of it. 

We do offer the USB-6259 which is housed in a metal enclosure.  That device will offer better shielding and may be preferable in your application.

Thanks,
Sal

On a side note.... I used to work at a high magnetic field laboratory.  We always kept our measurement equipment in a separate room several feet away and behind shielding.  These were pretty high fields.  We'd all have to degauss our monitors after running it.

[AnalogKid2DigitalMan]

The biggest source of error may be the EMI generating voltages in all your signal wiring that is external to the USB device.